An Approximation-Based Design Optimization Approach to Eigenfrequency Assignment for Flexible Multibody Systems

The use of flexible multibody simulation has increased significantly over recent years due to the increasingly lightweight nature of mechanical systems. The prominence of lightweight engineering design in mechanical systems is driven by the desire to require less energy in operation and to reach higher speeds. However, flexible lightweight systems are prone to vibration, which can affect reliability and overall system performance. Whether such issues are critical depends largely on the system eigenfrequencies, which should be correctly assigned by the proper choice of the inertial and elastic properties of the system. In this paper, an eigenfrequency assignment method for flexible multibody systems is proposed. This relies on a parametric modal model which is a Taylor expansion approximation of the eigenfrequencies in the neighborhood of a configuration of choice. Eigenfrequency assignment is recast as a quadratic programming problem which can be solved with low computational effort. The method is validated by assigning the lowest eigenfrequency of a two-bar linkage by properly adding point masses. The obtained results indicate that the proposed method can effectively assign the desired eigenfrequency.

Static Gait Scheme for Horizontal Posture Slope Climbing with Quadruped Robot

With a view to expanding serviceability in different applications, the slope climbing ability of a quadruped robot is important. In this paper, a gait scheme i.e. walking algorithm for slope climbing is proposed. It differs from the previous studies in terms of the posture of the robot while climbing. The presented scheme is designed such a way that the body of the robot maintains horizontal posture with positive static stability which can be used for carrying a load and disabled while climbing the slope. For this proposed scheme, different parameters of gait are shown. The algorithm is tested with a multibody simulation and based on the results of transformation of the inertial frame about the world frame; it is proven to be steady.

Self-Excited Full-Vehicle Oscillations Caused by Tire–Road Interaction: Virtual and Real-World Experimental Investigation

ABSTRACT In this article, self-excited full-vehicle oscillations (power-hops) are introduced. Initially, results of full-vehicle measurements are shown followed by the presentation of a specially build test rig (longitudinal dynamics test rig). Subsequently, these oscillations are investigated by using simulation-based tools within multibody simulation–related full-vehicle modeling. Tire–road interaction is evaluated in this process either by characteristic curves or by a proprietary quasistatic tire model that returns overall tangential forces by evaluating the state of every discretized element within the footprint area.

Calculation of the actuator system in swash plate axial piston machines by a coupled multibody and TEHL simulation

This paper presents a method for coupling a multibody simulation for the actuator system in axial piston machines in combination with a transient, three-dimensional, thermal elastohydrodynamic contact calculation. For the tribological investigation, the oscillating piston/cylinder contact is focused, whereby a simplified model of the actuator system simulates the loads. The developed method allows the integration of a complex tribological contact simulation under mixed friction conditions into a dynamic multibody simulation based on the Newton–Euler method. It is discussed how the accuracy of the results and the calculation time can be improved by the procedure.

Preliminary Study on Multibody Modeling and Simulation of an Underactuated Gripper With Differential Transmission

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.

Describing Road Booming Noise with a Hybrid Simulation Model Using a Time Segmentation of the Excitation Load Approach

One of the most important goals in vehicle acoustics is to describe the NVH behavior of a vehicle at sound pressure level using simulation models at an early stage of development. Different simulation models and methods are used for this purpose. To balance the advantages and disadvantages of the different methods, it is important to combine the simulation models. For the virtual description of the road booming noise behavior of a vehicle passing a rough road, we use a multibody simulation model excited with the elevation profile of the road in the time domain. To calculate the sound pressure inside the vehicle, the internal chassis forces of the multibody simulation model are combined with a finite element body model including the air cavity inside the cabin. The methodology for combining the chassis forces and body transfer functions to calculate the sound pressure is first validated using test data and then applied to the simulation data. The correlation of the calculated sound pressure based on test data () and based on simulation data () compared to a microphone measurement is very high.