Transient Finite Element Analysis Research Articles

Investigation of dimensional and heat source effects in Lock-In Thermography applications in semiconductor packages

Lock-In Thermography (LIT) is a powerful non-contact and non-destructive investigating technique that has recently emerged in the semiconductor industry. The current LIT applications interpret LIT data using the semi-infinite models. However, semiconductor package has finite geometry with convective heat transfer on surface. This paper studies the accuracy of the interpretation of LIT data based on the commonly used semi-infinite models. The effects of finite dimensions, heat source configuration, convective heat transfer coefficient, thickness of material, thermal diffusivity of material, and lock-in frequency are examined. Furthermore, the effects of heat source’s shape and location, as well as the problems involving non-homogeneous materials are also investigated. It has been found that the errors in phase shift estimate using semi-infinite models may occur at lower lock-in frequency with high diffusivity material and thinner specimen. When multiple materials are involved with various scenarios of heat source locations, the phase shift may decrease with the lock-in frequency, as observed in experiment. Finite element transient heat conduction analysis is a useful tool to derive the actual z-depth of heat source based on the phase shift data from experiment.

Continuous-Mass-Model-Based Mechanicaland Electrical Co-Simulation of SSR and Its Application to a Practical Shaft Failure Event

To accurately evaluate the damage caused by subsynchronous resonance (SSR) to a turbo-generator shaft, we have developed a novel mechanical and electrical co-simulation method, wherein the continuous-mass-model-based mechanical system is simulated in a close-loop or coupled way with the electrical power system so that the detailed torque profile along the shaft can be obtained for further analysis of fatigue loss of life. Nonlinear mechanical damping is also modelled to reflect the torsional inter action more precisely. The co-simulation is implemented using commercial electromagnetic transient program and finite element analysis software. A special dynamic data exchange mechanism is designed to make it proceed very efficiently. As a case study, the proposed method has been applied for the root-cause analysis of a recent shaft failure incident in an India power plant. The extensive simulation results have fully demonstrated its effectiveness in acquiring fine-grained torques and its advantages over previous methods. Finally the direct cause of the shaft failure is identified to be the sustained torsional interaction (one type of SSR) between the turbo-generator and its connected series-compensated power system.

Simplified Analysis of Nonoverlap Short-Circuited Coil Winding Slip Permanent Magnet Couplers

In this paper, a simplified analysis technique is introduced to allow the dq modeling of a nonoverlap, short-circuited coil winding slip permanent magnet (PM) coupler (S-PMC). The proposed technique for predicting the coil currents using a number of static finite-element (FE) solutions takes the effect of, amongst others, mutual coupling between the coils and layers into account. The technique also allows a difference in the currents of top- and bottom-layer coils, if such coil windings are used. This all makes the method particularly attractive for use in the design optimization of the S-PMC. Excellent correlation with measured and transient FE analysis results was found for a 2.2 kW S-PMC prototype with an efficiency of 97% at a rated load.

Transient thermal analysis for accelerated reliability testing of LEDs

Reliability of LED light sources is essential for many general and automotive lighting application where exchange of LED modules would be expensive. Reliability testing to predict the life-time of the devices is required. In this paper transient thermal testing is applied and further developed to monitor the structural integrity of the LED modules during accelerated stress testing. The temperature shock test is one important test because thermo-mechanical stress is a dominating root cause for structural failures as delamination in the package or cracking of solder joints between package and board. New flip chip LEDs (WLP-LEDs) are assembled directly on printed circuit boards (PCB). The initial assembly quality is tested using X-Ray, optical inspection and transient thermal analysis (TTA). In combination the methods deliver essential data to ensure initial assembly quality. Afterwards, the LED modules are exposed to temperature shock tests (−40°C to 125°C) and the TTA is performed repeatedly. By TTA the structural integrity is resolved and cracks or delamination can be identified. Failure modes can be separated and the root cause is investigated by support of transient finite element analysis. One test board is measured In-situ during temperature shock testing. Due to differences in thermo-mechanical stress under hot and cold conditions additional information can be obtained.

Analytical Solution of Plane-Strain Poroelasticity due to Surface Loading within a Finite Rectangular Domain

AbstractAn analytical solution is presented for plane-strain poroelasticity induced by surface-normal loading within a finite rectangular fluid-saturated domain. In this work, the porous medium is assumed to be isotropic, homogeneous, and composed of compressible constituents. Appropriate Fourier and Laplace transforms and inversions are used to derive the analytical solution. In particular, lateral boundary conditions for the displacement field are specifically prescribed with care to match the Fourier and Laplace transforms. The analytical solution is presented in terms of summations of multiple series. Then, a case study for the consolidation of a water-saturated soft clay layer is carried out. The analytical solution is compared to the finite-element (FE) solution through a nonlinear transient FE analysis software program. The excellent agreement between the FE solution and the analytical solution demonstrates the accuracy and reliability of the analytical solution presented in this paper. Meanwhile, ...

Modeling Water Motion near Seismic Waves Propagating across a Graded Seabed, as Generated by Man-Made Impacts

Seismic interface waves generated by seabed impacts are believed to have biological importance. Various wave types are of interest to seismologists, who can minimize the unwanted, but often dominant, ground roll waves with suitable instrumentation. Waves made by dredging and piling have been measured using geophones and found to be of this interface type, which propagate much more slowly than the pressure waves in the water column above. Short interface wavelets of a few cycles were modeled using transient finite element analysis (FEA). Wavelets with low losses have been modeled using graded sediment data from the literature. They do not radiate energy away from the interface because the evanescent acoustic pressures they generate decay rapidly with distance from the seabed. Associated water particle velocities are much greater than would be expected from similar acoustic pressure measurements in a free field. This motion is significant to aquatic life which is dependent on inertial sensors (otoliths, etc.) to respond to the environment. Additional amplification of the horizontal seabed motion of the adjacent water is predicted for a short seismic wavelet modeled in a graded solid seabed. Further recent analysis studied the distribution of the energy flux within the sediment layers.

Analysis and modeling of different topologies for linear switched reluctance motor using finite element method

In the present paper, an electromagnetic simulation model is introduced for the conventional type of linear switched reluctance motor (LSRM) in which the dynamic characteristics of the motor are predicted precisely by carrying out 2D finite element (FE) transient analysis using ANSYS FE package. The simulation model is created totally in ANSYS parametric design language (APDL) as a parametric model and it can be used easily for different designs of the conventional LSRMs. Introducing linear switched reluctance motor with segmental translator as a new type of LSRM, performance principles and design criteria are presented for two various topologies of this motor. Carrying out 2D FE transient analysis, dynamic characteristics of these two motors are predicted and compared to those obtained for the conventional LSRM.

Initial position estimation strategy for a surface permanent magnet synchronous motor used in hybrid electric vehicles

A novel nonlinear model for surface permanent magnet synchronous motors (SPMSMs) is adopted to estimate the initial rotor position for hybrid electric vehicles (HEVs). Usually, the accuracy of initial rotor position estimation for SPMSMs relies on magnetic saturation. To verify the saturation effect, the transient finite element analysis (FEA) model is presented first. Hybrid injection of a static voltage vector (SVV) superimposed with a high-frequency rotating voltage is proposed. The magnetic polarity is roughly identified with the aid of the saturation evaluation function, based on which an estimation of the position is performed. During this procedure, a special demodulation is suggested to extract signals of iron core saturation and rotor position. A Simulink/MATLAB platform for SPMSMs at standstill is constituted, and the effectiveness of the proposed strategy is verified. The proposed method is also validated by experimental results of an SPMSM drive.

Investigation and control of excessive cumulative girder movements of long-span steel suspension bridges

This paper presents an investigation on the premature damage to expansion joints and bearings of long-span suspension bridges, in which failure patterns, locations and mechanism are presented and discussed. According to the field monitoring and time-and frequency-domain analyses, it is observed that the small but rapid girder movements contributed mostly to the large cumulative movements, resulting in accelerated fatigue damage and wear of expansion joints and bearings. Several damage mitigation measures were applied, including the use of more durable friction material, more control springs and movement restraint belts, and their effectiveness is examined through field observation. A supplementary control measure using viscous dampers is finally suggested and the influence of various damper parameters is discussed based on the proposed transient finite element analysis method.

Computational and experimental study on laser heating of a Ni-based metal alloy

Both computational and experimental studies were conducted to characterize complex heat transport and damage evolution phenomena in a metal alloy material subjected to laser irradiation. A Ni-based alloy, Inconel 718, was subjected to various irradiances of a flat-top, 4cm diameter beam of continuous wave, 1.07μm wavelength light. In this numerical study, a nonlinear transient finite element (FE) analysis, based on conductive, convective and radiative heat transfer, was conducted to predict temperature evolution (i.e., during heating, melting, and cooling conditions), damage initiation, and damage progression. A two-dimensional axisymmetric model was built with experimentally relevant plate geometry. ANSYS, a commercial FE software package, was used to conduct the nonlinear transient analyses. Such analyses employ an element removal feature to predict realistic evolution of the melt front within the laser heated Inconel 718 plates. The element removal scheme ensured that the laser energy supplied to removed elements no longer contributed to heating the rest of the intact material portion, and that the melt elements would not reappear (e.g., during cooling stage). Spanning a wide range of laser irradiance levels (i.e., from 11W/cm2 to 828W/cm2), the numerical model demonstrated good agreement with the experimentally measured temperatures during heating and cooling. After confirming the validity of measured temperature progression, the numerical model provided predictions in good agreement with experimentally measured penetration times and final damage (hole) sizes.

The Finite Element Transient Structure Analysis of the Startup of the Sugarcane Harvester Transfer Case

The broken bearings and great noise and vibration often occurs with the small sugarcane harvester transfer case when it starts up working. To analyze the startup status of the transfer case conveniently and quickly, the finite element transient structure analysis is carried out. with virtual prototype technology to simulate the transfer case's startup dynamic process and measure the instantaneous load values. Stress distribution and load variation analysis results show that during startup, the stress concentration of node load increases rapidly with gear speed rising transiently. The maximum value that lying on the underside of the bearing base goes beyond the allowable range before dropping sharply to approach the steady state with stress within the allowable range. Therefore, at startup the impact load of the transfer case increases far greater than in the steady state which deteriorate the structure stress condition seriously. The strength of the transfer case is then enriched by structural improvement accordingly to reduce maximum stress 36.8%, the maximum deviation 18.5% and the vibration up to30%, improving the bearings working reliability notably.

Effects of semi-floating ring bearing outer clearance on the subsynchronous oscillation of turbocharger rotor

Semi-floating ring bearing(SFRB) is developed to control the vibration of turbocharger rotor. The outer clearance of SFRB affects the magnitude and frequency of nonlinear whirl motion, which is significant for the design of turbocharger. In order to explore the effects of outer clearance, a transient finite element analysis program for rotor and oil film bearing is built and validated by a published experimental case. The nonlinear dynamic behaviors of rotor-SFRB system are simulated. According to the simulation results, two representative subsynchronous oscillations excited by the two bearings respectively are discovered. As the outer clearance of SFRB increases from 24 μm to 60 μm, the low-frequency subsynchronous oscillation experiences three steps, including a strong start, a gradual recession and a combination with the other one. At the same time, the high-frequency subsynchronous oscillation starts to appear gradually, then strengthens, and finally combines. If gravity and unbalance are neglected, the combination will start starts from high rotor speed and extents to low rotor speed, just like a “zipper”. It is found from the quantitative analysis that when the outer clearance increases, the vibration amplitude experiences large value firstly, then reduction, and suddenly increasing after combination. A useful design principle of SFRB outer clearance for minimum vibration amplitude is proposed: the outer clearance value should be chosen to keep the frequency of two subsynchronous oscillations clearly separated and their amplitudes close.

An Analytical Method for Predicting 3-D Eddy Current Loss in Permanent Magnet Machines Based on Generalized Image Theory

This paper proposes an analytical method, based on the generalized image theory, for accurate prediction of 3-D eddy current distributions in the rotor magnets of permanent magnet (PM) machines and the resultant eddy current loss. The analytical framework is established in a 3-D rectangular coordinate system, and the boundary conditions that govern the eddy current flows on the surfaces of magnets are represented by equivalent image sources in a homogenous 3-D space extending into infinity. By introducing a current vector potential, the 3-D eddy current distributions in magnets are derived analytically by employing the method of variable separation, and the total eddy current loss in the magnets is subsequently established. The proposed method has been validated by a 3-D time-stepped transient finite-element analysis (FEA). It is shown that the proposed method is extremely computationally efficient. When combined with the 2-D FEA of magnetic field distributions, the proposed method provides an accurate and computationally efficient means for predicting 3-D eddy current loss in a variety of PM machines with due account of complex machine geometry, various winding configurations, and magnetic saturation.

Post-Demagnetization Performance Assessment for Interior Permanent Magnet AC Machines

This paper assesses the post-demagnetization performance of interior permanent magnet (IPM) ac machines by employing the more accurate recoil line approach based on a 2-D transient finite-element analysis (FEA). The method predicts continuous demagnetization of each magnet element undergoing partial demagnetization and evaluates the machine behavior after an event of short-circuit faults across its terminals. Along with the short-circuit faults, a failure in a drive controller or a position sensor, which may lead to a reverse voltage across the machine terminals that can eventually be more fatal and can cause significant reduction in the performance due to high levels of demagnetization, is analyzed as the worst case scenario. The FE predicted post-demagnetization performance is validated by experimental measurements in which a six-phase IPM machine designed for electric vehicle traction is allowed to lose its synchronization with the inverter when forced to operate on a torque–speed envelope, which is way beyond the drive voltage setting.

A simulation study to compare the phase-shift angle radiofrequency ablation mode with bipolar and unipolar modes in creating linear lesions for atrial fibrillation ablation

Purpose In pulmonary veins (PVs) isolation (PVI), radiofrequency (RF) energy is often used to create a linear lesion for blocking the accessory conduction pathways around PVs. By using transient finite element analysis, this study compared the effectiveness of phase-shift mode (PsM) ablation with bipolar mode (BiM) and unipolar mode (UiM) in creating a continuous lesion and lesion depth in a 5-mm thick atrial wall. Materials and methods Computer models were developed to study the temperature distributions and lesion dimensions in atrial walls created through PsM, BiM, and UiM. Four phase-shift angles – 45°, 90°, 135°, and 180° – were considered in PsM ablation (hereafter, PsM-45°, PsM-90°, PsM-135°, and PsM-180°, respectively). Results At 60 s/30 V peak value of RF voltage, UiM and PsM-45° did not create an effective lesion, whereas BiM created a lesion of maximum depth and width approximately 1.01 and 1.62 mm, respectively. PsM-135° and PsM-180° not only created transmural lesions in 5-mm thick atrial walls but also created continuous lesions between electrodes spaced 4 mm apart; similarly, PsM-90° created a continuous lesion with a maximum depth and width of nearly 4.09 and 6.12 mm. Conclusions Compared with UiM and BiM, PsM-90°, PsM-135° and PsM-180° created continuous and larger lesions in a single ablation procedure and at 60 s/30 V peak value of RF voltage. Therefore, the proposed PsM ablation method is suitable for PVI and linear isolation at the left atrial roof for treating atrial fibrillation.

Structural modification of a blu-ray type archiving system for high-speed transportation

Optical archive systems are subjected to many different types of vibration, primarily excited in the transport of Blu-ray discs. Archive systems comprise several components, so identifying the dynamic characteristics is complicated. In this paper, transient finite element analysis verified with experimental data, was carried out to improve the performance of anti-vibration systems. Based on the numerical model, system parameters were modified using a design of experiments method that considered the transport velocity and time. The performance of the archival system and velocity profile improved by 24.43 % with similar vibration levels.

Structure improvement and strength finite element analysis of VHP welded rotor of 700°C USC steam turbine

The optimized structure strength design and finite element analysis method for very high pressure (VHP) rotors of the 700°C ultra-super-critical (USC) steam turbine are presented. The main parameters of steam and the steam thermal parameters of blade stages of VHP welded rotors as well as the start and shutdown curves of the steam turbine are determined. The structure design feature, the mechanical models and the typical position of stress analysis of the VHP welded rotors are introduced. The steady and transient finite element analysis are implemented for steady condition, start and shutdown process, including steady rated condition, 110% rated speed, 120% rated speed, cold start, warm start, hot start, very hot start, sliding-pressure shutdown, normal shutdown and emergency shutdown, to obtain the temperature and stress distribution as well as the stress ratio of the welded rotor. The strength design criteria and strength analysis results of the welded rotor are given. The results show that the strength design of improved structure of the VHP welded rotor of the 700°C USC steam turbine is safe at the steady condition and during the transient start or shutdown process.

Characterization of elastic-plastic-creep crack-tip stress fields under load and displacement control

This paper characterizes the elastic-plastic-creep crack-tip stress fields under load and displacement control. The stress field has been calculated from finite element (FE) transient creep analysis under each load control condition and displacement control condition. Varying the magnitude of initial step load is considered to investigate the influence of plasticity to creep. Both same stress exponent and different stress exponent in power-law creep and plasticity were considered. In the displacement control condition, elastic-follow-up factor is estimated by comparing FE results with existing formula. This paper proposes an equation to predict crack-tip stress fields under transient creep using a modification of the existing formula and verifies the proposed equation by comparing with FE results.

Transient Dynamic Finite Element Analysis of the Air-defence Weapon System Mount Assembly of Tracked Vehicle

A detailed finite element model of the existing Air-Defence Weapon System (ADWS) mount assembly of a military tracked vehicle, has been developed in Abaqus/CAE and modal dynamic analyses have been carried out. A mathematical vibration model of the gun recoil system has been developed in Matlab, in order to estimate the transmitted force variation during gun firing as well as the gun recoil. The frequency spectrum of transmitted force variation, has been analysed in correlation with extracted eigen values of the mount assembly, followed by dynamic analysis during rapid firing of 5 rounds. Based on modal dynamic analysis, required design modifications have been carried out by stiffening the mount structure at appropriate locations, and firing accuracies were obtained within acceptable limits. This study would be a useful approach to design of any gun mount assembly.

Optimum Design of a Moving Coil Actuator for Fast-Switching Valves in Digital Hydraulic Pumps and Motors

Fast-switching seat valves suitable for digital hydraulic pumps and motors utilize direct electromagnetic actuators, which must exhibit superior transient performance to allow efficient operation of the fluid power pump/motor. A moving coil actuator resulting in a minimum valve switching time is designed for such valves using transient finite-element analysis of the electromagnetic circuit. The valve dynamics are coupled to the fluid restrictive forces, which significantly influence the effective actuator force. Fluid forces are modeled based on transient computational fluid dynamics models. The electromagnetic finite-element model is verified against experimental measurement, and used to design an optimum moving coil actuator for the application considering different voltage–current ratios of the power supply. Results show that the optimum design depends on the supply voltage–current ratio, however, the minimum switching time obtained is nearly independent on this voltage–current ratio. Selecting a suitable power supply based on thermal considerations yields a switching time just above one millisecond for a travel length of 3.5 mm while submerged in oil. The proposed valve has a pressure drop below 0.5 bar at 600 L/min flow rate, enabling efficient operation of digital hydraulic pumps and motors.