Amplitude Of Dynamic Load Research Articles

Optimized Fuzzy Skyhook Control for Semi-Active Vehicle Suspension with New Inverse Model of Magnetorheological Fluid Damper

To improve the performance of vehicle suspension, this paper proposes a semi-active vehicle suspension with a magnetorheological fluid (MRF) damper. We designed an optimized fuzzy skyhook controller with grey wolf optimizer (GWO) algorithm base on a new neuro-inverse model of the MRF damper. Because the inverse model of the MRF damper is difficult to establish directly, the Elman neural network was applied. The novelty of this study is the application of the new inverse model for semi-active vibration control and optimization of the semi-active suspension control method. The calculation results showed that the new inverse model can accurately calculate the required control current. The fuzzy skyhook control method optimized by the grey wolf optimizer (GWO) algorithm was established based on the inverse model to control the suspension vibration. The simulation results showed that the optimized fuzzy skyhook control method can simultaneously reduce the amplitude of vertical acceleration, suspension deflection, and tire dynamic load.

Study on Dynamic Response Characteristics of Rock Slope

After the wenchuan earthquake, the dynamic response law of rock slope under the action of dynamic load is a very concerned and urgent problem in the field of seismic engineering. This paper analyzed the dynamic response law of simplified rock slope under the cosine wave dynamic load by numerical simulation with FLAC3D software. This research emphatically analyzed the variation law of amplification coefficient of seismic displacement, acceleration and velocity of rock slope under the condition of different slope height, slope angle, dynamic load period and dynamic load amplitude, which provides a basis for reducing seismic damage of slope area and seismic design of engineering structure.

Coned Disc Spring Compound Vertical Isolation: Testing and Modelling

ABSTRACT To improve the isolation property of conventional-coned disc spring isolation (CDSI) bearings, novel coned-disc spring compound vertical isolation (CDSCI) bearings were proposed. These combined the conventional CDSI bearings with high–damping viscoelastic (HDV) layers. Static loading tests, dynamic loading tests, and temperature dependence tests were conducted to study the mechanical performance of the CDSCI bearings. The test results indicated that HDV layers can enhance the conventional CDSI bearings’ energy-dissipation capacity effectively; the preloading displacement has a positive correlation relationship with the equivalent damping ratio and equivalent stiffness of the CDSCI bearings; and the dynamic loading amplitude has a negative correlation with the equivalent damping ratio of the CDSCI bearings, while it has a positive correlation relationship with the equivalent stiffness. As the ambient temperature increases, the equivalent damping ratio and equivalent stiffness of the CDSCI bearing decrease. Furthermore, the mechanical behavior of the CDSCI bearing was simulated using a modified Bouc–Wen model. Last, seismic responses of a typical CDSCI-isolated structure was investigated using time history analysis. Numerical results show that force responses of a structure can be reduced by CDSCI bearings effectively.

Numerical simulation research on response characteristics of surrounding rock for deep super-large section chamber under dynamic and static combined loading condition

The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition. Based on the in-site geological conditions of Longgu coal mine, this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition. Results showed that under the static loading condition, the maximum vertical stress, deformation and failure range are large, where the stress concentration coefficient is 1.64. The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm, respectively. Then, under the dynamic and static combined loading condition: (1) The influence of dynamic load frequency on the two-sides is more obvious; (2) The dynamic load amplitude has the greatest influence on the stress concentration degree, and the plastic failure tends to develop to the deeper; (3) With the dynamic load source distance increase, the response of surrounding rock is gradually attenuated. On this basis, empirical equations for each dynamic load conditions were obtained by using regression analysis method, and all correlation coefficients are greater than 0.99. This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.

Dynamic Response of Machine Foundation Resting on End Bearing Piles

Herein, a finite element software (ANSYS. 11) is adopted which provides an effective tool for dynamic analysis and structural design of machine-foundations. As a case study, machine foundation on piles in sandy soil is investigated. Machine foundations supported by end-bearing piles are introduced. Sinusoidal dynamic load is applied. A study of parameters is conducted to investigate the influence of a number of parameters that include: geometry of the piles below the foundation, the dynamic load amplitude, damping ratio and frequency of the load. Linear elastic model is adopted for modeling the piles and their cap for machine foundation using eight node isoparametric (solid 65) element, while elastic model is adopted to model the soil behavior and eight node isoparametric elements are used to model the soil through (solid 45) element. It is concluded that the frequency ratio decreases with increase of spacing between piles values due to increase in natural frequency, except in the case of 3 m spacing where it increases due to decrease in natural frequency as the mass was increased obviously. The increase in spacing caused the increase of natural frequency by about 6% in the model having 1.5 m spacing more than the 1.25 m case and by about 3% for the 1.75 m spacing more than the 1.5 m reference case. The increase in pile cap length caused the natural frequency to decrease by about 18% for the 3.75 m pile cap length as compared with the reference case and by 29% in the case of 5 m less than the reference case. In the case of increasing pile cap thickness, there was only a slight difference in the values of natural frequency.

Mechanical behaviors of frozen clay under dynamic cyclic loadings with freeze-thaw cycles

This paper presents a comprehensive research about the coupled influence of freeze-thaw procedure and stress condition on cyclic mechanical properties of the frozen clay. According to cyclic test data of frozen clay at the temperature −10 °C, dynamic responses in various cases of confining pressures, cyclic loading amplitudes and freeze-thaw cycles are investigated in detail. Cyclic stress ratio is used to investigate the coupling effects of the freeze-thaw procedure, confining pressure and dynamic loading amplitude on permanent strain curves under same dynamic cycle-time. The permanent axial strain raises with increase of cyclic stress ratio. An empirical formula is presented to quantitatively characterize the coupled effects on the permanent deformation of frozen samples. Two-stage evolution features of resilient modulus in the cyclic loading process are clearly observed under all confining pressures and dynamic stress amplitudes. The inflection points of two-stage curves are rationally considered as the endpoints for the post-compaction compression stage. The axial strain value at this inflection point is defined as the yield strain under cyclic loading conditions. The yield strain point roughly occur around 3000th-3900th loading cycles. When the freeze-thaw cyclesreached at 6, the loading cycles at the inflection point (yield point) were approximate 3300. There was no obvious freeze-thaw cycle threshold for the dynamic elastic properties of frozen samples. Finally, based on the analysis for the loading cycle numbers at those yield points, the dynamic strength curves of samples under different confining pressures can be established.

Numerical Analysis of Dynamic Responses of Rock Containing Parallel Cracks under Combined Dynamic and Static Loading

Open-pit slopes contain numerous nonpenetrating, intermittent joints which maintain stability under blasting operations. The tip dynamic response coefficient (DRC) of parallel cracks in a typical rock mass under combined dynamic and static loading conditions was calculated in this study based on the superposition principle. The dynamic response law of the intermittent joint in the slope under blasting was determined accordingly. The influence of many factors (the disturbance amplitude of dynamic load, the lateral confining pressure, the length of rock bridge, the length between cracks, the staggered distance between cracks, and the crack inclination angle) on the dynamic response was theoretically analyzed as well. The ABAQUS numerical assessments were conducted on simulation models with parallel cracks under combined dynamic and static loading conditions. The results show that a larger dynamic load amplitude and smaller crack inclination angle/confining pressure result in greater Type II dynamic strengthening effect on the crack tip. When the length of the rock bridge between cracks (s) is smaller than the half length of the crack (a), the dynamic strengthening effect at the crack tip weakens gradually with increase ins; whens/a≥1, the strengthening effect is almost unchanged. With the increase in the staggered distance between cracks (h), the dynamic strengthening effect of the crack tip weakens at first and then strengthens; the strengthening effect is weakest whenh/a=0.4; the crack propagation under combined dynamic and static loading is the most sensitive to the lateral confining pressure (σ3) and is the least sensitive to the inclination angle of the cracks (α). Theoretical results are validated by comparison with numerical simulation results. Such information regarding the dynamic response law of the parallel cracks in rock masses under dynamic and static loading conditions is conducive to further research on the mesofailure mechanism of open-pit mine jointed rock slopes under blasting operations.

Three-dimensional simulation of rock breaking efficiency under various impact drilling loads

Percussion drilling is believed to be an efficient way to enhance the drilling performance, compared with the conventional drilling in deep wells, which could be achieved by applying impact loads above the drill bit. The finite simulation is an efficient method to predict the drilling performance when the drill bit interacts with rocks. In contrast, as results of finite element technology limitation, the conventional way is to apply the displacement or velocity boundary conditions on the bit; however, this is completely different from the real field drilling process. Therefore, in this paper, a 3-D rock-bit physical model is presented to simulate the practical percussion drilling under various types of loads; at the same time, experiment was conducted to validate the effectiveness of the rock-bit model. The results demonstrated that the drilling performance with the rectangular and sinusoidal loads was promoted than the other types of load, and rate of penetration (ROP) increases with increasing of the amplitude of dynamic load, which could provide the theoretical guidance to the down-the-hole drilling tool design, thereby proving a quite efficient and lower cost drilling in the exploration of hard formations.

Экспериментальное определение динамических нагрузок в приводной цепи при ее поперечных колебаниях как струны с закрепленными концами

Chain transmissions are widely used in drives of hoisting-and-transport and ag-ricultural machines, as well as in a number of machine tools and technological equipment in various branches of industry. However, a significant disadvantage of these transmissions is the high vibration activity under high dynamic loading. In this regard, the study of dynamic loads that occur during chain vibrations and affect the operability of the machine drive is one of the essential tasks of its dynamics. The article presents experimental studies performed in order to determine the maximum dynamic loads in a chain transmission of a machine drive with transverse vibrations of the chain. The most common case of transverse vibrations of a chain loop is studied as a string with fixed ends. This type of vibration is typical of chain transmissions with large masses of sprockets and parts attached to them. The article presents a description of an original test bench with an automated system for collecting and processing experimental data and a test procedure. The obtained experimental data are presented in the form of tables and graphical dependences of the maximum dynamic loads on the tension force of the chain average per cycle of vibrations and the amplitude of its transverse vibrations in the center of the span, related to its length. As a result of approximation of the experimental data array, an empirical formula is proposed that can be used in dynamic calculations of the drive. It is established that the maximum dynamic load and its amplitude increases with the increase of the ratio of the amplitude of transverse vibrations of the chain in the middle of its span to its length and the initial tension force of the chain. The ratio of the dynamic load amplitude to the tension force of the chain decreases with the increase of the latter.

Numerical Study on the Elastic Deformation and the Stress Field of Brittle Rocks under Harmonic Dynamic Load

In order to study the deformation displacement and the stress field of brittle rocks under harmonic dynamic loading, a series of systematic numerical simulations are conducted in this paper. A 3D uniaxial compression simulation is carried out to calibrate and determine the property parameters of sandstone and a model of the cylindrical indenter intruding the rock is proposed to analyze the process of elastic deformation. Four main parameters are taken into account, namely the position on the rock, the frequency and the amplitude of dynamic load, the type of indenter and the loading conditions (static and static-dynamic). Based on the analysis undertaken, it can be concluded that both of the deformation displacement and stress field of the rock change in a harmonic manner under the static-dynamic loads. The frequency and the amplitude of harmonic dynamic load determine the period and the magnitude of the rock response, respectively. In addition, the existence of harmonic dynamic load can aggravate the fatigue damage of the rock and allow a reduction in static load. Our investigations confirm that the static-dynamic loads are more conducive to rock fracture than static load.

Centrifuge model test and numerical interpretation of seismic responses of a partially submerged deposit slope

Abstract Partially submerged deposit slopes are often encountered in practical engineering applications. However, studies on evaluating their stability under seismic loading are still rare. In order to understand the seismic behavior of partially submerged deposit slopes, centrifuge shaking table model tests (50g) were employed. The responses of horizontal accelerations, accumulated excess pore pressures, deformation mode, and failure mode of the partially submerged deposit slope model were analyzed. In dynamic centrifuge model tests, EQ5 shaking event was applied numerically. The results indicated that in the saturated zone of the deposit slope, liquefaction did not occur, and the measured horizontal accelerations near the water table were amplified as a layer-magnification effect. It was also shown that the liquefaction-resistance of the deposit slope increased under multiple sequential ground motions, and the deformation depth of the deposit slope induced by earthquake increased gradually with increasing dynamic load amplitude. Except for the excessive crest settlement generated by strong shaking, an additional vertical permanent displacement was initiated at the slope crest due to the dissipation of excess pore pressure under seismic loading. The result of particle image velocimetry (PIV) analysis showed that an obvious internal arc-slip was generated around the water table of the partially submerged deposit slope under seismic loading.

Physico-mechanical Behaviors of Granite Under Coupled Static and Dynamic Cyclic Loadings

The stress distribution around constructions in deep rock can be modified by dynamic disturbances, such as earthquakes. For this, we proposed a new loading method applied to granite sample under coupled static and dynamic cyclic loading (CSDCL) condition. The variations in P-wave velocity, gas permeability, and mechanical properties of granite before and after CSDCL are revealed. It shows that with increasing axial static stress, the dynamic cyclic loading amplitude and cycle number, P-wave velocity, uniaxial compressive strength (UCS) and elastic modulus decrease, whilst the permeability and Poisson’s ratio increase. It seems that variations in those parameters have a close relation with the exciting frequency. In this case, CSDCL is applied for crack development along the axial direction in the rock samples, and subsequently results in degradation of mechanical properties, delay of P-wave propagation, and increase of the transport paths. The results show that the permeability and Poisson’s ratio are likely to be more sensitive to the CSDCL, in particular under the axial static stress. The empirical relationships of the P-wave velocity with permeability, UCS, and elastic modulus are established for a pragmatic monitoring purpose. From design point of view, we have established the relationships of the disturbance factors to damage variable. Then the correlations of the damage variable to permeability, UCS, and elastic modulus are analyzed. The testing results in this context could facilitate our understanding of rock stability upon excavation subjected to dynamic disturbances.

Experimental Investigation on the Dynamic Modulus Properties of Methane Hydrate Sediment Samples

Studying the strength and deformation properties of sediments containing gas hydrates is one of the key problems during the process of hydrate resource exploitation. In this paper, considering the effects of temperatures (−5, −3, −1 °C), confining pressures (0.5, 1, 2 MPa) and porosities (40%, 80%) on the dynamic modulus characteristics of sediments containing methane hydrates, several dynamic loading experiments were conducted. The results show that the sediment structure was more easily destroyed under a larger amplitude of dynamic loading. According to the dynamic stress–strain curves, the skeleton curves of the sediment samples were obtained, and it was shown that the deformation behaved with elastic characteristics in the initial stage, and then plastic deformation increased gradually and played a leading role with the increase in external loading. The maximum dynamic elastic modulus of sediments was reduced under the conditions of higher temperature and porosity, and effectively enhanced under higher confining pressure. Finally, on the basis of the Hardin–Drnevich equivalent model, and considering the influences of temperatures and confining pressures on model parameters, a viscoelastic constitutive model applied to analyze the dynamic modulus characteristics of sediments containing methane hydrate was established. The comparison showed that these calculated values of sediments’ dynamic elastic modulus accorded quite well with the experimental values.

Effect of frequency and amplitude on dynamic behaviour, stiffness degradation and energy dissipation of saturated cohesive soil

ABSTRACT Cohesive soil undergoes cyclic softening when experiences the dynamic loading conditions. Evaluation of strength loss under such loading conditions is essential for soil stability analysis. The present study investigates the cyclic response, stiffness degradation behaviour with number of loading cycles and cumulative energy dissipation characteristics within the soil mass of cohesive geomaterial. Slurry consolidated specimens of saturated cohesive soil were prepared to perform several series of strain controlled cyclic triaxial tests at varying loading frequency and axial strain amplitude under consolidated and unconsolidated testing conditions. A great influence of loading amplitude and frequency was observed on the hysteresis response and dynamic properties of cohesive soil under consolidated and unconsolidated testing conditions. Amount and rate of cyclic stiffness degradation in addition to cumulative dissipated energy were also evaluated at different dynamic loading (amplitude and frequency) and testing conditions (consolidated and unconsolidated). Cyclic strength and stiffness of saturated cohesive soil were obtained to be higher under consolidated testing conditions as compared to unconsolidated. A large decay in cumulative dissipated energy was observed with the increment in loading cycles.

Dynamic Simulation of a Fe-Ga Energy Harvester Prototype Through a Preisach-Type Hysteresis Model.

This paper presents the modeling of an Fe–Ga energy harvester prototype, within a large range of values of operating parameters (mechanical preload, amplitude and frequency of dynamic load, electric load resistance). The simulations, based on a hysteretic Preisach-type model, employ a voltage-driven finite element formulation using the fixed-point technique, to handle the material nonlinearities. Due to the magneto–mechanical characteristics of Fe–Ga, a preliminary tuning must be performed for each preload to individualize the fixed point constant, to ensure a good convergence of the method. This paper demonstrates how this approach leads to good results for the Fe–Ga prototype. The relative discrepancies between experimental and computational values of the output power remain lower than 5% in the entire range of operating parameters considered.

Tests, model, and applications for coned-disc-spring vertical isolation bearings

To study the mechanical performance and asymmetric hysteretic models of coned-disc-spring vertical isolation (CDSVI) bearings, their mechanical properties under reversed loading conditions were tested, and the characteristics of their load–displacement hysteretic curves were investigated. The test results indicate that the load–displacement hysteretic curves have asymmetric characteristics, and that the loading frequency has only a marginal influence on the mechanical properties of the bearings, whereas the preloading displacement and dynamic loading amplitude have a critical influence. Based on the test results, an origin-oriented hysteretic model (OO hysteretic model) was proposed for CDSVI bearings. The results indicate that the OO hysteretic model has asymmetric characteristics, and the frictional forces critically influence the restoring forces of the bearings. Furthermore, the experimental results were used to verify the OO hysteretic model. The results indicate that the OO hysteretic model can simulate the mechanical performance of the CDSVI bearings effectively, and the relative errors between the simulated and experimental results of both equivalent stiffnesses and equivalent damping ratios are within 5%. Finally, the nonlinear dynamic time-history analysis of a typical CDSVI-SDOF system was carried out to study the influences of the asymmetric hysteretic model on the calculated seismic responses of the structures. Numerical results show that CDSVI bearings can effectively reduce the earthquake responses of the structure.

Laboratory experiments on blockage removing and stimulation of CBM reservoirs by composite pulsating hydraulic fracturing of radial horizontal wells

It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely. In view of this, a technical idea of composite pulsating hydraulic fracturing of radial horizontal wells which is conducive to blockage removing and stimulation was put forward in this paper. Speaking of the hydraulic jetting in a multi-branch radial well, it is to conduct pulsating hydraulic fracturing moderately through a high-diversion radial hole, so as to crush and break coal beds near the main hole to the uttermost. Thus, an extensive pressure relief and permeability increase area where high-diversion pathways are combined with fracture networks is formed. Then, to verify its technical principles, laboratory tests on pulsating hydraulic fracturing of radial wells were designed and carried out. Besides, the relationships of the features of acoustic emission (AE) response during the formation of fractures by composite fracturing of radial horizontal wells vs. coal breaking degree and macro fracture morphology were experimentally studied by using a pulse servo fatigue testing machine and an acoustic emission detector. And the following research results were obtained. First, under experimental conditions, fractures initially occur when the pressure of composite pulsating hydraulic fracturing of radial horizontal wells is 1/3–1/4 of the peak pressure of conventional fracturing, and the amount of its AE events is 1.38–7.07 times that of conventional fracturing. Second, when composite pulsating hydraulic fracturing of radial horizontal wells is conducted, AE emission signals respond strongly, the peak pressure for macro fracturing is lower and a larger fracture network can be generated more easily under the same condition. Third, radial laterals amount, borehole length, dynamic loading frequency and amplitude are the important factors affecting the effect of composite pulsating hydraulic fracturing of radial horizontal wells. In conclusion, composite pulsating hydraulic fracturing of radial horizontal wells provides a new idea of removing the blockages in CBM reservoirs and developing CBM efficiently, realizing effective blockage removing and stimulation of CBM wells.

Centrifuge tests on liquefaction potential and slope stability of mine tailings

Several factors have led to the extended need for investigation of the static and dynamic behaviour of mine tailings and include the rising generation and surface storage of mine waste, its frequent use as a construction material for the retaining structures and the relatively high rate of associated failures, with seismic liquefaction being a rather common cause. In this experimental study, dynamic response and surface slope stability of a layered mine tailings deposit were examined by means of four centrifuge tests performed at the Center for Earthquake Engineering Simulation (Rensselaer Polytechnic Institute). The material under study was fine copper–gold tailings and the varying parameters were average degree of consolidation prior to dynamic loading and base acceleration amplitude. The material was found to be liquefiable and its performance in terms of acceleration, shear strain, slope stability, residual lateral deformation, pore-pressure build-up and liquefied depth was somewhat dependent on the aforementioned parameters. The response of the deposits changed with increasing depth and effective stress, which made centrifuge testing highly advantageous.

Active control of circular cylinder flow with windward suction and leeward blowing

This study is an experimental investigation of the effectiveness and mechanism of a concept for bluff-body control characterized by combined windward suction and leeward blowing (WSLB). Wind tunnel tests are performed at a subcritical Reynolds number (Re) of 3.33 × 104. Open-loop WSLB is used to control the flow around a cylindrical test model. Distributed suction and blowing nozzles are symmetrically arranged at the front and rear stagnation points. Steady suction and blowing are implemented simultaneously on both surfaces of the cylinder. WSLB control is characterized by the dimensionless momentum of the suction/blowing relative to the incoming airflow. Instantaneous pressure distributions on the midspan of the cylinder surface for the baseline and controlled cases are measured to quantify the modifications of WSLB control to the aerodynamic coefficients of the cylinder. In addition to surface pressure measurements, a particle image velocimetry (PIV) system is used to describe the wake flow structures of the baseline and controlled cylinders. Experimental results demonstrate that WSLB control decreases sectional drag at the midspan and reduces the fluctuating amplitudes of dynamic wind loads acting on the cylinder. The Strouhal number to characterize the vortex shedding frequencies of the controlled cylinders is also found to deviate from that of the natural cylinder. PIV measurement results show that the active blowing positioned at the leeward stagnation point forms a pair of vortices into the cylinder wake that modify the original vortex shedding process. As the blowing vortices convect into the wake, they stretch the unsteady shear flows from the upper and lower sides of the cylinder, increase the vortex-formation length and push the alternative vortex shedding further downstream. It is also shown that a steady and symmetric perturbation imposed on the periodic cylinder flow can reduce the von Karman vortices and modify the mode of wake vortex shedding significantly. With active control of windward suction and leeward blowing (WSLB), blowing positioned at the leeward stagnation point forms a pair of vortices in the cylindrical wake that modifies the typical vortex shedding process. As the blowing vortices convect downstream, they contribute to detaching the unsteady shear layers from the cylinder. It is shown that a steady and symmetric perturbation imposed on the periodic cylinder flow can lead to a symmetric mode of wake vortex shedding.

Oscillation impacter improves the rate of penetration

In order to improve the rate of penetration and drilling performance, a tool named oscillation impacter is designed, which enables hydraulic energy to transform into mechanic one and generate static-and-dynamic loading on the bit and local instantaneous low pressure at the bottom. This paper attempts to analyse the structure and working principle of oscillation impacter, study the rock breaking mechanism of local instantaneous low pressure through theoretical analysis and the rock breaking mechanism of static-and-dynamic loading by the method of numerical simulation. Reasonable working parameters are recommended after analysing the influence that frequency and the maximum amplitude of dynamic loading act on rock breaking. According to the simulation results, corresponding drilling technology is established and field tests are conducted in Huabei oilfield. The statistical results manifest that the performance of oscillation impacter is favourable in different formations and the ROP is improved significantly. [Received: July 6, 2015; Accepted: January 6, 2017]