Formal safety assessment based on relative risks model in ship navigation

Formal safety assessment (FSA) is a structured and systematic methodology aiming at enhancing maritime safety. It has been gradually and broadly used in the shipping industry nowadays around the world. On the basis of analysis and conclusion of FSA approach, this paper discusses quantitative risk assessment and generic risk model in FSA, especially frequency and severity criteria in ship navigation. Then it puts forward a new model based on relative risk assessment (MRRA). The model presents a risk-assessment approach based on fuzzy functions and takes five factors into account, including detailed information about accident characteristics. It has already been used for the assessment of pilotage safety in Shanghai harbor, China. Consequently, it can be proved that MRRA is a useful method to solve the problems in the risk assessment of ship navigation safety in practice.     

A simple orthotropic finite elasto–plasticity model based on generalized stress–strain measures

 In this paper we present a formulation of orthotropic elasto-plasticity at finite strains based on generalized stress–strain measures, which reduces for one special case to the so-called Green–Naghdi theory. The main goal is the representation of the governing constitutive equations within the invariant theory. Introducing additional argument tensors, the so-called structural tensors, the anisotropic constitutive equations, especially the free energy function, the yield criterion, the stress-response and the flow rule, are represented by scalar-valued and tensor-valued isotropic tensor functions. The proposed model is formulated in terms of generalized stress–strain measures in order to maintain the simple additive structure of the infinitesimal elasto-plasticity theory. The tensor generators for the stresses and moduli are derived in detail and some representative numerical examples are discussed. Received: 2 April 2002 / Accepted: 11 September 2002     

基于广义高斯噪声模型的低频线谱检测

研究浅海环境噪声中低频线谱的检测问题.首先对实测海洋环境噪声的统计特性进行分析,提出了应用广义高斯分布对海洋环境噪声建模方法.在此基础上,针对低频线谱检测问题,推导了广义高斯噪声场中的最大似然检测器和渐近检测器,给出了弱线谱条件下线谱频率的最大似然估计.最后,利用实测数据对三种检测器的线谱检测性能进行了验证,结果表明:...     

Two FMS scheduling methods based on Petri nets: A global and a local approach

We are interested in the Flexible Manufacturing System (FMS) scheduling problem. Different methods have been explored to solve this problem and to master its combinatorial complexity, which is NP-hard in the general case. In this paper we will give two different scheduling methods based on Petri nets. The first one tends to solve the general scheduling problem (acyclic schedule) using the Constraint Programming method to avoid exhaustive search. The second method is a dedicated cyclic scheduling method. The aim is not to compare the methods' performances (computation time, results' quality) because they do not solve exactly the same problem, but to compare their application domains in terms of parts number.     

基于受控混杂Petri网(CHPN)的分层优化模型及其在炼油厂氢气管理中的应用

提出了一种基于受控混杂Petri网(CHPN)的分层优化建模结构,并将其应用于炼油厂的氢气网络优化管理中.这种分层优化结构将CHPN建立的过程仿真模型同传统的数学优化方法紧密结合在一起,上层的数学优化模型根据经济指标寻求最优解,下层CHPN在上层最优解的控制下运行,可以根据工厂的实际生产条件的改变在计划期内及时调整调度安排,并保证经济指标的最优性.炼油厂氢气平衡管理建模实例显示,通过该方法获得的炼油厂氢气平衡调度方案减少了炼油厂生产过程中氢气资源的浪费现象,提高了企业的经济效益.     

A generalized micromechanics model with shear-coupling

Summary A unified mathematical framework for a higher-order transverse shear-normal stress coupled micromechanical model is presented. The model is developed based on the analysis of a repeating unit cell in a doubly periodic array of fibers. The behavior in subregions within the unit cell is modeled using an expansion for the displacement field. The order and form of the displacement expansions in the subregions are arbitrary. The higher-order terms in the displacement expansion result in coupling between the transverse shearing and the normal deformation responses (shear coupling). The formulation is sufficiently general to allow generic elastic, plastic, viscoelastic, viscoplastic, or damage constitutive models (within the context of infinitesimal strain theory) for history-dependent behavior to be incorporated into the micromechanical framework. The proposed approach is analytical and provides closed-form expressions for the effective macroscopic behavior of a continuous fiber composite.The model is validated by comparison with existing micromechanics models. The agreement between the predicted effective moduli obtained from the current model and other existing models indicates that the current formulation accurately predicts the effective elastic behavior of a composite. Furthermore, comparison with existing data for the local elastic stress distributions around the inclusion indicates that the current model correctly captures the trends and magnitudes in these distributions. The predictions obtained from the current theory are shown to be more accurate than the corresponding MOC predictions. The ability to more accurately capture the spatial stress distributions can be directly attributed to the incorporation of the shear-coupling phenomena.Finally, the influence of the presence of shear coupling on the local field distributions is considered for the simple macroscopic loading cases of transverse tension and transverse shearing. It is shown that signficant coupling between the local transverse shearing and normal deformation responses exists even when the composite is subjected to a macroscopically simple loading field. The existence of this coupling has potentially significant implications in the implementation of history-dependent constitutive models.     

SIMP-ALL: A generalized SIMP method based on the topological derivative concept

Topology optimization has emerged in the last years as a promising research field with a wide range of applications. One of the most successful approaches, the SIMP method, is based on regularizing the problem and proposing a penalization interpolation function. In this work, we propose an alternative interpolation function, the SIMP-ALL method that is based on the topological derivative concept. First, we show the strong relation in plane linear elasticity between the Hashin-Shtrikman (H-S) bounds and the topological derivative, providing a new interpretation of the last one. Then, we show that the SIMP-ALL interpolation remains always in between the H-S bounds regardless the materials to be interpolated. This result allows us to interpret intermediate values as real microstructures. Finally, we verify numerically this result and we show the convenience of the proposed SIMP-ALL interpolation for obtaining auto-penalized optimal design in a wider range of cases. A MATLAB code of the SIMP-ALL interpolation function is also provided.     

Evaluation of the logistic model of the reconfigurable manufacturing system based on generalised stochastic Petri nets

To reveal the influence on system performance by the logistic model of reconfigurable manufacturing system (RMS), the generalised stochastic Petri nets (GSPN) modular modelling approach is presented in this paper. It is based upon the characteristics of a bottleneck service. According to this approach, the bottleneck service in the production process is found first. By corresponding different resources in the service to different modules of the GSPN, the module is reconfigured. The analysis of the model using the Markov chain is hereby presented, as is the average utilisation factor of RMS. Following this, the production capacity of different products and the average productivity of reconfigurable manufacturing cells (RMCs) are discussed.     

One approach to study communication in science

The hypothesis proposed by the author expresses that Zipf's law is only fulfilled on rank distributions which correspond to highly integrated (closed) subject fields. This hypothesis was tested on vast amount of empirical data. It was shown that document files in integrated fields are characterised by thematic, chronological (and sometimes geographical) closedness, as well as closedness by citation. Relationships were found between empirical facts usually considered in isolation within the frameworks of different scientometric and bibliometric theories (the theory of information concentration and scattering, obsolescence theory, theory of changing source productivity).Paper presented at the Republican Seminar on Information Science in the Science of Science (Institute of Cybernetics, Academy of Sciences of the Ukrainian SSR, Kiev, 14 December, 1983).     

On the Hencky-Prandtl nets based on two orthogonal circles

Summary This paper gives all theHencky-Prandtl nets that can be constructed on the basis of two orthogonally intersecting circles of equal radii.

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Zusammenfassung Es werden alleHencky-Prandtl-Netze angegeben, die auf der Basis von zwei einander senkrecht schneidenden Kreisen gleicher Radien konstruiert werden können.

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With 7 Figures     

Deadlock prevention policy based on Petri nets and siphons

This paper presents a deadlock prevention method for a class of flexible manufacturing systems where deadlocks are caused by unmarked siphons in their Petri net models. This method is an iterative approach consisting of two main stages. At each iteration, a fast deadlock detection technique developed by mixed integer programming is used to find an unmarked maximal siphon. An algorithm is formalized that can efficiently obtain an unmarked minimal siphon from the maximal siphon. The first stage, called siphons control, of the proposed method is to add, for each unmarked minimal siphons, a control place to the original net with its output arcs to the sink transitions of the minimal siphon. The objective is to prevent a minimal siphon from being unmarked. The second stage, called augmented siphons control, is to add a control place to the modified net with its output arcs to the source transitions of the resultant net if the resource places are removed. The second stage is required since adding control places in the first stage may create new unmarked siphons. In addition, the second stage assures that there are no new unmarked siphons generated. The relation of the proposed method and the liveness and reversibility of the controlled net have been obtained. Finally, manufacturing examples are presented to illustrate the method and to allow comparison with earlier methods.     

基于广义粗糙集的知识约简方法研究

针对粗糙集理论在知识约简中的实际需要,提出了建立在一般二元关系基础上的广义粗糙集知识约简方法。首先证明了广义粗糙集是经典粗糙集的一般性推广,而经典粗糙集是广义粗糙集的特例;然后以一般二元关系为分类基础,给出一般关系决策系统中的知识约简判定定理和辨识矩阵;最后根据实例提取最小的属性集,验证了该方法的实用性。该方法摆脱了二元等价关系对经典粗糙集的困扰,既保证了粗糙集理论在知识发现研究中的理论优势,又拓展了粗糙集理论在实际应用中的适用范围,具有较强的实用性。     

A Bayesian generalized Eyring-Weibull accelerated life testing model

In this paper, a novel approach to a Bayesian accelerated life testing model is presented. The Weibull distribution is used as the life distribution and the generalized Eyring model as the time transformation function. This is a model that allows for the use of more than one stressor, whereas other commonly used acceleration models, such as the Arrhenius and power law models, incorporate one stressor. The use of the generalized Eyring-Weibull model developed in this paper is demonstrated in a case study, where Markov chain Monte Carlo methods are utilized to generate samples for posterior inference.     

A generalized model to predict the effect of voids on modulus in ceramics

An equation recently developed by the present author to describe the modulus of particulate composites as a function of the volume fraction of particles was modified in this study to describe modulus as a function of porosity. This new equation was applied to available modulus literature for ceramics where voids were the particulate phase. By varying the porosity interaction coefficient, σ, this new generalized void/modulus equation was shown to be able to yield equations previously used to predict modulus as a function of voids for ceramics. Wang theoretically described the mode of porosity interaction during compaction with a constant, α, to calculate the void/modulus relationship for three different compaction conditions. The generalized void/modulus equation developed in this study fit Wang's theoretical data exceptionally well, even though the porosity interaction coefficients, σ, obtained did not agree closely with Wang's values of α. Wang also experimentally measured the porosity and Young's modulus of manufactured alumina rods prepared with spherical and “egg-shaped” powders. The optimum fit for spherical particles occurred at σ=0.9 and an initial porosity of P _i=0.405 and for “egg-shaped” particles at σ=1.05 and P _i=0.475. The generalized void/modulus the equation for σ=−1 yields an equation that has the same form as Wang's proposed empirical equation that utilized two empirical constants, b and c. Wang's experimental data fitted with his proposed empirical equation gave a positive value for the constant c of 0.982 which corresponded to a negative value of P _i of -0.0743 which was not defined in the theoretical considerations developed in this study. While this value of the initial porosity, P _i, does give a better fit of the data for the interaction constant σ=-1, it still did not fit all the data as well as the results calculated for interaction coefficients nearer 1.0. The results of this study have shown that an excellent fit of most void/modulus data can be obtained using the generalized void/modulus equation developed in this study without making assumptions inconsistent with the theory presented.     

Transient inter-production scheduling based on Petri nets and constraint programming

In this article, we focus on the transient inter-production scheduling problem between two cyclic productions in the framework of flexible manufacturing systems. This problem is first formulated as a reachability problem in timed Petri nets (TPN), then solved using a methodology based on constraint programming. Our work is based on the controlled executions proposed by Chretienne to model the sequence of transition firing dates. Our methodology is based on a preliminary resolution of the state equation between initial and final states in the underlying non-TPN. Then, we choose a duration T _max corresponding to the maximal duration time of the scheduling. For each solution S of the state equation, we build a controlled execution from the sequence of firings in S. After the propagation of firing date constraints and reachability constraints in the TPN, we use constraint programming to enumerate the set of feasible controlled executions.     

A generalized midpoint algorithm for the integration of a generalized plasticity model for sands

This paper describes a method of performing the integration of generalized plasticity models, in which, unlike classical elastoplasticity, the yield surface is not explicitly defined. The algorithm is based on a generalized midpoint scheme and is applied to a specific generalized plasticity model for sands, in which a hyperelastic formulation is introduced to describe the reversible component of the soil response instead of the hypoelastic approach originally proposed. In this way, an efficient integration scheme is developed in the elastic strain space. The consistent, algorithmic tangent operator is derived. Isoerror maps are generated to study the local accuracy of the numerical integration algorithm. Results from a series of numerical examples based on the simulation of drained triaxial tests are given to illustrate the accuracy and convergence properties of the algorithm, both at the local and at the global level. Finally an example is given of the simulation of a cyclic triaxial test to illustrate the improvement on accuracy caused by the use of a hyperelastic law into the constitutive equations, as opposed to the hypoelastic formulation initially adopted in the model. Copyright © 2008 John Wiley & Sons, Ltd.