FEM Computations Research Articles

Evaluating Fire Resistance of Steel Girders in Bridges

In current practice, no special measures are applied for enhancing structural fire safety of steel bridge girders. Further, there is very limited information and research data in the literature on the fire resistance of structural members in bridges. In this paper, the fire response of a steel bridge girder under different conditions is evaluated using the FEM computer program ANSYS. In the analysis, the critical factors that influence fire resistance, namely, fire scenario, fire insulation, and composite action arising from steel-concrete interaction, are accounted for. Results from numerical studies show that the composite action arising from steel-girder-concrete-slab interaction significantly enhances the structuralperformance(and fireresistance)ofasteelbridgegirderunder fireconditions.Othersignificantfactorsthatinfluence fireresistanceof steel bridge girders are fire insulation and type of fire scenario. DOI: 10.1061/(ASCE)BE.1943-5592.0000412. © 2013 American Society of Civil Engineers. CE Database subject headings: Fires; Fire resistance; Girder bridges; Steel bridges. Author keywords: Bridge fires; Fire resistance; Steel girders; FEM analysis.

Effect of Magnetic Shunts on the Eddy Losses of a Transformer Tank

This paper presents a 3D FEM computation model for a power transformer structure, where several conductor disks in series are used to constitute each winding, this is different from the normal cylindrical shape models. Base on such model the simulated ohmic losses in windings can be the same as that of measured. Then the stray magnetic fields in the transformer, the eddy losses in tank, the effect of magnetic shunts on tank losses are all studied, the calculated decrease of eddy losses in tank when magnetic shunts are properly used is compared with that of measured, they are coincide in some degree, which imply this model is reasonable for the simulation

Analytical study of morphologies for ultra high elastic stiffness of composites with aligned cylindrical fibers

This paper is to develop a micromechanics-based model on predicting the effective transverse stiffness of composites reinforced with periodically dispersed cylindrical fibers. Six types of packing patterns are analyzed and their morphology characteristics are accounted for by Green’s function. It is noted that fiber packing configuration plays a great effect on the effective elasticity. The developed analytical model is assessed by the available FEM computations, and illustrates the dependence of the equivalent stiffness on the periodic microstructures. Additionally, it should be noted that the present model can be used to study some important issues, e.g. damage variables, matrix plasticity and so on.

A Parameterized Mesh Technique for Finite Element Magnetic Field Computation and Its Application to Optimal Designs of Electromagnetic Devices

A parameterized mesh generation is presented for design optimization of electromagnetic devices. The proposed method requires no mesh regeneration, and hence the numerical simulation time can be reduced significantly. When the coordinates of nodes in the refined mesh are changed, the mesh topology will be kept, that is, the node connection relationship will remain the same as before. Thus the nodal solutions can be carried over from previous FEM results to subsequent FEM computation without the need of mapping the nodes between two meshes. Additionally, the mesh quality can remain high using a swapping diagonal technique. Based on the sample points obtained from FEM with parameterized mesh, the optimal model is reconstructed using the response surface methodology (RSM). The particle swarm optimization (PSO) method is then used to arrive at the optimal solution swiftly and efficiently. An optimal design of electromagnetic device is reported to verify the efficiency and effectiveness of the proposed method.

Effects of Mining Excavation on Surface Structures

In order to study the effect of mining excavation on planed structure on ground surface, the effect of certain mining excavation on ground stabtility was calculated by use of the advanced Ansys FEM computation program. The recults can not only provide ground deformation parameters for planned structure, but also give light for understanding the deformation mechanism of mining excavation.

Research on Axisymmetric Vibration of Gear with Stepped Variable Thickness

Ultrasonic gear honing is a kind of precision processing technology with great application prospect. The gear is a special kind of load in ultrasonic machining, and its vibration characteristic and natural frequency has great influence on processing frequency of the system. According to the structure characteristic of the gear with stepped variable thickness, its equations of axisymmetric bending vibration frequency were derived on the basis of the thick plate theory in this paper, and then the gear’s natural frequency is obtained which is in accordance with the results of FEM computation. Besides, the main factors affecting the calculation accuracy are analyzed with some examples in this paper The analysis shows that within the application range of Mindlin’s plate theory, the gears’ frequency obtained by the suggested method is accurate.

ZrB2–SiC composite parts in oxyacetylenic torch tests: Experimental and computational assessment of chemical, thermal and mechanical behavior

The thermal shock and ablative behavior of ZrB2–SiC pyramidal mockups with different geometrical sizes were investigated using an oxyacetylene torch. Insignificant weight or configurational changes and the absence of surface cracks after testing were observed. The excellent resistance to thermal shock and ablation is attributed to the SiC addition. A satisfactory agreement between the measured temperature distributions and FEM computations was achieved. Results indicated that both the side length and radius of nose curvature exerted a prominent effect on the temperature gradient and thermal stress magnitude inside and/or on the surface of the pyramidal mockups. The magnitudes of heat flux and boundary layer temperature, Te influenced the head temperature, T1 and the undersurface temperature, T2 in a different way. A stronger heat flux yielded higher T1 value whereas T2 remained almost constant. Comparatively, Te showed a much more remarkable effect on T2 than it did on T1 owing to the different heat transfer mechanisms of these two parts.

Artificial neural network approach for locating internal faults in salient-pole synchronous generator

This paper presents an artificial neural network approach for locating internal faults in salient-pole synchronous generator. This method uses samples of magnetic flux linkages to reach a decision. Meyer wavelet probabilistic neural network (MWPNN) as main part of this fault diagnosis method is utilized to detect internal faults. The basic PNN is integrated with discrete wavelet transform (DWT) to construct the MWPNN. The MWPNN is trained by features extracted from the magnetic flux linkage data through the discrete wavelet transform (DWT). To implement this method practically, the training database for the PNN is generated by 3D-FEM. Since the FEM simulation is a time-consuming process, hence in order to reduce the number of FEM computations generalized regression neural network (GRNN) is used to estimate the flux linkages characteristics of synchronous generator under various conditions. The diagnosis performance of the proposed method is validated via experimental data, derived from a 4-pole, 380V, 1500rpm, 50Hz, 50KVA, 3-phase salient-pole synchronous generator.

An Approach to Determine the Circulation of Magnetic Field in FEM Computation Code With Vector Potential Formulation

To detect an electrical fault in a generator magnetic core with the ELCID method, a circulation of the magnetic field between two teeth is determined. To model this problem with the finite element method, two potential formulations can be used. With the scalar formulation, such circulation can be easily determined; this is not the case with the vector potential formulation. In this paper, we propose to use a supplementary relation to compute a magnetomotive force in the case of vector potential formulation.

Research on the Superficial Thermal Insulation Calculation Method of Massive Concrete Structure

In this paper, based on the principle of heat balance, the computing equation of temperature field which used the thermal coefficient, surface coefficient, and heat as the basic parameters of the heat conduction equation is derived, and thereafter the FEM computation procedure about temperature field named RCTS which used the thermal diffusivity as basic parameter is modified. The modified procedure can reasonably reflect the temperature field of composite construction which is made of a great variety of material with different thermal property, and also can simulate the effect of surface heat preservation at arbitrary periods and arbitrary parts of the bulk concrete structure. According to the calculation example, the similarities and differences of the heat preservation effect on the heated board calculation by using different methods: the equivalent surface coefficient method, the equivalent thickness method, the thermal conductivity method and the thermal diffusivity method are analyzed. The calculation results show that the computing results of the thermal conductivity method are closed to the result of the equivalent surface coefficient method, the results of the equivalent thickness method have certain differences but not quite because it is the approximation process of the equivalent surface coefficient method, and the reasonable result is often missed by using the thermal diffusivity method.

Enhanced mass balance Tafel slope model for computer based FEM computation of corrosion rate of steel reinforced concrete coupled with CO2transport

This research paper aims at computer based modeling of carbonation induced corrosion under extreme conditions and its experimental verification by incorporating enhanced electrochemical and mass balance equations based on thermo-hygro physics with strong coupling of mass transport and equilibrium in micro-pore structure of carbonated concrete for which the previous research data is limited. In this paper the carbonation induced electrochemical corrosion model is developed and coupled with carbon dioxide transport computational model by the use of a concrete durability computer based model DuCOM developed by our research group at concrete laboratory in the University of Tokyo and its reliability is checked in the light of experiment results of carbonation induced corrosion mass loss obtained in this research. The comparison of model analysis and experiment results shows a fair agreement. The carbonation induced corrosion model computation reasonably predicts the quantitative behavior of corrosion rate for normal air dry relative humidity conditions. The computational model developed also shows fair qualitative corrosion rate simulation and analysis for various pH levels and coupled environmental actions of chloride and carbonation. Detailed verification of the model for the quantitative carbonation induced corrosion rate computation under varying relative conditions, different pH levels and combined effects of carbonation and chloride attack remain as scope for future research.

Solving linear and nonlinear three-dimensional problems of fracture mechanics by a semi-analytic finite element method. Part 1. Theoretical background and a study of efficiency of fem procedure for solving three-dimensional problems of fracture mechanics

We present theoretical approaches and a procedure for the FEM computation of parameters of nonlinear fracture mechanics in prismatic bodies with a crack. The efficiency of the proposed approaches and the veracity of the results obtained have been analyzed.

FEM Analysis on Acoustic Performance of Wall Flow Diesel Particulate Filters

Diesel powered vehicles, in compliance with the more strict exhaust emission standards such as Euro V, is likely to require a diesel particulate filter (DPF). A DPF used on a vehicle will affect the acoustic emission of the diesel engine, so it is important to investigate the sound propagation rule in DPF and further to propose the optimum DPF design. However, due to the geometrical complexity of the DPF, the traditional analysis method, such as analytical method, can not assess the acoustic performance of DPF accurately in medium and high frequency band. In this paper, a combined approach of finite element analysis and viscosity correction is proposed to predict acoustic performance of DPF. A simplified model of the full DPF is established and is used to analyze the sound propagation characteristic of the DPF. The distribution of the sound pressure and velocity, the transmission matrix of the DPF are obtained using the finite element method. In addition, the method of the viscosity correction is used in the transmission matrix of the DPF to evaluate the acoustic performance of DPF. Based on the FEM computation and the viscosity correction, the transmission losses under the rated load and idle condition of a diesel engine are calculated. The calculation results show that DPF can effectively attenuate exhaust noise, and sound attenuation increase with the rise of the frequency. Sound attenuation is better under rated condition than idle condition of diesel engine, particularly in frequency above 1 000 Hz.

Stability analysis of multilayered composite shells with cut-outs

A numerical stability analysis of an axially compressed multilayered composite shell is presented. The authors examine how the stability performance of a panel can be influenced by a centrally located square cut-out. The computations are performed within FEM computer program NX-Nastran (ver. 6.0). The stability is investigated by means of a linearized buckling analysis as well as of a non-linear large deformations incremental analysis . To get more insight into the performance of the layered structure, the failure index according to Tsai–Wu criterion is monitored in the study.

Elasto-Plasticity Solution on Bearing Characteristic of Cast-in-Place Concrete Pipe Pile with Large Diameter in Layered Soil under Lateral Load

Aimed at problems lying in the exiting methods for calculation of laterally loaded piles installed in layered soils, the elasto-plasticity solution of cast-in-place concrete pipe pile with large diameter (PCC pile) in layered soil under lateral load based two-parameter foundation model and unity limiting force profile, deduced the finite difference solution based unity limiting force profile(LFP), established the calculation program of the displacement and internal force of pile. It was shown that the calculated pile moment and pile displacement coincided very well by computation and comparison of model test and FEM, verified the method’s correction. Meanwhile, the method was more precise and efficient than the existing conversion methods of subgrade modulus. Therefore, it could be useful for the design and analysis of PCC pile under lateral load.

Model of viscoplasticity with parallel deformation mechanisms. Part 1. Constitutive equations and choice of calculation coefficients*

A model of viscoplastic deformation of strengthening material is proposed. It is assumed that metal deformation is determined by two independent (parallel) mechanisms. Each of these mechanisms corresponds to anisotropic creep theory with linear strengthening, within which an isotropic strengthening parameter is introduced for both mechanisms. The concept of surface flow is not used. The model describes material behavior at both normal and elevated temperature when thermal recovery effects develop. Results of standard tensile and creep tests are used in order to determine model parameters. The order of determining model parameters from standard tensile and creep tests is provided. Features of austenitic stainless steel cyclic strengthening are considered. An algorithm is given providing implementation of the proposed viscoplasticity theory in structural design using FEM computer packages.

Scalability of Higher-Order Discontinuous Galerkin FEM Computations for Solving Electromagnetic Wave Propagation Problems on GPU Clusters

A highly parallel implementation of Maxwell's equations in the time domain using a cluster of Graphics Processing Units (GPUs) is presented. The higher-order Discontinuous Galerkin Finite Element Method (DG-FEM) is used for spatial discretization since its characteristics are matching the parallelization design aspects of the NVIDIA Compute Unified Device Architecture (CUDA) programming model. Asynchronous data transfer is introduced to minimize parallelization overhead and improve parallel efficiency. The implementation is benchmarked with help of a realistic 3-D geometry of an electromagnetic compatibility problem.

Application of evaluationary approach to thermo-mechanical optimization of gas turbine airfoil cooling configuration

Application of evaluationary approach to thermo-mechanical optimization of gas turbine airfoil cooling configurationCooling of the hot gas path components plays a key role in modern gas turbines. It allows, due to efficiency reasons, to operate the machines with temperature exceeding components' melting point. The cooling system however brings about some disadvantages as well. If so, we need to enforce the positive effects of cooling and diminish the drawbacks, which influence the reliability of components and the whole machine. To solve such a task we have to perform an optimization which makes it possible to reach the desired goal. The task is approached in the 3D configuration. The search process is performed by means of the evolutionary approach with floatingpoint representation of design variables. Each cooling structure candidate is evaluated on the basis of thermo-mechanical FEM computations done with Ansys via automatically generated script file. These computations are parallelized. The results are compared with the reference case which is the C3X airfoil and they show a potential stored in the cooling system. Appropriate passage distribution makes it possible to improve the operation condition for highly loaded components. Application of evolutionary approach, although most suitable for such problems, is time consuming, so more advanced approach (Conjugate Heat Transfer) requires huge computational power. The analysis is based on original procedure which involves optimization of size and location of internal cooling passages of cylindrical shape within the airfoil. All the channels can freely move within the airfoil cross section and also their number can change. Such a procedure is original.

Amplitude dependence of filler-reinforced rubber: Experiments, constitutive modelling and FEM – Implementation

The focus of the present paper is the experimental investigation, the constitutive representation and the numerical simulation of the amplitude dependence of filler-reinforced elastomers. A standard way to investigate the dynamic properties of viscoelastic materials is via the dynamic modulus which is obtained from stress signals due to harmonic strain excitations. Based on comprehensive experimental data, an amplitude-dependent constitutive model of finite viscoelasticity is developed. The model is based on a modified Maxwell chain with process-dependent viscosities which depend on additional internal state variables. The evaluation of this thermodynamically consistent model is possible in both the time domain, via stress-time signals, and in the frequency domain, via the dynamic modulus. This property is very profitable for the parameter identification process. The implementation of the constitutive model into the commercial finite element code ANSYS with the user-programmable feature (UPF) USERMAT for large deformations in updated Lagrange formulation is presented. This implementation allows simulating the time-dependent behaviour of rubber components under arbitrary transient loading histories. Due to physical and geometrical nonlinearities, these simulations are not possible in the frequency domain. But, transient FEM computations of large loading histories are sometimes not possible in an acceptable time. In the context of the parameter identification the fundamental ideas are presented, how this problem has been solved. Transient FEM simulations of real rubber components are also shown to visualize the properties of the model in the context of the transient material behaviour.

A New Fracture Toughness Test Covering Mixed-Mode Conditions and Positive and Negative T-Stresses

It is known that sign of T-stress in cracked specimens affects fracture toughness under mixed mode conditions. We suggest a new test involving an inclined edge cracked semi circular specimen subjected to asymmetric three-point bend loading (IASCB specimen) that covers a broad range of modes I and II SIFs and T-stress values. It can provide both positive and negative T-stresses. This is illustrated by FEM computations.