An approach for dynamic analysis of planar multibody systems with revolute clearance joints

Engineering with Computers - Clearance is inevitable for manufacture and assembly in the revolute joints of multibody systems. Excessive value of joint clearance will lead to the poor dynamic...     

一类动态互联复杂系统的稳定性分析

通过引入动态图及动态邻接矩阵相关理论,对具有动态互联信息结构约束的复杂系统进行描述和建模,并引入ＬｏｔｋａＶｏｌｔｅｒｒａ方程作为该系统的动态互联信息结构模型．根据李雅普诺夫方法,对系统的动态互联模型进行了详细分析,研究了非负定限内联结平衡的设定及其渐近稳定条件,进而研究了整个系统的稳定条件．最后得到了该类动态互联复杂系统联结稳定及整个系统稳定的相关结论．     

Physically based modeling and simulation with dynamic spherical volumetric simplex splines

In this paper, we present a novel computational modeling and simulation framework based on dynamic spherical volumetric simplex splines. The framework can handle the modeling and simulation of genus-zero objects with real physical properties. In this framework, we first develop an accurate and efficient algorithm to reconstruct the high-fidelity digital model of a real-world object with spherical volumetric simplex splines which can represent with accuracy geometric, material, and other properties of the object simultaneously. With the tight coupling of Lagrangian mechanics, the dynamic volumetric simplex splines representing the object can accurately simulate its physical behavior because it can unify the geometric and material properties in the simulation. The visualization can be directly computed from the object’s geometric or physical representation based on the dynamic spherical volumetric simplex splines during simulation without interpolation or resampling. We have applied the framework for biomechanic simulation of brain deformations, such as the brain shifting during surgery and brain injury under blunt impact. We have compared our simulation results with the ground truth obtained through intra-operative magnetic resonance imaging and real biomechanic experiments. The evaluations demonstrate the excellent performance of our new technique.     

Self-calibration of spherical rectification for a PTZ-stereo system

Since PTZ (pan–tilt–zoom) camera is able to obtain multi-view-angle and multi-resolution information, PTZ-stereo system using two PTZ cameras has much higher capability and flexibility compared with traditional stereo system. In this paper, we propose a self-calibration framework to deal with the calibration of spherical rectification, which can be deemed as a kind of relative pose estimation, for a PTZ-stereo system. The goal of this calibration is to guarantee high performance of stereo rectification, so that stereo matching can be achieved more efficiently and accurately. In this framework, we assume two PTZ cameras are fully calibrated, i.e., the focal length and the local camera orientation can be computed by given pan–tilt–zoom values. This approach, which is based on point matches, aims at finding uniformly distributed point matches in an iterative way. At each iteration, according to the distribution of previously used point matches, the system could automatically guide two cameras to move to collect a new match. Point matching is firstly performed for the lowest zoom setting (widest field of view). Once a candidate match is chosen, each camera is then controlled to zoom in on corresponding point to get a refined match with high spatial resolution. The final match will be added into the estimation to update the calibration parameters. Compared with previous researches, the proposed framework has the following advantages: (1) Neither manual interaction nor calibration object is needed. Calibration samples (point matches) will be added and removed in each stage automatically. (2) The distribution of calibration samples is as uniform as possible so that biased estimation could be avoided to some extent. (3) The accuracy of calibration can be controlled and improved when iteration goes on. These advantages make the proposed framework more practicable in applications. Experimental results illustrate its accuracy.     

An overview of dynamic parameter identification of robots

Due to the importance to model-based control, dynamic parameter identification has attracted much attention. However, until now, there is still much work for the identification of dynamic parameters to be done. In this paper, an overview is given of the existing work on dynamic parameter identification of serial and parallel robots. The methods for estimating the dynamic parameters are summarized, and the advantages and disadvantages of each method are discussed. The model to be identified and the trajectory optimization are reviewed. Further, the methods for validating the estimated model are summarized and the application of dynamic parameter identification is mentioned. The results of this review are useful for manufacturers of robots in selecting proper identification method and also for researchers in determining further research areas.     

基于UML的嵌入式建模方法改进策略研究

统一建模语言UML(unified modeling language)在嵌入式系统设计建模中已经获得了广泛的承认,有很多成功的应用.但UML在嵌入式建模中存在时间约束描述能力不强和所建模型形式化复杂、验证难及模型重用性不高等问题.针对这些问题提出了一种改进策略:定义实时语义和映射规则,建立实时描述模式模板,使用模板中实时描述模式描述时间约束信息.改进后的方法能可视化地分析模型、纠正错误和简单地进行形式化转换,能利用支撑工具对模型进行验证,较好地解决了UML在嵌入式系统建模中存在的问题.     

Auto-parametric semi-trivial and post-critical response of a spherical pendulum damper

The pendulum vibration damper modelled as a two degree of freedom strongly non-linear auto-parametric system is investigated. A kinematic external excitation in the suspension point is applied. The excitation is considered to be horizontal and harmonically variable in time. A semi-trivial solution and its stability are analyzed. Special attention is paid to the resonance domain. In certain domains of pendulum and excitation parameters the semi-trivial solution does not exist in this domain and various post-critical three-dimensional regimes occur. Some of them are non-stationary despite the harmonic excitation. Three different types of the resonance domain are investigated. Their main properties depend significantly on dynamic parameters of the pendulum and of the external excitation amplitude. An analytical and numerical study brings forth several recommendations for designers of these devices. Their aim is to avoid any post-critical response regimes endangering the pendulum functionality.     

Optimal production planning for a multi-product closed loop system with uncertain demand and return

We study the production planning problem for a multi-product closed loop system, in which the manufacturer has two channels for supplying products: producing brand-new products and remanufacturing returns into as-new ones. In the remanufacturing process, used products are bought back and remanufactured into as-new products which are sold together with the brand-new ones. The demands for all the products are uncertain, and their returns are uncertain and price-sensitive. The problem is to maximize the manufacturer's expected profit by jointly determining the production quantities of brand-new products, the quantities of remanufactured products and the acquisition prices of the used products, subject to a capacity constraint. A mathematical model is presented to formulate the problem and a Lagrangian relaxation based approach is developed to solve the problem. Numerical examples are presented to illustrate the model and test the solution approach. Computational results show that the proposed approach is highly promising for solving the problems. The sensitivity analysis is also conducted to generate managerial insights.     

Scheduling a dynamic job shop production system with sequence-dependent setups: An experimental study

This paper presents the salient aspects of a simulation-based experimental study of scheduling rules for scheduling a dynamic job shop in which the setup times are sequence dependent. A discrete event simulation model of the job shop system is developed for the purpose of experimentation. Seven scheduling rules from the literature are incorporated in the simulation model. Five new setup-oriented scheduling rules are proposed and implemented. Simulation experiments have been conducted under various experimental conditions characterized by factors such as shop load, setup time ratios and due date tightness. The results indicate that setup-oriented rules provide better performance than ordinary rules. The difference in performance between these two groups of rules increases with increase in shop load and setup time ratio. One of the proposed rules performs better for mean flow time and mean tardiness measures.     

UML动态建模方法在DDSS模型访问中的应用

统一建模语言(unified modeling language,UML)是面向对象软件开发方法的重要技术.决策支持系统中的模型库管理对于整体决策支持系统来说尤其重要,在分布式环境下,如何实现模型库中模型的查询、修改、增加和删除对于整体系统的性能起到决定作用,使用UML的动态建模技术,设计并实现了基于C/S模式下的DSS模型库管理系统的模型访问,并描述了通过UML来进行动态建模的详细过程.     

Steps towards a method for the formal modeling of dynamic objects

Fragments of a method to formally specify object-oriented models of a universe of discourse are presented. The task of finding such models is divided into three subtasks, object classification, event specification, and the specification of the life cycle of an object. Each of these subtasks is further subdivided, and for each of the subtasks heuristics are given that can aid the analyst in deciding how to represent a particular aspect of the real world. The main sources of inspiration are Jackson System Development, algebraic specification of data- and object types, and algebraic specification of processes.     

Symbolic integration of a product of two spherical Bessel functions with an additional exponential and polynomial factor

We present a Mathematica package that performs the symbolic calculation of integrals of the form

(1)     

基于ESD的动态系统安全性建模与实现

事件序列图(ESD)是系统安全性分析时采用的一种较新的手段,能有效地解决传统的安全性建模与分析在动态方面的不足。在对国内外动态系统安全性建模与分析方面的研究基础上,提出了一种扩展的ESD方法。对ESD的定义进行了完善,给出了ESD框架的动态逻辑图元表示形式及其数学描述,为提高其建模功能以及与系统结构关联的能力提出了层次化建模策略,并结合新的ESD算法开发了基于ESD的动态系统可视化建模与分析软件。最后,给出了一个实例以说明其有效性。     

An algorithm for automatic checking of exercises in a dynamic geometry system: iGeom

One of the key issues in e-learning environments is the possibility of creating and evaluating exercises. However, the lack of tools supporting the authoring and automatic checking of exercises for specifics topics (e.g., geometry) drastically reduces advantages in the use of e-learning environments on a larger scale, as usually happens in Brazil. This paper describes an algorithm, and a tool based on it, designed for the authoring and automatic checking of geometry exercises. The algorithm dynamically compares the distances between the geometric objects of the student’s solution and the template’s solution, provided by the author of the exercise. Each solution is a geometric construction which is considered a function receiving geometric objects (input) and returning other geometric objects (output). Thus, for a given problem, if we know one function (construction) that solves the problem, we can compare it to any other function to check whether they are equivalent or not. Two functions are equivalent if, and only if, they have the same output when the same input is applied. If the student’s solution is equivalent to the template’s solution, then we consider the student’s solution as a correct solution. Our software utility provides both authoring and checking tools to work directly on the Internet, together with learning management systems. These tools are implemented using the dynamic geometry software, iGeom, which has been used in a geometry course since 2004 and has a successful track record in the classroom. Empowered with these new features, iGeom simplifies teachers’ tasks, solves non-trivial problems in student solutions and helps to increase student motivation by providing feedback in real time.     

Multi-field coupling dynamic modeling and simulation of turbine test rig gas system

On the basis of early research on the 38-component system, this paper extends the established finite volume model to the multi-field coupling numerical system which can describe flow, heat transfer, combustion and rotation, and conducts, based on the experiment, dynamic modeling and simulation research on the turbine test rig gas system which includes turbine and load. The comparison among the simulation results, test data and early simulation results indicates the 42-component system established by this paper has made improvements against many weaknesses of the Previous simulation in an all-round way. Accordingly, it can be concluded that the case setting and algorithm improvement are effective. It is also found that the modeling of module with chemical reaction, the spool throttling modeling of various regulator valves, the modeling of the turbine characteristics and the modeling of wall heat transfer are four key factors which affect simulation accuracy, and that the coupling modeling of flow and combustion is the key factor which affects simulation stability.     

Design of a planar multibody dynamic system with ANCF beam elements based on an element-wise stiffness evaluation procedure

The absolute nodal coordinate formulation (ANCF) has been widely applied for large deformation analysis in flexible multibody dynamics. Although the formulation led to stable solutions for time integration under large rotations and deformations, excessive time consumption was recorded. The nonlinear relationship between the deformation and the internal force accounted for repeated adjustment to the force equilibrium state as the structure deformed. In this research, an equivalent model of the ANCF beam structure was constructed. The stiffness evaluation method was applied in an element-wise manner. In this model, the irrelevant parts were separated from those that relate to the displacements and design parameters enabling efficient updates of internal forces to achieve force equilibrium. Therefore, by using this model, optimization problems, in which displacements as well as design parameters keep changing can be efficiently approached. To verify the proposed method, two examples of optimization problems related to a free-falling pendulum and a slider-crank mechanism are demonstrated.     

An integrated crop and hydrologic modeling system to estimate hydrologic impacts of crop irrigation demands

The present paper discusses a coupled gridded crop modeling and hydrologic modeling system that can examine the benefits of irrigation and costs of irrigation and the coincident impact of the irrigation water withdrawals on surface water hydrology. The system is applied to the Southeastern U.S. The system tools to be discussed include a gridded version (GriDSSAT) of the crop modeling system DSSAT. The irrigation demand from GriDSSAT is coupled to a regional hydrologic model (WaSSI). GriDSSAT and WaSSI are coupled through the USDA NASS CropScape data to provide crop acreages in each watershed. The crop model provides the dynamic irrigation demand which is a function of the weather. The hydrologic model responds to the weather and includes all other anthropogenic competing uses of water. Examples of the system include an analysis of the hydrologic impact of future expansion of irrigation and the real-time impact of short-term drought.     

An improved thermodynamic modeling of the Fe-Cr system down to zero kelvin coupled with key experiments

A thermodynamic modeling of the Fe-Cr system down to 0 K is performed on the basis of our recent comprehensive review of this binary system [W. Xiong, M. Selleby, Q. Chen, J. Odqvist, Y. Du, Evaluation of phase equilibria and thermochemical properties in the Fe-Cr system, Crit. Rev. Solid State Mater. Sci. 35 (2010) 125-152]. The model predicts a sign change for the magnetic ordering energy of mixing rather than the enthalpy of mixing in the bcc phase at 0 K. Designed key experiments are performed not only to check the validity of the present modeling but also to assist in understanding the mechanism for spinodal decomposition of the Fe-Cr alloy. Heat capacities and Curie temperatures of several Fe-rich alloys are determined between 320 and 1093 K by employing differential scanning calorimetry. The measured heat capacities are found to be in remarkable agreement with the prediction based on the present modeling. Microstructural patterns and frequency distribution diagrams of Cr are studied in alloys containing 26.65, 31.95, and 37.76 at.% Cr by using atom probe tomography. The observed phase separation results correspond well with our model-predicted boundary for the spinodal decomposition. Interestingly, a horn on the Cr-rich spinodal boundary is predicted below 200 K for the first time. This work demonstrates a way to bridge the ab initio calculations and CALPHAD approach.     

Adaptive-like control methodologies for a CSTR system with dynamic actuator constraints

This paper deals with a catalytic continuous stirred tank reactor example, modeled as a two-input constrained nonlinear system. Under the Lyapunov-based linearization strategy, the saturation-type parameterized control design can reduce the effect of actuator subject to amplitude and rate constraints. Using the two-input control framework, it turns out to be robust against unknown disturbances, and it also ensures the asymptotic output regulation. For the purpose of practical implementation, the adaptive-like control methodology is developed. A reduced-order nonlinear observer plus the integration of both controllers is synthesized. Our results are illustrated via numerical simulation.