Dimensional Finite Element Method Research Articles

Effect of the Geometric Shapes of Elevated Tanks on their Dynamic Response

This study examines the impacts of geometric shapes of elevated tanks owing to the seismic loading action. Four typical tank shapes have been studied, namely: intze tank with a shaft, pure conical tank with a frame, combined conical tank, and cylindrical tank with a frame through a single degree of freedom, two degrees of freedom, and three dimensional finite element method, based on the full and empty condition using computer simulation program LUSAS FEA through added mass approach for accounting fluid-structure interaction. The results revealed that the intze shape is the most suitable shape to be analyzed based on mechanical approaches. While the impossibility of applying these approaches to conical tanks.

Transonic Flow Computation Over A Heat Shield Using Three Dimensional Finite Element Method

A three dimensional finite element method is employed for solution of the transonic full potential equation in mass conservation form. The finite element analysis allows the boundary conditions to be treated in simple and exact manner, without the use of a mapping scheme. The full potential equation is based on the assumption of irrotational flow and density of the fluid is calculated using isentropic relation and it is applicable for upstream local Mach number upto 1.6. The nonlinear full potential equation is reduced to a set of nonlinear algebraic equation using Galerkin’s formulation. An iterative scheme in conjunction with the artificial viscosity term is used to solve the set of algebraic equations. The artificial viscosity term stabilizes the numerical scheme and captures the shock very well. An appropriate grid arrangement is selected in the algorithm to maintain proper and continuous linkage between upstream and downstream of the flow at the centroid of the hexahedral element. The surface pressure distribution in the freestream Mach number range 0.80 - 0.95 and at an angle of incidence 5 degree shows a fairly good agreement with the experimental data. The present finite element discretization can be coupled with the commercially available software.

The geoelectric field coast effect: Results from two dimensional finite element method and analytic solutions

The geoelectric fields induced during geomagnetic disturbances (GMD) may affect the normal operation of technological systems at the Earth’s surface. The non-uniform Earth conductivity structure, especially large lateral conductivity contrasts, can lead to the enhancement of geoelectric fields near boundaries such as a coastline. In this paper, we give an overview of the applicability of a two-dimensional finite element method (2D-FEM) for studying lateral variations of the Earth’s conductivity, which can be considered as one of magnetotelluric sounding forward modelling methods, including both the E and the H polarization cases. Then the spatial distribution of the geoelectric field near a continent-ocean boundary is calculated with different models. This is compared with analytic solutions for simple models to verify the accuracy of the FEM modelling, which is calculated by using the ANSOFT software. More realistic scenarios are then developed to emphasize the advantages of FEM. The factors influencing the coast effect are discussed. Results show that frequency, the shape of seafloor boundaries, and the depth of ocean have a significant impact on the geoelectric fields. Therefore, these factors should attract more attention when assessing risk for man-made conducting systems located within the coastal influence range.

Numerical analysis of the ultra-wide tunability of nanofiber Bragg cavities.

Nanofiber Bragg cavities (NFBCs) are solid-state microcavities fabricated in optical tapered fiber. They can be tuned to a resonance wavelength of more than 20 nm by applying mechanical tension. This property is important for matching the resonance wavelength of an NFBC with the emission wavelength of single-photon emitters. However, the mechanism of the ultra-wide tunability and the limitation of the tuning range have not yet been clarified. It is important to comprehensively analyze both the deformation of the cavity structure in an NFBC and the change in the optical properties due to the deformation. Here, we present an analysis of the ultra-wide tunability of an NFBC and the limitation of the tuning range using three dimensional (3D) finite element method (FEM) and 3D finite-difference time-domain (FDTD) optical simulations. When we applied a tensile force of 200 μN to the NFBC, a stress of 5.18GPa was concentrated at the groove in the grating. The grating period was extended from 300 to 313.2nm, while the diameter slightly shrank from 300 to 297.1 nm in the direction of the grooves and from 300 to 298 nm in the direction orthogonal to the grooves. This deformation shifted the resonance peak by 21.5 nm. These simulations indicated that both the elongation of the grating period and the small shrinkage of the diameter contributed to the ultra-wide tunability of the NFBC. We also calculated the dependence of the stress at the groove, the resonance wavelength, and the quality Q factor while changing the total elongation of the NFBC. The dependence of the stress on the elongation was 1.68 × 10-2 GPa/μm. The dependence of the resonance wavelength was 0.07 nm/μm, which almost agrees with the experimental result. When the NFBC, assumed to have the total length of 32 mm, was stretched by 380 μm with the tensile force of 250 μN, the Q factor for the polarization mode parallel to the groove changed from 535 to 443, which corresponded to a change in Purcell factor from 5.3 to 4.9. This slight reduction seems acceptable for the application as single photon sources. Furthermore, assuming a rupture strain of the nanofiber of 10 GPa, it was estimated that the resonance peak could be shifted by up to about 42nm.

Numerical investigation of pullout capacity for inclined strip plate anchors in sand

Plate anchors have been widely regarded as one of the most efficiency solutions for offshore structures in deep sea. Most of previous studies focus on the vertical or horizontal plate anchors embedded in sand. However, after the caisson foundation is withdrawn, the vertical plate anchor rotates to a certain angle from the horizontal plane in the process of resisting tension, which makes the analysis of pullout capacity of inclined plate anchors in sand relatively complex. This study, by using two dimensional finite element (2D-FE) method, takes a deep insight on the behaviour of strip plate anchors with different inclinations in loose to dense sand. A modified soil model is adopted to explore the hardening and softening behaviour of medium dense and dense sand. The FE results show a good agreement with previous numerical results and centrifuge test data. A series of FE cases are conducted to explore the effect of embedment ratios, plate inclinations and sand relative densities on the pullout capacity of inclined strip plate anchors. A new equation is proposed to estimate the ultimate pullout capacity of strip plate anchors with different inclinations in different relative densities of sand, which serves as a guidance for engineering design of inclined strip plate anchors in sand.

Influence of soil–structure interaction on seismic demands of historic masonry structure of Kashan Grand Bazaar

Heritage structures are an important part of the history of each community as well as an economic resource. This study aims to investigate the earthquake damage and failure mechanism of a historic Bazaar located in Kashan (center of Iran), which dates back to the eighteenth century. Numerical models were built by a macro method, considering two cases of fixed support and soil–structure interaction (SSI). To assess the structural behavior, modal, nonlinear static, and dynamic time history analyses were performed using a three dimensional finite element method. The results of SSI analysis show an intense weakness of the structure against the required demand based on the design spectrum. Also, foundation flexibility has a great impact on the vibration characteristics, displacement demand, and damage distribution. By comparing the results of time history analysis to the pushover procedure, a lower shear value and higher displacement are obtained. Furthermore, the damage process is as dome collapse alongside short arch, consequently long arch collapse followed by pier wall overturning.

Mitigation of subway-induced low-frequency vibrations using a wave impeding block

The effective control of low-frequency vibrations induced by subway operation remains a problem, but wave impeding blocks (WIBs) have the potential to solve this issue. To investigate the vibration isolation behavior of WIB under subway loading, this study established a coupled track-tunnel-ground-WIB model using the two-and-a-half dimensional finite element method (2.5D FE). The effect of bedrock on wave propagation was first revealed by analyzing the eigenfrequencies of the soil layer with a tunnel. It was found that the bedrock reduced ground-borne vibrations with a frequency lower than the cut-off frequency of the soil layer. Based on this observation, the vibration isolation behavior of the WIB with different locations, embedding depths, material types, and dimension parameters was analyzed in detail. The WIB located beneath the tunnel invert (near-field active vibration isolation) exhibits a completely different behavior than that beneath the ground surface (far-field passive vibration isolation). The former can reduce ground vibrations in the entire ground surface, whereas the latter only works in a limited region directly above the WIB. The far-field vibration isolation effect is not sensitive to the vibration frequency and embedding depth, but the WIB dimension and rigidity have a significant impact. The near-field vibration isolation effect is most significantly influenced by the embedding depth, followed by the material property and dimension parameter. The WIB installed beneath the tunnel invert with a thinner embedding depth and stiffer rigidity more effectively isolates low-frequency vibrations induced by the subway.

Computational wear of knee implant polyethylene insert surface under continuous dynamic loading and posterior tibial slope variation based on cadaver experiments with comparative verification

BackgroundThe effect of posterior tibial slope on the maximum contact pressure and wear volume of polyethylene (PE) insert were not given special attention. The effects of flexion angle, Anterior-Posterior (AP) Translation, and Tibial slope on the max contact pressure and wear of PE insert of TKR were investigated under loadings which were obtained in cadaver experiments by using Archard’s wear law. This study uses not only loads obtained from cadaver experiments but also dynamic flexion starting from 0 to 90 degrees.MethodWear on knee implant PE insert was investigated using a 2.5 size 3 dimensional (3D) cruciate sacrificing total knee replacement model and Finite Element Method (FEM) under loadings and AP Translation data ranging from 0 to 90 flexion angles validated by cadaver experiments. Two types of analyses were done to measure the wear effect on knee implant PE insert. The first set of analyses included the flexion angles dynamically changing with the knee rotating from 0 to 90 angles according to the femur axis and the transient analyses for loadings changing with a certain angle and duration.ResultsIt is seen that the contact pressure on the PE insert decreases as the cycle increases for both Flexion and Flexion+AP Translation. It is clear that as the cycle increases, the wear obtained for both cases increases. The loadings acting on the PE insert cannot create sufficient pressure due to the AP Translation effect at low speeds and have an effect to reduce the wear, while the effect increases with the wear as the cycle increases, and the AP Translation now contributes to the wear at high speeds. It is seen that as the posterior tibial slope angle increases, the maximum contact pressure values slightly decrease for the same cycle.ConclusionsThis study indicated that AP Translation, which changes direction during flexion, had a significant effect on both contact pressure and wear. Unlike previous similar studies, it was seen that the amount of wear continues to increase as the cycle increases. This situation strengthens the argument that loading and AP Translation values that change with flexion shape the wear effects on PE Insert.

Thermomechanical design rules for photovoltaic modules

AbstractWe present a set of thermomechanical design rules to support and accelerate future (PV) module developments. The design rules are derived from a comprehensive parameter sensitivity study of different PV module layers and material properties by finite element method simulations. We develop a three dimensional finite element method (FEM) model, which models the PV module geometry in detail from busbar and ribbons up to the frame including the adhesive. The FEM simulation covers soldering, lamination, and mechanical load at various temperatures. The FEM model is validated by mechanical load tests on three 60‐cell PV modules. Here, for the first time, stress within a solar cell is measured directly using stress sensors integrated in solar cells (SenSoCells®). The results show good accordance with the simulations. The parameter sensitivity study reveals that there are two critical interactions within a PV module: (1) between ribbon and solar cell and (2) between front/back cover and interconnected solar cells. Here, the encapsulant plays a crucial role in how the single layers interact with each other. Therefore, its mechanical properties are essential, and four design rules are derived regarding the encapsulant. Also four design rules concern front and back sides, and three address the solar cells. Finally, two design rules each deal with module size and frame, respectively. Altogether we derive a set of 15 thermomechanical design rules. As a rule of thumb of how well a bill of material will work from a thermomechanical point of view, we introduce the concept of specific thermal expansion stiffness as the product of Young's modulus , coefficient of thermal expansion , joint area , and materials height . The difference between two materials is a measure of how much thermal strain one material can induce in another. A strong difference means that the material with the larger value will induce thermal strain in the other.

Field analyses of thickness shear bulk acoustic resonators with different electrode edge ratio using full three dimensional finite element method simulation

This paper is aimed at revealing origins of spurious resonances and Q deterioration of thickness shear bulk acoustic resonators (TSBARs) with the edge ratio W x /W y of rectangular electrodes by a field analyses. Here, W x and W y are distances between side edges giving the broadband and standard piston designs, respectively. The field distribution is calculated by applying traceback technique to the full three dimensional finite element method based on hierarchical cascading technique, its variation with the edge ratio is studied in detail, with assistance of the wavenumber domain analysis. The result indicates that the mode conversion and the leakage occur at the bump region causing Q reduction, and generated hybrid modes causing spurious resonances. The former is significant when W x /W y is large and the latter becomes obvious when W x /W y is small.

Analysis of sliding behavior of coated surfaces under shear traction

The tribological behavior of non conformal coated contacting surface i.e. rigid sphere on the coated flat material surface normal force and shear traction is studied through numerical results. The non-conforming contact is a fundamental problem in the contact mechanics, which has a wide range of applications. Contact is the science behind tribology, the interdisciplinary study of friction, wear and lubrication with major applications in particle handling or friction between contacting rough surfaces, brakes, Bearings and so on. In the present investigation, the contact between the coated flat and the rigid sphere under the combination of normal and tangential loading is analyzed using finite element software ABAQUS. The substrate material is chosen for the analysis High speed steel, Titanium alloy and coating material is TiN (E=305GPa) of 5µm thick with a bonding material is Chromium (379GPa) of 1µm thick at the interface between the coating and substrate is modeled by three dimensional finite element method (3DFEM) in order to optimize coating coated surface and bonding layer to coating fracture. The elastic-perfectly plastic contact is assumed on the flat model. The results obtained from the FEA are used in the understanding of the tribological behavior of the contact pair.

Investigation of saturation effects on vibrations of nearly saturated ground due to moving train loads using 2.5D FEM

An improved two-and-a-half dimensional finite element method (2.5D FEM) model is developed to predict ground-borne vibrations in coastal areas from passing high-speed trains (HSTs). The model treats the ground as nearly saturated layered half-space, and describes the pore water/air mixed fluid by the equivalent fluid approach. Reliability of the proposed model is verified by comparing with the field measurements for X-2000 train and published analytical solutions. On this basis, the ground vibrations and excess pore water pressure under different train speeds and on various soil cases are analyzed in detail. In particular, three kinds of water saturation are discussed to show the sensitivity of vibration responses to the minor change of saturation. Results show that the saturation would cause pronounced influence on vibration displacements and excess pore pressure, and a minor decrease in water saturation would lead to a much higher vibration displacement level and a big difference of excess pore pressure distribution along depth. The influence of saturation is dependent both on soil configurations and on train speeds. It is highlighted that the vibration level on coastal ground would be underestimated by using fully saturated model instead of the nearly saturated model.

Designing plasmonic metasurface absorbers with desirable absorption values for different thermal applications

In this paper, we demonstrate and explore an approach to designing absorbers based on using plasmonic metasurfaces in the visible spectrum. The approach opens up the possibility of rapidly choosing an absorber with the desired absorption value using an analytical expression. By using the three dimensional finite element method, we present a wide comparison between varieties of plasmonic absorbers based on using different nanoantennas in the proposed metasurface designs. The utilized plasmonic nanoantennas are such as the titanium nitride (TiN), Aluminum (Al), Gold (Au), and Silver (Ag) nanoantennas. The comparison between using these plasmonic nanoantennas will be according to the resulted absorption from the proposed designs. The plasmonic metasurfaces using the TiN nanoantennas demonstrates a high absorption compared to the obtained absorption from the other metasurface designs using (Al), (Au), and (Ag) nanoantennas. Accordingly, based on these results, we used a regression analysis to fit our simulated data to an analytical expression in order to generalize the concept of generation the absorbers of interest with the desired absorption based on the proposed metasurfaces. This promising technique provides a methodology to design preoptimized absorbers for practical applications such as sensing, thermal management, and solar cells.

Impact of Air-Hole on the Optical Performances of Epitaxially Regrown P-Side Up Photonic Crystal Surface-Emitting Lasers

Optical performances of 950 nm p-side up photonic crystal surface emitting lasers (PCSELs) with different types of air holes are numerically and experimentally investigated. Simulation results show an obvious distinction between effective index method and three dimensional finite-element method (FEM). Measured experiments including wavelength, threshold, and slope efficiency can well meet the FEM numerical predictions. It further reveals that the B mode dominates the laser action and the PCSELs accompanying with equilateral triangle and right isosceles triangle holes possess a lower threshold current and higher radiation than symmetric circle holes. The output power can be further enhanced by increasing the filling factor of air holes before the regrowth process.

Analytical calculation of leakage permeance of coreless axial flux permanent magnet generator

PurposeThis paper aims to study the relationship between leakage flux coefficient and the coreless axial magnetic field permanent magnet synchronous generator (AFPMSG) size and obtain the expressions of leakage flux coefficient.Design/methodology/approachIn this paper, a magnetic circuit model of coreless AFPMSG is proposed. Four kinds of leakage permeances of permanent magnet (PM) are considered, and the expression of no-load leakage flux coefficient is obtained. Solving the integral region of leakage permeances by generator size, which improves the accuracy of the solution.FindingsFinite element method and magnetic circuit method are used to obtain the no-load leakage flux coefficient and its variation trend charts with the change of pole arc coefficient, air gap length and PM thickness. The average errors of the two methods are 2.835%, 0.84% and 1.347%, respectively. At the same time, the results of single-phase electromotive force obtained by magnetic circuit method, three dimensional finite element method and prototype experiments are 19.36 V, 18.82 V and 19.09 V, respectively. The results show that the magnetic circuit method is correct in calculating the no-load leakage flux coefficient.Originality/valueThe special structure of the coreless AFPMSG is considered in the presented equivalent magnetic circuit and equations, and the equations in this paper can be applied for leakage flux evaluating purposes and initial parameter selection of the coreless AFPMSG.

THE OPERATIONAL MODE OF OPTICAL MICROSCOPE APPLYING PHOTONIC JET MICROSCOPY

The previous experimental research on microsphere parameters applying photonic jet microscopy in free space revealed if the relative indexes come near to two, it needs larger microspheres. It also means if the relative indexes come near to one, it needs smaller microsphere. In addition to these premises, the mode of ordinary optical microscope introducing photonic jet microscopy in its operation must be taken into account. That includes the light source or filter, and the fluidic environment - free space or immersion oil. These additional modes are predicted in two dimensional finite element method calculation. Which leads to more practical use of photonic jet microscopy in the near future.

Research on the similarity of vibration characteristics of naval gun bracket based on similarity theory

The similar scale model experiment can provide some reference for the research and development of naval gun weapons. This paper takes the naval gun bracket as an example to explain. Based on the dimensional analysis, equation analysis and finite element method, the modal parameter similarity relationship between the original model for bracket and the shrinkage ratio model is established. The results show that the error of predicting the natural frequency of the original model based on similarity relation is less than 2% comparing with the results of finite element numerical simulation, and the error is less than 10% comparing with the experimental results, and the mode of shrinkage model is close to that of the original model. It is proved that the theoretical method in this paper is feasible and practical in engineering. Therefore, the vibration characteristics of the original model can be estimated by analyzing the vibration characteristics of the carrier shrinkage ratio model, which provides a reference for ship gun designers.

Numerical prediction of the ductile damage for axial cracks in pipe under internal pressure

This study presents a numerical prediction of the ductile damage for axial cracks in pipe subjected to internal pressure. The three dimensional finite element methods used to evaluate the J-integral. The effect of the external radius (Rext),the thickness (t), length crack (a) , the applied loads (P) and the crack position of the pipes has studied. The Monte Carlo method was used to determine the probabilistic characteristics of the J-integral. It’s also used later to predict the failure probability based on initiation of the crack growth. We note that the crack size and the geometries of the pipe are an important factor influencing on the durability of the pipe.

Secondary Eddy Current Losses Reduction in a Double-Sided Long-Primary Fractional Slot Concentrated Winding Permanent Magnet Linear Synchronous Motor

A novel design method for the primary structure of a double-sided long-primary fractional-slot concentrated winding permanent magnet linear synchronous motor (DSLP-FSCW-PMLSM) is proposed in this article. Different from the traditional symmetric primary structure, the primary structure obtained by the proposed design method has two asymmetric primary cores and two asymmetric primary windings. This unique structure can reduce the variation of the flux density caused by the primary core slotting, and can effectively reduce the slot harmonic contents of the armature reaction magnetic field; thus, it can significantly reduce secondary eddy current losses. First, the basic structure is introduced. The air-gap magnetic field of permanent magnet and armature reaction are analyzed in detail. Second, the performance of the proposed motor is analyzed by means of three dimensional finite element method and compared with the traditional motor. The focus is on secondary materials, secondary eddy current losses, thrust, pole arc coefficient, magnet skew angle, and efficiency. Last, experiments are conducted on two prototypes of DSLP-FSCW-PMLSM. The validity of the proposed topology is verified by the test results of static thrust, back electromotive force, and armature reaction air-gap magnetic field.

Numerical simulation of critical particle size in asymmetrical deterministic lateral displacement

Microfluidics devices are widely used for particle separation. Deterministic Lateral Displacement (DLD) is a passive method for particle separation. DLD devices mainly separate particles based on their sizes. There are two main modes of movement in DLD arrays; the small particles move in a zigzag path, and the larger particles separate in the displacement mode. It is therefore important to estimate the critical particle size for the transition of modes before the fabrication of DLD devices. Asymmetry in the design of the arrays can affect the fluid behavior and the critical particle size. In this study, we investigate the effects of the asymmetry caused by changing the downstream gap size to the lateral gap size ratio on the fluid behavior and particle trajectories in DLD devices. We used two dimensional (2D) Finite Element Method (FEM) to study the variations in the flow lane's widths and combined the fluid analysis with structural mechanics to model the contact between the particles and the posts in DLD arrays. We simulated the spherical particles' trajectories with diameters ranging from 1.4 to 19.2 μm in circular post DLD arrays with a lateral gap size of 20μm. In contrast to the previous works, in these simulations, the effect of particle movement on the fluid flow profiles was considered. We evaluated the particle movement mode in seven different values of the downstream gap size to the lateral gap size ratio (ranging from 0.5 to 2) and eight different row shift fraction (ranging from 0.025 to 0.3). Our simulations showed that increasing the value of the downstream gap while the lateral gap is fixed increases the veering flow rate and width. By finding the particle with the largest diameter in the zigzag mode and the particle with the smallest diameter in the displacement mode, we estimated the critical particle diameter for each value of shift fraction in different values of the downstream gap to the lateral gap size ratio. Using these data, a curve was fitted for predicting the critical particle diameter in each ratio. Finally, a more general form of the formula for the critical particle diameter was proposed, which considers an extra parameter compared to the previous ones. The results of this study can lead to a better understanding of DLD devices' functions and, thus, save time and costs for better designs and experiments.