多边形和多面体顶点法矢的数值估计

证明了两个定理 :定理 1揭示了三点多边形的外接圆在中点处的法矢与两个边界法矢的关系 ;定理 2揭示了四面体外接球面在中点处的法矢与三个相邻三角平面的法矢量的关系 .给出了一个判别二维多边形和三维多面体顶点法矢计算方法优劣的准则 .在此基础上 ,提出一种用于估计三维多面体顶部的法矢量的计算方法 .

Adaptive nonlinear model predictive control design of a flexible-link manipulator with uncertain parameters

This paper presents a novel adaptive nonlinear model predictive control design for trajectory tracking of flexible-link manipulators consisting of feedback linearization, linear model predictive control, and unscented Kalman filtering. Reducing the nonlinear system to a linear system by feedback linearization simplifies the optimization problem of the model predictive controller significantly, which, however, is no longer linear in the presence of parameter uncertainties and can potentially lead to an undesired dynamical behaviour. An unscented Kalman filter is used to approximate the dynamics of the prediction model by an online parameter estimation, which leads to an adaptation of the optimization problem in each time step and thus to a better prediction and an improved input action. Finally, a detailed fuzzy-arithmetic analysis is performed in order to quantify the effect of the uncertainties on the control structure and to derive robustness assessments. The control structure is applied to a serial manipulator with two flexible links containing uncertain model parameters and acting in three-dimensional space.

Stability analysis of a thin-walled cylinder in turning operation using the semi-discretization method

In this work, the stability of a flexible thin cylindrical workpiece in turning is analyzed. A process model is derived based on a finite element representation of the workpiece flexibility and a nonlinear cutting force law. Repeated cutting of the same surface due to overlapping cuts is modeled with the help of a time delay. The stability of the so obtained system of periodic delay differential equations is then determined using an approximation as a time-discrete system and Floquet theory. The time-discrete system is obtained using the semi-discretization method. The method is implemented to analyze the stability of two different workpiece models of different thicknesses for different tool positions with respect to the jaw end. It is shown that the stability chart depends on the tool position as well as on the thickness.

Improving the dynamic stability of a workpiece dominated turning process using an adaptronic tool holder

In this contribution, inside turning of a thin-walled cylinder is investigated in simulation. Self-excited vibrations can arise due to repeated cutting of the same surface, that lead to instability.A flexible multibody system model of the system is the basis for a subsequent analysis of the stability of the process. Stability analysis is done using an approximation as a time-discrete system via the semi-discretization method. An adaptronic turning chisel comprising a piezo actuator and sensors is then used in combination with different control concepts to improve the stability of the process. The effectiveness of the different strategies is compared based on the influence on the stability charts. A classic H∞ controller based on a model of the coupled system of workpiece and tool can only yield some improvements, when an additional measurement of the workpiece displacement is added. Incorporating knowledge on the cutting process coupling workpiece and tool using a gain scheduled H∞ controller allows further improvements. However, robustness with respect to model uncertainties, notably concerning the force law, remains an issue. C 2013 The Chinese Society of Theoretical and Applie-d Mechanics. [doi：10.1063/2.1301308]

A high-order full-discretization method using Hermite interpolation for periodic time-delayed differential equations

A high-order full-discretization method （FDM） using Hermite interpolation （HFDM） is proposed and implemented for periodic systems with time delay. Both Lagrange interpolation and Hermite interpolation are used to approximate state values and delayed state values in each discretization step. The transition matrix over a single period is determined and used for stability analysis. The proposed method increases the approximation order of the semidiscretization method and the FDM without increasing the computational time. The convergence, precision, and efficiency of the proposed method are investigated using several Mathieu equations and a complex turning model as examples. Comparison shows that the proposed HFDM converges faster and uses less computational time than existing methods.

An approach for the coupled simulation of machining processes using multibody system and smoothed particle hydrodynamics algorithms

The prediction accuracy of a simulation method is limited by its theoretical background. This fact can lead to disadvantages regarding the simulation quality when investigating systems of high complexity, e.g. containing components showing a fairly different behavior. To overcome this limitation, co-simulation approaches are used more and more, combining the advantages of different simulation disciplines. That is why we propose a new strategy for the dynamic simulation of cutting processes. The method couples Lagrangian particle methods, such as the smoothed particle hydrodynamics （SPH） method, and multibody system （MBS） tools using co-simulations. We demonstrate the capability of the new approach by providing simulation results of an orthogonal cutting process and comparing them with experimental data. @ 2013 The Chinese Society of Theoretical and Applied Mechanics. [doi：10.1063/2.1301305]

A-posteriori error estimation for second order mechanical systems

One important issue for the simulation of flexible multibody systems is the reduction of the flexible bodies de- grees of freedom. As far as safety questions are concerned knowledge about the error introduced by the reduction of the flexible degrees of freedom is helpful and very important. In this work, an a-posteriori error estimator for linear first order systems is extended for error estimation of me- chanical second order systems. Due to the special second order structure of mechanical systems, an improvement of the a-posteriori error estimator is achieved. A major advan- tage of the a-posteriori error estimator is that the estimator is independent of the used reduction technique. Therefore, it can be used for moment-matching based, Gramian matrices based or modal based model reduction techniques. The capability of the proposed technique is demon- strated by the a-posteriori error estimation of a mechanical system, and a sensitivity analysis of the parameters involved in the error estimation process is conducted.

Development of new electromagnetic suspension-based high-speed Maglev vehicles in China:Historical and recent progress in the field of dynamical simulation

High-speed Maglev is a cutting-edge technology brought back into the focus of research by plans of the Chinese government for the development of a new 600 km/h Maglev train.A Chinese‐German cooperation with industrial and academic partners has been established to pursue this ambitious goal and bring together experts from multiple disciplines.This contribution presents the joint work and achievements of CRRC Qingdao Sifang,thyssenkrupp Transrapid,CDFEB,and the ITM of the University of Stuttgart,regarding research and development in the field of high‐speed Maglev systems.Furthermore,an overview is given of the historical development of the Transrapid in Germany,the associated development of dynamical simulation models,and recent developments regarding high-speed Maglev trains in China.

Letter of thanks for IJMSD's indexing in ESCI

Dear Authors/Reviewers/Editorial Board Members/Editorial Office Members/Readers,We are delighted to inform you that the International Journal of Mechanical System Dynamics(IJMSD)was officially indexed by Emerging Sources Citation Index(ESCI)on June 27,2023,after being indexed by Inspec,Scopus,DOAJ,Dimensions,and some other databases.We would like to take this opportunity,on behalf of the IJMSD Editorial Board,to extend our gratitude and sincere appreciation for your significant contributions and support to IJMSD.

An LSTM‐based approach to precise landing of a UAV on a moving platform

A machine learning‐based method for the precise landing of an unmanned aerial vehicle on a moving mobile platform is proposed.The proposed approach attempts to predict the mobile platform's future trajectory based on the past states of the mobile platform.To that end,it combines a long short‐term memory‐based neural network with a Kalman filter.Hence,it aims at combining the advantages of a machine learning method with those of a state estimation method from established control theory.Based on the predicted trajectory,the unmanned aerial vehicle attempts to land precisely on the moving mobile platform.The experiment is conducted in the Gazebo simulation platform with a quadrotor and an omni-directional mobile robot,and the proposed method is compared with the single‐method approaches of using only either the Kalman filter or the machine learning method alone.

IJMSD: A novel journal devoting to promote the progress of modern science, technology and industry by enhancing the capabilities of mechanical system dynamics

From the Stone Age to modern industry,the development of me-chanical systems has driven human civilization and the progress of science and technology.Inferior dynamic performances related to manufacturing precision,mobility,comfort,reliability,and safety have become the bottlenecks restricting the development of con-temporary industrial products,which can be regarded as complex and integrated mechatronical systems composed of many subsystems with highly coupled dynamical behaviors.With the advent of the fourth industrial revolution and the widely used complicated and integrated products,it has been found clearly that quasi‐static or local dynamics study can no longer capture the critical features of contemporary mechanical systems.

Simplified modeling of electromagnets for dynamic simulation of transient effects for a synchronous electric motor

This study aims to show an approach for the dynamic simulation of a synchro-nous machine.The magnetic forces in the air gap are calculated efficiently using simplified approaches without neglecting important effects.For the modeling of the magnetic forces,an equivalent magnetic circuit is constructed in which the magnetic saturation and the leakage flux are taken into account and coupled with the electrical circuit at the end.The calculated magnetic forces are then passed to a mechanical model of the motor.Together with a predefinable load torque,the resulting motor rotation and the forces in the bearings are identified.The presented model is then investigated in a small example.This novel ap-proach is intended to provide a method of calculating dynamically the forces transmitted from the shaft to the motor housing and to create the basis for evaluating electric motors for vibrations,noise,and harshness under varying loads and input voltages.