Behaviour of welded aluminium T-stub joints under monotonic loading

This paper deals with the behaviour of aluminium alloy T-stub joints subjected to monotonic tensile loads. In particular, a numerical model developed by means of the non linear code ABAQUS has been accurately calibrated on the basis of previous experimental test results related to 26 specimens, characterised by different geometry and connection type. In particular, four different geometries (by varying geometrical dimensions, plate thickness, number and location of the bolts), three aluminium alloys as base material and three types of bolts (including both aluminium and steel bolts) have been taken into consideration. Such parameters determine the modification of the connection response in terms of initial stiffness, ultimate strength and deformation capacity. The comparison with the experimental results shows that the proposed model is able to accurately reproduce the behaviour of the joint in all examined cases. Test results have been also compared with the ones derived from the application of the calculation method provided in the final version of Eurocode 9 (EN-1999-1-1), showing the reliability of the codified procedure, also in relation to a direct evaluation of the connection effective width (b_eff), as it is evidenced by the developed numerical simulations.     

Application of micromechanical models for elasticity and failure to short fibre reinforced composites. Numerical implementation and experimental validation

This paper deals with numerical modelling of the mechanical behaviour of short fibre reinforced plastic composites manufactured by the injection moulding process.First of all, an experimental program has been carried out in which the local fibre orientation distribution has been measured in an 80 × 80 × 2 mm injected plate by means of polished cut sections, analysed with SEM and image processing software. Tensile and three-point bending tests have been performed to obtain the elastic and strength response of the material in different locations along the plate and at two directions (parallel and normal to the flow direction).Analytical micromechanical models and averaging procedures have been implemented to relate the local fibre orientation distribution with the effective local anisotropic response of the material (elastic and strength). The models are validated by means of the finite element simulation of the performed characterisation tests.Finally, the methodology is applied to an injection moulded component with complex geometry. Fibre orientation data predicted with mould-flow software has been used to determine the local effective elastic stiffness and strength coefficients. A FE simulation of the functional behaviour of the component has been carried out. Results indicate that the proposed variable stiffness/strength anisotropic model predicts a lower load for onset of failure than when applying an equivalent isotropic material model.     

Haptically integrated simulation of a finite element model of thoracolumbar spine combining offline biomechanical response analysis of intervertebral discs

In this paper, we first describe the construction of a finite element model of the human spine that may be used to assist the investigation of clinical problems by predicting its biomechanical behaviour. A beam finite element (FE) spine model for haptic interaction is built based on a solid FE spine model, which is created in an offline finite element analysis (FEA) software. The mechanical properties of the beam FE spine model are tuned so that its deformation behaviour is very similar to that of the offline solid spine model. Furthermore, the online beam FE spine model is greatly simplified as compared to the offline solid FEA model and hence more appropriate for real-time simulations. Haptic feedback is provided in the real-time simulation of the beam FE spine model, in order to enhance the human–computer interaction. Based on the results of spine deformation obtained from the haptic online FE simulator, the offline FEA spine model again is used to reproduce the same deformation and hence to provide more detailed deformation and vertebrae’s stress/strain information, which the haptic beam FE model is not capable to provide. Then, we present a tetrahedral mass–spring system to model intervertebral discs, which are interposed between vertebrae, and the offline simulation can be run to achieve deformation responses of these intervertebral discs. In our research, combining the haptic beam FE model and the intervertebral disc model can be useful for studying biokinematics of the spine as well as assessing medical conditions in the spine or the biomechanical behaviour of new designs of artificial intervertebral discs.     

The use of finite-element and boundary-element models for predicting the vibro-acoustic behaviour of layered structures

Layered structures made from elastic and porous materials are widely used as insulation systems in the automotive industry. They have a complex dynamic behaviour that is influenced by the various interaction mechanisms within the porous material. This paper concentrates on modelling these systems using a three-dimensional finite-element (FE) approach for the structure combined with a boundary-element (BE) procedure for the acoustic radiation process. The key part is a Biot model for the two-phase porous material. A mixed displacement formulation is selected. The model can be used for predicting the surface impedance and/or the transmission loss characteristics of layered material. The combined use of this FE/BE model enables evaluation of the acoustic response (radiated power, field pressure). Numerical applications are presented in order to show the capabilities of the developed procedures.     

Modelling of Torsion Beam Rear Suspension by Using Multibody Method

The multibody systems analysis has become one of the main simulation techniques to calculate the elasto-kinematics characteristics of a car suspension under wheel loads or to realize complex full vehicle models in order to predict the handling performances or the NVH quality. The modelling of torsion beam rear suspensions—widely adopted in cars belonging to B or C class—presents some problems arising from the structural behaviour of this component. A linear method based on component mode synthesis was used to represent the flexible torsion beam within the multibody model. This kind of approach was compared with a non-linear FE analysis. The elasto-kinematics analysis of the suspension was performed by using SIMPACK multibody code. The main suspension parameters (toe angle, camber angle, wheelbase and track variation) were calculated by changing wheel travel and loads. Static analyses, involving great displacements, were performed and a different number of modes were considered in the modal condensation of the torsion beam. The results of multibody simulations were compared with those obtained from a non-linear FE model. Different stiffness values of the bushings that connect the torsion beam to the vehicle chassis were taken into account.     

A system for simulation, monitoring and diagnosis of controlled continuous processes with slow dynamics

This paper presents a modelling approach specifically designed to be used in a monitoring and diagnosis system based on the simulation of relevant process and control system variables. The model is based on semantically extended data flow diagrams with each computational process representing the incremental behaviour of a component of the plant to be modelled. Variable as well as delay time behaviour is associated with each component model to support an event-driven simulation which, in turn, reduces computation time. This plant model of independent but interacting computational processes is easily extendable, modifiable and adjustable according to changes in the plant.

The modelling approach is applied to a coal power plant process and is implemented in G2, an object-oriented, real-time expert system shell with built-in simulation and online external connection capabilities. Generic rules guiding the event-driven simulation and monitoring allow for modular adaptation of the model as the plant's structure and functionality change without requiring changes in the rule set.     

Reliable behaviour simulation of product interface in mixed reality

The validation of a product interface is often a critical issue in the design process. Virtual reality and mixed reality (MR) are able to enhance the interactive simulation of the product human–machine interface (HMI), as these technologies allow engineers to directly involve end users in the usability assessment. This paper describes a MR environment specifically addressed to the usability evaluation of a product interface, which allows the simulation of the HMI behaviour using the same models and the same software employed by engineers during the design phase. Our approach is based on the run-time connection between the visualisation software and the simulators used for product design and analysis. In particular, we use Matlab/Simulink to model and simulate the product behaviour, and Virtools to create the interactive MR environment in which the end user can test the product. Thanks to this architecture, any modification done on the behaviour models is immediately testable in MR.     

Equivalent post-buckling models for the flexural behaviour of steel connections

Analytical solutions for the evaluation of the behaviour of steel connections are presented which are able to reproduce their full non-linear behaviour. Because usual models for the analysis of steel connections consist of translational springs and rigid links whereby the springs exhibit a non-linear force–deformation response, usually taken as a bi-linear approximation, they require an incremental non-linear analysis. Using a substitute elastic post-buckling model where each bi-linear spring is replaced by two equivalent elastic springs in the context of a post-buckling stability analysis using an energy formulation, closed-form solutions are obtained for a connection loaded in bending. Application to a beam-to-column welded connection using the component (spring) characterisation of code regulations yields the same results in terms of moment resistance and initial stiffness, being additionally able to trace the full unstiffening response.     

Development of the object-oriented finite element modeling system — MODIFY

In this paper we present a new concept of FE modeling, based on the object-oriented principle, and develop the prototype program MODIFY (MODeling tool for Integrated Finite element analYsis). MODIFY has three novel features: (1) FE modeling by the part object concept, (2) a fully object-oriented data structure, and (3) a part-by-part fully automated mesh subdivision. When using MODIFY it is necessary to define and assemble part objects, which consist of geometry objects, analytical condition objects and relation objects, to describe the continuity between adjacent part objects.MODIFY automatically generates an appropriate FE model for each geometry object, satisfying continuity conditions with adjacent parts by referring to relation objects. If some part of the model is to be modified, the user needs only to change the corresponding part objects. Because of the object-oriented data structure, MODIFY also has a powerful capability for adaptive meshing. The existing version of MODIFY is applicable to FE models for3-D shell structures.     

A virtual fixture using a FE-based transformation model embedded into a constrained optimization for the dimensional inspection of nonrigid parts

Virtually mounting nonrigid parts onto their fixture is proposed by researchers to remove the need for the use of complex physical inspection fixtures during the measurement process. Current approaches necessitate the pre-processing of the free-state nonrigid part’s point cloud into a suitable finite element (FE) mesh and are limited by the use of the boundary conditions setting methods available in FE software. In addition to these limits, these approaches do not take into account the forces used to restrain the part during the inspection, as commonly mandated for aerospace panels. To address these shortcomings, this paper presents a virtual fixture method that predicts the fixed shape of the part without the aforementioned drawbacks of current approaches. This is achieved by embedding information retrieved from a FE analysis of the nominal CAD model into a boundary displacement constrained optimization. To evaluate the proposed method, two case studies on physical parts are performed using the proposed virtual fixture method to evaluate the profile and assembly force specifications of each part.     

热风炉热风竖管底板结构强度有限元分析

为设计更薄的热风炉热风竖管底板,解决试验结果和经验公式计算结果无法反映其实际受力情况的问题,用ANSYS分析某底板的结构强度.根据该底板的结构几何模型建立有限元模型,采用SOLID 185单元划分网格.分析中不考虑固定支座处的滑动;设定砖载荷、上部竖管自重载荷、内压载荷、温度载荷等边界条件.对底板、底板下部筋板、筒体和筒体外围筋板的应力与位移分布的分析表明:底板及其筋板与竖管筒体连接处易出现应力集中现象;在热膨胀和内压的作用下,最大位移出现在底板下部筋板与筒体交界处、筒体自由边界处和筒体外围筋板的上部.计算结果表明该底板能满足结构强度要求.     

A unique property of single-link distance and its application in data clustering

We prove a unique property of single-link distance, based on which an algorithm is designed for data clustering. The property states that a single-link cluster is a subset with inter-subset distance greater than intra-subset distance, and vice versa. Among the major linkages (single, complete, average, centroid, median, and Ward's), only single-link distance has this property. Based on this property we introduce monotonic sequences of iclusters (i.e., single-link clusters) to model the phenomenon that a natural cluster has a dense kernel and the density decreases as we move from the kernel to the boundary. A monotonic sequence of iclusters is a sequence of nested iclusters such that an icluster in the sequence is a dominant child (in terms of size) of the icluster before it. Our data clustering algorithm is monotonic sequence based. We classify a dataset of one monotonic sequence into to two classes by splitting the sequence into two parts: the kernel part and the surrounding part. For a data set of multiple monotonic sequences, each leaf monotonic sequence represents the kernel of a class, which then “grows” by absorbing nearby non-kernel points. This algorithm, proved by experiments, compares favorable in effectiveness to other clustering algorithms.     

Fault detection and isolation of the three-tank system using the modal interval analysis

Analytical redundancy is a widely used technique for fault detection. It consists of comparing the behaviour of a real system with a reference obtained by simulation of its model. The main problem is that there are always imprecisions and uncertainties which are not represented in the model so the behaviour of the real system and the behaviour of the model are not exactly the same. One way to represent these uncertainties in the model is using interval models. The results of the simulation of these types of models may be represented by envelopes. This paper proposes an approach to generate envelopes based on interval techniques of the modal interval analysis. As an example, this approach is used to detect and isolate faults in a physical system formed by three interconnected tanks.     

An access control model and its use in representing mental healthapplication access policy

The paper considers an access control model and proposes extensions to it to deal with authentication and revocation. The model is then applied to represent access control policy in a mental health system. In the first part of the paper, extensions to the schematic protection model (SPM) are presented. The authentication and revocation extensions are independent of one another in the sense that each one affects a different part of the decision algorithm. The extensions comprise a modification of the syntax to be able to represent the new concepts and, more importantly, a modification of the decision algorithm for the safety problem to take these changes into account. We introduce the concept of conditional tickets and use it to provide authentication. Apart from this, we have found this concept to be useful in modeling systems. Hence we have separated this (syntactical) issue from the definition of the new algorithm. The second part considers the access policy for a mental health application. We have used the extensions of SPM to model part of this access policy. Even with our extensions, SPM still remains a monotonic model, where rights can be removed only in very special cases, and this makes it impossible to represent all the aspects of the problem. Other than to serve as an example for the extensions we propose, the paper also helps to separate aspects of this access control policy which are inherently monotonic from parts which are defined in a non-monotonic way, but can still be represented in a monotonic model     

影响汽车纵梁前段变形模式的因素

在汽车前部40%偏置碰设计中,要求纵梁不能更改的前提下,希望纵梁前段由折弯变形改进为压溃变形.通过竞品车研究和CAE仿真,确定除纵梁本身的设计外,能较大影响纵梁前段变形模式的因素为前保横梁的强度、纵梁与吸能盒间安装板的强度,以及纵梁与安装板间的连接方式等.进一步的仿真分析发现,适当加强这些部位有利于纵梁的稳定压溃变形,并提升前端结构的能量吸收.     

Simulation of the dynamic response of a cracked beam

The experimental vibration behaviour of a free–free beam with a breathing crack is simulated for a sinusoidal input force using a simple FE model for a crack in beam. The present simulation was compared with an earlier study and found to be more realistic.     

Reorganizing knowledge in neural networks: an explanatory mechanismfor neural networks in data classification problems

We propose an explanatory mechanism for multilayered neural networks (NN). In spite of the effective learning capability as a uniform function approximator, the multilayered NN suffers from unreadability, i.e., it is difficult for the user to interpret or understand the "knowledge" that the NN has by looking at the connection weights and thresholds obtained by backpropagation (BP). This unreadability comes from the distributed nature of the knowledge representation in the NN. In this paper, we propose a method that reorganizes the distributed knowledge in the NN to extract approximate classification rules. Our rule extraction method is based on the analysis of the function that the NN has learned, rather than on the direct interpretation of connection weights as correlation information. More specifically, our method divides the input space into "monotonic regions" where a monotonic region is a set of input patterns that belongs to the same class with the same sensitivity pattern. Approximate classification rules are generated by projecting these monotonic regions.     

行动推理中循环因果关系的研究

近年来行动推理的研究成为人工智能领域的热门问题,而结果问题是目前行动推理研究的核心问题之一．该文针对许多行动推理系统不能处理循环因果关系的问题,提出了解决方法．基于适当修改后的McCain和Turner的因果理论,该文提出了一种能处理循环依赖的理论转化方法．转化后的因果理论消除了循环依赖,而且可以采用单调推理方法．基于因果闭包语义,证明了转化前后的因果理论具有相同的模型．当因果关系不存在循环依赖时,该文方法得到与McCain,Turner方法(1997)相同的结果．