Composites structural modelling with uncertain data

The aim of this paper is to propose a methodology to take into account the influence of uncertain data in structural calculations. A specific method, based on the approximation of the responses as a function of the uncertain data, is proposed. Classical methods from the literature are also considered. The different methods are compared on a simple example in terms of response (average value and standard deviation) and in terms of computational cost. The method proposed in the present work permits to estimate correctly the whole response and is very simple to use (pre and post processing). This method is applied to a structural calculation on a “hat-shapes” part called, manufactured in the quasi-isotropic IM7/977-2 composite.     

具有Fuzzy决策的信息系统的知识约简

知识约简是粗糙集理论的核心问题之一。讨论了具有Fuzzy决策的信息系统的知识约简问题。给出了知识约简的几种定义、相应的知识约简的判定定理和可辨识属性矩阵，从而为具有Fuzzy决策的信息系统的知识约简的计算提供了具体方法。     

Wind-excited response of structures with uncertain parameters

The wind-excited response of structures is classically evaluated by considering the model parameters as deterministic. Due to this assumption, the density function of the maximum response is so narrow and sharp as to make the expected maximum a suitable pseudo-deterministic representation of the maximum response. Based on Taylor series expansions retaining up to the first and second-order derivative terms, this paper provides closed form expressions of the first and second statistical moments of the maximum response taking the uncertainties of the parameters and the model error into account. It is shown that such uncertainties may spread and shift the density function of the maximum response to the point at which the classical value of the expected maximum is no longer representative of the structural behaviour.     

The future of work and uncertain labour alternatives as we live through the industrial age of possible singularity: Evidence from South Africa

This paper focused on uncovering the preparedness of the automobile labour force in embracing the outcome of technological domination in the motor industry in South Africa. Semi-structured in-depth interviews were initiated to generate data from three motor companies with purposively selected 30 participants. Findings revealed that auto employees who are not electrically inclined are self-encouraged to seek technical and electrical careers to secure a future in the automobile industry. These workers may also pursue careers in computer science. Many autoworkers have supplemented and stabilized their incomes through FOREX and Bitcoin mining trading. Simultaneously, these employees are receptive to changing careers in agriculture. Again, autoworkers prefer self-employment to the job insecurity associated with industrial positions. In general, motivation for upskilling for a future job in the automotive industry is low. Before the Covid-19 crisis, organizations were adopting new ways of doing business that tend to unready workers' readiness. This trend increased very steeply during the pandemic. Retraining and reskilling as steps for workers' readiness to face job automation are not outright answers that will lead to job security. Nonetheless, automobile workers have to treat their careers as businesses and invest in skills under the umbrella of non-automatable technical and non-technical job families.     

Warranty and redundancy design with uncertain quality

When products of an uncertain quality are sold with a warranty, the expected warranty cost depends on the reliability of the product and on the quality uncertainty. This cost can be reduced through the use of redundancy and/or quality control techniques. However, these routes increase the manufacturing cost. This paper develops a model to determine the optimal redundancy and quality control strategies that achieve a trade-off between the two costs.     

Conclusions vs Decisions

With the exception of appendices 2 and 3, the following is based on the after dinner talk given by Professor John W. Tukey at, the first meeting of the Section of the Physical and Engineering Sciences of the American Statistical Association held in New York City on May 26, 1955. This talk was repeated at a later date before a dinner meeting of the Metropolitan Section of the American Society for Quality Control. On both occasions considerable discussion ensued. The talk is published here both for the record, and in the hope that some readers may be stimulated to prepare written rejoinders.     

Deriving Reference Decisions

To solve a statistical decision problem from a Bayesian viewpoint, the decision maker must specify a probability distribution on the parameter space, his prior distribution. In order to analyze the influence of this prior distribution on the solution of the problem, Bernardo (1981) proposed to compare the results with those that one would obtain by using that prior distribution which maximizes the useful experimental information, thus introducing the concept of reference decision. This definition is too involved for most of the problems usually found in practice. Here we analyze situations in which it is possible to simplify the definition of the reference decision, and we provide conditions guaranteeing the existence of such decisions.     

Spectral stochastic analysis of structures with uncertain parameters

We present a probabilistic analysis of a structure with uncertain parameters subject to arbitrary stochastic excitations in a frequency domain. The problem of stochastic dynamic analysis of a linear system in a frequency domain is formulated by taking into consideration the uncertainty of structural parameters. The solution is based on the idea of a random frequency response vector for stationary input excitation and a transient random frequency response vector for nonstationary one which are used in the context of spectral analysis in order to determine the influence of structural uncertainty on the random response of structure. The numerical spectral analysis of the building structure under wind and earthquake excitation is provided to demonstrate the described algorithms in the context of computer implementation.     

Optimal acquisition policy with quantity discounts and uncertain demands

We study the acquisition policy decision problem for a supply network involving one manufacturer and multiple suppliers. The manufacturer produces multiple products under uncertain demands and each supplier provides price discounts. The problem is to determine the manufacturer's acquisition policy and production levels so as to maximise the manufacturer's expected profit, subject to both the manufacturer's and suppliers’ capacities. We present a mixed integer nonlinear programming (MINLP) formulation of the problem, for both single- and multiple-sourcing procurement policies. General algebraic modeling system (GAMS) and its solvers, combining external integration functions, are employed to solve the complex MINLP problem. The preliminary computation results and managerial analysis are reported.     

Evaluation of microalgae-based biorefinery alternatives

Microalgae-based biorefineries for the production of renewable biofuels like biodiesel, upgraded bio-oil, biochar, biogas and other high-value chemicals have received great attention in recent decades as potential major sources of energy for the future. Microalgae are a suitable species to produce biodiesel and other high energy density by-products; however, it is questionable whether a net energy gain can be realized or not considering the whole processing chain. In the present study, the energy balances of different algae-based biofuel and bioenergy production technologies are investigated in detail and compared to each other corresponding to a cradle-to-grave overall energetic analysis. The study includes cultivation, harvesting, cell pretreatments (cell disruption, drying, grinding), lipid extraction, transesterification, gasification and hydrothermal liquefaction with bio-oil stabilization and hydroprocessing. The energy consumption and energy gain are estimated for each operational step to determine the net energy ratio (NER, energy output over energy input) for the overall technologies studied. Our detailed investigation enables to detect the most energy consuming unit operation, that is, the bottleneck point(s) of the microalgae-based technologies which should be still improved in the future for the sake of more efficient algae-based biorefineries. The investigation makes also possible to evaluate and compare the different large scale alternatives for biomass transformation. Positive energy balances with a NER value of 1.109 and 1.137 are found in two already existing processes: open raceway ponds and closed photobioreactors, respectively. Our work gives also a detailed algorithm that can be followed at the evaluation of other microalgae-based biorefineries.     

Exponential stabilization of nonlinear uncertain systems with time-varying delay

The problem of robust exponential stabilization for dynamical nonlinear systems with uncertainties and time-varying delay is investigated. Based on the Razumikhin theorem and the Lyapunov function method, the continuous state feedback controllers for the studied systems are proposed and the robust exponential stabilization criterion is established in terms of solutions to the standard Riccati differential equations. Furthermore, a delay-dependent stabilization criterion is derived in terms of a linear matrix inequality and the restriction on the derivative of the delay function is removed. Finally, two numerical examples are presented to demonstrate the validity of the proposed method.     

Non-stationary random response analysis of structures with uncertain parameters

This paper proposes a non-stationary random response analysis method of structures with uncertain parameters. The structural physical parameters and the input parameters are considered as random variables or interval variables. By using the pseudo-excitation method and the direct differentiation method (DDM), the analytical expression of the time-varying power spectrum and the time-varying variance of the structure response can be obtained in the framework of first order perturbation approaches. In addition, the analytical expression of the first-order and second-order partial derivative (e.g., time-varying sensitivity coefficient) for the time-varying power spectrum and the time-varying variance of the structure response expressed via the uncertainty parameters can also be determined. Based on this and the perturbation technique, the probabilistic and non-probabilistic analysis methods to calculate the upper and lower bounds of the time-varying variance of the structure response are proposed. Finally the effectiveness of the proposed method is demonstrated by numerical examples compared with the Monte Carlo solutions and the vertex solutions.     

氟利昂替代品研究现状

通过概述氟利昂的危害、替代方案、替代成果等 ,阐述了氟利昂替代品的研究现状及各种替代品的性能比较 ,指出了氟利昂替代品的发展趋势     

具有随机路径的振动传递路径系统的随机响应分析

基于Kronecker代数、矩阵微分理论、向量值和矩阵值函数的二阶矩技术、矩阵摄动理论和概率统计方法,实用有效地提出了时域内振动传递路径系统的随机响应分析方法。在考虑传递路径参数,包括质量、阻尼、刚度、位置参数不确定性的条件下,对振动传递路径系统的随机响应问题进行了理论分析和数值计算,给出了系统随机振动响应的一阶矩和二阶矩的一般数学表达式,据此可以考虑工程实际中大量的传递系统中固有的不确定性,以便为解决不确定振动传递路径系统的问题提供有效方便的途径。通过算例表明,该法数值分析结果与Monte Carlo随机模拟结果比较,具有理想的精度。