Dynamic Finite Element Analysis Research Articles

Investigation of material deterioration and seismic behavior of Fertek and Hançerli Churches in Cappadocia Region

Cappadocia is among the rare natural and cultural centers on earth with its fairy chimneys, underground cities, rock churches, stone structures and natural beauties. Among these structures, Fertek and Hançerli Churches that are subjected to the scope of the study are very original artifacts with their superior construction techniques and rich workmanship according to the period they were built. In this study, the architectural features of Fertek and Hançerli Churches which were built in the 19th century and located within Niğde province in the Cappadocia Region were defined and material deteriorations were determined. In the light of these determinations, the existing static properties of these structures were examined using the Dynamic Finite Element Analysis program. Discoloration, vegetation, crack formation, moisture problems and partial mortar and stone losses were detected in both church structures. When the analysis results are evaluated, it has been determined that the structures need repair and improvement, depending on the region and soil class, considering the earthquake forces.

Strain prediction and benchmark with measurement in the Spallation Neutron Source mercury target without gas injection

The 1.4-MW Spallation Neutron Source (SNS) currently operates as the world's highest time-average power spallation source and uses mercury as the spallation target material. The mercury circulates through a stainless-steel target vessel and heat exchanger loop that removes the heat deposited from the incident proton beam in the target. The mercury vessel is part of the fixed but replaceable target module. The target module is not safety credited in the SNS design, but reliable long life is vital for meeting operational goals and minimizing cost and waste. SNS is a short-pulse ($\ensuremath{\sim}0.7\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$) neutron source with a repetition rate of 60 Hz with 1.0 GeV protons onto the target. The short-pulse operation introduces two mechanisms that threaten the longevity of the mercury vessel. The pulsed target heating is essentially isochoric, which results in a distributed pressure field in the mercury with each pulse. After each pulse, the pressure propagates, interacts with, and strains the stainless-steel vessel. For intermittent times, this pressure field leads to mercury cavitation. The first mechanism of concern for the target lifetime is high-cycle fatigue to the stainless-steel vessel and the second is cavitation erosion. At the onset of the SNS project, the R program sought to address the need for an accurate and practical method to estimate the fatigue life of the mercury vessel. Around 2000, the R team conducted a series of in-beam mercury target experiments at the Weapons Neutron Research Facility at Los Alamos Neutron Science Center. These experiments successfully produced a small database of pulse response strain data. The data were used to develop and benchmark an explicit dynamic finite element analysis technique for estimating target fatigue life. SNS is now a mature facility with about 15 years of operation and 29 SNS target modules consumed. Since 2015, strain measurements have been collected from actual targets, and abundant target vessel strain data are now available in greater detail than was possible in 2000. Variances in pulse response data have been characterized using tolerance interval analysis to benchmark the simulation technique more thoroughly. The simulated results were found to match measurements generally well, but the method is always conservative. A potential adjustment to the cavitation threshold parameter value was suggested. Variances in the pulse response data are moderate, which is largely explained by the fact that data were acquired in 60-Hz burst mode and by the lasting vibration of the vessel between pulses.

A comprehensive numerical analysis of EQ-induced lateral earth pressure on structures basement walls

Due to soil-structure interaction, dynamic lateral earth pressures on building embedded walls affect the dynamic performance of the building. Classic relations such as Mononobe-Okabe (M − O) and Seed & Withman (S–W) are applied to determine these dynamic lateral earth pressures in conventional design methods. Considering these relations' assumptions and their neglect of soil-structure interactions during an earthquake, using these relations may result in erroneous and inaccurate estimation of dynamic earth pressure. This paper attempts to understand this phenomenon better and estimate dynamic earth pressure on basement walls. Structure and soil mass are simulated simultaneously, using numerical models. Numerical (finite element) dynamic analyses are carried out for qualitative and quantitative evaluation of dynamic earth pressures on buildings with basements. Different excavation depths, ground topography, geotechnical parameters, and building stories above ground have been considered in these analyses. Finally, the soil-structure interaction response has been discussed using the obtained results, and approximate relations are derived to estimate the dynamic earth pressure.

Seismic Liquefaction of Saturated Calcareous Sands: Dynamic Centrifuge Test and Numerical Simulation

Both a dynamic centrifuge test and dynamic finite element analysis were carried out to assess the seismic liquefaction risk of a saturated-calcareous-sand site in a port project in Timor-Leste. Taking the in situ calcareous sands as the model material, two groups of horizontal free-field model tests for medium dense and dense saturated calcareous sands were completed based on the two-stage scaling law theory. Three natural earthquake records with varied peak accelerations were adopted as input motions. The experimental results indicate that the shallower the depth, the lower the relative density, the longer the seismic duration, the larger the peak acceleration, and the more susceptible the saturated site to liquefaction. The sands on site at a depth of five to ten meters is highly risky for liquefaction with the excess pore pressure ratio reaching up to about 1.0 under the seismic peak acceleration of 0.3 g. The risk of liquefaction for site sands is rather small under the seismic peak acceleration of 0.1 g. The study reveals the characteristics of the pore pressure development in sites of varied relative densities under different seismic loadings, which provides a scientific basis for the liquefaction risk assessment of the engineering site.

Analytical solutions for circular composite-lined tunnels under obliquely incident seismic SV and P waves

An analytical solution can easily and quickly give the internal forces in tunnels due to seismic waves, by which, the relationship between the key parameters could also be clarified. These methods are widely used in preliminary seismic design of tunnels. This paper presents new analytical solutions for thrust and moment of circular composite-lined tunnels with arbitrary layer linings under obliquely incident SV waves and P waves. Wherein, the lining is regarded as a thick-wall cylinder. Moreover, the proposed analytical solutions can consider different contact conditions of the ground-tunnel and lining-lining interface. The new analytical solutions are verified by comparing with the dynamic finite element analysis results. The results show the accuracy and applicability of the proposed analytical solutions. Parametric analyses are performed to explore the effects of the flexibility coefficient δ, incident angle and steel lining on the seismic response of tunnels.

On low-velocity impact behavior of sandwich composites with negative Poisson’s ratio lattice cores

In order to investigate the low-velocity impact performance of a new type of sandwich composite structure with negative Poisson’s ratio lattice cores, low-velocity impact tests were carried out using the sandwich composite specimens, which were prepared by 3D printing lattice cores and glass/epoxy composite sheets. A finite element dynamic analysis strategy was also employed to investigate the mechanical response, the total energy absorption, and energy absorptivity of the sandwich panel at impact energies of 5 J, 10 J, 15 J, 20 J, 30 J and 40 J, respectively. Results show that the new sandwich structure can better disperse the concentrated impact load received by the upper sheet and dissipate most of the impact energy in the process of transferring the loads during cushioning. The negative Poisson’s ratio lattice structure can guide damages, and it is found that the position of the impact point will affect the impact mechanical response and energy absorption ability of the sandwich panel.

Effect of degenerative factors on cervical spinal cord during flexion and extension: a dynamic finite element analysis.

Spinal cord injury (SCI) is a global problem that brings a heavy burden to both patients and society. Recent investigations indicated degenerative disease is taking an increasing part in SCI with the growth of the aging population. However, little insight has been gained about the effect of cervical degenerative disease on the spinal cord during dynamic activities. In this work, a dynamic fluid-structure interaction model was developed and validated to investigate the effect of anterior and posterior encroachment caused by degenerative disease on the spinal cord during normal extension and flexion. Maximum von-Mises stress and maximum principal strain were observed at the end of extension and flexion. The abnormal stress distribution caused by degenerative factors was concentrated in the descending tracts of the spinal cord. Our finding indicates that the excessive motion of the cervical spine could potentially exacerbate spinal cord injury and enlarge injury areas. Stress and strain remained low compared to extension during moderate flexion. This suggests that patients with cervical degenerative disease should avoid frequent or excessive flexion and extension which could result in motor function impairment, whereas moderate flexion is safe. Besides, encroachment caused by degenerative factors that are not significant in static imaging could also cause cord compression during normal activities.

Dynamic analysis of rock fall impact for a cantilever rock shed with geofoam cushion

In this study, the effect of geofoam compressible cushions on the impact response of the rockfall protection galleries located in a main artery highway connecting the southern Turkey to central Anatolia is investigated. Due to high occurrence risk of rockfall hazard at the mountainous region, permanent protection structures are required to prevent damage. Numerical analyses were carried out to evaluate the performance of EPS geofoam compressible layers with different stiffness characteristics on reducing the transmissibility of the impact forces caused by rockfalls. The kinetic energy levels, expected fall velocities for rock masses and the typical rockfall paths were assessed considering the topography of the hill. Dynamic explicit finite element analyses were performed to investigate the effect of the rockfall impact on a reinforced concrete rock shed. Stresses, strains and displacements on the structural section and the cushioning zone were monitored through the analyses. Based on the results, it was observed that geofoam has a significant effect on reducing the transmitted forces to the structure while increasing the impact duration. In terms of structural displacements, up to 75% reduction is observed when EPS cushions are placed on top of rock shed structure.

Life Prediction Method of Dissimilar Lightweight Materials Welded Joints with Precrack under Coupled Impact-Fatigue Loading.

This paper aims to explore the fatigue life estimation approach of welded joints with precrack under coupled impact and fatigue loading, and the base metal is dissimilar 5083H111 and 5754 aluminum alloy. Impact tests are first carried out on the dissimilar lightweight materials welded joint with precrack located in the middle of the specimen, and a stress and strain field is obtained to determine the fatigue damage model parameters by using finite element dynamic analysis to simulate the impact process. Based, on the S-N curve of welded joints, the predicted life expectancy is found to be inconsistent with the experimental results. According to the continuum damage mechanics, the lifetime assessment model is presented to calculate both impact and fatigue damage. The estimated results agree well with the experimental ones.

Study on the Response of Staggered Floor Isolated Structures in Mountainous Areas under Three-Dimensional Earthquakes

As coal mines are susceptible to safety accidents due to earthquakes, the requirements for structures in coal mining areas such as fire control centers and hospitals are higher, so base isolated structures, including staggered isolated structures, adapted to mountainous terrain are used in mining areas. The staggered floor isolated structure is a kind of isolated structure in mountainous areas which developed from the base-isolated structure. The theoretical research on staggered isolated structures is relatively few, and the theoretical research lags behind the practical application of engineering. In this paper, three staggered floor isolated structures with different heights of staggered floors are established. The responses of structures under one-dimensional, two-dimensional, and three-dimensional earthquakes are analyzed by the finite element dynamic time-history analysis method. The structural torsion, interstory shear force, maximum axial force, and floor displacement of the structure are compared. Due to the asymmetric characteristics of the staggered floor isolated structure, the center of stiffness of the staggered floor isolated structure deviates from the center of mass, which produces not only horizontal vibration but also obvious torsional vibration. The input of earthquakes in different dimensions also makes a difference in the response of the structure. The location between the upper isolated layer and the first floor above the upper isolated layer is a weak point of the structure. The results obtained in this study are distinguished from traditional basic isolated structures, which supplements the theoretical research of the staggered isolated structure.

A Study on Impact Force Detection Method Based on Piezoelectric Sensing.

Impact force refers to a transient phenomenon with a very short-acting time, but a large impulse. Therefore, the detection of impact vibration is critical for the reliability, stability, and overall life of mechanical parts. Accordingly, this paper proposes a method to indirectly characterize the impact force by using an impact stress wave. The LS-DYNA software is utilized to establish the model of a ball impacting the steel plate, and the impact force of the ball and the impact response of the detection point are obtained through explicit dynamic finite element analysis. In addition, on this basis, a correspondence between the impact force and the impact response is established, and finally, an experimental platform for impact force detection is built for experimental testing. The results obtained by the finite element method are in good agreement with the experimental measurement results, and it can be inferred that the detected piezoelectric signal can be used to characterize the impact force. The method proposed herein can guide the impact resistance design and safety assessment of structures in actual engineering applications.

A Drifter-Based Self-Powered Piezoelectric Sensor for Ocean Wave Measurements.

Recently, piezoelectric materials have received remarkable attention in marine applications for energy harvesting from the ocean, which is a harsh environment with powerful and impactful waves and currents. However, to the best of the authors’ knowledge, although there are various designs of piezoelectric energy harvesters for marine applications, piezoelectric materials have not been employed for sensory and measurement applications in marine environment. In the present research, a drifter-based piezoelectric sensor is proposed to measure ocean waves’ height and period. To analyze the motion principle and the working performance of the proposed drifter-based piezoelectric sensor, a dynamic model was developed. The developed dynamic model investigated the system’s response to an input of ocean waves and provides design insights into the geometrical and material parameters. Next, finite element analysis (FEA) simulations using the commercial software COMSOL-Multiphysics were carried out with the help of a coupled physics analysis of Solid Mechanics and Electrostatics Modules to achieve the output voltages. An experimental prototype was fabricated and tested to validate the results of the dynamic model and the FEA simulation. A slider-crank mechanism was used to mimic ocean waves throughout the experiment, and the results showed a close match between the proposed dynamic modeling, FEA simulations, and experimental testing. In the end, a short discussion is devoted to interpreting the output results, comparing the results of the simulations with those of the experimental testing, sensor’s resolution, and the self-powering functionality of the proposed drifter-based piezoelectric sensor.

Određivanje trajnih deformacija savitljivih kolničkih konstrukcija pomoću metode konačnih elemenata

The unbound granular material used in flexible road pavements exhibits an elastoplastic behaviour under repetitive traffic loads. Permanent deformation occurring on pavement surface under traffic load is one of the main road pavement problems affecting road performance. Therefore, many permanent deformation models for calculating road pavement rutting have recently been developed by researchers. Most of these studies involve performance of dynamic triaxial tests. In this study, deformation characteristics of unbound granular materials are determined using the resonant column test. Then, instead of determining the total permanent deformation by summing up the calculated permanent deformations obtained in each pavement layer, dynamic 2D axisymmetric finite element analyses are performed for four different pavement cross sections to predict the total permanent deformation occurring on pavement surface under certain load cycles. The first modelled cross section of unbound granular material consists of natural aggregate. The base and/or subbase of remaining three cross sections consists of steel slag waste material. The permanent deformation versus load cycle is presented for four multi-layer road cross sections using semi logarithmic graphs. Finally, the permanent deformation model equation is developed for each pavement cross section using their fitting curves.

APPLICATION OF BUCKLING RESTRAINED DAMPER TO TRUSS BRIDGE FOR BETTER SEISMIC PERFORMANCE

The buckling restrained bracing (BRB) is widely used to improve seismic behavior of buildings. It is employed for bridges as well, but the application is very limited. The BRB can be used also as a damper, in which case the device may be called a buckling restrained damper (BRD). Yet such application has not been explored. There are quite a few bridges designed by the old design codes in Japan. Their seismic resistance may not be satisfactory for the current seismic design codes. Against this background, the behavior of a steel truss bridge under a large seismic loading is investigated by the nonlinear dynamic finite element analysis. Some members are indeed found damaged in the earthquake. Retrofit is needed. To this end, the application of the BRD is tried in the present study: a parametric study on the seismic behavior of a steel truss bridge with BRD is conducted by changing the length and the cross-sectional area of the yielding core of the BRD. The study concludes that with the application of well-designed BRDs to appropriate locations, a steel truss bridge could go through a large earthquake without damage.

Finite Element Study of Periodontal Ligament Properties for a Maxillary Central Incisor and a Mandibular Second Molar Under Percussion Conditions

PurposeThe quantitative percussion diagnostics (QPD) response of a mandibular second molar and a maxillary central incisor including their supporting ligament/bone structure was simulated using dynamic 3D finite element analysis (FEA). The focus of the work was on the role of the periodontal ligament (PDL) which acts as a damper in the dental structure and dissipates occlusal forces transmitted from the tooth surface to the surrounding bone.MethodsSeveral FEA models were developed to examine the effects of mechanical characteristics that have been reported for the PDL. Specifically, the effects of changing the PDL’s quasi-static elastic modulus and Rayleigh damping properties were predicted.ResultsThe present FEA simulations indicate that the PDL can significantly reduce forces for both the incisor and the molar compared to when there is no PDL (i.e. ankylosed tooth) as long as the quasi-static elastic modulus of the PDL is among the lowest reported (~ 0.1 MPa). In addition, the FEA simulations for both the incisor and molar with this lower value of the PDL quasi-static elastic modulus are also in reasonably good agreement with experimental percussion data. A simple approximation for partitioning Rayleigh damping properties between the hard and soft tissues was also found to provide reasonable values of overall damping that are consistent with experimental data.ConclusionThe overall findings indicate that using a quasi-static elastic modulus of approximately 0.1 MPa for the PDL in combination with Rayleigh damping gives realistic predictions of the mechanical response of a tooth under QPD loading conditions.

Analytical and numerical analysis of slamming induced vibrations on composite plates

Analytical solutions to study the elastic dynamic responses of a flat composite plate are developed based on the orthotropic thin plate theory and modal analysis. The spatial uniform slamming pressure is simplified to two types of time-dependent impact loads, i.e. an exponentially decaying impulse and a triangle impulses, which are characterized by the peak value and loading duration. To investigate the influence of the peak pressure and the loading duration on the plate structural behaviour, the dynamic responses of a simply supported flat plate under various impulses are calculated. Results show that the peak pressure affects only the amplitude of the response, while the loading periods affect both the phase and amplitude. Two numerical methods, i.e. a finite element dynamic analysis and a fully coupled hydroelastic analysis are applied to validate the analytical model and to investigate the hydroelastic effects. Comparisons of the analytical solution and hydroelastic analysis show that the slamming pressures on the flat composite plate fit the proposed triangle load model. With proper values on the peak pressure and loading period, the analytical model could provide good predictions on the structural deflections.

APPLICATION OF BUCKLING RESTRAINED DAMPER TO TRUSS BRIDGE FOR BETTER SEISMIC PERFORMANCE

The buckling restrained bracing (BRB) is widely used to improve seismic behavior of buildings. It is employed for bridges as well, but the application is very limited. The BRB can be used also as a damper, in which case the device may be called a buckling restrained damper (BRD). Yet such application has not been explored. There are quite a few bridges designed by the old design codes in Japan. Their seismic resistance may not be satisfactory for the current seismic design codes. Against this background, the behavior of a steel truss bridge under a large seismic loading is investigated by the nonlinear dynamic finite element analysis. Some members are indeed found damaged in the earthquake. Retrofit is needed. To this end, the application of the BRD is tried in the present study: a parametric study on the seismic behavior of a steel truss bridge with BRD is conducted by changing the length and the cross-sectional area of the yielding core of the BRD. The study concludes that with the application of well-designed BRDs to appropriate locations, a steel truss bridge could go through a large earthquake without damage.

Stress intensity factors, T-stresses and higher order coefficients of the Williams series expansion and their evaluation through molecular dynamics simulations

Molecular dynamics method and finite element analysis are applied for the analysis of the stress field in the neighborhood of the crack tip in a copper plate with a single edge notch. The molecular dynamics simulations implemented in a classical molecular dynamics code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) are aimed at evaluating classical continuum linear elastic fracture mechanics parameters such as stress intensity factors, T-stresses and higher order coefficients of the Williams power series expansion of the near crack stress field for Mode I, Mode II and Mixed Mode (Mode I + Mode II) loadings of the cracked specimen in isotropic linear elastic materials. The key objective of the study is the comparison of continuum and atomistic approaches for the estimation of the near crack tip fields using the example of one of the most common cracked configurations. Stress intensity factors, T-stresses and higher order coefficients of the Williams series expansion for a copper plate with the single edge notch under Mode I and Mixed Mode loadings are evaluated by atomistic modeling and by finite element method. The wide class of the computations in LAMMPS is performed. The atomistic values of stress intensity factors and higher order terms of the Williams series expansion are compared with the values obtained from the numerical solutions given by finite element method. It is shown that the continuum fracture theory successfully describes fracture and the near crack tip fields even at extremely confined singular stress field of only several nanometers. The angular distributions of the stress components from atomistic modeling are retrieved and compared with the angular distributions of the stresses from continuum linear elastic fracture mechanics. The comparison shows good agreement between two approaches.

A multiscale soft-contact modelling method for rough surfaces in contact with coupled slipping/sliding and rolling

This paper presents a multiscale soft-contact modelling (SCM) method for characterising the rough surfaces in contact with coupled slipping/sliding and rolling. The microscale flattening of the random surface asperities subjected to a plastically deformed substrate was accommodated by a statistical analysis with a dynamic explicit finite element analysis (FEA). A soft-contact algorithm was developed to effectively treat the cross-scale deformation of the microscopic asperities and that of the macroscopic body. An efficient modularised strategy including an input module and a hybrid SCM-FEA module was established to analyse the interaction at the interface of the two contacting bodies associated with coupled slipping/sliding and rolling. The modelling method was validated by a typical metal forming process, cold rolling of metal strips.

The study of soft soil seismic subsidence based on the 3D OpenSees model

AbstractSoft soils are characterized by high sensitivity, low strength, and susceptibility to seismic subsidence. In this study, nonlinear dynamic finite element analysis was performed using the OpenSees numerical simulation method to evaluate the seismic subsidence response of soft soil sites to ground motions. Higher peak acceleration of ground motion was found to enhance the degree of uneven seismic subsidence, depth of the seismic depression, and damage to the horizontal surface. The frequency characteristic of ground motion is another factor that influences the seismic subsidence of soft soil. Ground motions with low-frequency contents or high amplitudes lead to a more pronounced seismic subsidence of soft soil, particularly in the case of ground motion that exhibits frequency predominantly close to one of the soil sites. The findings of this study expand the current understanding of seismic subsidence of soft soil.