Search

The article discusses a research study which presents a quasi chemistry-transport model mode (QCTM) for the ECHAM5/MESSy Atmospheric Chemistry model (EMAC). The said approach is designed to quantify chemical signals by suppression of responses between dynamics and chemistry. Findings reveal the importance of adequate offline chemical fields which can be produced from a non-QCTM simulation.

Variable compliant elements in the leg play an important role in quadruped mammals' locomotion. This paper mainly investigates the dynamics characteristics of a specific leg model with a variable stiffness element during the stance phase. By choosing appropriate initial states and planning joint motion under specific constraint conditions, the model is able to move normally and pivot about the contact point. Particularly, the passive motion of the variable stiffness element is planned based on forced vibration characteristics and is set to experience a compression and extension process. In a detailed study, the optimal combination of the system parameters, meeting constraint conditions, were evaluated. We investigated the effects of the initial states on the leg's motion, and obtained the necessary variable stiffness characteristics under different conditions. The ground reaction features of the leg model present similar characteristics to those of a canine. A variable stiffness device with a good adjustability feature and a large adjustable range is discussed. [ABSTRACT FROM AUTHOR]

In this paper, we consider a generalized fast marching method (GFMM) as a numerical method to compute dislocation dynamics. The dynamics of a dislocation hypersurface in ℝN (with N = 2 for physical applications) is given by its normal velocity which is a nonlocal function of the whole shape of the hypersurface itself. For this dynamics, we show a convergence result of the (IFMM as the mesh size goes to zero. We also provide some numerical simulations in dimension N=2. [ABSTRACT FROM AUTHOR]

This paper presents an application of multibody dynamics with unilateral contact to model the friction wedge interaction with the bolster and the side frame. The new friction wedge model is a three-dimensional, dynamic, stand-alone model of a bolster–friction wedge–side frame assembly. It allows the wedge four degrees of freedom: vertical displacement; longitudinal (between the bolster and the side frame) displacement; toe in and toe out; and yaw (rotation about the vertical axis). The dedicated train modeling software NUCARS (Transportation Technology Center, Inc., Pueblo, Colo.) has been used to run simulations with similar inputs and to compare—when possible—the results with those obtained from the new stand-alone MATLAB (MathWorks, Natick, Mass.) friction wedge model. The stand-alone model shows improvement in capturing the transient dynamics of the wedge better. Also, it can predict not only normal forces going into the side frame and bolster, but also the associated moments. Significant simulation results are presented and the main differences between the current NUCARS model and the new stand-alone MATLAB models are highlighted. [ABSTRACT FROM AUTHOR]

This paper presents the dynamic formulation and performance evaluation of the 6-d.o.f. parallel structure seismic simulator. By means of the principle of virtual work and the concept of link Jacobian matrices, the inverse dynamic model of the seismic simulator is set up. Then, a series of new dynamic performance indices with obvious physical meanings have been proposed. The dynamic performance index combining the acceleration, velocity and gravity terms of the dynamic equations has been achieved by decoupling the inverse dynamics in an exhaustive way. By using the index, it is possible for us to evaluate the performance in different directions. The index has been applied to the dynamic characteristic evaluation of the 6-d.o.f. parallel structure seismic simulator in the numerical simulation. Conclusions and results are provided at the end of the paper. [ABSTRACT FROM AUTHOR]

This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space. [ABSTRACT FROM AUTHOR]

In earthquakes and building collapse situations, volumes of people may need to move, suddenly, through spaces that have been destroyed and seem unfamiliar in configuration and appearance. Perception is significant in these cases, determining individual movement, collective egress, and phenomena in between. Alas, exploring how perception shapes critical egress is tricky because perception is both physical and cerebral in genesis and because critical scenarios are often hazardous. In this paper, we describe a computational sandbox for studying urban damage scenarios. The model is built as automata, specialized as human automata and rigid body automata, with interactivity provided by slipstreaming. Our sandbox supports parameterization of synthetic built settings and synthetic humans in fine detail for large interactive collections, allowing flexible analyses of damage scenarios and their determining processes, from micro-perspectives through to the macrocosm of the phenomena that might result. While we have much work to do to improve the model relative to real-world fidelity, our work thus far has produced some meaningful results, supporting practical questions of how urban design and parking scenarios shape egress, and pointing to potential phenomena of perceptual shadowing as a translation mechanism for processes at the built-human interface. [ABSTRACT FROM AUTHOR]

In this paper, the balance control of a ball and beam system is considered. Based on the T-S fuzzy modeling, the dynamic model of the ball and beam system is formulated as a strict feedback form with modeling errors. Then, an adaptive dynamic surface control (DSC) is utilized to achieve the goal of ball positioning subject to parameter uncertainties. The robust stability of the closed-loop system is preserved by using the Lyapunov theorem. In addition to simulation results, the proposed T-S fuzzy model-based adaptive dynamic surface controller is applied to a real ball and beam system for practical evaluations. Simulation and experimental results illustrate that the proposed control scheme has much better performance than that of conventional DSC. Furthermore, parameter uncertainties and external disturbance are considered to highlight the robustness of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

supply chain is a complex adaptive system that is very difficult to analyze, in particular, with respect to its dynamics, stochastic, and uncertainty. The traditional analytical model is unable to cope with these characteristics of supply chain. In addition, the analytical model may not be solved due to its complexity and nonlinearity. Simulation, especially the multi-agent-based distributed simulation, is one of the most effective tools to model and analyze supply chain. In this paper, a multi-agent platform framework with multi-layers for modeling and distributed simulation of the complex supply chain is presented. In this platform, generic agents for modeling entities in supply chain are described and a novel simulation modeling approach enabled by the platform is proposed. The platform provides a flexible environment for defining, deploying, simulating, and displaying agent-based simulation models and enables users to instantiate generic agents to model their required simulation models rapidly. A three-echelon supply chain model is developed and simulated to illustrate the use of the simulation platform. [ABSTRACT FROM AUTHOR]

By extending a widely cited benchmark model on the pitch-plane dynamics of a supercavitating vehicle, recent literature has proposed new models that include the memory effect in characterizing the interaction of the supercavitating vehicle and the cavity. Based on this time-delay supercavitating vehicle model, this paper develops delay-dependent control designs that explicitly address the cavity memory effect in the supercavitating vehicle dynamics. We first reformulate the pitch-plane dynamics of the supercavitating vehicle as a time-delay Quasi-Linear-Parameter-Varying system, and then develop delay-dependent H∞ controllers. Simulations have been conducted for both initial and tracking responses to evaluate the performance and robustness of the proposed delay-dependent controllers. [ABSTRACT FROM PUBLISHER]

A large corpus of data obtained by means of empirical study of neuromuscular adaptation is currently of limited use to athletes and their coaches. One of the reasons lies in the unclear direct practical utility of many individual trials. This paper introduces a mathematical model of adaptation to resistance training, which derives its elements from physiological fundamentals on the one side, and empirical findings on the other. The key element of the proposed model is what is here termed the athlete's capability profile. This is a generalization of length and velocity dependent force production characteristics of individual muscles, to an exercise with arbitrary biomechanics. The capability profile, a two-dimensional function over the capability plane, plays the central role in the proposed model of the training-adaptation feedback loop. Together with a dynamic model of resistance the capability profile is used in the model's predictive stage when exercise performance is simulated using a numerical approximation of differential equations of motion. Simulation results are used to infer the adaptational stimulus, which manifests itself through a fed back modification of the capability profile. It is shown how empirical evidence of exercise specificity can be formulated mathematically and integrated in this framework. A detailed description of the proposed model is followed by examples of its application-new insights into the effects of accommodating loading for powerlifting are demonstrated. This is followed by a discussion of the limitations of the proposed model and an overview of avenues for future work. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamical behaviour of an epidemic on complex networks with population mobility. In our model, the number of people on each node is unrestricted as the nodes of the network are considered as cities, communities, and so on. Because people can travel between different cities, we study the effect of a population's mobility on the epidemic spreading. In view of the population's mobility, we suppose that the susceptible individual can be infected by an infected individual in the same city or other connected cities. Simulations are presented to verify our analysis. [ABSTRACT FROM AUTHOR]

This research proposes a hybrid simulation approach based upon the principles of system dynamics (SD) and discrete event simulation (DES), which facilitates a better understanding of complex interactions among various processes in large-scale construction. The significance of the construction context that interacts with construction operations is highlighted, and a hybrid SD-DES approach is proposed as a means to capture the feedback between the two. In particular, this paper focuses on how to seamlessly integrate SD and DES within the framework of a modeling perspective. For the purpose of substantiating the discussion, a pipeline installation process is modeled using the proposed hybrid approach, with specific consideration given to how the approach can serve to address complex interactions between operation and context. [ABSTRACT FROM AUTHOR]

In nonlinear voter models the transitions between two states depend in a nonlinear manner on the frequencies of these states in the neighborhood. We investigate the role of these nonlinearities on the global outcome of the dynamics for a homogeneous network where each node is connected to m = 4 neighbors. The paper unfolds in two directions. We first develop a general stochastic framework for frequency dependent processes from which we derive the macroscopic dynamics for key variables, such as global frequencies and correlations. Explicit expressions for both the mean-field limit and the pair approximation are obtained. We then apply these equations to determine a phase diagram in the parameter space that distinguishes between different dynamic regimes. The pair approximation allows us to identify three regimes for nonlinear voter models: (i) complete invasion; (ii) random coexistence; and – most interestingly – (iii) correlated coexistence. These findings are contrasted with predictions from the mean-field phase diagram and are confirmed by extensive computer simulations of the microscopic dynamics. [ABSTRACT FROM AUTHOR]

The paper is concerned with application of mathematical modeling to the analysis of signaling pathways. Two issues, deterministic modeling of gene transcription and model-driven discovery of regulatory elements, are dealt with. First, the biological background is given and the importance of the stochastic nature of biological processes is addressed. The assumptions underlying deterministic modeling are presented. Special emphasis is put on describing gene transcription. A framework for including unknown processes activating gene transcription by means of first-order lag elements is introduced and discussed. Then, a particular interferon-β induced pathway is introduced, limited to early events that precede activation of gene transcription. It is shown how to simplify the system description based on the goals of modeling. Further, a computational analysis is presented, facilitating better understanding of the mechanisms underlying regulation of key components in the pathway. The analysis is illustrated by a comparison of simulation and experimental data. [ABSTRACT FROM AUTHOR]

Recent technological advances in geosensor networks demand new models of distributed computation with dynamic spatial information. This paper presents a computational model of spatial change in dynamic regions (such as may be derived from discretizations of continuous fields) founded on embeddings of graphs in orientable surfaces. Continuous change, connectedness and regularity of dynamic regions are defined and local transition rules are used to constrain region evolution and enable more efficient inference of a region's state. The model provides a framework for the detection of global high‐level events based on local low‐level ‘snapshot’ spatiotemporal data. The approach has particular relevance to environmental monitoring with geosensor networks, where technological constraints make the detection of global behaviour from local conditions highly advantageous. [ABSTRACT FROM AUTHOR]

A fully dynamic model of a microchannel evaporator is presented. The aim of the model is to study the highly dynamic parallel channel instabilities that occur in these evaporators in more detail. The numerical solver for the model is custom-built and the majority of the paper is focused on detailing the various aspects of this solver. The one-dimensional homogeneous two-phase flow conservation equations are solved to simulate the flow. The full three-dimensional (3D) conduction domain of the evaporator is also dynamically resolved. This allows for the correct simulation of the complex hydraulic and thermal interactions between the microchannels that give rise to the parallel channel instabilities. The model uses state-of-the-art correlations to calculate the frictional pressure losses and heat transfer in the microchannels. In addition, a model for inlet restrictions is also included to simulate the stabilizing effect of these components. In the final part of the paper, validation results of the model are presented, in which the stability results of the model are compared with the existing experimental data from the literature. Next, a parametric study is performed focusing on the stabilizing effects of the solid substrate properties. It is found that increasing the thermal conductivity and thickness of the solid substrate has a strong stabilizing effect, while increasing the number of microchannels has a small destabilizing effect. Finally, representative dynamic results are also given to demonstrate some of the unique capabilities of the model. [ABSTRACT FROM AUTHOR]

This paper presents mathematical modelling of an implanted surgical mesh used in the repair process of the abdominal hernia. The synthetic implant is simulated by a membrane structure. The author provides a material modelling of the implant based on the dense net model appropriate for technical fabrics. The accuracy of the proposed solution is evaluated by comparing the simulations of the dynamic behaviour of the system with the experiments carried out on physical models of implanted mesh. The model can be used to estimate the repair persistence for different mesh materials, fixing systems and different numbers of tacks to be provided during the surgery in order to resist the cough pressure and required action to avoid hernia recurrence. The persistence of the repaired hernia is assessed on the basis of the values of the forces in the tissue–implant joints because the usual form of the repair failure is due to as the joint disconnection or tissue failure. [ABSTRACT FROM PUBLISHER]

Copyright of Archive of Mechanical Engineering is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Transmission error is an important reason for instability in helical gears. A six-degree-of-freedom dynamic model coupled flexional, torsional and axial motion of a helical gear transmission system, which includes time varying mesh stiffness, bearing supporting stiffness, mesh damping and backlash, is developed, after taking into account the dynamic characteristics and vibration responses of helical gear in three dimensions. Influences of involute contact ratio, bearing supporting stiffness, mesh damping and backlash on the dynamic transmission errors and vibration stability of the helical gear system are investigated using numerical simulation technique. The effects on dynamic transmission errors and stabilities by contact ratio, supporting stiffness and mesh damping as well as gear backlash are analyzed. The intrinsic relationship between above parameters and dynamic transmission errors and stabilities for helical gear system are presented. The stable and unstable regions under different parameters are given. The results in this paper can be helpful to the dynamic and stable design of a helical gear transmission system. [ABSTRACT FROM AUTHOR]

The natural gas consumption of the operators connected to the gas transport system depends on the gas needs. As gas needs vary in time, the whole process of gas transportation is, therefore, nonstationary. The paper presents nonstationary simulations for a gas transportation network and highlights the parameters values (flows, pressures) that are necessary to assure the safety of the system. [ABSTRACT FROM AUTHOR]

In this paper, analytical techniques and fuzzy logic method are applied to the dynamic modeling and efficient swimming control of a robotic fish. The bioinspired robotic fish, which follows an exact replica of a live mackerel (Scomber scombrus), is modeled by treating the undulating body and flapping tail independently using analytical methods. Comparing the results of simulations and experiments shows the feasibility of the dynamic model. Using this model, we found that the harmonic control of the Strouhal number and caudal fin angle of attack is a principal mechanism through which the robotic fish can obtain high thrust efficiency while swimming. The fuzzy control method, which is based on the knowledge of the robotic fish's dynamic behavior, has successfully utilized this principal mechanism. By comparing the thrust performance of the robotic fish with different control methods via simulation, we established that the fuzzy controller was able to achieve faster acceleration and smaller steady-state error than what could be achieved from an open-loop and conventional proportional–integral-derivative controller. The thrust efficiency during steady state was superior to that with conventional control methods. We also found that, when using the fuzzy control method, robotic fish can always swim near a “universal” Strouhal number that approximates to the swimming of live fish. [ABSTRACT FROM PUBLISHER]

In this study, a time simulation model for long-term wind capacity investment decisions in the presence of an electricity market and a tradable green certificate (TGC) market is proposed. Decisions related to the investments in the wind capacity are fundamentally based on incentives gained from both of these markets. Fundamental concepts and models of these markets are described. The TGC price trend-following and value-trading strategies for both generation and distribution companies and the regulatory policies for the limitation of TGC holding time and TGC borrowing fraction are included. In this study, a new dynamic model of coupled TGC and electricity markets is considered in order to examine the performance of the hybrid trading strategies and regulatory policies in these markets. Besides, the paper analyses different strategies of the market players for trading TGCs and gives recommendations on the best combination of different strategies in order to reach the players' objectives. The decision model of this dynamic framework enables market players and regulators to determine the possible consequences of different decisions, such as adoption of different trading strategies and policies, and uncertainties in both the preliminary design and operating phases of a TGC market. [ABSTRACT FROM AUTHOR]

Fuzzy systems properly integrated with Qualitative Reasoning approaches yield a hybrid identification method, called FS-QM, that outperforms traditional data-driven approaches in terms of robustness, interpretability and efficiency in both rich and poor data contexts. This results from the embedment of the entire system dynamics predicted by the simulation of its qualitative model, represented by fuzzy-rules, into the fuzzy system. However, the intrinsic limitation of qualitative simulation to scale up to complex and large systems significantly reduces its efficient applicability to real-world problems. The novelty of this paper deals with a divide-and-conquer approach that aims at making qualitative simulation tractable and the derived behavioural description comprehensible and exhaustive, and consequently usable to perform system identification. The partition of the complete model into smaller ones prevents the generation of a complete temporal ordering of all unrelated events, that is one of the major causes of intractable branching in qualitative simulation. The set of generated behaviours is drastically but beneficially reduced as it still captures the entire range of possible dynamical distinctions. Thus, the properties of the correspondent fuzzy-rule base, that guarantee robustness and interpretability of the identified model, are preserved. The strategy we propose is discussed through a case study from the biological domain. [ABSTRACT FROM AUTHOR]

In this paper, the power system with an excitation controller is represented as a class of large-scale, uncertain, interconnected nonlinear continuous-time system in strict-feedback form. Subsequently, dynamic surface control (DSC)-based adaptive neural network (NN) controller is designed to overcome the repeated differentiation of the control input that is observed in the conventional backstepping approach. The NNs are utilized to approximate the unknown subsystem and the interconnection dynamics. By using novel online NN weight update laws with quadratic error terms, the closed-loop signals are shown to be locally asymptotically stable via Lyapunov stability analysis, even in the presence of NN approximation errors in contrast with other NN techniques where a bounded stability is normally assured. Simulation results on the IEEE 14-bus power system with generator excitation control are provided to show the effectiveness of the approach in damping oscillations that occur after disturbances are removed. The end result is a nonlinear decentralized adaptive state-feedback excitation controller for damping power systems oscillations in the presence of uncertain interconnection terms. [ABSTRACT FROM PUBLISHER]

This paper uses the cellular automaton model to study the dynamics of traffic flow around an on-ramp with an acceleration lane. It adopts a parameter, which can reflect different lane-changing behaviour, to represent the diversity of driving behaviour. The refined cellular automaton model is used to describe the lower acceleration rate of a vehicle. The phase diagram and the capacity of the on-ramp system are investigated. The simulation results show that in the single cell model, the capacity of the on-ramp system will stay at the highest flow of a one lane system when the driver is moderate and careful; it will be reduced when the driver is aggressive. In the refined cellular automaton model, the capacity is always reduced even when the driver is careful. It proposes that the capacity drop of the on-ramp system is caused by aggressive lane-changing behaviour and lower acceleration rate. [ABSTRACT FROM AUTHOR]

Within many domains, among which biological, cognitive, and social areas, multiple interacting processes occur among agents with dynamics that are hard to handle. This paper presents the predicate logical Temporal Trace Language (TTL) for the formal specification and analysis of dynamic properties of agents and multi-agent systems. This language supports the specification of both qualitative and quantitative aspects, and therefore subsumes specification languages based on differential equations and qualitative, logical approaches. A software environment has been developed for TTL, which supports editing TTL properties and enables the formal verification of properties against a set of traces. The TTL environment proved its value in a number of projects within different biological, cognitive and social domains. [ABSTRACT FROM AUTHOR]

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures. [ABSTRACT FROM AUTHOR]

This paper reviews recent developments related to oscillatory systems, their impact on and relationship to the cases of smooth, essentially anharmonic (non-linearizable) potentials, and vice versa. Special methods of treatment that allow the response regimes in dynamic vibro-impact systems to be computed have been discussed. Mathematical models that approximate purely elastic as well as inelastic impact, with the help of smooth functions, are presented and illustrated by specific examples. The use of ideas based on non-smooth time transforms to treat essentially non-linear systems with smooth potentials has also been discussed. Special attention has been paid to uncommon applications of vibro-impact models. [ABSTRACT FROM AUTHOR]

The design of a control oriented motorcycle model for the simulation of two-wheeled vehicles is widely recognized to be a very challenging task, as a complete analytical model is not directly available, due to its complexity and its high sensitivity to parameters' variations. Accordingly, a reliable model should be based on multibody modelling tools endowed with automated symbolic manipulation capabilities. This paper presents a simulation model for the dynamic behaviour of a motorcycle based on the object-oriented modelling paradigm developed in Modelica, within the Dymola environment. Specifically, we illustrate the modular approach to motorcycle modelling and discuss the tire-road interaction model, which is the crucial part of the proposed model. The validity of the proposed simulation model is assessed on real data, measured on an instrumented test vehicle. Further, to perform the verification phase a virtual driver model has been implemented, which allows to track both a roll angle and a target speed profile during different maneuvers. In particular, the behaviour of the driver is modelled as an inverse pendulum, with a rotational degree of freedom along the forward axis. This allows accounting for the driver lean angle, which is necessary to fully capture the real driving behaviour and its effects on the overall vehicle dynamics. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we investigate the convergence of a multi-layer population model to a single-layer limit. In a previous paper [Cusulin, C., Iannelli, M., Marinoschi, G. Age-structured diffusion in a multi-layer environment, Nonlinear Anal. Real World Appl. 6(1) (2005) 207–223], we considered a Gurtin–MacCamy type model based on the fact that the population diffuses through a one dimensional habitat, partitioned into homogeneous layers. In each layer the population has its own age-dependent growth and diffusion parameters, so that within each layer the dynamics is not subject to environmental variations, while changes occur from a layer to another, according to different conditions. Such kind of a model may describe the growth of a population in a fragmented environment, but the same framework may be used to give an approximate view of the population growth and diffusion in a general spatially heterogeneous habitat, because the layer structure may arise by approximation of the original problem. In the present paper we show that this view is actually mathematically sound and justified. In fact, on the basis of the previous results (see [Cusulin, C., Iannelli, M., Marinoschi, G. Age-structured diffusion in a multi-layer environment, Nonlinear Anal. Real World Appl. 6(1) (2005) 207–223]) the approximating problem actually converges and the multi-layer solution may be considered a patch-wise picture of the original problem. [Copyright &y& Elsevier]

Multiphase and multidomain fluid flows associated with interfacial dynamics, steep jump in fluid properties, and moving boundaries between different phases and materials pose substantial computational challenges. In this paper, recent progresses made in numerical simulation using continuum and lattice–Boltzmann methods are highlighted, with special attention paid to issues related to time varying geometries, adaptive grid refinement, interfacial and geometric tracking, topological changes, and reduced numerical dispersion and dissipation. Illustrative physical applications including: (1) multiple rising bubbles interacting with carrier phase and with each other; (2) wave reflected on an inclined wall; and (3) the Rayleigh–Taylor instability problem, are presented to highlight the various aspects of the techniques developed. [ABSTRACT FROM AUTHOR]

In this paper, a two dimensional hybrid model of a continuously variable transmission with push belt is provided. The system is characterized by a large number of contacts with impacts and friction. These interactions are modeled by uni- and bilateral constraints also considering friction. The established equations of motion are integrated numerically by a time-stepping algorithm. The simulation model allows for the computation of the dynamics of the push belt and all contact forces. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the specific framework and a set of simulations computed on the basis of a kinetic model of interest in the field of the Social Sciences. The model is a reduced version of a comprehensive more general one, and it relates to the specific case of a competing bipartisan political system. The model structure contains terms with localized interactions and mean field terms. In the first part of the paper the mathematical details of the model are recalled. In the second part the simulations are presented with reference to the various scenarios examined. Finally a discussion on research perspectives is formulated. [Copyright &y& Elsevier]

Mathematical regularization of the nonlinear terms in the Navier–Stokes equations is found to provide a systematic approach to deriving subgrid closures for numerical simulations of turbulent flow. By construction, these subgrid closures imply existence and uniqueness of strong solutions to the corresponding modelled system of equations. We will consider the large-eddy interpretation of two such mathematical regularization principles, i.e. Leray and LANS-a regularization. The Leray principle introduces a smoothed transport velocity as part of the regularized convective nonlinearity. The LANS-a principle extends the Leray formulation in a natural way in which a filtered Kelvin circulation theorem , incorporating the smoothed transport velocity, is explicitly satisfied. These regularization principles give rise to implied subgrid closures which are implemented in large eddy simulations of turbulent mixing. Comparison with filtered direct numerical simulation data and with predictions obtained from popular dynamic eddy-viscosity modelling shows that these mathematical regularization models provide considerably more accuracy at a lower computational cost than the dynamic approaches. In particular, the regularization models perform especially well in capturing the flow features characteristic of the smaller resolved scales. Variations in spatial resolution and Reynolds number establish that the Leray model is more robust but also slightly less accurate than the LANS-a model. The LANS-a model retains more of the small-scale variability in the resolved solution. However, this requires a corresponding increase in the required spatial resolution. When using second-order finite volume discretization, the potential accuracy of the implied LANS-a model is found to be realized by using a grid spacing that is not larger than the length scale a that appears in the definition of this model. This paper is associated with the focus-issue Cascade Dynamics: Fundamentals and Modelling. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the dynamic analysis of a flexible-joint robot colliding with its environments is presented. The system considered here is an n-rigidlink manipulator driven by n DC-motors through n revolute flexible-joints. The flexibility of each flexible joint is modelled as a linearly elastic torsional spring. 2n generalized coordinates are introduced to identify the configuration of the robot. The concept of impulse potential energy is introduced, and the generalized impulse-momentum equations along with the equation involving coefficient of restitution are used to establish the complete mathematic model for dealing with the case of a flexible-joint manipulator colliding with its environments (such as the ground, another manipulator, and so on). Solving for this mathematic model, one can obtain the jump discontinuities in system generalized velocities and the impulses at the impact points explicitly. To validate the algorithm presented in this paper, the dynamic simulation of a robot involving impact with its environments is given as an example. [Copyright &y& Elsevier]

The objective of this study is to develop a fabric drape mathematical model in order to simulate the dynamic behavior of a textile structure. Simulation of fabric drape is a significant issue in textile research, which contributes to advances within the framework of virtual models and clothing simulation. In the first part of this paper, the existing methods dealing with the fabric simulation are presented. In the following part, a mathematical model that has been selected for simulation is given. The third part is devoted to the identification of unknown parameters. Each parameter corresponds to a predefined test. In order to obtain reliable results, very specific samples were realized, testing the fabric weave method and the influence of the yarn nature. This choice is guided by industrial needs. Moreover, the proposed method enables a sensitivity analysis of the model parameters. Finally, in the fourth part, several simulation results are presented and they are compared with practical results by analyzing textile structural deformation according to parameter variation. [ABSTRACT FROM AUTHOR]

The Triaxial Attitude Control Testbed has been developed as part of a research program at the University of Michigan on multibody rotational dynamics and control. In this paper, equations of motion are derived and presented in various forms. Actuation mechanisms are incorporated into the models; these include fan actuators, reaction wheel actuators and proof mass actuators that are fixed to the triaxial base body. The models also allow incorporation of unactuated auxiliary bodies that are constrained to move relative to the triaxial base body. The models expose the dynamic coupling between the rotational motion of the triaxial base body, the relative or shape motion of the unactuated auxiliary degrees of freedom, and dynamics associated with actuation mechanisms. Many different model simplications and approximations are developed. Control models for the triaxial attitude control testbed are formulated that reflect specific assumptions. [ABSTRACT FROM AUTHOR]

The paper describes methods for setting up and solving theoretically the minimum time lap problem of contemporary Formula One cars. Emphasis is placed on computational efficiency and robustness of the calculations. The problem is treated as one of non-linear programming. Car and circuit models are set up and novel techniques are used to achieve effective optimisation in reasonable computer time. The vehicle representation includes seven degrees of freedom and realistic aerodynamic and tyre force systems. Results relating to the influence of total car mass on the minimum time achievable on two current Formula One circuits are included. to illustrate the kind of information which can be gained from the optimisation. Results concern the range 600-700kg, which spans the practically interesting circumstances. Results are shown to be repeatable from different starting conditions, precise and in general agreement with knowledge from testing. [ABSTRACT FROM AUTHOR]

The needs for analyzing vehicle dynamics rely on advanced modelling techniques, efficient program implementation and high-level computer environment. To match these requirements, two important assets should characterize modern modelling tools: computer efficiency (indispensable, for instance, for real time control or system optimization) and portability (indeed, multi-domain modelling is more and more required). In the frame of vehicle dynamics, a symbolic multibody approach is proposed in this paper. Vehicle model efficiency, which will be quantified through examples, results from a fully symbolic generation of the dynamical model in recursive form, and the resort to parallel computation techniques. Portability towards other computer environment is also ensured by the symbolic approach, the latter being able to export equations in a very versatile way. [ABSTRACT FROM AUTHOR]

This paper presents a new S trajectory kinematic measurement method to evaluate the dynamic accuracy of five-axis machine tools based on R-test measurements. The S trajectory is obtained by scaling the machining path of the S-shaped test piece to the measuring stroke of the R-test. A geometric and dynamic accuracy simulation model is established to analyze the influence of various error factors on the S trajectory test and compare with the conical kinematic test described in ISO10791.6 quantitatively. The simulation results shown that the S trajectory test is more sensitive to most geometric errors and dynamic errors than the conical test. Particularly, to reflect the dynamic error factors such as poor rigidity of machine tools, servo mismatch, reverse error and nonlinear error, the S trajectory test has obvious advantages. Meanwhile, compared with the actual S-shaped piece machining, which is under development for inclusion in ISO 10791.7, the proposed non-cutting kinematic test method can simply reflect the dynamic accuracy of five axis machine tools itself without the interference of other factors and does not require additional workpiece and testing equipment. The proposed method is verified through experiments on a five-axis machine tool. [ABSTRACT FROM AUTHOR]

Planetary rovers may traverse terrains with complex geometries and variable physical properties, but their mobility behaviors are complicated and difficult to simulate precisely. This article focuses on high-fidelity dynamic modeling and simulation for a type of rovers that incorporate single-input-multi-output joints to enhance terrain adaptability, which has been used on China's Tianwen-1 Mars rover. A novel multibody dynamic model and its solutions are derived first with consideration of single-input-multi-output joints. Then, a unified terramechanics model is proposed, considering variable terrain surfaces and covering rover's motion states of skidding, slipping, and steering, solved the problem of simulation instability caused by model switching between soft and hard terrains. As the contact areas of wheels with various terrains and resultant sinkage are dominant factors to ensure fidelity but difficult to determine, a new terrain modeling method for calculating contact area and wheel sinkage is developed using digital elevation map with physical properties. A simulation system is developed, integrating all the above models, and verified with physical experiments and commercial software. The relative simulation errors that have been achieved are less than 5.9% for bogie angles, 6.1% for drawbar pull, and 3.4% for slip ratios, demonstrating high fidelity simulation results. [ABSTRACT FROM AUTHOR]

During the early design phases of any complex aerospace system, Monte Carlo simulations are performed and analyzed to better understand the physics of the problem and to identify design variables that must be either changed or studied further. The Tool for Rapid Analysis of Monte Carlo simulations was developed to assist engineers in the postprocessing of Monte Carlo simulation results. This work combines two pattern-recognition algorithms, kernel density estimation and K nearest neighbors, into a practical analysis tool that ranks influential variables given a specific failure metrics. The Tool for Rapid Analysis of Monte Carlo simulations uses a failure metric to separate the simulation results into two groups: successful and failed simulation runs. The kernel density estimation and K nearest neighbors algorithms are used to estimate probability density functions of the two different groups of data, which are then used to calculate a cost function that quantifies the relative influence of each design variable. In addition to producing a ranking of influential design variables, the Tool for Rapid Analysis of Monte Carlo simulations can rank combinations of up to four design variables in the form of differences and ratios. This paper shows results for a dynamical system with an analytical solution to demonstrate how these methods can identify failure regions in a Monte Carlo data set. [ABSTRACT FROM AUTHOR]

A behavioral average-circuit model that analyzes hybrid converters that include a switched inductor and switched capacitors is presented. The model can be used to calculate or to simulate the average static, dynamic, and small-signal responses of hybrid converters. The model is valid for all operation modes of the switched capacitor converters (SCCs) operating in the continuous and discontinuous conduction modes of the switched inductor converter and is compatible with circuit simulators that include dependent sources. The model was verified with simulations and experimentally. The experimental converter included a boost converter followed by a \times 3 SCC. Good agreement was found between the behavior of the proposed average model, full circuit simulations, and experimental results. [ABSTRACT FROM PUBLISHER]

Simulation of complex scenarios and multi-direction pedestrian flow is a main challenge to microscopic model of pedestrian movement. It is an issue to simulate real pedestrian traffic with great fidelity while keeping its computational cost at an acceptable level. This paper reports on an improved floor field model called vector floor field model to simulate pedestrian flows in some basic scenarios. In this model, vectorization of static floor field and dynamic floor field are used to indicate preference directions and the pedestrian flow tendency, respectively. Pedestrian transition depends on both their preference directions and tendency. The simulations in some basic scenarios are conducted, quantitative comparison to the record of practical experiments and standard floor field model is given as well, and the results indicate the effectivity of this model. An adjusted static vector floor field is also proposed to simulate pedestrian flow in turning scenario. The vector floor field model is also sufficient to simulate some essential features in pedestrian dynamic, such as lane formation. This model can be widely used in the simulation of multi-direction pedestrian at turning, crossing and other junctions. [ABSTRACT FROM AUTHOR]

Riserless drilling poses numerous operational challenges that adversely affect the efficiency of the drilling process. These challenges include increased torque and drag, buckling, increased vibration, pool hole cleaning, tubular failures, poor cement jobs, and associated problems during tripping operations. These challenges are closely associated with complex bottomhole assemblies (BHAs) and the vibration of the drillstring when the topholes are drilled directionally. Current methods lack proper modeling to predict drillstring vibration. This paper presents and validates a modified model to predict severe damaging vibrations, analysis techniques, and guidelines to avoid the vibration damage to BHAs and their associated downhole tools in the riserless highly deviated wells. The dynamic analysis model is based on forced frequency response (FFR) to solve for resonant frequencies. In addition, a mathematical formulation includes viscous, axial, torsional, and structural damping mechanisms. With careful consideration of input parameters and judicious analysis of the results, the author demonstrates that drillstring vibration can be avoided by determining the 3D vibrational response at selected excitations that are likely to cause them. The analysis also provides an estimate of relative bending stresses, shear forces, and lateral displacements for the assembly used. Based on the study, severe vibrations causing potentially damaging operating conditions were avoided, which posed a major problem in the nearby wells. The study indicates that the results are influenced by various parameters, including depth of the mud line, offset of the wellhead from the rig center, wellbore inclination, cumature, wellbore torsion, and angle of entry into the wellhead. This study compares simulated predictions with actual well data and describes the applicability of the model. Simple guidelines are provided to estimate the operating range of the drilling parameter to mitigate and avoid downhole tool failures. [ABSTRACT FROM AUTHOR]

In this paper, we present an original and formal framework, the D2SNet model designed to combine both the social network evolution and the diffusion dynamics among individuals. We have conducted experiments on three social networks that show identical characteristics as real social networks. A formal definition of the model is provided and we describe its implementation in a simulation tool. We represent human behaviors and information dissemination strategies by standard and synthetic scheme. In a first step, we study the impact of network growing strategies only and we highlight important parameters such as the evolution speed and mainly the kind of strategies that favour or not the spread. Then we study a more complete evolution strategy that involves link creation and deletion. We provide a deep analysis on the impact of each parameter such as evolution speed, creation and deletion probabilities and dynamic human behaviors on the diffusion amplitude and coverage. Our study gives a novel and useful insight in the diffusion process in a dynamic context. [Copyright &y& Elsevier]