Finite-element dynamic inelastic analysis of beams and plates under combined loading

The response of beams and plates under multiple loading is considered taking into account the inelastic interactions between moments and axial (in-plane) forces. The plastic analysis is based on distribution of stresses and strains in three dimensions so that yielding remains a function of the uniaxial state of stress in beams and of the biaxial state of stress in plates. The interaction effects between dynamic transverse loads and static in-plane loads is studied by using initial stress stiffness matrices that modify the original stiffness matrices. Detailed response behavior of beams and plates in combined loading is presented. The response characteristics are found to exhibit interaction instability properties.     

基于应变测量的便携式汽车动态性能测试仪

汽车动态性能是评价汽车安全性的重要指标之一。介绍了一种基于应变测量的便携式汽车动态性能测试仪的原理、系统结构及实验结果,该测量仪具有成本低、体积小、测量结果可靠的特点。测试结果表明:该仪器对汽车动态性能的综合评价具有较高的实用性。     

Intelligent health monitoring of aerospace composite structures based on dynamic strain measurements

This work presents a study on an intelligent system for structural health monitoring of aerospace structures based on dynamic strain measurements, in order to identify in an exhaustive way the structural state condition. Four fiber Bragg grating (FBG) optical sensors were used for collecting strain data, representing the dynamic response of the structure and the expert system that was developed was based on the collected response data. Multi-sensor data fusion in a feature-level approach was followed. Advanced signal processing and pattern recognition techniques such as discrete wavelet transform (DWT) and support vector machines (SVM) were used in the system. For the current analysis, independent component analysis (ICA) was additionally used for the reduction of feature space. The results showed that SVMs using non-linear kernel is a powerful and promising pattern recognition scheme for damage diagnosis.The system was developed and experimentally validated on a flat stiffened composite panel, representing a section of a typical aeronautical structure. Within the frame of the present work the flat stiffened panel was manufactured using carbon fiber pre-pregs. Damage was simulated by slightly varying the mass of the panel in different zones of the structure by adding lumped masses. The analysis of operational dynamic responses was employed to identify both the damage and its position. Numerical simulation with finite element analysis (FEA) was also used as a support tool.     

The analysis of stress and strain at the videotex workplace

Abstract

Analyses of work demands, stress and strain were carried out at videotex workplaces in the laboratory and in private households. The demand analysis showed that a high degree of information resolution and accuracy during information reception leads to high strain and eye fatigue. This effect is increased by a heavy flicker of the CRT screen, an inadequate choice of colour contrast, an inadequately low CRT resolution, and an inadequately small distance between the worker and the screen. High demands in the field of information processing are caused by the degree of difficulty in extracting relevant information from the videotex system using the search trees. In addition, the application of a checklist for CRT workplaces indicates more than 30 design faults. The analysis of the subjective perception of strain showed a significant decrease of the motivation levels following videotex sessions, and a significant increase of the strain level. The only individual factor to increase during videotex sessions was self-confidence. A comparison with findings of Udris and Barth (1976) showed that even videotex sessions which are much shorter than an eight-hour working day result in strain reactions similar to those occurring for eight hours of card-punching.     

The analysis of stress and strain at the videotex workplace

Analyses of work demands, stress and strain were carried out at videotex workplaces in the laboratory and in private households. The demand analysis showed that a high degree of information resolution and accuracy during information reception leads to high strain and eye fatigue. This effect is increased by a heavy flicker of the CRT screen, an inadequate choice of colour contrast, an inadequately low CRT resolution, and an inadequately small distance between the worker and the screen. High demands in the field of information processing are caused by the degree of difficulty in extracting relevant information from the videotex system using the search trees. In addition, the application of a checklist for CRT workplaces indicates more than 30 design faults. The analysis of the subjective perception of strain showed a significant decrease of the motivation levels following videotex sessions, and a significant increase of the strain level. The only individual factor to increase during videotex sessions was self-confidence. A comparison with findings of Udris and Barth (1976) showed that even videotex sessions which are much shorter than an eight-hour working day result in strain reactions similar to those occurring for eight hours of card-punching.     

Identifiability of errors in variables dynamic systems

There has been substantial research carried out on the errors in variables (EIV) identifiability problem for dynamic systems. These results are spread across a significant volume of literature. Here, we present a single theorem which compactly summarizes many of the known results. The theorem also covers several cases which we believe to be novel. We analyze single input single output systems using second order properties. We also extend the results to a class of multivariable systems.     

Self-correction of errors in discrete dynamic systems

The ability of a discrete dynamic system for correcting functional errors is investigated. A method for enhancing the degree of self-correction is described.     

Topology optimization of dynamic stress response reliability of continuum structures involving multi-phase materials

This paper proposes a methodology for maximizing dynamic stress response reliability of continuum structures involving multi-phase materials by using a bi-directional evolutionary structural optimization (BESO) method. The topology optimization model is built based on a material interpolation scheme with multiple materials. The objective function is to maximize the dynamic stress response reliability index subject to volume constraints on multi-phase materials. To solve the defined topology optimization problems, the sensitivity of the dynamic stress response reliability index with respect to the design variables is derived for iteratively updating the structural topology. Subsequently, an optimization procedure based on the BESO method is developed. Finally, a series of numerical examples of both 2D and 3D structures are presented to demonstrate the effectiveness of the proposed approach.

     

材料热力学参数测试装置的结构设计和稳态热分析

为解决现有管式炉在高温烧结时存在不能测量温度和变形的问题,以现有管式炉为基础,设计并改进一种用于测试高温条件下材料热力学参数的装置。通过ANSYS Workbench对该测试装置的管式炉结构进行建模,采用实体单元对结构进行模拟;对管式炉结构进行稳态热分析,并得到法兰的温度,评估配置冷却系统的必要性;利用参数优化方法,得到法兰2右端温度为40 ℃时冷却系统需要具备的对流传热系数,为冷却系统中模温机的选型提供指导。     

Using genetic algorithms for early schedulability analysis and stress testing in real-time systems

Reactive real-time systems have to react to external events within time constraints: Triggered tasks must execute within deadlines. It is therefore important for the designers of such systems to analyze the schedulability of tasks during the design process, as well as to test the system's response time to events in an effective manner once it is implemented. This article explores the use of genetic algorithms to provide automated support for both tasks. Our main objective is then to automate, based on the system task architecture, the derivation of test cases that maximize the chances of critical deadline misses within the system; we refer to this testing activity as stress testing. A second objective is to enable an early but realistic analysis of tasks' schedulability at design time. We have developed a specific solution based on genetic algorithms and implemented it in a tool. Case studies were run and results show that the tool (1) is effective at identifying test cases that will likely stress the system to such an extent that some tasks may miss deadlines, (2) can identify situations that were deemed to be schedulable based on standard schedulability analysis but that, nevertheless, exhibit deadline misses.

Studies on stress concentration in tensile strips with large circular holes

The stress concentration factor K in a tensile strip with large circular hole is accurately determined using a high precision, plane stress, triangular element. The values of a/w where a is the diameter of the hole and w is the width of the strip, considered range from 0.99 to 0.999. The values of K obtained found to be very near to but greater than 2.0, when linear analysis is performed. Some discrepancies in the stress values at the outer free edge observed in the present linear analysis compared to the well documented experimental values prompted the authors to go for geometrically nonlinear analysis gave a K value which is a function of the load applied, less than 2.0 and for sufficiently large loads this value is very near but slightly greater than 1.0.     

Mental strain and the problem of repeated measurements

In the past, stress and strain arising from the execution of mentally demanding tasks have been measured by means of surveys. Such methods require repeated investigation of the individual perceptions and valuations during task fulfilment to record time-dependent changes in strain levels. However, it is possible that the individual measurement procedures employed in surveys-as artefacts-may cause a change in the stress situation and subsequently in the resulting mental strain. The results of the experiments carried out to investigate this hypothesis verify that repeated measurements have a similar effect as a short break. The repeated measurements taken during progressive studies are, therefore, likely to affect the conditions of stress. A change in the level of mental strain recorded can be expected, particularly if the post-test rating is preceded by a long period of low stress before or during which an additional measurement of strain is implemented.     

Performance analysis in a probabilistic re-entrant for an environmental stress testing operation

This paper presents an extended approximation model based on mean value analysis (MVA) technique for a probabilistic re-entrant line. The objective is to develop a solution method to determine the total cycle time and mean throughput of the environmental stress testing (EST) operation for a given number of lots loaded into the system. Further work was done to determine the maximum number of lots that can be loaded into the system and the target cycle time. This paper also looks at alternative ways to assign human resources within the operation in the event of large number of lots required. Using analytical and simulation methods, comparison results were made for a five-stage queuing system with re-entrant lines into the second stage under various probabilistic routing conditions. The method proposed can be used by operation managers to determine their lots’ cycle times, maximum number of lots and the operator assignments.     

路由器动态性能指标测试方法研究

路由器是整个网络互连环境中的关键设备之一。目前针对路由器性能测试,相关的标准和规范（如Request For Comment,RFC）描述得相当笼统,只有大致的测试框架和过程,没有具体的测试方法。尤其是,标准和规范中给出的是一种静态理想测试环境,不能测试路由器在实际应用中的真实性能。因此,以相关标准和规范为依据,设计了变化动态的测试环境,以尽量仿真实际网络环境中流的真实参数及其变化情况,因而其测试结果更接近真实网络环境下路由器的性能。在此基础上,基于一种多元统计方法--主成分分析法,提出了一种针对路由器必测性能指标的综合评价方案,为路由器设备的选型、性能的评价提供了一种新的参考指标。     

Mental strain and the problem of repeated measurements

In the past, stress and strain arising from the execution of mentally demanding tasks have been measured by means of surveys. Such methods require repeated investigation of the individual perceptions and valuations during task fulfilment to record time-dependent changes in strain levels. However, it is possible that the individual measurement procedures employed in surveys--as artefacts--may cause a change in the stress situation and subsequently in the resulting mental strain. The results of the experiments carried out to investigate this hypothesis verify that repeated measurements have a similar effect as a short break. The repeated measurements taken during progressive studies are, therefore, likely to affect the conditions of stress. A change in the level of mental strain recorded can be expected, particularly if the post-test rating is preceded by a long period of low stress before or during which an additional measurement of strain is implemented.     

A unified analysis for stress/strain hybrid methods of high performance

Several methods have been developed in the literatures of computational mechanics to improve the performance of the conventional lower-order displacement finite elements which yield poor results for problems with bending and for nearly incompressible medium. This paper is devoted to a unified analysis of convergence for Pian–Sumihara’s, Chen–Cheung’s and Piltner–Taylor’s enhanced stress/strain schemes. By virtue of the energy compatibility and the rank condition, error estimates for these typical finite elements of high performance are obtained in a unified framework, and especially, weakly locking-free error estimates with respect to the Poisson’s ratio ν in energy norms are obtained uniformly for ν⩽(1−Ch)/2 as h→0, where C is a constant independent of ν and the mesh size h. Very much the same about the three methods is pointed out.     

Effects of measurement errors on psychometric measurements in ergonomics studies: Implications for correlations,ANOVA, linear regression,factor analysis,and linear discriminant analysis

This paper aims to demonstrate the effects of measurement errors on psychometric measurements in ergonomics studies. A variety of sources can cause random measurement errors in ergonomics studies and these errors can distort virtually every statistic computed and lead investigators to erroneous conclusions. The effects of measurement errors on five most widely used statistical analysis tools have been discussed and illustrated: correlation; ANOVA; linear regression; factor analysis; linear discriminant analysis. It has been shown that measurement errors can greatly attenuate correlations between variables, reduce statistical power of ANOVA, distort (overestimate, underestimate or even change the sign of) regression coefficients, underrate the explanation contributions of the most important factors in factor analysis and depreciate the significance of discriminant function and discrimination abilities of individual variables in discrimination analysis. The discussions will be restricted to subjective scales and survey methods and their reliability estimates. Other methods applied in ergonomics research, such as physical and electrophysiological measurements and chemical and biomedical analysis methods, also have issues of measurement errors, but they are beyond the scope of this paper. As there has been increasing interest in the development and testing of theories in ergonomics research, it has become very important for ergonomics researchers to understand the effects of measurement errors on their experiment results, which the authors believe is very critical to research progress in theory development and cumulative knowledge in the ergonomics field.     

The effect of testing location on usability testing performance, participant stress levels, and subjective testing experience

The effect of testing location on usability test elements such as stress levels and user experience is not clear. A comparison between traditional lab testing and synchronous remote testing was conducted. The present study investigated two groups of users in remote and traditional settings. Within each group participants completed two tasks, a simple task and a complex task. The dependent measures were task time taken, number of critical incidents reported, and user-reported anxiety score. Task times differed significantly between the physical location condition; this difference was not meaningful for real world application, and likely introduced by overhead regarding synchronous remote testing methods. Critical incident reporting counts did not differ in any condition. No significant differences were found in user reported stress levels. Subjective assessments of the study and interface also did not differ significantly. Study findings suggest a similar user testing experience exists for remote and traditional laboratory usability testing.     

Body measurements of Chinese males in dynamic postures and application

It is generally accepted that there is a relationship between body dimensions, body movement and clothing wearing ease design, and yet previous research in this area has been neither sufficient nor systematic. This paper proposes a method to measure the human body in the static state and in 17 dynamic postures, so as to understand dimensional changes of different body parts during dynamic movements. Experimental work is carried out to collect 30 measurements of 10 male Chinese subjects in both static and dynamic states. Factor analysis is used to analyse body measurement data in a static state, and such key measurements describe the characteristics of different body figures. Moreover, one-way ANOVA is used to analyse how dynamic postures affect these key body measurements. Finally, an application of the research results is suggested: A dynamic block patternmaking method for high-performance clothing design.