The method of separation for evolutionary spectral density estimation of multi-variate and multi-dimensional non-stationary stochastic processes

The method of separation can be used as a non-parametric estimation technique, especially suitable for evolutionary spectral density functions of uniformly modulated and strongly narrow-band stochastic processes. The paper at hand provides a consistent derivation of method of separation based spectrum estimation for the general multi-variate and multi-dimensional case. The validity of the method is demonstrated by benchmark tests with uniformly modulated spectra, for which convergence to the analytical solution is demonstrated. The key advantage of the method of separation is the minimization of spectral dispersion due to optimum time- or space–frequency localization. This is illustrated by the calibration of multi-dimensional and multi-variate geometric imperfection models from strongly narrow-band measurements in I-beams and cylindrical shells. Finally, the application of the method of separation based estimates for the stochastic buckling analysis of the example structures is briefly discussed.     

浅析常微分方程的常数变易法

常数变易法是解决一阶非齐次线性微分方程通解的有效方法．但是多数教材只讲解了使用方法，而没有给出此法的由来。讨论常数变易法的由来，并对其进行推广，从而加深对常数变易法的理解和掌握。     

Investigation of cohesive FE modeling to predict crack depth during deep-scratching on optical glasses

Optical glass scratching can induce various types of cracks, among which median cracks are extremely detrimental and penetrate deeply under the surface. Due to deep-scratching process complexity, it is challenging to devise a method to predict median crack depth. Indentation testing has been examined comprehensively in prior research works. It has been found that using the correlation between scratch and indentation testing can simplify predictive method development. In this research, a numerical method based on indentation testing is proposed to determine median crack depth during deep scratching. In the first step, an FE model is configured to simulate the indentation testing process and the Cohesive Zone Method is applied to describe median crack behavior. The cohesive parameters calibrated through experimental indentation testing are implemented in the FE scratch model, and the results are compared with the experimental scratch test results. According to the results, the FE scratch model was enhanced by mode II fracture energy and the modeled friction coefficient. The indentation and scratch experiments were conducted with BK7, F2, Fused silica, K5, Pyrex, Quartz, SF6, and SF19. The experimental results prove that the nonlinearity of the median crack depth curve correlates with K_Ic. A comparison of the experimental and numerical results demonstrates the model is virtually functional for materials with K_Ic below 1000?kPa?m^1/2. Comparisons between the current findings and other studies infer the model and experimental results are accurate and reliable.     

Evaluation of behavior of the secondary columns in semi-supported steel shear walls

Semi-supported steel shear walls (SSSW), whose steel plate is connected to secondary columns rather than main columns of the frame, have been considered as an alternative steel shear walls to the traditional type. Many investigations have been made for proportionate designing of components of SSSW system. One of the important issues in this regard is the out of plane buckling of the secondary columns. In this paper, the plastic theory of structures is utilized to find out the axial force distribution, along the compressive column. Then, using energy method, for an assumed shear wall with specific geometry and material and a given shear force, the maximum overturning moment that makes the compressive secondary column buckles, can be determined. Repeating this method, for various shear forces, makes it possible to draw some interaction curves between overturning moments and shear forces. These curves can be used to analyze and design of semi-supported steel shear walls.     

Automated quantitative model-based fault diagnosistic protocol via Assumption State Differences

This treatment describes the details of a systematic protocol useful for performing optimal automated process fault analysis. This implementation generalizes the underlying Boolean logic version of the Method of Minimal Evidence (MOME) developed previously to a highly comprehensive algorithm for performing model-based fault diagnostics. This generalization allows for a more compact treatment of potential single and multiple fault situations, at all levels of possible diagnostic resolution, with both elegant and efficient uniform sensor validation and proactive fault analysis (SV&PFA) diagnostic rules for diagnosing those situations. This Assumption State Differences (ASD) Protocol version of the MOME algorithm thus automates the diagnostic reasoning necessary to continuously perform optimal process fault analysis so that only the underlying well-formulated models are required to achieve such performance. Using this algorithm consequently directly simplifies the solution of the more complicated problem of automated process fault analysis into the much more tractable, and incrementally solvable, problem of adequately modeling normal process operations.     

非结构化改进差分法在波动方程中的应用

在计算声学领域中,有限差分法是一种比较传统的数值模拟方法.差分法简单易行而且效果突出,然而此方法只能在结构网格中使用,很难计算几何边界较为复杂的区域.基于高斯定理构造单元梯度的方式,在二维空间上,提出了一种改进的有限差分法(Improved Finite Difference Method,IFDM).IFDM可以使用...     

架盘扭力天平刻度盘示值误差及其校准方法

架盘扭力天平是由普通架盘天平改型的衡量仪器。由于没有相应的计量检定规程或校准规范,在校准其刻度盘示值误差时因方法不规范而存在诸多问题。本文作者根据多年从事计量检测工作的经验,对架盘扭力天平刻度盘示值误差的要求和校准方法提出了一些实用性建议。     

Design formulations for non-welded and welded aluminium columns using Continuous Strength Method

Aluminium members are used in structural applications due to their high strength-to-weight ratio, corrosion resistance, attractive appearance, recyclability, ease of production and availability. Thin aluminium sections are susceptible to buckling at a relatively low stress and welding makes it even worse; the design stress i.e. 0.2% proof stress is almost halved in the vicinity of the heat affected zones (HAZs). Currently available design codes have their guidelines both for welded and non-welded aluminium columns, but the predictions for welded aluminium columns are often quite inconsistent. The current research exploits a newly developed strain based design approach the ‘Continuous Strength Method’ (CSM) to predict the behaviour of aluminium members with SHS and RHS cross-sections subjected to compression. A new design curve is proposed herein to predict the cross-sectional resistance in compression; this concept is further extended to propose a new Perry type buckling curve to predict the flexural buckling resistance of aluminium columns. A simplified technique is proposed to include the effect of heat affected zone (HAZ) in CSM formulations. The CSM predictions for aluminium columns are compared against those obtained using available guidelines proposed by the European, American and Australian/ New Zealand standards of aluminium structures. The CSM predictions for non-welded columns are in line with the code predictions, whilst the proposed simple technique for transversely welded columns seems to produce significantly improved predictions.     

Application of the Direct Strength Method to local buckling resistance of thin-walled steel members with non-uniform elevated temperatures under axial compression

This paper assesses the applicability of the Direct Strength Method (DSM) to calculating the local buckling ultimate strength of cold-formed thin-walled (CF-TW) steel members with non-uniform elevated temperature distributions in the cross-section. The assessment was carried out by checking the DSM calculation results with numerical simulation results using the general finite element software ABAQUS which was validated against ambient and uniform elevated temperature tests on short lipped channel sections. The validated numerical model was used to generate an extensive database (372 models) of numerical results of load carry capacity of CF-TW members with different uniform and non-uniform temperature distributions in the cross-sections, under different boundary and loading conditions and with different dimensions and lengths. It was concluded that the DSM local buckling curve was directly applicable for columns with uniform temperature distributions in the cross-section. For columns with non-uniform temperature distributions, a modification to the local buckling curve was necessary and this paper has proposed a new curve.     

地下游泳池高大模板配置与安装

某地下游泳池顶板支模架高度、支模净空等达到了国家规定的危险性较大的分部分项工程标准,为确保安全施工并保证质量,对高大模板支撑体系进行专项设计并验算,采用扣件式钢管满堂支模架体系,确定了模板选型、支撑形式、间距、步距及节点做法,通过软件验算符合要求。