Search

Abstract. In this paper, a prey, predator and apex predator food 4chain model4 is proposed and analyzed. The model includes the impact of fear on solution dynamics. All feeding processes in this ecological model are formulated in terms of Crowley-Martin-like functional responses. The primary goal of this work is to find the existence condition, uniqueness and boundedness of the solution. The second goal is to study the local and global stability of these solutions. Finally, the analysis results are verified by numerical simulation. [ABSTRACT FROM AUTHOR]

The paper discussed the problems related to a linear quadratic regulator (LQR) synthesis for the control implementation in a semi-active car suspension. The control is a combination between the state's feedback and compensation by the excitation. For this purpose, the state and the input disturbance are reconstructed using the observed variables. The physical nonlinearities of the controllable magneto-rheological semi-active damper are considered. The regulator structure also includes a model of the inverse magneto-rheological damper, based on neural networks. A "Quarter car model" is used for the vehicle suspension modelling as enough adequate and appropriate for real-time control. The main contribution of the research is the approach for determining the weight matrices of the regulators, based on a formulated multicriteria problem, and solved based on the Game Theory. Numerical simulations are given, allowing for comparison of the results, and confirming the effectiveness of the presented approach. [ABSTRACT FROM AUTHOR]

This paper presents a chaotic jerk circuit model concerned with a stochastic fractal-fractional order α, β ∊ (0, 1] by adding external white noise to the input voltage. A new differentiation operator as the convolution of the power law is investigated. The new operators will be pointed to fractal-fractional differentiation and integration in the Riemann-Liouville (R-L) sense. Some sufficient conditions are achieved for the existence and uniqueness of solutions for considered framework by employing the Banach contraction principle. Finally, numerical simulation is provided to confirm the theoretical consequences. [ABSTRACT FROM AUTHOR]

The paper is dedicated to identification and computational study of control laws for a spaceplane's ramjet aimed at providing a target value of thrust and impulse. An algorithm to identify the law of fuel mass flow rate control that provides a target value of thrust has been developed and implemented on software level. Resultant control laws have been verified by numerical simulation data. [ABSTRACT FROM AUTHOR]

The paper considers a relatively simple method for creating interactive electronic models of physical systems that does not require programming and automatic generation of numerical models of complex physical systems. The created training models are available for use via the Internet and allow almost unlimited on-line editing by users. The options of using the created electronic models to support mass individualized learning and the organization of independent educational and scientific research of students are discussed. The development is based on the original method of physical object-oriented modeling (POOM), which is an application of traditional ideas of object-oriented programming to the problems of constructing and configuring numerical models of relatively complex physical systems. Within its framework, a computer model of a physical system is constructed as a set of software objects that model the behavior of its components relative to separate physical elements: particles and fields. The interaction between the elements of the model is described using self-adapting algorithms, the choice of which is set during the construction of the model, depending on the physical approximation used: classical or relativistic. An electronic designer of interactive models of physical systems, represented in the form of arbitrary aggregates of classical and relativistic particles interacting with each other and external fields, has been created on the basis of the POOM ideology and Java-Script technology. The possibility of using an electronic designer as a basis for students to conduct independent research work on the study of the physical properties of complex mechanical systems, the analysis of which goes beyond the standard programs in physics and mathematics, is tested. The heuristic capabilities of the models created with the help of an electronic designer are demonstrated. The electonic designer is focused on the development of a series of virtual physical models to support classroom and online courses in physics and the organization of independent creative work of students in the MOOC–education system. [ABSTRACT FROM AUTHOR]

The paper analyzes the parametric uncertainty of the considered mathematical model, identifies the main parameters of the model, which undergo changes in the course of the real functioning of the studied pneumatic system. A nonlinear synergistic law for controlling the position of the piston of a pneumatic actuator has been developed, which has robust properties to changing the parameters of the model within the maximum permissible limits. The obtained results of computer modeling confirm the robust properties of the obtained nonlinear synergetic control laws and the achievement of the set technological control goal - moving the rod to a given position under conditions of parametric uncertainty. The robust properties of a closed-loop control system with integral adaptation are considered with an uncontrolled variation of the load mass within: m1 = 0,6 kg and m2 =0,9 kg and variations of the viscous friction coefficient in the following values:) Ƞ1 =101 N · s/m; and Ƞ1 =101 N · s/m. [ABSTRACT FROM AUTHOR]

The paper presents the numerical simulation of thermo-hydraulic behaviour of coolant in nuclear reactor VVER-440 under reactor pool filling conditions. Temperature distribution and mixing of coolant with different temperatures during filling process are discussed. [ABSTRACT FROM AUTHOR]

The structure of a market is determined by the number of active firms in it. Over time, this number is affected by the exit of existing firms, called incumbents, and entries of new firms, called entrant. In this paper, we considered a market governed by the Cobb-Douglas utility function such that the demand function is isoelastic. Each firm is assumed to produce a single homogenous product under a constant unit cost. Furthermore, firms are assumed to be boundedly rational in adjusting their outputs at each period. A firm is considered to exit the market if its output is negative. In this paper, the market is assumed to have zero barrier-toentry. Therefore, the exiting firm can reenter the market if its output is positive again, and new firms can enter the market easily. Based on these assumptions and rules, a mathematical model was developed and numerical simulations were run using Matlab. By setting certain values for the parameters in the model, initial numerical simulations showed that in the long run, the number of firms that manages to survive the market varies between zero to 30. This initial result is consistent with the idea that a zero barrier-to-entry may produce a perfectly competitive market. [ABSTRACT FROM AUTHOR]

The paper mainly focuses on the route design for community patrol by aircraft. On the basis of the surrounding condition, the aircraft will first build a model of the surrounding environment, grid the model next, and rectangle irregular barriers in the model. Based on Boustrophedon, the paper has raised a new strategy for gridding the surrounding environment. Under the new strategy, the overall environment will be divided into few patches. By covering all the patches, we will secure a full view of the surrounding environment. With the contribution of MATLAB, the aircraft has achieved experimental simulation over the whole area, as such, the whole environment has ensured a full coverage. [ABSTRACT FROM AUTHOR]

Today, the inverse identification or optimization of material model parameters is very often used to find input parameter values for use in relevant nonlinear material models. These parameter values should enable the responses of structures obtained from numerical simulations to very closely approximate the real responses of such structures obtained from experiments. Due to the popularity of concrete as a construction material, much attention is paid to nonlinear material models that aim to describe its behavior. This paper is focused on the optimization-based inverse identification of the parameters of two related nonlinear concrete material models which are known as the Karagozian & Case Concrete model and the Karagozian & Case Concrete model - Release III. Within this paper, the identification of the material model parameters is performed on the basis of interaction between nonlinear numerical simulations, optimization algorithms and experimental data, the latter of which take the form of a loading curve measured during a triaxial compression test. A comparison of the responses of both of the used material models when the optimized parameters are employed is, of course, part of this paper. [ABSTRACT FROM AUTHOR]

The ant colony algorithm has many advantages compared with other algorithms in path planning, but its shortcomings still cannot be ignored. For example, the convergence speed is very low at initial stage, it is easy to fall into the local optimal solution, and the solution speed is slow and so on. In order to solve these problems and reduce the search time, this paper firstly makes the assignment of the main parameters of α, β, M and ρ in the ant colony algorithm through a large number of experimental data analysis. Then an improved ant colony algorithm based on dynamic parameters and new pheromone updating mechanism is proposed in this paper. Simulation results show that the improved ant colony algorithm can not only greatly shorten the algorithm running time, but also has greater probability to get the global optimal solution, and the convergence rate of algorithm is better than traditional ant colony algorithm. It is very advantageous for solving large-scale optimization problems. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical simulation of the process of suppressing resonant vibrations in a thin-walled structure interacting with a fluid. The damping mechanism is based on the use of piezoelectric elements as a sensor and actuator incorporated into an active system of vibration suppression. The parameters of the control action are selected based on the analysis of the solutions to a series of harmonic problems. A comparison of transient processes obtained with optimal and non-optimal coefficients is carried out. [ABSTRACT FROM AUTHOR]

This work is devoted to the improvement of methods of calculation and design of jib cranes with devices balancing their own weight of jib systems. The paper proposes a solution to the problem for optimizing the parameters of balancing devices. The solution to this problem presupposes an increase in the efficiency, reliability, and safety of operation both directly of such cranes and other types of hoisting-and-transport machines with jib systems, including in cold climates. The authors considered in detail the requirements for geometric parameters, following from recommendations for effective balancing of jib system own weight, as well as for ensuring strength of structures, such as counterweight moment relative to the point at the maximum boom reach; transition of counterweight rocker through the vertical at the minimum reach; principle of heights determining of the console bases from the beams strength condition; ratio of thrust placement on the boom; apex angle of the counterweight arms, etc. Also, when solving the task, a set of requirements is met, and some assumptions are made. In the course of the work, we assume that the jib device and the balancing system are considered as framed structure, elastic deformations of their elements are not taken into account; weight loads are considered as concentrated and are applied at the following points: the jib weight at a certain distance relative to the jib length from its pivot axis; weight of the guy rod in the middle of the guy rod; the overarm weight at a certain distance relative to the jib-arm pin hinge. All stages of the task were performed using computer modeling tools, which implies both a decrease in the labor intensity of calculations themselves, and creation simplification of the current slice of dynamic model using a recursive approach, modern methods of dynamic data analysis and reengineering techniques. [ABSTRACT FROM AUTHOR]

The automobile contains several very important parts, one of which is the friction clutch. Its importance comes from being it is a mechanical coupling device that plays the role of connecting and transmitting the torque generated in the engine to the gear set in the gearbox. The friction material is an important parameter due to withstand the mechanical and thermal load generated in the clutch system. This paper focused on studying the thermal behavior of four different friction lining materials (LUK, Tiger, G95, and HCC) to identify the temperature distribution for each material separately and then compare these materials to arrive at the best material that you can choose in the dry clutch design. Modeling of the model was done by the method of finite element and with the help of the ANSYS program to perform numerical simulations and show results. It may be determined that the thermoelastic behavior of the clutch is influenced by the type of frictional lining material used. After comparing the data, it was discovered that the materials (HCC and G95) were vulnerable to clutch activation for long periods. In the current investigation, the lining materials stood out because they demonstrated a high thermal efficiency when compared to the other materials in the prior study. [ABSTRACT FROM AUTHOR]

In this paper, we thought that the supply chain management of blood is impacted both by the loss of products and the seasonal fluctuation of supply source. From practically-existed problem, with the hypothesis of two kinds of substitutable blood at different loss rates, and the impact on ordering strategy from seasonal fluctuation being expressed as the probability of products arrival, we constructed two ordering models respectively considering two situations of distributed decision making and centralized decision making. Through the solution, numerical simulation, and comparison analysis for the models, we concluded that both centralized decision making and distributed decision making could well reach the status of supply chain coordination. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the effect of boundary conditions in experimental modal analysis to approximate the free-free boundary conditions in the experimental modal analysis of a slender beam. Experimental modal analysis and numerical simulation of normal mode analysis were performed to obtain the modal parameters and predicted results in term of the natural frequencies and mode shapes. Two different boundary conditions have been considered in this paper which are the suspension location at the end points of the beam and at nodal points of the beam. The experimental results indicate that there is uncorrelated pattern for the type of mode (bending and torsional modes) for the suspension location at the end points of the beam. For the conclusion, the suspension at the location of the nodal points shows a better correlation in term of mode shapes and MAC values in comparison to the end points suspension location. [ABSTRACT FROM AUTHOR]

The PHYSOR project conducted by ALTRAN TECHNOLOGY is part of the research and development theme of new small modular reactor SMR concepts. An innovative project aims to improve the performance, design and safety of an SMR installation by integrating new technologies. In the SMR facilities, the steam generator (SG) plays an important role in the transmission of energy between the primary circuit and the secondary circuit of the reactor. For this, we have interested in this work to study the thermo-hydraulic behavior of steam generator. The aim of this paper is to develop a numerical model to simulate the heat exchange within the SG. The approach used in these numerical tools varies considerably according to the required accuracy. This paper gives a short overview of the early development of a tool that aims to describe the thermal and fluidic behavior of heat exchanger. The modelling approach is based on an averaged resolution of the Navier-Stokes equations using a coupling method between the primary and the secondary circuits. The results concerning temperature contours and velocity profiles for the two circuits were studied for different cases. The method used features a suitable compromise between results accuracy and time consuming numerical simulation. [ABSTRACT FROM AUTHOR]

Additive technology (AM) using selective laser melting (SLM) is widely used to produce parts with complex shapes made of metal alloys, composites and ceramics. One of the main problems of SLM is ensuring dimensional accuracy. The paper presents the study of the influence of selected parameters of the SLM process, such as laser power, scanning speed, distance between tracks, powder layer thickness and volumetric energy density on the dimensional accuracy of the product. The mathematical model was obtained based on a dimensional analysis describing the dependence of the SLM process parameters on the dimensional deviations of the product. Computer simulation of the SLM process was carried out using COMSOL Multiphysics® software. Theoretical results were verified experimentally on Cr-Co alloys. [ABSTRACT FROM AUTHOR]

The paper analyzes the influence of the adaptive mechatronic system parameters on the process of stabilizing the step of moving materials during automatic assembly. Dependences of variances and mathematical expectations of the displacement step are obtained depending on the parameters of the system under a random external action. Numerical simulation of the operation of the algorithms used is carried out, recommendations are given for the optimal choice of system parameters. [ABSTRACT FROM AUTHOR]

In this paper, a system of nonlinear partial differential equations describing the spread of viruses in computers has been solved using the Exp-Function method, studying the solution for these types of systems helps to mitigate the effects of viruses by predicting their occurrence, in addition to that, the effect of parameters on the behavior and spread of viruses is studied. Figures are present to illustrate the effect of parameters in solving the nonlinear system. [ABSTRACT FROM AUTHOR]

The paper presents a procedure for numerical simulation of the air permeability in the transversal direction of protective face masks. Two types of three-layer face masks were considered, and their air-permeability was experimentally measured together with the masks' structural, geometric and mass characteristics. Two simulation approaches were tested with the actual thickness of the mask (Model 1-1) and a scaled model, corresponding to 4 times augmentation of the mask's thickness (Model 1-4). A total of 12 steady-state simulations were conducted with a complete comparative analysis between the two models and the two masks (porous medium). An adapted ENGYS® version of the computational code OpenFoam® was applied. The numerical results were verified with the experiments and showed a very good correlation. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulations using an open boundary algorithm with modified dynamic boundary condition (mDBC) for weakly compressible smoothed particle hydrodynamics models from particle-based code Dualsphysics. The problems of piping erosion in earth dams are aimed at studying the algorithm. The case 2D model of fluid flow past around a fixed cylinder is simulated, where various values of Reynold's numbers (Re 20 to Re 100) and different viscosity terms are considered. A constant velocity with different values of viscosity for generating various Reynold's numbers is modeled. The interaction between solid particles of the cylinder and fluid particles is concerned, the cylinder is affected by the hydrodynamics force caused by the flow of fluid particles. The solid particles of the cylinder are the observation points to obtain force and pressure due to the hydrodynamics forces. As a result of the simulation which is to show the capability to model 2D fluid flow with various Reynold's numbers. Drag coefficient, lift coefficient, and Strouhal number are compared to the previous work from literature. [ABSTRACT FROM AUTHOR]

NNW-UGKS, an engineering-oriented solver package based on the Unified Gas Kinetic Scheme(UGKS) for flows covering various regimes, is briefly introduced in the current paper. Then the hypersonic flowfield around a sharp-edged vehicle at high altitude is simulated with NNW-UGKS. The aerodynamic force coefficients, the pressure, the stress and heat distributions on the surface are compared with DSMC results. Good agreements have been achieved. [ABSTRACT FROM AUTHOR]

In this paper, a two-temperature nonlinear coupled constitutive Relations (NCCR) model is utilized to simulate the flows over a flat plate. The two-temperature NCCR model is implemented by involving the rotational relaxation term for the rotational energy equation. Thus, the rotational temperature and translation temperature in the flow field could be obtained simultaneously. The flow contours and temperature profiles over the flat plate are compared with those of multiple-temperature Navier-Stokes (NS) solver. The final results show that the two-temperature NCCR model would reproduce the solutions of NS solver at Ma=2. However, it behaves quite differently from the NS solver at Ma=5. It is also noted that the rotational temperature and translational temperature are close to each other at Ma=2. In contrast, the rotational temperature and translational temperature are totally different at Ma=5. [ABSTRACT FROM AUTHOR]

The development of blast-protective devices that direct blast and shock waves resulting in HE explosion to the safest side for humans and engineering constructions remains an urgent task in modern conditions. To optimize the design parameters of blast protection means, comprehensive research is required and the development of an optimal methodology that can help to improve the existing protective characteristics of those devices. The first stage in this direction is the study of an elevated (caused at some height above ground or floor) open explosion using experimental, analytical and numerical methods. In this paper, we obtained an assessment of the parameters characterizing the explosion of a 0.2 kg TNT charge. The features of shock wave propagation in an open explosion are determined using experimental, analytical and numerical methods. Authors revealed that it is necessary to use numerical methods with caution in modeling and decision-making. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical simulation of the thermal stress state in the process of 3D printing using the SLM (selective laser melting) technology for one layer of a growing body with a cylindrical cross section, taking into account the real technological parameters of the 3D printing machine. [ABSTRACT FROM AUTHOR]

The paper presents the finite element modeling of the spatial heat transfer to identify the temperature and the heat flux distributions both in the linear and point thermal bridges in various up-to-date wall systems. The paper considers the spatial heat transfer in the corner zone of the brickwork fragment. The ANSYS finite element program is used for the numerical simulation of the temperature fields and thermal fluxes for the brickwork connection with a hollow-core slab and a balcony slab. The influence of hollow cores in the floor slab is considered in relation to the temperature behavior along the inner surface of the brickwork fragment. To eliminate the negative effect from thermal bridging, it is suggested to increase the temperature on this inner surface. The brickwork thermal properties are investigated herein. [ABSTRACT FROM AUTHOR]

In this paper, we propose a numerical method for solving the problem of the propagation and gorenje of a methane jet in an axisymmetric satellite air flow. Dimensionless equations of the turbulent boundary layer of reacting gases in the Mises coordinates are used for modeling. To solve the problem in the Mises coordinates, a two-layer, six-point implicit finite-difference scheme is used, which provides a second-order accuracy of approximation by coordinates. Due to the nonlinearity of the equations of conservation and transfer of substances, an iterative process was organized. Separate results of the computational experiment are presented. Comparison of the calculation results for the change of the axial flow temperature according to k−ε and Prandtl models of turbulence and experimental data. [ABSTRACT FROM AUTHOR]

There are three decisions available for each participant in bi-cooperative games which can depict real life accurately in this paper. This paper researches the Shapley value of bi-cooperative games and completes the unique characterization. The axiom similar to classical cooperative games which could be used to characterize the Shapley value of bi-cooperative games as well. Meanwhile, it introduces a structural axiom and a zero excluded axiom instead of effective axiom in classical cooperative games. [ABSTRACT FROM AUTHOR]

Determination of the effective viscosity in the Brinkman's filtration equation by numerical simulation of an imagined physical experiment in volume flow rate viscometer is presented in this paper. Porous medium is modeled by the bundle of parallel fibers ordered in a regular square array. Such bundle is placed in a square duct. In the first step, a micro-structural flow problem is solved by the Trefftz method using special purpose Trefftz functions. In the second step the bundle of fibers is treated as a porous medium with the Brinkman's filtration equation as governing equation. Comparison the volume flow rate of these two flows permits as to determine a effective viscosity in filtration equation. [ABSTRACT FROM AUTHOR]

The hydrogen jet injection through a circular orifice into a transverse supersonic M = 3.38 flow is investigated numerically in the current paper. The 3D computations are performed under the conditions of the experiments by Ben-Yakar (2006). The Delayed Detached Eddy Simulation (DDES) approach is used to describe the transient flow's features. The results of the numerical simulations are compared to the experimental data. A good qualitative agreement between the calculations and the experiment is obtained for the mean flow structure, bow shock position, and jet penetration depth. The use of the scale-resolving DDES approach made it possible to obtain in the calculations large vortex structures developing at the boundary between the jet and the main flow, making a considerable contribution to mixing primary and secondary gases. [ABSTRACT FROM AUTHOR]

City canyon is a typical urban development configuration with two rows of tall buildings located along the road. Green infrastructure (tree alleys, green hedges/roofs/walls) inside urban canyons are a part of a city planning strategy, and it is actively used by architects around the world to ensure pedestrian comfort, reduce noise and the adverse effects of the urban heat island as well as to combat gaseous and dust pollution. However, a relatively large amount of data indicates a possible adverse effect of alleys with tall trees on the airflow characteristics inside urban canyons. The aim of the work is to numerically investigate the distribution of impurities from vehicles in urban canyons. The paper presents a description of microclimatic models built in ANSYS Fluent. It is based on the Reynolds-averaged Navier-Stokes equations closed with a two-equation k - ε realizable model, and the multi-species approach is used to simulate the impurities dispersion. Models are considered to take into account the influence of green spaces on the mean flow field and impurities concentration in the urban canyon. The simulation model is tested against the CODASC 2008 experimental data. [ABSTRACT FROM AUTHOR]

The paper proposes a method for determining of an aircraft wing thermal state during flight in icing conditions. The method is based on a probabilistic representation of a boundary value problem for a parabolic type equation and numerical solution of stochastic differential equations. It is assumed that the heat exchange process in a problem of the type under consideration is described quite well by the boundary value problem for the two-dimensional heat equation. The approximate solution definition at a given point is reduced to the numerical simulation of the diffusion random process paths. [ABSTRACT FROM AUTHOR]

The bidomain and monodomain models are types of nonlinear reaction-diffusion system and are widely used to study cardiac electrical activity. The numerical simulation of these models calls for extremely fine meshes to accurately predict the depolarization and repolarization wave fronts, which leads to huge computational challenges. In this paper, we will show the advantage of a parallel mesh adaptation method for solving the monodomain model. A comparison between parallel adapted and uniform meshes will be presented. The computational efficiency of the proposed methodology is assessed using an example of spiral wave. [ABSTRACT FROM AUTHOR]

Simulation of the aircraft assembly process is an important problem arising from the airline industry. To address this problem, a methodology was developed in previous studies, which is based on the contact problem solving. This paper is devoted to further development of numerical methods for simulation of fuselage junction riveting process. The methodology of a contact problem solving was developed to simulate the aircraft assembly process. In the developed algorithm, the initial contact problem is transformed into the problem of quadratic programming with linear constraints. As the installed fasteners restrict relative tangential displacements of assembled parts in the junction area, the relative tangential displacements are negligible in comparison with normal ones. This special feature of the problem justifies implementation of node-to-node contact model that is much simpler than general surface-to-surface model.However, this implementation imposes the restriction that all finite element nodes of parts in the contact area should coincide completely. This restriction creates difficulties during mesh building because it is much easier to build meshes of the parts independently from each other. The main contribution of this paper is introducing the method and extending the existing algorithm for airframe assembly simulation to the case of non-conformal meshes. This article introduces the method and the modernized algorithm for the riveting process with non-conformal meshes. [ABSTRACT FROM AUTHOR]

In this paper, we present the implementation of a lattice Boltzmann free surface algorithm for the simulation of water entry problems. The aim of this work is to isolate the effects of asymmetric impact on the water entry of a rigid wedge. Simulations for different heel angles were conducted in order to evaluate the influence of this parameter on the wedge dynamics, pile-up evolution, and velocity distribution. Our results indicate that the heel angle remarkably influences the physics of water impact. [ABSTRACT FROM AUTHOR]

Seamless pipe elbows are important components in mechanical, plant and apparatus engineering. Typically, they are produced by the so-called ‘Hamburg process’. In this hot forming process, the initial pipes are subsequently pushed over an ox-horn-shaped bending mandrel. The geometric shape of the mandrel influences the diameter, bending radius and wall thickness distribution of the pipe elbow. This paper presents the numerical simulation model of the hot mandrel bending process created to ensure that the optimum mandrel geometry can be determined at an early stage. A fundamental analysis was conducted to determine the influence of significant parameters on the pipe elbow quality. The chosen methods and approach as well as the corresponding results are described in this paper. [ABSTRACT FROM AUTHOR]

Nowadays polymers are commonly used in various applications, which make it difficult to avoid its usage even though it causes environmental problems. Natural fibers are best alternate to overcome the polymer based environmental issues. Natural fibers play an important role in developing high performing fully newline biodegradable green composites which will be a key material to solve environmental problems in future. In this paper deals the properties analysis of banana fiber is combined with epoxy resin in order to create a natural composite, which has special characteristics for aerospace applications. The objective of this paper is to investigate the characteristics of failure modes and strength of natural composite using experimental and numerical methods. The test specimen of natural composite has been fabricated as per ASTM standard, which undergoes tensile and compression tests using Tinius Olsen UTM in order to determine mechanical and physical properties. The reference model has been designed by CATIA, and then numerical simulation has been carried out by Ansys Workbench 16.2 for the given boundary conditions. [ABSTRACT FROM AUTHOR]

Compact devices for generation of high-voltage pulses are in demand in areas such as portable lightning simulation, expendable electron beam and X-ray sources, as well as advanced laser power supplies, multi-mode high-power microwave sources, and compact radar technologies. The pulsed transformer is a critical component of these devices. It increases a voltage pulse from thousand volts to tens or hundreds thousand volts, with the advantage of being compact, efficient, and safe. Modern nanomaterials, such as NanoPerm, or other advanced ferromagnetics, are quite attractive for use in pulsed transformer cores as they reduce a size and weight compared to steel cores. There are numerous challenges in a transformer design for high energy pulses of short duration in the micro to nanosecond range. A high magnetic inductance generated in the core may lead to a saturation, reducing the magnetic permeability of these materials. High frequencies (a nanosecond pulse width) cause decline of magnetic properties as well. Keep in mind that magnetic properties of these materials are nonlinear, depend on the field strength (a pulse amplitude), and frequency (a pulse width). Numerical simulation of pulsed transformers is an efficient way to meet all these challenges, and to find the optimal device design that needs to be compact (pocket size). In this paper, we will present the numerical simulation approach (circuits and fields) and optimization of a compact high voltage pulsed transformers, that we have performed for the development and implementations of the compact (mobile phone size) pulsed power source. The developed device has the output pulse voltage 70KV, pulse energy 6J, and the required pulse duration of 1us. This high-performance device is able to generate >5000 pulses using a small cell phone battery without recharging. [ABSTRACT FROM AUTHOR]

In this paper, we consider numerical modeling and experimental testing of the process of heat dissipation from a computer processor. The mathematical model is described using the non-stationary heat transfer equation, taking into account the air flow inside the cooler. The calculation area consists of three subdomains: air, heat sink, processor. The velocity distribution in the subdomain with air is calculated using the Stokes equation. To eliminate oscillations in the calculation of heat distribution, the method of artificial diffusion is used. Time approximation is performed using a purely implicit scheme. The experimental data were obtained by loading the processor with the OCCT test with a variation of the processor frequency multiplier. [ABSTRACT FROM AUTHOR]

The first corona virus disease case was reported in Wuhan City, China in December 2019 and spreads worldwide very quickly. On 9th March 2020, World Health Organization declared COVID-19 as a global pandemic. Mathematical models can be very effective in understanding the transmission patterns of COVID-19. This paper proposes a fractional-order susceptible, exposed, infected, asymptomatic, hospitalized, removed (SEIAHR) model. The fractional models help understand the disease epidemic. To formulate its fractional derivative, we consider the Caputo operator and discuss the uniqueness and existence of the solution for the model by applying the Banach contraction mapping principle. We performed numerical simulation by the Adams- Bashforth-Moulton method, which shows that the fractional models provide a better understanding and more biological insights about the dynamics of disease than traditional integer-order models. [ABSTRACT FROM AUTHOR]

Reliability Block Diagrams (RBDs) allow us to model the failure relationships of complex systems and their sub-components and are extensively used for system reliability, availability, dependability and maintainability analyses of many engineering systems. Traditionally, Reliability Block Diagrams (RBD) are analyzed using paper-and-pencil proofs or computer simulations. Recently, formal techniques, including Petri Nets and higher-order-logic theorem proving, have been used for their analysis as well. In this paper, we provide a concise survey of these available RBD analysis techniques and compare them based on their accuracy, user friendliness and computational requirements. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present some aspects regarding the computational model and technical solutions for multistage suborbital launcher for testing (SLT) used to test spatial equipment and scientific measurements. The computational model consists in numerical simulation of SLT evolution for different start conditions. The launcher model presented will be with six degrees of freedom (6DOF) and variable mass. The results analysed will be the flight parameters and ballistic performances. The discussions area will focus around the technical possibility to realize a small multi-stage launcher, by recycling military rocket motors. From technical point of view, the paper is focused on national project "Suborbital Launcher for Testing" (SLT), which is based on hybrid propulsion and control systems, obtained through an original design. Therefore, while classical suborbital sounding rockets are unguided and they use as propulsion solid fuel motor having an uncontrolled ballistic flight, SLT project is introducing a different approach, by proposing the creation of a guided suborbital launcher, which is basically a satellite launcher at a smaller scale, containing its main subsystems. This is why the project itself can be considered an intermediary step in the development of a wider range of launching systems based on hybrid propulsion technology, which may have a major impact in the future European launchers programs. SLT project, as it is shown in the title, has two major objectives: first, a short term objective, which consists in obtaining a suborbital launching system which will be able to go into service in a predictable period of time, and a long term objective that consists in the development and testing of some unconventional sub-systems which will be integrated later in the satellite launcher as a part of the European space program. This is why the technical content of the project must be carried out beyond the range of the existing suborbital vehicle programs towards the current technological necessities in the space field, especially the European one. [ABSTRACT FROM AUTHOR]

In this paper, a path following controller for nonholonomic unicycle-type mobile robots is presented. First, a kinematic model in error coordinates appropriate for path following applications is developed. Using the classical linear control theory, a feedback path control based on distance-only measurements is proposed. The stability of the closed-loop system is analyzed and the performance of the control system is studied for rectilinear and circular path with unknown curvature. Numerical simulations and experiments are conducted to validate the synthesized feedback path following control scheme. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical simulation of flue gas in a Selective Catalytic Reduction (SCR) system which is connected to a combined heat and power (CHP) unit. The main subject is the evaluation the basic design and to search for any possible improvements, but there are quite strict restrictions related to this. We present numerous design geometry modifications which have been created according to previous knowledge obtained from similar projects and some of the variants are also inspired by other researchers. ANSYS Fluent is used to create the models and for the evaluation. More than thirty modifications were designed but only a selection of them is presented here. [ABSTRACT FROM AUTHOR]

In this paper we shall study a system of integro-differential equations which arises in nanostructures. We shall approximate it with the Cellular Nanoscale Networks (CNN) architecture. Then we shall study the dynamics of the obtained integro- differential CNN model via the local activity method. We shall determine the region called edge of chaos in which complex behavior can occur. We shall design hybrid control regulator for the CNN model under consideration in order to stabilize the chaotic motion to admissible solutions which is connected in some way to the original behavior of the system. Numerical simulations will be presented which will illustrate the obtained theoretical results. [ABSTRACT FROM AUTHOR]

Analysis of the dynamics of the vibration-driven planetary rover is considered. Numerical simulation using ADAMS MBD software shown that it is fundamentally possible to create a Venus rover with internal moving mass that will be able to move along the surface with the required average speed 0.16 m/s for a certain time. When operating on the surface of Venus for one and a half hours, a 300-kg planetary cruiser can travel about 500 meters. In the scheme under consideration, it is possible to vary part of the design parameters within wide limits, which facilitates the design study of the rover. It turns out that it is more efficient to use an actuator, the mass of which is more than half the mass of the entire rover. It should be noted that the possible practical application of an automatic robot-rover with a hermetic spherical body and without external moving parts is not limited to studies on the surface of Venus. Such a device may be used in conditions of high external temperature and pressure, as well as in a chemically aggressive environment. [ABSTRACT FROM AUTHOR]

Earthquakes may induce serious dynamic loads acting on buildings, which can lead to damage or even destruction of the whole structure. In densely populated areas, it is quite common that buildings are located very close one to another which can result in pounding between them during ground motions. Due to the environmental awareness, multi-story timber frame buildings are gaining popularity and therefore there is a need to investigate the effects of structural collisions on seismic response of such buildings. In this paper, the results of advanced numerical FEM simulation, focused on inter-story pounding between two adjacent multi-story timber frame buildings, are presented. The results of the study show that structural interactions have a significant influence on the overall response of buildings exposed to damaging seismic excitations. Moreover, due to deformability of buildings made of wood, pounding may change response of such buildings much more, as compared to steel, reinforced concrete or masonry structures. Finally, the results confirm that the use of the nonlinear FEM with detailed representation of material and geometric structural properties can be considered as the effective approach in obtaining the accurate response of colliding timber frame buildings during earthquakes. [ABSTRACT FROM AUTHOR]

Residual fatigue lifetime assessment of a cracked structure is a common task for engineering and scientific community. Fatigue crack may appear on the surface or in the initial defect, e.g. pores in weldments. Such a structure needs to be examined, whether is it safe to be operated. Various assessment methods of different difficulties exist. In this paper, numerical and experimental study on fatigue crack propagation is presented. Propagation of a fatigue crack starting from an initial surface defect of semi-elliptical shape through the flat specimen is considered. Two load ratios were employed in order to compare their effects, as loading at low asymmetry R = 0.1 ensures presence of a plasticity induced crack closure, while at load ratio R = 0.6 fatigue crack growth without premature closure is expected. Beach marks were created on the fracture surface in order to study the fatigue crack evolution, number of cycles spent for fatigue growth and also the influence of premature closure on the crack front evolution. One of the well-known methods was applied for numerical fatigue lifetime evaluation and estimated number of cycles required for crack growth through the body was compared to the experimentally measured data. Second part of the paper deals with fatigue crack front curvature, which is always affected at the vicinity of the free surface due to the corner singularity of the stress field. However, when crack closure appears, fatigue crack propagation is retarded and furthermore, crack front is curved even more at the free surface as a result of earlier closure than in the middle of the body. Separation of these two effects allows direct comparison of their impact on fatigue crack front propagation. [ABSTRACT FROM AUTHOR]

The aim of this paper is to explore the possibilities of applying a simple method of the solution of the differential equations of the 2nd order. Such equations describe the behavior of the structure under dynamic load (seismic effects, starting of rotating machines). A friction damper was developed at the Fraunhofer-Institut für Holzforschung in Braunschweig in order to limit the oscillation of the structure. Here is analyzed the mathematical model where hysteresis behavior (energy dissipation) is described. The model is basically based on a strongly non-linear stiffness change of the joints. [ABSTRACT FROM AUTHOR]