Nonlinear Finite Element Method Model Research Articles

Research on Structural Collapse of a Containership under Combined Bending–Torsion by Oblique Waves

Large waves cause a great number of collapsed-ship accidents, resulting in the loss of many lives and properties. It has been found that most of these collapses are caused by encountering oblique waves. As a result, the ship structure experiences a complex collapse under combined bending and torsion. This paper utilizes a numerical hydroelasto-plastic approach, coupling CFD (Computational Fluid Dynamics) with the nonlinear FEM (Finite-Element Method), to study the structural collapse of a containership in oblique waves. First, a 4600 TEU containership was selected to study its collapse mechanism under oblique waves. Second, a hydroelasto-plastic numerical coupling of CFD and nonlinear FEM is used to co-calculate the wave loads and structural collapse of containership. The hydrodynamic model is constructed and used to solve wave loads in the CFD solver, and a nonlinear FEM model of containership with finer meshes is also modeled to solve the structural collapses, including plasticity and buckling. Third, several oblique-wave cases involving heading angles of 120°, 135°, 150°, and 180° are determined and calculated. Typical cases are discussed for time-domain stress histories and collapsed courses. Finally, the influence of oblique-wave parameters on structural collapse is discussed, and the collapse mechanism of containerships under the action of oblique waves is obtained, which provides a new understanding of ship structure design.

HTS Tape Mechanical Behavior Sensitivity on Material Properties and Thickness of Material Layers

Multilayer 2G high-temperature superconductor (HTS) tapes undergo various mechanical loading steps as part of a superconducting magnet operation. The mechanical loading steps include cool-down to cryogenic temperatures and Lorentz forces when powering up the magnets. Studying the mechanical behavior of the constituent layers in a HTS tape can reveal the strain or stress level in each layer and help in predicting the probability of mechanical failure or critical current degradation. A detailed finite element method (FEM) -based simulation models enable us to estimate the mechanical behavior in each layer. However, defining the model parameters for material mechanical properties or thickness of each material layer can have consid-erable uncertainty due to variation in manufacturing processes and missing measurements of material properties within these tapes. The material properties in thin layers may not exactly comply with bulk materials of the same kind. In this paper we present a sensitivity analysis for mechanical behavior dependence on material properties variation in the constituent layers of a HTS tape. The results give important insight about the accuracy and reliability of mechanical simulation results and guide the priorities in future material characterization. In addition, we will investigate the effect of the thickness of Hastelloy layer on effective macroscopic mechanical behavior of the tape. A nonlinear elastoplastic FEM model is used for performing the simulations.

Parametric study for shear design of cold-formed channels with elongated web openings

Cold-formed steel members are commonly perforated with elongated web openings in practice to allow more access for the building service systems. The presence of such extended web holes in the members, when subjected to high shear forces, influences the shear buckling characteristics, the shear failure modes and generally leads to a reduction of shear capacity as well. In order to provide a better insight into the shear behaviour of cold-formed members with elongated web cut-outs, this paper presents a numerical study using finite element method (FEM) models employing ABAQUS/Standard to investigate the elastic shear buckling and post-buckling behaviour of cold-formed members in the form of thin channel sections. A full non-linear FEM model is developed and calibrated against previous shear tests with elongated web holes carried out using a dual actuator test rig. Based on the successful calibration against the tests, a parametric investigation is conducted to extend the resulting database. Further, a new proposal for the Direct Strength Method (DSM) of design of perforated channels in shear with both non-elongated and elongated web holes is further validated by using the results from the parametric study. A comparison between the empirical approach (“qs” method) and the new DSM of design derived from the Vierendeel mechanism approach is also provided to enhance the applicability of the new proposal to different cases of perforated channel members in shear with a wider range of sectional dimension and thicknesses.

Lumped Parameter Modeling and Snap-Through Stability Analysis of Planar Hydraulically Amplified Dielectric Elastomer Actuators

AbstractIn this paper, we established an analytical model that avoids extensive numerical computation for the analysis of a hydraulically amplified dielectric elastomer actuator. This actuator comprises a thin elastomer shell filled with an incompressible dielectric fluid coupled with a pair of electrodes placed in the central area. Application of high voltage on the electrodes inflates the actuator due to the induced Maxwell stress that pressurizes the incompressible dielectric fluid. The lumped parameter model predicts the stable functional region and the snap-through instability in the actuator. The model was compared with multi-physics finite element models that considered both linear elastic and nonlinear Mooney–Rivlin materials. The proposed model showed good agreement in the estimation of the actuation strain and the hydrostatic pressure as a function of voltage when compared to the finite element results. The average error in the axial and radial actuation using the proposed analytical model and nonlinear finite element method models was 1.62% and 3.42%, respectively. This shows the model strength in the estimation of the actuator states and the critical voltage to avoid snap-through instability, required in applications such as control algorithms.

EVALUATION OF REINFORCING BARS RATIO EFFECTS ON SCC BEAM-COLUMN JOINT PERFORMANCE

Beam-column joints require a high ductility during the unexpected loadings that necessitate the need for ductile concrete in such unprotected locations. Alternatively, self-compacting concrete (SCC) is a sort of concrete which has generated tremendous interest throughout the last decades in order to reach a ductile structural elements during the seismic actions. Specific properties of this type of concrete include high performance, high resistance against segregation and needless to internal or external vibration in order to compact. In the seismic regions, ductility is one of the most important factors in the design of reinforced concrete (RC) members, especially structural joints flexural performance; it is due to the enhance in the capability of plastic deformability. This paper describes load-displacement behavior of experimental and theoretical analysis of four SCC beam-column joints with different percentage of the ratio of the reinforcing bars (ρ). In the theoretical phase of this investigation three-dimensional nonlinear finite element method (FEM) model i.e., Seismostruct was used and the load-deflection diagrams were plotted to compare the test results with the numerical output. The experimental results and nonlinear FEM modeling indicate that using SCC as a workable concrete in beam-column joints of reinforced concrete structures has satisfactory performance in terms of ductility and energy dissipations.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

Highly orthotropic panels structural stability, Farrar and Bloch waves theory

PurposeThe purpose of this paper is to present the studies to develop structural highly orthotropic panels. These types of panels provide the capabilities required for structural morphing. They are highly deformable in one given direction; and in the perpendicular direction, one must be compliant to sustain the internal loads per certification stiffness and strength requirements.Design/methodology/approachNeither classic orthotropic panels nor regular cellular solids Bloch wave theories are strictly applicable on their study. A combination of computational method, MATLAB-coded, to analyze stability and classic structural beam theory is studied. Then, non-linear finite element method models are developed for an aerospace control surface application; their results are compared with reported Bloch wave sequences on periodic cellular solid panels.FindingsThe stability along stiffer direction is a requirement to obtain a continuous deformation and plasticization sequence of the cell rows in the perpendicular direction. A sample panel is sized and 3D modeled, and then produced using additive layer manufacturing process to demonstrate the initial stages of a validation and verification campaign.Originality/valueThis paper provides a new method to mechanical characterize highly orthotropic panels.

Study on influence of nonlinear finite element method models on ultimate bending moment for hull girder

The various assessment methods of ultimate strength for hull girder of ships or offshore structures might lead to different results and computation time. The nonlinear finite element (FE) analyses include the implicit static analysis and explicit dynamic analysis, which both can consider the large deflection and material nonlinearity during the process of progressive collapse. Comparing with the implicit static analysis, the explicit dynamic analysis can consider the transient influence of time and avoid the convergence issue in iterative procedure. The object of the present paper is to figure out a reliable and suitable FE modelling in the explicit dynamic method, which could keep the balance of the acceptable accurate results and computation resources. Several influential factors on the collapse behaviours of hull girder are discussed including boundary conditions, geometric ranges of finite element model, element types, loading methods and loading time. The results of a Suezmax oil tanker and Reckling models assessed by the explicit dynamic method are compared with that by the other analytical methods or in the experiment.

Analytical and parametric study on masonry infilled reinforced concrete frames using finite element method

A nonlinear finite element method model for masonry infilled reinforced concrete frames was used to conduct a parametric study on the effects of reinforced concrete frame—masonry infill interface s...

On Buckling Collapse of a Fusion-welded Aluminum-stiffened Plate Structure: An Experimental and Numerical Study

The primary objective of the present paper is to experimentally examine the buckling collapse characteristics of fusion welded aluminum-stiffened plate structures under axial compression until and after the ultimate limit state is reached. The secondary objective of the paper is to study a nonlinear finite element method modeling technique for computing the ultimate strength behavior of welded aluminum structures. A set of aluminum-stiffened plate structures fabricated via gas metal arc welding is studied. The test structure is equivalent to a full scale deck structure of an 80 m long high speed vessel. The plate part of the structures is made of 5383-H116 aluminum alloy, and extruded stiffeners are made of 5083-H112 aluminum alloy. Welding induced initial imperfections such as plate initial deflection, column type global initial deflection of stiffeners, sideways initial distortion of stiffeners, welding residual stresses, and softenng in the heat-affected zone are measured. The ANSYS nonlinear finite element method is employed for the numerical computations of the test structure’s ultimate strength behavior by means of a comparison with experimental data. Insights and conclusions developed from the present study are documented.

Effects of Welding Residual Stresses on High Tensile Steel Plate Ultimate Strength: Nonlinear Finite Element Method Investigations

The primary objective of the present paper is to examine the effects of welding residual stresses on ultimate strength of high tensile steel plates under axial compression in terms of their magnitude and pattern. The ANSYS nonlinear finite element method is employed for the purpose. The secondary objective of the present paper is to study a nonlinear finite element method modeling technique for welded plate structures with residual stresses. Three levels of residual stresses, namely slight, average, and severe, are considered. As another important parameter of influence on the plate ultimate strength, the plate thickness is also varied in the numerical computations to examine their role and trend. Important insights and conclusions developed from the present study are documented.

Collision-Accidental Limit States Performance of Double-Hull Oil Tanker Structures: Pre-CSR versus CSR Designs

To mitigate the impact of consequences of ship collisions in terms of health, safety, and the environment, it has been made mandatory that hull structures of all oil tankers have double sides and double bottoms. In recent years, International Association of Classification Societies (IACS) has developed Common Structural Rules (CSR) for structural design of double-hull oil tankers on the basis of limit states, together with the traditional approach using the allowable working stress that has been a basis of pre-CSR. The application of CSR may result in some differences in terms of structural performance, among other aspects. The main objective of the present paper is to investigate the structural performance of CSRdesigned tankers associated with ship collisions. This aspect might be interesting, although CSR are not intended specifically to improve collision performance. As an illustrative example, an AFRAMAX-class double-hull oil tanker structure with same deadweight designed by both pre-CSR and CSR methods is studied by comparing their collision energy-absorption capabilities as obtained by nonlinear finite element methods. It is found that the collision performance of the CSR design could be improved by 5% to 25% compared with that of the pre-CSR design, depending on the accidental limit state criteria. However, it is concluded that the strength performance of the CSR vessel is similar to that of the pre-CSR vessel in terms of collision-accidental limit states, considering the uncertainties involved in conjunction with collision scenarios and nonlinear finite element method modeling techniques. Although the present study deals with some very specific scenarios of collisions, the insights and conclusions developed will still be useful for recognizing a structural design trend related to collision-accidental limit states

Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part I: Plate elements

For design and strength assessment of various types of structures such as ships, offshore platforms, land-based structures, and aerospace structures, it has been realized that ultimate limit states (or ultimate strength) are much better basis than the allowable working stresses. Within the framework of ultimate limit state design and strength assessment, the primary task is to determine the level of imposed actions which causes the ultimate limit states. The aim of the present study is to develop some useful insights on nonlinear finite element method application for ultimate limit state assessment of steel stiffened-plate structures subject to combined biaxial compression and lateral pressure actions. As an illustrative example, outer bottom stiffened-plate structures of 100,000 ton class double-hull oil tankers are considered. The present study consists of two parts; Part I deals with plate elements surrounded by stiffeners or support members, and Part II treats stiffened panels, where some important factors of influence such as structural dimensions, initial imperfections, loading types and computational techniques in association with ultimate limit states are studied. For ultimate limit state computations, ANSYS nonlinear finite element method together with ALPS/ULSAP semi-analytical method is employed. Important insights developed from the present study are documented.

Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part II: Stiffened panels

The present paper (Part II) is a sequel to the previous paper (Part I) [Paik JK, Seo JK. Nonlinear finite element method models for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions—Part I: Plate elements. Thin-Walled Struct 2008, this issue, doi:10.1016/j.tws.2008.08.005.] on the application of nonlinear finite element methods for ultimate strength analysis of steel stiffened-plate structures under combined biaxial compression and lateral pressure actions. In contrast to Part I dealing with plate elements, the present paper (Part II) treats stiffened panels surrounded by strong support members such as longitudinal girders and transverse frames. In similar to Part I, some important factors of influence such as structural dimensions, initial imperfections, loading types and computational techniques in association with ultimate limit states are studied. Some useful insights in terms of nonlinear finite element method modeling are developed using ANSYS code together with the ALPS/ULSAP semi-analytical method, the latter being for the purpose of a comparison.

Application of the Improved Immune Algorithm to Structural Design Support System

Genetic algorithms (GAs), based on a multipoint search method and a crossover operation, are useful search procedures for combinatorial optimization problems. They also are applied to many kinds of practical optimization problem. However, in general, the GAs have a tendency to decrease rapidly of population diversities in processes of searching. In order to address this drawback, some researchers have proposed new algorithms for maintaining the population diversity. On the other hand, immune algorithms (IAs) are optimization techniques that imitate immune systems in an organism. The IAs are able to obtain a multiple quasi-optimum solution while maintaining the population diversity compared with GAs. In this paper, in order to consider the application of the IAs to optimum structural design problems, we developed a useful design support system for reinforced concrete (RC) slabs by combining a three-dimensional (3D) nonlinear dynamic finite element method (FEM) and an improved immune algorithm (IA). For the analysis of impact failure behavior of RC slabs, layered nonlinear FEM models with thin plate bending elements, and 3D elastoplastic FEM models with eight-node isoparametric hexahedral elements were used. First, an existing IA was modified to make it suitable for RC slab design, and both genetic and immune algorithms were applied to optimization problems with multiple optimum solutions. This modified IA was also applied to quasi-optimization problems with multiple maximum values. By comparing the above two approaches, the usefulness of the IA for design problems with discrete parameters was verified. Next, indices for evaluating impact resistance were discussed, and design simulation was conducted, based on these indices, by combining the layered nonlinear FEM and the IA. From results obtained, the accuracy and usefulness of the IA-based design support system were discussed. For obtaining a more practical design support system, shear reinforcement will be taken into account by combining the IA with the 3D elastoplastic FEM. Furthermore, the effectiveness and future potential of the design support system were confirmed by investigating an effect of introducing a database of design plans.

Numerical simulation of steel-plate strengthened concrete beam by a non-linear finite element method model

Strengthening with epoxy bonded steel plate is one of the most widely used techniques for flexural upgrading of reinforced concrete (RC) beams. However, debonding failure at the plate cut-off zone and or in the vicinity of flexure and shear cracks leads to catastrophic failure of the upgraded beams. This particular failure depends on several factors such as the distance of plate curtailment from the support, plate thickness and the provision of end anchors. Since the conventional beam theory cannot predict the debonding failure of such beams, a finite element model capable of predicting the overall behavior of strengthened beams including different failure modes accurately is developed. This paper presents the formulation of finite elements and material models and simulation results of some RC beams tested for flexural strengthening with epoxy bonded steel plates.

Modeling of poling behavior of ferroelectric 1-3 composites

Piezoelectric 1-3 composites are typically prepared from a polymer matrix and an unpoled Pb(ZrxTi1−x)O3 (PZT) based ceramic. During the subsequent poling process the PZT cannot strain freely due to the clamping by the surrounding polymer, which after poling results in the occurrence of residual mechanical stress in the composite. The poling process is investigated theoretically by a nonlinear finite element method modeling, which takes into account the ferroelectric and ferroelastic properties of PZT ceramics. Furthermore, an analytical model is developed, which predicts the remanent strain of the composite and the residual mechanical stress. The compressive residual mechanical stress acting on the PZT in the poling direction increases continuously with decreasing volume content va of the PZT ceramic. For values of va higher than about 20% it is lower than half of the coercive stress necessary to cause a mechanical depolarization. For va lower than 20% the residual stress rises rapidly. It may cause a mechanical depolarization of the PZT ceramic for va<11%. With increasing volume content the longitudinal and the transversal components of the remanent strain increase monotonously in similar way like the corresponding linear effective piezoelectric coefficients.

On the design of NMR sensor for well-logging applications

The magnetic fields of antenna and magnet used in inside-out nuclear magnetic resonance (NMR) well-logging tool are computed using a finite-element method (FEM). A typical operating frequency of such tools is 2 MHz, at which the skin depth is about 47 /spl mu/m for copper conductor. A direct application of FEM to evaluate power loss at such frequency, therefore, requires very fine discretization of the conductors, which, in turn, makes the problem numerically ill-conditioned. A perturbation technique along with FEM is used to evaluate the power loss in conductors that avoids the need for small discretization steps along the conductor thickness. The design of the magnet, on the other hand, is complicated by the fact that the model is nonlinear in nature because of the presence of ferrites and steel materials surrounding the magnet and because the size of the problem is usually quite large; quarter of a million unknowns is fairly common. A typical nonlinear FEM model requires about 35 h of central processing unit (CPU) time on a Sun Ultra 60 296 MHz workstation with one gigabyte of RAM. The magnet is built by stacking several magnet segments along the axial direction and the objective of the design is to magnetize these segments in such a way so as to produce a desired field profile in front of the magnet. It generally requires many executions of the nonlinear FEM model. An optimal control technique is used in conjunction with the FEM to speed up the design process. Very good agreement between the measured and computed antenna efficiency and magnetic field is obtained thus validating the numerical model.