A bicycle model for education in multibody dynamics and real-time interactive simulation

This paper describes the use of a bicycle model to teach multibody dynamics. The bicycle motion equations are first obtained as a DAE system written in terms of dependent coordinates that are subject to holonomic and non-holonomic constraints. The equations are obtained using symbolic computation. The DAE system is transformed to an ODE system written in terms of a minimum set of independent coordinates using the generalised coordinates partitioning method. This step is taken using numerical computation. The ODE system is then numerically linearised around the upright position and eigenvalue analysis of the resulting system is performed. The frequencies and modes of the bicycle are obtained as a function of the forward velocity which is used as continuation parameter. The resulting frequencies and modes are compared with experimental results. Finally, the non-linear equations of the bicycle are used to create an interactive real-time simulator using Matlab-Simulink. A series of issues on controlling the bicycle are discussed. The entire paper is focussed on teaching engineering students the practical application of analytical and computational mechanics using a model that being simple is familiar and attractive to them.     

Transient simulation of friction-induced vibrations using an elastic multibody approach

In this paper, by the use of elastic multibody dynamics and a master–slave contact approach with penalty formulation, computationally efficient time integrations of a brake system are performed for constant and time-dependent input parameters. As a result, the amplitudes of the friction-induced vibrations and the contact forces at the disc–pad interfaces are predicted. Besides, system outputs are viewed in phase diagrams, and the creation of a stable limit cycle for a low friction coefficient is identified. In this way, conclusions on the stability of the system are drawn, and statements based on frequency-domain analyses are complemented. Finally, a distinct need for a new criterion that quantifies the squeal propensity of such systems in the time domain is identified.     

Validation of flexible multibody dynamics beam formulations using benchmark problems

As the need to model flexibility arose in multibody dynamics, the floating frame of reference formulation was developed, but this approach can yield inaccurate results when elastic displacements becomes large. While the use of three-dimensional finite element formulations overcomes this problem, the associated computational cost is overwhelming. Consequently, beam models, which are one-dimensional approximations of three-dimensional elasticity, have become the workhorse of many flexible multibody dynamics codes. Numerous beam formulations have been proposed, such as the geometrically exact beam formulation or the absolute nodal coordinate formulation, to name just two. New solution strategies have been investigated as well, including the intrinsic beam formulation or the DAE approach. This paper provides a systematic comparison of these various approaches, which will be assessed by comparing their predictions for four benchmark problems. The first problem is the Princeton beam experiment, a study of the static large displacement and rotation behavior of a simple cantilevered beam under a gravity tip load. The second problem, the four-bar mechanism, focuses on a flexible mechanism involving beams and revolute joints. The third problem investigates the behavior of a beam bent in its plane of greatest flexural rigidity, resulting in lateral buckling when a critical value of the transverse load is reached. The last problem investigates the dynamic stability of a rotating shaft. The predictions of eight independent codes are compared for these four benchmark problems and are found to be in close agreement with each other and with experimental measurements, when available.     

Impacts in multibody systems: modeling and experiments

This paper outlines a novel approach to the modeling and analysis of impact involving multibody systems. This approach is based on an analysis of energy absorption and restitution during impact, using a decomposition of the kinetic energy, which decouples the parts associated with the spaces of admissible and constrained motions of the underlying unilateral constraints. Such a decomposition turns out to be useful in the analysis of energy dissipation during impact, and leads to a generalized definition of the energetic coefficient of restitution, which targets particularly collisions in multibody systems. The applicability of the approach reported is investigated by conducting an experimental study on a robotic testbed. It is shown that impact between multibody systems is considerably affected not only by the local dynamics characteristics of the interacting bodies, but also the configuration of the whole multibody system. The results reported here show that our decomposition can offer a sound characterization of impact in several problems of multibody systems.     

Integration of simulation modeling and computer aided production management in computer integrated enterprise

Designing efficient and integrated manufacturing systems is the first step in attaining computer integrated enterprises (CIE). Integration of planning and implementation phases of manufacturing is essential for taking full advantage of the CIE. In order to design reliable and efficient manufacturing systems, the designers must consider the impacts of planning decisions made by computer aided production management (CAPM) modules on implementations held in manufacturing cells.

This paper focuses on two issues. The first issue is importance and necessity of integrating CAPM modules with manufacturing cells. The second issue includes major features of the object-oriented approach and their relevance to our objective of modeling a design framework which focuses on integration of CAPM modules and simulation models which emulate the manufacturing cells in the CIE environment.     

Developments of multibody system dynamics: computer simulations and experiments

It is an exceptional success when multibody dynamics researchers Multibody System Dynamics journal one of the most highly ranked journals in the last 10 years. In the inaugural issue, Professor Schiehlen wrote an interesting article explaining the roots and perspectives of multibody system dynamics. Professor Shabana also wrote an interesting article to review developments in flexible multibody dynamics. The application possibilities of multibody system dynamics have grown wider and deeper, with many application examples being introduced with multibody techniques in the past 10 years. In this paper, the development of multibody dynamics is briefly reviewed and several applications of multibody dynamics are described according to the author’s research results. Simulation examples are compared to physical experiments, which show reasonableness and accuracy of the multibody formulation applied to real problems. Computer simulations using the absolute nodal coordinate formulation (ANCF) were also compared to physical experiments; therefore, the validity of ANCF for large-displacement and large-deformation problems was shown. Physical experiments for large deformation problems include beam, plate, chain, and strip. Other research topics currently being carried out in the author’s laboratory are also briefly explained. Commemorative Contribution.     

SimpleScalar: an infrastructure for computer system modeling

Designers can execute programs on software models to validate a proposed hardware design's performance and correctness, while programmers can use these models to develop and test software before the real hardware becomes available. Three critical requirements drive the implementation of a software model: performance, flexibility, and detail. Performance determines the amount of workload the model can exercise given the machine resources available for simulation. Flexibility indicates how well the model is structured to simplify modification, permitting design variants or even completely different designs to be modeled with ease. Detail defines the level of abstraction used to implement the model's components. The SimpleScalar tool set provides an infrastructure for simulation and architectural modeling. It can model a variety of platforms ranging from simple unpipelined processors to detailed dynamically scheduled microarchitectures with multiple-level memory hierarchies. SimpleScalar simulators reproduce computing device operations by executing all program instructions using an interpreter. The tool set's instruction interpreters also support several popular instruction sets, including Alpha, PPC, x86, and ARM     

Analysis of a linear walking worker line using a combination of computer simulation and mathematical modeling approaches

It has become increasingly important in the last few years to develop rapid, dynamic, responsive and reconfigurable manufacturing processes and systems. This is because manufacturing enterprises are now being forced to develop and constantly improve their production systems so that they can quickly and economically react to unpredictable conditions such as varying production volumes and product variants with small lot size, high quality and low costs. One effective method to achieve this is to create a more flexible, highly skilled and agile workforce capable to perform multiple or all the required tasks in a production area where the system can be reconfigured easily as needed to accommodate changes of production requirement on a daily or weekly basis.This paper presents a study of a so-called linear walking worker assembly line based on a combination of computer simulation and mathematical analysis. The linear walking worker assembly line is a flexible assembly system where each worker travels down the line carrying out each assembly task at each station; and each worker accomplishes the assembly of a unit from start to finish. This design attempts to combine the flexibility of the U-shaped moving worker assembly cell with the efficiency of the conventional fixed worker assembly line. The paper aims to evaluate one critical factor of in-progress waiting time that affects the overall system performance providing a dynamic simulation outlook as well as an insight into the mechanism of such a flexible and reconfigurable manufacturing system.     

Multiphysics modeling and optimization of mechatronic multibody systems

Modeling mechatronic multibody systems requires the same type of methodology as for designing and prototyping mechatronic devices: a unified and integrated engineering approach. Various formulations are currently proposed to deal with multiphysics modeling, e.g., graph theories, equational approaches, co-simulation techniques. Recent works have pointed out their relative advantages and drawbacks, depending on the application to deal with: model size, model complexity, degree of coupling, frequency range, etc. This paper is the result of a close collaboration between three laboratories, and aims at showing that for “non-academic” mechatronic applications (i.e., issuing from real industrial issues), multibody dynamics formulations can be generalized to mechatronic systems, for the model generation as well as for the numerical analysis phases. Model portability being also an important aspect of the work, they must be easily interfaced with control design and optimization programs. A global “demonstrator”, based on an industrial case, is discussed: multiphysics modeling and mathematical optimization are carried out to illustrate the consistency and the efficiency of the proposed approaches.     

Mathematical modeling and computer simulation of elevated foundations supporting vibrating machinery

Structures supporting machines which give rise to dynamic loads must be carefully analyzed and designed to assure satisfactory performance. These highly complex systems must be reduced to mathematical and computer models which will behave in a similar fashion as the structure-machine-soil prototype. Four models are considered and a comparison of significant results is given. A lumped-mass model with complete soil-structure interaction (Model D) is recommended for best overall results provided a high speed digital computer and software is available.     

Physically-based modeling,simulation and rendering of fire for computer animation

We give an up-to-date survey on techniques and methods for fire simulation in computer graphics. Physically-based method prevails over traditional non-physical methods for realistic visual effect. In this paper, we explore visual simulation of fire-related phenomena in terms of physically modeling, numerical simulation and visual rendering. Firstly, we introduce a physical and chemical coupled mathematical model to explain fire behavior and motion. Several assumptions and constrains are put forward to simplify their implementations in computer graphics. We then give an overview of present methods to solve the most complicated processes in numerical simulation: velocity advection and pressure projection. In addition, comparisons of these methods are also presented respectively. Since fire is a participating medium as well as a visual radiator, we discuss techniques and problems of these issues as well. We conclude by addressing several open challenges and possible future research directions in fire simulation.     

Forward dynamics simulation using a natural knee with menisci in the multibody framework

Information on knee loading and the relationship between muscle force and tissue response would benefit orthopaedic medicine, the development of engineered tissues, and our understanding of degenerative joint disease. As a step toward developing subject specific musculoskeletal simulations that predict loading on knee structures, this study combines a cadaver-based validated natural multibody knee model with a muscle driven forward dynamics simulation from a subject of similar height and weight for prediction of joint contact mechanics. Geometries for the multibody model were obtained from magnetic resonance images of a cadaver knee. The ligaments were represented with non-linear spring-damper elements with insertions and zero-load lengths derived from experimental measurements. The menisci were represented as discrete elements connected by 6×6 stiffness matrices and to allow prediction of contact pressure, the medial tibia plateau cartilage was divided into discrete elements. The force-displacement relationships of the knee model were validated by placing it in a model of a dynamic knee simulator and comparing predicted kinematics to experimental kinematics of the identically loaded cadaver knee. Motion, ground reaction forces, and surface electromyography were measured during a dual-limb squat on a female subject with similar height and weight as that of the cadaver donor. The gait data were used in a forward dynamics simulation of the dual-limb squat that included the cadaver knee model. The resulting tibio-femoral contact forces and pressures were compared for versions of the model with and without representation of the menisci. Inclusion of the menisci decreased the peak contact pressure on the medial tibia plateau by 20% and the cartilage-to-cartilage contact force on the lateral side was reduced by 40% through the squat cycle.     

Physical modeling and computer graphic simulation of the depletion of world energy reserve

A physical modeling device and a computer graphic simulation program of the depletion of world energy reserve are developed to demonstrate how rapidly our energy reserve is depleted, how quickly and enormously our demands for energy grows, and how important energy conservation is to us. In both modeling and simulation cases, the total world energy reserve, the current energy usage annual growth rate, and the current energy consumption rate are given as parameters. One can view the energy shortage in terms of the rapidly falling levels in the physical water tank or the simulated oil barrels.     

Quantum computer simulation using the CUDA programming model

Quantum computing emerges as a field that captures a great theoretical interest. Its simulation represents a problem with high memory and computational requirements which makes advisable the use of parallel platforms. In this work we deal with the simulation of an ideal quantum computer on the Compute Unified Device Architecture (CUDA), as such a problem can benefit from the high computational capacities of Graphics Processing Units (GPU). After all, modern GPUs are becoming very powerful computational architectures which is causing a growing interest in their application for general purpose. CUDA provides an execution model oriented towards a more general exploitation of the GPU allowing to use it as a massively parallel SIMT (Single-Instruction Multiple-Thread) multiprocessor. A simulator that takes into account memory reference locality issues is proposed, showing that the challenge of achieving a high performance depends strongly on the explicit exploitation of memory hierarchy. Several strategies have been experimentally evaluated obtaining good performance results in comparison with conventional platforms.     

The effect of dependence on the performance of Bayes' theorem: an evaluation using a computer simulation

A computer simulation is described which generates 'cases' of vaginal discharge. This simulation was used to evaluate the potential effects of dependence between clinical features on the diagnostic performance of Bayes' theorem. The following observations were made: (1) dependence between some but not all pairs of features reduced the overall diagnostic efficiency (judged by the number of true positive diagnoses); (2) the overall reduction in efficiency was never substantial; (3) the largest effects on the diagnosis of individual conditions was observed with rarer diseases, and with combinations of features which were inherently unlikely to be dependent. It is concluded that the diagnostic efficiency of Bayes' theorem will not be greatly influenced by dependence if a reasonable amount of commonsense is applied to the selection of the knowledge base.     

Graph theoretic modeling and analysis of multibody planarmechanical systems

A methodology of modeling and analysis of planar mechanical systems is developed based on graph theoretic methods, with improvements in component models. The system model based on cutset and circuit topologies is used to derive a new hybrid cutset-circuit method of formulation of the equations of motion for planar systems. Computer-aided formulation is based on analysis of the substitution procedure mandated by the hybrid cutset-circuit formulation. A new graphical representation of the formulation process is introduced: substitution graphs. No special programming is needed for computer-aided formulation which can be achieved in a symbolic form using the off the shelf Maple symbolic mathematics system. Symbolic formulation requires only inputting the systems equations in an order and form as derived from the analysis of the hybrid formulation. An algorithm for symbolic formulation using Maple is given. A compact set of differential-algebraic equations results, which can be solved numerically. Some simple systems will result in closed-form solutions. A number of examples are given to illustrate the modeling and formulation. Numerical solutions are also given to demonstrate the effectiveness and correctness of the formulation procedure