Efficient formulation of the Gibbs–Appell equations for constrained multibody systems

Multibody System Dynamics - In this study, we present explicit equations of motion for general mechanical systems exposed to holonomic and nonholonomic constraints based on the Gibbs-Appell...     

New efficient method for dynamic modeling and simulation of flexible multibody systems moving in plane

Efficient, precise dynamic analysis for general flexible multibody systems has become a research focus in the field of flexible multibody dynamics. In this paper, the finite element method and component mode synthesis are introduced to describe the deformations of the flexible components, and the dynamic equations of flexible bodies moving in plane are deduced. By combining the discrete time transfer matrix method of multibody system with these dynamic equations of flexible component, the transfer equations and transfer matrices of flexible bodies moving in plane are developed. Finally, a high-efficient dynamic modeling method and its algorithm are presented for high-speed computation of general flexible multibody dynamics. Compared with the ordinary dynamics methods, the proposed method combines the strengths of the transfer matrix method and finite element method. It does not need the global dynamic equations of system and has the low order of system matrix and high computational efficiency. This method can be applied to solve the dynamics problems of flexible multibody systems containing irregularly shaped flexible components. It has advantages for dynamic design of complex flexible multibody systems. Formulations as well as a numerical example of a multi-rigid-flexible-body system containing irregularly shaped flexible components are given to validate the method.     

Erratum to: New efficient method for dynamic modeling and simulation of flexible multibody systems moving in plane

Efficient, precise dynamic analysis for general flexible multibody systems has become a research focus in the field of flexible multibody dynamics. In this paper, the finite element method and component mode synthesis are introduced to describe the deformations of the flexible components, and the dynamic equations of flexible bodies moving in plane are deduced. By combining the discrete time transfer matrix method of multibody system with these dynamic equations of flexible component, the transfer equations and transfer matrices of flexible bodies moving in plane are developed. Finally, a high-efficient dynamic modeling method and its algorithm are presented for high-speed computation of general flexible multibody dynamics. Compared with the ordinary dynamics methods, the proposed method combines the strengths of the transfer matrix method and finite element method. It does not need the global dynamic equations of system and has the low order of system matrix and high computational efficiency. This method can be applied to solve the dynamics problems of flexible multibody systems containing irregularly shaped flexible components. It has advantages for dynamic design of complex flexible multibody systems. Formulations as well as a numerical example of a multi-rigid-flexible-body system containing irregularly shaped flexible components are given to validate the method.     

On the choice of boundary conditions for mode shapes in flexible multibody systems

The modal representation of the deformation field is a widespread and efficient approach in the analysis of flexible multibody systems. However, it requires a pre-processing in advance to the actual multibody survey that includes the imposition of boundary conditions for the evaluation of the mode functions as an essential user input. Quite often the appropriateness of these boundary conditions is a point of discussion. Therefore the present paper reviews the theoretical background and the implications of this task. Then, a consistent and comprehensive proposal is made how these boundary conditions may be chosen. The suggestion is justified by theoretical considerations and compared to alternative approaches from the literature in a simulation study with three representative examples. It may be concluded that several approaches lead to reasonable results for a sufficient number of mode functions. However, the proposed approach turned out to be the most efficient one and provides a consistent framework.     

Methods for constraint violation suppression in the numerical simulation of constrained multibody systems – A comparative study

Multibody systems are frequently modeled as constrained systems, and the arising governing equations incorporate the closing constraint equations at the acceleration level. One consequence of accumulation of integration truncation errors is the phenomenon of violation of the lower-order constraint equations by the numerical solutions to the governing equations. The constraint drift usually tends to increase in time and may spoil reliability of the simulation results. In this paper a comparative study of three methods for constraint violation suppression is presented: the popular Baumgarte’s constraint violation stabilization method, a projective scheme for constraint violation elimination, and a novel scheme patterned after that proposed recently by Braun and Goldfarb [D.J. Braun, M. Goldfarb, Eliminating constraint drift in the numerical simulation of constrained dynamical systems, Comput. Meth. Appl. Mech. Engrg., 198 (2009) 3151–3160]. The methods are confronted with respect to simplicity in applications, numerical effectiveness and influence on accuracy of the constraint-consistent motion.     

Simulation of multibody systems with the use of coupling techniques: a case study

Simulation coupling (or cosimulation) techniques provide a framework for the analysis of decomposed dynamical systems with the use of independent numerical procedures for decomposed subsystems. These methods are often seen as very promising because they enable the utilization of the existing software for subsystem analysis and usually are easy to parallelize, and run in a distributed environment. For example, in the domain of multibody systems dynamics, a general setup for “Gluing Algorithms” was proposed by Wang et al. It was intended to provide a basis for multilevel distributed simulation environments. The authors presented an example where Newton’s method was used to synchronize the responses of subsystem simulators.     

Discussion of the Gear–Gupta–Leimkuhler method for impacting mechanical systems

In multibody simulation, the Gear–Gupta–Leimkuhler method or stabilized index 2 formulation for persistent contacts enforces constraints on position and velocity level at the same time. It yields a robust numerical discretization of differential algebraic equations avoiding the drift-off effect and is often more effective than decreasing the time step size to preserve geometric characteristics. In this work, we carry over these benefits to impacting mechanical systems with unilateral constraints. For this kind of a mechanical system, adding the position level constraint to an (event-capturing) timestepping scheme on velocity level even maintains physical consistency of the impulsive discretization. Hence, we propose a timestepping scheme based on Moreau’s midpoint rule, which enables to achieve not only compliance of the impact law, but also of the nonpenetration constraint. The choice of a decoupled and consecutive evaluation of the respective constraints can be interpreted as a not energy-consistent coordinate projection to the nonpenetration constraint at the end of each time step. It is the implicit coupling of position and velocity level, which yields satisfactory results. An implicit evaluation of the right hand side improves stability properties without additional cost. With the prox function formulation, the overall set of nonsmooth equations is solved by a nonsmooth Newton method. Results from simulations of a slider-crank mechanism with unilateral constraints demonstrate the capability of our approach.     

Proof of the circle criterion for state space systems via quadratic Lyapunov functions — Part 2

In Part 1 of this paper a detailed analysis of the stability of a closed-loop system containing a single nonlinearity was made. The analysis is repeated here, but with stronger assumptions on the nonlinearity. The class of Total Derivative matrices is introduced and the role played by this class in generating quadratic Lyapunov functions for certain dynamical systems is considered. A new approach for deriving stability criteria is presented which is equivalent to the path integral method of Brockett.     

The space of EDF deadlines: the exact region and a convex approximation

It is well known that the performance of computer controlled systems is heavily affected by delays and jitter occurring in the control loops, which are mainly caused by the interference introduced by other concurrent activities. A common approach adopted to reduce delay and jitter in periodic task systems is to decrease relative deadlines as much as possible, but without jeopardizing the schedulability of the task set. In this paper, we formally characterize the region of admissible deadlines so that the system designer can appropriately select the desired values to maximize a given performance index defined over the task set. Finally we also provide a sufficient region of feasible deadlines which is proved to be convex.

Use of third generation data for the elements to model the thermodynamics of binary alloy systems: Part 1 – The critical assessment of data for the Al-Zn system

Over the last four years there has been a renewed interest in the development of new critically assessed data using physically based models. Nearly all work so far has been concerned with the critical assessment of data for the elements. This has involved the selection of Einstein or Debye temperatures for the stable crystalline phases and the liquid phase and associated parameters. However, until now, these data have not been extended in a comprehensive way to model the thermodynamic properties of binary, ternary and multicomponent systems. In this paper the way in which the parameters underlying these physical models vary with composition is explored. This includes a method to define the Einstein temperature for metastable phases of the elements and its relation to the so-called lattice stabilities used in the past, and the variation of the Einstein temperature with composition to account for the composition dependence of the excess entropy. This approach is demonstrated for the Al-Zn system which shows extensive regions of solid solution and complete miscibility in the liquid phase. Here Einstein temperatures are derived for Al in the HCP_ZN phase and Zn in the FCC_A1 phase together with parameters describing the variation of the Einstein temperature with composition for the HCP_ZN, FCC_A1 and liquid phases.     

The ‘hijacking’ of the Scandinavian Journal of Information Systems: Implications for the information systems community

Journal hijacking, which refers to the attempted brand takeover of a journal by a third party, is a nascent threat confronting the information systems (IS) community, as evidenced by cybercriminals having established an online presence, masquerading as the Scandinavian Journal of Information Systems (SJIS). The SJIS hijacking damages the journal's reputation, leads to payment and publication scams, involves identity theft among unsuspecting IS researchers, and results in tarnished author reputations. Beyond SJIS, journal hijacking presents a threat, not only to the IS community, but also to science and academic integrity in general if researchers and readers cannot distinguish between fake publications by hijacked journals and real publications by legitimate journals. In this opinion article, we relate the story of the SJIS hijacking from the victims' perspectives. We describe its many aspects, draw attention to the key factors that contribute to the problem, and offer our perspectives on different response strategies in the absence of simple solutions. We hope to create awareness about the problem and stimulate a discussion in the IS community, not least in the face of digital innovations, such as ChatGPT and other artificial intelligence technologies that may inadvertently support paper mills and the production of fake research results.     

The model matching problem for a class of polynomial non-linear discrete input–output systems with cross-products. An algorithmic approach

In this paper we examine the model matching problem that concerns non-linear input–output discrete systems, containing products among delays of input and output signals, through a special factorisation. The algebraic framework of δε-operators and the star-product that we adopt describe these systems. Moreover, a certain procedure that resembles the Euclidean division allows us to discover the linear factors of those systems, with respect to the above mentioned operations. The entire approach is symbolically algorithmic and involves the use of suitable software.     

A new recurslve method for the analysis of linear time invariant dynamic systems via double-term triangular functions （DTTF） in state space environment

This paper presents a new recursive method for system analysis via double-term triangular functions (DTTF) in state space environment. The proposed method uses orthogonal triangular function sets and proves to be more accurate as compared to single term Walsh series (STWS) method with respect to mean integral square error (MISE). This has been established theoretically and comparison of error with respect to MISE is presented for clarity. A numerical example is treated to establish the proposed method. Relevant curves for the solutions of states of the dynamic system are also presented with plots of percentage error for DTTF-based analysis.     

He’s homotopy perturbation method: A strongly promising method for solving non-linear systems of the mixed Volterra–Fredholm integral equations

In this paper, He’s homotopy perturbation method is applied to solve non-linear systems of mixed Volterra–Fredholm integral equations. Two examples are presented to illustrate the ability of the method. Also comparisons are made between the Adomian decomposition method and the homotopy perturbation method. The results reveal that He’s homotopy perturbation method is very effective and simple and in these examples leads to the exact solutions.     

The study of the Pb–Se–Te phase diagram: Part 2 – The thermodynamic assessment of the Se–Te and Pb–Se–Te systems

Pb–Se–Te ternary system is of significant importance for thermoelectric applications. In spite of this, no systematic experimental or theoretical study of its phase diagram has been carried out up to now. The CALPHAD type theoretical assessment was done in the scope of this work for the Se–Te and Pb–Se–Te systems based on our own experimental work and the experimental results from literature. It was found out that the reassessment of the existing Se–Te phase diagram assessments is necessary because of some discrepancies between the experimental results and calculations for this system. This new dataset was consequently used for the new assessment of the Pb–Se–Te system and very good agreement was reached with existing experimental data.     

A method for building ontology-based electronic document management systems for quality standards—the case study of the ISO/TS 16949:2002 automotive standard

Different methods and methodologies have been developed for building ontologies. However, neither of these methods consider to build an ontology with characteristics of an electronic document management system (EDMS) nor define the basic classes to begin the ontology. In this paper we propose a method, called “OntoDocMan”, to build an ontology-based EDMS which captures the knowledge associated with a company’s processes related to a quality standard. We leverage the use of ontology tools, such as Protégé, to obtain the functionality of an EDMS. Our method complements and details the On-To-Knowledge methodology during its ontology development phase. The essential point of our method is to make it easy to develop an EDMS for quality standards by means of an ontology-based system. The OntoDocMan method is illustrated by a case study for developing an ontology based on the ISO/TS 16949, which is a Technical Specification (TS) and we show that the Ontology system is friendly and easy to use as any EDMS. Different from common EDMS, our ontology-based EDMS is developed without any programming. In addition, we have discovered that this kind of ontology-based EDMS is an excellent tool for helping auditors to search and validate information, besides new employees can learn about the company’s processes.     

Contribution of the Rietveld method to non-stoichiometric phase modeling. Part II: α-Tl5Te3 and μ Nb-Ni as experimental examples

Two detailed examples are considered to show the ability of powder diffraction data analyzed with the Rietveld method to get insight into the detailed structure of non-stoichiometric phases. Both the γ-phase in Tl-Te system and μ-phase in Nb-Ni system were investigated as a function of composition across their whole homogeneity domain. In the case of the γ Tl-Te phase, the excess Tl relative to the stoichiometric composition is accommodated by Tl substitution on one of the two Te sites. In the μ Nb-Ni, three of the five sites of the structure are partially disordered for all the compositions studied. The results are analyzed in view of Calphad modeling of both phases.