Finite Element Method Program Research Articles

Small strain based method for predicting three-dimensional soil displacements induced by braced excavation

Displacement control is a critical indicator of foundation design. Maximum deformations of soil induced by excavations are controlled by the allowable deformations of the adjacent structures. In order to evaluate potential damage of surrounding structures, Finite Element Method (FEM) is commonly adopted, predicting soil responses caused by excavations. As the numerical results obtained from FEM are greatly influenced by input material parameters of soil, inverse analysis is an effective method to obtain these parameters, which is based on the results of on-site testing. In this paper, inverse analysis based on the data of on-site testing considering Chicago clays is firstly conducted to get material parameters of soil. Then, with these input parameters, considering Hardening Soil model with Small Strain stiffness (HSS model), FEM program PLAXIS is used for parameter studies, producing coefficients in the equations of attenuation law of the displacements of the soil. Finally, considering the coupled relationship between the soil and the retaining wall, an empirical method is proposed by the authors to predict the three-dimensional displacements of soil induced by braced excavations. Validation has been done by comparisons between the results obtained by the proposed method and by other methods in the literature.

Numerical modeling of heating and hydration experiments on bentonite pellets

In a common, designed disposal system for high-level radioactive waste, bentonite is used worldwide as a buffer material due to its favorable thermodynamic properties. In-situ experiments at different scales are being conducted in several underground laboratories to investigate the long-term coupled thermo-hydro-mechanical (THM) and chemical behavior of bentonite. Simultaneously, numerous laboratory experiments under well-defined conditions were performed to determine the material properties of bentonite. Since 2012, a laboratory heating and hydration test on MX-80 bentonite has been performed by CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas). The obtained data during the test were analyzed by different research teams within the international DECOVALEX project in order to understand the coupled THM behavior of bentonite and furthermore to determine the thermal-mechanical properties of bentonite. This paper presents a numerical model for fully-coupled THM processes in bentonite based on the finite element method program OpenGeoSys (Kolditz et al., 2012a). In this model, the description of heat conduction is based on Fourier's law, and advection is also considered in the heat transfer. As an important coupling factor from hydraulic process to thermal process, the dependency of thermal conductivity on the water saturation is intensively analyzed. A multiphase flow model considering water evaporation and vapor diffusion is used to describe the hydraulic process. Special attention was also paid on the analysis of the water retention behavior. An elastic constitutive model based on generalized Hook's law was applied to describe the material's mechanical behavior complemented with consideration of the thermally induced strain and the swelling deformation. Good agreement between the calculated and measured data has been achieved concerning temperature, relative humidity, total stress, and water intake. The main coupling processes and bentonite behavior in the experiment could be captured and well analyzed in this model. However, further investigations are also needed, especially for the long-term THM process with respect to water intake.

Extended precision data types for the development of the original computer aided engineering applications

Computer aided engineering is based on models of the phenomena which are expressed as algorithms. The implementations of the algorithms are usually software applications which are processing a large volume of numerical data, regardless the size of the input data. In this way, the finite element method applications used to have an input data generator which was creating the entire volume of geometrical data, starting from the initial geometrical information and the parameters stored in the input data file. Moreover, there were several data processing stages, such as: renumbering of the nodes meant to minimize the size of the band length of the system of equations to be solved, computation of the equivalent nodal forces, computation of the element stiffness matrix, assemblation of system of equations, solving the system of equations, computation of the secondary variables. The modern software application use pre-processing and post-processing programs to easily handle the information. Beside this example, CAE applications use various stages of complex computation, being very interesting the accuracy of the final results. Along time, the development of CAE applications was a constant concern of the authors and the accuracy of the results was a very important target. The paper presents the various computing techniques which were imagined and implemented in the resulting applications: finite element method programs, finite difference element method programs, applied general numerical methods applications, data generators, graphical applications, experimental data reduction programs. In this context, the use of the extended precision data types was one of the solutions, the limitations being imposed by the size of the memory which may be allocated. To avoid the memory-related problems the data was stored in files. To minimize the execution time, part of the file was accessed using the dynamic memory allocation facilities. One of the most important consequences of the paper is the design of a library which includes the optimized solutions previously tested, that may be used for the easily development of original CAE cross-platform applications. Last but not least, beside the generality of the data type solutions, there is targeted the development of a software library which may be used for the easily development of node-based CAE applications, each node having several known or unknown parameters, the system of equations being automatically generated and solved.

Micro-Macro Analysis and Phenomenological Modelling of Salt Viscous Damage and Application to Salt Caverns

This paper aims to gain fundamental understanding of the microscopic mechanisms that control the transition between secondary and tertiary creep around salt caverns in typical geological storage conditions. We use a self-consistent inclusion-matrix model to homogenize the viscoplastic deformation of halite polycrystals and predict the number of broken grains in a Representative Elementary Volume of salt. We use this micro-macro modeling framework to simulate creep tests under various axial stresses, which gives us the critical viscoplastic strain at which grain breakage (i.e., tertiary creep) is expected to occur. The comparison of simulation results for short-term and long-term creep indicates that the initiation of tertiary creep depends on the stress and the viscoplastic strain. We use the critical viscoplastic deformation as a yield criterion to control the transition between secondary and tertiary creep in a phenomenological viscoplastic model, which we implement into the Finite Element Method program POROFIS. We model a 850-m-deep salt cavern of irregular shape, in axis-symmetric conditions. Simulations of cavern depressurization indicate that a strain-dependent damage evolution law is more suitable than a stress-dependent damage evolution law, because it avoids high damage concentrations and allows capturing the formation of a damaged zone around the cavity. The modeling framework explained in this paper is expected to provide new insights to link grain breakage to phenomenological damage variables used in Continuum Damage Mechanics.

Simulation Modeling of Barrel Bore Wear under Dynamic Pressure Load

Wear is one of the major forms of material deterioration, often limiting both the life and the performance of the industrial components and requiring frequent replacement of the components. Wear is a very complex process and occurs by combination of several factors, such as the type of lubrication, loading speed, temperature materials, surface finishing and hardness. To simulate wear as a whole is very difficult, in many cases even not possible. The simulation by using the finite element method (FEM) is becoming increasingly popular and accessible. The FEM can also be used by solving mechanical wear, where it is critical to know the right way and method for arriving to the correct results. The method for obtaining additions of wear in the paper is developed on the base of previous practice, which used the combination of finite-element models and external algorithm for calculating wear. A FEM program ABAQUS has been used in this paper. The additions of degradation were obtained from an own developed script from MATLAB software, which is used to calculate selected equations and specific outputs in ABAQUS.

Theoretical analysis on ground vibration attenuation using sub-track asphalt layer in high-speed rails

Using a finite element method (FEM) program, a Portland cement concrete slab trackbed (S 0), and a sub-track asphalt roadbed (RAC-S) were modeled under high-speed train loads to analyze their responses to ground vibration attenuation, by considering 10, 15, 20, 25, and 30 thick sub-track asphalt layer replaced on the top of the upper subgrade. FEM results show that the vibration amplitude of RAC-S is at least three times lower than the vibration for S 0. The maximum vibration amplitude of RAC-S is linearly increased with train speed. The vertical acceleration is found to be reduced by more than 10 % when the asphalt layer thickness is increased from 10 to 20 cm. However, the reduction in vertical acceleration is only about 1 % when the thickness of the asphalt layer changes from 20 to 30 cm. The vibration level is slightly lower if the asphalt layer has higher resilient modulus in the seasons of autumn or winter. This theoretical analysis indicates that a railway substructure that consists of a 10–20 cm thick high modulus asphalt layer located at the top of trackbed shows a good performance in ground vibration control for high-speed rails.

Brittle interfacial cracking between two dissimilar elastic layers: Part 2—Numerical verification

A thorough program of 2D finite element method (FEM) simulations is carried out parametrically on a bimaterial double cantilever beam (DCB) model in MSC/NASTRAN. The Young’s modulus ratio, the Poisson’s ratio, the thickness ratio, and the DCB tip loads are varied over their entire practically useful domains for different values of the crack extension size. Extensive comparisons are made between the results of the analytical theory that was developed in Part 1 by Harvey et al. (2015) and FEM results. This paper reports the outcome of these comparisons. The present analytical theory and the supporting mathematical techniques are thoroughly verified. Overall, excellent agreement is observed between the present analytical theory and the FEM results for the crack extension size-dependent energy release rate (ERR) components and the stress intensity factors (SIFs).

An Investigation on the Parameters that Affect the Performance of Hydrogen Fuel Cell

Most of the energy used in the world is obtained from fossil fuels. Some reasons like air and environmental pollution, high-energy costs and depletion of fossil fuels, increased the importance of studies about new and renewable energy sources in the world. Among the new and renewable energy sources hydrogen has great importance. Hydrogen which exists in great amounts in the world has the highest energy content per unit mass. The subject of fuel cells is one of the main research topics in hydrogen energy. The purpose of this study, is to analyze the performance of fuel cells. to do this a model of fuel cell is created in Finite element method program. membrane thickness and electrolyte type of fuel cell is selected as variables.

Development of toroid-type HTS DC reactor series for HVDC system

This paper describes design specifications and performance of a toroid-type high-temperature superconducting (HTS) DC reactor. The first phase operation targets of the HTS DC reactor were 400mH and 400A. The authors have developed a real HTS DC reactor system during the last three years. The HTS DC reactor was designed using 2G GdBCO HTS wires. The HTS coils of the toroid-type DC reactor magnet were made in the form of a D-shape. The electromagnetic performance of the toroid-type HTS DC reactor magnet was analyzed using the finite element method program. A conduction cooling method was adopted for reactor magnet cooling. The total system has been successfully developed and tested in connection with LCC type HVDC system. Now, the authors are studying a 400mH, kA class toroid-type HTS DC reactor for the next phase research. The 1500A class DC reactor system was designed using layered 13mm GdBCO 2G HTS wire. The expected operating temperature is under 30K. These fundamental data obtained through both works will usefully be applied to design a real toroid-type HTS DC reactor for grid application.

Induced Current-Based Performance Measurement System for Wide and Stacked HTS Wires

Recently, high-temperature superconductor (HTS)-based devices have been applied to practical electric power systems. In order to increase the critical currents of HTS wires, wide and stacked HTS wires are being extensively researched. However, general systems for testing critical currents via voltage taps are not accurate for measuring the critical currents of wide and stacked HTS wires. This paper proposes an induced current-based performance measurement system for wide and stacked HTS wires. The system consists of wide and stacked HTS wires and induction coils made of 2G HTS wire. The electromagnetic performance of the HTS wires and induction coil is analyzed using a finite element method program. The basic structure of the performance measurement system is designed and fabricated based on the electromagnetic analysis results. In the experiment, the characteristics of the HTS wire are analyzed under charge and discharge conditions from the viewpoint of induced currents. The current of the stacked HTS wires is measured by a Rogowski coil. As a result, we can accurately identify the characteristics of the wide and stacked HTS wires, such as critical current and joint resistance.

A thermo-mechanically coupled finite strain model considering inelastic heat generation

The procedure for reuse of finite element method (FEM) programs for heat transfer and structure analysis to solve advanced thermo-mechanical problems is presented as powerful algorithm applicable for coupling of other physical fields (magnetic, fluid flow, etc.). In this case, nonlinear Block-Gauss–Seidel partitioned algorithm strongly couples the heat transfer and structural FEM programs by a component-based software engineering. Component template library provides possibility to exchange the data between the components which solve the corresponding subproblems. The structural component evaluates the dissipative energy induced by inelastic strain. The heat transfer component computes the temperature change due to the dissipation. The convergence is guaranteed by posing the global convergence criterion on the previously locally converged coupled variables. This enables reuse of software and allows the numerical simulation of thermo-sensitive problems.

Generating characteristics of a tension activated π-shaped piezoelectric harvester

A π-shaped piezoelectric harvester which can be applied for using tension and vibration of cables in cable-stayed bridge and suspension bridge was proposed and the generating output characteristics were studied depending on the ceramic and the elastic body size. The harvester consists of a π shaped elastic body and a rectangular piezoelectric ceramic which is attached on the upper surface of the elastic body. If contraction and release are given symmetrically at both ends of the elastic body legs, bending of the elastic body and the ceramic plate is occurred and electricity is generated by the piezoelectric effect of the ceramic. Structure of the π-shaped harvester has advantage to protect the ceramic from direct pressure and vibration and it is easy to change the design by changing the position of the legs and the leg length and thickness. Generating characteristics of the harvester were analyzed by using finite element method program ANSYS. The generating characteristics of the harvester were analyzed depending on the elastic body thickness, ceramic size and the applied forces on the legs. The harvester was fabricated on the basis of the analyzed results and a frequency controllable vibrator was used to measure the output characteristics. The generating output characteristics of a single harvester and arrayed harvesters were measured.

Three-dimensional characteristics analysis of the wire-tool vibration considering spatial temperature field and electromagnetic field in WEDM

In this paper, a three-dimensional multi-physics coupling model (thermal model, electromagnetic field model and structural model) is proposed for analyzing and controlling the vibration of wire electrode in cutting thin plate process. Firstly, a three-dimensional thermal model is developed to evaluate temperature distribution of wire electrode considering heat convection and heat conduction, and the numerical solutions of wire temperature increment are performed under different process parameters. Secondly, the mechanism of electromagnetic force acting on wire tool is clarified in detail, and a spacial finite element method (FEM) program is designed to analyze the electromagnetic field considering electromagnetic induction. Then, combining thermal model with electromagnetic field model, and conventional structural model, a multi-physics coupling model is established to acquire the frequency and amplitude of wire vibration under random multiple-spark discharges. Furthermore, the simulational results of multi-physics coupling model on wire vibration show a good agreement with experimental data, and the influencing rules of processing parameters on wire vibration are also illustrated to seek the best parameter combination. Eventually, three practical methods are presented to restrain wire vibration performance, and the significant effects on suppressing the wire vibration and improving geometric accuracy have been obtained. • A three-dimensional characteristics analysis of the wire-tool vibration considering spatial temperature and electromagnetic field has been carried out in this paper. Furthermore, combining the thermal model with electromagnetic field and structural mechanics, a multi-physics coupling model has been developed to calculate frequency and amplitude of wire vibration by finite element method. • A set of Taguchi experiment ( L 27 5 3 ) has been performed to investigate the reliability and feasibility of the proposed coupling model. Moreover, the simulational results of multi-physics coupling model on wire vibration show a good agreement with experimental data. • Three practical methods have been presented to restrain wire vibration performance, and the lateral vibration has been reduced with approximately 50% and corner-accuracy of a workpiece has been improved significantly.

Designs of 10 MW Air-core and Iron-core HTS Wind Power Generators

High Temperature Superconducting (HTS) synchronous generators can be designed with either an air-core type or iron-core type. The air-core type has higher efficiency under rated rotating speed and load than the iron-core type because of the iron losses which may produce much heat. However, the total length of HTS wire in the air-core type is longer than the iron-core type because the generated magnetic flux density of the air-core type is low. This paper deals with designs of 10 MW air-core and iron-core HTS wind power generators for wind turbines. Fully air-core, partially iron-core, and fully iron-core HTS generators are designed, and various stator winding methods in the three HTS generators are also considered, such as short-pitch concentrated winding, full-pitch concentrated winding, short-pitch distributed winding, and full-pitch distributed winding. These HTS generators are analyzed using a 3D finite elements method program. The analysis results of the HTS generators are discussed in detail, and the results will be effectively utilized for large-scale wind power generation systems.

ON THE CALCULATION OF REINFORCED CONCRETE PLATES OF VARIABLE THICKNESS IN THE COMPUTER PROGRAMM «PRINS»

The features of modeling of reinforced concrete slabs of varying thickness in computer finite element method program PRINS are described. An example of the cantilever reinforced concrete slab, made in this program, is given. Two options section of the plate - fixed and variable, are considered. Calculation results are compared to stresses and strains.

Rigid Joints Transferring Forces outside Box Columns with Deviation of Column's Location Axis-Finite Element Method Simulation

location axis, joints, force-transforming plates, carrying capacityAbstract: Steel structure has been widely used all over the world. In actual construction process, steel structure inevitably has initial defects, which may have bad influences on its performance. Three groups of specimens were designed in this paper to compare the performance of rigid joints transferring forces outside box columns to that of perfect traditional joints and that of traditional joints with uniaxial and biaxial deviation of column's location axis by finite element method program ANSYS. From the analysis of stiffness, yielding capacity, and ultimate carrying capacity, the impact of force-transforming plates can be evaluated. The adding force-transforming plates were helpful to reduce the influence from column imperfect.

Active Power Losses in Pressure Rings for Contact Shoes of Ore-Thermal Furnace

Results of electromagnetic problem solution for three-phase electrodes system in ore-thermal furnace for electrodes equivalent electric circuit parameters calculation made by using 3D-models in numerical finite element method program package ANSYS are presented. Contact shoes pressure rings and heat shield of energy feeding unit are taken into account.

Temperature Operation Mode of Hydraulic Pressure Rings for Contact Shoes in Ore-Thermal Furnace

Numerical simulation of temperature fields for justification of material choice for contact shoes pressure rings in ore-thermal furnaces are carried out using 3D-models in numerical finite element method program package ANSYS. Results are shown and recommendations for water-cooling parameters are given.

Effects of misalignment error, tooth modifications and transmitted torque on tooth engagements of a pair of spur gears

In the last research [S. Li, Effects of machining errors, assembly errors and tooth modifications on load-carrying capacity, load-sharing rate and transmission error of a pair of spur gear, Mech. Mach. Theory 42 (2007) 698–726], effects of machining errors, assembly errors and lead crowning on tooth surface contact stresses (CS), root bending stresses, load-sharing ratios (LSR) and transmission errors of a pair of spur gears were investigated through performing loaded tooth contact analysis (LTCA) with developed finite element method (FEM) programs. But this research couldn't investigate the effects of tooth profile modification and lead relieving on tooth engagements. Also, the effects of machining errors, assembly errors and tooth modifications on tooth mesh stiffness (MS) couldn't be investigated. So, as a continuous study of the last research, this paper investigates the effects of tooth profile modification and lead relieving on tooth engagements of a pair of spur gears and the effects of misalignment error of gear shafts on the plane of action, tooth lead crowing and transmitted torque on tooth MS. An arc curve is used to modify tooth profiles of a pair of spur gears in this paper. This is because this method is used very popularly for the spur gears. Methods used in the last research are also used here to investigate the effects of the tooth profile modification, lead relieving and transmitted torque on tooth engagements. Based on the results, it is found that the tooth profile modification and lead relieving have significant effects on tooth CS, LSR and MS. It is also found that transmitted torque has a little effect on tooth MS, but has no effect on LSR of the gears. For the lead-relieved gears, calculation results show that edge-loads happened at the joint parts of the relieved part and the non-relieved part of tooth lead when the lead is relieved with straight lines. Since the edge-loads resulted in greater contact stresses at the joint parts and weakened tooth contact strength, attention must be paid to the lead relieving. It is necessary to reduce the edge-loads as small as possible through making the joint part smooth when the lead relieving is made.

Optimal Configuration of Fluid Viscoelastic Seismic Dampers on a Ten Stories Building Using Finite Elements Method

This paper presents a study made in order to find different optimal configurations of positioning fluid dampers on high buildings for dissipating the seismic energy. The study was made using Finite Elements Method and ANSYS program, on a ten stories building structure. The first step of this optimization process is to consider the fluid dampers having linear damping properties in order to achieve a quicker convergence of the solutions. In order to obtain the influence of the dampers configurations on the structure damping there were made multiple different configurations of dampers positioned on different locations on the building. All these models were analyzed using modal analysis and it was obtained the modal damping of the building structure for the first vibration modes of the structures for each configuration. The graphics obtained can be used for achieving different degrees of seismic energy dissipation for the analyzed building.