Transient Finite Element Analysis Research Articles

Prediction of Earth Dam Seepage Using a Transient Thermal Finite Element Model

With the majority of the United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS)-sponsored earthen dams exceeding their planned service life, seepage is a concern since it is a common failure mechanism among earthen dams as a whole. Seepage occurs when water penetrates a hydraulic barrier to create open pathways, channels, or piping leading to internal erosion or stability issues due to increased effective stress. Due to the complex geometries of these hydraulic structures, time-dependent boundary conditions, and complicated failure analyses, numerical approaches have been used to estimate seepage. However, the existing numerical models are either computationally expensive or assume steady-state conditions. This work develops the framework for using a transient thermal finite element analysis (FEA) model as an analogy to predict transient seepage. The FEA model is compared to a transient analytical model to verify the approach. A sensitivity analysis of the FEA model shows that the time aspect of seepage flow is dependent on the medium, i.e., soil, and not on the fluid properties.

Permeable Cornified Envelope Layer Regulates the Solute Transport in Human Stratum Corneum

To unravel the diffusion mechanisms of percutaneous drug delivery, suitable numerical analysis of stratum corneum structure is essential. In this research paper, we accounted for the permeable envelope layer in the brick-and-mortar finite element models of human stratum corneum. Both penetration and desorption experiments for tritiated water were simulated by transient finite element analysis. Rivet-shaped corneodesmosomes were included in the brick and mortar model. Results showed that cornified lipid permeability (Penv) is a determinant in desorption of the solute, while lipid transverse diffusion coefficient (Dlip-trans) is prominent during penetration. These two major unknowns (Penv and Dlip-trans) were obtained by extensive fitting of the finite element model to the experimental water data. Penv and Dlip-trans were determined to be 1×10−2 cm/s and 5.7×10−10 cm2/s, respectively.

A model order reduction of hysteretic eddy-current fields in electric machines using Cauer ladder network method

This study aims to establish a hysteretic model order reduction method for electric machines using the Cauer ladder network (CLN) method. The first inductor of the CLN represents the hysteresis effect, which is computed using the scalar play model identified from the static I–ϕ (current–magnetic flux) loops. An iron-core inductor was analyzed, and pulse-width modulation (PWM) voltage input was applied to the coil. The proposed method yielded results that agreed with the transient finite element (FE) analysis and effectively reduced the computation time.

Unsaturated modelling, testing and monitoring towards the rehabilitation of a slope on National Route 3, KwaZulu-Natal, South Africa

The stability of over-steep road embankments often worsens with time. In many cases the slope deterioration can be ascribed to continual downslope creep of a surficial layer of soil that has been affected by infiltration of rainfall. Such infiltration reduces the suction in the surficial layer interacting with the environment. With every season the surficial layer moves further downslope, often resulting in cracks in theslow lane and placing structures constructed at the crest of fill slopes in potential jeopardy. A slope on the National Route 3 (N3), in the South African Province of KwaZulu-Natal, constructed at roughly 40° from the horizontal showed signs of distress in the slow lane many years after construction. The rehabilitation of this slope required stabilisation design using unsaturated soil testing, modelling, and in-situ suction measurement. The slope was stabilised using soil nails, a high-tensile steel mesh, and a suction measurement system was installed. An overview of the emergency works design, subsequent investigation, and monitoring is provided in this paper. It was found that the suction profile determined by transient finiteelement analysis matched well with the measured suction profile and provided a good basis for the emergency design works prior to full investigation.

Identification of the anisotropic thermal conductivity by an inverse solution using the transient plane source method

The identification of the anisotropic thermal conductivity of material was performed using the transient plane source (TPS) method coupled with an inverse solution. The proposed method requires three measurements to be performed on three orthogonal planes of the cubic samples. Transient finite element analysis was used to solve a direct problem: three-dimensional heat conduction in anisotropic media due to a circular planar heat source. 3D printing technology was used to manufacture two sets of samples, isotropic samples were used to identify intrinsic properties of the polymer, and samples with specially designed anisotropic microstructure were used for the identification of an anisotropic conductivity tensor by the proposed method. To validate obtained results, the thermal conductivity was calculated using a finite element solution for a periodic unit cell, representing the microstructure of the material. Good agreement was observed between conductivity values obtained by two different methods, with a difference of ≤10 %.

Assessment of the Blasting Efficiency of a Long and Large-Diameter Uncharged Hole Boring Method in Tunnel Blasting Using 3D Numerical Analysis

Cut blasting is one of the most essential processes to reduce blast-induced vibration in tunnel blasting. The long and large-diameter uncharged hole boring (LLB) method is an example of one of the cut blasting methods, which utilizes large-diameter uncharged holes drilled in the tunnel face. In this study, blasting simulations were performed to analyze its blasting mechanism, and the LLB method and the traditional burn-cut method were simulated to compare their blasting efficiency. A 3D numerical analysis using LS-DYNA code, a highly non-linear transient dynamic finite element analysis using explicit time integration, was used to simulate the blasting process, and a Johnson–Holmquist constitutive material model, which is optimal for simulating brittle materials under dynamic conditions, was used to simulate the rock behavior under blasting. The modified LLB method showed a 3.75-fold increase in the advance per round compared to the burn-cut method, due to the increased formation of long and large-diameter uncharged holes compared to blast holes. This modified LLB method used 30% less explosives, so its failure range was approximately 1.25 times less than that of the burn-cut method, but its advance was approximately 4 times larger than the burn-cut method, which was similar to the original LLB method. This confirmed that the modified LLB method is significantly more efficient in terms of increased blasting efficiency (particularly the advance per round) as well as reduced blast-induced vibration, compared to the traditional cut blasting method.

Multi-objective optimum design of five-phase squirrel cage induction motor by differential evolution algorithm

Compared with the traditional induction motors, five-phase squirrel cage induction motor (FSCIM) have the advantages of lower torque ripple and single-phase power, flexible control strategy, higher power density and fault-tolerant operation, which has been widely applied on electrical vehicles, rail transit, underwater vehicles and so on. This paper presents an analytical design optimization method based on the coupling of electromagnetic equivalent circuit (EEC) and differential evolution algorithm (DEA). Furthermore, the difference between three and five-phase winding on harmonic specific leakage permeance is investigated in detail. The nonlinear and oeolotropic influences of design geometrical parameters (slots openings, main dimension ratio, yoke height, airgap length, etc.) on the performances of the basic FSCIM model are evaluated with analytical model. For more accurate results, the harmonic characteristics of five-phase winding structure, iron core saturation, rotor slot skew width, stator end winding, slot leakage inductance and stator and rotor slot structure are considered. Meanwhile, the efficiency, power factor, maximum torque, slot fill factor and material consumption of FSCIM are calculated as the comprehensive objective function. The transient finite element analysis (TFEA) and experimental test verify the accuracy of the proposed optimum model. In addition, the feasibility of the multi objective optimization design scheme provided by the analytical model is verified by TFEA.

Performance Analysis of an Outer Rotor Variable Reluctance Resolver

Variable reluctance resolver (VR-Resolver) is a robust electromagnetic sensor that provides position information for closed-loop control systems of permanent magnet synchronous motors (PMSMs). For specific motion control applications, an outer rotor structure is presented for the VR-Resolver in this article with a nonoverlapping tooth-coil windings configuration to simplify the manufacturing process. The study on the structure of the proposed position sensor is carried out, followed by the description of the working principle. The presented outer rotor VR-Resolver is simulated and its performance is investigated in detail with the aid of transient finite-element analysis (TFEA). Sensitivity analysis is carried out on the rotor shape factors and slot opening, and the effect of manufacturing tolerances is investigated as well. Finally, the effectiveness of the optimal design is verified by 3-D TFEA.

Human-Induced-Vibration Response Analysis and Comfort Evaluation Method of Large-Span Steel Vierendeel Sandwich Plate

A steel Vierendeel sandwich plate used as a large-span lightweight floor structure for vibration comfort during crowd gatherings was considered. Taking the steel Vierendeel sandwich plate in Guizhou Museum as an example, through finite element transient analysis, the effects of the structural damping, pedestrian self-weight, floor span, surface concrete slab thickness, and structural parameters on the floor’s acceleration response distribution were deeply studied. According to the distribution characteristics of the acceleration response, a distribution model function was constructed, and a distribution Gauss model of the relationship between the peak acceleration response and the position of the steel Vierendeel sandwich plate was established. A field test of the sandwich plate under human-induced fixed-point excitation was carried out, and the model fitting results were compared with the actual test results. The results showed that the Gaussian model could effectively estimate the peak acceleration response at different positions on the floor. In addition, according to the distribution model, a comfort evaluation method based on the comfort assurance rate was proposed that could greatly reduce the representative value of the acceleration evaluation. The research results provide a reference for the comfort evaluation and corresponding vibration-reduction design of long-span steel Vierendeel sandwich plates.

Orientation impact on structural integrity of a shell and tube latent heat thermal energy storage system

Latent heat thermal energy storage systems can regulate the intermittency of electricity generation in a grid powered by renewable energy sources. Such systems could be used in conjunction with Brayton power generation cycles operating at high temperatures (520 °C–750 °C) delivering higher efficiency. However, a trade-off of higher thermal efficiency can be higher thermal stresses. The isothermal latent heat thermal energy storage and release can reduce the thermal stresses for a specific design. This study investigates the impact of the orientation on the melting process and the consequent thermal stresses in a lab-scale latent heat shell and tube system using a combination of transient computational fluid dynamics and finite element analyses. With a high temperature phase change material melting at 705.8°C, two initial temperatures of 700°C and 650°C were considered in transient analyses, leading to a 50 K and 100 K initial temperature difference across the tubes, respectively. For the structural analysis, an elastic method was employed for the condition of 50 K temperature difference, and an elastic-plastic analysis for the condition of 100 K to account for plastic deformation. The results of the elastic analysis presented the maximum thermal stresses of 63.5 MPa and 106.7 MPa in tubes in the horizontal and vertical orientations, respectively. The stress in the tube sheet was slightly higher (94.5 MPa) for the horizontal system compared with 90.4 MPa in the vertical position. For the condition of 100 K, the results of the elastic-plastic analysis identified the highest stresses of 172.5 MPa and 147.4 MPa in the tube sheets of the horizontal and vertical systems, respectively. For both initial temperature conditions, the stress level in tubes is lower in the horizontal orientation, which is where most cost occurs in a shell and tube system. Particularly important for the 100 K condition, the results show a lower stress of 100 MPa in tubes for a horizontal system compared with 140 MPa in a vertical orientation. In general, the lowest thermal stress occurs where a melt layer forms around tubes during the early stages of a melting process. A higher stress occurred in parts in contact with argon. The highest level of stress occurred in parts in contact with solid PCM, which has direct implications for larger vessel designs. This study provides insights into hydrothermal and mechanical design of a PCM system to prevent and/or manage localised maximum thermal stresses for a cost-effective thermal energy storage system.

Optimal disc brake design for reducing squeal instability using slip-dependent complex eigenvalue analysis

This paper proposes an improved disc brake system optimization method for squeal instability reduction using slip-dependent eigenvalue results. Although complex eigenvalue analysis is widely used for minimizing brake squeal instability, conventional optimization approaches still have the limitation of not being able to reflect slip rate-varying squeal instability characteristics. While relative angular velocity between the pad and disc declines due to braking, disc brake system instability gradually increases up to a specific peak velocity point and decreases until the vehicle stops, which means a maximum instability point exists during the braking process. Therefore, instability optimization should target the prevention of a maximum value during a braking scenario. The proposed optimization formulation is conducted considering maximum instability during full braking. To obtain braking time profiles, a model-based design method is employed and utilized instead of full finite element transient dynamic analysis to reduce computational cost. Kriging surrogate modeling is also used for solving the optimization problem and better express the multi-variable squeal problem. The proposed optimal design method produces minimal squeal instability during the full vehicle braking time range. The effectiveness of the proposed disc brake optimal design is demonstrated via acceleration power value comparison of the structure acceleration with that derived by conventional optimization approach.

Optimization of structural design with pendulum dynamic vibration absorber using genetic algorithm

In this study, a genetic algorithm is introduced to determine optimal locations of pendulum dynamic vibration absorbers (PDVAs) in vibrating structures. A PDVA is composed of a pendulum system and spring-mass system, and aims to attenuate structural vibrations at two resonance frequencies, that is, the square root of stiffness over mass and square root of a length over gravity of the hosting structure. An optimization method involving nonlinear transient finite element analysis was applied to increase the engineering efficiency of PDVAs. With the incorporation of a genetic algorithm, the optimal locations of PDVAs in various structures can be determined and vibrations at the desired resonant frequencies can be attenuated. In addition, the Voronoi diagram concept is applied to realize a uniform distribution of PDVAs in vibrating structures. Several optimization examples were solved using the proposed genetic algorithm and demonstrated decreases in frequency responses by up to 98.6549%, showing the effectiveness of PDVAs in suppressing structural vibrations.

An Efficient Method for Litz-Wire AC Loss Computation in Transient Finite Element Analysis

An efficient method is proposed to predict eddy current loss of Litz wire coils, or completely transposed multi-strand coils, in transient finite element analysis (FEA). The method is based on analytical solutions of eddy current loss in a solid wire due to skin effects and proximity effects. The bundle of Litz or solid wires is homogenized by introducing a fill factor to describe the conducting area ratio. The analytical solutions in the frequency domain for round, square, and rectangular wires are further expanded to those in the time domain. The wire length direction in each 3-D mesh is automatically detected so that the flux density vector in each mesh can be correctly decomposed to the orthogonal and tangential components for anisotropic proximity effect loss computation. The method is applied to calculating eddy current loss of a gapped inductor in both 2-D and 3-D, and the results are compared with that using real solid wires.

Fast and Accurate Traction Induction Machine Performance Calculation Method for Integrated Onboard Charging in Vehicle to Grid Application

Reusing traction electric machine windings in electric vehicles as an integrated filtering inductor is a promising solution to reduce the size of the vehicle to grid (V2G) charging/discharging system. Obviously, the integrated inductors need to meet the requirements of traction and charging/discharging, which brings challenge for the design of traction machines. As one of the most popular traction electric machine types, the high-speed induction machine usually has large electrical time constant and consequently unacceptably long transient time in the design stage when finite element analysis is adopted. In this article, a method is proposed to quickly and accurately calculate the steady state performance of the induction machine by time-stepping transient magnetic finite element analysis. First, the stator current magnitude is ramped up from zero to full magnitude gradually to control the DC component in rotor flux and torque. Second, a multistep equivalent resistance method is adopted to decrease rotor time constant and suppress slot-tooth harmonic transient response. The proposed method can predict the FEA computation load before running the calculation, and it does not rely on the machine parameter and feedback signal. Its performance is tested by an example induction machine. The result shows that the proposed method can reduce the finite element calculation time of a high-speed operating point by 99%.

Effect of damping rate on fatigue failure tendency of a topology-optimised swing arm for a heavy commercial truck cab suspension

The effect of damping rate on the failure tendency of a truck cab suspension swing arm was numerically investigated. Firstly, the mechanical design of the swing arm was carried out using topology optimisation by taking the standard load cases into account. Displacement differences which occurred in the front cab suspension springs, as a result of the cab roll, were obtained for an uneven road surface by using the Multibody Dynamics (MBD) model of the truck. Using these data, full transient Finite Element (FE) analyses and arm fatigue analysis were conducted for various damping characteristics of the shock absorber. Results showed that, reducing the damping ratio of the shock absorbers by, e.g., 50% in comparison with the reference value, may result in swing arm damage under dynamic loading conditions. Therefore, it was concluded that, damping rate should be considered in the design stage of cab suspension components which can be categorised as a safety system.

On the influence of Additive Manufacturing defects on the energy absorption capability of a lattice structure

The present paper investigates the influence of AM defects on the energy absorption capability of lattice structure specimens made of carbon nylon. Two typologies of defects are considered through numerical simulations: i) the variation of the diameter of the beam with respect to the nominal value; ii) the presence of lack-of-fusion portions of material within the beams. The defects are randomly disposed in the unit cell and different defect populations are then simulated. Transient nonlinear finite element analyses of the lattice structure subjected to compression tests are performed in the LS-Dyna environment. The numerical model is validated with experimental data collected in a previously published work. Results show that both beam diameter variations and lack-of-fusion defects affect the absorbed energy although with different severities. The increasing degradation of the absorbed energy with the increasing numerosity of the defects confirms the necessity of accounting for these defects when designing lattice-based energy absorbers.

Novel Quasi-Three-Dimensional Modeling of Axial Flux In-Wheel Motor With Permanent Magnet Skew

This paper presents a characteristic analysis of axial flux permanent magnet machines (AFPMMs) for in-wheel electric vehicles. Preferentially, a novel quasi-3-D model is developed for the fast and accurate design of AFPMMs. In electromagnetic field analysis, combined with field reconstruction method, the computation time of 2-D solutions is significantly reduced. With the use of time sweeping of the basis function, only the static finite element (FE) analysis is performed to calculate the air-gap flux distribution at the entire rotor position, whereas the conventional 2-D solutions require a transient FE analysis. In the shape sweeping process of the basis function, the virtual air-gap section method is introduced to take into account that the ratio of slot opening to slot pitch is different depending on the radius of analysis plane, which causes errors in the analysis results of the conventional quasi-3-D method. The virtual air-gap sections are obtained by interpolation of the spatial field between the mapped cylindrical planes. The proposed technique reduces the number of 2-D analysis planes required for high accuracy in the conventional quasi-3-D method, and it can also predict the air-gap magnetic flux distribution for skewed permanent magnets without additional FE analysis. Finally, using the magnetic fields calculated in the proposed method, the electromagnetic performances of the AFPMM are calculated, such as load torque, cogging torque, attraction force, and back-EMF. The analysis results were verified by comparison with the measurement results.

Splitting Time Integrator for Transient Analysis of Nearly Incompressible Elasticity

Since the velocity of the P-wave may be much larger than that of the S-wave in nearly incompressible materials, explicit time integrators are hardly applied to such problems. This paper presents a novel time integration scheme for transient finite element analysis of nearly incompressible elasticity. The proposed time integrator is derived by extending the Rattle algorithm for constrained Hamiltonian systems. The proposed approach works as an implicit scheme for the P-wave propagation while it works as an explicit one for the S-wave. Thus its numerical stability depends on only the Swave velocity.

The analyses of frictional losses and thermal stresses in a diesel engine piston coated with different thicknesses of thermal barrier films using co-simulation method

This study comparatively presents the thermal and mechanical effects of different Thermal Barrier Coatings (TBCs) and their thicknesses on the performance of aluminum diesel engine piston by combining Finite Element Analyses (FEA) and Artificial Neural Network (ANN) methods. The piston structure of MWM TbRHS 518S indirect injection six-cylinder diesel engine was modeled. The clustered TBCs (NiCrAlY–Gd2Zr2O7, NiCrAlY–MgO-ZrO2, NiCrAl–Yttria Partially Stabilized Zirconia (YPSZ), and NiCrAlY–La2Zr2O7) were implemented to the related surface of aluminum alloy piston and then static, thermal, and transient structural FEA were conducted for each model. Based on both of the temperature and equivalent stress distributions, NiCrAlY–Gd2Zr2O7 coated model displayed the best performance. Additionally, the effects of top coating thicknesses of TBCs were investigated in the range of 0.1–1.0 mm with 0.1 mm increments in FEAs. The thermally effective top coating thickness was predicted as 0.95 mm for the selected TBC using ANN method. Then the effects of coating thickness on frictional performance were revealed by generating transient structural FE models and utilizing stribeck diagram. The uncoated and 0.95 mm NiCrAlY–Gd2Zr2O7 coated models were adjusted as transient and the related crank angle – dependent in-cylinder combustion pressure data was implemented. The friction force was reduced by at least 15% in NiCrAlY–Gd2Zr2O7 coated model.

Design Issues of a Rotating to Linear Motion Magnetic Converter for Short-Distance Transport Applications

This paper discusses some design issues of a magnetic rotating to linear motion converter (RLMC), suitable for the propulsion system of a short-distance low-capacity vehicle. It basically operates like a magnetic rack, which executes the contactless conversion of the motor torque into a propulsion thrust, deriving from the interaction of on-board permanent magnet (PM) modules and stationary ferromagnetic steel pieces. A design procedure is set up that deals with both the PM module arrangement and the geometric shape of the steel pieces to optimize different performance aspects. A simplified modeling based on 2D transient finite element analyses is carried out to determine the thrust profile and the RLMC losses, which are essential to assess its practical feasibility. Finally, the characteristics as functions of the load angle and speed are determined to enable the prediction of the dynamic power exchange and then of the net energy demand useful to size the on-board source.