Peak Dynamic Loads Research Articles

Damping of Suddenly Changing Loads by Drive Means of the Driving Mechanism of the Scraper Conveyor

Abstract An electromechanical method is proposed to avoid peak dynamic loads in a steady state, the condition of smooth start and emergency stop, as well as correction of the scraper conveyor productivity depending on the load flow level of the blasting combine, which will increase the reliability and reduce the energy and metal consumption of the transport link of the mining complex.

Досвід застосовування теплових акумуляторів в умовах блекауту

This study is the first and so far the only one in Ukraine dedicated to the experience of using mobile thermal energy storage in emergencies, in particular blackouts. The article considers the issue of ensuring energy security. The classification of heat storage system parameters is given. The considered model of an autonomous heating system with a heat storage system. The impact on the thermal energy storage heating system with different designs of heat generators and fuel types is shown. The results of the operation of a combined system consisting of an autonomous heating system of a separate building equipped with an electric boiler and thermal energy storage are presented. Thermal energy storage is used not only as a buffer between the heat generator and the heating system but also as a source of heat. Integrating the thermal energy storage into the building's heating system ensures constant heat supply to the building, 100% coverage of peak dynamic loads, halving the boiler unit capacity and operating costs by 20%. It has been proven that the presence of thermal energy storage allows solving the problem of providing a stable heat supply in the conditions of a power outage. A detailed description of the conducted study of methods and equipment used during field operation and data processing is given. The results of the field tests of the thermal energy storage in winter operation conditions are provided. Features of the use of the controller for monitoring the heating system's operation with thermal energy storage are provided. The results of field tests are given. An analysis of the received data was carried out. Formulated directions for further scientific research, development, and practical recommendations for the use of mobile heat accumulators in the national economy and the state emergency service of Ukraine. Economic criteria and efficiency criteria aimed at reducing operational costs are considered. The obtained research results can be used to predict the operation of heating and cooling systems equipped with thermal energy storage. Keywords: Heating system, security, blackout, thermal energy storage, monitoring.

Influences of dynamic load phase shifts on the energetics and biomechanics of humans.

Using load-suspended backpacks to reduce vertical peak dynamic load exerted on humans can reduce metabolic costs. However, is it possible to further reduce metabolic cost by modulating dynamic load phase shift? If so, is anti-phase better than the others? In this study, we investigated the biomechanics, energetics and trunk response under phase shifts. Nine subjects wearing an active backpack with 19.4 kg loads walked on a treadmill at 5 km h-1 with four phase shift trials (T1-T4) and a load-locked trial (LK). Our results show that anti-phase trial (T3) assists ankle more and reduces the moment and gastrocnemius medialis activity, while T4 assists knee more and reduces the moment and rectus femoris activity. Due to the load injecting more mechanical energy into human in T3 and T4, the positive centre-of-mass work is significantly reduced. However, the gross metabolic rate is lowest in T4 and 4.43% lower than in T2, which may be because the activations of erector spinae and gluteus maximus are reduced in T4. In addition, T3 increases trunk extensor effort, which may weaken the metabolic advantage. This study provides guidance for improving assistance strategies and human-load interfaces and deepens the understanding of the energetics and biomechanics of human loaded walking.

Failure analysis of gas explosion load based on structural impact failure characteristics

The purpose of this study is to obtain the peak of the gas explosion load which is affected by many factors and is not easy to determine. Explosion peak is a key factor in the time-load curve of the explosion field. In this paper, the static and dynamic modal analysis method of gas explosion fracture of reinforced concrete prefabricated slabs is used to obtain the static fracture, maximum reflective pressure applied and peak dynamic load of prefabricated plates. In the actual explosion study, all three prefabricated plates broke at one-third, and the peak dynamic load was 6.743 times the span buckling load in the plate. The analysis also shows that when plastic hinges appear at one-half, the above ratio is 3 times. The calculated peak is within the pressure range of the explosion test. The Baker model is used to fit the explosion time-load curve. This function is applied to the dynamic analysis of the finite element analysis of the explosion plate, and the failure of the plate is more consistent with the explosion case site. The median value of the explode field load time-load equation with the curve function can be applied to the rapid evaluation of post-explosion structure.

Experimental Study of Slamming Effects on Wedge and Cylindrical Surfaces

Slamming is a very significant phenomenon that occurs in marine structures operating under extreme conditions. Slamming significantly reduces the design life of floating offshore wind turbines, as well as marine structures, and causes structural damage. Thus, the slamming load should be considered sufficiently during the design phase of the structure, and the results of experiments of good quality should be incorporated. The phenomenon of slamming should be analyzed using peak pressure, width, duration, and dynamic loads that depend on the design and natural frequency of the structure. In the case of a slamming experiment, the deadrise angle shows the greatest pressure between 3° to 10°. In this study, pressure values were compared using a model with a deadrise angle of 10° and a cylinder model most commonly used for the fabrication and installation of offshore structures. The peak pressure of the cylindrical model is greater than those of the flat model and the wedge model with a 10° deadrise angle. Pressure and strain were measured using free drops from heights of 1.0 and 1.7 m from the water surface, and the elastic effects were studied accordingly. Also, the peak pressure due to a slamming impact occurs several times depending on the natural frequency of the structure. In order to understand the behavior of the structure against the elastic effect, the second peak in the experimental results was theoretically and experimentally analyzed. The second pressure peak is greater than the first pressure peak due to the elastic behavior effects based on the natural frequency of models used in the slamming test. Also, a single slamming results in several peak pressures and it greatly deteriorates the fatigue strength. Experiments and simulations were carried out to derive the effects of repeated slamming loads on the structure. In the structural design considering the slamming loads, information on the elastic effect of the structure and accumulated loads is very important. This can be an important variable in the design of the floater and can play an important role in assessing the impact on the floater. These results raise questions as to the extent that slamming pressures are replaced with equivalent hydrostatic pressures in most design rules of the recognized certification society.

Comparison of Responses of Guyed and Freestanding Transmission Line Towers Under Conductor Breakage Loading

Cascades have been a prominent feature of many transmission line (TL) accidents around the world. During these events, a localized member failure changes the boundary conditions of the structural system, magnifying member loads over a considerable extension of the line. This results in the progressive failure of successive support structures. Phase conductor breakage is regarded as the most severe cascade triggering event, generating a shock wave that propagates through the conductor and induces large unbalanced longitudinal loads on the transmission line components. Under such an extreme loading event, nonlinear time-history dynamic analysis has to be employed to predict the response of the TL system. In the present work, an explicit dynamic analysis scheme is developed to predict the response of a multi-span TL section. The analysis includes all the main structural components of a TL section. This procedure was used to investigate the response of two types of suspension steel latticed towers, guyed and freestanding, subjected to conductor breakage loading. Results indicate the occurrence of peak dynamic loads (PDLs), that significantly increase the internal forces in system components, exceeding their design capacities, particularly in tower's members. The results also show that the guyed tower accommodates such a loading event more adequately than the freestanding tower.

Study on the Dynamic Response of Prestressed Concrete Beam under Explosive Load

The dynamic performance of the 12m span prestressed concrete beam is analyzed by finite element method. Based on the finite element analysis, with the change of the peak dynamic load, the risetime of dynamic load and the reinforcement ratio of prestressed reinforcement, the change laws of mid-span maximum deflection and the maximum stress of prestressed reinforcement in prestressed concrete beam are studied. At the same time, have further understanding to the stress and deformation of the prestressed concrete beam under explosive load. It can provide references for study on dynamic performance of the prestressed concrete beam under explosive load.

Limiting Peak Dynamic Loads in Linear Oscillators due to Transient Excitation

Limiting Peak Dynamic Loads in Linear Oscillators due to Transient Excitation

Wave slamming loads on wave-piercer catamarans operating at high-speed determined by hydro-elastic segmented model experiments

Catamaran vessels operating at high-speed can be exposed to deck diving and bow damage and one resolution of this problem is the wave-piercer design of INCAT Tasmania. Owing to the complexity of the unsteady non-linear flow in the bow area during large wave encounter model testing has been undertaken to identify the peak dynamic slam loads on the ship structure. This paper provides experimental benchmark information relating to the wave slam loads on wave-piercing catamaran ferries. Since the time frames of transient slam loadings and whipping vibration of the entire hull in its first bending mode are similar it is important that the test model replicates the whipping response and therefore needs to be a hydro-elastic model. A 2.5 m hydro-elastic segmented catamaran model has been developed based on the 112 m INCAT Tasmania wave-piercer catamaran to establish the peak wave slamming loads acting on the full-scale vessel. Towing tank tests were performed in regular seas at a maximum full-scale operating speed of 38 knots. The model was instrumented to measure the dynamic slam loads acting on the centre bow and vertical bending moments acting in the demihulls of the catamaran model as a function of wave frequency and wave height. Peak slam loads measured on the centre bow were found to approach the total weight of the model, this being a broadly similar result to the peak loads measured at full-scale. It was found that global dimensionless heave and pitch accelerations peaked in the same range of encounter frequency as did the peak slam load.

The influence of track modelling options on the simulation of rail vehicle dynamics

This paper investigates the effect of different models for track flexibility on the simulation of railway vehicle running dynamics on tangent and curved track. To this end, a multi-body model of the rail vehicle is defined including track flexibility effects on three levels of detail: a perfectly rigid pair of rails, a sectional track model and a three-dimensional finite element track model. The influence of the track model on the calculation of the nonlinear critical speed is pointed out and it is shown that neglecting the effect of track flexibility results in an overestimation of the critical speed by more than 10%. Vehicle response to stochastic excitation from track irregularity is also investigated, analysing the effect of track flexibility models on the vertical and lateral wheel–rail contact forces. Finally, the effect of the track model on the calculation of dynamic forces produced by wheel out-of-roundness is analysed, showing that peak dynamic loads are very sensitive to the track model used in the simulation.

Bones' adaptive response to mechanical loading is essentially linear between the low strains associated with disuse and the high strains associated with the lamellar/woven bone transition

There is a widely held view that the relationship between mechanical loading history and adult bone mass/strength includes an adapted state or “lazy zone” where the bone mass/strength remains constant over a wide range of strain magnitudes. Evidence to support this theory is circumstantial. We investigated the possibility that the “lazy zone” is an artifact and that, across the range of normal strain experience, features of bone architecture associated with strength are linearly related in size to their strain experience. Skeletally mature female C57BL/6 mice were right sciatic neurectomized to minimize natural loading in their right tibiae. From the fifth day, these tibiae were subjected to a single period of external axial loading (40, 10-second rest interrupted cycles) on alternate days for 2 weeks, with a peak dynamic load magnitude ranging from 0 to 14 N (peak strain magnitude: 0–5000 µε) and a constant loading rate of 500 N/s (maximum strain rate: 75,000 µε/s). The left tibiae were used as internal controls. Multilevel regression analyses suggest no evidence of any discontinuity in the progression of the relationships between peak dynamic load and three-dimensional measures of bone mass/strength in both cortical and cancellous regions. These are essentially linear between the low-peak locomotor strains associated with disuse (∼300 µε) and the high-peak strains derived from artificial loading and associated with the lamellar/woven bone transition (∼5000 µε). The strain:response relationship and minimum effective strain are site-specific, probably related to differences in the mismatch in strain distribution between normal and artificial loading at the locations investigated. © 2012 American Society for Bone and Mineral Research.

Functional adaptation to mechanical loading in both cortical and cancellous bone is controlled locally and is confined to the loaded bones

In order to validate whether bones' functional adaptation to mechanical loading is a local phenomenon, we randomly assigned 21 female C57BL/6 mice at 19 weeks of age to one of three equal numbered groups. All groups were treated with isoflurane anesthesia three times a week for 2 weeks (approximately 7 min/day). During each anaesthetic period, the right tibiae/fibulae in the DYNAMIC+STATIC group were subjected to a peak dynamic load of 11.5 N (40 cycles with 10-s intervals between cycles) superimposed upon a static “pre-load” of 2.0 N. This total load of 13.5 N engendered peak longitudinal strains of approximately 1400 microstrain on the medial surface of the tibia at a middle/proximal site. The right tibiae/fibulae in the STATIC group received the static “pre-load” alone while the NOLOAD group received no artificial loading. After 2 weeks, the animals were sacrificed and both tibiae, fibulae, femora, ulnae and radii analyzed by three-dimensional high-resolution (5 μm) micro-computed tomography (μCT). In the DYNAMIC+STATIC group, the proximal trabecular percent bone volume and cortical bone volume at the proximal and middle levels of the right tibiae as well as the cortical bone volume at the middle level of the right fibulae were markedly greater than the left. In contrast, the left bones in the DYNAMIC+STATIC group showed no differences compared to the left or right bones in the NOLOAD or STATIC group. These μCT data were confirmed by two-dimensional examination of fluorochrome labels in bone sections which showed the predominantly woven nature of the new bone formed in the loaded bones. We conclude that the adaptive response in both cortical and trabecular regions of bones subjected to short periods of dynamic loading, even when this response is sufficiently vigorous to stimulate woven bone formation, is confined to the loaded bones and does not involve changes in other bones that are adjacent, contra-lateral or remote to them.

Alteration of the amount and morphology of wear particles by the addition of loading profile transitions during artificial hip wear testing

Current validation tests of total hip arthroplasty endo-prostheses capture only a single activity performed by patients: continuous walking. A more representative test that includes transitions from a static loaded position to dynamic motion would simulate common motions by patients in which they change from standing to walking. The introduction of such transitions into a traditional test protocol could provide insight into actual wear behaviours and more realistic wear particle properties such as size and shape. First, the introduction of transitions will increase the measured wear rate. Second, the amount of wear will be positively correlated to the number of transitions per day. Finally, the size and shape of polyethylene particle produced via testing with transitions will differ from those of a conventional continuous walking test. Three identical sets of four cobalt chromium femoral heads and sterilized acetabular cups sterilized in ethylene oxide were tested in 30 per cent bovine serum under three conditions: continuous walking (0 transitions/day), 10 transitions/day, and 100 transitions/day. A day was defined as 2500 steps. The static and peak dynamic loads were 260 N and 1.9 kN respectively. A testing duration of 106 cycles was completed for each of the three tests. The wear rate was found to be inversely related to the number of transitions. Particle analysis showed that the particle size decreased as the number of transitions increased. Particles from the 100 transitions/day test were more fibular and produced more particles of the size known to promote an immune reactive response. Contrary to our hypothesis, as the number of transitions performed by patients increased, the wear rate and accumulated wear decreased. In addition, as the number of transitions increased, a larger percentage of wear particles were in the submicron size range. Consequently, despite a decrease in wear due to the presence of loading profile transitions, there is a potentially greater risk of osteolysis owing to the increased production of immunoreactive particles.

Estimating peak wind load effects in guyed masts

Guyed masts subjected to turbulent winds exhibit complex vibrations featuring many vibration modes, each of which contributes to various structural responses in differing degrees. This dynamic behaviour is further complicated by nonlinear guy cable properties. While previous studies have indicated that conventional frequency domain methods can reliably reproduce load effects within the mast, the system linearization required to perform such an analysis makes it difficult to relate these results directly to corresponding guy forces. As a result, the estimation of peak load effects arising jointly from the structural action of the mast and guys, such as leg loads produced as a result of guy reactions and mast bending moments, is uncertain. A numerical study was therefore undertaken to study peak load effects in a 295 m tall guyed mast acted on by simulated turbulent wind. Responses calculated explicitly from nonlinear time domain finite element analyses were compared with approximate methods in the frequency domain for estimating peak values of selected responses, including guy tension, mast axial loads and mast leg loads. It was found that these peak dynamic load effects could be accurately estimated from frequency domain analysis results by employing simple, slightly conservative assumptions regarding the correlation of related effects.

Experimental study of static and fatigue strengths of pultruded GFRP rods bonded into LVL and glulam

Glass fibre-reinforced plastic (GFRP) pultruded rods were bonded into LVL and glulam cubes with room temperature cured epoxy resin in two glue-line thicknesses (2 and 4 mm). The strength properties were investigated under static and tension–tension ( R=+0.1) fatigue loading. Also, the effect of rate of loading was assessed in a rate of force application range from 0.01 to 35 kN/s in three glue-lines thicknesses (0.5, 2 and 4 mm). The results demonstrate that the fatigue life increases as the peak dynamic load is reduced as expected. Better static strength is measured for 4 mm glue-lines than for 0.5 and 2 mm glue-lines at lower rates of loading, but a reduction in strength at higher rates is observed for 4 and 2 mm glue-lines. Glue-line thickness and rate of loading dictate the mode of failure observed including failure in timber, failure at the resin–rod interface and a mixed failure mode.

Low-cycle fatigue crack growth considerations in pipe fracture analyses

This paper presents some results from an ORNL cyclic pipe experiment that demonstrated the magnitude of low-cycle fatigue crack growth from simulated seismic loading. The concern with this result is that current pipe flaw evaluation procedures do not consider the cyclic crack growth during a seismic event, i.e. the peak dynamic load is used in a static analysis. This was the main incentive for the analyses developed in this paper. Additional applications of the methodology developed in this paper would be high stress-low cycle fatigue transients that can occur in service. In this paper, we show that the low-cycle fatigue crack growth data from the ORNL pipe test agreed well with the extrapolation of high-cycle fatigue crack growth data from small specimens. The next step was to evaluate the accuracy of several different methods to predict the low-cycle fatigue crack growth. In this evaluation it was found that for low-cycle fatigue LEFM analysis would significantly underpredict the crack growth and EPFM analyses were needed. Three different EPFM analyses were used. The GE/EPRI method was found to be overly conservative, which is consistent with comparisons with past pipe fracture data. The LBB.NRC and LBB.ENG2 J-estimation schemes provided good predictions of the experimental crack growth data when the crack-closure load was taken into account.

Electromyographic activity of the cervical musculature during dynamic lateral bending.

Electromyographic profiles from the neck muscles of five young, healthy men were obtained to study the muscular, activation patterns during dynamic external loading. To examine the myoelectric activity of selected cervical muscles during dynamic loading, and to explore the reaction of the cervical muscles to different loading conditions. The response of cervical muscles throughout dynamic external loading is not well understood. Electromyography provides information, within certain limitations, about the neural drive to various components of the musculature. Such information on activation, combined with geometric parameters of the musculoskeletal tissues, constitutes a tool for helping to understand the mechanism of head and neck impact-related injury. Subjects were tested with the head and neck in the neutral and prebent positions. Dynamic loads were applied laterally to each subject by free-falling masses to create peak dynamic loads ranging from about 40 to 100 N. Force and electromyographic data were recorded, and cross-correlations from linear envelope electromyography were calculated. The peak electromyogram showed large differences between the two applied loads and between subjects. There were time delays (75-165 msec) between the peak applied force and the peak electromyogram. The muscles on the contralateral side demonstrated different electromyographic profiles between subjects. Within subjects, the electromyographic profiles from each muscle were consistent for the same trial conditions. Electromyographic profiles and the cross-correlator coefficients for cervical muscles have shown reproducible intrasubject muscle synergies, which were not sensitive to the magnitude of applied load and the posture of the head. Intersubject muscle activity patterns varied.

A Model of Whole-Life Flexible Pavement Performance

A new ‘whole-life’ pavement performance model (WLPPM), which is capable of making deterministic pavement damage predictions due to realistic traffic and environmental loading, has been developed. A vehicle simulation is used to generate dynamic tyre forces that are a function of distance along the road. These dynamic tyre forces are then combined with the appropriate pavement primary response influence functions (stress, strain and displacement) to give primary response histories at regularly spaced points along the pavement. The primary response histories are then transformed into pavement damage (fatigue and permanent deformation) using an appropriate damage model. The result is an increment of damage at each point along the pavement due to a single vehicle pass. The pavement surface profile is then updated to reflect permanent deformation damage and the layer material parameters are changed to reflect fatigue damage. The procedure is then repeated for the next vehicle pass. Particular attention is given to modelling strength variations in the pavement and dynamic tyre forces. The model is used to investigate the relationship between ‘hot spots’ (due to peak dynamic loads), ‘weak spots’ (due to initial pavement stiffness variations) and long-term pavement damage.

Behaviour of nonlinear supports on a PWR coolant system during a postulated LOCA: Part 1: Effect of modelling methods

A 4-loop Pressurised Water Reactor (PWR) primary coolant system has been analysed for the postulated Loss of Coolant Accident (LOCA) event in order to derive peak dynamic loads for qualifying the design of equipment supports and pipe whip restraints. Pipe whip restraints as well as pipe and equipment supports are nonlinear by nature because of the presence of gaps and the different directional stiffnesses arising from snubber, steelwork and geometric and material interaction at the concrete to steel embedment. The different structural idealisations for the supports and restraints have an influence on the dynamic response of the structure. In the first of the two part paper a range of idealisation models for the Steam Generator and Reactor Coolant Pump vertical columns ranging from elastic stiffnesses to bilinear stiffnesses with or without preload were examined. Due to both structural and loading complexity, the behaviour of these supports were analysed by the Nonlinear Modal Superposition Method [1] and [2]. Analyses with the different models that are within the capabilities of the WESTDYN [3] piping analysis code enabled variations in the peak dynamic loads at the supports, restraints and equipment nozzles and other parameters to be determined and the design acceptability of the hardware established.

Effect of Axial Impact on the Static Flexure of Graphite/Epoxy Beams

Graphite-epoxy beams were subjected to an eccentric axial impact load in a drop tower test fixture in order to study their large displacement flexural behavior. The time history of the transient axial load exhibited a large magnitude occurring just after impact, which was many times greater than the static failure load. The damage caused by this peak dynamic load was measured by the reduction in energy absorption of the impacted beam relative to a virgin beam in static tests. For the thirty-ply specimens, the amount of damage increased with increasing axial stiffness.