Nonlinear Dynamic Finite Element Simulations Research Articles

Fire‐Induced Collapse of Automated Rack‐Supported Warehouses

AbstractAutomated self‐supporting rack warehouses are becoming increasingly common in the international logistics sector. Their static and seismic design has been studied in the literature; however, the fire design still needs to be improved. Some Standards, such as the Eurocodes or Italian Fire Code, accept the collapse of rack warehouses during fires but require avoiding a progressive collapse or obtaining an implosive collapse regardless of any other active or passive fire protection systems. A hierarchy that guides the kinematics of collapse needs to be defined appropriately but without any Code going into further details. Moreover, the scientific literature focuses more on optimizing fire protection systems for racks, such as sprinklers, rather than preventing fire‐induced progressive collapse. Here, a case study is presented, which, using finite element modelling, provide a first robustness evaluation and highlights some possible aspects to be considered in the structural design to avoid a progressive collapse in the event of a fire. The analyses are performed using the LOCAFI method for localized fires and nonlinear dynamic finite element simulations.

Influence of aboveground structure on connected underground structure seismic response within an integrated system

Increasing numbers of integrated underground-aboveground structure systems (IUASS) are being constructed in densely populated urban areas. The complex dynamic interaction between the underground structure, its connected aboveground structure, and surrounding soil, brings challenges to the seismic design of such structure systems. This study aims to analyze the influence of an aboveground structure on a connected underground structure seismic response within an integrated system using nonlinear dynamic finite element simulations. The seismic response of an IUASS is compared with that of a single underground structure in both time and frequency domains, under the excitation of 9 seismic records and 0–10 Hz simple harmonic waves. The results reveal the sensitivity of the underground structure’s seismic response to the aboveground structure. Generally, the presence of aboveground structure can significantly increase the racking deformation and internal force of underground structure, particularly for the first underground story and for the underground spans directly below the aboveground structure. In such cases, the aboveground structure aggravates the tensile damage of first and second underground stories and overall compressive damage while alleviates the tensile damage of bottom story. However, when the input motion is dominated by high frequency content, the aboveground structure can act to reduce the underground structure seismic response.

Experimental and numerical assessment of welded steel beam-column connections under impact loading

This paper describes experimental and numerical investigations into the behavior of fully welded steel beam-to-column connections subjected to static and dynamic impact loads. The experimental assessment includes static and dynamic tests on four large-scale specimens, depicting two connection configurations incorporating different weld access-hole details. After providing a detailed account of the specimen details and testing arrangements, the main results and observations are presented and discussed. Particular emphasis is placed on assessing the static and dynamic forces, displacement response, and energy dissipation. Additionally, in order to provide further insights into the performance, detailed nonlinear dynamic finite element simulations are carried out and compared against the experimental results. The validated finite element models are employed in order to examine the effects of the local weld detail on the behavior of the connection, in terms of sectional internal forces and energy absorption under impact loading conditions. The numerical model is also adopted within a parametric assessment to develop a simplified relationship between the plastic rotation of the connection and the input impact energy, for use in practical application.

Research on the simulation modelling of high‐voltage switchgear ring‐shaped spring contact force

In order to explore the simulation method of the contact force for the ring-shaped spring and provide the support for the design of high-voltage switchgear-rated current and mechanical operating power, the parametric equation was derived, based on NX software the three-dimensional model was built, considering the influence of contact, friction, and large deformation, the non-linear dynamic finite element simulation model for the process of assembling and operating was established, the stress, resistance force, and friction force at any moment were obtained by simulation, and the variation of resistance and friction force during contact insertion was analysed. The results show that during the mechanical operating process, the resistance force rapidly increased to the extreme value and then gradually decreased to a stable value of 238N, and the friction force quickly increased and then slowly rose to the steady value of 238N, which is consistent with the experience and proved the rationality of the simulation model. Finally, according to the Coulomb friction law, the contact force of the spring contact was calculated as 1190N.

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.

Blast test and numerical simulation of point-supported glazing

The blast resistance of point-supported laminated glass curtain wall has been investigated by means of field blast tests and numerical simulation. Nine site blast tests were carried out, considering two types of glass thickness and six TNT charges ranging from 0.4 to 30 kg. The overpressure and displacement time histories were measured and the failure modes were observed. The overpressure obtained from the measurement panel exhibited a typical pattern of near-field blast with a steep increase followed by a rapid decay within a few milliseconds. The displacement response of the laminated glass panels increased with the increase in the TNT charge almost linearly in the smaller tests (scaled distance ranging 4.5–7 m/kg1/3), which was in line with the increase in the blast impulse in these tests. The failure mode of the point-supported laminated glass panels was featured by tearing off of the polyvinyl butyral layer around the support area, while the glass shards still adhered to the polyvinyl butyral interlayer. Nonlinear dynamic finite element simulation agrees reasonably well with the results from the blast tests. Severe stress concentration has been predicted to occur at the rim of the support holes, leading to initiation of failure at these supports, and this also agrees with the failure mode observed from the blast test. Finally, parametric studies are carried out to investigate the influence of TNT charge weight and the geometric parameters of the panel on the blast response of the glass curtain wall.

Computing the stresses and deformations of the human eye components due to a high explosive detonation using fluid–structure interaction model

IntroductionIn spite the fact that a very small human body surface area is comprised by the eye, its wounds due to detonation have recently been dramatically amplified. Although many efforts have been devoted to measure injury of the globe, there is still a lack of knowledge on the injury mechanism due to Primary Blast Wave (PBW). The goal of this study was to determine the stresses and deformations of the human eye components, including the cornea, aqueous, iris, ciliary body, lens, vitreous, retina, sclera, optic nerve, and muscles, attributed to PBW induced by trinitrotoluene (TNT) explosion via a Lagrangian-Eulerian computational coupling model. Materials and methodsMagnetic Resonance Imaging (MRI) was employed to establish a Finite Element (FE) model of the human eye according to a normal human eye. The solid components of the eye were modelled as Lagrangian mesh, while an explosive TNT, air domain, and aqueous were modelled using Arbitrary Lagrangian-Eulerian (ALE) mesh. Nonlinear dynamic FE simulations were accomplished using the explicit FE code, namely LS-DYNA. In order to simulate the blast wave generation, propagation, and interaction with the eye, the ALE formulation with Jones-Wilkins-Lee (JWL) equation defining the explosive material were employed. ResultsThe results revealed a peak stress of 135.70kPa brought about by detonation upsurge on the cornea at the distance of 25cm. The highest von Mises stresses were observed on the sclera (267.3kPa), whereas the lowest one was seen on the vitreous body (0.002kPa). The results also showed a relatively high resultant displacement for the macula as well as a high variation for the radius of curvature for the cornea and lens, which can result in both macular holes, optic nerve damage and, consequently, vision loss. ConclusionThese results may have implications not only for understanding the value of stresses and strains in the human eye components but also giving an outlook about the process of PBW triggers damage to the eye.

Simulation of 3D needle-tissue interaction with application to image guided prostate brachytherapy

To improve global control of disease and reduce global toxicity, a complex seed distribution pattern should be achieved with great accuracy during brachytherapy. However, the interaction between the needle and prostate will cause large deformation of soft tissue. As a result, seeds will be misplaced, sharp demarcation between irradiated volume and healthy structures is unavailable and this will cause side effects such as impotence and urinary incontinence. In this paper, a 3D nonlinear dynamic finite element simulation method with application to robot-assisted image guided brachytherapy is proposed. A magnetic resonance imaging (MRI) based simulation model is built which considers real patient data, nonlinear material property and interaction between the needle and soft tissue. The sensitivities of seed placement error to the needle insertion point, needle orientation and insertion distance are analysed. The result shows that shorter distance between insertion point and target position with compensation in distance can reduce placement error effectively. This method can be used as a complementary instruction for robot-assisted image guided brachytherapy.

Nonlinear dynamic simulations of progressive collapse for a multistory building

The paper presents a case study of progressive collapse analysis of a selected multistory building. The subject of the numerical study is an existing 8-story steel framed structure built for fire tests in the Cardington Large Building Test Facility, UK. The problem is investigated using nonlinear dynamic finite element simulations carried out following the GSA guidelines. The paper focuses on model development for global models subject to increasing vertical loading and notional column removal. Taking advantage of parallel processing on multiprocessor computers, a detailed 3D model with large number of finite elements has been developed for the entire structure. The objective of the presented feasibility study is to identify modeling parameters affecting the final result (potential of progressive collapse) and propose a hierarchical verification and validation program for reducing outcome uncertainties.

Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes

The variation characteristics of dynamic stress in crustal blocks and its relationship with earthquakes are comprehensively studied by analyzing geophysical data and calculating the dynamic response of crustal blocks in North China to the tide level change of Bohai Sea and Yellow Sea using a 3D nonlinear dynamic finite element simulation. This study has noticed some new features of crustal dynamic stress: (a) High stress level appears at the place where the stress waves superpose and interference during the process of propagation, and the enhancement of dynamic shear stress is more significant as compared with that of compressive stress; (b) Variation of dynamic stress has influence on seismogenic environment and hence earthquake occurrence; (c) As viewed from the variation characteristics of crustal dynamic stress, the superimposing process of shear stress manifests the preparation process of earthquakes.