Finite element analysis and modeling of structure with bolted joints

In this work, in order to investigate a modeling technique of the structure with bolted joints, four kinds of finite element models are introduced; a solid bolt model, a coupled bolt model, a spider bolt model, and a no-bolt model. All the proposed models take into account pretension effect and contact behavior between flanges to be joined. Among these models, the solid bolt model, which is modeled by using 3D solid elements and surface-to-surface contact elements between head/nut and the flange interfaces, provides the best accurate responses compared with the experimental results. In addition, the coupled bolt model, which couples degree of freedom between the head/nut and the flange, shows the best effectiveness and usefulness in view of computational time and memory usage. Finally, the bolt model proposed in this study is adopted for a structural analysis of a large marine diesel engine consisting of several parts which are connected by long stay bolts.     

Finite element simulation for material accumulation and welding processes including a free melt surface

A modeling and simulation approach for problems with solid-liquid-solid phase transitions and a free surface, feasible for material accumulation processes based on laser-based free form heading and welding processes for joining different metallic materials is presented. Both named processes are modeled within the framework of continuum mechanics by coupling the Stefan problem with the Navier-Stokes equations including a free capillary surface. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite element approximation of a prestressed shell model

This work deals with the finite element approximation of a prestressed shell model formulated in Cartesian coordinates system. The considered constrained variational problem is not necessarily positive. Moreover, because of the constraint, it cannot be discretized by conforming finite element methods. A penalized version of the model and its discretization are then proposed. We prove existence and uniqueness results of solutions for the continuous and discrete problems, and we derive optimal a priori error estimates. Numerical tests that validate and illustrate our approach are given.     

Modeling of thermal phenomena in single laser beam and laser-arc hybrid welding processes using projection method

This paper concerns mathematical and numerical modeling of thermal phenomena accompanying single laser and laser-arc hybrid butt welding of steel sheets. Coupled heat transfer and fluid flow in the fusion zone were described respectively by transient heat transfer equation and Navier–Stokes equation. Laser beam and electric arc heat sources were modeled using different heat source power distributions. Latent heat associated with the material’s state changes, buoyancy forces and liquid material flow through a porous medium were taken into account in considerations. Differential governing equations were numerically solved using projection method combined with finite volume method. Elaborated solution algorithm was implemented into computer solver used for simulation of heat transfer and fluid flow during welding. The geometry of the weld and heat affected zone as well as cooling rates were estimated on the basis of numerically obtained temperature field.     

Finite element analysis of the clamp band joint

In this paper, the clamp band joint commonly used to connect cylindrical shells with end flanges is modeled using the finite element analysis software ANSYS. The joint model is validated by a series of static experiments. Then the response of the joint components to the preload and the axial load is analyzed in detail, from which the axial load capability, the axial stiffness and the damping characteristics of the clamp band joint are discussed. Finally, parametric studies are carried out to investigate the effects of the preload, the wedge angle, the friction coefficient, and the number and size of the V-segment on the behavior of the clamp band joint. This paper presents the general mechanical behavior of the clamp band joint subjected to axial loads.     

Finite element analysis of pressure vessel using beam on elastic foundation analysis

In this study, we first applied the variation principle to derive a new finite element method (FEM) based on the theory of beam on elastic foundation using line element. The derived FEM was then applied to solve, for the first time, the pressure vessel problems with uniform thickness. Our FEM results, obtained even by using only one line element, agreed exactly with the available closed-form solution, confirming the validity and computing efficiency of our finite element formulation. Moreover, we have applied our new FEM to solve pressure vessel problems with non-uniform thickness where no exact analytical solution is known to exist. The distributions of discontinuity stress in the cylindrical part were obtained. We found that shear force and bending moment were indeed discontinuous at the geometrically discontinuous juncture, due to the bending rigidity and elastic constant change by the non-uniform thickness. Finally, the case of discontinuity stresses in a bimetallic joint was also studied. The locations of maximum shear force and bending moment were found to be affected by the bending rigidity of the material.     

Numerical and experimental study of mitigation of welding distortion

Welding stresses and deformations are closely related phenomena. During the heating and cooling cycles thermal strains may occur in the weld and adjacent area. The strains produced during the heating stage of welding are always accompanied by plastic deformation of the metal. The stresses resulting from these strains combine and react to produce internal forces that cause a variety of welding distortions. Welding deformation needs to be minimized and also the designer should know before hand the extent of deformation so that it can be accounted for in the design as well as in the construction stages.In this paper, heat sinking as a method of distortion mitigation has been studied. Heat sinking has been affected by circulating water through channel clamped at the bottom surface of the plates undergoing welding. The pseudolinear equivalent constant rigidity concept has been used in this investigation for thermo-mechanical analysis of plates undergoing welding with simultaneous heat sinking. The initial nonlinear problem with varying modulus dependent on temperature is transformed into a pseudolinear equivalent system of constant rigidity that is solved by linear analysis.The numerical results compared very well with those of the experimental ones. The proposed concept is found to be computationally more efficient and simpler to model compared to FEM for solving similar thermo-elasto-plastic nonlinear problems. The procedure presented in this work and the results thus obtained, holds a great promise for determining the heat sinking parameters for effectively controlling welding distortion.     

Pseudolinear equivalent constant rigidity concept for analyzing welding residual deformation

To ascertain the extent of deformation due to the thermal cycles caused by welding it calls for solving a complex thermal elasto-plastic problem, which is non-linear and involves plastic deformation of the medium at high temperature varying in both time and space. Analytical solutions turned out to be inadequate. At the same time conventional numerical techniques proved to be highly time consuming and thereby prohibitively expensive in real life situations. The concept of pseudolinear equivalent constant rigidity system was developed in this investigation for thermo-mechanical analysis of plates undergoing variation of rigidity due to a continuously changing temperature profile as is encountered in welding situations. The initial non-linear problem with modulus varying with temperature was transformed into a pseudolinear equivalent system of constant rigidity that was solved by applying linear analysis.     

Enriched finite element spaces for transient conduction heat transfer

This paper presents an alternative approach via finite elements to treat numerically the thermal shocks in heat transfer finite element analysis. The method consists in using the standard enriched finite element approaches with time-interpolation. It will be applied here to the transient conduction heat equation where the classical Galerkin method is shown to be unstable. The proposed method consists in adding and eliminating bubbles to the finite element space and then to interpolate the solution to the real time step. This modification is equivalent to the addition of a stabilizing term tuned by a local time-dependent stability parameter, which ensures an oscillating-free solution. To validate this approach, the numerical results obtained in classical 2D and 3D benchmark problems are compared with the Galerkin and the analytical solutions.     

Finite element modeling of the nonlinear oscillations in axisymmetric acoustic resonators

Oscillation of a gas in closed resonators has gained considerable interest in the past years. In this paper, the nonlinear equations governing the behavior of the gas oscillations inside the resonator are formulated in a weak form and then modeled using the finite element method. The pressure ratios, predicted by the proposed model, are in close agreement with the exact solutions available for simple geometries such as cylindrical, exponential and linearly varying area resonators. The presented comparisons validate the accuracy of the finite element model and emphasize its potential for predicting the performance or resonators of more complex geometries which are necessary for generating high pressures from the standing waves. Also, gas flow through the boundaries of the resonator is implemented in the proposed model. The presented finite element model presents an invaluable tool for designing a new class of acoustic compressors which can be used, for example, in refrigeration and vibration control applications.     

Finite element modeling of a PE pipe heap leachate collection system

Results of finite element modeling for a series of corrugated polyethylene pipes under a typical 120 m high heap leach pad of copper bearing ore are presented. The modeling results for two different configurations illustrate the phenomena of soil structure interaction between the ore and the pipes. A trenchless configuration showed significantly smaller radial soil stresses at the springline of the pipes when compared to a shallow trench configuration with the pipes laid within a trench. Radial soil stresses at the crown and invert were of similar magnitude for both configurations. Circumferential stresses within the soil around the pipes were also similar. Pipe thrust and bending moment at the invert location were significantly reduced in the trench-less configuration.     

Extended finite element modeling of deformable porous media with arbitrary interfaces

In this paper, an enriched finite element method is presented for numerical simulation of saturated porous media. The arbitrary discontinuities, such as material interfaces, are encountered via the extended finite element method (X-FEM) by enhancing the standard FEM displacements. The X-FEM technique is applied to the governing equations of porous media for the spatial discretization, followed by a generalized Newmark scheme used for the time domain discretization. In X-FEM, the material interfaces are represented independently of element boundaries and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of elements. Finally, several numerical examples are analyzed, including the dynamic analysis of the failure of lower San Fernando dam, to demonstrate the efficiency of the X-FEM technique in saturated porous soils.     

Finite element modeling of galvanic corrosion during chemical cleaning of westinghouse series 51 steam generator

Galvanic corrosion rates during the chemical cleaning of the Westinghouse Series 51 Steam Generator have been calculated using a finite element method. The results show that the galvanic action between the I-600 tube bundle and various carbon steel structures produces low galvanic corrosion rates on the base metal of the carbon steel surfaces, but high rates on the heat affected zones of welds. An explanation of the large difference in galvanic corrosion rates as well as methods to minimize the galvanic corrosion rate on the heat affected zones are discussed. Based on the modeling results, a test configuration to simulate the galvanic action in the steam generator is suggested.     

Stability of welding problem with perturbations

This paper discusses the stability of the welding problem of the infinite plane with a hole and a plate which are welded together. Using the complex variable methods, error estimates of stresses and displacement are obtained.     

Finite element modeling of a generic stemless hip implant design in comparison with conventional hip implants

In this study, the finite element modeling and comparison of the stress and strain analyses were carried out for three different structures that are intact bone, stemless implant and stemmed one. Currently proposed stemless design studied here is the generic concept of stemless implant. This generic stemless implant reconstruction was numerically compared to the conventional stemmed implant and also to the intact bone as control solution. Two loading conditions were applied to the most proximal part of the models, while the most distal part was fixed for all degrees of freedom. The models were divided into two regions and studied along two paths of medial and lateral aspect. The results of this study showed that the stemless implant had less deviation from the control solution of the bone in all regions and in both loading conditions, comparing to the large deviation of the stemmed implant from the intact bone. However, it was shown that the fixation of this type of implant and its effect on sub-trochanter region must be carefully considered for designing the final product of any specific design of stemless implant.     

Finite element analysis of laminar and turbulent flows using LES and subgrid-scale models

Numerical simulations of laminar and turbulent flows in a lid driven cavity and over a backward-facing step are presented in this work. The main objectives of this research are to know more about the structure of turbulent flows, to identify their three-dimensional characteristic and to study physical effects due to heat transfer. The filtered Navier–Stokes equations are used to simulate large scales, however they are supplemented by subgrid-scale (SGS) models to simulate the energy transfer from large scales toward subgrid-scales, where this energy will be dissipated by molecular viscosity. Two SGS models are applied: the classical Smagorinsky’s model and the Dynamic model for large eddy simulation (LES). Both models are implemented in a three-dimensional finite element code using linear tetrahedral elements. Qualitative and quantitative aspects of two and three-dimensional flows in a lid-driven cavity and over a backward-facing step, using LES, are analyzed comparing numerical and experimental results obtained by other authors.     

Finite element approximation of -surfaces

In this paper a piecewise linear finite element approximation of -surfaces, or surfaces with constant mean curvature, spanned by a given Jordan curve in is considered. It is proved that the finite element -surfaces converge to the exact -surfaces under the condition that the Jordan curve is rectifiable. Several numerical examples are given.

     

Finite element simulation for dynamic large elastoplastic deformation in metal powder forming

In this paper, a transient dynamic analysis of the powder compaction process is simulated by a large displacement finite element method based on a total and updated Lagrangian formulation. A combination of the Mohr–Coulomb and elliptical yield cap model, which reflects the stress state and degree of densification, is applied to describe the constitutive model of powder materials. A Coulomb friction law and a plasticity theory of friction in the context of an interface element formulation are employed in the constitutive modelling of the frictional behaviour between the die and powder. Finally, the powder behaviour during the compaction of a plain bush, a rotational flanged and a shaped tip component are analysed numerically. It is shown that the updated Lagrangian formulation, using a combination of the Mohr–Coulomb and elliptical cap model, can be effective in simulating metal powder compaction.     

Applications of the three dimensional finite element alternating method

This paper describes some recent applications of the three dimensional finite element alternating method (FEAM). The problems solved involve surface flaws in various types of structure. They illustrate how the FEAM can be used to analyze problems involving mechanical and thermal loads, residual stresses, bonded to composite patch repairs, and fatigue.     

Modelling of heat affected zone in cylindrical steel elements surfaced by welding

Computational models of a temperature field in cylindrical steel elements surfaced by the following methods: controlled pitch, spiral welding sequence and spiral welding sequence with swinging motion of the welding head are presented in the paper. The lateral surface of regenerated cylindrical object, subjected to the welding heat source, has been treated as a plane rolled on cylinder and temperature field of repeatedly surfaced plain massive body was solved. Temperature rises, caused by overlaying consecutive welding sequences and self-cooling of areas previously heated, were taken into consideration in the solution. The computations of the temperature field for continuous casting steel machine roll made of 13CrMo4 steel were carried out.