Nonlinear Static Finite Element Analysis Research Articles

Design and testing of an arc resistant power transformer with a reinforced turret

This paper presents the design and testing of a full-scale 510-kV, 415-MVA HVDC converter transformer prototype designed to withstand the resulting pressure of a 20 MJ low-impedance fault in oil occurring inside a bushing turret, which is one of the major causes of transformer fires. In addition, there is currently few studies and recommendation regarding this failure mode, which is the main motivation for initiating this study. In total, two full-scale units were designed and built: First consisting of a reinforced turret and a transformer tank designed for arc resistance using nonlinear static finite-element analysis with design pressures retrieved from explicit dynamic simulations, and a second reference unit, with a conventional turret design. Both units were then experimentally tested with a methodology based on injecting pressurized air into the water-filled units, with test equipment dimensioned and calibrated to achieve a linear injection of energy equivalent to a 23 MJ arc in oil in 100 ms. The reinforced turret and transformer tank was able to contain the arc energy and performed as predicted by the nonlinear static and explicit dynamic simulations. The energy levels used in tests are, to our knowledge, the highest reported for a low-impedance fault occurring inside a turret, demonstrating the feasibility of designing a transformer to safely withstand mentioned faults without rupturing. The suggested reinforced turret is a robust and maintenance free solution offering passive protection against internal arcing, without the need of additional relive devices. It will significantly reduce the risk of fires, improve overall safety of the substation, and has the potential to be optimized for different arc energy levels and voltage class for turrets, cable boxes and chimneys.

Выбор оптимальной конструктивно-силовой схемы лонжеронного композитного крыла

This paper describes a method for optimizing the design of a spar-type composite aircraft wing structure based on multi-criterion approach. Two types of composite wing structures such as two-spar and three-spar ones were considered. The optimal design of a wing frame was determined by the Pareto method basing on three criteria: minimal weight, minimal wing deflection, maximal safety factor and minimal weight. Positions of wing frame parts, i.e. spars and ribs, were considered as optimization parameters. As a result, an optimal design of a composite spar-type wing was proposed. All the calculations necessary to select the optimal structural and design of the spar composite wing were performed using nonlinear static finite element analysis in the FEMAP with NX Nastran software package.

Topology Optimization of Aircraft Components for Increased Sustainability

The aim of this work is to explore a topology optimization approach for the design of load-bearing aircraft components. The main objective of the approach is to develop a design methodology that reduces the maximum stress in a component for a given applied load and weight constraint. Consequently, the load carrying capacity and fatigue life of the component are maximized, resulting in less downtime and increased sustainability of the aircraft. A representative component geometry has been selected that is a potential candidate for additive manufacturing in order to enable the enhanced design freedom required of topology optimization approaches. Both linear and nonlinear-static finite element analyses are performed to validate the improved performance of the topologically optimized component, as well as contact analyses to demonstrate that the resulting design cannot be further improved without redesigning the complete assembly. The optimization problem is formulated and solved using a bidirectional evolutionary structural optimization method. The method demonstrates large reductions in maximum stress, leading to significant increases in fatigue life, potentially compensating for the degradation in fatigue properties inherent in additively manufactured metallic structures. The added design flexibility of additive manufacturing combined with topology optimization offer the potential for an anywhere, anytime manufacturing capability that would greatly benefit aircraft sustainability.

Многокритериальная оптимизация двухлонжеронного композитного крыла легкого самолета

The article considers the results of optimization of the two-spar composite wing for the K-8 training aircraft. The geometric characteristics of the main structural elements of the wing such as spars, ribs and skin; orientation angles of the reinforcing layers and their thicknesses for each wing structural element, as well as the type of composite material and cost were selected as optimization parameters. The proposed optimization procedure includes several steps; each step uses a multi-criteria approach. The minimum deflection, weight, and cost are taken as optimization criteria. All the necessary calculations for selecting the optimal optimization parameters were performed using nonlinear static finite element analysis in the FEMAP software package.

Nonlinear static finite element analysis of sinking a floating pipeline to the bottom in calm water

ABSTRACT This paper describes a nonlinear static finite element analysis for simulating a process of submerging a floating pipeline to the bottom in calm water. Soil–pipe interaction elements, fully submerged pipe elements, partially submerged pipe elements, and floating pipe elements were used. Also, a load stiffness matrix associated with hydrostatic pressure was illustrated. Then, an incremental iterative procedure was developed to analyze large deformation of the pipeline during the sinking process and to take into account pipe-seabed interaction. The paper concentrates on the modeling of filled-in water loads and boundary conditions related to an offshore tugboat. Some numerical examples are provided to show the capabilities of the proposed analysis to model the continuous float-and-sink procedure of the pipeline.

Numerical analysis of hip bone replacement design parameters

Biomedical era has variety new technology adaptation in day to date life. In which bone replacement is major problem due to ortho complexity. In this paper study on a parametric analysis of the femoral stem. In this work determines the effects of the parameters on femoral stem design. The aim is to minimize the stress and deformation limit for the diverse condition. Aseptic releasing of the embed is predominantly affected by bone resorption in some femur regions when the prosthesis is embedded. Bone resorption shows up because of stress protecting that says the lessening of the stress level in the embedded femur brought about by the prosthesis's heap conveying because of its higher solidness. The most significant stress and deformation kept away from dependent on the parametrical analysis. Non-linear static finite element analysis of the femur bone is decreased stress and protect the femur. Here two information boundaries like force and meshing size of the analysis, and two yield boundaries like deformation and stress are Optimized..

Design and implementation of variable inclined air pillow soft pneumatic actuator suitable for bioimpedance applications

The technological revolution has caused the modernization of human–machine relationship changing our approach in problem solving our society issues and deviated the science of robotic all together. An example for one of the most important pawn in this revolution is soft robotics, the soft robots are robots that are made of deformable materials that provide an alternative approach to rigid robots. The soft pneumatic actuator (SPA) is one of the most widely used and studied form of this type of robotics. In this study, a new geometrical parameter of the SPAs is introduced by studying the effect of the change of the air pillow Inclination angle on the SPA work envelope and tip reaction force against wide range of positive and vacuum pressure applied on SPAs inner surfaces. We are elaborating this effect by using nonlinear static Finite Element Analysis. (FEA) basing it on the hyper-elastic material model identified by testing a specimen from the SPA fabricated material. Three SPAs are fabricated using Fused Deposition Modeling (FDM) 3D printer for the experimental validation of two aspects the work envelope and the tipping force. The test was performed by the image processing of the work envelope comparing the FEA and the experimental work envelope results and the tipping force was validated by using the load force scales. Based on the FEA and the experimental results, two different grippers with two work envelopes and tips was created to observe the change in the effect of the gripper on the weight and surfaces of the grasped object. By the integration of the SPA gripper with bio-impedance measurements, the SPA gripper was enabled to be translated to an agricultural application for fruit picking. A device that is monitored by having soft gripper to have no detrimental effect on the collected fruit's tissues, hybrid with Electrochemical Impedance Spectroscopy (EIS) test for quality assurance. Finally, this work can be interrogated in the future to a gripper that have modifiable synchronized work envelope and tip force for each object.

Extremely large-amplitude dynamics of cantilevers under coupled base excitation

Extremely large-amplitude nonlinear dynamics of a cantilever with a mass at the tip under coupled base excitations is examined for the first time. An exact model of the centreline rotation of the cantilever is developed capable of accurately predicting the cantilever dynamic response even at extremely large amplitudes; a nonlinear static finite element analysis is conducted to verify the accuracy of the proposed model at very large deflection amplitudes. The proposed model is based on the theory of Euler-Bernoulli and the internal damping model of Kelvin-Voigt; the centreline of the cantilever is assumed to remain inextensible. The proposed model for the cantilever centreline rotation is discretised via the Galerkin modal decomposition method while keeping all terms exact. Extensive numerical simulations are conducted to examine the primary and parametric resonance of the cantilever due to transverse and axial base excitations, respectively. It is shown that under the same axial and transverse amplitudes of excitation, the parametric resonance is much stronger than the primary resonance.

The Optimum Reinforced Concrete Deck Stiffness of Cable-Stayed Bridge Decks

This paper aims to find optimum deck stiffness and optimum girder profile in terms of vertical deformation and cable stresses. The feasibility of this study was achieved by analyse and develop eighteen models twice using ABAQUS software; six different deck stiffness and three different girder profile. A nonlinear static finite element analysis was performed on the previous models. The results show that the maximum stress found at maximum deck stiffness and the maximum cable stress found at maximum girder cross section. Also, the deflection decreased dramatically with the increase of deck stiffness. Therefore, the relationship between the vertical displacement and deck stiffness is inverse. Referring to the data obtained and collected from these analytical models the concrete deck slab with 50 MPa grade is the optimum grade in terms of strength and serviceability requirements.

The Effect of Plastic Hinge Location on the Flexural Strength Demand of Welded Flange Plate Connections

A Welded Flange Plate (WFP) connection consists of top and bottom flange plates that are fillet welded to the flanges of a beam and are complete joint penetration groove welded to a column flange. Four WFP design examples including various beam sizes, beam lengths, and/or assumed plastic hinge locations are presented in this paper. In these design examples, the relationships among the following three factors are in-vestigated: the assumed location of the plastic hinge, the probable peak flexural demand at the end of the beam, and the required length of the flange plates for the WFP connections. Nonlinear static finite element analyses considering both the material and geometric nonlinearities are also carried out for these examples to verify the actual location of the plastic hinge as well as the relationship between the actual location of the plastic hinge and the length of the flange plates used for the WFP connections.

Design and Testing of an Arc Resistant Power Transformer Tank

This paper presents the design and testing of a full-scale 330-kV, 210-MVA transformer tank designed to withstand the pressure effects of a 20 MJ, three-cycle low-impedance fault in oil, and fail at its cover in a safe and controlled manner above that amount of energy. The transformer tank, equipped with a mockup active part, was designed for arc resistance using nonlinear static finite-element analysis and a specific rupture criterion. It was then tested using an experimental methodology based on injecting pressurized air into the water-filled tank. To adequately reproduce the effects of an arc in oil, the test parameters were determined using explicit dynamic simulations. The transformer tank performed as predicted by the finite-element and explicit dynamic simulations. The energy levels used in the tests here are, to our knowledge, the largest ever reported. This study demonstrates that it is feasible to design a power transformer to safely withstand high-energy low-impedance faults of short duration.

Numerical study on influence of dent parameters on critical buckling pressure of thin cylindrical shell subjected to uniform lateral pressure

One of the common failure modes of thin cylindrical shells subjected to external pressure is buckling. The critical buckling pressures of these shell structures are mainly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, numerical parametric study is carried out to study the influence of dent parameters of centrally located dent (dent length, dent width, dent depth and angle of orientation of the dent), cylindrical shell parameters (L/R ratio and R/t ratio) and yield stress on the critical buckling pressure of externally pressurized thin dented cylindrical shells with simply supported boundary conditions at both top and bottom edges using non-linear static finite-element analysis of ANSYS.

A crack length control scheme for solving nonlinear finite element equations in stable and unstable delamination propagation analysis

An automatic incremental solution algorithm for nonlinear static finite element analysis of delamination propagation problems is presented. This load–displacement–constraint method iterates in the load displacement space utilizing the Newton–Raphson method, allowing to trace out the complete equilibrium path. The procedure can calculate pre- and post-critical responses of bi-dimensional problems, ranging from stable delamination growth to structural collapse by unstable growth or delamination buckling with arbitrarily sharp snap-back instabilities. Benchmark solution examples of established composite materials structural problems illustrate the effectiveness of the method.

Static buckling analysis of thin cylindrical shell with centrally located dent under uniform lateral pressure

One of the common failure modes of thin cylindrical shell subjected to external pressure is buckling. The buckling pressure of these shell structures are dominantly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the critical buckling pressure of thin cylindrical shells with a centrally located dent is studied using non-linear static finite-element analysis of ANSYS under external pressure with simply supported boundary conditions at the top and bottom edges of the thin cylindrical shell.

Effect of size and orientation of a centrally located dent on the ultimate strength of a thin square steel plate under axial compression

Thin steel plates are widely used in many structural applications because of its high load carrying capacity with less weight. The load carrying capacity of thin plates mainly depends on the imperfections present in them. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the ultimate strength of a thin square plate with a centrally located dent is studied using nonlinear static finite-element analysis, under uni-axial compressive loading with simply supported boundary conditions.

Numerical buckling analysis of thin cylindrical shells with combined distributed and local geometrical imperfections under uniform axial compression

In this paper, individual and combined effects of distributed and local geometrical imperfections on the limit load of an isotropic, thin-walled cylindrical shell under axial compression are investigated. First eigen affine mode shape imperfection pattern (FEAMSIP) is taken as distributed geometrical imperfections and dent as local geometrical imperfections. Limit load of the cylindrical shells are determined using non-linear static finite-element analysis module of general purpose FE software ANSYS. A parametric study on the effect of both imperfection patterns is done by varying the size and orientation of the dent. From the numerical results obtained, it is found that distributed geometrical imperfections namely, FEAMSIP have more influence on buckling strength than local geometrical imperfections namely dent.

Optimization of laminated composite plates and shells using genetic algorithms, neural networks and finite elements

Structural optimization using computational tools has become a major research field in recent years. Methods commonly used in structural analysis and optimization may demand considerable computational cost, depending on the problem complexity. Therefore, many techniques have been evaluated in order to diminish such impact. Among these various techniques, Artificial Neural Networks (ANN) may be considered as one of the main alternatives, when combined with classic analysis and optimization methods, to reduce the computational effort without affecting the final solution quality. Use of laminated composite structures has been continuously growing in the last decades due to the excellent mechanical properties and low weight characterizing these materials. Taken into account the increasing scientific effort in the different topics of this area, the aim of the present work is the formulation and implementation of a computational code to optimize manufactured complex laminated structures with a relatively low computational cost by combining the Finite Element Method (FEM) for structural analysis, Genetic Algorithms (GA) for structural optimization and ANN to approximate the finite element solutions. The modules for linear and geometrically non-linear static finite element analysis and for optimize laminated composite plates and shells, using GA, were previously implemented. Here, the finite element module is extended to analyze dynamic responses to solve optimization problems based in frequencies and modal criteria, and a perceptron ANN module is added to approximate finite element analyses. Several examples are presented to show the effectiveness of ANN to approximate solutions obtained using the FEM and to reduce significatively the computational cost.

Finite element analysis of misaligned rotors on oil-film bearings

The present work deals with a two-step nonlinear finite element analysis for misaligned multi-disk rotors on short oil-film bearings of various types (cylindrical, pocket, symmetrical three-lobed, unsymmetrical three-lobed). As a first step, the conventional parallel, angular and combined parallel and angular misalignments are modelled using Lagrange multipliers. The static equilibrium position of the journal within the bearing is determined using an iterative nonlinear static finite element analysis. The present work proposes a method for computing the displacement-dependent stiffness terms from the experimental static load-displacement data. Finally, the orbit of the rotor around the static equilibrium is determined using a time-integration scheme.

Effect of mid-connection detail on the behavior of x-bracing systems

In this paper, the effect of mid-connection detail of x-bracings comprised of build-up sections on the elastic–plastic behavior of braced systems is investigated. Then, a proposed symmetric mid-connection detail is compared with the commonly used one, analytically. In common mid-connection detail for build-up sections, one diagonal member (which is comprised of a pair of channels or angles) is usually discontinuous at the mid-connection and the other continuously passes through the connection. A rectangular gusset plate is used to join the discontinuous and continuous diagonals in practice. In the proposed method, one section from each diagonal member is discontinuous and the other is continuous. Buckling and post-buckling behavior of single span and single story models of cross-braced systems have been verified during a nonlinear static finite element analysis. The results show that the proposed mid-connection detail can improve both strength and ductility of cross-braced systems. Also, it is shown that adding two cover plates on both sides of discontinuous diagonal members in common mid-connection detail can partially improve the overall behavior of the system.

Product design optimisation with microstructure-property modelling and associated uncertainties

In this paper, we present a methodology for simulation-based product design optimisation using an internal state variable (ISV) constitutive modelling approach that captures the microstructure-property relations in the material. By modelling the stochastic uncertainties in the material model and the loading conditions, the design optimisation problem is formulated and solved using the reliability-based design optimisation (RBDO) methodology. The application problem considers the design optimisation of an A356-T6 cast aluminium component under maximum stress and damage constraints. Alternative metamodelling techniques are used to develop appropriate surrogate models in lieu of direct coupling of non-linear static finite element analysis and numerical design optimisation. Probabilistic design constraints are modelled using the safety index approach with the solution of the nested optimisation problem facilitated with the help of analytical surrogate models. Comparison of the optimisation results reveals the importance of using an ISV-based constitutive model that is sensitive to the growth of damage in material. Moreover, the solution of the RBDO problem captures the effects of uncertainty on finding the minimum weight design for the cast component.