Finite Element Idealization Research Articles

Fibre reinforced polymer for strengthening cylindrical metal shells against elephant’s foot buckling: An elasto-plastic analysis

This article describes the use of fibre reinforced polymer composites to increase the strength of an isotropic metallic cylindrical shell against elephant’s foot buckling. This form of buckling occurs when a cylindrical shell structure is subjected to high internal pressure together with an axial force, such as those that may occur in tanks and silos. It is particularly relevant to tanks under seismic action. Although fibre reinforced polymer composites have been widely applied to different types of structures under several loading conditions, its use to strengthen thin steel cylindrical shells has been very limited. Here, a non-linear elasto-plastic finite element idealisation is used to explore the strengthening effect of a fibre reinforced polymer strip on a thin cylinder. The optimum size and position of the fibre reinforced polymer sheet were obtained and empirically formulated. This study has shown that the strength after repair is sensitive to minor changes in the fibre reinforced polymer parameters so that a close adherence to the optimum parameter values is very desirable.

Several seam weld finite element idealizations challenged in fatigue within a French industrial collaborative workgroup

In industry with fatigue strengthening concern, there are as many ways to make an FE seam weld idealization as factories involved in these types of simulations. Tens of ways to model a seam weld are available as soon as it is necessary to get out of direct connection assumption and if it is needed to take into account local weld stiffness and secondary bending effect of the fillet weld. Then it becomes mandatory to be able to discriminate such idealization processes while evaluating associated life prediction accuracy and industrial idealization efficiency (automation). This concern leads the idea to create a French industrial workgroup including CETIM and about 20 industrial companies, members of the “Mobile Machinery Program Committee”. The main goal of this collaborative project being to challenge well documented and most promising seam weld idealization models (with associated methods) to converge at the end towards the most capacitive ones (with better results on given fatigue metrics).As a first part of the multi-partner project work, a complete and precise technical review was achieved, giving a state of the art of the idealization models and methods available. Then the workgroup started extensive comparisons between well documented fatigue tests on seam welded components and associated FEA for some retained models and methods (Fayard, Lohr, IIW Hot Spot Stress, Notch Stress). Several components were considered, with more than 100 fatigue test results. This paper presents most of the obtained results, the Round Robin being still on-going. Preliminary results comparisons demonstrate general applicability of classical methods introduced in the standards or recommendations, these being also in most cases conservative. Results of this work aim to help choosing the right methodology, depending of the seam weld configuration and the in service loadings. It is also intended to try building partnerships with FE software editors to include most efficient methodologies in an automated way, making less tedious the seam weld modelling task on huge chassis frames. Small and medium factories should then reach an efficiency gain and improved accuracy level when building their virtual seam welded frames with new automated scripts integrated in their own FEA solutions.

An online input force time history reconstruction algorithm using dynamic principal component analysis

Abstract The knowledge of dynamic loads acting on a structure is always required for many practical engineering problems, such as structural strength analysis, health monitoring and fault diagnosis, and vibration isolation. In this paper, we present an online input force time history reconstruction algorithm using Dynamic Principal Component Analysis (DPCA) from the acceleration time history response measurements using moving windows. We also present an optimal sensor placement algorithm to place limited sensors at dynamically sensitive spatial locations. The major advantage of the proposed input force identification algorithm is that it does not require finite element idealization of structure unlike the earlier formulations and therefore free from physical modelling errors. We have considered three numerical examples to validate the accuracy of the proposed DPCA based method. Effects of measurement noise, multiple force identification, different kinds of loading, incomplete measurements, and high noise levels are investigated in detail. Parametric studies have been carried out to arrive at optimal window size and also the percentage of window overlap. Studies presented in this paper clearly establish the merits of the proposed algorithm for online load identification.

Effect of tool surface topography on friction with carbon fibre tows for composite fabric forming

The effect of tool surface roughness topography on tow-on-tool friction relevant to the dry forming of composite fabrics is investigated. A comprehensive range of tool average surface roughness Ra values from 0.005 to 3.2 μm was used in friction testing with carbon fibre tows. The measured slope of these surfaces, which is the critical surface topographical characteristic, increased significantly with increasing roughness amplitude. Friction was found to be sensitive to roughness topography for very smooth surfaces (Ra<0.1μm) and increased with decreasing roughness slope and amplitude. For rougher surfaces (Ra>0.1μm), friction was relatively insensitive to roughness slope and amplitude. A finite element idealisation of the tow-on-tool contact was used to explain these results in terms of the level of tow-tool conformance. Smooth surfaces have low slopes which allow good conformance, and hence high real contact area and friction. Rougher surfaces have high slopes, particularly at shorter wavelengths, which prevents good conformance. In this case, point contact between fibres and surface dominates, leaving the resulting friction less sensitive to roughness.

Aerothermoelastic-Acoustics Simulation of Flight Vehicles

This paper describes a novel computational-fluid-dynamics-based numerical solution procedure for effective simulation of aerothermoacoustics problems with application to aerospace vehicles. A finite element idealization is employed for both fluid and structure domains, which fully accounts for thermal effects. The accuracies of both the fluid and structure capabilities are verified with flight- and ground-test data. A time integration of the structural equations of motion , with the governing flow equations, is conducted for the computation of the unsteady aerodynamic forces, which uses a transpiration boundary condition at the surface nodal points in lieu of the updating of the fluid mesh. Two example problems are presented herein to that effect. The first one relates to a cantilever wing with a NACA 0012 airfoil. The solution results demonstrate the effect of temperature loading that causes a significant increase in acoustic response. A second example, the hypersonic X-43 vehicle, is also analyzed; and relevant results are presented. The common finite element-based aerothermoelastic-acoustics simulation process, its applicability to the efficient and routine solution of complex practical problems, the employment of the effective transpiration boundary condition in the computational fluid dynamics solution, and the development and public domain distribution of an associated code are unique features of this paper.

Vibroacoustic performance of fiber metal laminates with delamination

ABSTRACTIn the present work, the numerical assessment of vibroacoustic (VA) performance of fiber metal laminates (FML) with mid-plane center delamination is presented. A fluid structure interaction study has been done using finite element method (FEM). Experimental validation is performed on an aluminium (AL) panel for verifying the correctness of finite element (FE) idealization procedure to simulate the fluid-structure interaction. Delamination is introduced in the FE model of FML panel and VA analysis is subsequently carried out. Sound transmission loss (STL) is computed on the panel with center delamination and without delamination. The overall sound pressure level (OASPL) shows that the presence of delamination (40% in total area) in FML has not changed the total energy of the transmitted sound when compared to aluminium and composites. However, in the narrow frequency bands (150–200 Hz, 200–250 Hz), the sound transmission nature has been significantly affected due to local delamination modes participating in the fluid-structure interaction process.

A coupled hydrodynamic–structural model of the M4 wave energy converter

A method is developed for modelling wave energy converters consisting of floats connected by slender structural elements. The hydrodynamic and structural dynamic analyses are separated in a two-stage process, though the model is fully coupled. The method of dynamic substructuring is used to achieve this separation. The linear diffraction/radiation problem is solved with a finite element idealisation for axisymmetric floats, and drag forces are incorporated by equivalent linearization. Results for a planar representation of the M4 device, and comparisons of theory and experiments undertaken for two scale models tested in regular and random waves, confirm the validity of the theoretical approach. A series of parametric studies is performed to clarify the important physical variables, including natural periods, the ratio of a characteristic length of the device to the wave length, and power take-off.

Finite Elements in Rotordynamics

Equation of motion of rotating structures may be derived referring to co-rotating as well as fixed reference systems. Correspondingly, different additional matrices must be taken into account in finite element idealization. Symmetry is very important since axisymmetric as well as cyclic-symmetric structures after Coleman transformation may be investigated in fixed coordinates whereas unsymmetric rotors with isotropic support are usually studied in co-rotating coordinates. In the most general case one gets a system of equation with periodic coefficients which may be solved using Floquet's theory.

Impact of finite element idealisation on the prediction of welded fuselage stiffened panel buckling

Lap joints are widely used in the manufacture of stiffened panels and influence local panel sub-component stability, defining buckling unit dimensions and boundary conditions. Using the finite element method it is possible to model joints in great detail and predict panel buckling behaviour with accuracy. However, when modelling large panel structures such detailed analysis becomes computationally expensive. Moreover, the impact of local behaviour on global panel performance may reduce as the scale of the modelled structure increases. Thus this study presents coupled computational and experimental analyses, aimed at developing relationships between modelling fidelity and the size of the modelled structure, when the global static load to cause initial buckling is the required analysis output. Small, medium and large specimens representing welded lap-joined fuselage panel structure are examined. Two element types, shell and solid-shell, are employed to model each specimen, highlighting the impact of idealisation on the prediction of welded stiffened panel initial skin buckling.

Optimal Protection of Reactor Hall Under Nuclear Fuel Container Drop Using Simulation Methods

Abstract This paper presents of the optimal design of the damping devices cover of reactor hall under impact of nuclear fuel container drop of type TK C30. The finite element idealization of nuclear power plant structure is used in software ANSYS. The steel pipe damper system is proposed for dissipation of the kinetic energy of the container free fall in comparison with the experimental results. The probabilistic and sensitivity analysis of the damping devices was considered on the base of the simulation methods in program AntHill using the Monte Carlo method.

Warping torsion in commercial vehicle frames, taking into consideration flexible joints

The torsional behaviour of commercial vehicle frames is dominated by warping torsion, because warping is inhibited in the joints where the cross–members are attached to the side–members. This paper presents a hybrid method of analysis, which combines finite element idealization of the joint areas with analytically derived beam elements for the cross–members and side–member sections. The beam element includes warping torsion force–displacement relationships. Thus, the flexibility of the joints is included together with the compatibility of warping displacements. The method gives close agreement with experimental results.

Bus vibration study - finite element modelling and determination of the eigenpairs

This paper describes the finite element idealisation of a typical Indian transport bus and uses this model to predict the first few eigenpairs. The eigenvalue problem has been solved by the simultaneous iteration method and Lanczos' scheme and by using two different finite element models. The first model consists of chassis elements, the axles, the suspensions and the tyres, the mass of the superstructure being lumped at the appropriate nodes. The second is a more comprehensive model in which, in addition to the chassis, axles, suspension and tyres, the framework of the superstructure and the plates constituting the bus body and floor have been taken into account. The eigenfrequencies obtained by using both these models match well with frequencies arrived at experimentally.

Time-dependent analysis of cable domes using a modified dynamic relaxation method and creep theory

The stiffness of cable domes is conditioned by their states of prestress. The decrease of prestress due to creep of cables determines the serviceability and load bearing capacity of the cable dome. In this paper, a modified dynamic relaxation method for a time-dependent non-linear static analysis of cable domes based on the application of creep theory is presented. Creep constitutive equations in logarithmic forms are directly used for the adjustment of cable lengths. The applicability of the modified dynamic relaxation method to this type of structures composed of steel and synthetic cables and struts with a finite element idealisation is demonstrated.

Optimal Design of NPP Containment Protection Against Fuel Container Drop

This paper presents a optimal design of a damping devices for the protection of the reinforced concrete structure of a nuclear power plant (NPP) against the impact loads from a container of nuclear fuel of the type TK C30 drop. The finite element idealization of the building structure is used in space. The interaction of the soil-structure, as well as the fluid-structure of the deactivated basin is considered in space. A steel pipe damper system is proposed for the dissipation of the kinetic energy of the container is free fall. The Newmark’s integration method is used for the solution of the dynamic equations.

Free and forced vibration analyses of ship structures using the finite element method

With increases in ship size and speed, shipboard vibration becomes a significant concern in the design and construction of vessels. Excessive ship vibration is to be avoided for passenger comfort and crew habitability. In addition to the undesired effects on humans, excessive ship vibration may result in the fatigue failure of local structural members or malfunctioning of machinery and equipment. The propeller induces fluctuating pressure on the surface of the hull, which induces vibration in the hull structure. These pressure pulses acting on the ship hull surface above the propeller are the predominant factor for vibrations of ship structures are taken as excitation forces for forced vibration analysis. Ship structures are complex and may be analyzed after idealization of the structure. Several simplifying assumptions are made in the finite element idealization of the hull structure. In this study, a three-dimensional finite element model representing the entire ship hull, including the deckhouse and machinery propulsion system, has been developed using solid modeling software for local and global vibration analyses. Vibration analyses have been conducted under two conditions: free–free (dry) and in-water (wet). The wet analysis has been implemented using acoustic elements. The total damping associated with overall ship hull structure vibration has been considered as a combination of the several damping components. As a result of the global ship free vibration analysis, global natural frequencies and mode shapes have been determined. Moreover, the responses of local ship structures have been determined as a result of the propeller-induced forced vibration analysis.

Fatigue Analysis of Aluminum Alloy Wheel Under Radial Load

In this paper a detailed “Fatigue Analysis of Aluminum Alloy Wheel under Radial Load”. During the part of project a static and fatigue analysis of aluminum alloy wheel A356.2 was carried out using FEA package. The 3 dimensional model of the wheel was designed using CATIA. Then the 3-D model was imported into ANSYS using the IGES format. The finite element idealization of this modal was then produced using the 10 node tetrahedron solid element. The analysis was performed in a static condition. This is constrained in all degree of freedom at the PCD and hub portion. The pressure is applied on the rim. We find out the total deformation, alternative stress and shear stress by using FEA software. And also we find out the life, safety factor and damage of alloy wheel by using S-N curve. S-N curve is input for a A.356.2 material.

Deterministic and probabilistic analysis of damping device resistance under impact loads from nuclear fuel container drop

Deterministic and probabilistic analysis of damping device resistance under impact loads from nuclear fuel container dropThis paper presents a deterministic and probabilistic solution of damping devices for the protection of the reinforced concrete structure of a nuclear power plant (NPP) from impact loads from a container of nuclear fuel of the type TK C30 drop. The finite element idealization of the building structure is used in space. The interaction soil-structure, as well as the fluid-structure of the deactivated basin is considered in space. A steel pipe damper system is proposed for the dissipation of the kinetic energy of the container in free fall. The Newmark integration method is used for the solution of the dynamic equations. The sensitivity and probabilistic analysis of the damping devices was realized using the AntHILL and ANSYS software.

Coupling FEM and symmetric BEM for dynamic interaction of dam–reservoir systems

A numerical model coupling boundary and finite elements suitable for dynamic dam–reservoir interaction is presented herein. This model involves standard finite element idealization of the dam structure displacements and a new symmetric boundary element formulation of the unbounded reservoir domain leading to an equivalent symmetric stiffness matrix for the discretized pressure field. These two basic parts of the computation are directly coupled by imposing an equilibrium condition at the fluid–structure interface, then the resulting algebraic system is reduced by localizing the coupled terms in the global mass matrix such as usually achieved in the added-mass formulation. Finally, the performance and the accuracy of this model are examined by comparing its results to those obtained from three other numerical models.

Blended wing body structures in multidisciplinary pre-design

The structural analysis of blended wing body (BWB) aircraft configurations is presented in the context of a preliminary, multidisciplinary aircraft design process by means of the aircraft design and optimization program (PrADO) of the Institut of Aircraft Design and Lightweight Structures of the TU Braunschweig. A multidisciplinary process is described that enables parametric creation of detailed finite element models and its loads. Iteratively different flight conditions are trimmed and corresponding pressure distributions calculated by the higher-order subsonic and supersonic panel code HISSS. Each defined loading condition is used for the iterative structural sizing of the primary structure. Based on finite element idealization, a mass estimation of all structural masses is performed. The primary and secondary masses are fed back into the closed overall aircraft optimization loop of PrADO until this iterative procedure shows convergence on calculated aircraft variables (e.g., aircraft masses and static engine thrust). This automated process enables further configuration improvements using manual parametric variations or optimization features of PrADO with an objective function being defined by fuel consumption, aircraft mass, or direct operating costs. Different structural solutions and their integration in the global model are presented for passenger versions of a 700 passenger BWB with special consideration of a pressurized cabin. As an example, structural masses and parametric studies on the influence of the center body rib spacing are presented and compared by weight breakdowns.

Equivalent gas permeability of concrete samples subjected to drying

The aim of this work is to give an equivalent gas permeability in order to estimate the associated flow through a concrete specimen exposed to drying, for example with a non-uniform moisture distribution inside (equivalent to a saturation profile), and related to the apparent permeability value, calculated for the same dry sample. The chain of reasoning to obtain this permeability for a given drying situation requires estimation of the water content profile via a model of drying, and of the relative permeability (determined for a given constant moisture content in concrete) over the entire saturation field. The method is based on a finite element idealisation of the sample thickness by a discrete approach in one dimension. It is the analogy between Darcy's law and Ohm's law that allows the local relative permeability to be likened to a local conductivity. Then the existing relation between conductivity and conductance leads to the determination of an equivalent conductance that is transformed into an equivalent conductivity. Thus the equivalent permeability that is calculated on the basis of this modelling is representative of a real in-situ phenomenon. This approach allows a more precise estimation of the flow rate variation in structures subjected to pressure increase as, for instance, in security tests of nuclear containment vessels.