Nonlinear Dynamic Finite Element Research Articles

Numerical investigation of nonlinear fluid–structure interaction dynamic behaviors under a general Immersed Boundary-Lattice Boltzmann-Finite Element method

A numerical approach based on the immersed boundary (IB), lattice Boltzmann and nonlinear finite element method (FEM) is proposed to simulate hydrodynamic interactions of very flexible objects. In the present simulation framework, the motion of fluid is obtained by solving the discrete lattice Boltzmann equations on Eulerian grid, the behaviors of flexible objects are calculated through nonlinear dynamic finite element method, and the interactive forces between them are implicitly obtained using velocity correction IB method which satisfies the no-slip conditions well at the boundary points. The efficiency and accuracy of the proposed Immersed Boundary-Lattice Boltzmann-Finite Element method is first validated by a fluid–structure interaction (F-SI) benchmark case, in which a flexible filament flaps behind a cylinder in channel flow, then the nonlinear vibration mechanism of the cylinder-filament system is investigated by altering the Reynolds number of flow and the material properties of filament. The interactions between two tandem and side-by-side identical objects in a uniform flow are also investigated, and the in-phase and out-of-phase flapping behaviors are captured by the proposed method.

Structural Optimization for Roof Crush Test Using an Enforced Displacement Method

A roof crush test has been utilized to reduce passengers’ injuries from a vehicle rollover. The Federal Motor Vehicle Safety Standards (FMVSS) 216 and the Insurance Institute for Highway Safety (IIHS) perform actual vehicle tests and evaluate the vehicle’s ratings. Nonlinear dynamic response structural optimization can be employed not only for achievement of a high rating but also minimization of the weight. However, the technique needs a huge computation time and cost because many nonlinear dynamic response analyses are required in the time domain. A novel method is proposed for nonlinear dynamic response structural optimization regarding the roof crush test. The process of the proposed method repeats the analysis domain and the design domain until the convergence criteria are satisfied. In the analysis domain, the roof crush test is simulated using a high fidelity model of nonlinear dynamic finite element analysis. In the design domain, a low fidelity model of linear static response structural optimization is utilized with enforced displacements that come from the analysis domain. Correction factors are employed to compensate the differences between a nonlinear dynamic analysis response and a linear static analysis response with enforced displacement. A full-scale vehicle problem is optimized with a constraint on the rigid wall force from the analysis in the design domain.

Mechanical response of a lined pipe under dynamic impact

Abstract An experimental and numerical investigation on the mechanical response of a lined pipe (compound pipe) under a dynamic impact is presented. The influence of the impact energy has been studied in terms of the depth of the dent formed, and of the strains and residual stresses. To this end, a three-dimensional explicit dynamic non-linear finite element model has been developed and successfully validated against the results of impact-test experiments conducted on pipes made of AISI 10305 steel, with and without the AISI304 stainless steel liner. The validation was made by comparing numerically computed strains with those measured by strain gauges, as well as in terms of permanent deformation. The model is then utilized to evaluate the residual stresses, the amount of energy dissipation and the velocity of impact process as a function of different pipes (i.e. with or without liner) and of the free drop heights.

Research and application of reaming subsidence control in horizontal directional drilling

In the reaming operation of horizontal directional drilling, a centralizer is often attached to a reaming-bottomhole assembly (R-BHA) to change the reamer side force. This can address the problem of large-diameter reamer subsidence. However, there is no scientific basis for how to attach the centralizer in the R-BHA. In this paper, an equation for the reamer side force in a two-centralizer R-BHA is derived, based on three moment equations. Then, using the Drucker-Prager criterion as a rock constitutive relation and the shear criterion for predicting damage initiation, a nonlinear dynamic finite element model is established using the finite element method (FEM). In addition, the trajectory of the reamer and the failure of the drilling tools are analyzed. The study results show that the combination of the analytical and finite element methods can effectively improve the installation accuracy of the centralizer. The attachment range of the centralizer can be quickly determined by a simple calculation of the analytical method, and the FEM (with high computational precision) can be used to analyze the subsidence control capacity of the R-BHA in detail. Application to a field case demonstrates the feasibility of the method, and the study conclusions provide a scientific basis for the centralizer attached to the R-BHA, which is important for controlling reaming subsidence.

A nonlinear dynamic corotational finite element model for submerged pipes

A three dimensional finite element model is built to compute the motions of a pipe that is being laid on the seabed. This process is geometrically nonlinear, therefore co-rotational beam elements are used. The pipe is subject to static and dynamic forces. Static forces are due to gravity, current and buoyancy. The dynamic forces exerted by the water are incorporated using Morison’s equation. The dynamic motions are computed using implicit time integration. For this the Hilber-Hughes-Taylor method is selected. The Newton-Raphson iteration scheme is used to solve the equations in every time step. During laying, the pipe is connected to the pipe laying vessel, which is subject to wave motion. Response amplitude operators are used to determine the motions of the ship and thus the motions of the top end of the pipe.

A 3D FEM model for floating wind turbines support structures

The relevance of the interaction between the structural stiffness and the wind turbine dynamics are well known by the industry from decades of expertise. However, the novel floating concepts are commonly designed by tools that disregard the individual structural stiffness of the elements which compose the floating platform. Usually, these elements are treated as rigid body elements in the design process. However, their flexibility can be relevant in the long time structural life assessment, particularly for the fatigue assessment. Then, a structural analysis that includes the dynamic effects over the deformation of the structure is required. The paper proposes a model that integrates the instantaneous deformation of the structure by a nonlinear dynamic Finite Element Analysis (FEA) computation in a fully coupled Offshore Wind Turbine (WT) model in the time domain.A 3D hydro-aero-servo-elastic coupled numerical model in time domain for structural analysis of floating or bottom fixed structures has been developed at the UPC-BarcelonaTech. The code integrates the forces exerted by the waves and currents as well as the aerodynamic loads, including the wind turbine, and the mooring system. For the hydrodynamic loads the Morison’s equation is used to compute waves and current forces. Both Airy (regular and irregular) and Stokes 5th order wave theories are implemented. The mooring system can be computed in a quasi-static way or considering their fully dynamics. The aerodynamic loads are computed with AeroDyn standalone module from NREL, which is coupled to the FE model. The structure is discretized with one-dimensional beam finite elements, in which the formulation considers small strains as well as large motions under the implementations of the Euler beams theory. With this approach, the dynamic interaction between the wind turbine and the structure, as well as the effects on the internal forces are implicitly coupled in the formulation.A comparison of the Windcrete concrete SPAR concept experimental Response Amplitude Operators (RAO) against the numerical results are presented, as well as some results from simulations under normal operation conditions.

06.07: Comparison of Blast Performance of Steel Modular Buildings with Anchored and Sliding Foundations

ABSTRACTA two‐module blast‐resistant steel building with overall dimensions of 12 m by 6 m floor plan and 3.4 m height was designed to resisted 80 kPa free field overpressure with 140 microsecond duration. The building was designed to remain within “high damage/response” level when it is anchored to its foundation. The effect of anchored and unanchored or sliding (free‐to‐slide) foundation on blast performance of structural elements on the wall and roof, foundation loads, building sliding, and building total friction and kinetic energy were investigated using nonlinear dynamic finite element analysis tools. The comparison of analyses results revealed that building foundation reactions and maximum deflection demands for structural members can significantly decrease with unanchored foundation. For unanchored foundation, several friction coefficients (i.e., 0.2, 0.5, and 0.8) for the interaction between the building and its foundation were considered. The analyses results show that the maximum relative deflections of the structural members of the building with unanchored foundation to be between 43% and 120% with an average of 80% of that for the building with anchored foundations. The most significant effect of unanchored foundation on blast performance of the building was the significant decrease in the foundation maximum horizontal reaction, which was approximately 15% to 60% of that for the building with anchored foundation. However, the unanchored foundation had negligible effect on building vertical foundation reactions. The computed maximum sliding displacements were approximately 10 m, 2 m and 0.3 m for the building with unanchored foundation for friction coefficient of 0.2, 0.5, and 0.8, respectively. For the building with unanchored and anchored foundations, both friction energy and kinetic energy versus time plots were very similar for initial stages of the blast loading. The overall results show that providing even limited permissible sliding between blast resistant structures and their foundation can significantly reduce their foundation reactions and improve blast performance of structural members. A controlled‐sliding mechanism between blast resistant structures and their foundation with steel cables is recommend to improve blast performance of the structure while limiting maximum sliding within desired permissible limits.

Passive Control Systems for the Blast Enhancement of Glazing Curtain Walls Under Explosive Loads

Glass curtain walls are used in modern buildings as envelopes for wide surfaces due to a multitude of aspects. In glass curtain walls, tensile brittle panels are connected - through mechanical or adhesive joints - with steel frameworks or aluminum bracing systems, and due to the interaction of several structural components, the behaviour of the so assembled system is complex to predict, especially under exceptional loading conditions such as explosive events. In the paper, glazing curtain walls are investigated by means of Finite-Element (FE) numerical simulations, under the effect of air blast pressures of variable intensity. Their typical dynamic behaviour and criticalities under high-strain impact loads are first analyzed. By means of extended nonlinear dynamic FE parametric studies, innovative devices are applied to traditional curtain walls, at their support points, in order to improve their expected dynamic response. Two possible solutions, namely consisting of viscoelastic (VE) or elasto-plastic (PL) dampers, are proposed as passive control systems for the mitigation of maximum effects in the façade components deriving from the incoming blast pressures. As shown, although characterized by specific intrinsic mechanical behaviours, either VE or PL dampers can offer beneficial structural effects. In the first case, major advantages for the façade components derive from the additional flexibility and damping capacities of VE devices. In the latter case, PL dampers introduce additional plastic energy dissipation in the traditional curtain wall assembly, hence allowing preventing severe damage in the glazing components. It is thus expected that the current outcomes could represent a valid background for further experimental validation as well as detailed assessment and optimization of the proposed design concept.

Amplification of strong ground motions at Heathcote Valley during the 2010–2011 Canterbury earthquakes: Observation and 1D site response analysis

The strong motion station at Heathcote Valley School (HVSC) recorded intense ground accelerations (peak value of 1.4g in horizontal and 2.2g in vertical component) during the 22 February 2011 Christchurch earthquake. More importantly, ground motions recorded at HVSC in numerous other events during the 2010–2011 Canterbury earthquake sequence also exhibited consistently larger peak ground accelerations compared with nearby strong motion stations, which suggests significant near-surface site amplification effects.This paper presents a quantitative case study of near-surface site effects of Heathcote Valley during the 2010–2011 Canterbury earthquake sequence, by means of one-dimensional nonlinear dynamic finite element analyses based on the recorded ground motions and a rigorous site characterisation study. Various geophysical and geotechnical in-situ tests are performed to establish a simplified three-dimensional representation of wave velocities, mass densities and the geological structure (i.e. layering) of Heathcote Valley. Simulations are performed using the velocity profile at the location of station HVSC with the finite element analysis program OpenSees. Overall, simulations agree well with the recorded motions and suggest that ground motions at HVSC are amplified in a wide band of frequencies. However, the one-dimensional simulations tend to underestimate the site response at frequencies higher than the site fundamental frequency, likely due to its inability of modelling surface waves caused by the inclined soil-rock interface. Comparison between the nonlinear and the equivalent linear model shows that, although both approaches produce similar level of peak amplitude, the equivalent linear model significantly underestimates the high frequency motions.

Modeling of multiple shots for analyzing shot peening controlled parameters on formed curvature radius

The desired peening outcome of the peening process like curvature is based on the reasonable determination of shot peening (SP) parameters. In this work, an assessment about accuracy of randomly distributed shots model was performed by comparing the experimental test. And, the comprehensive nonlinear dynamic elastic-plastic finite element analysis was conducted to reveal the difference between the regularly ordered shots model and the randomly distributed shots model in terms of induced stress and residual stress. The comparison indicated a difference between those two kinds of models under high coverage. Based on the randomly distributed shots model, we also found curvature radius increased with increasing thickness but decreased with shot velocity and increasing coverage. At last, we analyzed the reason by associating the residual distributions. Contrary to the shot peening parameters, shot velocity and coverage, the thickness of the strip is the most influential factor which inhibits the decrease of curvature radius. It should be noted that the over-high impact velocity will lead to a buckling distortion on the strip. Furthermore, the relation between the impact velocity and coverage was developed.

Elementary analysis on application of ANSYS/LS-DYNAD in the detection of integrate pile

In this paper, by using the ANSYS/LS-DYNA nonlinear dynamic finite element analysis method. The numerical simulations for the integrity pile, and get the rules and characteristics of stress wave about complete pile. Verify the feasibility of the method of ANSYS/LS-DYNA nonlinear dynamic finite element analysis in the pile integrity detection applications. The research results can provide guidance for the pile integrity detection of different types. Then this paper simulated pile necking. And we get the patterns and characteristics of stress wave reflection about the necking pile, which show the method of ANSYS/LS-DYNA nonlinear dynamic finite element analysis can detect the type and location of pile foundation defect accurately.

Structural response analysis of slamming impact on free fall lifeboats

The evaluation of impact induced slamming loads experienced by ships and offshore structures using advanced fluid structure interaction methods may be a challenging task involving complex and time consuming engineering solutions. This is the reason why to date the application of well understood and validated quasi-response approaches remains the most rational alternative used by experts for preliminary design assessment. Based on a benchmark study carried out by the International Ship and Offshore Structures Congress Technical Committee II.1 on Quasi-Static Response this paper demonstrates the practical use of “quasi-response” prediction methods for the assessment of impact loads on modern free fall lifeboats. The case study presented is considered relevant in terms of technical background and ship design for safety. Following a brief review rationalising the practical relevance of the engineering solutions examined, the influence of high speed impact is evaluated using linear-elastic and nonlinear beam models, as well as a nonlinear transient dynamic finite element analysis idealisation. Comparisons of the methods presented against experimental results led to the conclusion that the nonlinear quasi-dynamic beam approach accounts for the influence of the dynamic effects of strain by suitably idealising the effects of nonlinear geometric stiffness. It may therefore be more appropriate to employ this approach at preliminary stage, especially when conducting comparisons against simplistic linear methods used for rigid structures (e.g. stiffened steel and aluminium panels), or advanced nonlinear finite element analysis and other multi-physics methods that may be computationally complex and time consuming.

Modelling dental implant extraction by pullout and torque procedures

Dental implants extraction, achieved either by applying torque or pullout force, is used to estimate the bone–implant interfacial strength. A detailed description of the mechanical and physical aspects of the extraction process in the literature is still missing.This paper presents 3D nonlinear dynamic finite element simulations of a commercial implant extraction process from the mandible bone. Emphasis is put on the typical load-displacement and torque-angle relationships for various types of cortical and trabecular bone strengths. The simulations also study of the influence of the osseointegration level on those relationships. This is done by simulating implant extraction right after insertion when interfacial frictional contact exists between the implant and bone, and long after insertion, assuming that the implant is fully bonded to the bone. The model does not include a separate representation and model of the interfacial layer for which available data is limited.The obtained relationships show that the higher the strength of the trabecular bone the higher the peak extraction force, while for application of torque, it is the cortical bone which might dictate the peak torque value. Information on the relative strength contrast of the cortical and trabecular components, as well as the progressive nature of the damage evolution, can be revealed from the obtained relations. It is shown that full osseointegration might multiply the peak and average load values by a factor 3–12 although the calculated work of extraction varies only by a factor of 1.5.From a quantitative point of view, it is suggested that, as an alternative to reporting peak load or torque values, an average value derived from the extraction work be used to better characterize the bone–implant interfacial strength.

Low-velocity impact to transmission line conductors

This combined experimental and numerical study addresses mechanical effects associated with the energy dissipation from transverse low-velocity impacts on a novel High Temperature Low Sag (HTLS) transmission line conductor, subjected to either free or constrained end conditions and large axial tensile loads. Impact experiments were conducted on one type of Polymer Composite Core Conductor (PCCC) belonging to the family of HTLS designs. The experimental work performed using an original approach was supported by non-linear static and dynamic finite element analysis.Despite their geometrical simplicity, the numerical models provided useful information regarding the response of the conductor to both static and dynamic conditions. Most importantly it has been determined that the PCCC exhibits good resistance to impact under constrained end conditions with and without initial axial tension. It was also identified that the most damaging condition under impact is when the conductor had free ends and was thus subjected to severe bending. It has been shown in this work that the suggested approach to the impact testing of transmission lines could result in useful predictions of their structural integrity after low-velocity impact either during installation or in service.

Dynamic Responses of Subway Tunnel in Clay Stratum to Moving Loads

An elaborate three-dimensional nonlinear numerical model of a rail-tunnel-foundation system in a clay stratum was developed. The model closely represented an actual subway tunnel and described the rail, sleeper, track slab, inverted arch, lining and foundation. Operation of a subway train with six wagons traveling at 100 km/h was simulated. Large-scale nonlinear dynamic finite element computation for the system was performed. The analysis showed that the system is in a state of loading and unloading repeatedly as the train passes through the tunnel. The spatial distributions of dynamic displacement, velocity, acceleration and stresses in different parts of the system all vary simultaneously with time and space. The characteristics of dynamic stresses in the clayey stratum are much different from those in the inverted arch and lining. The dynamic stresses in the tunnel lining and inverted arch have small values, but the rate effects of dynamic stress for ballastless track slab, inverted arch and tunnel lining are much higher than that of the foundation clay. The rotations of principal stress axes in the XY and YZ planes are predominant for ballastless track slab, inverted arch, tunnel lining and foundation soil just below the tunnel lining, while rotation in the YZ plane is predominant for deeper foundation soil elements. These results justify a conclusion that the thickness of inverted arch and backfill concrete can be optimized. Much attention should be paid during design to the long-term stability of a clayey foundation. The results can be referred in the dynamic design of subways.

Seismic Response of Long-Span Triple-Tower Suspension Bridge under Random Ground Motion

Multitower suspension bridge is of different style compared to the traditional suspension bridge with two towers, and consequently the dissimilarity of static and dynamic behaviors is distinct. As a special case of multitower suspension bridge, two long-span triple-tower suspension bridges have been constructed in China and the seismic random response of triple-tower suspension bridges is studied in this paper. A nonlinear dynamic analysis finite element model is established in ABAQUS and the Python language is utilized to facilitate the preprocess and postprocess during the finite element analysis. The procedure for random response calculation of structures based on the pseudoexcitation method is presented, with the initial equilibrium state of structure considered, which may be ignored for long-span bridges during calculating of stochastic response. The stationary seismic random responses of triple-tower suspension bridge under uniform excitation in firm, medium, and soft soil conditions and under spatially varying excitation in soft soil are investigated. The distribution of RMS of random responses of displacements and internal forces of the stiffening girder and towers is presented and discussed in detail. Results show that spatially variable ground motions should be considered in the stochastic analysis of triple-tower suspension bridge.

Sub-impacts of simply supported beam struck by steel sphere—part II: Numerical simulations

This part of the article describes numerical simulations of the problem investigated experimentally. A three-dimensional finite element model of elastic–plastic for sphere falling on beam has been implemented using the nonlinear dynamic finite element software LS-DYNA. From the numerical simulations, it was found that the LS-DYNA is suitable to study complex sub-impact phenomenon, and good agreement is in general obtained between the simulation and experimental results. The numerical simulations show that the initial impact velocity, equivalent elasticity modulus, contact curvature radius of the sphere, and equivalent mass have great influence on the contact–impact time of the sub-impact, and an applicable range of the theoretical expression of contact–impact time of the sub-impact was determined. In addition, the numerical simulations demonstrate the ratios of maximum amplitudes of the first-, second-, and third-order vibrations to the maximum amplitudes of the beam vibrations, and the phase angle of the first-order vibration will change suddenly when the sub-impacts occur. Furthermore, the occurrence conditions of the sub-impacts were clarified numerically. It was found that the occurrence conditions of the sub-impacts can be represented by a mass ratio threshold, and the thickness or length of the beam has also a great influence on the occurrence of the sub-impacts. Once the sub-impacts occur, which would result in an uncertain behavior of the apparent coefficient of restitution.

Behavior Prediction of Ship Structure due to Side Impact Scenario by Dynamic-Nonlinear Finite Element Analysis

The development of safety has become issue especially for marine and ocean vessels. However, the limitless possibilities of various phenomenon on the sea, make the observation and prediction of ship structure are continuously needed. Side impact is one of those phenomenon. Due to the complexity of ship structure, this phenomenon occurs and produces high nonlinearities, which influence the extent and contour of structural behavior. Such interesting phenomenon was reviewed and studied in present paper using dynamic finite element analysis as the effect of the dependent characteristic of phenomenon to time. Several side scenario models were used to obtain different results in respect of impact location. The kinetic and total energies were presented together with the contours of stress and displacement at two sides of side constructions. Results indicated that the contribution of construction arrangement was significantly affected stress distribution in longitudinal direction of ship hull, while displacement contour from certain scenario produced high intensity on longitudinal member of side construction.

Static and dynamic analyses of insulated concrete sandwich panels using a unified non-linear finite element model

Insulated concrete sandwich panels are comprised of two outer concrete wythes and an inner layer of foam insulation. They have been increasingly used because of their advantages of light weight and energy efficiency. Various shear connectors can be used to connect the two outer concrete wythes. More recently, Fiber-Reinforced Polymer (FRP) shear connectors have been used, which can eliminate thermal bridging and improve the thermal performance. Typical approaches to Finite Element (FE) analysis treat static and dynamic analyses separately. However, due to the flexibility of the FRP shear connectors and the cracking of the concrete in insulated concrete sandwich panels, a nonlinear static analysis model would often diverge early based on a preliminary FE study conducted by the authors. To address this issue, a nonlinear explicit dynamic FE model using ABAQUS© was developed, which can study both the panels’ static behavior under typical flexural loading and dynamic behavior under blast loading. Nonlinear material properties were incorporated and damaged plasticity model was used to model concrete in both compression and tension. In order to simulate the static behavior, the time loading control was applied to the FE model to slow down the rate of loading to smoothly capture the response. For dynamic analysis under blast loading, a verification study was conducted first using the developed FE model, where good correlations can be obtained between the FE and test results on a panel tested in a previous study. The FE model was further used to study the dynamic behavior of two panels under blast loading: one is a solid concrete panel and the other is an insulated concrete sandwich panel. It can be concluded that, although the insulated concrete sandwich panel is lighter, it still performs relatively well compared to the solid panel under blast loading. Therefore, it is promising to use insulated concrete sandwich panels for both conventional and blast-resistant structures.

Finite element model for predicting post delamination behaviour in FRP-retrofitted beams in flexure

To predict the debonding load, shear stresses and strain profile along the FRP-concrete interface for FRP strengthened reinforced concrete members, eleven 4.5m long RC T-beams are built and tested to failure, and their complete load-deflection responses are measured. Three beams are not strengthened and are used as control specimens while the remaining eight beams are strengthened with different amount of CFRP sheet. The same beams are analyzed using LS-DYNA nonlinear dynamic finite element analysis procedure. The predicted load-deflection curve of each beam is compared with its experimental counterpart over its entire loading range up to complete failure, and the two curves are found to be in reasonable agreement. The distinguishing feature of the present analysis is that it not just captures the initiation and propagation of the delamination process, but also the complete post-peak load or softening response of each beam. It is found that the response of FRP strengthened beams is not always brittle and that after the initiation of delamination, the retrofitted beams continue to carry load and undergo appreciable deformation.