Regression models for predicting peak and continuous three-dimensional spinal loads during symmetric and asymmetric lifting tasks

Most biomechanical assessments of spinal loading during industrial work have focused on estimating peak spinal compressive forces under static and sagittally symmetric conditions. The main objective of this study was to explore the potential of feasibly predicting three-dimensional (3D) spinal loading in industry from various combinations of trunk kinematics, kinetics, and subject-load characteristics. The study used spinal loading, predicted by a validated electromyography-assisted model, from 11 male participants who performed a series of symmetric and asymmetric lifts. Three classes of models were developed: (a) models using workplace, subject, and trunk motion parameters as independent variables (kinematic models); (b) models using workplace, subject, and measured moments variables (kinetic models); and (c) models incorporating workplace, subject, trunk motion, and measured moments variables (combined models). The results showed that peak 3D spinal loading during symmetric and asymmetric lifting were predicted equally well using all three types of regression models. Continuous 3D loading was predicted best using the combined models. When the use of such models is infeasible, the kinematic models can provide adequate predictions. Finally, lateral shear forces (peak and continuous) were consistently underestimated using all three types of models. The study demonstrated the feasibility of predicting 3D loads on the spine under specific symmetric and asymmetric lifting tasks without the need for collecting EMG information. However, further validation and development of the models should be conducted to assess and extend their applicability to lifting conditions other than those presented in this study. Actual or potential applications of this research include exposure assessment in epidemiological studies, ergonomic intervention, and laboratory task assessment.     

从面向功能到面向对象模型的转换策略研究

有不少软件公司在软件开发过程中同时使用了面向功能的和面向对象的技术,例如在开发某一系统时,在采用了面向功能的分析模式后又使用了面向对象的设计方法,因此找到一种方法来实现从一种模式向另一种模式的转换是相当有必要的.提出了一种灵活可行的从面向功能的分析模型到面向对象的设计模型的转换策略.     

Topology optimization framework for structures subjected to stationary stochastic dynamic loads

The field of topology optimization has progressed substantially in recent years, with applications varying in terms of the type of structures, boundary conditions, loadings, and materials. Nevertheless, topology optimization of stochastically excited structures has received relatively little attention. Most current approaches replace the dynamic loads with either equivalent static or harmonic loads. In this study, a direct approach to problem is pursued, where the excitation is modeled as a stationary zero-mean filtered white noise. The excitation model is combined with the structural model to form an augmented representation, and the stationary covariances of the structural responses of interest are obtained by solving a Lyapunov equation. An objective function of the optimization scheme is then defined in terms of these stationary covariances. A fast large-scale solver of the Lyapunov equation is implemented for sparse matrices, and an efficient adjoint method is proposed to obtain the sensitivities of the objective function. The proposed topology optimization framework is illustrated for four examples: (i) minimization of the displacement of a mass at the free end of a cantilever beam subjected to a stochastic dynamic base excitation, (ii) minimization of tip displacement of a cantilever beam subjected to a stochastic dynamic tip load, (iii) minimization of tip displacement and acceleration of a cantilever beam subjected to a stochastic dynamic tip load, and (iv) minimization of a plate subjected to multiple stochastic dynamic loads. The results presented herein demonstrate the efficacy of the proposed approach for efficient multi-objective topology optimization of stochastically excited structures, as well as multiple input-multiple output systems.

     

基于机器视觉的口杯酒瓶盖旋转角度测量方法

针对口杯酒瓶盖对激光打码角度的特殊要求,研究一种口杯酒瓶盖旋转角度测量方法,该方法提出使用几何法与模板匹配法两种方法测量口杯酒拉环及中心文字与水平线的角度。其中,几何法通过连通域搜索和计算重心,定位圆环感兴趣区域,基于圆环被拉环切割部分的特征,得到凹凸方向的特征加强区域,有效计算出口杯酒瓶盖拉环与水平线之间的角度。模板匹配法通过分析在理想情况下口杯酒的文字字样,得到文字字样轮廓,平滑轮廓,并以此作为匹配时的形状模型。匹配过程中,对新图像查找形状模型,得出口杯酒中心文字与水平线的角度。该测量方法高速、准确、稳定,满足高速生产线的实时在线检测需求,解决了现有的口杯酒瓶盖激光打码的问题。     

Automated structural synthesis for nondeterministic loads

Optimal design of structural systems subjected to probabilistic loads is posed as a standard nonlinear programming problem. The salient complexities of the problem are identified and solution strategies are proposed. Realistic design constraints pertaining to structural integrity of the optimized design are formulated. Structural fatigue is examined from the standpoint of crack propagation rates. The optimization system consists of a sequence of finite element subroutines interfaced with a feasible directions optimization algorithm through the COMMAND language on a VAX 11-750 computer. Representative numerical results are presented.     

An imbedding method for buckling loads

An imbedding method for determining the critical length of buckling columns is presented. The method can be applied to a large class of problems and requires the integration of only one initial value equation. Integration proceeds until the integral becomes excessively large, indicating that the critical length has been reached. Alternately the reciprocal of the equation can be integrated, and the critical length determined by the zero crossing. Utilizing this method the critical length for an example is shown to be obtained to an accuracy of greater than of one percent. Computation time is less than approximately 3 sec.

In this development, new imbedding equations are obtained.     

Multiround algorithms for scheduling divisible loads

Divisible load applications occur in many fields of science and engineering and can be easily parallelized in a master-worker fashion, but pose several scheduling challenges. While a number of approaches have been proposed that allocate load to workers in a single round, using multiple rounds improves overlap of computation with communication. Unfortunately, multiround algorithms are difficult to analyze and have thus received only limited attention. In this paper, we answer three open questions in the multiround divisible load scheduling area: 1) how to account for latencies, 2) how to account for heterogeneous platforms, and 3) how many rounds should be used. To answer 1), we derive the first closed-form optimal schedule for a homogeneous platform with both computation and communication latencies, for a given number of rounds. To answer 2) and 3), we present a novel algorithm, UMR. We evaluate UMR in a variety of realistic scenarios.     

车辆橡胶防尘罩静力学特性分析

通过橡胶标准试件的轴向拉伸试验,得到有限元计算所需要的材料模型参数,分析了车辆防尘罩结构的刚度和强度,以及实际工况下防尘罩结构与轴杆是否存在干涉.根据橡胶产品的国家标准进行标准试样的拉伸试验,采用有限元模型中建立材料模型和建立相应的标准试样和橡胶防尘罩产品的有限元模型,并通过非线性有限元软件MSC-Marc进行了计算,得到标准试样和橡胶防尘罩产品的刚度,计算结果与原理分析吻合,从而验证了有限元计算中所建立材料模型是正确的,并对有限元软件分析的橡胶防尘罩应力分布问题.计算结果表明,能满足车辆防尘罩静力学分析的需要.     

Nonlinear response of undrained clay to footings

An analytical study of the static response of a homogeneous undrained clay stratum to footing loads is presented. Clay is modeled as a linear elastic-perfectly plastic material with the von Mises yield condition and associated flow rule. The effect of large deformations on the response of the clay is included in the analysis. Numerical results are obtained within the framework of the finite element method and a step-by-step integration procedure. In particular a single, strip surface footing bearing on a finite stratum of undrained clay is considered. The footing is assumed to be rigid and the interface between the footing and soil may be either smooth or rough. The base of the soil stratum is rigid and perfectly rough. A plane strain condition is assumed. Load-displacement curves, stress distributions, zones of yielding and velocity fields are presented. It was found that for a rough footing bearing on a undrained clay, the mode of failure corresponds to the so-called Prandtl velocity field. For a smooth footing, however, the failure mechanism appears to be a combination of the Hill and Prandtl type velocity fields.     

Nonlinear response of drained clay to footings

An analytical study of the static response of a homogeneous drained clay stratum to footing loads is presented. Clay is modelled as a linear elastic-perfectly plastic material with the Drucker-Prager yield condition and associated flow rule. The effect of large deformations on the response of the clay is included in the analysis. Numerical results are obtained within the framework of the finite element method and a step-by-step integration procedure.In particular a single, strip surface footing bearing on a finite stratum of overconsolidated clay is considered. The footing is assumed to be rigid and the interface between the footing and soil may be either smooth or rough. The base of the soil stratum is rigid and perfectly rough. A plane strain condition is assumed. Load-displacement curves, stress distributions, zones of yielding and velocity fields are presented. It was found that for a rough footing bearing on a weightless clay, the mode of failure corresponds to the so-called Prandtl velocity field. For a smooth footing, however, the failure mechanism contains elements of both the Hill and Prandtl type velocity fields.     

Intra-abdominal pressure responses of mineworkers to standard loads

Intra-abdominal pressure (IAP) has been used as the basis for a series of force limits for manual handling based on a limiting pressure criterion of 12 kPa (90 mm Hg). Measurements of the IAP responses to a series of standard loads were carried out on a group of eight instructors from the British coal mining industry. The results showed that there was a very low probability (.0016 or less) of obtaining an IAP value of 12 kPa or greater from the population represented by our sample. Average responses were 33% lower than would have been expected from previous reports on force limits based on IAP measurements. While more data are necessary in order to confirm the applicability of these findings to the general mining population, the results clearly suggest that greater loads could safely be lifted by mineworkers than can be lifted by the industrial population represented by the guidelines.     

Optimal laminate design subject to single membrane loads

In this paper we investigate optimization of laminates for maximal membrane stiffness under single in-plane loads. The design parameters are the relative ply thicknesses and fiber orientations of an arbitrary number of plies. The design is allowed to vary in a pointwise fashion throughout the structure.From prior work on lamination parameters (Hammeret al. 1997), it is known that the optimal design is given by either some sort of two ply lay-up in special strain situations or otherwise by just a single rotated ply. This is exploited in the present analysis to derive analytically the unique parameters of the optimal design (cross-ply, angle-ply or single ply) as expressions of the membrane forces. Both high and low shear stiffness material are treated. Furthermore the analysis covers all possible local strain or membrane force situations.Finally, it is shown how these expressions for the optimal configuration of the laminate also appear as bounds on the principal membrane forces in order to obtain alignment between the numerically largest principal membrane force and principal strain.     

Generating time-series of dry weather loads to sewers

Availability of appropriate methods for quantifying temporal and spatial variations of inflows to sewer systems is a prerequisite to effective sewer system modelling. To contribute to this goal, an empirical generator of sub-catchment wastewater outputs, for use as flow and water quality inputs to dynamic simulations of the larger sewerage system, is developed and evaluated. The deterministic part of the model is represented by means of Fourier series to generate diurnal profiles and a linear regression to generalise between sites, while a novel application of a multivariate error model with a lag-one autoregression term provides a stochastic component. Using a case study of Bogotá (Colombia), the validities of model assumptions are analysed and model results are compared with available dry weather measurements. The transferability of the methodology to other drainage systems is partially assessed using Linz (Austria) as a case study. It is concluded that the stochastic generator is a useful tool for generating flow and water quality at gauged and ungauged sub-catchment outlets in Bogotá and potentially other catchments.     

A TM Tasseled Cap equivalent transformation for reflectance factor data

A transformation of TM waveband reflectance factor data is presented which produces features analogous to TM Tasseled Cap brightness, greenness, and wetness. The approach to adjusting the transformation matrix to other types of reflectance factor data (different instrument or band response) is described in general terms.     

Simplified procedures for vibration serviceability analysis of footbridges subjected to realistic walking loads

This paper deals with the vibration serviceability analysis of footbridges subjected to realistic pedestrian traffic conditions, based on a probabilistic characterization of pedestrian-induced forces. The dynamic response to three different loading conditions is analysed through a non-dimensional approach, which permits the identification of the essential non-dimensional parameters governing the dynamic behaviour. Two simplified procedures are then proposed, founded on the sound definition of two coefficients, the Equivalent Amplification Factor and the Equivalent Synchronization Factor, which allow the evaluation of the vibration serviceability without requiring numerical analyses. Final applications confirm the efficiency of the proposed methods.     

Nonlocal thermoelastic model for temperature-dependent thermal conductivity nanobeams due to dynamic varying loads

Microsystem Technologies - The present paper produces a new nonlocal model for thermoelastic nanobeams of temperature-dependent thermal conductivity. A nanobeam excited by harmonically varying heat...     

From CSP models to Markov models

It is shown how a probabilistic dependability model of a safety-critical system can be derived from a trace-based functional model of the system. The functional model is a communicating sequential process (CSP) that includes command, failure, and repair events. The dependability model is a time homogeneous Markov process with transitions determined by these events. The method applies to deterministic systems that can be described in terms of a finite number of states and in which all event occurrences are stochastic with exponential time distribution. The derivation is carried out in two steps. An algorithmic determination is made of a finite automaton from the specification of the CSP process. The automaton is transformed into a Markov process. The Markov model for this system is used to determine the waiting time to terminal failure. The theory is applied to a larger and more realistic example: a gas burner system operating in the on-off mode. For this system, the waiting time to terminal failure is calculated, and the number of failures per year in a large population of identical, independently operated systems is estimated     

Permissible loads for the Dutch construction industry

The Foundation for Occupational Health Care in the Dutch Construction Industry has developed a research programme and a health campaign in order to prevent low-back pain. One of the activities was the development of directives for permissible loads for manual handling. On the basis of a study of the literature and of the legal requirements of several countries, we have tried to draw up such directives on behalf of the construction industry. We came to the conclusion, that there is no scientific basis for a regulation that has such a solid basis, that it can be forcefully advised, or even obliged. Nevertheless we have drawn up tentative directives, that can be adjusted when scientific progress gives reason to do so.