Based on vibration state in transition from the mass to the inerter, a passive realization method of ideal skyhook damping was presented. According to such a method, a passive groundhook-damping suspension was designed. After the simscape model of the inerter was founded, the full-car simscape model was built by using the network approach of physical topology. By comparing the performances of conventional passive, ideal and passive groundhook-damping suspensions, the proposed realization method was verified. The results show that the proposed suspension can suppress wheel resonance, reduce RMS values of dynamic tire load by 30% or greater, and significantly improves ride safety. The results also indicate the performances of the ideal and passive groundhook-damping suspensions are basically the same.
The influence of rotational speed fluctuation and the phase shift between forward and backward contact on mesh point position are analyzed, combined with boundary conditions of single tooth meshing, double tooth meshing, profile modification and analytical method of calculating mesh stiffness, the nonlinear mesh stiffness model is established which can achieve real-time feedback with nonlinear model of spur gears and produce more precise mathematical model of gear meshing process. A two-degree-of-freedom nonlinear model of spur gear pair with input torque fluctuation is established by taking the backlash and nonlinear mesh stiffness into consideration. Based on the nonlinear dynamic model, the influence of profile modification on dynamic behavior of spur gear pair is studied. The resluts show that the amount of profile modification significantly affect the dynamic characteristics of spur gear pair, and existing an optimal amount of profile modification to make the dynamic load factor reach to a minimum. When the amount of profile modification exceeds a certain critical value, single-side-impact or double-side-impact occur and gear dynamic loads significantly increase. Increasing the length of profile modification can reduce the minimum value of dynamic load factor under certain input torque. The maximum amount of profile modification should be the combined tooth deflection evaluated at the highest point of single tooth contact under the minimum input torque.
In order to study the influence of cross wind on pantograph-catenary dynamic behaviors, the stochastic wind field of pantograph-catenary system was established to obtain the wind speed time series on the pantograph and catenary based on the linear filtering method of AR model and the Davenport power spectrum. The aerodynamic model of pantograph/high-speed train was built and the computational fluid dynamics method was used to calculate the aerodynamic uplift forces of the pantograph for different cross wind speeds while the train running at a speed of 300 km/h, then the time series of aerodynamic uplift force was obtained under the average wind speed of 20m/s. The three dimensional pantograph-catenary coupled dynamic model was used to analyze the influence rule of the cross wind on pantograph-catenary dynamic systematically. The results show that the aerodynamic uplift force of the pantograph is increased while it is acted by cross wind and is directly proportional to the square of the cross wind speed. Moreover, the increase and fluctuation of the pantograph aerodynamic uplift force induced by the cross wind make the mean and standard deviation of the contact force increased. The contact status between the collector strip and the contact wire is changed due to the wind-induced vibration of the catenary which increases the fluctuation range of the contact force. Therefore, while the train running in the cross wind environment, not only the contact force is increased and will intensify the abrasion of the collector strip and the contact wire, but also the current collection quality is deteriorated because of the minimum value of the contact force decreased while the standard deviation increased.
Based on Fluent 6.3 software, the Reynolds mean Navier-Stokes equations were selected to simulate 3D steady wind field of complex dish frame. Computational domain model which conform to unrestraint flow field and grid independent solutions was built by applying multi-angle wind modeling methods with inner domain subarea on cylindrical. And, 45 group results of total wind load, wind pressure distribution and flow around characteristic were acquired by simulation. Change regulations of wind load with different working condition were analyzed, and, the reasonableness of simulation results were verified by qualitative comparative analysis between load curve and parabolic radar antenna wind tunnel test. The ratio of condenser mirror load on total wind load of frame was explored by adopting dimensionless method. Condenser shape factor distribution and extremes of each subarea load were acquired under typical working conditions. And, load generating mechanism was revealed by further analysis of the flow around characteristics, which provide a load basis on wind-resistant design of the whole structure of dish photo-thermal solar energy.
During the pressure signal measurement of explosion field, the interference signal of experiment field causes easily the false triggering resulting in the failed measurement. A measurement technology based on mass storage and less read is proposed for the distributed storage measurement system. Long signal acquisition is achieved by mass storage of measurement data, to avoid the failure due to false triggering. On the other hand, small valid data segment is extracted by signal identification, which improves the efficiency of data transmission and data processing. A measurement system based on mass storage and less read technology is designed and implemented for ground pressure of explosion field, and the measurement node is characterized by sampling rate of 1Msps, data storage of 128Gb, valid data segment of 512kW, and Wi-Fi wireless network coverage.
Concrete material under the dynamic load has different characteristics with itself under the static load. This paper study on the CT test,the plain concrete specimen under dynamic loading as the object of study. Analysis the concrete meso structure change effect on the dynamic mechanical properties such as strength, deformation and damage morphology under the sine wave dynamic pressure and dynamic tensile load. Through the research of CT difference image, the moving crack in concrete compressive loads is developed rapidly, short failure process, failure crack is much, damage area is large, etc; Through CT number density segmentation image research, the dynamic tensile loading concrete micro crack suddenly merged to form a main crack through the specimen, the specimen breaks suddenly. By research the CT number change law in the process of loading, the concrete density decrease after a first increases under the dynamic pressure load, specimens experienced compaction, expansion, crack coalescence until finally the failure process, and the specimen under the dynamic tensile load density continuously reduced until fracture, early without load compaction. Different stress state of concrete under dynamic pressure, dynamic, lead to the damage degree is different, the formation of the crack area is different, the total energy required is different also, eventually led to the determination of the strength of the different, different stress state is the root cause of the dynamic pressure, the difference of dynamic tensile strength.
An in-situ simulation explosion test is carried out at a site with Ningbo marine silt soft soil. The history and evolution laws of excess pore water pressure, shock pressure and temperature on the conditions of different explosive quantity and buried depth are obtained. The test results reveal the existence of coupling phenomena of seepage, stress and temperature. It is also shown that the peak of excess pore water pressure increases with the increase of explosive quantity and the dissipation of pore pressure is relatively quick in early minutes after the explosion and then it decreases. A dividing pressure which means a value from shock wave to elastic wave is determined and it found that the dividing pressure is related to the soils’ character,especially dependent on the air content. The explosion temperature has a certain conduction time and rise time in soft soil, and it rises more slowly than that in the air. Besides, relevant theories are used to compute the pressure and temperature.The calculated results are compared with the measured results. The conclusions of this paper provide a reference for the design of underground civil air defense engineering and ground compaction engineering in coastal soft soil area.
A sensitive damage detection method is proposed in this paper, which is based on analyzing ultrasonic guided waves signal using Lyapunov exponents of Duffing equation. The feasibility of the method is verified by indetifying Guided wave signal in a steel pipe. Firstly, the Duffing Inspection System and the inspection principle are explained. The determination of system parameters is described in detail. Secondly, the propagation of guided wave in 3m-in-length steel pipe is measured experimentally, and the measured signals are analyzed by the Duffing Inspection System. The experimental results show that the Lyapunov exponents of Duffing Inspection System can effectively identify small defect echo and has strong immunity to the noise simultaneously. In addition, a damage index is defined by the ratio of the Lyapunov Exponent when inputting measured guided wave signal with noise to the one when only inputting measured noised signal. It can help us evaluate the damage level of defect. This method is significant for improving the sensitivity of small defects detection using ultrasonic guided wave.
The tension-shear chain model and 2D finite element model of nacre—a kind of stacking composite material—are built up, and its band gap is computed based on a multi-level substructure scheme. The results show that the nacre-like material is a kind of Bragg phononic crystal holding a relatively wide first band gap in low frequency domain and several flat bands in high frequency domain. So this kind of material can lead to the vibration reduction in a wide frequency range. Moreover, these materials are more efficient to realize the goal of vibration reduction in low frequencies, because it doesn’t have the Fano-like interference phenomena, which will happen in the locally resonant phononic crystals for the mechanism of their band gaps. Furthermore, the transmission characteristics are computed to verify the result of band gap. The further research demonstrates that band gap characteristics are mainly influenced by density of the mineral (“Brick”) component and elastic modulus of the protein (“Mortar”) component and the first band gap of nacre-like material subjects to the coupling influence of the two material parameters. An appropriate match of the two material parameters can contribute to a larger relative band gap. And the band gap is adjustable as well, which makes the nacre-like material a novel idea for the design of new vibration reduction structure.
For the large vertical displacement between the frame and rocking wall, energy consumption components should be added to protect the main structure. Based on this, additional damping frame-rocking wall is proposed and structural single type of damper amount also could be calculated through the equivalent linearization theory, by defining the objective function, the best damper layout of structure with viscous damper and metal damper which can make the minimum value of the function could be determined, and conclusions are as follows: (1) for the shear-bending structure, the viscous damper can be arranged along the total height of structure when acceleration is considered and the metal damper arranged at two thirds the lower part while the viscous damper arranged at one third the upper when displacement, acceleration and storey drift are considered; (2) for the shearing structure, the metal damper arranged at half the lower part while the viscous damper arranged at half the upper when storey drift is considered, in addition, the metal damper arranged at one third the lower part while the viscous damper arranged at two thirds the upper when displacement, acceleration and storey drift are all considered.
Based on the Non-Gaussian Simulation of multivariate stochastic processes method, one prediction method for wind pressure extreme value is proposed. The wind pressures time histories of several taps on opening roof are simulated by Multivariate Non-Gaussian Simulation method based on wind tunnel test data. It is shown that the power spectra density, coherence, deviation, skewness, kurtosis of simulated non-gaussian time histories are very close to the destination. Then the peak factors of wind pressures on opening roof are predicted from Multivariate Non-Gaussian Simulation time histories for several times by typical extreme value theory, and the results are compared with that of several general methods. It is shown that Davenport method overestimated the positive peak factor by 60% whose skewness is negative, and underestimated the negative peak factor by 43%; Sadek-Simiu method overestimated the peak factor by 50% which have high kurtosis; the proposed method can predict the peak factor effectively, and the overall error is smallest.
a dynamic model for parallel-axis helical gears is proposed including friction between the contact teeth which can be used in dynamic analysis of variable speed process. In this model, the position of the action line and sliding velocity are determined by the angular displacement of the driving gear, and the translational displacements and angular displacements are chosen as generalized coordinates, so the model can be used in analysis of the process of variable speed of gear transmission system, furthermore the friction is calculated by variable friction coefficient. The acceleration process of an example is numerically simulated with the model proposed in this paper and the dynamics responses are compared with that from the model utilizing constant friction coefficient and without friction. Some conclusion can be obtained from the comparison: friction decreases the critical speed of meshing aparting of helical gear transmission and has effects of damping and excitation, which affects the dynamic responses of helical gears. Moreover, the variable friction coefficient has different effects on the dynamic responses of helical gears than the constant friction coefficient.
The coupling-vibration of spacecraft with large ring-shaped deployable antenna induced by temperature variations during the spacecraft entering and leaving the Earth’s shadow was numercially analysized. The transient temperature field of large deployable antenna was solved using the finite element method, and a rigid-flexible coupling dynamic model was established for the coupling-vibration analysis. The results show that temperature gradient of the antenna itself is mainly between the light side and the backlight side, and with which the thermal response characteristic time of antenna can be estimated. Obvious thermally induced coupling-vibration of antenna structure and the satellite attitude can be observed. The method present in this paper can reasonably be used to predict the thermally induced coupling-dynamic of deployable satellite antenna system.
It will make damage detection based on lamb wave more effectively to obtain accurate damage-scattered signal. Meanwhile, one of the key obstacles in the process of extracting damage-scattered signal is the fact that damage-scattered signal is often overlapped with many other reflected signals from structural features such as the boundary. To solve overlap, the baseline subtraction approach which is sensitive to external factors such as structure and environment is adopted in many existing methods to obtain damage-scattered signal. Due to the signal after incident wave in the damage signal captured by sensor is not an arbitrary signal, but rather a superposition of several reflected waves, so as long as the superposition of reflected waves which is most similar to the target signal is got, the target signal is considered to be interpreted successfully, and consequently, damage-reflected signal is got. Therefore, an approach is proposed based on the maximum likelihood for damage signal decomposition. Damage-reflected signals and boundary-reflected signals are simulated on the basis of analysis of lamb wave propagation characteristics, and then the various parameters of the synthesis of the above signals are optimized through genetic algorithm based on similarity index in order to make the similarity between the synthetic signal and the target signal reach the maximum. Finally, damage is localized through Time of Flight (ToF). The experimental results on an aluminum plate indicate that damage- reflected signal can be accurately extracted from the aliasing signal by means of the proposed method.