A solution for the integration of finite element analysis in a ship design environment

The DEMAIN system for the pre- and post-processing of finite element analyses of ship structures is presented. It is shown that this new modelling concept, although being self-contained and specialized, has features which relate it to computer-aided design applications of a more general nature. Thus, compared to other finite element pre/post-processors, it allows a more natural occurrence of the structural analysis task in the design flow and can be considered a major step towards an integrated design and analysis system.     

Review of continuum, finite element and hybrid techniques in the analysis of stress concentrations in structures

When a uniform flow of any nature is interrupted, the readjustment of the flow results in concentrations and rare-factions, so that the peak value of the flow parameter will be higher than that which an elementary computation would suggest. When stress flow in a structure is interrupted, there are stress concentrations. These are generally localized and often large, in relation to the values indicated by simple equilibrium calculations. With the advent of the industrial revolution, dynamic and repeated loading of materials had become commonplace in engine parts and fast moving vehicles of locomotion. This led to serious fatigue failures arising from stress concentrations. Also, many metal forming processes, fabrication techniques and weak-link type safety systems benefit substantially from the intelligent use or avoidance, as appropriate, of stress concentrations. As a result, in the last 80 years, the study and and evaluation of stress concentrations has been a primary objective in the study of solid mechanics.Exact mathematical analysis of stress concentrations in finite bodies presents considerable difficulty for all but a few problems of infinite fields, concentric annuli and the like, treated under the presumption of small deformation, linear elasticity. A whole series of techniques have been developed to deal with different classes of shapes and domains, causes and sources of concentration, material behaviour, phenomenological formulation, etc. These include real and complex functions, conformal mapping, transform techniques, integral equations, finite differences and relaxation, and, more recently, the finite element methods. With the advent of large high speed computers, development of finite element concepts and a good understanding of functional analysis, it is now, in principle, possible to obtain with economy satisfactory solutions to a whole range of concentration problems by intelligently combining theory and computer application. An example is the hybridization of continuum concepts with computer based finite element formulations. This new situation also makes possible a more direct approach to the problem of design which is the primary purpose of most engineering analyses. The trend would appear to be clear: the computer will shape the theory, analysis and design.     

Thermal stresses in rectangular plates: Variational and finite element solutions

This paper deals with the development of an approximate method for the analysis of thermal stresses in rectangular plates (plane stress problem) and an evaluation of the relative accuracy of the finite element method. The stress function is expanded in terms of polynomial coordinate functions which identically satisfy the boundary conditions, and a variational approach is used to determine the expansion coefficients. The results are in good agreement with a finite element approach.     

Finite element analysis of thick annular and sector plates

A finite element displacement formulation based on Reissner's thick plate theory is presented for the bending analysis of annular and sector plates. An annular element and an annular sector element, associated with six and twenty degrees of freedom, respectively, are developed. One of the significant features of these elements, which include both bending and shear deformation effects and which conform with respect to all degrees of freedom considered, is the ability to satisfy exactly the condition of vanishing shear stress resultant along a free edge. Numerical results are presented for substantiating the proposed procedure.     

Elastic-plastic finite element analysis using superposition

This paper concerns the method of calculation and solution using the superposition technique of analytic and finite element solutions, which is applied to elastic-plastic plane problems. The incremental form of the principle of virtual work is employed to derive the equations, from which the nodal displacements of the finite elements together with the generalized displacements of the analytic solution are calculated simultaneously. Several example problems are solved for elastic-plastic material with the use of the von Mises yield criteria and the associated flow rule. It is concluded that the present method is so effective as to give enough accuracy in strain concentration problems with small numbers of elements.     

A status report on computational techniques for finite element analyses

Fifteen years of research, development, and application of the finite element concept, primarily to structural analysis, has yielded a host of techniques for computer implementation. The importance of using these techniques is shown by an estimated reduction in total computer costs by a factor of 20 over not using them. This paper describes the techniques which play an important role in currently available computer software. It indicates research work in the engineering literature which can be expected to stimulate development of new techniques in the next decade. It concludes that the thrust for better techniques will be provided by the expanding need for software in newer applications such as nuclear fusion, fracture mechanics, bioengineering simulations, and vehicle crashes. New techniques will yield computer software which more highly automates finite element use, will more efficiently solve large sets of equations, and which will be engineering discipline transportable.     

Penalty methods in finite element analysis of fluids and structures

This paper discusses the use of penalty techniques in finite element Galerkin equations. It shows that earlier results relating penalty methods to mixed and Lagrange multiplier methods through the use of reduced-selective numerical integration formulas extend to problems in which there is no extremum principle. It is also shown that penalty techniques can be employed in nonlinear dynamical problems and can lead to the substantial computational benefits arising from the ability to impose constraints without Lagrange multiplier unknowns. But they also may lead to costs involving the illconditioning of certain matrices and the complication of some iterative solution procedures. Nevertheless in many problems the benefits well outweigh the costs.     

Soil-structure interaction parameters from finite element analysis

A series of two-dimensional finite element computer runs were made to compute the frequency dependent soil-structure interaction coefficients. Variations in the element size, mesh dimensions, boundary conditions, and soil hysteretic damping ratio to determine their influence on the computed interaction coefficients were made. From the calculations, it has been determined that the primary requirement of the mesh is a transmitting boundary formulation. For low damping conditions, roller support boundary conditions must be placed exceedingly far from the structure to ensure convergence of the results to the analytic solution. In addition, with such boundary conditions, the addition of artificial hysteretic soil damping cannot be used to simulate radiation damping behavior of the continuum. A frequency dependent criteria is also presented to determine minimum size elements that must be used in any calculation.     

Elbow stress indices using finite element analysis

Existing ASME Code provisions allow for an experimentally determined collapse load. This collapse (limit) load can then be used in the Code equation defining stress indices to obtain a stress index experimentally. This paper describes a research project to investigate the use of inelastic finite element analysis, rather than experiments, to obtain the collapse load. An example is given for a 2-in., schedule 40, long radius, 90°, stainless steel elbow with 10-in.-long straight pipes on each end. A B₂ index is found using this approach which is nearly 50% lower than the one obtained using the Code equation for B₂.     

On finite element analysis of pipe whip problems

The nonlinear dynamic finite element solution of pipe whip problems is presented. The finite element modelling used, the step-by-step incremental solution of the nonlinear equations of motion and design considerations are discussed. The influence of various physical parameters on the response of the pipe and the restraint, and the effects of using different finite element models are considered. Specific emphasis is directed to the verification of the accuracy of the solutions obtained using energy balance checks.     

Recent developments in the finite element analysis of prestressed concrete reactor vessels

This paper describes recent developments in the nonlinear deformation and ultimate load analysis of prestressed concrete reactor vessels using finite elements. First, a number of finite element models are called into attention for the idealization of composite structures such as reinforced and prestressed concrete components. Then different inelastic constitutive models are proposed for the behaviour of concrete in the pre- and post-failure regime. Subsequently various numerical techniques are examined for the solution of nonlinear problems, especially with regard to their distortion of the constitutive model. In conclusion these modelling techniques are applied to the analysis of four typical examples, the nonlinear deformation analysis of a concrete specimen subjected to biaxial compression, the crack analysis of a thick-walled concrete cylinder, the overload analysis of the THTR 1 : 5 scale model, and the ultimate load analysis of a concrete top closure model.     

Some computational capabilities for nonlinear finite element analysis

The computational capabilities available in the current version of the computer program ADINA for stress analysis of structures and continua are described. The program can be employed effectively for various linear and nonlinear static and dynamic finite element analyses. The solutions of some problems using ADINA are presented to indicate the solution capabilities of the program.     

Concepts underlying finite element methods for structural analysis

Several topics which underlie the finite element method tools commonly in use in the nuclear power industry are reviewed. They are important because of the understanding which they provied to the user of finite element method tools. They are collected here to popularize them and enlarge the engineer's ability to critically examine the results of his calculations. The topics are time integration and mass representation, creep analysis, finite strain plasticity, and nearly incompressible analysis.     

Further finite element structural analysis of FAST Load Assembly

The FAST (Fusion Advanced Study Torus) machine is a compact high magnetic field tokamak, that will allow to study in an integrated way the main operational issues relating to plasma-wall interaction, plasma operation and burning plasma physics in conditions relevant for ITER and DEMO. The present work deals with the structural analysis of the machine Load Assembly for a proposed new plasma scenario (10 MA – 8.5 T), aimed to increase the operational limits of the machine.A previous paper has dealt with an integrated set of finite element models (regarding a former reference scenario: 6.5 MA – 7.5 T) of the load assembly, including the Toroidal and Poloidal Field Coils and the supporting structure. This set of models has regarded the evaluation of magnetic field values, the evaluation of the electromagnetic forces and the temperatures in all the current-carrying conductors: these analysis have been a preparatory step for the evaluation of the stresses of the main structural components.The previous models have been analyzed further on and improved in some details, including the computation of the out-of-plane electromagnetic forces coming from the interaction between the poloidal magnetic field and the current flowing in the toroidal magnets.After this updating, the structural analysis has been executed, where all forces and temperatures, coming from the formerly mentioned most demanding scenario (10 MA – 8.5 T) and acting on the tokamak's main components, have been considered. The two sets of analysis regarding the reference scenario and the extreme one have been executed and a useful comparison has been carried on.The analyses were carried out by using the FEM code Ansys rel. 13.     

Discontinuity stress analysis of pressure vessels using the finite element method

In pressure vessels the centre lines of the cylinder and dome portions often do not coincide thereby leading to a discontinuity at their junction. Structural analysis of such a structure assuming the centrelines of the cylinder and dome portions to be coincident leads to an incorrect estimation of stress and displacement distributions around the discontinuity. To predict accurately the stress and displacement distributions around the discontinuity, an iterative finite element scheme is developed in this paper using a conical shell finite element. The method is applied to two typical pressure vessels, one with hemispherical end domes and the other with ellipsoidal end domes. It is found that the solution converges in a few iterations.     

有限元在杆式支撑结构力学分析中的应用

介绍有限元分析软件ANSYS在一种杆式支撑结构设计中的应用,通过模拟各种载荷工况对结构的影响分析,对HT-7U超导托卡马克冷质部件支撑结构初步设计方案做进一步的优化和完善。     

A high precision triangular plate bending element for the analysis of thick plates

A high precision triangular plate bending element for the analysis of thick plates is developed in thin paper. The element has three nodes and 12 degrees of freedom per node. Explicit expressions for stiffness coefficients are derived. The superiority of the element is demonstrated by the accuracy of the results obtained by applying it to some typical thick plate problems.     

Fully coupled strain and damage finite element analysis of ductile fracture

The local approach to fracture presented in this paper is based upon the continuum damage theory. The numerical implementation of this theory is made within the framework of the displacement approach of the finite element method. The fully coupled approach used to predict both initiation and propagation is described in detail. To demonstrate the usefulness of this type of local approach, it is applied to the prediction of initiation in an axisymmetrically notched tensile bar subjected to monotonous loading in ductile fracture conditions. The numerical problems arising when propagation of a localized completely damaged zone is modelled are outlined. To overcome these convergence problems, it is proposed to implement a new local fracture criterion together with a new method ensuring a C₀ continuity of the damage field throughout the finite element discretized structure.     

A fluid-structure finite element method for the analysis of reactor safety problems

A method is presented for the safety analysis of reactor containment structures by means of finite elements. The finite element equations of both fluid and structural elements for arbitrarily large, non-linear response are developed and the way in which they are combined is indicated. Both explicit and implicit integration of the equations in time is considered. Three examples of the application of these methods to the analyses of reactor safety problems are described.     

The structure analysis of ITER cryostat based on the finite element method

In the ITER project the cryostat is one of the most important components. Cryostat shall transfer all the loads that derive from the TOKAMAK inner basic machine, and from the cryostat itself, to the floor of the TOKAMAK pit (during the normal and off-normal operational regimes, and at specified accidental conditions). This paper researches the dynamic structure strength of the ITER cryostat during the operation of TOKAMAK. Firstly the paper introduces the types of loads and the importance of every type load to the research. Then it gives out the method of building model and principle of simplified model, boundary conditions and the way of applying loads on the cryostat. Finally the author discussed the analysis result and the strength questions of cryostat, also, the author pointed out the opinions according to the analysis results.