发动机排气歧管热应力分析

应用Fire软件建立排气歧管CFD计算分析模型,模拟计算发动机在不同工况下的温度和换热系数(Heat Transfer Coefficient,HTC).用Abaqus建立热机疲劳分析模型,利用CFD结果中的温度和换热系数作为热机械疲劳分析的边界条件,计算各工况点下排气歧管的温度场和塑性变形等结果,并对结果进行评估,提出相应的改善意见,为后续发动机零部件结构强度开发提供参考,从而大大减少试验开发的工作量和费用,加快开发进度.     

发动机排气歧管流固耦合仿真

应用AVL-fire软件和Abaqus软件对某发动机排气歧管进行流固耦合仿真.对排气歧管材料进行各温度下的材料试验,得到准确的材料在不同温度下的属性曲线.由AVL-fire软件和Abaqus软件进行流固耦合仿真得到排气歧管的温度场分布,并进行排气歧管应力和应变分析.仿真结果与试验结果的对比表明,塑性应变高的区域正是发生开裂的区域.     

排气歧管流固耦合仿真与试验

针对发动机排气歧管的断裂问题,对某发动机排气歧管的热负荷进行流固耦合分析,并在台架试验中测量其温度场和应变.考虑热辐射和材料的非线性,建立排气歧管的内流场CFD模型、传热模型和有限元模型,分析得到排气歧管的温度场、应力场和塑性应变云图等.仿真结果与试验结果吻合较好.仿真结果表明排气歧管汇合处的温度最高,塑性应变最大位置与试验测得的断裂危险区域吻合.     

Shape optimal design using B-splines

Shape optimal design of an elastic structure is formulated using a design element technique. It is shown that Bezier and B-spline curves, typical of the CAD philosophy, are well suited to the definition of design elements. Complex geometries can be described in a very compact way by a small set of design variables and a few design elements. Because of the B-splines flexibility, it is no longer necessary to piece design elements together in order to agree with the shape complexity, nor to restrict the shape variations. Moreover, the additional optimization constraints that are most often needed to avoid unrealistic designs when the shape variables are the nodal coordinates of a finite element mesh, are automatically taken into account in the new formulation. An analytical derivation of the sensitivity analysis will be established, giving rise to numerical efficiency. It will be seen that the resulting optimization problem does not involve highly nonlinear functions with respect to the shape variables, so that simple mathematical programming algorithms can be applied to solve it. Some numerical examples are offered to demonstrate the power and generality of the new approach presented in this paper.     

Shape optimal design and free mesh generation

The concept of structural optimization was introduced in the early sixties. It was at that time that Professor Schmit, from Los Angeles, California University, suggested a combination of structural analysis by finite element and optimization methods (Schmit 1960).At present, the use of optimization methods is generally well understood. The capabilities (and limitations) of these methods are known and some industrial softwares exist. One of these is SAMCEF which can be applied to design of thin-walled structures or to shape optimization. The techniques used for the solution of large scale problems are presented in this paper. A summary of the main difficulties involved in shape optimization is also given. Several industrial problems are solved to illustrate the proposed concepts.     

Shape optimal design—A CAD-oriented formulation

In this paper a convenient geometrical representation for shape optimal design is first briefly recalled, as well as the corresponding sensitivity analysis formulation (stress and displacement derivatives). Two-dimensional structures are decomposed into a few design elements described by Bezier or B-splines blending functions. Next, the choice of the optimization algorithm is discussed. It is shown that well-known and efficient methods of structural sizing can be advantageously extended to shape optimal design problems. Experiments are performed with different approximation schemes and a new general optimization algorithm is introduced, which combines mixed approximations and dual methods. Three examples are also treated to demonstrate the generality and the efficiency of the new formulation.     

Modeling and optimal design of Neuro-Mechanical Shape Memory Devices

In this paper we describe the modeling and optimization of what we refer to as Neuro-Mechanical Shape Memory Devices (NMSMDs). These are active mechanical structures which are designed to take on specific shapes in response to certain external stimuli. An NMSMD is a particular example of a Neuro-Mechanical Network (NMN), a mechanical structure that consists of a network of simple but multifunctional elements. In the present work, each element contains an actuator and an artificial neuron, and when assembled into a structure the elements form an actuated truss with a superimposed recurrent neural network. The task of designing an NMSMD is cast as an optimization problem in which a measure of the error between the actual and desired shape for a number of given stimuli is minimized. The optimization problems are solved using a gradient based solver, and some numerical examples are provided to illustrate the results from the design process and some aspects of the proposed model.     

Nonlinear robust observer design using an invariant manifold approach

This paper presents a method to design a reduced order observer using an invariant manifold approach. The main advantages of this method are that it enables a systematic design approach, and (unlike most nonlinear observer design methods), it can be generalized over a larger class of nonlinear systems. The method uses specific mapping functions in a way that minimizes the error dynamics close to zero. Another important aspect is the robustness property which is due to the manifold attractivity: an important feature when an observer is used in a closed loop control system. A two degree-of-freedom system is used as an example. The observer design is validated using numerical simulation. Then experimental validation is carried out using hardware-in-the-loop testing. The proposed observer is then compared with a very well known nonlinear observer based on the off-line solution of the Riccati equation for systems with Lipschitz type nonlinearity. In all cases, the performance of the proposed observer is shown to be very high.     

Case studies on the application of the stable manifold approach for nonlinear optimal control design

This paper presents application results of a recently developed method for approximately solving the Hamilton–Jacobi equation in nonlinear control theory. The method is based on stable manifold theory and consists of a successive approximation algorithm which is suitable for computer calculations. Numerical approach for this algorithm is advantageous in that the computational complexity does not increase with respect to the accuracy of approximation and non-analytic nonlinearities such as saturation can be handled. First, the stable manifold approach for approximately solving the Hamilton–Jacobi equation is reviewed from the computational viewpoint and next, the detailed applications are reported for the problems such as swing up and stabilization of a 2-dimensional inverted pendulum (simulation), stabilization of systems with input saturation (simulation) and a (sub)optimal servo system design for magnetic levitation system (experiment).     

Fuzzy modeling and control of an engine air inlet with exhaust gas recirculation

The purpose of this paper is to present an original fuzzy modeling method applied to a highly non- linear physical system, an engine air inlet with exhaust gas recirculation. This system is modeled with fuzzy logic rules of the Takagi–Sugeno type. The rule base switches between local linear models defined in the whole state space. The control objective is to preserve the linear behavior of the closed-loop system in all operating conditions. To reach this objective, the linear control tools are applied to each local linear model. The fuzzy model rule-base structure is then used to switch between local controllers.     

Convergence of an algorithm in optimal design

The convergence of an algorithm in optimal design for problems in which the material properties are described by a second-order tensor is proved in this paper. The heat conductance context has been chosen for the presentation. Numerical results by using this kind of algorithm have already been obtained by Allaireet al. (1996) in elasticity.     

基于Abaqus的某柴油机排气歧管热固耦合分析

排气歧管在工作状态下会承受很高的环境温度,而在较高的环境温度下金属材料的力学性能和热学性能通常会发生较大变化.通过添加实测的各种部件材料随温度变化的性能参数,介绍某柴油机排气歧管热固耦合分析过程,展现使用AVL系列软件与Abaqus软件进行的排气歧管热固耦合分析流程.     

基于Abaqus的某汽油机排气歧管隔热罩优化分析

用Abaqus对不同类型非线性复合材料隔热罩进行振动分析,预测不同设计方案的排气歧管和催化器隔热罩的振动情况,并展示使用LMS.TestLab对噪声优化效果验证的主要过程.     

排气歧管热机耦合强度和密封压力模拟分析

应用Abaqus对某发动机排气系统进行温度场计算,并在冷热循环工况下计算排气歧管的热应力、塑性变形以及密封压力.结果可以为排气歧管结构设计提供参考.     

On an asymptotically optimal adaptive classifier design criterion

A new approach for estimating classification errors is presented. In the model, there are two types of classification error: empirical and generalization error. The first is the error observed over the training samples, and the second is the discrepancy between the error probability and empirical error. In this research, the Vapnik and Chervonenkis dimension (VCdim) is used as a measure for classifier complexity. Based on this complexity measure, an estimate for generalization error is developed. An optimal classifier design criterion (the generalized minimum empirical error criterion (GMEE)) is used. The GMEE criterion consists of two terms: the empirical and the estimate of generalization error. As an application, the criterion is used to design the optimal neural network classifier. A corollary to the Γ optimality of neural-network-based classifiers is proven. Thus, the approach provides a theoretic foundation for the connectionist approach to optimal classifier design. Experimental results to validate this approach     

On a problem of analytic design of an optimal controller

This article is devoted to the further development of the technique of analytic design of an optimal controller for the case of functionals with an integrand of the form x′Qx+x′Pu+ u′ Ru. In this case the problems of analytic design are considered both without disturbances and at constantly acting disturbances. The statement of the problem for optimal control of a vibration-protective system (VPS) is given, for the solution of which the technique outlined in the article can be used for the solution of the problem of analytic design of the optimal controller.     

Automatic design of diagnosis systems with application to an automotive engine

It is highly desirable to systematize and automate the process of designing diagnosis systems. The reason is that in many applications, high diagnosis performance is required, and at the same time, the time-consuming engineering work of designing diagnosis systems must be minimized. Here, model-based diagnosis based on structured hypothesis tests is considered. Principles for evaluating diagnosis systems are developed, and a systematic and automatic design procedure is proposed. The procedure is successfully applied to the problem of designing a diagnosis system for the air-intake system of an automotive engine. The resulting diagnosis system is then experimentally validated using a real engine.     

排气压力波用于发动机失火检测的实验研究

提出了一种发动机失火检测的新方法.通过分析发动机排气压力波动与发动机工况之间的映射关系,设计出基于排气压力波的发动机失火检测实验系统;模拟发动机失火故障,通过监测排气压力波动态特性的变化实现失火检测.实验结果表明:利用排气压力波检测失火故障的方法准确可靠、直观、便捷,为汽车发动机性能监测和不解体故障诊断提供了一条新的途径.