Force Time Histories Research Articles

Dynamic response of single curved fiber-metal hybrid lamina composites subject to low-velocity impact

Fiber-metal hybrid lamina composites (FM-HLCs) are a new kind of fiber-metal composites, which aims at addressing the metal-composite interface failure in conventional fiber-metal laminates. In the current study, the low-velocity impact tests were conducted to examine the dynamic response of single curved FM-HLCs. The influence of weave pattern of fiber-metal hybrid lamina, impact velocity and radius of curvature on the dynamic response is considered in the experiment. The deformation/failure modes, force-time histories and energy absorption were obtained. The high-speed cameras were used to capture the deformation/failure processes of FM-HLCs and the instantaneous images for digital image correlation analysis. The results indicate that the “fiber-metal hybrid lamina” strategy can efficiently help maintain the integrity of FM-HLCs outside the impact region. The increase of fiber content can efficiently decrease the deformation/failure region and permanent deflection of FM-HLCs, thus, enhancing its impact resistance. When the fiber content along circumferential and longitudinal directions is not consistent or the radius of curvature decreases, there forms an elliptical deformation region of FM-HLCs. The current work is expected to be of significance for the follow-up research and the potential applications of FM-HLCs. In addition, it is also a good reference for investigating the dynamic response of orthotropic panels/shells under low-velocity impact.

Response-based bridge deck limit state considering component-level failure under extreme wave

Coastal bridges are crucial components of transportation systems; however, they are susceptible to increasing failure risk from extreme waves due to climate change scenarios. Previously, most of the studies focused on the extreme wave forces on the bridge superstructure, while the effects of the overturning moment, bearing constraints, and local damage were seldom discussed. This research conducts an in-depth investigation on the wave-bridge interaction to explore the structural limit state of the coastal bridges subjected to extreme waves considering component failure. Firstly, a three-dimensional (3D) Computational Fluid Dynamics (CFD) model is established and validated to simulate the wave-bridge interaction under various wave scenarios. To lend confidence to the CFD model, laboratory experiments are conducted to improve and validate the simulation results. Subsequently, based on the numerical results, wave force prediction methods are proposed by considering the solitary wave characteristics. Accordingly, the time histories of wave forces are imported into a spatial Finite Element (FE) model of the investigated bridge FE model to compute dynamic structural responses, including bearing reaction forces, bridge displacements, and bearing working states. Then, based on the dynamic structural response, a novel structural limit state incorporating component damage is developed to prevent bearing damages under the wave impacts and corresponding structural demand is parametrically studied and quantified with different wave parameters. Such a study could help optimal and robust designs of coastal bridges and modifications of existing ones.

Wind Forces and Flow Patterns of Three Tandem Prisms with a Small Height–Width Ratio

Wind tunnel tests and large eddy simulations were conducted to investigate the dependency of wind forces and flow patterns on the spacing (S) for three tandem prisms with a small height–width ratio H/W = 0.4. At the spacing ratio S/W = 0.7, mean and root-mean-square drag of downstream prisms have large local peaks, and their magnitudes are larger than those at adjacent spacing ratios; these should be noted to ensure the safety and economy of the wind-resistant design of prism-like low-rise buildings. These phenomena are different from that of a small group of tandem prisms with a large H/W and a large group of tandem prisms with a small H/W. At S/W = 0.7, tap pressure time histories of downstream prisms are non-stationary with abrupt changes, but wind force time histories of downstream prisms are stationary, unlike a small group of tandem prisms with a large H/W, where both tap pressure and win d force time histories are non-stationary. Above phenomena at S/W = 0.7 are attributed to a special asymmetric time-averaged wake regime, which has two modes with symmetric wake flow directions and they irregularly switch. The duration of each mode is ruleless. This special wake regime was not observed in previous studies on tandem prisms.

Experimental and numerical investigation on wave impacts on box-girder bridges

Climate change could result in more extreme weather events and induce increasing challenges to the low-lying coastal bridges. The structural performance of box-girder bridges under wave impacts was seldom investigated. In this paper, a three-dimensional (3D) computational fluid dynamics (CFD) model is established to simulate the wave-bridge interactions, and laboratory experiments are conducted to investigate wave impacts on a bridge. The experiments and 3D CFD simulations are unique as compared with other relevant studies since they provide the complex wave-bridge interactions through dynamic and spatial analyses. Specifically, time histories of vertical and horizontal wave forces are measured through experiments. The time-dependent pressure distributions, wave-induced forces, and overturning moments on the bridge model are computed with the CFD model. The effects of different parameters on the maximum wave forces are discussed. Also, comparisons of the differences between two-dimensional (2D) and 3D CFD models are conducted. Then, the results are converted to a prototype scale to explore the effects of wave impacts, and prediction formulas are proposed accordingly. This study combining experimental and 3D numerical investigations could help improve understanding of the wave-bridge interaction mechanism, and further aid the optimal and robust designs of coastal bridges.

Structural behavior of piles under vehicular collision load on bridge substructure – A case study

Vehicular collision is one of the leading causes of structural failure and the large impact loading leads to failure of the bridge structure. Therefore, the structural behavior of bridge substructure including the piles is the chief topic in this paper. Numerical finite element analysis (FEA) software ANSYS was used for simulating the FE model. This paper describes a numerical analysis of the pile structural behavior of a bridge substructure under vehicle collision as a case study. The aim of this case study was to evaluate the response of the bridge substructure and soil to impact loading as well as to discuss the interaction between soil and piles. Validation of the model was conducted by comparing the experimental result from pendulum impact test with the numerical result from FEA software. Detailed 3D FE models of the bridge superstructure, substructure, and soil were developed for this purpose. The bridge model was developed on the basis of the verified model’s material detail and contact types. A half-length bridge deck with two piers was supported at the bottom edge. Pile caps and piles were embedded into rectangular soil. Soil springs were also defined to emulate the behavior of soil. An impact force-time history was subjected to the bridge pier; the response of bridge substructure and soil are also discussed. The numerical FE bridge model is able to provide an explanation of the displacement of bridge substructure and soil. Responses of the bridge substructure and soil were primarily concentrated the lateral displacement, vertical displacement, and equivalent stress. This response was investigated in accordance with the length, height, and depth of the bridge structure component. In addition, the soil–pile interaction under vehicular collision was also inspected. On the basis of the obtained results, it can be deduced that the soil is affected by the movement of piles and the soil itself after being subjected to the impact load.

DNS of the spatiotemporal evolution of the vorticity in (pure) mode B of a circular cylinder’s wake

In the present paper, the spatio-temporal evolution of the vorticity field in the second wake instability, i.e. (pure) mode B is investigated to understand the wake vortex dynamics and sign relationships among the three vorticity components. Direct numerical simulation of the flow past a circular cylinder in the three-dimensional (3D) wake transition is performed, typically at a Reynolds number of 300. According to the time histories of fluid forces and frequency analysis, three different stages are identified. In the fully developed wake (FDW), the spanwise vortex core is almost two-dimensional, while the vortex braid is 3D due to the dominant streamwise interaction. However, streamwise and vertical vorticities owing to the intrinsic 3D instability are already generated first on cylinder surfaces early in the computational transition (CT). The evolution of additional vorticities with the same features as mode B shows that (pure) mode B could already be formed in the late CT. In the FDW, a special sign symmetry of these additional vorticities on the rear surface is observed, which is exactly opposite to that in (pure) mode B. Similarly, the two sign laws found in (pure) mode A are also verified in three typical regions, independent of the Reynolds number, for (pure) mode B. Particularly, the mechanism for the physical origin of streamwise and vertical vortices in the shear layers is the vortex generation on the wall first and then dominant vortex induction just near the wall. The entire process of the formation and shedding of vortices with three components of vorticity is first and completely illustrated. Other characteristics of the evolution of mode B are presented in detail.

Effects of Barrier Stiffness on Debris Flow Dynamic Impact—II: Numerical Simulation

The destructive and impactful forces of debris flow commonly causes local damage to engineering structures. The effect of a deformable barrier on the impact dynamics is important in engineering design. In this study, a flow–structure coupled with Smoothed Particle Hydrodynamics model was presented to investigate the effects of barrier stiffness on the debris impact. A comparison of the results of physical tests and simulation results revealed that the proposed smoothed particle hydrodynamics model effectively reproduces the flow kinematics and time history of the impact force. Even slight deflections of the deformable barrier lead to obvious attenuation of the peak impact pressure. Additionally, deformable barriers with lower stiffness tend to deform more downstream upon loading, shifting the deposited sand toward the active failure mode and generating less static earth pressure. When the debris flow has a higher frontal velocity, the impact force on the barrier is dominated by the dynamic component and there is an appreciable effect of the stiffness of the deformable barrier on load attenuation.

An efficient axial-flexure-shear fiber beam model for dynamic analyses of beam–column framed structural systems under impact loading

Impact loadings induced by collisions from an external impacting object (e.g. a vessel, a vehicle) severely threaten the safety of our infrastructural systems such as bridges and buildings. It is therefore critical to develop effective strategies to quantify the impact loadings and dynamic structural responses so that the safety of structures can be pre-estimated. Although the extensively used finite-element simulations can generally provide realistic predictions of impact forces and dynamic responses of structures subjected to vessel or vehicle collisions, they are often computationally expensive. Therefore, the development of computationally efficient simplified impact models using macro-elements has drawn the attention of many researchers. This paper aims to develop a more general-purpose simplified impact model for dynamic analyses of beam–column framed structural systems under impact loading with consideration of shear effects in beam–column members. The well-known Timoshenko beam theory is adopted to develop a fiber beam model that couples the axial, flexural and shear actions in beam–column members at the fiber and material level. A parametric study is then conducted to thoroughly assess the numerical performance of the proposed simplified impact model using several sets of circular columns with different cross-section diameters and height–diameter ratios under the impact from a barge vessel, the complex finite-element model of which was developed and validated by the author previously. The study indicates that the proposed simplified impact model using the axial–flexure–shear fiber beam model enables a sufficiently accurate prediction of the time-histories of impact forces and dynamic responses of both flexure-dominant high columns and shear-dominant short columns under different impact scenarios.

Research on Analysis Method of Shock Absorption Behavior of Cellular Solid in Volumetric Contact

This study proposes a numerical analysis model that considers volumetric contact in cellular solid such as metal foam. Volumetric contact refers to contact with uneven or curved surfaces. The proposed analytical model is based on a motion analysis method of multibody system with contact and yield using linear complementarity problem. The current analytical method assumes surface contact. In order to consider volumetric contact, a discrete analytical model is proposed. In addition, the tearing phenomenon of cells observed in indentation tests is used to express the yield force by introducing tearing energy in addition to the stress required for compression. Numerical analysis was performed on the proposed analytical model. Numerical analysis was performed assuming the case of carbon steel crashing on a portion of aluminum foam so that deformation occurs in the unevenness. The volumetric contact is evaluated from the analysis results of time history of plastic strain and contact force.

Nonlinear Response and Collapse Analysis of Double‐Channel Aqueduct under Strong Earthquake

As a common water conveyance structure, aqueduct is widely used in cross‐regional water conveyance and diversion projects. However, large double‐trough aqueduct structures are prone to damage under earthquake, resulting in water leakage and even interruption, endangering the safety of people’s lives and property in surrounding areas. In this paper, the nonlinear reinforced‐concrete material program is compiled based on the FORTRAN language. Taking the Shuangji River aqueduct project as an example, the numerical model of the fiber beam element of the double‐trough aqueduct structure is established, and the nonlinear dynamic time‐history response analysis of different ground motion inputs is carried out. Based on the midspan displacement and acceleration time history, pier bottom bending moment and shear force time history, the nonlinear response law of large aqueduct structure is studied. A criterion for determining the overall collapse of aqueduct structure based on effective energy is proposed. The correctness and feasibility of the nonlinear numerical model of the aqueduct structure and the dynamic catastrophe analysis method are verified by focusing on the overall seismic response of the aqueduct structure and the material yield status of key parts, and comparing with the collapse criterion based on the limit value of pier top displacement angle. The conclusions will provide a basis for seismic analysis, optimization design, and operation and maintenance safety assessment of large aqueduct structures and have important theoretical significance and engineering application value.

Pendulum impact loading tests of precast concrete columns with various column base connections

In the present study, pendulum impact loading tests were performed to investigate the lateral impact resistance of precast concrete (PC) columns with various column base connections. To maintain axial compression force during the impact process and subsequent collapse, a set of specially designed loading facility with solid counterweights was proposed. The test parameters included three PC columns using grouted sleeve connection (PC1), lap splice in grout-filled hole connection (PC2), and bolt connection (PC3), and a cast-in-place concrete (RC) column as a counterpart specimen. The dynamic responses including the damage mode, crack development process, impact force–time history, deflection-time history, strain–time history, and acceleration-time history were investigated. Further, the energy dissipation and stress wave transmission law of the specimen were analyzed. The test results showed that semi-rigid boundary conditions of PC columns decreased the column damage, but the lateral deformation increased, indicating relatively low impact resistance. The mechanical performance of each PC connection method was also discussed.

ANALYSIS OF THE WATER IMPACT OF SYMMETRIC WEDGES WITH A MULTI- MATERIAL EULERIAN FORMULATION


 
 
 The two-dimensional hydrodynamic problem of a symmetric wedge vertically impacting in calm water is analysed by using an explicit finite element method based on a multi-material Eulerian formulation. The slam-induced loads on wedges with different deadrise angle at a constant velocity are calculated, including pressure distribution, maximum pressure coefficient, force coefficient and time history of vertical force, which are compared with available theoretical and analytical results. The time evolution of pressure distribution and free surface elevation are presented. Furthermore, the effects of impact velocity are investigated. It shows that this method is capable of predicting the local slamming loads, and as well assessing the effects of the deadrise angle and the impact velocity on the slamming pressure for the wedge-shape section.
 
 

Numerical study on breaking solitary wave force on box-girder bridge

Solitary wave is often used to simulate tsunami propagating in deep water and breaking solitary wave is often used to simulate tsunami bore propagating in shallow water or on land. The breaking solitary wave force on box-girder, which has been widely used in bridge engineering in coastal areas of China, receives few attentions. This study aims to investigate characteristics and generation mechanism of breaking solitary wave force on box-girder numerically. A numerical wave flume with a 1:20 slope was built firstly, then the solitary wave generation ability, wave deformation and wave breaking on the slope, as well as wave force calculation precision, are validated. The water depth 0.6 m, the slope gradient 1:20 and the distance between slope top and box-girder 2.0 m remain unchanged, while the wave height and clearance changes in different cases. The time histories of horizontal force and vertical force on box-girder can be divided into three and four stages respectively according to their characteristics. The surface of box-girder is decomposed into a series of panels to facilitate exploring tsunami bore force generation mechanism. Results show horizontal force is dominated by static pressure on upstream vertical panels and vertical force is mainly contributed by static pressure on upstream horizontal panels and on panels in the chambers. Tsunami bore overtopping the box-girder deck impacts the top panel vigorously and results in the peak value of negative vertical force.

Data Filtering in Vehicle–Bridge Impact Simulations: Evaluation of Different Force Filtering Methods and Recommendations

Abstract The impact force time history obtained from a crash test or high-fidelity simulation is usually contaminated by numerical noise. The noise signal usually appears as a series of short durat...

Experiment and Simulation Study on the Dynamic Response of RC Slab under Impact Loading

Reinforced concrete (RC) slab is an important component in civil construction and protection engineering, and its dynamic response under impact loading is a complex mechanical problem, especially for two or multiple continuous impact loads. In this paper, a series of drop hammer impact tests were carried out to investigate the dynamic response of RC slabs with two successive impacts. The time history of impact force and the failure characteristic of the slab surface were recorded. Moreover, four influence factors, including slab thickness, reinforcement ratio, impact location, and drop hammer height have been discussed. Besides, a 3D numerical model based on the finite element method (FEM) was established to expand the research of constrained force, deflection, and vertical stress of an RC slab. The results show that increasing the slab thickness and reinforcement ratio can improve the impact resistance of an RC slab. The impact point location and drop hammer height have a great influence on the dynamic response of the RC slab. In addition, the RC slab will have more obvious damage under the second impact, but the dynamic response becomes weaker. It may be because of the local damage in the concrete caused by the first impact that would weaken the propagation of vibration.

MEM vs. FEM: practical crashworthiness insights for macro element modelling applied to sub-assembly and full vehicle automotive structures

This paper proposes a modelling approach for integral vehicle structures, applied to frontal crash loading, based on the Macro element approach. Addressing the idealisation of complex sub-structures and full vehicle was through identification of critical parameters for conversion of validated FEM into MEM equivalents through sensitivity analyses. Two examples of impact onto rigid barriers are presented; 1). Frontal crash energy management system (consisting crush-can and longitudinal engine rail), impacting at 8.6 m/s and 2). A complete vehicle impact at 56 km/hr (15m/s). Both case studies predict key features of collapse, with force-time histories agreeing within ±10–15% against FEM. Case study 1 required a 3 second solution time versus 1.5 h (8CPUS) mass-scaled FEM (105k element). For Case study 2, MEM required 7.5mins versus 16.5 hrs for a 3 M element FEM vehicle. For all simulations, LS-DYNA R10.0 and Visual Crash Studio R4.0 used. Developing a framework to overcome accuracy/stability problems, together with issues related to robustness and error reduction is discussed. Model complexity was progressive, involving a-priori knowledge of collapse and/or analysing several sub-assemblies to guide idealisation. The level of agreement demonstrates the advantages of MEM as a complementary method to support conceptual vehicle design and offers significant advantages for design exploration, particularly across multiple crash certification cases. Highlights Idealisation of complex sub-structures into Macro element modelling (MEM) equivalents using high fidelity finite element models (FEM) Methodology based on critical parameters for conversion of validated FEM into MEM Proposed MEM conversion for complete vehicle frontal impact onto a rigid barrier Correlation of critical parameters with structural behaviour through sensitivity analyses MEM error in force-time histories within 10–15%, relative to high fidelity FEM FEM Solution times reduced from several hours to several minutes for MEM equivalents

Ballistic Limit of Sandwich Plates With a Metal Foam Core

Abstract The ballistic perforation of sandwich plates comprising two identical/unidentical aluminum alloy face sheets and an aluminum foam core is investigated to gain insights into the factors governing the penetration processes. The impact velocities of projectiles with conical, flat, and hemispherical noses range from 60 ms−1 to 220 ms−1 in the experiments. Against conical-ended projectiles, petalling failure is found to be an active failure mode at the rear face sheet. Against projectiles with flat and hemispherical noses, both petalling failure and petalling-flipped-cover failure are observed. Finite element simulations considering the effect of foam meso-structure on the ballistic limit of sandwich plates are performed and validated against the experimental results. It is shown that the local bending and fracture of the cell walls significantly dissipate the kinetic energy of the projectile and restrain the occurrence of the high stress regions. Characteristic double-peak and single-peak modes of contact force time histories are observed for projectiles with various nose shapes. It is also found that a sandwich plate with thicker front face sheet has higher ballistic resistance, which may facilitate the instructional arrangement of face sheets with regard to mass distribution to achieve higher ballistic resistance. Finally, a three-stage theoretical model based on energy balance principle is developed for each type of projectile to predict the residual velocities after perforation of sandwich plate.

Моделирование воздействия объекта малого космического мусора на защитный экран трансформируемой ловушки

The growth in the number of space debris, especially small-size debris undetectable by radars, urges the development of protective equipment for the crucial satellites and space station. Passive multilayer shields are the most effective means of protection. As the shields are big, it makes sense to make them out of flexible composite materials that allow them to be deployed in orbit. The article determines the loads acting on the composite load-bearing frame of the trap for small-size debris during impact. For a rational choice of the structural trap layout and optimization of its design parameters it is critical to know these loads. The hypervelocity impact of the projectile on the shield was modeled in the Altair Radioss software package using a combined model based on the Smoothed Particle Hydrodynamic (SPH) method and mesh finite elements. The simulation of the shield penetration at various locations was carried out. For each simulation case, a time history of the reaction force in the attachment point of the protective shield to the load-bearing frame was determined. It was shown that the maximum load of about 2000 N acts for around 6 milliseconds on the joint closest to the impact point for the debris projectile size of 10 mm and velocity of 2 km/s.

Numerical simulation of the dynamic launching process for high-altitude balloons

Abstract In this paper, we establish a mathematical model to simulate the dynamic behavior of the high-altitude zero-pressure balloon system during the ground dynamic launching process. The dynamic launching mathematical model includes the solution of the bubble shape and the dynamics model derived by taking the bubble, the membrane bundle, the cable, and the gondola as a whole. The bubble shape is considered as a combination of zero circumferential stress shape at the bottom and fully expanded shape at the top. Under the hypothesis, we use the multiple shooting method and the sequential quadratic programming method together to solve the partially expanded shape in the lower bubble region. Based on bubble shapes, the bubble is modeled as a “spring damping system” and we can establish its dynamic model. The “membrane bundle-cable system” is equivalent to a variable mass rope structure and we solve its dynamic behavior by using the mass particle model. We calculate the swing angle of the gondola by its geometry constraint and force analyses. The Hertz contact model and the Coulomb friction law are used to analyzing the contact between the “membrane bundle-cable system” and the ground or the main boom of the launching vehicle. Based on these dynamic models, we calculate the dynamic launching simulation under three operating conditions of the launching vehicle, which corresponds to three ambient wind speeds. The three operational modes of the launching vehicle are the static operation (2 m/s wind speed), the forward operation to chase the bubble (4 m/s), and the backward operation to increase the gondola releasing angle (0 m/s). We analyze the influence of the wind speed and the launching vehicle action on the force and geometric time history of the dynamic launching system. Furthermore, we discuss the three times typical overload in the dynamic launching system and its influencing factors, which are the opening of the roller, the straightening of the “membrane bundle-cable system” and the releasing of the gondola. The purpose of this paper is to present a set of methods and models for the dynamic launching simulation. It not only calculates the shapes of the bubble and simulates the motion of the quasi rope structure system individually, but also the bubble, the “membrane bundle-cable system” and the gondola are combined to establish a complete set of dynamic models to reflect the main characteristics of the dynamic launching process.

Earthquake response of linear-elastic arch-frames using exact curved beam formulations

PurposeThis study aims to obtain earthquake responses of linear-elastic multi-span arch-frames by using exact curved beam formulations. For this purpose, the dynamic stiffness method (DSM) which uses exact mode shapes is applied to a three-span arch-frame considering axial extensibility, shear deformation and rotational inertia for both columns and curved beams. Using exact free vibration properties obtained from the DSM approach, the arch-frame model is simplified into an equivalent single degree of freedom (SDOF) system to perform earthquake response analysis.Design/methodology/approachThe dynamic stiffness formulations of curved beams for free vibrations are validated by using the experimental data in the literature. The free vibrations of the arch-frame model are investigated for various span lengths, opening angle and column dimensions to observe their effects on the dynamic behaviour. The calculated natural frequencies via the DSM are presented in comparison with the results of the finite element method (FEM). The mode shapes are presented. The earthquake responses are calculated from the modal equation by using Runge-Kutta algorithm.FindingsThe displacement, base shear, acceleration and internal force time-histories that are obtained from the proposed approach are compared to the results of the finite element approach where a very good agreement is observed. For various span length, opening angle and column dimension values, the displacement and base shear time-histories of the arch-frame are presented. The results show that the proposed approach can be used as an effective tool to calculate earthquake responses of frame structures having curved beam elements.Originality/valueThe earthquake response of arch-frames consisting of curved beams and straight columns using exact formulations is obtained for the first time according to the best of the author’s knowledge. The DSM, which uses exact mode shapes and provides accurate free vibration analysis results considering each structural members as one element, is applied. The complicated structural system is simplified into an equivalent SDOF system using exact mode shapes obtained from the DSM and earthquake responses are calculated by solving the modal equation. The proposed approach is an important alternative to classical FEM for earthquake response analysis of frame structures having curved members.