日本现代住宅应变边界对我国乡村住宅的启示——低碳视角下内外边界可变性的研究

作为建筑内外空间能量交换的媒介,内外边界是住宅低碳设计的重要内容。鉴于外部自然环境和内部居住需求并非一成不变,能够随之做出灵活回应的内外边界在住宅节能减排上将具有更多的潜力。本研究中,这种能够显著调节性质、形态或位置来回应各种变化的边界被定义为应变边界。日本现代住宅为探索现代技术背景下的应变边界提供了样本,而我国乡村住宅与日本的一户建(独栋住宅)在规模和建造环境上相近,这些样本中应变边界的低碳策略的研究对我国乡村住宅设计具有参考价值。本研究通过探讨“建具化”的日常可调边界、空间热舒适分区的季节性边界、利用材料可逆性的可再建边界3类应变边界在应对的变化因素、调节的时间跨度、调节带来的居住空间变化、低碳策略等方面的特征,总结了其对我国乡村住宅低碳设计的启示:1)引入和利用外部自然风能热能等能量,打破以阻隔内外能量交换为主的思维定势;2)不局限于绝对的数值标准,通过边界调节居住空间体验,提升居住者生理和心理舒适度;3)结合季节气候特征对居住空间进行热舒适需求细分,并采取不同的围护结构做法;4)考虑未来潜在的居住空间需求变小的应对策略;5)挖掘材料和构造方式潜在的可逆性。

平面应变边界元的位移反分析在阿拉坦隧道中的应用

隧道工程材料特性参数确定一直是人们应用各种方法定量认识的一大工程问题。结合阿拉坦隧道在施工过程中的监控量测所得位移,采用平面应变边界元BPM90程序对隧道岩体物理力学参数进行反分析,并用TSP地质资料说明位移反分析求解的岩体参数有比较高的可信度。

边界单元初应变法中域积分项的计算

利用适当坐标变换和张量转换关系,导出用边界单元初应变法求解弹塑性问题时边界积分方程中含初应变的域积分项的解析计算公式,并用算例验证了该公式的正确性。

粘弹性人工边界单元及地震动输入方法比较研究

本文引用一致粘弹性边界的概念,推导了与一致粘弹性边界等效的粘弹性边界单元,得到了粘弹性边界单元的刚度矩阵和阻尼矩阵。通过对比粘弹性边界单元阻尼系数不同取值的计算精度,给出了阻尼系数推荐取值。在输入地震动时,采用一种基于局部人工边界的子结构输入方法,实现了和波动法相同的输入效果,并且避免了复杂的应力计算和荷载作用方向判断等问题,应用更加方便。采用自由场的算例,比较了人工边界和不同输入方式的组合在SV波垂直入射时的模拟精度。为了说明边界单元的变形对计算结果的影响,提出了使用底边界输入位移幅值u max和边界单元宽度b的比值ε=u max/b作为变形指标,调节边界单元边长尺寸。通过算例给出了ε的推荐取值。最后,选取合适的ε后建立一个圆形孔洞散射场地模型,对散射场地模型的模拟结果验证了粘弹性边界单元和子结构输入方式应用于散射场地时仍具有较高精度。

工程应用中弹性力学问题的光滑边界有限元法研究

文章详细介绍了光滑有限元法(ES-FEM)的基本原理,并将其应用于求解弹性力学问题。ES-FEM采用光滑应变技术,在三角形单元边界围成的光滑区域内重构低阶有限元的应变场,从而改善低阶有限元系统矩阵"过刚"的问题。数值实验表明,ES-FEM的计算精度和效率都比FEM-T3的要高。

Mechanical model of control of key strata in deep mining

Based on the characteristic of deep rock layers and the theory of key strata,we analysed elastic mechanical characteristics of key strata by using elastic plate theory.The results show that the deformation and distribution of internal forces of key strata vary with different mine boundary conditions.The boundary values of key strata with three point boundaries and one fixed boundary is greater than that with four fixed boundaries.Considering the rheology of key strata under low stress conditions,we selected a generalized Kelvin model to analyse the rheology characteristics of the key strata and discovered their instantaneous elastic phases.The rate of deformation decreased over time to the point where the key strata reached stability.But over this time,the effect on deformation became very clear. For high stress conditions,we chose a Burgers model and found deformation of key strata in the form of attenuation and steady-state creep and although the rate of deformation remained constant,secondary creep was obvious,causing instability in the system.As well,we analysed the effect of creep buckling and derived a relation between buckling force and time.

An Extreme Value Approach to Test the Effect of Price Limits on Volatility

Many stock exchanges around the world enforcing daily price limits on the amount asset prices can change to prevent the market from overreacting and to reduce volatility. Price limits are artificial boundaries set by market regulators who restrict price changes of a stock to a pre-specified range during a trading day or a single trading session. The primary aim of price limit rules is to stabilize the markets during panic trading, to moderate vitality by repressing excessive speculation, and to allow stocks to be traded at prices close to their fair value. However, their impact on the market is a somewhat unresolved issue （Harris, 1998）. Using a methodology of comparing volatility based on the extreme value technique, the authors empirically investigate the impact of price limits on the volatility of the Stock Exchange of Thailand. The empirical results support price limits advocates, suggesting that price limits rules moderate stock price volatility.

A strain smoothing formulation for NURBS-based isogeometric finite element analysis

A strain smoothing formulation for NURBS (non-uniform rational B-splines) based isogeometric finite element analysis is presented. This approach is formulated within the framework of assumed strain methods and strain smoothing operations. The strain smoothing is defined through strain averaging in the element sub-domains which are subsequently used for numerical integration of the Galerkin weak form. This formulation satisfies the orthogonality condition of the assumed strain methods. Meanwhile the present formulation totally avoids the gradient computation of the rational NURBS basis functions in the formulation of stiffness matrix. A transformation method is employed to accurately enforce the displacement boundary conditions. Numerical results demonstrate that the present formation gives very satisfactory solution accuracy simultaneously with improved computational efficiency.

BOUNDS ON AVERAGE CONTROLLED DIRECT EFFECTS WITH AN UNOBSERVED RESPONSE VARIABLE

This paper considers the problem of estimating the bounds on the average controlled direct effects （ACDEs） of a treatment variable on an unobserved response variable in the presence of unobserved confounders between an intermediate variable and the response variable. When the response variable is observed, Cai, et al.（2008） derived the formulas for the sharp bounds on the ACDEs. When the response variable is unobserved, the authors propose a graphical criterion for selecting variables affected by the response variable to derive the formulas for the bounds on the ACDEs, which is an extension of the result of Kuroki（2005） to ACDEs. The results enable us not only to judge from the graph structure whether the bounds on the ACDEs can be expressed through observed variables when the response variable is unobserved, but also to provide their formulas when the answer is affirmative.

Modeling and behaviours of rockfill materials in three-dimensional stress space

A bounding surface model incorporating a unified nonlinear strength criterion is proposed.The proposed bounding surface model contains 9 model parameters,which can be determined from the conventional triaxial tests.The bounding surface model can reproduce such behaviours as the strain hardening,the post-peak strain softening,and the volumetric strain contraction and expansion.Based on the comparisons between the predictions and the test results,the proposed strength criterion and model can well reproduce the experimental results of the strength and stress-strain behaviours of rockfill material in three-dimensional stress space.The strength behaviour of rockfill material is summarized as:(a) the failure stress ratio decreases with the initial confining pressure on the meridian plane;(b) the failure deviatoric stress decreases with the Lode angle from 0o to 60o on the deviatoric plane.The stress ratio decreases with increasing one of such factors as the initial void ratio,the intermediate principal stress ratio and the minor principal stress at the same strain when the other factors are given.

Thermal stresses around a circular inclusion with functionally graded interphase in a finite matrix

Based on the theory of the complex variable functions, the analysis of non-axisymmetric thermal stresses in a finite matrix containing a circular inclusion with functionally graded interphase is presented by means of the least square boundary collocation technique. The distribution of thermal stress for the functionally graded interphase layer with arbitrary radial material parameters is derived by using the method of piece-wise homogeneous layers when the finite matrix is subjected to uniform heat flow. The effects of matrix size, interphase thickness and compositional gradient on the interfacial thermal stress are discussed in detail. Numerical results show that the magnitude and distribution of interfacial thermal stress in the inclusion and matrix can be designed properly by controlling these parameters.

Thermodynamic properties and constitutive relations of crystals at finite temperature

The dynamics equation for each individual atom is established directly around the equilibrium state of the system of N atoms based on the inter-atomic potential energy of EAM model.Using the theory of lattice dynamics and periodical boundary condition,the 3N×3N stiffness matrix in eigen equations of vibration frequencies for a parallelepiped crystal is reduced to a 3n×3n matrix of eigen equations of vibration frequencies for a unit lattice.The constitutive relation of the crystal at finite temperature is extracted based on the quantum-mechanical principle.The thermodynamic properties and the stress-strain relationships of crystal Cu with large plastic deformation at different temperatures are calculated,the calculation results agree well with experimental data.

Modeling of strength and deformation of overconsolidated clays based on bounding surface plasticity

An elastoplastic constitutive model for overconsolidated clays is established in the framework of the critical state theory and bounding surface plasticity theory. The bounding surface is defined as the maximum yield surface in the loading history. A yielding ratio, i.e., an internal variant, is defined as the size ratio of the current yield surface to the corresponding bounding surface. The yielding ratio instead of the overconsolidation ratio(OCR) is used to evaluate the strength and stress-strain behaviors of overconsolidated clays in the shearing process. The bounding stress ratio incorporating the effect of the yielding ratio is used to characterize the potential failure strength of the overconsolidated clays. The dilation stress ratio taking into account the effect of the yielding ratio is applied to describe the dilatancy behaviors of the overconsolidated clays. Comparisons between model predictions and test data show that the proposed model could well capture the strength and stress-strain behaviors of normally consolidated and overconsolidated clays.

Interaction between strain and vorticity in compressible turbulent boundary layer

The interaction of strain and vorticity in compressible turbulent boundary layers at Mach number 2.0 and 4.9 is studied by direct numerical simulation(DNS)of the compressible Navier-Stokes equations.Some fundamental characteristics have been studied for both the enstrophy producing and destroying regions.It is found that large enstrophy production is associated with high dissipation and high enstrophy,while large enstrophy destruction with moderate ones.The enstrophy production and destruction are also correlated with the dissipation production and destruction.Moreover,the enstrophy producing region has a distinct tendency to be‘sheet-like’structures and the enstrophy destroying region tends to be‘tube-like’in the inner layer.Correspondingly,the tendency to be‘sheet-like’or‘tube-like’structures is no longer obvious in the outer layer.Further,the alignment between the vorticity vector and the strain-rate eigenvector is analyzed in the flow topologies.It is noticed that the enstrophy production rate depends mainly on the alignment between the vorticity vector and the intermediate eigenvector in the inner layer,and the enstrophy production(destruction)mainly on the alignment between the vorticity vector and the extensive(compressive)eigenvector in the outer layer.