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This paper is devoted to the asymptotic stability of diverging traveling waves for reaction–advection–diffusion equation u t - Δ u + α (t , y) u x = f (t , y , u) in cylinders. By the sliding method, we first establish a Liouville-type result. Then, using the Liouville-type result and truncation technique, we prove the asymptotic stability of the diverging traveling wave. [ABSTRACT FROM AUTHOR]

Although precombustion chambers, or prechambers, have long been employed for improving large-bore two-stroke natural gas engine ignition and combustion stability, their design predates modern analysis techniques. Employing the latest computational fluid dynamics (CFD) modeling techniques, this study investigates the importance of temperature and chemistry for ignition of the main chamber, with an emphasis on eliminating unburned methane. The sensitivity of the ignition and complete combustion to main chamber air/fuel mixture homogeneity was also explored. This study compares the effect of purely thermal ignition, purely chemical ignition, and how their interplay can influence the complete combustion of methane in typical mixtures and in homogeneous distributions of fuel in the combustion chamber. The CFD results demonstrated that temperature and chemistry are equally important in the ignition mechanism, and combining the two phenomena is effective at igniting the main chamber. Reduction of residual methane in the main combustion chamber (MCC) is most effective when chemical intermediates and thermal ignition are combined. A rudimentary analysis of the effect of fuel/air stratification was also conducted, and it demonstrated that a dramatic reduction in methane emissions is observed for homogeneous mixtures. The flow field in the main combustion chamber was shown to create detrimental stratification of the fuel/air mixture, which inhibited complete combustion of the methane in the main chamber. By contrast, in the extreme case of a perfectly homogeneous distribution of both chemical intermediates and fuel in the combustion chamber, it is possible to completely eliminate unburned methane in the main combustion chamber. [ABSTRACT FROM AUTHOR]

This article is devoted to the study of a class of reaction-advection-diffusion equations of the form u t − Δ u + β (y) u x = f (t , u) in cylinders, where f is a tristable or multistable nonlinearity satisfying f (⋅ , 0) = f (⋅ , 1) = 0. We establish the alternative of wave solutions, that is, either there is a unique, asymptotically stable periodic traveling wave connecting 0 to 1 directly, or there is a unique propagating terrace connecting 0 to 1. Under the assumption that all wave speeds in propagating terrace are not equal to each other, we further obtain that the propagating terrace is asymptotically stable if it exists. Moreover, the sufficient and necessary conditions for the existence of periodic traveling waves connecting 0 to 1 are given respectively. Our arguments are based on the parabolic maximum principle, sliding method and the super- and sub-solution method. [ABSTRACT FROM AUTHOR]

Failures in hydraulic systems in offshore wind turbines represent an enormous challenge for manufacturers and operators, as the pitch system statistically is one of the subsystems contributing the most to the downtime of the turbines, which is the case for both electrical and hydraulic pitch systems. However, the complex failure mechanisms of the various different hydraulic components mean that, typically, the critical components of hydraulic systems must be tested to better understand the failure mechanisms. Nonetheless, conventional testing procedures are lengthy and costly. Accelerated testing plays a critical role as it can mimic hydraulic system failure mechanisms in a shorter period. However, the lack of standardized test methods and detailed knowledge about the failure-accelerating effects complicates the process. Therefore, this paper offers a comprehensive examination of approaches applicable to conducting accelerated tests on hydraulic systems. It identifies and discusses five primary component types or sub-components related to the acceleration of testing in hydraulic systems: pumps, cylinders, seals, valves, and hoses. Each section references studies that delve into accelerated testing methodologies for these individual components. Furthermore, within each component, a concise overview of the current techniques is provided, followed by a discussion and summary based on the state of the art. [ABSTRACT FROM AUTHOR]

Floating breakwaters (FBs) are frequently used to protect marinas, fisheries, or other bodies of water subject to wave attacks of moderate intensity. New forms of FBs are frequently introduced and investigated in the literature as a consequence of technological advancements. In particular, a new possibility is offered by High-Density Polyethylene (HDPE) by extruding pipes of large diameters (e.g., 2.5 m in diameter) and with virtually no limit in length (hundreds of meters). By connecting two or three such pipes in a vertical layout, a novel low-cost floating breakwater with deep draft is devised. This note investigates numerically and experimentally the efficiency of this type of multi-cylindrical FBs in evaluating different geometries and aims at finding design guidelines. Due to the extraordinary length of the breakwater, the investigation is carried out in two dimensions. The 2D numerical model is based on the solution of the rigid body motion in the frequency domain, where the hydrodynamic forces are evaluated (thanks to a linear potential flow model), and the mooring forces do not include dynamic effects nor drag on the lines. The numerical predictions are compared to the results of a 1:10 scale experimental investigation. An atypical shape of the wave transmission ( k t ) curve is found, with a very low minimum in correspondence with the heave resonance frequency. The results essentially point out the influence of the position of the gravity center, the stiffness, and the mutual distance among cylinders on k t . [ABSTRACT FROM AUTHOR]

As part of the research carried out in the field of processing systems and the production process of oil-hydraulic cylinders of large dimensions and power, the specifics of fluid power transmission, in the functioning of hydropower facilities, were analyzed. The research also includes the optimization of the physical–mathematical model of non-stationary processes, which take place inside the chamber of a large hydrocylinder. In parallel with the definition of the optimization model, the work parameters that affect the process of fluid flow and piston movement were determined. The operating and technological construction parameters of the hydraulic cylinder, which most significantly affect the operation of the hydraulic cylinder, were defined, and the observed parameters were optimized, based on which a prototype with improved characteristics compared to existing solutions was realized. [ABSTRACT FROM AUTHOR]

Failures in hydraulic systems in offshore wind turbines represent an enormous challenge for manufacturers and operators, as the pitch system statistically is one of the subsystems contributing the most to the downtime of the turbines, which is the case for both electrical and hydraulic pitch systems. However, the complex failure mechanisms of the various different hydraulic components mean that, typically, the critical components of hydraulic systems must be tested to better understand the failure mechanisms. Nonetheless, conventional testing procedures are lengthy and costly. Accelerated testing plays a critical role as it can mimic hydraulic system failure mechanisms in a shorter period. However, the lack of standardized test methods and detailed knowledge about the failure-accelerating effects complicates the process. Therefore, this paper offers a comprehensive examination of approaches applicable to conducting accelerated tests on hydraulic systems. It identifies and discusses five primary component types or sub-components related to the acceleration of testing in hydraulic systems: pumps, cylinders, seals, valves, and hoses. Each section references studies that delve into accelerated testing methodologies for these individual components. Furthermore, within each component, a concise overview of the current techniques is provided, followed by a discussion and summary based on the state of the art.

In the present paper, the dynamic behaviors of a bubble collapsing at the symmetrical positions of the double cylinders within a narrow gap are qualitatively and quantitatively investigated. Using a high-speed photographic technique, the morphological evolution of a bubble near the double cylinders in a two-dimensional flow field is explored and qualitatively demonstrated. The mechanism by which the position of the bubble affects its dynamics is revealed. At the symmetrical position of the double cylinders, the bubble's dimensionless abscissa shows significant impacts on the collapse behaviors, and its increase weakens the bubble deformation and strengthens the centroid movement. [ABSTRACT FROM AUTHOR]

Let B be a commutative ℤ -graded domain of characteristic zero. An element f of B is said to be cylindrical if it is nonzero, homogeneous of nonzero degree, and such that B(f) is a polynomial ring in one variable over a subring. We study the relation between the existence of a cylindrical element of B and the existence of a nonzero locally nilpotent derivation of B. Also, given d ≥ 1, we give sufficient conditions that guarantee that every derivation of B (d) = ⊕ i ∈ ℤ B d i can be extended to a derivation of B. We generalize some results of Kishimoto, Prokhorov and Zaidenberg that relate the cylindricity of a polarized projective variety (Y,H) to the existence of a nontrivial Ga-action on the affine cone over (Y,H). [ABSTRACT FROM AUTHOR]

New generations of spark-ignition engines include exhaust gas recirculation (EGR) to improve the engine efficiency. Depending on the design of the EGR routing, some differences in the total amount of recirculated gases that reach each cylinder can be induced. This affects the air-to-fuel ratio on each cylinder due to the combination of the different temperature and composition of the gases at the intake valve closure. As a consequence, significant deviations in the combustion process and the subsequent composition upstream the three-way catalyst can be reached. This paper explores these effects on catalyst performance and tailpipe emissions, individualizing the behavior for each regulated species. The study was performed in a four-cylinder naturally aspirated engine with Atkinson cycle and a close-coupled three-way catalyst. The most significant deterioration in conversion efficiency appeared for the nitrogen oxides, directly linked to the EGR dispersion level. In the case of carbon monoxide (CO) emissions, no significant impact was observed except at high average EGR rates, where one or more of the cylinders exceeded the EGR tolerance for that speed and load. Based on these results, a strategy where the fuel injector command is adapted to correct the air-to-fuel ratio deviations induced by the EGR was developed and implemented. [ABSTRACT FROM AUTHOR]

Floating breakwaters (FBs) are frequently used to protect marinas, fisheries, or other bodies of water subject to wave attacks of moderate intensity. New forms of FBs are frequently introduced and investigated in the literature as a consequence of technological advancements. In particular, a new possibility is offered by High-Density Polyethylene (HDPE) by extruding pipes of large diameters (e.g., 2.5 m in diameter) and with virtually no limit in length (hundreds of meters). By connecting two or three such pipes in a vertical layout, a novel low-cost floating breakwater with deep draft is devised. This note investigates numerically and experimentally the efficiency of this type of multi-cylindrical FBs in evaluating different geometries and aims at finding design guidelines. Due to the extraordinary length of the breakwater, the investigation is carried out in two dimensions. The 2D numerical model is based on the solution of the rigid body motion in the frequency domain, where the hydrodynamic forces are evaluated (thanks to a linear potential flow model), and the mooring forces do not include dynamic effects nor drag on the lines. The numerical predictions are compared to the results of a 1:10 scale experimental investigation. An atypical shape of the wave transmission (kt) curve is found, with a very low minimum in correspondence with the heave resonance frequency. The results essentially point out the influence of the position of the gravity center, the stiffness, and the mutual distance among cylinders on kt.

As part of the research carried out in the field of processing systems and the production process of oil-hydraulic cylinders of large dimensions and power, the specifics of fluid power transmission, in the functioning of hydropower facilities, were analyzed. The research also includes the optimization of the physical–mathematical model of non-stationary processes, which take place inside the chamber of a large hydrocylinder. In parallel with the definition of the optimization model, the work parameters that affect the process of fluid flow and piston movement were determined. The operating and technological construction parameters of the hydraulic cylinder, which most significantly affect the operation of the hydraulic cylinder, were defined, and the observed parameters were optimized, based on which a prototype with improved characteristics compared to existing solutions was realized.

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In the present paper, the dynamic behaviors of a bubble collapsing at the symmetrical positions of the double cylinders within a narrow gap are qualitatively and quantitatively investigated. Using a high-speed photographic technique, the morphological evolution of a bubble near the double cylinders in a two-dimensional flow field is explored and qualitatively demonstrated. The mechanism by which the position of the bubble affects its dynamics is revealed. At the symmetrical position of the double cylinders, the bubble’s dimensionless abscissa shows significant impacts on the collapse behaviors, and its increase weakens the bubble deformation and strengthens the centroid movement.

This article deals with two activities of the Lithuanian Science Society (LSS, 1907-1938) and the history of the folklore collections it accumulated. Its members encouraged people to record folk songs, fairytales, stories, riddles, and other forms of folklore, and they tried to gather in one place all the older manuscripts that contained folklore. This way, the LSS's folklore archive was formed at the beginning of the twentieth century. In 1908, Eduard Wolter, a member of the LSS, made the first folklore sound recordings with a phonograph apparatus. The chair of the Society, Jonas Basanavičius, knew about the Phonogram Archives of Vienna and Berlin; therefore, he encouraged the establishment of such an archive in Vilnius. Another idea of the LSS, initiated by Mykolas Biržiška, was to gather all the songs in one place and to publish a national songbook. Unfortunately, these goals were visionary and utopian for this period of cultural development in Lithuania. In this study, the birth of these ideas and the path to their realisation are chronologically reviewed. The author discusses the reasons why they were not accomplished in the first part of the twentieth century, and gives explanations for why they were successfully implemented in the second part of the twentieth - beginning of the twenty-first centuries. The historical-political context as well as the actual digitisation of intangible heritage archives help clarify the process. [ABSTRACT FROM AUTHOR]

Impact tests are the most common tests for high-strength materials. These tests not only specify the rigidity of the component but also determine the life expectancy of a machine part. Therefore, it is important to test various machine components for using different impact analyses. In this work, a single plate made of steel is impacted by two cylinders at each end also made of steel. The analysis was carried out using the Dynamic Analysis module of ANSYS Workbench.The distance between the cylinders is kept constant for simplified analysis. Also, the impact velocity was kept the same for the two cylinders. Furthermore, a plate of epoxy carbon UD (395 GPa) was also simulated for deformation, stress, and strain. The analysis yields the reaction of the steel plate and epoxy carbon UD (395GPa) prepreg material when impacted by two cylinders simultaneously. The deformation, stress, and strain simulation results show the effect of impact on the plate. [ABSTRACT FROM AUTHOR]

Global decarbonization requires the increased use of zero-carbon fuels. Compared to hydrogen, ammonia is easier to store, transport, and produce. In addition, products of complete combustion of ammonia are water and nitrogen. Therefore, ammonia is an ideal green fuel for internal combustion engines. Drawbacks relate to the high ignition energy and low laminar flame speed of ammonia. This three-dimensional numerical study investigated the potential of converting existing diesel engines to ammonia spark ignition operation. Results indicated a slower kernel inception process, but the speed of the fully developed turbulent flame was enough to complete the bulk combustion process despite the lower laminar flame speed. The problem with pure ammonia operation was the reduced combustion efficiency and the high level of unburned ammonia emissions since the slow spark inception process can be compensated by a larger compression ratio. The results also suggested that emissions formation and subsequent oxidation were a more complex phenomenon. For example, lean ammonia combustion produced higher nitrogen oxides (NOX) concentrations due to the nitrogen in the fuel, despite the lower combustion temperature. Moreover, advancing spark timing reduced the NOX emissions, which was opposite to the traditional spark ignition engines. Additionally, the ammonia in engine crevices that escaped the late oxidation process was the main source of nitrous oxide (N2O) species in the exhaust gas that usually do not appear in traditional engines. Overall, all these results suggested that more fundamental research on ammonia combustion is needed to understand its use in efficient, decarbonized engines. [ABSTRACT FROM AUTHOR]

Spark assisted compression ignition (SACI) represents an efficacious technique to extend the operating range and control combustion timing in homogeneous charge compression ignition (HCCI) engines. Recently, a hot surface ignition system (HSI) was demonstrated to enable hot surface assisted compression ignition (HSACI) featuring similar combustion characteristics compared to SACI. This work compares both combustion processes with regard to control and combustion characteristics, the strength of the ignition systems, and cycle-by-cycle variations (CCV). Engine trials were conducted using a single-cylinder research engine fueled with natural gas. The engine operated naturally aspirated at an engine speed of 1400 1/min and steady-state conditions. Experimental conditions cover relative air-fuel ratios λ = 2.1-3.1, intake temperatures Tin = 140-170 °C and intake pressures pin = 993-995 mbar. Results show similar capabilities of SACI and HSACI to control combustion timing by means of spark timing in SACI and hot surface temperature in HSACI. Heat release analyses of individual combustion cycles point out the similarity of both combustion processes. The evaluation of the strength of the ignition systems reveals that HSACI extends the lean limit by Δλ = 0.05-0.10 and advances the earliest applicable combustion timing (MinCA50) by ΔMinCA50 = 1.0-4.5 °CA provided that ringing is not of concern. Comparison of CCV in HCCI, SACI, and HSACI shows highest combustion stability for HCCI, followed by SACI. HSACI evinces highest CCV due to a larger variation at the start of combustion. [ABSTRACT FROM AUTHOR]

Hydraulic actuation systems have a broad range of applications covering almost all areas of manufacturing and production and also the service industry. However, it is usual for systems to have low energy efficiency. In recent decades, due to global environmental concerns, research in the field of digital hydraulics to develop more efficient hydraulic systems has increased. In this paper, an analysis of the possible combinations of chambers in a multichamber cylinder is presented. A mathematical expression is derived to verify the total number of combinations of chambers that it is possible to achieve for a cylinder with four or more chambers and that result in different constant velocities without cavitation occurring. In addition, a digital hydraulic pump is considered a supply unit and, since it has discrete output flow rates, an analytical method to combine the pump with a multichamber cylinder is developed resulting in a total number of cylinder velocities with a required resolution. For application in a positioning system, design guidelines for an actuator using a cylinder with four chambers and a digital hydraulic pump with three fixed displacement units are presented in which an optimization algorithm for the calculation of the cylinder areas and the volumetric displacement of the pumps is applied. The proposed approaches were applied to design a proof-of-concept and the experimental values presented very good accuracy when compared with the results obtained with the model. Closed-loop position control responses show that the system can achieve the required setting time with a smooth movement and steady-state error of around 1 mm. [ABSTRACT FROM AUTHOR]

This paper documents the 2D numerical study of magnetohydrodynamic unsteady natural convective heat transfer in a circular enclosure with four heating cylinders in both the horizontal and the vertical mid-plane. The fluid is an incompressible Newtonian fluid. The main transport equations based on the conservation of mass, momentum, and energy are calculated and solved using a finite element numerical solver with the following parameter ranges: dimensionless distance between cylinders S = 0.05–0.29, Rayleigh number R a = 10 3 – 10 6 , and Hartmann number for Ha = 0–120. COMSOL Multiphysics, a numerical simulation program, was used to solve the governing equations. It was demonstrated that for lower Ra values, heat transfer through an applied magnetic field is unaffected for a specific S value because the mechanism of transport is diffusion, whereas for larger Ra, there is a complex interaction among magnetic field and physical thermal properties. The features of the heat transfer rate are determined by the interaction. The Nusselt number virtually stays constant as Ha rises at smaller Ra. However, at high Ra, the Nusselt number initially declines with Ha and thereafter essentially stays constant, and at high Ra values, the switch from conduction to convective heat transfer takes place. Additionally, Nu rises slightly with S at increasing Ra. [ABSTRACT FROM AUTHOR]

Wiebe functions, analytical equations that estimate the fuel mass fraction burned (MFB) during combustion, have been effective at describing spark-ignition (SI) engine combustion using gasoline fuels. This study explores if the same methodology can be extended for SI combustion with syngas, a gaseous fuel mixture composed of H2, CO, and CO2, and anode-off gas; the latter is an exhaust gas mixture emitted from the anode of a Solid Oxide Fuel Cell, containing H2, CO, H2O, and CO2. For this study, anode off-gas is treated as a syngas fuel diluted with CO2 and vaporized water. Combustion experiments were run on a single-cylinder, research engine using syngas and anode-off gas as fuels. One single Wiebe function and three double Wiebe functions were fitted and compared with the MFB profile calculated from the experimental data. It was determined that the SI combustion process of both the syngas and the anode-off gas could be estimated using a governing Wiebe function. While the detailed double Wiebe function had the highest accuracy, a reduced double Wiebe function is capable of achieving comparable accuracy. On the other hand, a single Wiebe function is not able to fully capture the combustion process of a SI engine using syngas and anode off-gas. [ABSTRACT FROM AUTHOR]

Inverse problems for line sources radiating inside a homogeneous magneto-dielectric cylinder are investigated. The developed algorithms concern the determination of the location and the current of each source. These algorithms are mostly analytical and are based on proper exploitation of the moments obtained by integrating the product of the total field on the cylindrical boundary with complex exponential functions. The information on the unknown parameters of the problem is encoded in these moments, and hence all parameters can be recovered by means of relatively simple explicit expressions. The cases of one and two sources are considered and analyzed. Under certain conditions, the permittivity and permeability of the cylinder are also recovered. The results from two types of numerical experiments are presented: (i) for a single source, the effect of noise on the boundary data is studied, (ii) for two sources, the pertinent nonlinear system of equations is solved numerically and the accuracy of the derived solution is discussed. [ABSTRACT FROM AUTHOR]

The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for indexing engine stability and identifying abnormal combustion cycles are explored through experimental investigations on a low speed, single-cylinder engine. Exhaust temperature and pressure are measured using a fine wire 50 µm thermocouple and a piezoresistive pressure transducer, respectively. Synchronously recorded cylinder pressure data is used to continuously index combustion variations, and then anomalous combustion event detection and engine stability monitoring are attempted using HS exhaust temperature and pressure measurements. Two types of abnormal combustion cycles, namely, misfiring and overload cycles are used to typify low and high intensity anomalous combustion cycles, respectively. The results demonstrate that if suitable cyclic exhaust pressure and temperature metrics are used, anomalous combustion cycles can be identified, and overall combustion variability levels can be indexed. The comparative diagnostic performance of HS measured exhaust pressure and temperature and slow speed measured exhaust temperature are also discussed. A thermodynamic simulation of the engine and the HS thermocouple is used to provide theoretical support for the discussion by comparing measured and simulated "actual" exhaust temperature and identifying the flow, heat transfer, and thermodynamic influences that act as limits to the thermocouple's dynamic performance. [ABSTRACT FROM AUTHOR]

During a national lockdown and curfew, most concrete projects are left without curing; therefore, the building elements need to be strengthened. An effective strengthening method is the use of post-tensioned metal strip (PTMS), which is a relatively new method. In this study, the effectiveness of PTMS in strengthening cylindrical samples without curing was tested. Fifteen cylinders were cast, 12 of which were left without curing for 28 days. Three samples that did not undergo strengthening were used as control samples. The remaining specimens were strengthened using one, two, three, and 5 layers of PTMS. To compare the strengths of the cylinders, three cylinders from the same batch were prepared and cured for 28 days. We found that the compressive strength of the cylinders increased by 39%, 57%, 84%, and 125% when the samples were strengthened using one, two, three, and full layers of PTMS, respectively. Additionally, the failure of the cylinders became ductile as the number of layers increased. [ABSTRACT FROM AUTHOR]

A higher order boundary element method (HOBEM) is presented for inviscid flow passing cylinders in bounded or unbounded domain. The traditional boundary integral equation is established with respect to the velocity potential and its normal derivative. In present work, a new integral equation is derived for the tangential velocity. The boundary is discretized into higher order elements to ensure the continuity of slope at the element nodes. The velocity potential is also expanded with higher order shape functions, in which the unknown coefficients involve the tangential velocity. The expansion then ensures the continuities of the velocity and the slope of the boundary at element nodes. Through extensive comparison of the results for the analytical solution of cylinders, it is shown that the present HOBEM is much more accurate than the conventional BEM. [ABSTRACT FROM AUTHOR]

Modern internal combustion engines (ICE) operate at the ragged edge of stable operation characterized by high cycle-to-cycle variations (CCV). A key scientific challenge for ICE is the understanding, modeling, and control of CCV in engine performance, which can contribute to partial burns, misfire, and knock. The objective of this study is to use high-fidelity numerical simulations to improve the understanding of the causes of CCV. Nek5000, a leading high-order spectral element, open source code, is used to simulate the turbulent flow in the engine combustion chamber. Multicycle, wall-resolved large-eddy simulations (LESs) are performed for the General Motors (GM), Transparent Combustion Chamber (TCC-III) optical engine under motored operating conditions. The mean and root-mean-square (rms) of the in-cylinder flow fields at various piston positions are validated using particle image velocimetry (PIV) measurements during the intake and compression strokes. The large-scale flow structures, including the swirl and tumble flow patterns, are analyzed in detail and the causes for cyclic variabilities in these flow features are explained. The energy distribution across the different scales of the flow are quantified using one-dimensional (1D) energy spectra, and the effect of the tumble breakdown process on the energy distribution is examined. The insights from this study can help us develop improved engine designs with reduced cyclic variabilities in the in-cylinder flow leading to enhanced engine performance. [ABSTRACT FROM AUTHOR]

In additive manufacturing, geometric shape deviations are built through statistical deviation models. Nonetheless, the resource constraints limit the manufacturers to test shapes. However, in addition to the power, the simplicity of the deviation models has been demonstrated with illustrative cases for in-plane deviation modelling for regular pentagon, irregular octagon as well as straight edges in free-form shapes utilizing only data and models for single regular pentagon and cylinders. Bayesian deviation models, built for geometric shapes, provide a better fit on the data and help in achieving better predictive accuracy. The main aim of this study is to assess the effect of the error distribution, generally assumed as the normal, and evaluate its impact on the deviation model. In particular, we consider Laplace, logistic, Cauchy, and exponential distributions for the errors. It is shown that logistic distribution provides better alternative error distribution for deviation models as compared to the normal distribution.

The present study aims to investigate the dominant frequency ranges of a cylinder free to vibrate transversally to the flow positioned in the first, the second or in both positions of the tandem assembly for L/D = 1.26, 1.4, 1.6, and 3.52 with the increase in the flow velocity. Accelerometers and hot wire anemometers were the experimental tools applied in this study. The range of study encompassed the reduced velocity with values from 6 to 72 and Reynolds number from 7.1 × 103 to 2.4 × 104. Fourier transform, continuous wavelet transform, magnitude-square coherence, and wavelet coherence were applied to analyze the cylinder acceleration results for all L/D and wake velocity values studied. The results show that the amplitudes of vibration are below 1.5% of the diameter for all the cases, except for the lower L/D, where the amplitude increases. The first cylinder free to vibrate presents the highest amplitudes observed. Fourier and continuous wavelet analysis showed high energy associated with the two natural frequencies of the system and a third frequency, which may be associated with the flow excitation. In the second cylinder free to vibrate, energy spreads across the monitored spectrum, justifying the smaller amplitudes but the energy level increases with increasing L/D and may be associated with wake-induced vibration. The cases with both cylinders free to vibrate show that the relation between the assembly parameters of each cylinder is relevant to the vibration response and the excitation frequency range. The results showed that even with a clear excitation in a higher frequency, the main energy in the vibration signals is in the natural frequency range.

This study is a systematic review of research on heat transfer analysis in cavities and aims to provide a comprehensive understanding of flow and heat transfer performance in various kinds of cavities with or without the presence of fins, obstacles, cylinders, and baffles. The study also examines the effects of different forces, such as magnetic force, buoyancy force, and thermophoresis effect on heat transfer in cavities. This study also focuses on different types of fluids, such as air, water, nanofluids, and hybrid nanofluids in cavities. Moreover, this review deals with aspects of flow and heat transfer phenomena for only single-phase flows. It discusses various validation techniques used in numerical studies and the different types and sizes of mesh used by researchers. The study is a comprehensive review of 297 research articles, mostly published since 2000, and covers the current progress in the area of heat transfer analysis in cavities. The literature review in this study shows that cavities with obstacles such as fins and rotating cylinders have a significant impact on enhancing heat transfer. Additionally, it is found that the use of nanofluids and hybrid nanofluids has a greater effect on enhancing heat transfer. Lastly, the study suggests future research directions in the field of heat transfer in cavities. This study's findings have significant implications for a range of areas, including electronic cooling, energy storage systems, solar thermal technologies, and nuclear reactor systems. [ABSTRACT FROM AUTHOR]

Carbon dioxide is one of the leading contributors to global warming. Oxy-fuel combustion (OFC) integrated with carbon capture and storage (CCS) technology is an efficient way to reduce carbon dioxide emissions. In OFC, pure oxygen (O2) is used instead of air to react with hydrocarbon fuel. Consequently, the products of combustion mainly include carbon dioxide (CO2) and water vapor (H2O) under lean conditions. Meanwhile, due to the absence of N2 in the intake charge, nitrogen-related emissions such as NOx are greatly removed from the exhaust gases. In the present study, the effect of intake charge temperature on OFC has been investigated in a diesel engine under the homogeneous charge compression ignition (HCCI) mode. In order to control combustion temperature and avoid overheating problems caused by oxygen in OFC, a portion of the exhaust CO2 was added to the O2. For this purpose, different CO2 dilutions ranging from 79-85% have been employed. It has been found that OFC can significantly reduce CO and particulate matter (PM) emissions while eliminating NOx emissions. With a higher intake charge temperature, combustion occurs earlier with shorter main stages, reducing the indicated mean effective pressure (IMEP) and increasing the indicated specific fuel consumption (ISFC), whereas, with a lower intake charge temperature, combustion stability deteriorates leading to incomplete OFC. By raising the intake charge temperature from 140 °C to 220 °C and applying 21% O2 and 79% CO2 v/v, the indicated thermal efficiency (ITE) is reduced from 34.6% to 29.2% while ISFC is increased from 0.24 to 0.285 Kg/kWh. [ABSTRACT FROM AUTHOR]

The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions. [ABSTRACT FROM AUTHOR]

• Presents new correlation for CHF during subcooled flow across a cylinder. • New correlation gives good agreement with all published test data. • Data are from five sources, include five fluids and diameters 0.25 o 19.1 mm. • Other published correlations give large deviations with the same data. • This correlation will be useful in design of evaporators/boilers with crossflow. A correlation is presented for prediction of CHF (critical heat flux) during upward flow of subcooled liquids across single cylinders. The correlation was verified against all available published test data. It includes five fluids (water, R-12, R-113, isopropanol, FC-72), tube diameter 0.25 – 19.1 mm, reduced pressure 0.0046 – 0.3554, liquid velocities 0.01 – 6.8 m/s, CHF 0.14 – 28.7 MW/m2, and quality −0.001 to −0.34. The new correlation predicts 496 data points from 28 data sets from 12 sources with mean absolute deviation (MAD) of 16.4%. The same data were also compared to other published correlations; their MAD ranged from 47% to 319.0%. [ABSTRACT FROM AUTHOR]

This paper argues that in the understandable enthusiasm to use the now readily available high- fidelity numerical software allowing the analysis of the complexities of shell buckling, and especially the notorious case of the axially loaded cylinder, there has been insufficient consideration of classical shell buckling theory and its more recent reduced stiffness extension. If future design is to be able to effectively exploit the potential benefits of the use of advanced composite materials and/or the use of rib reinforcement, it is suggested that these numerically driven research programmes would benefit from more explicit integration within the framework of classically extended buckling theory. This suggestion is reinforced in what follows by highlighting the results from a longstanding research programme in which classically extended buckling theory has been demonstrably enhanced through its integration with reliable numerical experimentation. This enhancement has helped to resolve a number of important issues including: identification of the most critical forms of imperfection affecting the buckling loads; how the most critical knockdown factors are influenced by changes in the shells' geometric and material characteristics and how safe design might be more explicitly related to the prescribed levels of geometric tolerances. Recommendations are made as to how such integrated research programmes could in the future further enhance our ability to design materially efficient shells against buckling. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on predicting natural frequency of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) cylinders in similitude. To solve the problem of non-scalability caused by the thickness and material distribution, the energy similitude correction method, a novel similitude approach proposed by the author in recent years, is applied to derive the similitude relationship. With the similitude relationship, a brief predictive formula of natural frequency is derived, which reveals the inherent law of natural frequency varying with radius-to-thickness ratio; and the natural frequency of FG-CNTRC cylinders with arbitrary radius-to-thickness ratio can be predicted by two or three models with known frequency. Through numerical cases of various FG-CNTRC cylinders with different volume fractions, distribution patterns of CNTs and edge-to-radius ratios, the results with high accuracy verify the correctness and wide applicability of the derived formula. [ABSTRACT FROM AUTHOR]

A correlation is presented for prediction of CHF (critical heat flux) during upward flow of saturated liquids across single cylinders. The correlation was verified against all available published test data. It includes six fluids (water, R-12, R-113, methanol, isopropanol, acetone), tube diameter 0.26 - 19.1 mm, reduced pressure 0.0046 - 0.3554, liquid velocities 0.01 - 10.7 m/s, and CHF 0.14 – 10.7 MW/m2. The new correlation predicts 558 data points from 62 data sets from 15 sources with mean absolute deviation of 18.0%. The same data were also compared to seven other published correlations; their MAD ranged from 24.1% to 287.0%. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the flow over a stationary square cylinder in the test section of a subsonic wind tunnel. Hotwire anemometry (CTA type), particle image velocimetry (2C-PIV), and flow visualization techniques are used in the study to characterize the flow properties. The study is carried out at four intermediate Reynolds numbers (blocking width 'B' as the characteristic length) 600, 800, 1000, and 2000. The flow over the circular cylinder and square cylinder differs, particularly at intermediate Reynolds numbers, but the literature lacks detailed flow behavior over a square cylinder beyond the wake transition regime. Re = 600 is the critical Reynolds number as the flow changes from a disordered fine-scale three-dimensional regime to a shear layer transition regime. The effects of the regime alterations on the flow properties, vortex shedding frequency, and mean drag coefficient are reported in the study for all Reynolds numbers. The flow visualization supplements the CTA and PIV measurements. The turbulent kinetic energy budget has also been compared for all Reynolds numbers. [ABSTRACT FROM AUTHOR]

The flow around curved tandem cylinders of equal diameter has been investigated for the first time, by means of direct numerical simulations. A convex configuration was used. The nominal gap ratio was L/D = 3.0 and a Reynolds number of 500 was chosen. Due to the change in effective gap ratio along the cylinder axis, there is a variation of tandem flow regimes, from alternating overshoot/reattachment, via stable reattachment, to co-shedding, in this case called gap shedding. The combination of reattachment and gap shedding gives near-zero drag and vertical forces for the downstream cylinder, whereas the corresponding forces on the upstream cylinder are comparable to single curved cylinders. Meanwhile, the opposite is true for the lift forces. A low-frequency variation of horizontal and vertical forces is seen, and this is attributed to a slow variation of the position where gap shedding commences. Finally, the concept of a critical angle is proposed to describe the transition to gap shedding, for a given combination of nominal gap ratio and Reynolds number. [ABSTRACT FROM AUTHOR]

Let γ t (P p □ C q) and γ pr (P p □ C q) be the total domination number and the paired domination number, respectively, of cylinders, that is, the Cartesian product of a path P p and a cycle C q for p ≥ 2 and q ≥ 3 . Hu et al. (J Comb Optim 32(2):608–625, 2016) determined the exact values of γ t (P p □ C q) and γ pr (P p □ C q) for p ≥ 2 and q ∈ { 3 , 4 } . In this paper, we compute their exact values for p ∈ { 2 , 3 , 4 } and q ≥ 5 and obtain the upper and the lower bounds for other values of p and q. [ABSTRACT FROM AUTHOR]

Powders of magnetic particles are used e.g. in additive manufacturing of magnets, necessitating an investigation of the properties of such powders. In this work we consider hard magnetic particles modeled as infinitely long cylinders in 2D and randomly packed in a square container. The particles have a nonlinear magnetization curve with defined remanence and coercivity and their radii follow a lognormal distribution with the standard deviation distinguishing different packings. Using a finite element approach we calculate the average and standard deviation of the magnetization of the individual particles in the packings and from these subtract the value of the corresponding regions in a solid square box to remove the shape demagnetization effect of the overall packing. We find that at applied fields close to the coercivity the average magnetization of the individual particles have the highest probability to deviate 5% from the average magnetization in the corresponding regions in the box. Away from the coercivity the packings have an near-identical magnetization to the solid box. Considering the magnetization internally in each particle, near the coercivity the standard deviation of the magnetization has the highest probability to deviate 10% from the standard deviation in magnetization in the corresponding region in the box. Thus while the overall magnetization in a packing appear to be the same as in a solid box, near the coercivity there is a larger variation of magnetization both between and within the magnetic particles, compared to a solid box. • We systematically investigate the magnetization of a packing of particles. • Using a numerical hysteresis model we compute the magnetization of the particles. • We subtract the demagnetization field caused by the shape of the container. • We find that near the coercivity the particles magnetization deviate from that of a solid. • The standard deviation of the individual particles is most likely 10% larger for a solid. [ABSTRACT FROM AUTHOR]