Influence of PM fouling on effectiveness of heat exchanges in a diesel engine with fin-type EGR coolers of different sizes

The particulate matter (PM) fouling in exhaust gas recirculation (EGR) coolers degrades the heat transfer performance considerably, which in turn has a significant influence on the design of the EGR cooler. To investigate the effects of PM fouling on the heat exchange effectiveness in the fin-type EGR coolers of six different sizes, engine dynamometer experiments were performed. The experimental results show that the heat exchange effectiveness varies with the size of the fin-type EGR cooler.     

含J2摄动的有限时间航天器追逃博弈问题研究

航天器追逃博弈是航天器在轨捕获任务的一个重要问题,具有极高的军民两用双重价值．针对有限时间且考虑J2摄动的航天器追逃博弈问题,本文提出了一种精确的求解方法．该方法的核心思想是将有限时间的航天器追逃博弈问题建模为有限时间二人零和对策,则博弈中两航天器的最优控制策略可以转化为有限时间二人零和对策的鞍点解．在鞍点解的求解过程中,本文首先基于考虑J2摄动的非线性动力学方程,将两航天器动力学方程和始末边值条件与鞍点解必要条件结合得到两点边值问题,然后提出一种结合遗传算法和配点法的混合算法求解该两点边值问题以得到精确的鞍点解．本文利用数值仿真对所提方法的有效性进行了验证．结果表明：(i) 在航天器追逃博弈过程中,J2摄动对两航天器的最优控制策略具有较大影响;(ii) 所提方法能够精确求解出两航天器在有限时间的追逃博弈过程中的最优控制策略．     

An optimization of a multi-layered plate under ballistic impact

This paper may be the first trial regarding the optimal design of a multi-layered plate under ballistic impact. An optimal design of a multi-layered plate to endure ballistic impact is suggested by using size optimization based on numerical simulations. The NET2D, a Lagrangian explicit time-integration finite element code for impact analyses, is used to find the optimal parameter values. Three different materials such as mild steel and aluminum for a multi-layered plate structure and die steel for the pellet are assumed. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, the Johnson–Cook model is used as the constitutive models for the simulation. Several mesh types of different size and aspect ratio are tried to check the effect of mesh on the solution and to obtain the appropriate mesh density. The measuring domain is selected to reduce the analyzing time without affecting the sensitivity.The response surface method based on the design of experiments is used to obtain the optimal design. The average temperature or the equivalent plastic strain is introduced as a response for the optimization of the impact problem. Furthermore, the perforation criteria with the equivalent plastic strain to determine whether the plate structure is perforated or not is suggested. The optimized thickness of each layer in which perforation does not occur and the strength of multi-layer is maximized is obtained at a constant velocity of a pellet with a designated total thickness.     

结构边界约束修改后的重分析方法

在结构设计优化中经常将结构边界约束作为设计优化对象,结构边界约束的修改通常导致系统的求解规模发生改变,使得快速准确分析修改后结构的响应成为一个挑战。本文发展了逐次矩阵逆(SMI)方法,提出了一种适合各种结构边界约束(包括初始结构中的约束)修改的快速重分析算法。该方法利用边界约束修改后对应刚度矩阵的对称性,有效缩减了计算量。数值算例表明,本文方法能够快速给出精确的重分析结果。     

Optimum shape and topology design using the boundary element method

A procedure is developed for simultaneous shape and topology design optimization of linear elastic two-dimensional continuum structures. An intuitive approach is presented to treat such topological problems whereby material is eliminated from within the structure (by introducing holes at regions of low stress) through a sequence of shape optimization processes. A mathematical programming technique coupled with the boundary element (BE) method of response and sensitivity analyses enables the optimal positioning of these holes plus optimization of the overall structural shape. The analytical derivative BE formulation is explained together with the use of appropriate design velocity fields, and example problems are solved to demonstrate the optimization procedure.     

传热结构的多目标拓扑优化设计研究

深入分析了传热结构多目标拓扑优化设计中的几个关键问题。提出了基于结构柔度最小化和结构散热弱度最小化的多目标拓扑优化设计方法,建立了传热结构的多目标拓扑优化设计模型,推导了传热结构多目标拓扑优化中用于迭代分析求解的优化准则算法和敏度分析方程。通过数值计算验证了理论和算法的有效性。     

The effect of interface plate compliance on dynamometers incorporating octagonal strain rings

This paper reports on the design, calibration, and accuracy check of a six-load component dynamometer incorporating octagonal strain rings. The dynamometer was designed using the computer-aided design procedure described in an earlier article by Kroencke and Hull¹. The accuracy check revealed inaccuracy which was traced to non-linearity in cross-sensitive load-strain relations. Interface plate compliance was determined as the cause of the nonlinearity by means of finite-element analysis. From this analysis two methods for avoiding the nonlinearity were identified. One is to insure that the interface plates are much stiffer than the octagonal strain rings and the other is to connect the interface plates to the environment so that the boundary conditions are identical for both plates.     

航天器天线桁架结构多目标优化设计

针对有附加结构的卫星天线桁架结构,提出了一种实现结构多目标优化的综合设计方法。首先,探讨了附加结构刚度对桁架结构动力学特性的影响,以便建立精确的有限元模型,为进行优化设计奠定基础。之后,交替采用代理模型方法和人机交互方式进行结构拓扑构型设计。其中代理模型是采用优化拉丁超立方法进行试验设计,结合径向基函数近似方法生成的。最后,应用NSGA-II全局优化方法实现以重量最小化和频率最大化的多目标优化设计,并根据分层图定量可视化地从Pareto前端和Pareto最优解集中筛选最优设计方案。优化结果表明,相对于初始方案可以在基频几乎不变的情况下,重量减小29.66%。该方法有利于提高设计效率,降低全局优化的复杂度,同时能够得到满足设计要求的设计方案,适用于多目标结构优化设计。     

Optimum design of laminated composite foam-filled sandwich plates subjected to strength constraint

Optimum design of laminated composite sandwich plates with both continuous (core thickness) and discrete (layer group fiber angles and thicknesses) design variables subjected to strength constraint is studied via a two-level optimization technique. The strength of a sandwich plate is determined in a failure analysis using the Tsai–Wu failure criterion and the finite element method which is formulated on the basis of the layerwise linear displacement theory. In the first level optimization of the design process, the discrete design variables are temporarily treated as continuous variables and the corresponding minimum weight of the sandwich plate is evaluated subject to the strength constraint using a constrained multi-start global optimization method. In the second level optimization, the optimal solution obtained in the first level optimization is used in the branch and bound method for solving a discrete optimization problem to determine the optimal design parameters and the final weight of the plate. Failure test of laminated composite foam-filled sandwich plates with different lamination arrangements are performed to validate the proposed optimal design method. A number of examples of the design of laminated composite foam-filled sandwich plates are given to demonstrate the feasibility and applications of the proposed method.     

蜂窝夹芯圆环的拓扑优化设计及尺度效应研究

采用尺度关联的一体化设计方法开展了旋转周期圆环结构的拓扑优化设计研究，以宏观 结构的最大刚度为目标，研究了材料表征体胞尺度、构型以及不同载荷作用形式对蜂窝夹芯 圆环结构优化结果的影响. 所提出的无量纲结构构型因子实现了优化结构的结构效率量化评 估. 结合SIMP材料模型和周长控制方法，实现了宏观结构和细观表征体胞的优化设计，获得 清晰的材料分布. 数值算例表明，尺度关联的一体化设计方法能有效地完成圆环结构的拓扑 优化设计，设计结果充分反映体胞尺度效应对旋转周期圆环结构夹芯构型的影响.     

Randomness effects in crashworthiness analysis

—Crashworthiness studies involve computational analyses of complex structures. If the randomncss of the structural properties is neglected, however, the results of the analysis turn out not to be in agreement with the ones of laboratory tests. The paper systematizes a probabilistic approach to this problem which uses a response surface approximation in terms of spatial averages of the design variables. It includes the randomness of variables, vectors, and fields; it is shown to be efficient and accurate. The method requires an accurate design of the experiments to be carried out in order to identify the response surface parameters. The correlation between response variables is also analysed. A numerical example is presented. The derived results are validated by simulation.     

The anti‐dissipative,non‐monotone behavior of Petrov–Galerkin upwinding

The Petrov–Galerkin method has been developed with the primary goal of damping spurious oscillations near discontinuities in advection dominated flows. For time‐dependent problems, the typical Petrov–Galerkin method is based on the minimization of the dispersion error and the simultaneous selective addition of dissipation. This optimal design helps to dampen the oscillations prevalent near discontinuities in standard Bubnov–Galerkin solutions. However, it is demonstrated that when the Courant number is less than 1, the Petrov–Galerkin method actually amplifies undershoots at the base of discontinuities. This is shown in an heuristic manner, and is demonstrated with numerical experiments with the scalar advection and Richards' equations. A discussion of monotonicity preservation as a design criterion, as opposed to phase or amplitude error minimization, is also presented. The Petrov–Galerkin method is further linked to the high‐resolution, total variation diminishing (TVD) finite volume method in order to obtain a monotonicity preserving Petrov–Galerkin method.     

变厚度圆柱壳的强度优化设计

对在任意轴对称分布荷载作用下体积保持常数的变厚度圆柱壳的强度优化设计问题进行了研究。当中面形状固定时 ,采用阶梯折算法 ,用传递矩阵导出了变厚度圆柱壳的初参数解的显式表达式。根据Huber-Mises-Hencky强度准则 ,将变厚度圆柱壳的强度优化转化为极小化当量应力的非线性规划问题 ,并采用投影梯度法建立了问题的优化方法。文中对几个典型问题进行了计算。与等厚度圆柱壳相比较 ,优化圆柱壳的最大当量应力得到了显著降低。本文的研究方法和结果可以用于指导大型圆柱壳体的加肋设计     

组合截面工程结构离散变量优化设计的通用模型及启发式算法

建立了组合截面离散变量优化设计的通用模型;提出了一种启发式求解算法。通过对截面设计变量的合并,把截面整体作为一个设计变量;将约束条件按其作用范围分为三类:局部约束、全局约束、中间约束,即介于局部和全局约束之间的约束;根据离散结构实体杆件在结构中受力和传力的特点,将杆件分为5类。针对三类约束的不同特点,分别给出了启发式求解算法。最后通过一个三维的空间结构实例给出验证,优化效率高,效果明显。六个工程实例的优化结果比经验设计可节省材料5.0～19.0%。实践表明本文提出的模型通用性强,启发式求解方法效率高且实用,适合大规模离散变量工程结构最轻设计问题。     

基于Kriging代理模型的结构形状优化方法研究

建立了一种进行结构形状优化的工程方法。该方法利用试验设计法选取位置变量样本点,并对各个样本点对应的结构进行尺寸优化,然后根据样本点和尺寸优化结果建立Kriging代理模型,再利用遗传算法求出位置变量最优解,进而得到结构最优解。最后进行了15杆平面拱式桁架、悬臂梁和25杆空间桁架三个形状优化算例,算例分析结果表明:该方法思路清晰、适应性强、优化效果明显,具有较大的工程应用价值。     

Measurement of yield points of high polymers with resistance-wire dynamometer

A new load dynamometer utilizing electricresistance wire consists of a cylinder around which the resistance wire is coiled tightly. When the cylinder is compressed axially and deforms elastically, the resistance wire is strained an amount equal to the circumferential strain of the cylinder resulting from Poisson's ratio. The dynamometer is designed with attention to electrical insulation, rate of heat dissipation, compensation for temperature change of electric resistance and material for the stressed body. The reading of this load dynamometer is not affected by the bending moment due to eccentric loading, and the bridge unbalance to be measured is larger than by any other type of strain gage utilizing resistance wire. This load dynamometer can be applied to the measuring of dynamic or transient changes in load. As one example, the tardy yielding phenomenon of thermosetting cast resins has successfully and reasonably been measured by this dynamometer without any inertia effect.     

SDRE-based near optimal nonlinear controller design for unified chaotic systems

This paper proposes a near optimal controller design method for unified chaotic systems based on state-dependent Riccati equation (SDRE) approach. A parameterization of the optimal nonlinear control gain is given in terms of the solution matrix of an SDRE. A simple algorithm to compute the near optimal control gain is proposed. The proposed near optimal control design method is also extended to the synchronization problem for unified chaotic systems. Finally, the effectiveness of the proposed design method is verified via numerical simulations.     

Prediction of drawbar test performance

Standard tests of agricultural tractors include measurement of drawbar performance on a concrete or tarmacadam surface. Because these tests are time-consuming and expensive, the possibility of replacing them with axle dynamometer tests is under consideration. To maintain comparability with conventional drawbar tests it would be desirable to estimate drawbar performance on a hard surface from results of axle dynamometer tests. This requires a method for predicting slip-pull relationships on a hard surface. Ninety-nine drawbar tests carried out in France, Germany, U.K. and U.S.A. have been analysed and equations of varying complexity derived to predict performance. It was found that, whereas drawbar pull at maximum drawbar power could be predicted fairly accurately, the corresponding slip and consequently maximum drawbar power could not be predicted with sufficient accuracy to enable valid comparisons to be made with drawbar tests. It is suggested that the reason for the kack of accuracy is the presence of unquantifiable variables such as differences in rubber compound, tread pattern or track condition. It is suggested that these throw doubt on the validity of the drawbar tests themselves as a means of comparison and suggestions are made of ways in which the test could be modified to make it more suitable for comparing different drawbar tests and for comparing drawbar tests with axle dynamometer tests.     

Optimal design of spiral casing tongue and wicket gate angle by decomposition method

A method of optimal design of Francis turbine tongue and wicket gate angle for given spiral casing is proposed. The potential flow in the doubly connected domain is decomposed into basic and circulation flows. The intensity of circulation is then calculated by the least-squares method minimizing the error function equal to the sum of squares of differences between given and calculated circumferential velocities in the outflow boundary nodes. It is shown that the error function has a sharp minimum, which qualifies the proposed method as well defined. For given numerical example, the variations in the outflow velocity angles are much smaller for optimal than for already used non-optimal design. A finite element method is used, with originally developed pre- and post-processor and frontal solver suited for personal computers.     

Optimization of the take-off movement of ski jumping with the method of mathematical programming

This paper is based on the finite and dispersed data which were obtained from the experiments of the wind tunnel and of the force measurement and from the high-speed photography. It analyses and optimizes the take-off movement of ski jumping with the theory of dynamics of systems of rigid bodies and with the method of mathematical programming. The paper describes the optimal take-off movement of ski jumping. Furthermore, it presents an example and compares the result with those of other papers published at home and abroad. The comparison shows that our computation and optimization are reasonable and well-grounded.