A physics conservation-based mesh patching algorithm for multi-body modeling and simulation

It difficult to achieve consistency and sharing storage of model library and data resources, realize modeling and functional classification and improve low efficiency based on multi-body simulation and optimization. Cloud computing concept and method are introduced in order to solve these problems. In addition, a multi-body dynamics system modeling and simulation platform for the cloud computing is established and the basic solution process of the platform is explained, which can realize security sharing, optimization and reuse of model resources of system, computing resources and data resources. Finally, feasibility analysis is to be made.

It difficult to achieve consistency and sharing storage of model library and data resources, realize modeling and functional classification and improve low efficiency based on multi-body simulation and optimization. Cloud computing concept and method are introduced in order to solve these problems. In addition, a multi-body dynamics system modeling and simulation platform for the cloud computing is established and the basic solution process of the platform is explained, which can realize security sharing, optimization and reuse of model resources of system, computing resources and data resources. Finally, feasibility analysis is to be made.

This paper describes the Dynamics Algorithms for Real-Time Simulation (DARTS) software for multibody dynamics modeling, analysis and simulation. DARTS is in use for closed-loop simulation for aerospace, ground vehicle, robotics applications and large, multi-scale molecular dynamics applications. DARTS is designed for high-fidelity multibody dynamics, fast computational speed, to handle run-time configuration changes, and to provide a broad family of computational algorithms for analysis and model based control. This paper describes DARTS capabilities, novel aspects of its architecture and design, and application examples.

The article focuses on the interface between multibody software and tyre models as well as on the applications and limitations of tyre models implemented in multibody codes. Basic principles of multibody simulation will be followed by a classification of the range of applications of multibody codes for vehicle dynamics design and assessment and the corresponding classification of tyre models in multibody simulation. The classification will be made along occurring oscillation amplitudes ranging from very small to large part displacements and along occurring frequencies ranging from quasistatic movements up to the acoustic frequency range. The basic structure of the interfaces between tyre model, road description and multibody model will be revealed and the different call modes of tyre models in multibody codes will be summarized. As examples some industrial applications of tyre models in multibody simulation will be explained. This includes quasistatic tyre model-based simulation scenarios as well as lateral and longitudinal dynamic simulation scenarios in quite a low-frequency range and finally vertical and combined dynamic simulation scenarios in higher-frequency ranges.

There is a growing interest towards multi-body modelling and simulation that play a critical role in the development and testing of new mechanical systems, in general, and formula cars specifically to avoid expensive and time-consuming experimental track testing. Recent advances in computer-aided engineering packages, allows one not only to evaluate the basic properties that define the dynamic behavior of a newly-designed formula car, but as well as to investigate the impact on the performance of the many adjustable parameters that collectively are referred to as the car set-up. Therefore, by providing a rapid feedback of a given set-up expectation, optimal configurations can be obtained ensuring the highest level of performance. In this paper, a Formula SAE vehicle is expressly targeted. First, a full multi-body model of the prototype is described detailing the properties of each subassembly, e.g., suspensions and antiroll bars, steering system, and powertrain. Then, the basic handling characteristics are obtained via simulated track testing. Based on vehicle dynamics principles, the fine tuning of the vehicle setup is thoroughly discussed to gain the best performance in each of the contest events of the Formula SAE competition. For example, in the skidpad event where cars are required to drive along an eight-shaped track, an almost 2 km/h gain in the maximum travel velocity can be achieved by adjusting the camber angles of all tires.

Robotic grippers have represented a challenge for designers and engineers since at least three decades, due to the complexity of grasping and manipulation tasks. Underactuated and soft robotic grippers are a technology that allows good dexterity and manipulating capabilities, by reducing the number of actuators. However, this type of device requires the use of complex mechanical systems to compensate the underactuated implementation limits, such as differential mechanisms. The differential mechanism is necessary to decouple finger closures and distribute forces. The multibody simulation allows to evaluate the main parameters of the elements to understand how the differential system can work. The development and design of complex mechanical systems is simplified by this technique. In particular, this paper presents a multibody simulation analysis which recreates an elementary model of a gripper with two links and a single actuator; the developed model reproduces the grasping of an object using a mechanical differential pulley system, placed beneath the fingers. Some results are presented to study the role of the differential when the fingers grasp an object with different configurations. The aim of this work is to show how an accurate and still manageable multibody model integrated in Matlab environment is able to extend the classical grasp metrics to a more general dynamic setup.

BackgroundTo reach Vision Zero, injuries with long-term consequences (LTCs) need to be considered in the development of (public) vehicles. In the EU project ProtAct-Us, methods for the assessment and principles for countermeasures will be developed.MethodsThe German GIDAS and MHH database were analyzed to identify bus and shuttle occupant injuries and the accident scenarios in which they occur. Accident type, collision partners and collision speeds as well as gender, age, passenger position (seated or standing), impact points in the bus, injured body regions and associated injuries were identified.ResultsThis led to the definition of three basic use cases, all in an urban environment. The main scenario leading to injuries was braking maneuver, followed by frontal and side collisions. The velocities / decelerations are 7 m/s² (braking) and 30 kph for frontal/side collision. Scenarios will be simulated with standing, forward and sideward sitting passengers. For the identified scenarios, Finite Element (FE) and Multibody (MB) simulations are conducted in several ways. The first option is to use MB models of the full body and determine the boundaries (angle, velocity) of their contact at potentially unsafe spots in the bus. Further, the kinematics is transferred to more detailed FE models which are then used to calculate the injury risk. The second option is to run simulations with FE full body models (Human body models) which are directly assessed. For the calculation of the head injury risk it is further possible to transfer the kinematic boundaries to the Strasbourg University Finite Element Head Model (SUFEHM). For those body regions, which are known from statistics to be most likely injured, the risk is assessed. This includes head, rib and in some cases femur injuries.ConclusionsIn order to mitigate the long-term consequences of these injuries, the project will develop concepts for countermeasures, the principles of which are presented in this publication.Key messages• A method for the assessment of injuries with long-term consequences for bus occupants is presented. FE and MB simulations are used to quantify the injury risk for most vulnerable body regions.• Injured body regions of bus occupants and the impact locations on buses are identified in accident statistics. Principles of countermeasures for these spots are presented to avoid these injuries.TopicBus occupants, Long-term injuries, MB/FE simulation.

ABSTRACTWe described in this paper the development of a high fidelity vehicle aerodynamic model to fit wind tunnel test data over a wide range of vehicle orientations. We also present a comparison between the effects of this proposed model and a conventional quasi steady-state aerodynamic model on race vehicle simulation results. This is done by implementing both of these models independently in multi-body quasi steady-state simulations to determine the effects of the high fidelity aerodynamic model on race vehicle performance metrics. The quasi steady state vehicle simulation is developed with a multi-body NASCAR Truck vehicle model, and simulations are conducted for three different types of NASCAR race tracks, a short track, a one and a half mile intermediate track, and a higher speed, two mile intermediate race track. For each track simulation, the effects of the aerodynamic model on handling, maximum corner speed, and drive force metrics are analysed. The accuracy of the high-fidelity model is shown to reduce the aerodynamic model error relative to the conventional aerodynamic model, and the increased accuracy of the high fidelity aerodynamic model is found to have realisable effects on the performance metric predictions on the intermediate tracks resulting from the quasi steady-state simulation.

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.

A recent trend in robotics is the development of lightweight manipulators. Safety, power consumption, and productivity can significantly benefit of weight reductions. However, a lightweight design can significantly affect stiffness and accuracy performance. Accordingly, this paper investigates the effect of joint and link flexibility for an in-depth understanding of their contributions towards an optimal trade-off design of lightweight manipulators. The proposed work is based on using Flexible Multibody (FMB) simulations. The structural flexibility of a whole manipulator is evaluated by calculating a set of Frequency Response Functions (FRF) at different robot poses. Namely, a simplified model of an anthropomorphic robot is simulated within a multibody simulation environment. The results of the multibody simulations are analyzed and compared with finite element analyses. Results are discussed for two specific robot configurations.

Multi-body Motion Modeling and Simulation for Tilt Rotor Aircraft

Geometric irregularities on rail surfaces increase dynamic forces in wheel-rail contact, causing damage and wear to track and vehicle components. Multi-body simulation is a practical tool for optimizing the rail-wheel system. The choice of excitation type and the multi-body model significantly impact the accuracy of the results and computational efficiency. Rigid-body models with moving sleepers are commonly used in the dynamic analysis of railway vehicles. On the other hand, flexible multi-body models with finite element (FE) rails, incorporate track flexibility. This study shows that multi-body models with FE components offer advantages in capturing the dynamic behaviour of vehicles on realistic tracks, especially when the effects of short-wave track irregularities are taken into account, but the computational effort increases significantly. For the investigation of ballast damage, a rigid body model with multiple masses offers a good compromise between computational effort and the quality of results. It covers a frequency range up to 150 Hz and represents the loads in what is known as the P2 force range well with 2% to 8% deviations from the measured values. For higher frequencies, flexible FE bodies are required that can cover frequencies up to 1000 Hz and primarily lead to damage to the rail surface.

<div class="section abstract"><div class="htmlview paragraph">Automotive crash data analysis and reconstruction is vital for ensuring automotive safety. The objective of vehicle crash reconstruction is to determine the vehicle’s motion before, during, and after the crash, as well as the impact on occupants in terms of injuries. Simulation approaches, such as PC Crash<sup>TM</sup>, have been developed to understand pre-crash and post-crash vehicle motion, rather than the crash phase behavior. Over the past few decades, crash phase simulations have utilized vehicle finite element models.</div><div class="htmlview paragraph">While multibody simulation tools are suitable for crash simulations, they often require detailed crash test data to accurately capture vehicle behavior, which is not always readily available. This paper proposes a solution to this limitation by incorporating crash test data from databases, such as NHTSA, Global NCAP, consumer rating reports, and videos, along with a multibody-based approach, to conduct crash phase simulations.</div><div class="htmlview paragraph">In this study, multibody vehicle models were created in MADYMO<sup>TM</sup> and validated using existing vehicle crash test reports. The multibody simulations were further validated against the crash data for a known crash scenario. The impact conditions of the vehicle occupants with the vehicle interior, as obtained from the multibody simulations, were then used in finite element simulations to estimate injuries and compare them with known injury data.</div><div class="htmlview paragraph">To establish confidence in the proposed method, a vehicle model was developed and validated using detailed crash test data obtained from NHTSA. Subsequently, a real-world crash case from the National automotive sampling system/Crashworthiness data system (NASS/CDS) was simulated, followed by implementation with a crash case from the Delhi-Jaipur highway. The proposed method demonstrated promising results even with limited data availability.</div><div class="htmlview paragraph">The proposed multibody simulation method emerged as an effective alternative for vehicle crash reconstruction and occupant simulations. It played a crucial role in determining occupant crash conditions, such as occupant velocities and the orientation of impact with interiors. These occupant crash conditions were further utilized to simulate the occupant’s impact with the vehicle interior using finite element human body and interior surface models. Injuries to the human body were estimated from these simulations and correlated with known injuries, providing additional confidence in the proposed methodology.</div></div>

Multibody simulation has evolved significantly over the last decades but simultaneously has become a field of specialists and commercial software products. Body coordinates avoid complex simulation algorithms even for arbitrary system topology and simulation scenario, while exhibiting lower but in most practical cases still satisfactory computational efficiency. Currently, when body coordinates are used, special measures are required to robustly constrain the angle of relative revolution between two bodies to a predefined value. This constraint is required, e.g. for inverse dynamic simulation of a mechanism with rotational actuators. This paper presents a new formulation of this constraint, which is efficiently evaluated and makes special measures as mentioned above obsolete, thus increasing straightforwardness and simplicity of consequent multibody simulation. A multibody simulation program which is based on the new constraint formulation and provides a plain, universal, and adaptable simulation platform is presented in addition. The program is defined in Matlab and Octave, open source, freely accessible and was validated against the Matlab toolbox SimMechanics revealing similar simulation accuracy.

Implementation of a new bogie concept is an integrated part of the vehicle design which must follow a rigorous testing and validation procedure. Use of multibody simulation helps to reduce the amount of time and effort required in selecting a new concept design by analysing results of simulated dynamic behaviour of the proposed design. However, the multibody simulation software mainly looks at the dynamics of a single vehicle; hence, forces from the train configuration operational dynamics are often absent in such simulations. Effects of longitudinal-lateral and longitudinal-vertical interactions between rail vehicles have been found to affect the stability of long trains [1,2]. The effect of wedge design on the vertical dynamics of a bogie has also been discussed in [3,4]. It is important to apply the lateral and vertical forces from a train simulation into a single multibody model of a wagon to check its behaviour when operating in train configuration. In this paper, a novel methodology for the investigation of new bogie designs has been proposed based on integrating dynamic train simulation and the multibody vehicle modelling concept that will help to efficiently achieve the most suitable design of the bogie. The proposed methodology suggests that simulation of any configuration of bogie needs to be carried out in three stages. As the first stage, the bogie designs along with the wagon configurations need to be presented as a multibody model in multibody simulation software to test the suitability of the concept. The model checking needs to be carried out in accordance with the wagon model acceptance procedure established in [5]. As the second stage, the wagon designs need to be tested in train configurations using a longitudinal train dynamics simulation software such as ‘CRE-LTS’ [2], where a train set consisting of the locomotives and wagons will be simulated to give operational wagon parameters such as lateral and vertical coupler force components. As the third stage, the detailed dynamic analysis of bogies and wagons needs to be performed with a multibody software such as ‘Gensys’ where lateral and vertical coupler force components from the train simulation (second stage) will be applied on the multibody model to replicate the worst case scenario. The proposed methodology enhances the selection procedure of any alternate bogie concept by the application of simulated train and vehicle dynamics. The simulated case studies show that simulation of wagon dynamic behaviour in multibody software combined with data obtained from longitudinal train simulation is not only possible, but it can identify issues with a bogie design that can otherwise be overlooked.