Finite Element Method Program Research Articles

A recurrence algorithm of time-dependent analysis for concrete bridges

This paper proposes an algorithm for time-dependent effects in the finite element analysis of concrete bridges. Based on the primary influence of concrete shrinkage and creep on bridge structures, the calculation formulas for the equivalent nodal load increments of beam elements caused by the shrinkage and creep effects were deduced according to the initial strain method. To simplify the calculation process and improve calculation speed, the formulas for shrinkage and creep in the bridge design code were fitted with an exponential function, and the recurrence equations for shrinkage and creep calculation were obtained. Thus, a finite element method formulation for concrete shrinkage and creep calculated according to the divided time steps was established. The algorithm was programmed into a self-developed program, and the correctness of the program's calculation was verified through 20 years of on-site monitoring results of a concrete girder cable-stayed bridge with a main span of 500 m. The method proposed in this paper can substantially improve the speed of the program to calculate the time-dependent effects during the construction and operation of large-span concrete bridges, while ensuring the reliability of the calculation results, and is easy to be applied in various types of finite element method programs.

Structural response of submerged floating tunnels with free-end boundary condition based on an analytical approach

Until now, the investigation of structural behavioral characteristics of submerged floating tunnels (SFTs) has primarily relied on numerical methods that demand intensive calculations. This preference stems from the challenges in deriving an analytical solution, given the complexity of the structural system and applied loadings. To address this, an analytical approach based on practical assumptions has been developed to assess the structural responses of SFTs. Mainly, to mitigate excessive internal forces in tunnel segments and facilitate an analytical approach, a free-end boundary condition is assumed. Under these assumptions, the analytical approach can effectively determine the structural response of SFTs in the time domain. The proposed approach was validated by a hydrodynamics-based numerical analysis using the finite element method program ABAQUS/AQUA. In the harsh wave conditions of the Messina Strait, this approach matches well with numerical analyses, except in cases of extremely low submergence depth or exceptionally large tunnel diameter compared to mooring stiffness. This analytical approach can rapidly and accurately evaluate the structural behavior of SFTs, especially when considering the specific environment and design loads at the basic design stage. Therefore, this method is practically valuable. However, its application should be carefully exercised due to the several limitations.

Determination of Replacement Material Thickness in the Case of Expansive Soil in Dams

One simple solution to reduce the impact of damage caused by swelling on expansive soil is to replace it with soil that has better properties. Unlike replacing expansive soil material in the subgrade or foundation layer, replacing expansive material in a constructed dam requires special consideration, as fluctuating reservoir water levels and rainfall cycles affect the active zone of expansive soil, which will affect the stability of the dam. Therefore, this study was conducted to determine the thickness of the replacement layer, which is also the active zone of expansive soil in the dam, by modeling the stability of the dam against changes in reservoir water levels and rainfall cycles with parent analysis using finite element and limit equilibrium method programs. One example of dam damage caused by expansive soil was used as a case study. The study results show that changes in the wet-dry active zone can be used as a basis for determining the thickness of the replacement material in cases of expansive soil in dams.

Seismic Behavior of an Inter-story Hinged Lateral Resistance Braced Frame

Based on the deflection behavior of structural components occurring at the lateral deformation of moment frames, a new lateral force-resisting system, the R-BRACE Frame (RBF) system, was proposed. This system is capable of effectively limiting the inter-story drift response of tall buildings. An evaluation was conducted using the finite element method program SAP2000 to simulate the internal force distribution and deformation of the system. The equivalent lateral force procedure (ELFP), the capacity spectrum method (CSM), a linear time-history analysis and the pushover method were applied to assess the yielding mechanism of the structure under different earthquake intensity levels. The findings revealed that the sub-unit, referred to as an R-BRACE, had a major impact on improving a structure's lateral stiffness. The placement of R-BRACE units could guarantee controllable stiffness degradation and enhanced seismic ductility, but would not alter the vertical load transfer path of the initial structure, which makes the RBF system an ideal option for seismic retrofitting. KEYWORDS: Lateral force-resisting system, R-BRACE frame, Enhanced lateral stiffness resistance, Seismic ductility

Structural analysis of shield machine cutting monopile using p-y curve based finite element method

In this study, the structural response of piles during shield machine cutting is analyzed using p-y curves based on the finite element method (FEM). In the FEM program, the tangent stiffness matrix of the nonlinear soil-pile spring is derived from the tangent modulus of the p-y curve. The nonlinear finite element equation is solved using the Newton-Raphson iterative method. The program can consider the influence of the shield thrust force, the soil reinforcement, and the cross-sectional area decrease during shield cutting. The program output comprises the lateral displacement, internal force, and bending moment of the laterally loaded monopile. The correctness and accuracy of this method are validated with both field test data and commercial finite difference method (FDM) program. The results show that shield thrust force is the main factor affecting the lateral displacement and bending moment of the pile; as the cutting section area of the pile is decreasing, the maximum negative moment increases while the maximum positive moment decreases; soil reinforcement has a negligible effect on the internal force but can effectively reduce the lateral displacement of the pile head.

Finite element implementation of a certain class of elasto-viscoplastic constitutive models

In this paper a selected type of elasto-viscoplastic constitutive equations is considered. The viscoplastic model which was proposed by Marquis is generalized by allowing multiple terms describing the isotropic and the kinematic hardening. Furthermore, the presented model formulation enables one to use an arbitrary equivalent plastic strain function to describe the isotropic hardening behavior. What is more, the backstress evolution equation which was proposed by Marquis was modified so that any equivalent plastic strain function can be used in the recovery term now. The general form of the generalized constitutive model obtained this way was subsequently implemented into the finite element method (FEM). For that purpose, the radial-return mapping algorithm was utilized. The consistent tangent operator was derived for the considered class of models and is presented in the paper. A developed user material subroutine (UMAT) which allows one to use the viscoplastic models under consideration in the FEM program CalculiX is attached in the appendix section. A number of numerical simulations were conducted in order to verify the performance of the developed UMAT code.

Design and Characteristic Analysis of an Axial Flux High-Temperature Superconducting Motor for Aircraft Propulsion.

In line with global environmental regulations, the demand for eco-friendly and highly efficient aircraft propulsion systems is increasing. The combination of axial flux motors and superconductors could be a key technology used to address these needs. In this paper, an axial flux high temperature superconducting (HTS) motor for aircraft propulsion was designed and its characteristics were analyzed. A 2G HTS wire with high magnetic flux characteristic was used for the field winding of the 120 kW axial flux HTS motor, and the rotational speed and rated voltage of the motor were 2000 rpm and 220 V, respectively. The axial flux HTS motor implements a revolving armature type for solid cooling of the HTS field coil. The electromagnetic and thermal features of the motor were analyzed and designed utilizing a 3D finite element method program. The HTS coil was maintained at the target temperature by effectively designing the current lead and cooling system to minimize heat loss. These results can be effectively used in the design of propulsion systems for large commercial aircraft in the future as well as for the design of small aircraft with less than 4 seats.

Design optimization of conformal cooling channels for injection molds: 3D transient heat transfer analysis

This research aims to enhance the design of an injection mold in order to minimize ejection time and increase temperature uniformity by repositioning cooling channels. For 3D transient thermal simulations, the ANSYS finite element method (FEM) program was employed, while the MATLAB program was used for optimization. It was discovered that the method could be used successfully to optimize the design of Conformal Cooling Channels (CCCs) in injection molds. The objective function value of the optimized model represents a near 40% improvement in relation to the initial model. The combined parameterization, simulation, and optimization method has proven beneficial for enhancing the arrangement of channels in an injection machine mold. The methodology is generalizable. As such, it can be employed in any industrial applications involving injection molding machines, for the improvement of the quality of the manufactured part.

Using 3D‐scanners and finite element method to assess the fatigue life of welded joints based on the actual geometry of seam welds: realistic modelling of notches at the weld toe

AbstractTo predict the service life of welded joints, the seam welds of samples (cross joint, K‐seam, sheet thickness 15 mm and a laser‐welded butt joint, sheet thickness 6 mm, both made of steel quality S 355) are recorded using a 3D scanner. The data obtained in this way is processed and transferred to a finite element method program. The meshing of the weld seams is very detailed. A finite‐element‐method stress calculation is then carried out. The real samples are tested in a fatigue test up to the point of cracking. The results from calculation and test are then compared. A possible crack location can be predicted very well using the finite element method results. The cracks in the real test are always in the area of very high or often the absolute highest calculated stresses. A prediction of the service life in the fatigue test is possible with a certain scatter – close to the usual scatter for welded joints. Based on the results of 19 samples, a fatigue class for local stress (based on the real geometry) of FAT 300 can be preliminary estimated for the cross‐joint specimens. Definition according to the specifications of the International Institute of Welding (FAT at 2 mio. cycles, survival probability 97.7 %).

Comparative Analysis of Composite Box Girder Bridges Using Beam on Elastic Foundation (BEF) Method, Space Frame Method, Finite Element Method and Computer Programming

Comparative Analysis of Composite Box Girder Bridges Using Beam on Elastic Foundation (BEF) Method, Space Frame Method, Finite Element Method and Computer Programming

FEM‐Modeling of thermal and viscous effects in piezoelectric MEMS loudspeakers

AbstractLoudspeakers based on piezoelectric micro‐electro‐mechanical system (PMEMS) are attracting an increasing interest due to their small size, low electronic power consumption, and easy assembly. These aspects are particularly advantageous in applications like earphones, mobile phones, and in‐ear hearing aid devices. However, creating sufficiently high sound pressure levels challenges many existing MEMS loudspeakers. Furthermore, their small dimensions require the consideration of additional physical phenomena like thermoviscous losses, which are often negligible in large loudspeakers. We model and characterize a 3D piezoelectric MEMS loudspeaker in this work using our open‐source finite element method (FEM) program openCFS. We use the linearized conservation of mass, momentum, and energy (thermoviscous acoustic PDEs) for a compressible Newtonian fluid (air) and describe the linear elastic solid using the linearized balance of momentum. The coupling between flow and solid fields is then applied using a non‐conforming FEM formulation. The standard acoustic partial differential equation (PDE) is used in the far‐field, where the thermal and viscous effects are negligible. We study the viscous effects on the displacement and the sound pressure levels (SPLs) of the loudspeaker by parameter studies. These results indicate that at a distance of 13 mm, an SPL of 55 dB at 5 kHz is achieved by a single PMEMS loudspeaker with a footprint of 1.7×1.7 mm2 under a low driving voltage of only 1 V, which is promising considering its dimensions.

Numerical and experimental analyzes of forming parameters of low carbon steel

Understanding sheet metal forming presses are important to reduce manufacturing costs. Thus, the best method of finding the optimum values of processing is by studying the effect of forming parameters on the behavior of formability, friction, and die radius. In this work, the deep drawing process of a low-carbon steel cup was studied and the significance of two important process parameters are investigated which are the friction coefficient and the radius of the die. The finite element method program, ANSYS, is used to study the effect of these parameters on forming load in the deep drawing process. The three ​​levels of friction coefficient are considered which are 0.08, 0.00, and 0.15, and three die shoulder radius of 4, 6, and 8 mm. The results show that the predicted behavior of the punch load coincided well with both experimental and practical behaviors and the confidence is exceeding 94%. The wrinkling defect is happening when using a high die radius, Rd=8mm although the punch load is low due to the increase in the surface area on the edge of the die.

Coupled DEM-FEM methods for analyzing contact stress between railway ballast and subgrade considering real particle shape characteristic

To investigate the stress concentration at the interface between crushed ballast and soil subgrade, this study developed a coupling program of discrete element method (DEM) and finite element method (FEM) using OOFEM and YADE software. Based on the penalty function method, an interface element was introduced for the DEM-FEM coupling simulation. Moreover, an adaptive volume coupling algorithm was proposed to address the unrestricted behavior of the particles across the interface elements. Therefore, the change in the interface contact stress distribution was analyzed in the process of ballast particles penetrating the subgrade soil. Based on the statistical analysis of the ballast shape scanning results, a morphology reconstruction method was adopted to restore the real irregular shapes of the ballasts. Consequently, a DEM-FEM coupling model of a ballasted railway was established and validated through laboratory test results. The meso-scale mechanism revealed the discontinuous characteristics of the contact stress caused by the ballast aggregates. In addition, the adaptive volume coupling algorithm in the case of ballast penetrating subgrade soil was preliminarily proven to be reasonable. This study provides a more accurate approach for calculating the interface stress between ballast and subgrade, which can support a further refined analysis of ballast railway subgrade deterioration.

Modeling of the Lamb wave asymmetric modes with an improved two-dimensional thin plate theory

For the modeling of Lamb wave propagation, the accuracy of some two-dimensional (2D) plate theories like the first order shear deformation theory (FSDT) may decline at a high frequency, since their displacement fields cannot match those complicated Lamb wave structures. To address this issue, this paper proposes an improved 2D thin plate theory which has a more accurate high frequency modeling ability of Lamb wave than the FSDT. This is done by designing the displacement field according to the high frequency Lamb wave structure. Since the shear stress curves of the Lamb wave are complicated and would vary with the frequency, the initial displacement field takes a combination of polynomial and trigonometric forms, which has two coefficients that need to be determined by fitting the shear stress curve at a certain frequency. Then, a strategy is applied to determine the eventual displacement field by searching the high frequency range for the optimum coefficients that enable a best modeling accuracy. The relative error of its modeling result of A0 mode can be controlled within 0.03 % below 800 kHz·2 mm, and keeps the highest error of 1.43 % up to 2500 kHz·2 mm. To verify its high frequency modeling performance, a finite element method program is finally built. Results show that both the wavefields of A0 and A1 can be accurately simulated with the improved two-dimensional thin plate theory.

Numerical evaluation of the coupled/uncoupled effects of lower marine riser package and/or blowout preventer with a lower flex joint in a hang-off drilling riser

Lower marine riser package and/or blowout preventer (LMRP/BOP) are key marine riser components. However, they are often oversimplified or ignored in traditional studies, which inevitably causes certain calculation deviations, especially when the risers are in hang-off modes. Considering the full size of LMRP/BOP and rotational stiffness of the lower flex joint (LFJ), a fully coupled multibody model compared with the traditional single lumped mass model, is developed using the self-made finite element method program. Different numerical methods and the results in the literature verify this model's accuracy. The coupled and decoupled effects of the LFJ and the LMRP/BOP in the two numerical models versus LMRP/BOP weight, LFJ rotational stiffness, pipe wall thickness, riser suspension length, and ship heave motion in different running stages are comprehensively studied. Significant differences in the inherent vibration and time-domain characteristics between the two models indicate the coupled effects of the large-diameter LMRP/BOP and the rotational stiffness of LFJ of a hang-off drilling riser during running and installation procedures should not be oversimplified but should be well equivalent and considered for accurate evaluations in ocean engineering.

Discrete element approach to determining rock mass pressure on ore pass walls

A critical safety factor of ore pass walls is the correct evaluation of rock flow pressure on the walls at the design stage. This study uses the discrete element method to determine load of rock flow on the ore pass walls. This method is the most effective in modeling ore flow through a trapdoor. On the other hand, modeling of each discrete particle can create an illusion that the model automatically takes into account all typical phenomena of granular medium. From this point of view, the method of discrete elements can be discredited in practice. Therefore, it is necessary to describe the methodology of constructing and correcting the discrete element and finite element models of ore passes. At the first stage, the grain size distribution of rock flow is analyzed, and the representative sample volume is determined. At the second stage, the shear tests are performed at the particle–particle and particle–ore pass wall contacts. It is required to implement both tests as the difference between internal and external friction angles can be assumed to be the cause of bridging (a silo phenomenon). At the third stage, due to essentially different kinematics of shearing andconical pile formation, the calibration criterion is chosen to be the angle of repose. The fourth stage is the bridging modeling and comparison of the model data with the analytical results. This stage is only limited to the numerical modeling as there are yet no fully developed techniques to reconstruct bridging in ore passes on a laboratory scale. At the fifth stage, the numerical experiments on filling an ore pass and on ore outflow from it are carried out. The results are transferred to a finite element method program.

Symulacja procesu pracy dwuobwodowego wgłębnego systemu wypływowego

The article is devoted to a study of the flow's nature distribution in the above-bit ejection system as part of a series and parallel connection of two jet pumps designed to improve the technical and economic indicators of drilling production wells. Using the finite element method and computer programs, the critical value has been determined of the hydraulic resistance of the sludged section of the bottomhole, which provides an automatic change in the ejection system operation mode from injection to injection-suction. Regularities of changes in the hydrodynamic parameters of the ejection system have been established and the probability and conditions for the existence of non-operating modes of jet pumps have been analyzed. When conducting experimental studies, the influence of the flow rate of the working medium on the flow characteristic of a jet pump of a direct-flow and swirling working flow has also been determined. To swirl the flow, a plate with an inclination angle of the guide elements of 15° placed in the working nozzle of the jet pump has been used. The swirling of the working flow makes it possible to increase the injection ratio of the jet pump. The maximum increase in the value of the injection coefficient is 20.84% and corresponds to small (up to 104) Reynolds numbers of the working flow. The ratio between the maximum and minimum values of the injection coefficient of the flow characteristics of the jet pump when swirling the working flow is halved.

Weight-strength optimization of wooden household chairs based on member section size

Weight-strength optimization of wooden household chairs was performed based on the member section size in this study. Member section sizes of the Scotch pine (Pinus sylvestris) and Oriental beech (Fagus orientalis) chairs were optimized and resulting re-manufactured optimized chairs were tested under the cyclic “front to back”, “back to front” and “backrest” loads according to American Library Association (ALA) specification. Finite element method (FEM) and MATLAB nonlinear programming were utilized for the optimization. Firstly, the internal forces and moments acting on each member were analyzed by FEM in order to obtain the maximum critical stresses in each type of member; then, optimized cross-sectional sizes of the members were determined by Gradient Descent method, and all constraints were treated with Logarithmic Barrier Functioning. As a result, the minimum section sizes of members were determined, and cyclic performance tests were performed to determine whether the optimized chairs were strong enough to carry the acceptable loads. According to the results, member section size of both beech and pine chairs could be significantly reduced. The reduction was 32 % in the total weight and volume for beech chairs while 16 % for pine chairs without sacrificing the performance required for domestic usage by ALA. In conclusion, the method used is suitable for the optimization of furniture frames, making it lighter and reducing the material costs.

Developing Equations for Free Vibration Parameters of Bistable Composite Plates Using Multi-Objective Genetic Programming.

For the last three decades, bistable composite laminates have gained publicity because of their outstanding features, including having two stable shapes and the ability to change these states. A common challenge regarding the analysis of these structures is the high computational cost of existing analytical methods to estimate their natural frequencies. In the current paper, a new methodology combining the Finite Element Method (FEM) and Multi-Objective Genetic Programming (MOGP) is proposed for the analysis of bistable composite structures, leading to some analytical relations derived to obtain the modal parameters of the shells. To achieve this aim, the data extracted from FEM, consisting of the ratio of the length to width (a/b) and the thickness (t) of the laminate, is split into Train and Validation, and Test, subsets. The former is used in MOGP, and four formulas are proposed for the prediction of the free vibration parameters of bistable laminates. The formulas are checked against the Test subset, and the statistical indices are calculated. An excellent performance is observed for all GP formulas, which indicates the reliability and accuracy of the predictions of these models. Parametric studies and sensitivity analyses are conducted to interpret the trend of input parameters in the GP models and the level of sensitivity of each natural frequency formula to the input parameters. These explicit mathematical expressions can be extended to the other bistable laminates to obtain their natural frequencies on the basis of their geometrical dimensions. The results are validated against the experimental data and verified against FEM outcomes.

Predictive Simulation for Surface Fault Occurrence Using High-Performance Computing

Numerical simulations based on continuum mechanics are promising methods for the estimation of surface fault displacements. We developed a parallel finite element method program to perform such simulations and applied the program to reproduce the 2016 Kumamoto earthquake, where surface rupture was observed. We constructed an analysis model of the 5 × 5 × 1 km domain, including primary and secondary faults, and inputted the slip distribution of the primary fault, which was obtained through inversion analysis and the elastic theory of dislocation. The simulated slips on the surface were in good agreement with the observations. We then conducted a predictive simulation by inputting the slip distributions of the primary fault, which were determined using a strong ground motion prediction method for an earthquake with a specified source fault. In this simulation, no surface slip was induced in the sub-faults. A large surface slip area must be established near a sub-fault to induce the occurrence of a slip on the surface.