Impulsive Loading Research Articles

Relationship between ankle–foot-complex mobility during static loading and frontal moment impulses of knee and hip joints during the stance phase

BackgroundAnkle–foot-complex mobility impairments, which can be assessed by the difference between the sitting and standing positions, are related to an increase in the load on the knee and hip joints during the stance phase of the gait. Research questionWhat is the relationship between the ankle–foot-complex mobility during static weight bearing and the mechanical stresses on the knee and hip joints throughout the stance phase? MethodsAnkle–foot-complex mobility and gait data were collected from 26 healthy adults. The complex mobility was established by comparing the foot indices, measured using a three-dimensional foot scanner, in sitting and standing positions. The gait data were acquired using eight cameras (recording at 100 Hz) and three force plates (recording at 1000 Hz). Stance phase data were collected via ground reaction forces. The stance phase was dissected into shock absorption and propulsion phases, during which the external knee and hip adduction moment impulses (KAMi, HAMi) were recorded. The correlation between the ankle–foot-complex mobility during static weight bearing and KAMi and HAMi during the stance phase was examined using Pearson's product–moment correlation coefficients. ResultsThis study revealed that KAMi correlated with medial malleolus mobility (r = −0.44) throughout the stance phase. Furthermore, in the propulsive phase, KAMi correlated with calcaneus (r = 0.51) and navicular (r = −0.50) mobilities, whereas HAMi correlated with calcaneus mobility (r = −0.40). SignificanceThe study provides insights into the relationship between the static mobility of the ankle–foot complex in healthy individuals and mechanical stress during the stance phase. Calcaneus and navicular mobilities were related to efficient push-off in the propulsive phase. Medial malleolus mobility was related to the control of the lateral tilt of the lower limb and ankle dorsiflexion motion throughout the stance phase.

Highly Transparent Piezoelectric PVDF Electrospun Membranes

In this work, electrospun membrane with excellent optical transparency has been developed and the study focuses on the optical and electromechanical properties of the membrane. Highly transparent PVDF based membrane fabricated by electrospinning exhibited appreciable piezoelectric property. Thus the study mainly focus on the multifunctional behaviour of these nanomembrane in the field of transparent sensors and energy harvesting systems. The transmittance of the fabricated membrane is measured using spectrophotometer and beta sheets content associated with the piezo activity of the membrane is measured using the Fourier Transform Infrared spectra. The surface characterization of the electrospun membrane were performed using Scanning Electron Microscope (SEM). The piezo response range of these membrane were tested using impulse loading and force voltage-based measurements. The utilization of these transparent optical membranes in the field of micro and nanoenergy harvesting systems based on piezoelectric transduction mechanism is focused.

ДИНАМІЧНІ ВИПРОБУВАННЯ МОСТІВ ІМПУЛЬСНИМ НАВАНТАЖЕННЯМ

Introduction. This article deals with the practice of applying the method of dynamic testing of bridges, namely, modal control using impulse loading. The possibilities of this method for determining the technical condition of a bridge span structure by determining its natural characteristics: actual stiffness and parameters of natural vibration forms are shown. Problem Statement. The article is devoted to the problem of practical implementation of the latest theoretical developments in the field of diagnostics of the technical condition of road bridges by conducting full-scale dynamic tests. Purpose. The main purpose of the article is to demonstrate the effectiveness of dynamic impulse testing as a method for assessing the technical condition of bridges. The method involves the excitation of vibrations of bridge structures by means of pulse loads, recording the response of the structure and analyzing the data obtained. Materials and methods. The material for this article is the results of field tests of a curved overpass made of monolithic reinforced concrete located near Kyiv. The following research methods were used: information analysis, mathematical modeling, and general methods of theoretical research.

Empirical scaling of formation fracturing by high-energy impulsive mechanical loads

Recent technological advances to trigger high-energy seismic waves from within the wellbore have spurred interest in their potential application to induce fracturing within deep subsurface formations. Although a considerable body of experimental observations at the bench scale (on the order of 1 cubic foot) show promise, there remains considerable uncertainty in how the process may scale to the field. This work characterizes the relationship between the extent and intensity of fracturing and the duration and strength of the dynamic load. Our approach uses a direct numerical simulation of the elastodynamic equations while accounting for nonlinear fracture mechanics. A hybrid Finite-Discrete Element Method (FDEM) is applied whereby cohesive (elastoplastic) laws hold mesh elements together until complete failure. Beyond failure, elements act as deformable free bodies that can interact via contact constraints, including friction. The consistency of the model is first verified and it is validated with observations from previously reported physical experiments. Subsequently, we apply the model to conduct a numerical exploration of the dimensionless parameter space that defines plausible loading waveforms. We model an infinite domain that contains a spherical inclusion within which various impulsive loads are applied. The dynamic loading waveform is parameterized by its rise time to peak stress, followed by a decay period, and occurring within micro- to milliseconds. The dimensionless parameter space is sampled by varying loading characteristics (rise time, peak pressure, and impulse) to reveal the stimulated damaged bulk volume and crack intensity. Consistent with reported experimental observations, the model reproduces a nearly linear trend between the radius of damage and the maximum stress on the bench scale. Beyond that scale, however, the model predicts that this scaling slows considerably to a fractional power law between the damaged radius and the peak stress. This limitation coincides with a geometric increase in the intensity of damage within the stimulated volume. We present loci curves of the expected damage radii as functions of the loading waveform properties.

Nonlinear dynamic analysis of a geometrically imperfect sandwich beam with functionally graded material facets and auxetic honeycomb core in thermal environment

In this study, a model for the nonlinear dynamic analysis of the geometrically imperfect sandwich beam with functionally graded material (FGM) facets and auxetic honeycomb core is proposed. The auxetic feature of the honeycomb material is realized by a homogenization method, which gives the expressions of the effective material coefficients in terms of material property and cellular geometric parameters. The nonlinear motion equation of the geometrically imperfect beam is derived based on the Reddy's higher shear deformation theory, von Kármán nonlinear theory, as well as general geometric imperfection function. The thermal effect on the material properties and structural rigidity is also taken into account in this model. The Newmark method and Newton–Raphson iterative method are employed to solve the nonlinear motion equation of the sandwich beam. In numerical examples, the dynamic response of the sandwich beam under two types of load, i.e. moving load and impulse load, are discussed in details. The influences of various factors (such as material parameter, geometric imperfection, and thermal condition) on the nonlinear dynamic behaviors of the sandwich beam are elaborately investigated. The numerical results show those factors can play significant roles in the bearing ability, structural stiffness, or nonlinear dynamic behaviors of the sandwich beam in certain conditions. Some key conclusions on the influences are drawn from the numerical results, which can be a useful reference for future investigations.

Electrical microparticle acceleration by high-speed membrane deformation

In this study, we conducted experiments to explore the potential of a low-power exploding foil initiator for accelerating microparticles through high-speed membrane deformation. This involved the use of a conductive layer with a conversion section known as a “bridge,” which was positioned between the substrate and the cover layer. The application of pulsed electrical energy led to Joule heating at the bridge, while the vaporized gas generated impulsive loading, resulting in the deformation of the cover layer. According to the principles of energy conservation, 8.7% of the electrical input energy was converted into kinetic energy for the membrane. This deformation process achieved a velocity of 800 m/s, with a corresponding strain rate of 1.6 × 107 s−1. The applied impulse predominantly induced extension stresses in the cover layer rather than bending stresses. Under these conditions, a 17.5-µm radius polylactic acid bead was propelled and subsequently captured by a silicone gel layer, resembling human dermic skin. Considering factors such as particle clustering and deceleration due to air resistance during supersonic flight, assuming a normal incident angle, it was estimated that approximately half of the ejected particles could reach the human dermic layer, located 200 µm beneath the skin surface. These findings suggest that pulse discharge is a promising method for inducing high-speed membrane deformation, and the electrical microparticle accelerator holds potential for applications in needle-free drug delivery.

Numerical study on rock fracturing with pulsed pressure in hard rocks with a pipe-domain seepage model

The disintegration process and the fracture propagation degree in rock masses under pulsed pressure are of great interest to the engineering community. This study presents a novel numerical simulation method for pulsed pressure-induced rock fractures based on the stress analysis in the elastic medium and the use of the boundary conditions with internal and external pressures. To enclose the particles, a method of constructing pipe network is proposed via the particle flow code (PFC2D) method, which facilitated the control of fluid flow and pressure by incremental pressure. This method was rooted in the pipe domain percolation approach and allowed for the understanding of the loading process and crack propagation mechanism through the laboratory experiments and engineering cases. The results demonstrated that the fracturing of rock mass under impulsive loading was a combined effect of stress waves and high-pressure fluids. The action of the stress wave induced initial cracks in the rock masses, while the fluid penetrated into these cracks, exerting pressure on the surrounding particles. This led to an increase in fracture width and an influx of more fluid, which enhanced the fracturing process. The fracture lengths induced by the fluid splitting action accounted for over 60 % of the total. The method provides a solid foundation for analyzing the mechanisms of pulsed pressure-induced rock fracturing and offers invaluable insights into predicting the degree of disintegration.

Optimal shape design of spherical squeeze film bearings using genetic algorithms

The optimal shape design of hydrodynamic axisymmetric spherical bearings under conditions of transient axisymmetric pure squeeze is investigated using genetic algorithms (GA). The optimization problem is to determine the radial clearance shape which maximizes the load impulse resulting from transient ball motion to a target minimum film thickness specification. For fully-hemispherical cups, non-dimensional analysis shows that GA-based optimal designs yield significantly larger non-dimensional impulse values when compared with those obtained either randomly or from optimal ellipsoidal geometry. A sample design application with specified load history shows that an optimal GA-inspired composite clearance specification amenable to fabrication can be constructed from preferred features obtained from the GA-based optimal shapes. The optimal composite shape design is shown to provide significantly better bearing performance, as measured by minimum film thickness, after a specified time interval than an optimal ellipsoidal design. The optimal composite shape design is also found to be less sensitive to realistic deviations in clearance shape, load impulse, and viscosity variation when compared with similar variations to an optimal ellipsoidal cup design.

Substructure-level damage identification based on the spectrum-probability space of the transmissibility function

In structural health monitoring (SHM), the measured data is insufficient to accurately identify the potential damages when the measurements are contaminated by noise. In this study, a spectrum-probability space-based methodology is developed to manage the uncertainty in damage detection, integrated with the substructure division strategy to localize damage. The transmissibility function (TF), that is an output-only quantity and sensitive to changes in structural stiffness, is used to detect an anomaly. The variation of the probability-spectrum space of a TF is used as the damage indicator, and it is measured by a novel damage indicator, the spectrum-weighted Kullback-Leibler divergence. This indicator jointly considers the changes in spectrum density and statistics of a TF due to damage. The damaged sub-domain of a structure is subsequently identified out from all monitored sub-domains. Numerical and experimental models are tested to verify the approach in the ambient and impulse load conditions. The results demonstrate that the developed method can correctly detect anomalies and localize the damaged substructure with high sensitivity and robustness, and it is convenient to implement in practice.

NUMERICAL MODELING OF DYNAMIC DEFORMATION OF A THREE-LAYER RIBBED CYLINDRICAL SHELL UNDER AXISYMMETRIC IMPULSE LOADS

The non-stationary vibrations of three-layer composite cylindrical shell under axisymmetric impulse loads have been researched. The mathematical model and method for calculating the dynamic deformation of the shell system under consideration is based on the geometrically nonlinear theory of Timoshenko’s type shells and ribs. The results of numerical analysis of the problem are presented.

Out of-plane failure analysis of masonry walls subjected to hydrostatic and hydrodynamic loads induced by flash floods

Damage surveys from past flash flood events show that the combined hydrodynamic impulsive loading and the subsequent hydrostatic loading due to rising water levels caused the failure of masonry walls/buildings. However, limited studies have been conducted to understand the responses of masonry walls to these loading states. To bridge this knowledge gap, an explicit 3D shell element based finite element modelling method that incorporates a homogenised anisotropic masonry material model was developed and applied to analyse the out-of-plane collapse behaviour of masonry walls under flash flooding conditions. The developed modelling method was validated with an available experimental study of masonry wall subjected to hydrostatic loading conditions. It was then extended to comprehend the behaviour of masonry walls under hydrodynamic impulsive water pressures. Results reveal that the effect of hydrodynamic impulsive loading generated by the first hit of the flash flood water is significant in reducing the stiffness of the masonry. This reduction in stiffness can result in an early collapse of the wall, even with a gradual rise of hydrostatic water level. This study has also evaluated the behaviour and damage patterns of masonry walls with two different slenderness ratios (single brick/24.5 and double brick/11.7) under flash flooding and prescribed the maximum percentage of surface area of inundation that the walls can resist. The importance of considering hydrodynamic impulsive loading in designing masonry buildings vulnerable to flash flooding and the capability of the modelling technique developed in this research for evaluating their vulnerability under these flooding scenarios are highlighted.

Patellar Tendon Load Progression during Rehabilitation Exercises: Implications for the Treatment of Patellar Tendon Injuries.

This study aimed to evaluate patellar tendon loading profiles (loading index, based on loading peak, loading impulse, and loading rate) of rehabilitation exercises to develop clinical guidelines to incrementally increase the rate and magnitude of patellar tendon loading during rehabilitation. Twenty healthy adults (10 females/10 males, 25.9 ± 5.7 yr) performed 35 rehabilitation exercises, including different variations of squats, lunge, jumps, hops, landings, running, and sports specific tasks. Kinematic and kinetic data were collected, and a patellar tendon loading index was determined for each exercise using a weighted sum of loading peak, loading rate, and cumulative loading impulse. Then the exercises were ranked, according to the loading index, into tier 1 (loading index ≤0.33), tier 2 (0.33 < loading index <0.66), and tier 3 (loading index ≥0.66). The single-leg decline squat showed the highest loading index (0.747). Other tier 3 exercises included single-leg forward hop (0.666), single-leg countermovement jump (0.711), and running cut (0.725). The Spanish squat was categorized as a tier 2 exercise (0.563), as was running (0.612), double-leg countermovement jump (0.610), single-leg drop vertical jump (0.599), single-leg full squat (0.580), double-leg drop vertical jump (0.563), lunge (0.471), double-leg full squat (0.428), single-leg 60° squat (0.411), and Bulgarian squat (0.406). Tier 1 exercises included 20 cm step up (0.187), 20 cm step down (0.288), 30 cm step up (0.321), and double-leg 60° squat (0.224). Three patellar tendon loading tiers were established based on a combination of loading peak, loading impulse, and loading rate. Clinicians may use these loading tiers as a guide to progressively increase patellar tendon loading during the rehabilitation of patients with patellar tendon disorders and after anterior cruciate ligament reconstruction using the bone-patellar tendon-bone graft.

Experimental study of load characteristics caused by underwater explosion bubble collapsing in the neighborhood of a rigid wall

In this paper, a series of underwater explosion (UNDEX) experiments were carried out in a cubical explosion tank, to investigate the complex behaviors of one bubble collapsing near a vertical rigid wall. The evolution of the bubble was captured by a high-speed camera and the pressure caused by both the primary shock wave and the bubble collapse on the surface of the wall was measured by several sensors installed on the wall surface. Experimental results of the measured wall pressure and the resultant load impulse are compared with theoretical results that are calculated from the corrected empirical formula. A good agreement between the experimental and theoretical results is achieved. On this basis, the effects of the bubble-wall distance on the bubble behaviors and the corresponding explosion load characteristics on the rigid surface are analyzed and discussed. The result aims to provide a feasible reference for the study of near-field UNDEX bubble dynamics and the resultant load on structures nearby.

Improved analysis for impact response prediction of reinforced concrete structures considering stress wave propagation and time dependent shape function

In the design of reinforced concrete (RC) structures subjected to impulsive loading, usually an equivalent Single-Degree-of-Freedom (SDOF) system is derived based on a constant deflection shape assumption corresponding to static-loading condition. It is commonly known that this idealized assumption may not necessarily lead to accurate predictions of structural responses. This paper presents an improved analytical approach to predict the dynamic response of RC beams with consideration of stress wave propagation effect in the beam in the initial stage upon impact load application, and time-dependent shape function for SDOF analysis. The response of a structural component is divided into two phases: local response phase which is calculated using governing equations of stress wave propagations; and global response phase analyzed using the equivalent SDOF systems with considerations of time-dependent deformation shapes. Laboratory drop-weight impact tests are performed on RC beams, which are used to validate the developed method. Further validation is carried out against existing testing results by other researchers, demonstrating the proposed approach offers more accurate predictions of RC beam responses under impact loading compared to the conventional SDOF method.

PHYSICAL EXPERIMENTS ON OVERHANGING PARAPETS UNDER NON-BREAKING WAVE CONDITIONS

The use of sea-wall and storm-wall structures within valuable landscape or urban areas often imposes rather restrictive limits in terms of structures height. A viable solution to address the safety against overtopping and the architectonical requirements is the use of recurved parapets. However, this type of structure is exposed to large impulsive loads that have been recently described and named as confined-crest impact, (C-CI), (Castellino et al., 2018) and caused several failures such as those in Strand (South Africa), Pico Island (Portugal) and Civitavecchia (Italy), (Castellino et al., 2021; Dermentzoglou et al., 2020; Martinelli et al., 2018). Accordingly, tools to properly design these curvilinear structures and to carry out comparative assessments between the induced advantage in terms of overtopping and increased structural complexity due to its shape and the C-CI are required. This work aims to identify practical design tools and provide benchmark data for the validation of the CFD model presented in the abstract n. 1643: “Castellino et al., Numerical experiments on overhanging parapets under non-breaking wave conditions”. A series of non-breaking regular and irregular waves experiments have been performed at the TU Delft Hydraulic Engineering Laboratory to investigate the contrasting behaviour of the overtopping phenomena and the exerted impulsive wave load on recurved parapets.

STABILITY ANALYSIS OF OLD BREAKWATERS: CASE STUDIES OF FAILURES AND SUCCESSES

Until about 1930, analysis of wave loads on vertical breakwaters was based on trial and error. Russell(1) noted it was unfortunate that “the young engineer …should be left to be guided entirely by circumstances, without the aid of any one general principle.” Stevenson(2) noted “the engineer has always a difficulty in estimating the force of the waves with which he has to contend.” Wave force formulae by Sainflou(3) and Goda(4) improved design methods, but were 50 to 100 years too late for many ‘old’ breakwaters, and do not apply to many composite breakwaters – ignoring the seminal influence of shoals or mounds on wave breaking and impulsive loadings. This paper presents case studies using empirical methods developed over the last 20-30 years to calculate loads and stability of example ‘old’ breakwaters including: Wick (failed before completion); Alderney (multiple breaches during construction, and only survives to 1/2 of its original length); and Dover (survives with substantial Factors of Safety). The screening analysis(5) used empirical methods developed over the previous 20 years(10), summarised in the case studies(6,7). Methods used here are empirical (no numerical modelling) so that the calculations can easily be repeated by local engineers.

NUMERICAL STUDY ON THE INTERACTION BETWEEN PERIODIC WAVES AND A FLEXIBLE WALL

Coastal structures were usually considered as stiff in the majority of studies related to wave structure interaction I n certain situations, such as impulsive wave loading on flexible breakwaters, ship hulls, tank walls hydroelasticity can be of importance for both wave dynamics and structural responses Akrish et al. (2018) showed that hydroelastic effects can either relax or amplify the hydrodynamic characteristics (i.e., wave run up and force) and structural oscillations in a deformable cantilever wal l interacting with an incident wave group. For flexible coastal defenses, Huang and Li (2022) showed that an elastic horizontal plate breakwater can exhibit a better performance of wave damping than a rigid one. Sree et al. (2021) experimentally investigated a submerged horizontal viscoelastic plate under surface waves. They reported a complete cutoff of the wave energy with the flexible plate. However, the hydroelasticity of a steep fronted structure in nonlinear progressive waves was not yet studied in a de tailed manner , which requires advanced numerical methods for modelling the nonlinear interaction between the fluid and the solid with finite deformations. The present study focus es on the hydroelastic behavior of a flexible vertical wall in nonlinear periodic waves with different wave periods (or frequencies )). The effects of the structural stiffness on the wave evolution and the structural deformation are investigated with a fully coupled wave structure interaction model.

Heart rate modeling and prediction of construction workers based on physical activity using deep learning

Construction projects require long working hours where workers are subjected to intensive tasks such as hard manual labor, heavy weightlifting, and compulsive working postures. Among the physiological metrics, Heart Rate (HR) is reported to be a good indicator of physical stress and workload. HR forecasting models have been used in various areas including cardiopathy research, heart attack warning indicator, and early physical fatigue detection. However, there are no reported studies on HR modeling and forecasting in the construction field. Modeling and forecasting the HR of construction workers using construction field data is of paramount importance due to the direct relationship between activity level and HR. The objective of this study is to (1) analyze the effect of physiological factors including breathing rate, acceleration of torso movements, torso posture, and impulse load on the HR of construction workers, and (2) model and forecast one-minute ahead HR for construction workers based on their physical activity using deep learning algorithms. To this end, physiological metrics of five bridge maintenance workers performing several construction activities were collected. According to the Pearson correlation and entropy based mutual information analysis, time-lagged variables including acceleration of torso movements, torso posture, and impulse load have significant effect on the HR data. The results of deep learning models indicate that Long Short-Term Memory Network (LSTM), Bidirectional LSTM (BiLSTM), Gated Recurrent Unit (GRU), and Bidirectional GRU (BiGRU) have similar predictive performance. However, LSTM had the best overall performance in HR prediction with Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and Mean Absolute Percentage Error (MAPE) of 5.4, 7.34, and 5.77%, respectively. These models have the potential to facilitate the mitigation of cardiovascular strain and enable proactive prevention of accidents in the construction industry.

Impulsive Load Destructive Effects Reduction in Launch Vehicles Using Structural Joint

Impulsive Load Destructive Effects Reduction in Launch Vehicles Using Structural Joint

Experimental investigations into the dynamic response of sandwich panels with multi-layered corrugated cores subjected to underwater impulsive load

Sandwich panels with multi-layered core have attractive performance due to the excellent designability and tailorable mechanical properties. In present study, the dynamic responses of the sandwich panels with multi-layered corrugated core were investigated experimentally under underwater impulsive loads. In order to exploit the potential for performance improvement, some attempts have been made by designing core configuration from several aspects including stack orientation, layer number, core gradation and core topology. Experimental results indicate that the core in the cross-stacked would deteriorate back face deflection. The core with three layers performed best in constraint back face deflection because of the well balance between energy absorption and residual flexural stiffness. The core gradation in wall thickness would reduce back face deflection, while the one in corrugation angle would increase back face deflection. The core topology designed into reentrant trapezoidal corrugation behaved effectively in inhabiting back face deformation due to the periodic progressive collapse mechanism of core webs.