关于流体力学方法论问题

 力学是以实验为基础的科学. 流体力学中绝大多数重要的概念和原理都源于实验. 对 于流体力学问题，数值模拟与物理实验的本质区别并未消失；数值模拟不能代替物理实验， 大规模数值模拟的结果仍需由巧妙设计的物理实验来检验其正确性.     

力学史与方法论研究应当肩负的重任

提出力学史与方法论研究和教学中应当关注的3个问题: 力学学科的性质问 题、发掘搜集和整理我国的力学学科的历史资料问题和力学史需要放眼世界的问题.     

Data processing methodology in the characterization of the mechanical properties of terrain

The methodology for processing load-sinkage and shear test data obtained using the bevameter is examined. A weigthed least squares technique is proposed for deriving terrain values from experimental data. To streamline data processing time, a portable automatic data processing unit for the bevameter has been developed. The basic features and functions of the unit are described. The automatic data processing unit, together with associated bevameter, has undergone extensive field trials. They have been employed to measure the properties of various types of natural terrain. The results indicate that this new system can provide a basis for the development of a reliable, convenient and standardized technique for identifying terrain properties in relation to off-road mobility.     

A methodology to model the complex morphology of rough interfaces

A methodology is proposed to model the complex morphology of rough interfaces using Fourier techniques and image analysis. It allows an optimal representation of a rough interface so as to enable a realistic calculation of the local stress and strain fields in the interface vicinity using finite element techniques. The methodology is illustrated through a sensitivity analysis carried out on a thermal barrier coating system. Typical bi-material interfaces with different levels of morphological complexity are described in 2D and 3D using both periodic (sinusoidal) and Fourier functions. The results are discussed in terms of their relative accuracy.     

A numerical methodology for investigating the formation of adiabatic shear bands

In this paper, we present a numerical approach for analyzing thermo-visco-plastic deformation in one dimension. The method, which is accurate to second order, is based on integration along the characteristic lines. It is able to simulate fully localized plastic flow with high resolution and good efficiency. We apply this numerical scheme to the analysis of shear localization, emphasizing the interactions between a single shear band and its surroundings and among the members of a periodic array of shear bands. It is found that a shear band may grow intermittently due to interactions with other bands. The developed method is specifically adequate for analyzing the self-organized multiple adiabatic formation process, which will be discussed in the follow-up paper.     

A non-intrusive methodology for the representation of crack growth stochastic processes

In this paper, we present a methodology to pursue the uncertainty quantification of the stochastic process that represents the crack growth problem. The main idea of this methodology is to discretize the crack growth process in a sequence of random variables and then, approximate each of them using a stochastic polynomial approach. This methodology is non-intrusive, i.e. it is based on the representation of random variables using stochastic polynomials, whose coefficients are evaluated using a least squares method and only a few realizations of the stochastic process. The Paris–Erdogan law was used as crack growth model in order to focus the reader's attention on the uncertainty quantification methodology. We modeled the parameters of the Paris–Erdogan law as random variables, i.e. the initial crack length and the coefficients of the Paris–Erdogan model are treated as random variables. Two numerical examples are presented in order to shown the effectiveness and accuracy of the proposed methodology. From the results of these examples, it is shown that the proposed methodology is able to successfully approximate the stochastic process that represents the crack growth for the Paris–Erdogan model, with a much lower computational cost than the MCS. The main limitation of the proposed approach is that, in the form it was presented, it is not able to handle random processes as input parameters.     

PANSYSTEMS METHODOLOGY AND CONSTRUCTION OF MAGIC SQUARES

ＩｎｔｒｏｄｕｃｔｉｏｎＡｒｅｆｉｎｅｄｅｐｉｔｏｍｅｏｆｖａｒｉｏｕｓｐａｎｓｙｓｔｅｍｓｍｅｔｈｏｄｓｉｓｔｏｃｏｍｐｒｅｈｅｎｄａｎｄｏｐｅｒａｔｅａｂｏｕｔ 2 0ｐａｎｓｙｓｔｅｍｓｃａｔｅｇｏｒｉｅｓｗｈｉｃｈｃａｎｂｅｅｘｐａｎｄｅｄａｓｔｈｅｆｏｌｌｏｗｉｎｇｐｉｔｈｙｆｏｒｍｕｌａｓｅｘｐｒｅｓｓｉｏｎｓ:Ｔｈｅｐａｎｄｅｒｉｖａｔｉｖｅｓ (ｏｒｔｈｅｃｈａｎｇｅ＿ｃｈａｎｇｅｒｅｌａｔｉｏｎｓ)ｏｆｔｈｅｅｘｔｅｒｉｏｒ＿ｉｎｔｅｒｉｏｒ(ｏｒｔｈｅｆｕｎｃｔｉｏｎ＿ｓｔｒｕｃｔｕ…     

周培源先生学术思想初探

周培源先生是蜚声海内外的著名理论物理学家、流体力学家、教育家和社会活动家,是我国力学事业的奠基人之一. 他在爱因斯坦广义相对论引力论和湍流理论领域攻坚70余年,取得了卓越的成就. 通过周培源先生的生平、学术成就及学术品格方面的重要事迹初步探索周培源先生的学术思想,以共享这宝贵的精神财富.     

刘先志先生学术思想初探

著名力学家、教育家刘先志先生离开我们16年了．为了纪念刘先志先生百年诞辰,探索他的学术思想,我再次研读《刘先志论文集》,从中感受他当年的研究历程,领悟他的研究思路,学习他的研究方法和成果．该文集收录了刘先志先生在1953年-1981年期间撰写的,刊登在(《Zeitschrift fuer Angewandte Mathematik und Physik》、《Ingenieur Archiv》、《中国科学》、《力学学报》、《应用数学和力     

关于土力学理论模型与科研方法的思考(续)

科学研究是创造性的工作，笔者感到以下几点是很有益的．     

A proposed methodology for the design and characterisation of concrete screw anchors

In recent years the construction fixings industry has begun to look to the concrete screw anchor to alleviate lengthy installation cycles and expansion issues, whilst introducing temporary fixing capability and suitability for use in cracked concrete. The screw anchor, often used in heavy-duty structural applications, operates on a mechanical interlock principle by creating a threaded cut in the substrate. Previous research has revealed this operational principle to show similarities to both expansion and chemical anchors—the two predominant fixings systems in current construction practice. Still in its infancy, the product lacks a certified test procedure and program for attaining technical approvals. This paper describes the development of an improved methodology for analysing the performance of the concrete screw anchor both physically and theoretically. Having reviewed the current test procedures, a range of products available on the market were assessed manually in the interest of developing an understanding of product operation. Standard test approaches were then customised to suit the unique product characteristics, before continuing to gather performance data. This research work then focuses upon theoretical performance calculation. Currently two theoretical models are potentially applicable to the concrete screw anchor; the concrete capacity method and the bond strength calculation method. Through comparison of the physical test data and the two current theoretical models, realisation of partial conformity with each model pointed towards promising routes for future research and a foundation for improved design of the product.     

关于土力学理论模型与科研方法的思考

为了提高研究生的理论水平和科研创新能力,在研究生教育中加强了理论模型和科研方法方面的素质教育,结合笔者多年从事岩土力学与工程的教学与科研的经验,对理论模型的定义、作用、结构,建模的原则、方法、过程、关键及修正方法,理论模型的评价标准等做了系统的阐述,并针对岩土力学创新研究提出了10点意见.     

A methodology to achieve the set of operation modes of reconfigurable parallel manipulators

The demand for increasingly more versatile machinery has boosted the development of the so-called reconfigurable mechanisms. In this paper, the authors present a general methodology to assess the multioperational capacity of a 6-DOF parallel manipulator basing on the possible motion patterns having Lie group structure that the manipulator owns. This ability of having different operation modes enables the manipulator to adapt to diverse tasks. To show the potential of the methodology, this approach has been applied to the 6-DOF 3-CPCR which is capable of generating multiple motion patterns. In addition to carrying out the complete theoretical study in which all the different operation modes are obtained, and validating the procedure with GIM software designed for kinematic analysis and design of mechanisms, a demonstration prototype of the 3-CPCR parallel manipulator has been also built.

     

高空长航时无人机高升阻比两段翼型设计研究

针对某特定无人机的使用设计要求,在单段翼型设计研究的基础上,尝试了高升阻比低雷诺数两段翼型的设计方法的分析与研究.采用求解椭圆型方程加控制点约束条件的"椭圆-控制点切割法"完成了两段翼型外形的生成,并针对巡航构型的襟翼偏角对缝道参数进行了优化;应用MSES计算分析程序对所设计的两段翼型的气动特性进行了分析评估.计算结果表明:本文所设计的两段翼型的最大升力系数达到2.72,最大升阻比为158.71;与原始单段翼型相比,最大升力系数增大了74.35%,最大升阻比增大了28.64%.     

A wavelet-based methodology for monitoring thermoelastic structures

A wavelet-based methodology for detecting critical events in displacement and temperature histories, obtained by monitoring in-situ thermoelastic structures, is proposed. It is based on the wavelet analysis of thermoelastic potentials furnishing also the possibility to detect separately cases in which sudden jumps occur in the displacement history from those in which they occur on temperature history.     

Bonded-particle model calibration using response surface methodology

The bonded-particle model (BPM) is commonly used in numerical analysis of the mechanical behavior of rock samples. Constructing a BPM model requires specification of a number of microstructural parameters, including the parallel-bond tensile strength, parallel-bond cohesion strength, parallel-bond effective modulus, parallel-bond friction angle, and parallel-bond stiffness ratio. These parameters cannot be easily measured in the laboratory or directly related to either measurable or physical material parameters. Hence, a calibration process is required to choose the values to be used in simulations of physical systems. In this study, response surface methodology along with the central composite design approach is used to calibrate BPMs. The sensitivities of the microparameters related to the uniaxial compressive strength (UCS) and elasticity modulus (i.e., the macroscopic responses of the models) are thoroughly scrutinized. Numerical simulations are performed to carefully assess the performance of the model. It is found that the elasticity modulus is highly correlated with the parallel-bond effective modulus. In addition, the parallel-bond tensile and cohesion strengths are the two most significant microparameters with a considerable effect on the UCS. The predicted values determined by the proposed approach are in good agreement with the observed values, which verifies the applicability of the proposed method.     

A methodology for the development of discrete adjoint solvers using automatic differentiation tools

A methodology for the rapid development of adjoint solvers for computational fluid dynamics (CFD) models is presented. The approach relies on the use of automatic differentiation (AD) tools to almost completely automate the process of development of discrete adjoint solvers. This methodology is used to produce the adjoint code for two distinct 3D CFD solvers: a cell-centred Euler solver running in single-block, single-processor mode and a multi-block, multi-processor, vertex-centred, magneto-hydrodynamics (MHD) solver. Instead of differentiating the entire source code of the CFD solvers using AD, we have applied it selectively to produce code that computes the transpose of the flux Jacobian matrix and the other partial derivatives that are necessary to compute sensitivities using an adjoint method. The discrete adjoint equations are then solved using the Portable, Extensible Toolkit for Scientific Computation (PETSc) library. The selective application of AD is the principal idea of this new methodology, which we call the AD adjoint (ADjoint). The ADjoint approach has the advantages that it is applicable to any set of governing equations and objective functions and that it is completely consistent with the gradients that would be computed by exact numerical differentiation of the original discrete solver. Furthermore, the approach does not require hand differentiation, thus avoiding the long development times typically required to develop discrete adjoint solvers for partial differential equations, as well as the errors that result from the necessary approximations used during the differentiation of complex systems of conservation laws. These advantages come at the cost of increased memory requirements for the discrete adjoint solver. However, given the amount of memory that is typically available in parallel computers and the trends toward larger numbers of multi-core processors, this disadvantage is rather small when compared with the very significant advantages that are demonstrated. The sensitivities of drag and lift coefficients with respect to different parameters obtained using the discrete adjoint solvers show excellent agreement with the benchmark results produced by the complex-step and finite-difference methods. Furthermore, the overall performance of the method is shown to be better than most conventional adjoint approaches for both CFD solvers used.