Full Three-dimensional Finite Element Research Articles

Thin Film Encapsulation for RF MEMS in 5G and Modern Telecommunication Systems

In this work, SiNx/a-Si/SiNx caps on conductive coplanar waveguides (CPWs) are proposed for thin film encapsulation of radio-frequency microelectromechanical systems (RF MEMS), in view of the application of these devices in fifth generation (5G) and modern telecommunication systems. Simplification and cost reduction of the fabrication process were obtained, using two etching processes in the same barrel chamber to create a matrix of holes through the capping layer and to remove the sacrificial layer under the cap. Encapsulating layers with etch holes of different size and density were fabricated to evaluate the removal of the sacrificial layer as a function of the percentage of the cap perforated area. Barrel etching process parameters also varied. Finally, a full three-dimensional finite element method-based simulation model was developed to predict the impact of fabricated thin film encapsulating caps on RF performance of CPWs.

Seismic Behaviour of RC Building with Raft Foundation in the Ganges Basin, India

Many highly populated and important cities of India are situated in the Ganges basin. Deep alluvium deposit of this basin enhances the earthquake vulnerability of these cities due to amplification of seismic energies in the case of an earthquake. Raft foundations are generally provided for critical facility buildings due to their perceived effectiveness against differential settlement during earthquakes. However, the literature available on seismic behaviour of buildings with raft foundation considering soil deformability is relatively limited. In this context, a full three-dimensional finite element model of a four-storeyed building with raft foundation considering the typical layered soil profile of the Ganges basin has been developed in this study. The effects of different seismic parameters on the structural responses and moments induced in the raft have been studied with ground motions from 10 different earthquakes. Since the alluvium deposit of the Ganges basin is prone to get liquefied, effects of liquefaction of soil on the building with raft foundation have been considered simplistically. The results show that the raft foundation reduces the lateral displacement of the structure considerably. However, an increase in the vertical settlement of the raft in case of liquefiable soil is a matter of concern.

Thermoelastic effect on inter-laminar embedded delamination characteristics in Spar Wingskin Joints made with laminated FRP composites

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

The modulation of groundwater exploitation on crustal stress in the North China Plain, and its implications on seismicity

In the North China Plain (henceforth, “NCP”), continuous over-exploitation of groundwater resources forms widespread groundwater depression cones. The removal of massive groundwater unloads the local lithosphere and therefore significantly perturbs regional crustal deformation and stress evolution patterns. Unfortunately, its ramifications to seismicity are yet poorly understood. In this work, we adopt a full three-dimensional (3D) viscoelastic finite element model to estimate the crustal deformation and stress changes triggered by groundwater unloading, and analyze its effect on major active faults by calculating the induced Coulomb stress changes. Meanwhile, variations on regional seismicity in association with the successive groundwater removal over the past 60 years in NCP is examined under scrutiny. The stunning results emphasize apparent crustal uplift occurs in most of the groundwater depression zones, reaching up 4.0 cm, and vertical normal stress increases by up to 70 kPa at the depth of 10 km, concentrating in the deepest groundwater depression cone. Overall, Coulomb stress significantly increases by above 10 kPa on major active faulting zones. Compared with the tectonic stress loading rate of 0.5 kPa/yr, the stress perturbation by groundwater removal is definitely non-negligible, which may eventually introduce an extra incentive to expedite the failure of active faults and even trigger earthquake events in NCP.

A study of interlaminar properties for a unidirectional glass fiber reinforced epoxy composite

In this work, a numerical–experimental study of the interlaminar zone for an unidirectional glass fiber reinforced epoxy composite is carried out in order to predict the load–displacement curves of a double cantilever beam test. First, an experimental mechanical characterization of the laminated composite was made through quasi-static in-plane tensile and bending tests and out-of-plane delamination tests (i.e. double cantilever beam tests or opening mode I). The main results have shown that the elastic module in the fiber direction is E1 = 32.1 GPa and the fracture process is characterized by a critical energy release rate G IC = 1466 N/m. In order to be able to predict delamination using finite element analysis, a bilinear cohesive zone model is adopted. This law has two parameters—the initial stiffness [Formula: see text] and the critical traction [Formula: see text]—to be fit for reducing the distance between numerical and experimental double cantilever beam load–displacement curves. That means an optimization problem, which is here solved by proposing a very simple and cheap three-step procedure, avoiding expensive three-dimensional simulations: (i) the numerical double cantilever beam test is coded in the OCTAVE software using one-dimensional beam elements and the bilinear cohesive zone model; (ii) several one-dimensional simulations are performed varying at the cohesive law's parameters in order to build the objective function; and (iii) a genetic algorithm from the Scilab optimization toolbox is then used to determine the interface's parameters minimizing the objective function. This method has proposed [Formula: see text] = 2.74 × 1014 N/m3 and [Formula: see text] = 1.99 MPa as the best parameters fitting the curves. Finally, the identified bilinear cohesive law's parameters are used to carry out a full three-dimensional finite element analysis simulation in ANSYS, showing the same response than the simplified beam code, but with the possibility to obtain more accurate information about the fracture process (e.g. the shape of the process zone) or to use more complicated geometries or boundary conditions. In this work, we show the ability to predict the material behavior through different methods, using the best characteristics of each one.

Modeling Analysis of Guided Ultrasonic Waves in Composite Plates with Impact Damage

This paper investigates the propagation of guided ultrasonic waves and the interaction with impact damage in composite plates using a full three-dimensional Finite Element analysis. Impact damage in the composite plate was modeled as rectangular- and T-shaped delaminations. In order to provide guidelines for extending the modeling of realistic multimode impact damage, the impact damage was modeled as a combination of the delamination and reduced materials properties. The information obtained from these methods was compared to the experimental results around the damage area for a validation. There was a reasonable similarity between the experimental and FE results. The FE simulations can effectively model the scattering characteristics of the A0 mode wave propagation in anisotropic composite plates. This suggests that the simplified and easy-to-implement FE model could be used to represent the complex impact damage in composite plates. This could be useful for the improvement of the FE modeling and performance of guided wave methods for the in-situ NDE of large composite structures.

Nonlinear Seismic Response of a Hydraulic Tunnel Considering Fluid-Solid Coupling

The seismic response of hydraulic tunnels is a complex nonlinear process. What makes the case even more interesting is that the large amount of water in hydraulic tunnels which is likely to induce considerable hydrodynamic pressure acted on tunnel structures during earthquakes. In this work, a full three-dimensional (3D) dynamic finite element model is adopted to conduct a comprehensive assessment of the seismic behaviors of a hydraulic tunnel system. In this analysis, the plastic-damage model is employed to reflect the nonlinear mechanical behaviors of the concrete lining, and a fluid-solid coupling method based on an explicit weighted residual approach is proposed to consider the effects of the hydrodynamic pressures on the seismic response of the hydraulic tunnel. The numerical results indicate that the hydrodynamic pressure contributes to a greater seismic response of the tunnel structure. When the hydrodynamic pressure is considered, the magnitudes of the maximum principal stresses are likely to increase by 50% and the displacement amplitudes are approximately 2 cm more than that of without hydrodynamic pressure. The hydrodynamic pressure exacerbates the damage degree of the tunnel structure, and the waist suffers the most severe damage.

A rolling resistance estimate using nonlinear finite element numerical analysis of a full three-dimensional tyre model

In accordance with the worldwide trend for developing energy-efficient vehicles and meeting environmental regulations, there exists a large potential for decreasing energy losses due to tyre rolling resistance and significantly reduce fuel consumption and greenhouse gas emissions and also improve tyre tread durability. To achieve a quantitative estimate of tyre rolling resistance force, in the present paper, we carry out rolling resistance modelling in order to introduce a comprehensive relation for predicting rolling resistance force variations with speed taking into account the most influential parameters. To accomplish this goal, full three-dimensional finite element modelling of a visco-hyperelastic inflated rubber tyre under the deformation of vertical loading is performed and validated by making use of available test data. Free rolling simulations are performed and rolling resistance diagrams at various vehicle speeds and inflation pressures are extracted by analysing the results. According to the simulation results, a general formula is suggested to predict the tyre rolling resistance force in terms of the influential factors such as velocity, inflation pressure and tyre load. Results obtained using the proposed equation compared with recorded coast down test data clearly indicate excellent agreement between the results, confirming the validity of the relation. The presented solution can be built into models for comprehensive techno-economic evaluation of vehicle performance and fuel economy where changes in velocity, load and inflation pressure can be considered.

Seismic damage assessment and mechanism analysis of underground powerhouse of the Yingxiuwan Hydropower Station under the Wenchuan earthquake

The Yingxiuwan underground powerhouse is one of the closest large-scale underground structures from the epicenter of the Wenchuan earthquake and suffered significant damage during this earthquake. What makes this case even more interesting is that the seismic damage is mainly distributed in the upper part of the concrete structure in the underground powerhouse. A full three-dimensional dynamic finite element model of the underground structure and rock system is adopted to make a reasonable assessment for the seismic damage observed in the field and to study the damage characteristics and mechanisms of the underground powerhouse. Additionally, to approximate actual field conditions, the oblique incidence of seismic waves and the rock-structure interaction (RSI) are both considered in this study, and their effects on the seismic response are evaluated. The numerical results indicate that the oblique incidence of the seismic wave and the RSI both contribute to a larger seismic response, and the results compare well with the field observations when the two are considered. The damage distribution of the concrete structure is mainly dominated by the structure feature itself. The main cause of the severe damage in the upper structure is due to the lack of sufficient constraints on it, which leads to a large deformation in the upper structure.

Rotation-Frequency-Driven Extension–Torsion Coupled Self-Twisting Rotor Blades

This paper describes the effects of a composite coupled blade spar on the performance of a slowed-rotation-frequency helicopter rotor in high-speed edgewise flight. Antisymmetric composite coupling in the spar of a UH-60A-like rotor can provide a significant efficiency increase when rotation frequency is reduced. Comprehensive analysis was performed using a full three-dimensional finite element analysis-based aeroelastic computational structural dynamics solver with the inclusion of a free-wake aerodynamics model. This was validated using existing UH-60A test data for high advance ratios. The current study shows that a composite blade can achieve a maximum increase in the lift-to-drag ratio of 1.3 (20% improvement) at 85% of the nominal rotation frequency (NR) of . This efficiency gain is achieved through a combination of delayed stall drag along the retreating side of the rotor and reduced negative lift along the advancing side. A further reduction to 65NR showed a maximum efficiency improvement of 15% and was attributed only to the alleviation of negative lift. A hygrothermally stable layup was shown to perform as well as a nominal coupled layup at 85NR and marginally better at 65NR. Close study of the strains in the rotor showed that these rotors would be within the realm of practical manufacturability as axial strains fell within IM7/8552’s allowable tensile strain of 6000 microstrain.

Wide area condition monitoring of power electric drives in wind power generation system using radiated electromagnetic fields

Electric components in numerous applications (particularly wind generation) are not straightforwardly accessible for monitoring. Therefore, the monitoring and protection through voltage/current measurement may not be dependable since the current value passes numerous segments to reach the observing element. Accordingly, finding an unusual phenomenon of a specific element is difficult. To resolve this issue, using transmitted electromagnetic field of an element for wide area condition monitoring is proposed. It is planned to diagnose and locate short-circuit in induction generator drive such as interturn, intercoil and terminal-to-turn failures. The frequency characteristics of the propagated field is then utilized for finding the short-circuit. The theoretical foundation that relate the behavior of each elements to their frequency response is analyzed and used. To utilize the derived technique for different practical circumstances, two distinctive methods are used for locating the short-circuit. As the experimental test of major fault cases could destruct the winding, the full three-dimensional finite element analysis is used in these cases and some are verified experimentally through the wide area communication. Identifying the areas of partial faults Prevents the whole winding failure prior to a massive destruction, which is costly especially for cases in inaccessible situations such as offshore wind towers.

Soil arching in highway piled embankments subjected to moving shakedown limit loads

Shakedown analysis provides the loading variation limit of a structure, under which the plastic deformation occurred in first loading cycles will cease to further develop and the structure will respond purely elastically to the remaining load cycles. This paper investigated the arching in highway piled embankments under moving shakedown limit loads, which was calculated by the shakedown solutions. The shakedown solutions for materials obeying Mohr–Coulomb criterion was firstly presented based on Melan’s shakedown theorem, which utilised elastic stress fields obtained from the full three-dimensional (3D) finite element (FE) method. Finally, the shakedown limit load for pure rolling condition (i.e. only normal load) was applied onto the surface of pavement as a moving vehicle load. The FE results under moving shakedown limit loads captured similar trend with those under the static loads in terms of settlement and vertical stress, but gave the normalised settlement and vertical stress 33 and 24% larger. The soil arching remained existed in the highway piled embankments under moving shakedown limit loads, but was reduced. The inclusion of moving shakedown limit loads increased the vertical stress of the embankment and thus resulted in a reduction of the maximum value of lateral earth pressure coefficient by approximately 38%.

General shell section properties and failure model for cross-laminated timber obtained by numerical homogenization

In this study homogenized mechanical properties are derived for structural finite element analysis of cross-laminated timber (CLT) discretized by means of shell elements. In the first step, based on the results of experimental three-point bending tests on a CLT slab component, a numerical optimization procedure is applied to identify the elastic and plastic properties of the individual spruce wood laminates, considering orthotropic elasticity and Hill’s yield criterion. Taking into account its periodic structure, a repeating unit cell (RUC) of the CLT is defined in the subsequent step. To this RUC specific loading conditions are imposed successively, yielding the entries of the homogenized elastic stiffness matrix of a general shell section. Extending the RUC simulations into the inelastic domain of deformation results in a homogenized failure surface on the structural scale, which is implemented as a postprocessing variable in a commercial finite element program. Throughout all analyses, in sensitivity studies the most decisive material properties are identified. Results of comparative simulations on a homogenized structural model and an elaborate full three-dimensional finite element model of a point-supported CLT slab show the accuracy and efficiency of the proposed approach based on homogenized mechanical properties.

A lightweight optimal design model for bolted flange joints without gaskets considering its sealing performance

The lightweight optimal design of bolted flange joint system without gaskets is still a challenging problem, mainly owing to two issues: the relatively large number of mutually dependent geometric design parameters and the complicated role played by the contact details between members. With these two issues properly addressed, this article aims for devising a concise formulation for lightweight optimal design of bolted joint systems without gaskets. After a systematic examination of the correlations between design parameters, the total number of free design variables is reduced to three: member thickness, bolt spacing, and bolt specification, respectively. Besides, a finite element analysis that can resolve more contact details between members is conducted, and the influencing factors on the pressure distribution at the member surface are thus identified, with a criterion for the system sealing failure incorporated. Based on the findings in this work, a novel design scheme for the joint system is proposed, and good agreement between our predictions and results obtained by a full three-dimensional finite element analysis is shown. The proposed approach can be used to optimize the design parameters of bolted joint systems considering sealing performance without heavy finite element computation and can find applications in many relevant engineering fields.

A Three Dimensional Comparative Study of Seismic Behaviour of Vertical and Batter Pile Groups

To a practicing foundation engineer, the performance of batter pile under seismic conditions still remains a questionable prospect. The contradictory findings reported by various investigators with regard to the performance of batter piles add to this dilemma. This calls for a rigorous three-dimensional investigation to evaluate seismic behavior of batter pile groups. In this study, a comparative assessment of three-dimensional seismic behavior of a 2 × 2 vertical and batter pile groups having batter angle of 15° was carried out using a full three-dimensional finite element code developed in MATLAB (Sarkar 2009). The effects of centre to centre spacing of piles and soil modulus values were investigated. Idealized soil profiles having constant and triangular variation of soil modulus were adopted for the study. Results of analyses for both the vertical and batter pile groups are presented in terms of dynamic stiffness and kinematic interaction factors. Results indicate better seismic performance of batter pile groups in comparison to that of vertical pile groups. To demonstrate the importance of the findings, a five-storied portal frame structure supported separately on vertical and batter pile groups were considered and analyzed for El-Centro Earthquake (1940) time history. The difference in structural response considering vertical and batter pile groups is highlighted.

A Finite Element Model for Prediction of the Bending Stress of Umbilicals

Umbilical is an important equipment in the subsea production to supply a connection between the floater and the subsea well. Analyzing strength and fatigue behaviors under bending is a key requirement to assure safety. An analytical model is proposed for predicting the bending behavior of a steel tube wounded helically around a frictionless cylinder. A full three-dimensional (3D) finite element (FE) model of an umbilical is developed by considering the frictions and contacts among its components. The numerical results of the bending stress of a steel tube were validated against that of the analytical model. The impacts of friction coefficients on the bending stress, contact pressure, and friction stress have been further investigated by the established FE model.

Evaporating pure, binary and ternary droplets: thermal effects and axial symmetry breaking

The Greek aperitif Ouzo is not only famous for its specific anise-flavoured taste, but also for its ability to turn from a transparent miscible liquid to a milky-white coloured emulsion when water is added. Recently, it has been shown that this so-called Ouzo effect, i.e. the spontaneous emulsification of oil microdroplets, can also be triggered by the preferential evaporation of ethanol in an evaporating sessile Ouzo drop, leading to an amazingly rich drying process with multiple phase transitions (Tan et al., Proc. Natl Acad. Sci. USA, vol. 113 (31), 2016, pp. 8642–8647). Due to the enhanced evaporation near the contact line, the nucleation of oil droplets starts at the rim which results in an oil ring encircling the drop. Furthermore, the oil droplets are advected through the Ouzo drop by a fast solutal Marangoni flow. In this article, we investigate the evaporation of mixture droplets in more detail, by successively increasing the mixture complexity from pure water over a binary water–ethanol mixture to the ternary Ouzo mixture (water, ethanol and anise oil). In particular, axisymmetric and full three-dimensional finite element method simulations have been performed on these droplets to discuss thermal effects and the complicated flow in the droplet driven by an interplay of preferential evaporation, evaporative cooling and solutal and thermal Marangoni flow. By using image analysis techniques and micro-particle-image-velocimetry measurements, we are able to compare the numerically predicted volume evolutions and velocity fields with experimental data. The Ouzo droplet is furthermore investigated by confocal microscopy. It is shown that the oil ring predominantly emerges due to coalescence.

In-plane and out-of-plane vibration modes of laminated composite beams with arbitrary lay-ups

This paper mainly presents the in-plane and out-of-plane vibration analysis of thin-to-moderately thick composite beams with arbitrary lay-ups using the first order shear deformation theory. The material couplings, i.e. bending–stretching, bending–twisting and stretching–twisting couplings, along with the effects of shear deformation, rotary inertia and Poisson's effect are taken into account. In order to obtain the free response of the structure, a semi-analytical solution is adopted based on the variational formulation and solving the weak form of the governing equations by extremizing the objective functional with respect to unknown displacement components and Lagrange multipliers. We also propose a higher order beam element which is a convenient tool for numerical implementation in one-dimensional finite element analysis of the problem. Semi-analytical and finite element solutions are utilized and verified for various numerical case studies. Numerical examples are presented for both the semi-analytical and finite element solutions. The results show excellent agreement with the solutions obtained by the full three-dimensional finite element model in commercial package ANSYS. These numerical examples also demonstrate that ignoring the role of out-of-plane displacement in the conventional one-dimensional models can lead to significant error in calculating the torsional modes of laminated composite beams.

Numerical and Experimental Analysis of Umbilical Cables under Tension

Umbilical cables are composite structures that consisting of metallic material and polymeric material. Analysing tension behaviour under axial loading is a key requirement to design the structure. A full three-dimensional finite element model is established in which the effect of radial deformation is given more attention. A plane finite element analysis is proposed to predict the radial stiffness of the inner core with several components. The tension behaviour of an umbilical cable is analysed by the proposed models. Tension tests of the umbilical cable were carried out. Compared with the available theoretical models in the literature, the finite element model has a satisfactory agreement with the experimental results. In addition, the finite element model is used for the assessment of the influence of the important parameters on the tension behaviour, which is helpful for the design of umbilical cable.

A finite element method assessment of a Steel Tube Umbilical (STU) cable subjected to crushing load: Comparison between two and three-dimensional approaches

Umbilical cables are fundamental equipment used in deep and ultra-deep water oil and gas production systems. The complexity of such structures usually enforces the use of numerical tools. This paper presents and compares two different numerical approaches for prediction of stress and strain fields in the umbilical cable components under crushing loads, which are imposed to the umbilical during laying operation. The first approach, presented in a previous work [1], is based on a joint analysis using a two-dimensional finite element model fed by analytical models, which represent three-dimensional effects. The second approach, used here as a paradigm, is based on a full three-dimensional finite element model, in which the three-dimensional effects are intrinsically considered. An armoured Steel Tube Umbilical Cable is used as a case study in order to compare both methodologies. It is shown that, while being much faster, the two-dimensional approach yields consistent results when focus is directed onto the components of the central core, as steel tubes. Elastic-plastic behavior is adopted for the steel tubes in both models.