Search

Wind energy is a commercially proven and rapidly developing type of electricity generation. Wind power plants with a vertical axis are more attractive and better suited for use in cities and urban environments where wind flow is less predictable compared to widespread wind power plants with a horizontal axis of rotation. This makes them a much better choice for both ground installation and/or for mounting on buildings and roofs that would otherwise limit the installation of higher horizontal turbine structures. The paper describes an experimental study of the drag force and its coefficient for wind turbines with a vertical axis of rotation. The object of the study is a laboratory model of a wind turbine with blades made in the form of rotating cylinders with a fixed blade. Experimental studies were carried out in the T-1-M wind tunnel, measurements of aerodynamic force were carried out using three-component scales. A distinctive feature of the work is the combined use of the lifting force of the cylinders, as well as the lifting force of the fixed plate. Due to this solution, when comparing with existing wind turbines with a vertical axis of rotation, it was found that the wind turbine in question prevails by 25‒100 % in the number of revolutions. The dependences of the drag force on the flow velocity and the drag coefficient on the Reynolds number from 1·104 to 4·104 are obtained. An uncertainty analysis was also carried out in order to determine the uncertainty by type A, B and the total uncertainty, from which it was found that the measurement error was 1.13 %. The field of the practical application of the results obtained in laboratory studies will be useful in the development of prototypes of wind turbines with a vertical axis of rotation, Вітроенергетика є комерційно перевіреним видом виробництва електроенергії, що швидко розвивається. Вітрові електростанції з вертикальною віссю є більш привабливими і краще підходять для використання в містах та міському середовищі з менш передбачуваним потоком вітру в порівнянні з поширеними вітроелектростанціями з горизонтальною віссю обертання. Це робить їх набагато кращим варіантом як для наземної установки, так і/або для установки на будівлях і дахах, що в іншому випадку обмежувало б установку більш високих горизонтальних турбінних конструкцій. У роботі описано експериментальне дослідження сили лобового опору та її коефіцієнта для вітрогенераторів з вертикальною віссю обертання. Об’єктом дослідження є лабораторна модель вітрогенератора з лопатями, виконаними у вигляді обертових циліндрів з нерухомою лопаттю. Експериментальні дослідження проводилися в аеродинамічній трубі Т-1-М, вимірювання аеродинамічної сили виконані з використанням трикомпонентних ваг. Відмінною рисою роботи є комбіноване використання підйомної сили циліндрів, а також підйомної сили нерухомої плити. Завдяки такому рішенню при порівнянні з існуючими вітрогенераторами з вертикальною віссю обертання встановлено, що розглянутий вітрогенератор переважає на 25‒100 % за кількістю обертів. Отримано залежності сили лобового опору від швидкості потоку та коефіцієнта лобового опору від числа Рейнольдса від 1·104 до 4·104. Також проведено аналіз невизначеності для визначення невизначеності за типом A, B та загальної невизначеності, з якого встановлено, що похибка вимірювання становить 1,13 %. Область практичного застосування результатів лабораторних досліджень буде корисна при розробці дослідних зразків вітрогенераторів з вертикальною віссю обертання

In the current study, numerical analysis of passive control flow with a control rod for Ahmed body is performed at different slant angles and velocities and placed rod locations on the slant surface. The aim of the study is to improve aerodynamic performance by preventing flow separation on the slant surface of Ahmed body using a control rod. This passive flow control method uses a control rod that has not been applied for simplified ground vehicles before. Therefore, it can be said that this study is a new example in point of a passive flow control application for Ahmed body. The solution of the study is performed by using the Computational Fluid Dynamics (CFD) method. The solutions are firstly performed for baseline geometry, and the results are compared with experimental data reported in the literature for validation. CFD solutions are carried out by means of the ANSYS and RNG k-(sic) turbulence model is used to simulate flow -field since it captures the effect of turbulent flow. The solutions used a control rod with a 20 mm diameter performed at a dimensionless location (X/L=0.057 and 0.153) for Ahmed body. The results are presented visually in the figures, and drag coefficient values are also given in Table format. It is concluded that the rod application is useful for some specified slant angles and velocities since flow separation delays and suppresses the slant surface. The maximum drag reduction is achieved at about 6.153% at a slant angle of 35 degrees and 20 m/s velocity of air, and location of control rod of 0.057, while the minimum drag reduction is about 1.048% at slant angle of 25 degrees and velocity of air at 40 m/s and location of control rod of 0.153.

Neste trabalho desenvolvemos as equações referentes ao movimento de uma esfera lisa na presença de forças de arrasto, no regime de altas velocidades, onde a força resistiva é proporcional ao quadrado de sua velocidade. Esse regime é comumente encontrado em várias situações do cotidiano em que objetos de toda natureza são arremessadas no ar. As equações que são estudadas nos cursos básicos de graduação desconsideram o arrasto do ar e, portanto, são equações idealizadas, não condizentes com a real natureza do movimento observado. Aqui, pretendemos auxiliar o leitor a viajar um pouco mais próximo da realidade e contemplar a complexidade de algumas equações quando tentamos modelar o mundo como de fato ele é. Esse assunto é de extrema importância para estudantes de graduação na área de engenharia aeroespacial e mecânica, pois é fundamental entender como as forças de arrasto afetam o comportamento dos objetos em movimento. In this work, we developed the equations regarding the movement of a smooth sphere in the presence of drag forces, in the high-speed regime, where the resistive force is proportional to the square of its velocity. This regime is commonly found in various everyday situations in which objects of all kinds are thrown into the air. The equations studied in basic undergraduate courses disregard the drag of the air and, therefore, are idealized equations, not consistent with the actual nature of the observed movement. Here, we intend to assist the reader in traveling a bit closer to reality and contemplating the complexity of some equations when we try to model the world as it truly is. This subject is of extreme importance for undergraduate students in the field of aeronautical engineering and mechanics, as it is essential to understand how drag forces affect the behavior of objects in motion.

Background. For effective magneto-abrasive machining (MAM) of complex-shaped parts, comprehensive information is needed on the processes that occur when the magneto-abrasive tool (MAT) contacts with the surfaces being machined. Effective magneto-abrasive machining occurs in the presence of sufficient values of the normal and tangential components of the interaction forces between the MAT and the machined surfaces and the powder mixing during machining. Previously carried out analytical studies of dynamic parameters did not take into account the real conditions of the interaction of grains and their groups with machined surfaces. Objective. Complex analysis of the processes that occur during magneto-abrasive machining of parts made from different types of materials, based on the results of the study of the friction forces between the magneto-abrasive tool and the surface being machined and the drag forces during the movement of parts in the working zone of the machine. Methods. To achieve the set goal, the forces acting on the samples during their magneto-abrasive machining were measured with subsequent analytical analysis. Results. The complex analysis of the processes occurring during MAM in conditions of the annular working zone with large working gaps of parts made of various materials was carried out based on the results of the study of the friction and drag forces that occur when the part moves relative to the magneto-abrasive tool. Conclusions. It has been determined that when machining non-magnetic samples at the constant value of the magnetic field in the working zone, the specific drag forces are practically independent of the shape of the used powder. According to the analytical representation of the friction and drag forces, their ratio between their specific values was calculated. By the nature of the change in this ratio, it was found that it decreases with an increase in the velocity of samples movement along the working zone, and with an increase in the angular velocity of rotation of the samples around its axis, this value increases in the studied velocity range. It has been determined that at the velocity of movement along the working zone of 2.2 m/s, there is a slight increase in the ratio between the specific forces of friction and drag, which is associated with the action of ponderomotive forces that appear near the surface of the machined parts and lead to an increase in local magnetic forces in these zones., Проблематика. Для ефективного магнітно-абразивного оброблення (МАО) деталей складної форми необхідна вичерпна інформація про процеси, які відбуваються при контакті магнітно-абразивного інструменту (МАІ) з оброблюваними поверхнями. Ефективне магнітно-абразивне оброблення відбувається при наявності достатніх величин нормальної та тангенційної складових сил взаємодії МАІ та оброблюваних поверхонь та перемішування порошку в процесі оброблення. Виконані раніше аналітичні дослідження динамічних параметрів не враховують реальних умов взаємодії зерен та їх груп з оброблюваними поверхнями. Мета. Комплексний аналіз процесів, які виникають при магнітно–абразивному обробленні деталей виготовлених з різних типів матеріалів, за результатами дослідження сил тертя між магнітно–абразивним інструментом та оброблюваною поверхнею та за силами лобового опору при русі деталей в робочій зоні верстату. Методика реалізації. Для досягнення поставленої мети виконувалось вимірювання сил, що діють на зразки під час їх магнітно–абразивного оброблення з наступним їх аналітичним аналізом. Результати. Виконано комплексний аналіз процесів, які відбуваються при МАО в умовах великих робочих зазорів кільцевого типу деталей, виготовлених з різних матеріалів за результатами дослідження сил тертя та лобового опору, які виникають при русі деталі відносно магнітно–абразивного інструменту. Висновки. Встановлено, що при обробленні немагнітних зразків при постійній величині магнітного поля в робочій зоні сили питомого лобового опору практично не залежать від форми використовуваного порошку. За аналітичним представленням сил тертя та опору розраховано їх співвідношення між питомими їх величинами. За характером зміни цього співвідношення встановлено, що воно зменшується зі збільшенням швидкості руху зразків вздовж робочої зони, а зі збільшенням кутової швидкості обертання зразків навколо власної осі ця величина збільшується в досліджуваному діапазоні швидкостей. Встановлено, що при швидкості руху вздовж робочої зони 2.2 м/с має місце незначне зростання величини співвідношення між питомими силами тертя та опору, що пов'язано з дією пондеромоторних сил, що проявляються поблизу поверхні оброблюваних деталей і призводять до збільшення локальних магнітних сил в цих зонах.

A novel framework for describing suffusion in cohesionless soil, incorporating ideally gap-graded soil, is presented in this paper. The key assumption of the proposed simulation is that an erodible particle flow is induced primarily by drag force. The multiphase flow simulation for seepage-soil particle flow phenomena is conducted based on the proposed framework. The validity of the proposed method is checked through a simulation of past laboratory experiments, in which the variation in grain size distributions is grasped by a sieve analysis. The primary results show cumulative fines loss; therefore, a comparison of the cumulative fines loss is mainly discussed in this research. In addition, a discussion is given on the two different parameters affecting the erosion behavior, namely the 𝑝−𝑣𝑎𝑙𝑢𝑒 in the tortuosity function, 𝑇(∅) , and the clogging relaxation time, 𝛽𝑐𝑙𝑜𝑔 . The tortuosity is the ratio of the actual flow path and the distance between its ends, while clogging relaxation time is the parameter that considers the particle flow through the bottleneck. The results show that the numerical simulation provides a good correlation with the experiment, while the 𝑝−𝑣𝑎𝑙𝑢𝑒 is 3 which is the highest value for a geo-material. Moreover, the simulation results of the cumulative fines loss for each particle size also confirm that smaller particles will be fully eroded earlier than larger ones, and that larger particles will slowly become detached from the soil mass.

Biyomimikrinin sunduğu yöntemlerle, doğadan esinlenilerek oluşturulan biyomimetik kanatlar, aerodinamik ve rüzgâr enerjisi alanında yenilikçi çözümleri sunma potansiyeli barındırmaktadır. Bu çalışmada; doğada gösterdiği aerodinamik performansla dikkat çeken akçaağaç tohumundan esinlenilerek oluşturulan özgün biyomimetik kanat modelleri incelenmiştir. Deneysel ve nümerik olarak belirli rüzgâr hızlarında ve geniş bir hücum açısı aralığında analizleri yapılan modellerin, kaldırma kuvveti katsayıları (𝐶L) ve sürükleme kuvveti katsayıları (𝐶𝐷) belirlenmiştir. İlk model M0, ortalama akçaağaç tohumunun belirli bölgelerinden kesilmesiyle elde edilen 36 eğriyle tasarım programında modellenmiştir. Bu biyomimetik kanadın her bir eğrisi, Fourier serisi denklemleriyle en az %99,5’lik bir oranla temsil edilmiş ve denklemlerin katsayıları bulunmuştur. Böylece kanadın tasarım parametreleri, geleneksel bir kanat profili gibi sunulmuştur. M0 modelinin, akçaağaç tohumu ile daha önce yapılan çalışmalarda da bahsedilen geç stol özelliği ve kaldırma kuvvetine katkı sağladığı düşünülen, LEV (Leading Edge Vortex) yapısı dikkat çekmiştir. M0 üzerinde, LEV’i oluşturan model yapısı incelenip, yapıyı oluşturduğu düşünülen topografik özellik, M0 modelinin kanat yüzeyinin tamamına uygulanmıştır. Böylece, aerodinamik performans kriterini (𝐶𝐿⁄𝐶𝐷) artırmak amacıyla yapılan iki aşamalı kanat performansı geliştirme çalışmasının ilki olan topografya optimizasyonu gerçekleştirilmiş ve çalışma sonucunda “M5” modeli elde edilmiştir. M5 modeli, M0 modeline göre, değişen hücum açılarında, %15 ile %52 arasında daha üstün bir performans sergileyebilmiştir. İkinci kanat performansı geliştirme çalışması olarak da, M5 modelinin tohum kısımlarındaki eğrilerinin yüksekliklerinin düşürülüp, yerel veter uzunluklarının, belirli bir seviyeye kadar artırılacağı şekil optimizasyonu gerçekleştirilmiştir. Eğrilerin boyutlarının optimize şekilde ölçeklendirilmesi adına, istatiski bir metot olan Taguchi metodunun kullanıldığı bu şekil optimizasyonu sonucu elde edilen M5C modeli, M0 modeline göre, değişen hücum açılarında, %99 ile %320 arasında performans artışı göstermiştir. Ayrıca, oluşturulan bu biyomimetik modellerin rüzgâr enerjisi kullanan sistemler için potansiyeli de tartışılmıştır. Biomimetic wings, inspired by nature with the methods offered by biomimicry science, have the potential to offer innovative solutions in the field of aerodynamics and wind energy. In this study, unique biomimetic wing models inspired by the maple seed, which attracts attention with its superior aerodynamic performance at low wind speeds in nature, were examined. The lift force coefficients (𝐶𝐿) and drag force coefficients (𝐶𝐷) of the models, which were analyzed experimentally and numerically at certain wind velocities and a wide angle of attack were determined. The first model, M0, was modeled in the design program with 36 curves obtained by cutting a selected average maple seed from certain parts. Each curve of this modeled biomimetic wing was represented by the Fourier series equations with a ratio of at least 99,5% and the coefficients of the equations were found. Thus, the design parameters of the wing are presented like a conventional airfoil. The stall delay feature of the M0 model, whose aerodynamic performance was measured, and the LEV (Leading Edge Vortex), which is thought to contribute to the lift force, attracted attention. The model structure forming the LEV on M0 was examined and the topographic feature, which is thought to form this structure, was applied to the entire wing surface of the M0 model. Thus, topography optimization, which is the first of the two-stage wing performance development work carried out to increase the aerodynamic performance criterion (𝐶𝐿⁄𝐶𝐷), was carried out and the M5 model was obtained as a result of this study. The M5 model was able to outperform the M0 model by 15% to 52% at varying angles of attack. As the second wing performance development study, shape optimization was carried out by reducing the height of the curves in the seed parts of the M5 model and increasing the local chord lengths up to a certain level. The M5C model, which was obtained as a result of this shape optimization, in which the Taguchi method, a statistical method for optimizing the scaling of the dimensions of the curves, was used, showed an aerodynamic performance increase between 99% and 320%, at varying angles of attack, compared to the M0 model. In addition, the potential of these biomimetic models created in the study for systems using wind energy is also discussed. Yükseköğretim Kurulu (YÖK) - 100/2000

The calculation of the drag force is a fundamental requirement in the design of any submerged system intended for marine exploration. The calculation can be performed by analytic analysis, numerical modeling, or by a direct calculation performed in a designated testing facility. However, for complex structures and especially those with a non-rigid design, the analytic and numerical analyses are not sufficiently accurate, while the direct calculation is a costly operation. In this paper, we propose a simple approach for how to calculate the drag coefficient in-situ. Aimed specifically at the complex case of elastic objects whose modeling via Computer-Aided Design (CAD) is challenging, our approach evaluates the relation between the object’s speed at steady-state and its mass to extract the drag coefficient in any desired direction, the hydro-static force, and, when relevant, also the thruster’s force. We demonstrate our approach for the special case of a highly complex elastic-shaped floater that profiles the water column. The analysis of two such floaters in two different sea environments shows accurate evaluation results and supports our claim for robustness. In particular, the simplicity of the approach makes it appealing for any arbitrary shaped object.

Background. For effective magneto-abrasive machining (MAM) of complex-shaped parts, comprehensive information is needed on the processes that occur when the magneto-abrasive tool (MAT) contacts with the surfaces being machined. Effective magneto-abrasive machining occurs in the presence of sufficient values of the normal and tangential components of the interaction forces between the MAT and the machined surfaces and the powder mixing during machining. Previously carried out analytical studies of dynamic parameters did not take into account the real conditions of the interaction of grains and their groups with machined surfaces. Проблематика. Для ефективного магнітно-абразивного оброблення (МАО) деталей складної форми необхідна вичерпна інформація про процеси, які відбуваються при контакті магнітно-абразивного інструменту (МАІ) з оброблюваними поверхнями. Ефективне магнітно-абразивне оброблення відбувається при наявності достатніх величин нормальної та тангенційної складових сил взаємодії МАІ та оброблюваних поверхонь та перемішування порошку в процесі оброблення. Виконані раніше аналітичні дослідження динамічних параметрів не враховують реальних умов взаємодії зерен та їх груп з оброблюваними поверхнями.

The article presents the development of the unmanned glider tug project, a description of the stages of a new technical solution, submitted to the patent office in December 2017 and developed to date. The proposed towing system consists of a universal drone ground control station and a tugboat rigidly connected to the sailplane. The proposed solution is aimed at reducing operating costs and limiting the number of people necessary to service sailplane flights. В статье представлена разработка проекта беспилотного буксира-планера, описание этапов нового технического решения, представленного в патентное ведомство в декабре 2017 года и разработанного на сегодняшний день. Предлагаемая буксирная система состоит из универсального наземного поста управления дроном и буксира, жестко связанного с планером. Предложенное решение направлено на снижение эксплуатационных расходов и ограничение количества людей, необходимых для обслуживания полетов планеров. У статті представлено розробку проекту безпілотного буксира-планера, опис етапів нового технічного рішення, представленого до патентного відомства у грудні 2017 року та розробленого на сьогоднішній день. Пропонована буксирна система складається з універсального наземного поста керування дроном і буксира, жорстко пов'язаного з планером. Запропоноване рішення спрямоване на зниження експлуатаційних витрат та обмеження кількості людей, необхідних обслуговування польотів планерів.

Solar panels are used in wide range of applications like power generation, automobiles, electronic devices etc. They are trending devices which develop power from abundantly available solar energy. Inspite of this advantage, they are effected by wind loads, which result in wind induced loading. Determining this is very essential because, the drag and lift forces applied on the solar panels due to the wind loads play a crucial role in the accomplishment of performance in the solar panels. In this work, an attempt is made to carry out a comparative analysis of the effect caused by the wind Forces on different array sizes, altitudes, orientation of the solar panels at different wind speeds (5m/s, 25 m/s) and at different inclination angles the wind (00, 450, 1350 and 1800. The ultimate objective of this work is to analyze the effect caused by wind forces based on these combinations of the parameters. Different shapes of solar panels like rectangular and hexagonal shaped are analyzed for normal and optimized conditions. Also wind load analysis is carried out for different altitudes like on the ground and on the roof top. Outcomes depict that the wind forces on front region of the conventional solar panels is higher when compared to the optimized solar panel.

Ovaj rad bavi se aerodinamikom aviona. Prvi dio rada odnosi se na izradu 3D modela aviona s prilagođenim novim krilom, odnosno NACA 2411 profilom u programu Autodesk Inventor. Nakon izrade 3D modela, korišten je Hypermesh za izradu numeričke mreže. Dobivena numerička mreža ubačena je u Virtual Wind Tunnel gdje je provedeno nekoliko simulacija koje su uspoređene i na temelju kojih su doneseni zaključci., The topic of this final thesis is the aerodynamics of airplanes. The first part refers to the creation of a 3D model of the airplane with an adapted new wing NACA 2411 profile in the Autodesk Inventor program. After a 3D model was created, Hypermesh was used to create the numerical mesh. The resulting numerical network was inserted into Virtual Wind Tunnel, where several simulations were performed, compared, and based on which conclusions were drawn.

The ability to cross both natural and man-made obstacles have always been crucial for good mobility and is vitally important for various operations. The series of Pontoons are used as floating bridge to allow the transport vehicles and personnel over water and marshy grounds. Floating bridges are cost-effective solutions for crossing large bodies of water with unusual depth. Friction drag is observed when relative motion exists between pontoon and fluid. In view of this drag force is required to be evaluated correctly so that arrangement to fix the pontoon can be accurately designed considering the load and safety factors. For this required to carry out experiment to measure drag forces acting on the pontoons due to water resistance at various weights and water velocities. To study and collect numerous data, three pontoons of various shapes and materials were chosen for experiments. The drag force of pontoons is measured at 0, 5 and 10 degrees by add on various loads and submergence levels. During the experiments, a pontoon freely suspended to Rating Trolley when towed at a predetermine speed in straight open water tank, the drag force induced is measured by precise load cell. Experimental outcomes of all three pontoons for drag forces at 0, 5 and 10 degrees at various submergences and velocities will limit its application in specific velocity range and weight applied on it. Experimental analysis indicates the drag force is directly proportional to the frontal resistive area, water velocity and depth of submergence.

In the simulation of dilute gas-solid flows such as those seen in many industrial applications, the Lagrangian Particle Tracking method is used to track packets of individual particles through a converged fluid field. In the tracking of these particles, the most dominant forces acting upon the particles are those of gravity and drag. In order to accurately predict particle motion, the determination of the aforementioned forces become of the upmost importance, and hence an improved drag force formula was developed to incorporate the effects of particle concentration and particle Reynolds number. The present CFD study examines the individual effects of particles located both perpendicular and parallel to the flow direction, as well as the effect of a particle entrain within an infinite matrix of evenly distributed particles. Results show that neighbouring particles perpendicular to the flow (Model 2) have an effect of increasing the drag force at close separation distances, but this becomes negligible between 5–10 particle diameters depending on particle Reynolds number (Rep). When entrained in an infinite line of particles co-aligned with the flow (Model 1), the drag force is remarkably reduced at close separation distances and increases as the distance increases. The results of the infinite matrix of particles (Model 3) show that, although not apparent in the individual model, the effect of side particles is experienced many particle diameters downstream.

The method has been developed and systematic studies have been carried out to measure the drag forces, that exerted by a magneto-abrasive tool on machined cylindrical parts with a diameter of 16 mm and the height of 30 mm, made of para-, ferro- and diamagnetic materials, in an annular working zone with the diameter of 200 mm with the working height of 30 mm at machining speeds in the range of 1 - 3 m / s, magnetic induction in the working areas varying in the range of 0.2 - 0.25 T. It is shown that the drag forces significantly depend on the magnetic and rheological properties of the magneto-abrasive tool. During magneto-abrasive finishing (MAF), the drag force for non-magnetic parts is almost the same and does not depend on the machining speed, and with an increase in magnetic induction in the working areas, its linear growth takes place. The coefficient of magnification of drag force determined by the magnetic field, for powders with a particle size of 400/315 µm is 960 N/T, and for a size of 200/100 µm it is 720 N/T. It is shown that the drag forces during the MAF of ferromagnetic parts vary in the range from 160 to 220 N and are 1.2–1.45 times higher than for non-magnetic parts, which is due to the action of forces of magnetic origin, the features of the interaction of structural elements of MAT with machined surfaces and the formation of blocking up zones between the surface of the part and the pole pieces of the annular bath. The periodic change in the drag forces of the MAT of the workpiece was established near their average value, and at elevated MAF speeds of more than 2–2.5 m/s, instabilities were recorded associated with a periodic decrease in the oscillation amplitudes of the drag forces as a result of rearrangement, changes in the dimensions and volumes of the structural elements of the magneto-abrasive tool and the conditions of their interaction with the machined surfaces., Розроблено методику та виконано систематичні дослідження по вимірюванню сил лобового опору, що виникають в магнітно-абразивному інструменті (МАІ) при обробленні циліндричних деталей діаметром 16мм і висотою 30мм, виготовлених з пара-, феро- та діамагнітних матеріалів, в кільцевій камері діаметром 200мм з робочою висотою 30мм при швидкостях оброблення в діапазоні 1–3м/с, магнітній індукції в робочих зонах, що змінюється в діапазоні 0,2–0,25Тл. Показано, що сили опору суттєво залежать від магнітних та реологічних властивостей магнітно-абразивного інструменту. При магнітно–абразивному обробленні (МАО) лобовий опір для немагнітних деталей практично однаковий і не залежить від швидкості оброблення, а зі збільшенням магнітної індукції у робочих зонах має місце його лінійне зростання. Коефіцієнт збільшення лобового опору, що визначається магнітним полем, для порошків розміром частинок 400/315мкм становить 960Н/Тл, а для розміру 200/100мкм – 720Н/Тл. Показано, що сили лобового опору при МАО феромагнітних зразків змінюються в діапазоні від 160 до 220Н та в 1,2–1,45 разів вищі, ніж для немагнітних деталей, що пов'язано з дією сил магнітного походження, особливостями взаємодії структурних елементів МАІ з оброблюваними поверхнями та формуванням зон заклинювання між поверхнею деталі та полюсними наконечниками кільцевої ванни. Встановлено періодичну зміну сил опору МАІ оброблюваній деталі поблизу їх середнього значення, а при підвищених швидкостях МАО понад 2–2,5м/с зафіксовані нестійкості, пов'язані з періодичним зменшенням амплітуд коливань сил опору внаслідок перебудови, зміни розмірів та об'ємів структурних елементів магнітно-абразивного інструменту та умов їх взаємодії з оброблюваними поверхнями.

Introduction Almonds (Prunus amygdalus) belongs to the family of Rosaceae and the subspecies of Pronoideae. Its kernel contains a lot of energy, amino acids, sugars and mineral elements. Iran is ranked fifth in terms of producing almonds after United States, Australia, Spain, and Morocco, but at the same time, Iran's position is not very suitable in the world export market. The processing of this product involves three stages of shell breaking, kernel separation, and packaging. One of the important methods of separation of the kernel from the wooden crust is the use of pneumatic separation and this method can be used to grade, clean, and separate the seeds of different materials. Materials and Methods Almond samples of the Shokofeh variety (A.H.3) were obtained from Maragheh gardens in East Azarbaijan province. The moisture content of the shell, the kernel, and mixture of them was determined using the oven drying method. Also, some physical and mechanical properties were measured. In order to design the almond separator system, it is important to determine aerodynamic properties. The most important aerodynamic properties such as terminal velocity and drag force were determined. The first step in designing and manufacturing a device is to select the cross-sectional shape and dimension. The cross-section of the machine is selected based on parameters such as simplicity and construction costs. With the assumption of a machine with a separation capacity of 2 kg (mixed product) per minute, the length and the width of the machine were obtained to be 18 cm and 15 cm. Using the terminal velocity and dimensional data, the blower distance to the outlet, the tunnel length, the power and flow rate of the blower were calculated and then the design and construction were done. To evaluate the separation and evaluation of the apparatus, parameters such as blower speed, shell size, and moisture content of the mixture were investigated for each parameter at three levels. Airflow rates of the wind tunnel were 3, 5, and 7 m s-1, moisture content (7%, 13%, and 19%), shell size in three groups: small, medium, and large. Results and Discussion The average geometric properties including length, width, thickness, geometric mean diameter, and spherical coefficient for almonds were 20.64, 13.25, 7.4, 12.64 mm, and 0.612, respectively, as well as properties for large shells (25.17, 16.5, 11.15, 16.66 mm, and 0.66), for average size (17.36, 13.5, 6.4, 11.44 mm, and 0.65) and fine size (13, 9.9, 3.5, 7.66 mm, and 0.59), respectively. The mechanical properties of the samples (shell and almond kernel) were measured at three levels of moisture content of 7%, 13%, and 19%. The results showed that by increasing the moisture content, the fracture force for both shell and kernel increases. Almond shell had the highest angle of rotation at all levels of moisture. This was due to its heterogeneous shape, broken edges and rough surface. On the other hand, almonds had the lowest degree of rotation, due to the greater weight of the kernel and the more homogeneous and spherical shape than the shell. The results obtained from measuring the terminal velocity of the samples selected from the kernel and shell in terms of their weight indicated that the velocity limit for the almonds was 10.2-12.2 m s-1 and for the shell, the range was 1.8-6 m s-1. The variance analysis of the effect of particle size, velocity, and moisture parameters on the level of separation of shell in almond mixture showed that all major effects and interactions of factors were significant at 1% probability level. Particle size and moisture content did not affect the separation rate at 7 m s-1. With decreasing velocity, the separation rate in the particle size was reduced, which was due to the higher speed of the separation rate. At low velocity, the best separation was related to the fine particle size, which was due to the harmonization of the fine particle velocity and the separation rate. Conclusions Pneumatic separation of almond kernel and shell was affected by air velocity, particle size and moisture content. As the flow rate increases, the amount of shell separation from the kernel increases. Particle size and moisture content did not affect the separation rate at 7 m s-1. The results at medium moisture content indicated that in addition to the acceptable separation level (relative to other moisture levels) at this level (13%), the harvesting time of this product can be managed and the use of additional energy in the processing of this product is prevented.

Prvim dijelom ovog završnog rada objašnjene su sve teorijske osnove vezane za fizikalne veličine koje se javljaju u daljnjim razmatranjima i u razmatranju aerodinamike općenito. Daljnjim ulaskom u problematiku zadatka definirane su vrste strujanja fluida i osnove aerodinamike zgrada. Za praktični dio završnog rada promatrana je jednostavna geometrija kocke koja sukladno stvarnosti najbolje opisuje model zgrada u simulacijama. Pojašnjenjem računalne dinamike fluida i korištenih programa u samoj izradi simulacija i analiza, došlo se je do brojčanih i grafičkih rezultata generiranih post-procesorom za dva različita slučaja opstrujavanja neaerodinamičnog tijela. Prema dobivenim podacima izveo se kratak zaključak temeljen na ključnim razlikama između dvije simulacije, a na samom kraju izveden je zaključak o cjelokupnom radu i računalnoj dinamici fluida., The first part of this final paper explains all the theoretical bases related to fluid mechanics and aerodynamics in general. Moving deeper into the problems of the task, the types of fluid flow and the basics of building aerodynamics are defined. For the practical part of the final work, a simple geometry of a cube was observed, which is the best description of the building model in simulations and in reality. By using computational fluid dynamics methods and related programs for the creation of simulations and analyses, numerical and graphical results generated by the post-processor for two different cases of obstruction of a non-aerodynamic body were obtained. According to the obtained data, a short conclusion was given, which was based on the key differences between the two simulations. Also, at the very end, a conclusion was drawn about the overall CFD and data in this paper.

Remotely Operated Vehicle (ROV) is mainly used for many tasks and applications such as exploration in the sea. The designing and optimization of ROV systems have a great potential in order to enhance performance and working mechanism. In this research work, Computational Fluid Dynamics (CFD) analyses of five different ROV underwater vehicles were performed for the design modification. In addition, CFD analysis of best suitable thruster design was also conducted in order to examine the flow behavior around the thruster body. Moreover, performance of ROV systems and thruster were also conducted in order to select optimized ROV design. For this purpose, Computational Fluid Dynamics (CFD) analyses of five different ROV models and one modified thruster model were performed using ANSYS FLUENT. CFD analyses were performed at different water flow velocities such as 1 m/s, 1.5 m/s, 2 m/s, 2.5 m/s, 3 m/s and 3.5 m/s for the depth range of 4m to 50m. Drag force, pressure contours, velocity contours, were computed at different water flow velocities in order to examine and select the modified ROV model having lowest drag force. According to computed results, the maximum drag forces are observed for design 4 and minimum drag forces are observed for design 5. The reason behind larger computed values of drag forces are due to maximum contact area of water flowing around the ROV model. In design 5 of ROV model, the flow water impact minimum on the frontal area and observed lowest value of drag force. The maximum and minimum values of the drag forces for design 5 are 6.40062 N and 0.60606 N at water flow velocities of 3.5 m/s and 1 m/s respectively. On the other hand, it can be observed from the computed results of thruster design that the maximum hydraulic pressure was obtained at water flow velocity of 3.5 m/s and minimum value observed at 1 m/s. Finally, it was concluded from the obtained results that ROV design 5 is best suitable design for underwater application at depth range of 4m to 50m. The obtained results from this study can be very helpful for engineers and researchers in order to design and optimization of ROV models using numerical approach.&nbsp

Large structures such as tall buildings, towers, and bridges transfer their loads to competent soil layers through pile skin friction and/or end bearing. When a pile is installed in a compressible soil layer, it may experience additional skin frictional force called “drag force” due to excessive soil settlement relative to the pile resulting from external loadings such as embankment construction. The location of maximum drag force, where skin friction is equal to zero or soil settlement and pile settlement become equal, is called the “neutral plane”. This thesis discusses the results of a comprehensive long-term field-monitoring program of three instrumented abutment piles and adjacent soil in order to evaluate the developed drag forces along the shafts of the three piles. The data collected from the field-monitoring program are presented and discussed in terms of measured responses with time, and load distribution along the pile shafts. In addition, the results were used to examine the unified design method and assess the design codes with respect to drag force. The findings indicated that the piles most likely behaved independently, and each experienced different magnitude of drag forces that extended to different elevations (i.e., neutral plane locations). A reasonable prediction of drag force can be achieved using the unified design method by considering the soil in the pile vicinity to be normally consolidated using both the total stress method (a) and effective stress method (b). The design of piles subject to drag force can be costly when following the AASHTO (2014), while the design following CHBDC (CSA 2006) and FHWA (2016) would result in safe and efficient design. Furthermore, the data were utilized to validate three-dimensional (3D) finite element models that were then employed to conduct a comprehensive parametric study to assess different aspects related to negative skin friction on single piles as well as group effects on drag force distribution among piles installed in small and large groups. The results revealed that the soil along the pile shaft moved with the pile and no soil plug was observed at the pile toe. Moreover, the analysis showed that the group effect might be neglected for piles installed in one row; however, it cannot be neglected for piles installed in large groups. Finally, design charts to calculate the toe resistance and group factor to calculate the drag force for a group of piles are presented in this study.

The rapid electrokinetic patterning (REP) technique has been demonstrated to enable dynamic particle manipulation in biomedical applications. Previous studies on REP have generally considered particles with a size less than 5 μm. In this study, a REP platform was used to manipulate polystyrene particles with a size of 3~11 μm in a microfluidic channel sandwiched between two ITO conductive glass plates. The effects of the synergy force produced by the REP electrothermal vortex on the particle motion were investigated numerically for fixed values of the laser power, AC driving voltage, and AC driving frequency, respectively. The simulation results showed that the particles were subject to a competition effect between the drag force produced by the toroidal vortex, which prompted the particles to recirculate in the bulk flow adjacent to the laser illumination spot on the lower electrode, and the trapping force produced by the particle and electrode interactions, which prompted the particles to aggregate in clusters on the surface of the illuminated spot. The experimental results showed that as the laser power increased, the toroidal flow range over which the particles circulated in the bulk flow increased, while the cluster range over which the particles were trapped on the electrode surface reduced. The results additionally showed that the particle velocity increased with an increasing laser power, particularly for particles with a smaller size. The excitation frequency at which the particles were trapped on the illuminated hot-spot reduced as the particle size increased. The force and velocity of polystyrene particles by the REP toroidal vortex has implications for further investigating the motion behavior at the biological cell level.

Models of the passenger car without and with rear spoiler (types S1 and S2) are created using SolidWorks software. The ANSYS software/Fluid Flow (CFX) module was used to analyze deeply these models based on the numerical approach in order to achieve higher speed for vehicle with maintaining the stability of the car at the same time. Results of the numerical analysis proved that the spoiler has great influence on the longitudinal stability incensement, especially under high speeds conditions. While the shape of the spoiler is not significant factor on the stability. The lift force was reduced 7.6 times when used the spoiler (type S2) compared with to the vehicle without spoiler. While the drag force was increased 12% when used the spoiler (type S2). It was analyzed the influence of existence the rear spoiler on the passenger car, as well as the effect of the shape and construction dimensions of the spoiler on the longitudinal stability. It was developed integrated approach that included the design and numerical analysis of the vehicle stability. It was proved based on the developed approach how can reduced the negative effect of some factors in order to enhance the stability of the vehicle. Graphical Abstract: [Figure not available: see fulltext.].

U ovom završnom radu je generalno objašnjeno područje aerodinamike unutar Mehanike Fluida. Izrađen je 3D model Airbusa A320 sprofilom krila NACA 4415 u programu SolidWorks. Za izradu simulacije je upotrijebljen program Altair HyperWorks. Numerička mreža 3D modela izrađena je u HyperMeshu te je ista kasnije ubačena u Virtual Wind Tunnel. Provedeno je više simulacija s različitim postavkama strujanja fluida da možemo usporediti dobivene rezultate te izvući zaključak., This final thesis generally explains the area of aerodynamics in Fluid Mechanics. 3D model of Airbus A320 with NACA 4415 wing profile was made in SolidWorks. For simulation purposes, Altair HyperWorks was used. Numerical mesh for the 3D model was made in HyperMesh and imported into Virtual Wind Tunnel for simulations. Multiple simulations were made with different presets for fluid flow so we could compare results and draw a conclusion.

An understanding of fish movement behavior in response to flow field variables is important for exploring the hydrodynamic strategies of fish in fish passages. In this paper, bighead carps were taken as an example. The fish movement behavior response to water flow field information by means of estimating the energetic expenditure using an IBM approach in an experimental fishway was investigated. Fish swimming velocity, drag force, and energy expenditure were analyzed in varied flow conditions related to hydraulic variables, including velocity (V), turbulent kinetic energy (TKE), and strain rate (SR). The result indicated that the fish will require more energy in high TKE zones. This study provides a reference for optimizing the design of fish passages and fisheries management. This method can be applied to assess the efficiency of fish bypass structures and conduct fish survival studies.

Masonry arch bridges form an essential part of existing transport infrastructure around the world, including mainland Europe and the northeastern US. Recent extreme flood events highlight that masonry arch bridges spanning watercourses are vulnerable to flood-induced hydrodynamic and debris impact loads. When the flow interacts with the bridge superstructure, with or without discrete floating debris, a complex interaction is observed. This paper presents both experimental and numerical studies to investigate this complex phenomenon, including fluid–structure and structure–structure interactions. A typical single-span masonry arch bridge and large woody debris representing a tree log are investigated. Experimental observations from a scaled hydraulic model, with and without debris in the flow, are first presented for the case where the abutment of the bridge is fully submerged. Next, the capability of the numerical method smoothed particle hydrodynamics (SPH) in simulating the hydrodynamic behaviour and debris impact observed in the experiment is discussed. Following this, both hydrodynamic and debris-induced pressure–time histories on the bridge are obtained using the SPH model. Results reveal that the debris impact leads to a significantly more localised load on the bridge compared to the situation with hydrodynamic load only.

Evaluating the hydrodynamic force fluctuations acting on each structure in a group of subsea objects of different cross-section shapes, sizes and relative positions represents a challenge due to the sensitivity of the vortex shedding process, especially for a variety of sheared flows. The present study uses the numerical 2D computational fluid dynamics model to estimate the flow-induced forces on a group of small circular and D-shaped cylinders in the linear and parabolic sheared flow, which are placed in proximity to a larger structure of the squared cross-section. This allows us to evaluate loads, which are affected by the presence of subsea equipment located on the seabed. The average Reynolds number of the considered linear flow profile is 3900, while the parabolic flow profile has the maximum Reynolds number of 3900. The k-ω SST turbulence model is used for simulations. The work demonstrates the effect of the cross-sectional shape of smaller cylinders on hydrodynamic coefficients, explores the effect from the spacing in between the structures and highlights differences between loads in the linearly sheared and parabolic flow. The results obtained show that the presence of the squared cylinder notably influences the mean drag coefficient on the first cylinder, for both circular and D-shaped cylinders. The parabolic sheared flow profile in this series leads to the highest mean drag and the highest amplitudes of the fluctuating drag and lift coefficients.

Studies have demonstrated that hurricanes can drive selection in Neotropical anoles. In a recent study, it was shown that post-hurricane survivors showed longer toepad areas and, surprisingly, shorter femurs. 2. One potential explanation for the reduction in femur length is that increased drag on individuals with longer femurs causes them to be blown off their perch. Consequently, lizards with shorter femora might survive better in hurricanes. 3. To gain insight into the form-function relationships of drag reduction in perched lizards exposed to high-velocity winds, we quantified drag forces on Anolis lizard models in realistic grasping positions using computational fluid dynamics. 4. We showed that overall drag, as well as the relatively high drag at the hindlimbs strongly increase with the distance of the pelvic region from the perch. As optimal postures to resist sustained arboreal pulling involve extended limbs, longer hindlimbs increase the chance of having the limbs and pelvic region positioned outside the zone in which efficient shielding from the wind by the perch occurs. 5. Our study underlines the complexity of performance trade-offs on the evolution of limb morphology in arboreal lizards, and emphasizes the importance of generally ignored functions such as aerodynamic drag reduction in arboreal ecosystems.

Micromotors have spread widely in order to meet the needs of new applications, including cell operation, drug delivery, biosensing, precise surgery and environmental decontamination, due to their small size, low energy consumption and large propelling power, especially the newly designed multifunctional micromotors that combine many extra shape features in one device. Features such as rod-like receptors, dendritic biosensors and ball-like catalyzing enzymes are added to the outer surface of the tubular micromotor during fabrication to perform their special mission. However, the structural optimization of motion performance is still unclear. The main factor restricting the motion performance of the micromotors is the drag forces. The complex geometry of a micromotor makes its dynamic behavior more complicated in a fluid environment. This study aimed to design the optimum structure of tubular micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the micromotors. By using the computational fluid dynamics software Fluent 18.0 (ANSYS), the drag force and the drag coefficient of different conical micromotors were calculated. Moreover, the influence of the Reynolds numbers Re, the semi-cone angle δ and the ratios ξ and η on the drag coefficient was analyzed. The results show the drag force monotonically increased with Reynolds numbers Re and the ratio η. The extreme point of the drag curve is reached when the semi-cone angle δ is 8° and the ratio ξ is 3.846. This work provides theoretical support and guidance for optimizing the design and development of conical micromotors.

The processes of sediment particle movement were studied through numerical simulation using a coupled method with focus on discussing the characteristics of sliding or rolling and saltation sediment particles, respectively. Turbulent flow was simulated using large eddy simulation (LES). The sediment particle was simulated using the combined finite-discrete element method (FDEM). The interaction forces of turbulent flow and sediment particle were calculated using the immersed boundary method (IBM). It indicated that the collisions of saltating particle with low concentration increase the saltation length and flight time. In response, sediment particle velocity also increases. The particle angular velocity is largest at the takeoff moment, and decreases gradually in the saltation progress. The drag and lift forces near the bed are large, and away from the bed decrease and trend to be a stable value, gradually. From the relative magnitudes of the drag and lift forces, the lift force plays a more important role than the drag force in the sediment saltation. The relative magnitudes of drag and lift forces influence the incident and takeoff angles. The sediment transport rate calculated based on the characteristics of saltation sediment particles is overestimated, ignoring the effect of sliding or rolling sediment particles and inter-particle collisions.

Diving beetle, an excellent biological prototype for bionic underwater vehicles, can achieve forward swimming, backward swimming, and flexible cornering by swinging its two powerful hind legs. An in-depth study of the propulsion performance of them will contribute to the micro underwater vehicles. In this paper, the kinematic and dynamic parameters, and the hydrodynamic efficiency of the diving beetle are studied by analysis of swimming videos using Motion Capture Technology, combined with CFD simulations. The results show that the hind legs of diving beetle can achieve high propulsion force and low return resistance during one propulsion cycle at both forward and backward swimming modes. The propulsion efficiencies of forward and backward swimming are 0.47 and 0.30, respectively. Although the efficiency of backward swimming is lower, the diving beetle can reach a higher speed in a short time at this mode, which can help it avoid natural enemies. At backward swimming mode, there is a long period of passive swing of hind legs, larger drag exists at higher speed during the recovery stroke, which reduces the propulsion efficiency to a certain extent. Reasonable planning of the swing speed of the hind legs during the power stroke and the recovery stroke can obtain the highest propulsion efficiency of this propulsion method. This work will be useful for the development of a bionic propulsion system of micro underwater vehicle.

Application of the block ramp technique in steep gradient streams for energy dissipation as well as to maintain river stability finds increasing favor amongst researchers and practitioners in river engineering. This paper dwells on a comprehensive state-of-the-art review of flow resistance, energy dissipation, flow characteristics, stability, and drag force on block ramps by various investigators in the past. The forms and equations for each type are thoroughly discussed with the objective of finding the grey areas and gaps. More research is warranted further to improve the equations, which are essential for design analysis. Block ramps can be a promising simple technique to achieve reasonable attenuation of devastating fluvial forces unleashed in gravel-bed streams during cloud bursts. HIGHLIGHTS A critical review of recent advancement in flow resistance, energy dissipation, flow characteristics, stability and drag forces on block ramps.; Highlights the grey areas and gaps.; Need for 3D turbulent burst analysis for better understanding of the internal mechanism of turbulent structures.; Application of all the equations in design with limitations and suggestions for improvement are well discussed.; Formulation of block ramps is based on steady flow assumption but in reality flows are highly turbulent with unsteady flow in mountain streams.

Numerical simulations of contaminated spherical drops falling through a stagnant liquid at low Reynolds numbers are carried out using the finite difference method. The numerical results are used to describe the behavior of the surfactant concentrations and to understand the surfactant effects on the fluid motions in detail. The predicted interfacial surfactant concentration, Γ, is almost zero for angles, θ, below a certain value (the stagnant-cap angle, θcap ), whereas it steeply increases and reaches a large value for θ > θcap (the stagnant-cap region). The increase in the initial surfactant concentration, C0, in the drop enhances the adsorption from the drop to the interface, which results in the increase in Γ and the decrease in θcap . Peaks appear in the predicted Marangoni stresses around θcap, which causes similar peaks in the pressure distribution. The high-pressure spots prevent the fluid motion along the interface, which results in the formation of the stagnant-cap region and the attenuation of the tangential velocity in the continuous phase. The surfactant flux from the bulk to the interface decreases C in the vicinity of the interface for θ < θcap and the weak diffusion cannot compensate for the reduction in C by adsorption, which results in C at the interface smaller than C0 . The pattern of the low C region is determined by the advection and does not smear out because of a small diffusive flux.

Розроблено методику та виконано систематичні дослідження по вимірюванню сил лобового опору, що виникають в магнітно-абразивному інструменті (МАІ) при обробленні циліндричних деталей діаметром 16 мм і висотою 30 мм, виготовлених з пара-, феро- та діамагнітних матеріалів, в кільцевій камері діаметром 200 мм з робочою висотою 30 мм при швидкостях оброблення в діапазоні 1 – 3 м/с, магнітній індукції в робочих зонах, що змінюється в діапазоні 0,2 – 0,25 Тл. Показано, що сили опору суттєво залежать від магнітних та реологічних властивостей магнітно-абразивного інструменту. При магнітно–абразивному обробленні (МАО) лобовий опір для немагнітних деталей практично однаковий і не залежить від швидкості оброблення, а зі збільшенням магнітної індукції у робочих зонах має місце його лінійне зростання. Коефіцієнт збільшення лобового опору, що визначається магнітним полем, для порошків розміром частинок 400/315 мкм становить 960 Н/Тл, а для розміру 200/100 мкм – 720 Н/Тл. Показано, що сили лобового опору при МАО феромагнітних зразків змінюються в діапазоні від 160 до 220 Н та в 1,2 – 1,45 разів вищі, ніж для немагнітних деталей, що пов'язано з дією сил магнітного походження, особливостями взаємодії структурних елементів МАІ з оброблюваними поверхнями та формуванням зон заклинювання між поверхнею деталі та полюсними наконечниками кільцевої ванни. Встановлено періодичну зміну сил опору МАІ оброблюваній деталі поблизу їх середнього значення, а при підвищених швидкостях МАО понад 2 – 2,5 м/с зафіксовані нестійкості, пов'язані з періодичним зменшенням амплітуд коливань сил опору внаслідок перебудови, зміни розмірів та об'ємів структурних елементів магнітно-абразивного інструменту та умов їх взаємодії з оброблюваними поверхнями. The method has been developed and systematic studies have been carried out to measure the drag forces, that exerted by a magneto-abrasive tool on machined cylindrical parts with a diameter of 16 mm and the height of 30 mm, made of para-, ferro- and diamagnetic materials, in an annular working zone with the diameter of 200 mm with the working height of 30 mm at machining speeds in the range of 1 - 3 m / s, magnetic induction in the working areas varying in the range of 0.2 - 0.25 T. It is shown that the drag forces significantly depend on the magnetic and rheological properties of the magneto-abrasive tool. During magneto-abrasive finishing (MAF), the drag force for non-magnetic parts is almost the same and does not depend on the machining speed, and with an increase in magnetic induction in the working areas, its linear growth takes place. The coefficient of magnification of drag force determined by the magnetic field, for powders with a particle size of 400/315 µm is 960 N/T, and for a size of 200/100 µm it is 720 N/T. It is shown that the drag forces during the MAF of ferromagnetic parts vary in the range from 160 to 220 N and are 1.2–1.45 times higher than for non-magnetic parts, which is due to the action of forces of magnetic origin, the features of the interaction of structural elements of MAT with machined surfaces and the formation of blocking up zones between the surface of the part and the pole pieces of the annular bath. The periodic change in the drag forces of the MAT of the workpiece was established near their average value, and at elevated MAF speeds of more than 2–2.5 m/s, instabilities were recorded associated with a periodic decrease in the oscillation amplitudes of the drag forces as a result of rearrangement, changes in the dimensions and volumes of the structural elements of the magneto-abrasive tool and the conditions of their interaction with the machined surfaces.

The Computational Fluid Dynamics (CFD) tool pafiX (particle flow simulation in explosion protection) focuses on modeling the electrostatic charging of particle-laden flows. In CFD simulations of two-phase flows, accurate drag force modeling is essential for predicting particle dynamics. However, since all existing drag correlations were established for specific flow situations, a generally valid formulation is lacking. In particular, these correlations have not been evaluated for particle-laden flows subjected to electrostatic forces. This thesis reports on the effect of drag force modeling on the flow of electrically charged particles. To this end, we implemented different drag correlations in pafiX. Then, we performed highly-resolved Direct Numerical Simulations (DNS) using a Eulerian-Lagrangian approach of a particle-laden channel flow of a friction Reynolds number of 180. The simulations generally revealed a strong influence of the precise drag correlation on particles in the near-wall region and a minor effect on the particles far from the walls. Due to their turbophoretic drift, particles accumulate close to the channel walls. For uncharged particles, the simulations show large deviations of the particle concentration profile in the near-wall region depending on the drag force correlation. Therefore, the disturbance of the flow surrounding a particle by a nearby wall or other particles is important for its drag. Driven by electrostatic forces, charged particles accumulate even closer to the wall. Contrary to the uncharged cases, when the particles carry a high charge (in our case one femto-coulomb), we found minor effects of a nearby wall and nearby particles on the drag force. In conclusion, for the investigated conditions, we propose to account for the effect of nearby particles and walls on the drag of charged and uncharged particles., Hesaplamalı Akışkanlar Dinamiği (HAD) aracı olan pafiX (patlama korumasında parçacık akışı simülasyonu), parçacık yüklü akışların elektrostatik yüklenmesi olayını modellemeye odaklanır. İki fazlı akışların HAD simülasyonlarında, parçacık dinamiklerini tahmin etmek için doğru sürükleme kuvveti modellemesi esastır. Mevcut sürükleme kuvveti korelasyonları ancak belirli akış durumları için mevcut olduğundan, genel olarak geçerli bir formülasyon eksikliği vardır. Özellikle, bu korelasyonlar, daha önce elektrostatik kuvvetlere maruz kalan parçacık yüklü akışlar için değerlendirilmemiştir. Bu tez, sürükleme kuvveti modellemesinin elektrik yüklü parçacıkların akışı üzerindeki etkisini bildirmektedir. Bu etkiyi inceleyebilmek amacıyla pafiX'e farklı sürükleme kuvveti korelasyonları uygulandı. Ardından, sürtünme Reynolds sayısı 180 olan parçacık yüklü kanal akışının Eulerian-Lagrange yaklaşımı kullanılarak yüksek çözünürlüklü Doğrudan Sayısal Simülasyonu (DNS) gerçekleştirildi. Simülasyon sonuçları genel olarak duvara yakın bölgedeki parçacıklar üzerinde sürtünme korelasyonunun güçlü bir etkisi olduğunu, duvarlardan uzaktaki parçacıklar üzerinde ise etkisinin küçük olduğunu ortaya çıkardı. Turboforetik sürüklenme nedeniyle, parçacıkların kanal duvarlarına yakın bir yerde biriktiği görüldü. Yüksüz parçacıklar için simülasyonlarda, sürükleme kuvveti korelasyonuna bağlı olarak duvara yakın bölgedeki parçacık derişim profilinde büyük sapmalar görüldü. Buradan, bir parçacığı çevreleyen akışın yakınındaki bir duvar veya diğer parçacıklar tarafından bozulmasının, sürükleme kuvveti için önemli bir etki olduğu sonucuna varılmıştır. Elektrostatik kuvvetler tarafından yönlendirilen yüklü parçacıkların, yüklü olmayan parçacıklara göre, duvara daha da yakın bir yerde biriktiği görüldü. Yüksüz durumların aksine, parçacıklar yüksek bir yük taşıdığında (bu incelemede 1 femto Coulomb), yakındaki bir duvarın ve parçacıların sürükleme kuvveti üzerindeki etkilerinin oldukça düşük olduğu görüldü. Sonuç olarak, yüklü ya da yüksüz tüm parçacıkların sürüklenmesi üzerinde hem yakınlarındaki parçacıkların ve hem de duvarların etkisinin göz önüne alınması gerektiği ortaya konulmuştur.

Inducible defenses are a wide-spread defensive mechanism in Daphnia. For example, D. cucullata is known to form different adaptive morphologies under changing environmental conditions. In this species, predator presence elicits defensive helmets. Defended animals perform better and survive more frequently in predation attempts. Another peculiarity of D. cucullata is that they develop these defenses also in response to turbulence. The mechanisms that underly this defensive effect are so far unclear. Therefore, we investigated the three-dimensional morphology of the typical, the turbulence- and Chaoborus-exposed morph and analyzed their surface and volume alterations. We furthermore measured the swimming velocities of these morphs. With the determined shapes and the measured velocities, we simulated the drag force under different angles of attack and determined the energy necessary to move through the water. In the light of previous findings and hypotheses we here discuss biomechanical mechanisms that improve D. cucullata’s fitness in the investigated environments.

Значение воздушного сообщения между различными пунктами земного шара в современном мире трудно переоценить. Однако использование этого вида транспорта сопряжено с высокими рисками для пассажиров, экипажа, грузов и самого воздушного судна в связи с возможностью серьезных аварий на всех этапах полета, но особенно при взлете и посадке. В данной статье представлена физико-математическая модель разбега самолета при взлете, анализ которой позволяет избежать аварий при возникновении нештатных ситуаций. Эта модель дает возможность создать электронное устройство для контроля взлетных динамических характеристик и предупреждения экипажа воздушного судна о возникающих несоответствиях. В статье приведены дифференциальные уравнения, описывающие динамические характеристики самолета при разбеге. А также получены решения этих уравнений, определяющие в явном виде функциональные зависимости необходимой для безопасного взлета дистанции от времени, прошедшего с начала разбега. Рассмотрено, как влияют на рассчитываемые характеристики внешние факторы, такие как температура окружающего воздуха, скорость ветра при взлете, наклон взлетно-посадочной полосы. Также в статье представлены в качестве примера результаты моделирования нештатного взлета с использованием современных программных средств (авиасимулятор flightgear 2020.3, математическая программа GeoGebra). С точки зрения авторов, материалы статьи могут представлять практическую ценность для разработчиков невстраиваемых бортовых контрольных устройств, а также для пользователей этих устройств., The importance of air communication between various points of the globe in the modern world is difficult to overestimate. Yet the employment of this means of transport is associated with high risks for passengers, crew, cargo and the aircraft itself due to the possibility of serious accidents at all phases of the flight, but especially during takeoff and landing. This article presents a physical and mathematical model of an aircraft takeoff-run. Its analysis helps to avoid accidents in the event of emergency situations. This model enables the creation of an electronic device for monitoring takeoff dynamic characteristics and warning the aircraft crew about arising inconsistencies. The article presents differential equations describing the dynamic characteristics of the aircraft during takeoff-run. Additionally, solutions of these equations are obtained, which explicitly determine the functional dependencies of the distance necessary for a safe takeoff on the time elapsed since the start of the takeoff-run. The influence of external factors, such as ambient air temperature, wind speed during takeoff and runway slope on the calculated characteristics is considered. As an example, the article also offers the results of an emergency takeoff modeling with the aid of modern software (flight simulator flightgear 2020.3, GeoGebra mathematical program). From the authors’ point of view, the materials of the article may be of practical value for developers of non-embedded on-board control devices, as well as for users of these devices., МОДЕЛИРОВАНИЕ, ОПТИМИЗАЦИЯ И ИНФОРМАЦИОННЫЕ ТЕХНОЛОГИИ, Выпуск 2 (37) 2022, Pages 1-2

Trees are important natural wind engineering elements in both the urban and the agricultural contexts, but their aerodynamic description has been limited by its focus on young, flexible trees. Here, we provide a reformulation of the classical drag equation, which is also suitable for mature and wind-adapted trees. The new formulation is based on results from a full-scale experiment with focus on a solitary oak tree, for which we determined all terms in the drag equation experimentally. We also present a new photographical method for the accurate quantification of the tree’s frontal area under highly variable outdoor lighting conditions. We used a database of images from a surveillance camera, from which a high-quality subset was automatically selected with machine learning algorithms. Compared to previous work on younger and smaller trees, the mature tree has a lower absolute value of the Vogel exponent, which indicates a relatively low degree of reconfiguration. The presented results underline the high efficiency of mature trees in reducing the momentum of the wind. The results can be used to quantify the effect of similar trees in wind simulations, and the new method for determining the frontal area can be applied in other tree measurement campaigns.

Drying of the sewage sludge layer was investigated in a convective laboratory dryer at air temperatures of 65 °C and 80 °C and air speeds of 0.53 m/s and 0.83 m/s. The sludge layer was formed by loading cylindrical extrudates on a grate of 0.5 m × 0.5 m size. The drying air was directed through the layer, as typically encountered in industrial belt dryers. Under such setup, the sludge layer structure and porosity significantly affect the air flow conditions and thus the drying rates. Shrinkage and cracking of the material during drying caused changes in the layer’s porous structure, that affected the pressure drop and the drag force due to passing of air through the layer. The decreasing of drag force over time was modeled by a simple function that showed excellent agreement to the selected measured data. The sludge layer drying kinetics was determined by fitting the measured data to the most common drying models. Two models, the modified Nadhari and the Wang Singh model, were determined as most suitable for modeling of drying curves. The total drying time per kilogram of sludge was modeled as a function of drying air temperature, drying air velocity and initial sludge dry matter content. The coefficient of determination (R2) of the model is 0.944. Total drying times between 43 minutes per kilogram and 76 minutes per kilogram of sludge were obtained for the investigated range of drying air conditions.

The aerodynamics of powerboats used in inshore powerboat racing has a significant impact on their performance. The aerodynamic drag forces generated on individual elements of this type of boats were tested. The solid model of the boat developed in the CAD software was used for the calculations. The computational grid was generated, and the boundary conditions and the turbulence model were determined. Based on such assumptions, numerical calculations were carried out using the CFD method. The results from numerical simulations consist of a description of the velocity and pressure distribution around the tested object and an identification of the drag force on the components of the powerboat with a description of the relationship between them. Additionally, the variation of the drag force as a function of speed in the range from 0 to 60 m/s is presented. The tests were performed for 5 values of the angle of attack the boat to the surface of water in the range from 0° to 12°. The scope of the research allowed for the development of a drag force map depending on the defined parameters. The test results can be used to optimize the shape of the boat structure in order to reduce the aerodynamic drag generated on its individual elements.

In this paper, we have numerically examined models that are capable of describing free falling regimes of a rigid sphere in a thixotropic fluid as Laponite. By simultaneously solving the dynamical equations governing both sphere and fluid systems, different regimes referred to in the experimental methods, are obtained. Three common behavioral regimes are: i) quickly stopping object, ii) fall with decreasing velocity, and iii) falling with a constant velocity in a steady-state mode. The initial state of the fluids (which is a function of the aging time), the characteristic relaxation time of microstructure's building up under shear, the characteristic thickness of the yielded zone around the sphere, and critical yield stress value besides the diameter and density of the sphere are effective parameters that change the regime.

Fluid flows around a pointed object, e.g. the flow around a triangular prism, are often encountered. In this study, numerical simulation of the flow around a triangular prism was carried out using COMSOL Multiphysics® software. Two cases were considered: the entire area of the triangular prism is fixed; and only the center is fixed. The first case is divided into three different flow models according to the flow state: the separation bubble model, the edge separation model and the attached flow model. The effects of different flow models on the lift coefficient, drag coefficient and Strouhal number were discussed from the perspective of fluid flow. For the second case, the triangular prism periodically rotates while the vortices are separated from the surface. It was found that a stable rotation stage exists after a certain period of time for prisms with different initial positions. The lift and drag coefficients of the triangular prism satisfy the jagged and sinusoidal variation.

Immersed interface method is a non-matching boundary approach that has been taken into consideration in recent years. In this method, there is no need to coincide between the fluid and the solid grids. Eulerian grid is used for fluid domain and Lagrangian grid is used for solid domain. Using the Dirac Delta function, the connection between these two grids is established. Separation of the flow from the cylinder surface causes a high pressure drop in some parts of the cylinder, resulting in a dramatic increase in drag force. Drag force reduction is very important in some engineering issues, and several methods have been proposed to achieve this goal. In this study, the flow around a rigid cylinder is simulated. The goal is to reduce the drag force on the cylinder through one and two horizontal plates. The results are in good agreement with prior numerical results

This paper is focused on investigating the boundary effects of the steady translational motion of a semipermeable sphere located at the center of a spherical envelope filled with an incompressible micropolar fluid. Stokes equations of micropolar fluid are employed inside the spherical envelope and Darcy’s law governs in semipermeable region. On the surface of semipermeable sphere, the boundary conditions used are continuity of normal velocity, vanishing of tangential velocity of micropolar fluid, and continuity of pressure. On the surface of the spherical envelope, the Happel’s, Kuwabara’s, Kvashnin’s, and Cunningham’s boundary conditions, are used along with no spin boundary condition. The expression for the hydrodynamic normalized drag force acting on the semipermeable sphere is obtained. The limiting cases of drag expression exerted on the semipermeable sphere and impermeable solid sphere in cell models filled with Newtonian fluid are obtained. Also, in absence of envelope, the drag expression for the micropolar fluid past a semipermeable sphere is obtained.

WOS: 000506179900001, The work presents a three-dimensional modeling of air flow around the research object. The purpose of this work was to perform numerical calculations to identify the magnitude of the aerodynamic drag force generated on individual elements of a high energy efficiency vehicle body. This vehicle, specially designed for the Shell Eco-marathon competition, needs to show the lowest possible fuel consumption while maintaining the prescribed speed. Minimizing the drag force at an early designing stage plays an important role here. The calculations were performed using the ANSYS Fluent calculation solver. The result of the conducted research is a description of the velocity and pressure distributions around the tested vehicle as well as an identification of the drag force on the external surfaces of the components and a description of the relationship between them. The work also discusses the dependence of the drag force as a function of speed in the range from 0 to 12 m/s. The influence of the ground on the drag force in the case when the object was immobilized in relation to the walls at the flowing medium, as in a wind tunnel, was investigated. On the basis of the calculations performed, no impact of the ground on the generated drag force magnitude was found.

This work introduces a numerical investigation of the fluid flow and thermal convection phenomena using the double multiple relaxation time of the lattice Boltzmann method (DMRT-LBM). The work concentrates on the simulation of the fluid flow and the isotherms lines around the heated square cylinder controlled by three-flat plates placed side by side in a bidimensional channel at a fixed Reynolds number (Re=150). The inclusion of the plates is to control the vortex shedding and improve the characteristics of the heat transfer around the squares cylinder. The numerical code is validated with the numerical and experimental results available in the literature for flow past around a square cylinder with and without a control instrument. The influence of the position of the flat plates on the streamlines, the isotherms lines, the drag and lift forces are studied. The results obtained show the inclusion of the partitions decreases the drag force and the lift fluctuate and allows for regular heat exchange.

Understanding fluid flow in granular materials is essential for many engineering applications, including petroleum recovery, groundwater movement and embankment stability. This study investigates the influence of particle angularity on permeability and fluid-particle interaction forces. A random shape generator based on spherical harmonics is used to create irregular-shaped particles with different levels of angularity. Granular packings of uniformly sized (monodisperse) particles are then constructed with the discrete element method (DEM), and pore-scale computational fluid dynamics (CFD) simulations are used to determine the flow fields and the resulted fluid-particle interaction. The more angular particle assemblies thus generated are less permeable, and their fluid-particle interaction forces are higher. However, angularity has limited influence on flow rate distribution and flow tortuosity. The influence of angularity is localized. An increase in angularity generates a larger variance of the pressure distribution on the particle surfaces, thus increasing the pressure component of the fluid-particle interaction force.

We continue to explore the dynamics of a heavy quark in a strongly coupled rotating quark-gluon plasma within the holographic framework. We use the 5d Kerr-AdS black hole with two arbitrary rotating parameters to describe the rotating quark-gluon plasma. We present the relations for the drag force acting on the heavy quark both in the rotating- and static-at-infinity frames for arbitrary choice of the rotational parameters. We also calculate the thermal mass of a static quark in different frames and show that at high-$T$ limit the dependence on rotation is suppressed., 28 pages, refs. to 2 SageMath notebooks; v2: clarifications added, typos corrected; corrections in Sec.5 and app; matches published version in Nucl.Phys.B

Lift force is an important parameter for the performance evaluation of an H-Darrieus wind turbine. The rotational direction of the streamlined force is effective on the performance of the wind turbine. In order to analyze the flow characteristics around the turbine blades in real-time, a numerical analysis using three-dimensional unsteady Reynold-averaged Navier–Stokes equations has been introduced. Experimental data were obtained from a field test facility constructed on an island in South Korea and was introduced to compare the numerical simulation results with measured data. The optimum tip speed ratio (TSR) was investigated via a multi-variable optimization approach and was determined to be 3.5 for the NACA 0015 blade profile. The turbine displays better performance with the maximum power coefficient at the optimum TSR. It is due to the delay in the flow separation from the blade surface and the relatively lower strength of the tip vortices. Furthermore, the ratio between lift and drag forces is also the highest at the optimum TSR, as most of the aerodynamic force is directly converted into lift force. For one rotation of the turbine blade at the optimum TSR, the first quarter of motion produces the highest lift as the static pressure difference is maximum at the leading edge, which helps to generate maximum lift. At a TSR less than the optimum TSR, small-lift generation is dominant, whereas at a higher TSR, large drag production is observed. Both of these lead to lower performance of the turbine. Apart from the TSR, the optimum wind angle of attack is also investigated, and the results are prepared against each TSR.

Offshore installations with pile foundations in shallow water are vulnerable to submarine landslides, which cause serious damage to engineering facilities, loss of life, and loss of money. Due to a shortage of real observation data and the difficulty of reproduction, we lack insight into the interaction behavior between submarine landslides and monopiles. This study capitalized on ANSYS Fluent 20.0 to develop a three-dimensional biphasic (water and slurry) numerical model. This CFD model was used to analyze the interaction between a monopile and submarine landslides at different flow heights. The velocities of submarine landslides were from low to high values. Two modes of interactional forces acting on the monopile are proposed, which are (i) interaction force with peak value and (ii) interaction force without peak value. The influence of flow height and velocity on interaction forces was investigated. Results show that the effect of the flow heights on the interaction force is significant at low velocity stage, while the peak force representing a hazard level of the pile was non-negligible under high flow velocity and low flow height conditions, which should be considered in a future study. The related mechanisms are revealed with a hybrid model considering different components of the force.

Entrapped air in the chambers of a T-girder bridge generates a considerably large vertical force which is harmful to the safety of the bridge superstructure. The contribution of the entrapped air is not considered when calculating flood force in the related specifications, and also it has not been taken into account by researchers. Two-dimensional, scaled-down models at a 1:40 scale are selected as the research object. Analytical and numerical methods are employed to investigate the contribution of entrapped air in T-girder chambers to flood forces. Results show that the entrapped air in the rear chambers could escape easier than that in the front chambers and the compressibility of entrapped air has a small influence on drag force and vertical force (generated by dynamic pressure) coefficients, but it reduces the buoyancy of the T-girder. Considering the entrapped air compressibility and entrapped air escape, the calculation method of the buoyancy of entrapped air is proposed to improve the precision of the existing flood force calculation method.

Aquest treball es contextualitza en el sector de l’automobilisme de competició, on es detecta un problema concret entorn el qual es proposa dissenyar el concepte d’un sistema aerodinàmic, que té per objectiu principal reduir la força d’arrossegament i millorar la càrrega aerodinàmica d’un vehicle, mitjançant un conjunt de peces externes que varien el flux de l’aire al voltant d’aquest. Per acotar aquest treball s’estableix un model determinat d’automòbil. Partint d’aquestes condicions i tenint en compte d’altres requisits de disseny es desenvolupen les peces i es realitzen els plànols corresponents. La metodologia utilitzada presenta un ordre lineal i s’inicia amb la definició dels diferents components aerodinàmics que entren en joc. El disseny evoluciona al llarg de diverses versions de modelat CAD. influenciades per les conclusions que es van extraient de les diverses activitats experimentals efectuades en cada cas. Finalment, s’obté un resultat final que no decep respecte als objectius plantejats inicialment. Aquests resultats són vàlids i prometen una millora en termes d’aerodinàmica. This project is contextualised on the automotive competitive sector, where a problem is detected, around which a conceptual aerodynamic system will be designed on, with the main objective of reducing the drag force and improving the downforce of a vehicle, using a set of external parts that will modify the way the air passes around the vehicle. To narrow down this project, a specific car model is selected to work on. Starting out that initial conditions and taking some other design requirements, the parts will be developed with their corresponding blueprints. The used methodology presents a linear order, it begins with the definition of the various aerodynamic components. The design evolves through several versions of CAD modelling, influenced by the conclusions taken from the several experimental activities done to each one of the parts. In the end, a result is obtained, those results are not disappointing at all based on the objectives set initially. The results are valid, and they vow an improvement on aerodynamic terms.