Use of Penalty Formulations in Dynamic Simulation and Analysis of Redundantly Constrained Multibody Systems

[Abstract] The determination of particular reaction forces in the analysis of redundantly constrained multibody systems requires the consideration of the stiffness distribution in the system. This can be achieved by modelling the components of the mechanical system as flexible bodies. An alternative to this, which we will discuss in this paper, is the use of penalty factors already present in augmented Lagrangian formulations as a way of introducing the structural properties of the physical system into the model. Natural coordinates and the kinematic constraints required to ensure rigid body behaviour are particularly convenient for this. In this paper, scaled penalty factors in an index-3 augmented Lagrangian formulation are employed, together with modelling in natural coordinates, to represent the structural properties of redundantly constrained multibody systems. Forward dynamic simulations for two examples are used to illustrate the material. Results showed that scaled penalty factors can be used as a simple and efficient way to accurately determine the constraint forces in the presence of redundant constraints

Efficient Implementations and Co-Simulation Techniques in Multibody System Dynamics

[Abstract] Current research in simulation of multibody systems (MBS) dynamics is focused on two main objectives: the increase of the computational efficiency of the software that carries out the simulations, and the diversification of the problems this software is able to tackle, sometimes through the inclusion in the calculations of non purely mechanical phenomena. This work deals with these two objectives, studying the effect of source code implementation in software performance, as well as the different communication methods with external software that can contribute the interaction of the MBS code with elements of a non mechanical nature. The first Chapter of this thesis contains a brief introduction to the present state of the art of MBS simulation software. It introduces the research lines this thesis forms part of and outlines its main objectives. The second Chapter describes the software architecture for MBS simulation that has been developed for this research. The C++ language has been used for its implementation, according to the object–oriented programming paradigm. This Chapter also enumerates the programming tools employed in the process and draws general conclusions about the development of MBS programs. The third and fourth Chapters introduce efficient implementation techniques in the field of linear algebra operations, and in the parallelization of the code, respectively. The obtained improvements in performance have been quantified, and the range of application of each technique has been delimited. The fifth and sixth Chapters deal with the communication of the developed software with external simulation software packages. A comparative study between the different ways in which the coupling can be performed has been carried out and, besides, the impact on the efficiency and accuracy of the use of multirate co–simulation techniques has been assessed. A generic interface for multirate integration has been designed to link the MBS software with MATLAB/Simulink, a mathematical and block diagram package very popular in the multibody community. Finally, the seventh Chapter summarizes the conclusions of the present work, and proposes future research lines that can be derived from it.[Resumen] La investigación actual en simulación dinámica de sistemas multicuerpo (MBS) gira en torno a dos objetivos principales: el incremento de la eficiencia computacional del software que lleva a cabo las simulaciones y la diversificación de las tareas que este es capaz de realizar, a veces mediante la inclusión en los cálculos de fenómenos no puramente mecánicos. Este trabajo aborda ambos objetivos, estudiando el efecto de la implementación del código fuente en el rendimiento del software, así como las diferentes estrategias de comunicación con programas externos que puedan aportar a la simulación multicuerpo la interacción con elementos de naturaleza no mecánica. El primer capítulo de esta tesis consiste en una breve introducción al estado actual del software para simulaci´on de sistemas multicuerpo. En él se muestran también las líneas de investigación en las que se enmarca el proyecto y se señalan sus objetivos principales. El segundo capítulo describe la arquitectura del software para la simulación de sistemas multicuerpo que se ha creado en esta investigación. Para su implementación se ha utilizado el lenguaje C++, dentro del paradigma de programación orientada a objetos. En este capítulo se enumeran también las herramientas de programación utilizadas en el proceso y se obtienen conclusiones de validez general para la generación de programas multicuerpo. Los capítulos tercero y cuarto presentan técnicas de implementación eficiente de las operaciones de álgebra lineal y en la paralelización del código, respectivamente. Se han cuantificado las mejoras en el tiempo de ejecución obtenidas y se han delimitado los campos de aplicación de cada estrategia. En los capítulos quinto y sexto se aborda la comunicación del software desarrollado con otros programas de simulación externos. Se ha realizado un estudio comparativo de los diversos modos posibles en que se puede realizar esta unión y, además, se ha evaluado el impacto del empleo de técnicas de cosimulación multirate sobre la eficiencia y la precisión de los cálculos. Se ha diseñado para ello una interfaz genérica entre el software MBS y MATLAB/Simulink, una aplicación matemática y de diagramas de bloques de gran aceptación entre la comunidad de investigación en sistemas multicuerpo. Por último, en el capítulo séptimo se resumen las conclusiones del presente trabajo y se proponen líneas de investigación futuras que pueden derivarse de él

Index-3 divide-and-conquer algorithm for efficient multibody system dynamics simulations: theory and parallel implementation

[Abstract] There has been a growing attention to efficient simulations of multibody systems, which is apparently seen in many areas of computer-aided engineering and design both in academia and in industry. The need for efficient or real-time simulations requires high fidelity techniques and formulations that should significantly minimize computational time. Parallel computing is one of the approaches to achieve this objective. This paper presents a novel index-3 divide-and-conquer algorithm for efficient multibody dynamics simulations that elegantly handles multibody systems in generalized topologies through the application of the augmented Lagrangian method. The proposed algorithm exploits a redundant set of absolute coordinates. The trapezoidal integration rule is embedded into the formulation and a set of nonlinear equations need to be solved every time instant. Consequently, the Newton–Raphson iterative scheme is applied to find the system coordinates and joint constraint loads in an efficient and highly parallelizable manner. Two divide-and-conquer based mass-orthogonal projections are performed then to circumvent the effect of constraint violation errors at the velocity and acceleration level. Sample open- and closed-loop multibody system test cases are investigated in the paper to confirm the validity of the approach. Challenging simulations of multibody systems featuring long kinematic chains are also performed in the work to demonstrate the robustness of the algorithm. The details of OpenMP-based parallel implementation on an eight-core shared memory computer are presented in the text and the parallel performance results are extensively discussed. Significant speedups are obtained for the simulations of small- to large-scale multibody open-loop systems. The mentioned features make the proposed algorithm a good general purpose approach for high-fidelity, efficient or real-time multibody dynamics simulations.Ministerio de Economía y Competitividad; JCI-2012-12376Poland. National Science Center; DEC-2012/07/B/ST8/0399

Behaviour of Augmented Lagrangian and Hamiltonian Methods for Multibody Dynamics in the Proximity of Singular Configurations

This is a post-peer-review, pre-copyedit version of an article published in Nonlinear Dynamics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11071-016-2774-5.[Abstract] Augmented Lagrangian methods represent an efficient way to carry out the forward-dynamics simulation of mechanical systems. These algorithms introduce the constraint forces in the dynamic equations of the system through a set of multipliers. While most of these formalisms were obtained using Lagrange's equations as starting point, a number of them have been derived from Hamilton's canonical equations. Besides being efficient, they are generally considered to be robust, which makes them especially suitable for the simulation of systems with discontinuities and impacts. In this work, we have focused on the simulation of mechanical assemblies that undergo singular configurations. First, some sources of numerical difficulties in the proximity of singular configurations were identified and discussed. Afterwards, several augmented Lagrangian and Hamiltonian formulations were compared in terms of their robustness during the forward-dynamics simulation of two benchmark problems. Newton-Raphson iterative schemes were developed for these formulations with the Newmark formula as numerical integrator. These outperformed fixed point iteration approaches in terms of robustness and efficiency. The effect of the formulation parameters on simulation performance was also assessed

Kinematic Modelling and State Estimation of Exploration Rovers

This is a post-peer-review, pre-copyedit version of an article published in IEEE Robotics and Automation Letters. The final authenticated version is available online at: http://dx.doi.org/10.1109/LRA.2019.2895393.[Abstract] State estimation is crucial for exploration rovers. It provides the pose and velocity of the rover by processing measurements from onboard sensors. Classical wheel odometry only employs encoder measurements of the two wheels in the differential drive. As a consequence, input noise can lead to large uncertainties in the estimated results. Also, the estimation models used in classical wheel odometry are nonlinear, and the linearization process that propagates the mean and covariance of the estimated state introduces additional errors in the process. This letter puts forward a novel wheel odometry approach for six-wheeled rovers. A kinematic model is formulated to relate the velocity of the wheels and the chassis, and later used to develop the corresponding estimation model. The components of the velocity of the chassis, decomposed in the chassis-fixed coordinate frame, are selected as the system state in the estimation, which results in a linear model. The motions of all wheels are fused together to provide the measurements. Wheel slip is considered random Gaussian noise in this kinematic model. The continuous-time Kalman filter is employed to process the model. Experimental validation with six-wheeled rover prototypes was used to confirm the validity of the proposed approach.MINECO; RYC-2016-2022

The influence of customer integration, integrated information technology, and relationship commitment on performance: a mediating and moderating analysis in supply chain management context

Esta investigación amplía el creciente cuerpo de la literatura sobre la integración de la cadena de suministro. A partir de diferentes teorías, desarrollamos hipótesis que proponen relaciones positivas entre la tecnología de información integrada, la integración de clientes, el compromiso relacional y el rendimiento financiero. Además, investigamos los roles complementarios del tamaño del departamento de TI y el apoyo de la alta dirección. Los resultados a partir de una muestra de 205 empresas de Egipto indican que la tecnología de información integrada y la integración de clientes pueden mejorar el rendimiento financiero. Adicionalmente, los resultados muestran un efecto mediador positivo de la integración de clientes en la relación entre tecnología de información integrada y el rendimiento financiero. Además, se confirma que el tamaño del departamento de TI y el apoyo de la alta dirección están relacionados significativamente con la tecnología de información integrada. Finalmente, nuestros resultados también muestran un efecto positivo directo del compromiso relacional en la integración de clientes, así como un efecto moderador positivo del compromiso relacional en la relación entre la tecnología de información integrada y la integración de clientes.This research extends the developing body of literature on supply chain integration. Theorizing from the supply chain integration literatures, we develop hypotheses proposing direct, mediating, and moderating relations between integrated information technology, customer integration, relationship commitment, and financial performance. Also, we investigate the complementary roles of IT department size and top management support. Our findings from a sample of 205 firms in Egypt indicate that integrated information technology and customer integration can improve financial performance. In addition, our results show a mediating and positive effect of customer integration on the relation between integrated information technology and financial performance. Also, information technology department size and top management support are significantly related to integrated information technology. Finally, our results also show a direct and positive effect of relationship commitment on the customer integration, and a moderating and positive effect of relationship commitment on the relationship between integrated information technology and customer integration

Assessment of Methods for the Real-Time Simulation of Electronic and Thermal Circuits

[Abstract] Time–domain simulation of electronic and thermal circuits is required by a large array of applications, such as the design and optimization of electric vehicle powertrain components. While efficient execution is always a desirable feature of simulation codes, in certain cases like System-in-the-Loop setups, real-time performance is demanded. Whether real-time code execution can be achieved or not in a particular case depends on a series of factors, which include the mathematical formulation of the equations that govern the system dynamics, the techniques used in code implementation, and the capabilities of the hardware architecture on which the simulation is run. In this work, we present an evaluation framework of numerical methods for the simulation of electronic and thermal circuits from the point of view of their ability to deliver real-time performance. The methods were compared using a set of nontrivial benchmark problems and relevant error metrics. The computational efficiency of the simulation codes was measured under different software and hardware environments, to determine the feasibility of using them in industrial applications with reduced computational power.Ministerio de Economía y Competitividad; RYC-2016-20222Xunta de Galicia; ED431B2016/03

An Automated Methodology to Select Functional Co-Simulation Configurations

[Abstract] The development of machinery often requires system-level analysis, in which non-mechanical subsystems, such as hydraulics, need to be considered. Co-simulation allows analysts to divide a problem into subsystems and use tailored software solutions to deal individually with their respective dynamics. On the other hand, these subsystems must be coupled at particular instants in time, called communication points, through the exchange of coupling variables. Between communication points, each subsystem solver carries out the integration of its states without interacting with its environment. This may cause the integration to become unstable, especially when non-iterative co-simulation is used. The co-simulation configuration, i.e., the parameters and simulation options selected by the analyst, such as the way to handle the coupling variables or the choice of subsystem solvers, is often a critical factor regarding co-simulation stability. In practice it is difficult to anticipate which selection is the most appropriate for a particular problem, especially if some inputs come from external sources, such as human operators, and cannot be determined beforehand. We put forward a methodology to automatically determine a stable and computationally efficient configuration for Jacobi-scheme co-simulation. The method uses energy residuals to gain insight into co-simulation stability. The relation between energy residual and communication step-size is exploited to monitor co-simulation accuracy during a series of tests in which the external inputs are replaced with predetermined input functions. The method was tested with hydraulically actuated mechanical examples. Results indicate that the proposed method can be used to find stable and accurate configurations for co-simulation applications.Ministerio de Economía; RYC-2016-2022

Real-time Simulation of Cable Pay-Out and Reel-In with Towed Fishing Gears

[Abstract] Achieving real-time simulation of fast cable pay-out and reel-in manoeuvres with towed fishing gears is a challenging task. This work presents two new simulation methods based on simplified cable models for this kind of application. First, three numerical techniques are proposed to enhance a classical spring-based cable model, increasing its computational efficiency in manoeuvres that involve reeling the cable around a winch drum. Second, the development of an efficient multibody modelling approach based on natural coordinates is reported. The performance of these methods was assessed with two realistic examples. The numerical experiments involved different values of cable axial stiffness and spatial discretization levels, since these parameters were found to have a major impact on computational efficiency. The proposed methods achieved real-time performance in the simulation of systems modelled with up to a few thousand variables. Each modelling approach has advantages and limitations that must be considered when addressing a given application.MINECO; JCI-2012-1237

A novel concept for analysis and performance evaluation of wheeled rovers

[Abstract] - The analysis, design, and operation planning of rovers are often based on predictive dynamic simulation, where the multibody model of the vehicle is combined with terramechanics relations for the representation of the wheel–ground interaction. There are, however, limitations in terramechanics models that prevent their use in parametric analysis and simulation studies. Increasing mobility is generally a primary objective for the design and operation of rovers. The models and assumptions used in the analysis phase should target this objective. In this paper we put forward a new concept for the analysis of wheeled rovers, particularly for applications in off-road environments on soft soil. We propose a novel view of the problem based on the development of models that are primarily intended to represent how parameter changes in the robot design can influence performance. These models allow for the definition of indicators, which gives information about the behavior of the system. We term such models observative. In the reported work, a set of indicators for rover performance is formulated using such models. The ability of these indicators to characterize the behavior of a rover is assessed with a series of simulation tests and experiments. The indicators defined using observative models succeeded to capture the changes in rover performance due to variations in the system parameters. Results show that the proposed models can provide a useful tool for the design and operation of planetary exploration rovers