Aseismic performances of constrained damping lining structures made of rubber-sand-concrete

Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using a rubber-sand-concrete(RSC)as the aseismic material,is proposed.The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests.The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis,composite loss factor and damping ratio of the transfer function analysis,and total vibration level of octave spectrum analysis were discussed.The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear,and that the hollow damping layer had a better aseismic performance than the flat damping layer one.The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated.The effects of the peak ground acceleration(PGA)and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain(PEEQ)were discussed.The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance,with PGA in the range(0.2-1.2)g and tunnel overburden depth in the range of 0-300 m.

Prediction of Damping Capacity Demand in Seismic Base Isolators via Machine Learning

Base isolators used in buildings provide both a good acceleration reduction and structural vibration control structures.The base isolators may lose their damping capacity over time due to environmental or dynamic effects.This deterioration of them requires the determination of the maintenance and repair needs and is important for the long-termisolator life.In this study,an artificial intelligence prediction model has been developed to determine the damage and maintenance-repair requirements of isolators as a result of environmental effects and dynamic factors over time.With the developed model,the required damping capacity of the isolator structure was estimated and compared with the previously placed isolator capacity,and the decrease in the damping property was tried to be determined.For this purpose,a data set was created by collecting the behavior of structures with single degrees of freedom(SDOF),different stiffness,damping ratio and natural period isolated from the foundation under far fault earthquakes.The data is divided into 5 different damping classes varying between 10%and 50%.Machine learning model was trained in damping classes with the data on the structure’s response to random seismic vibrations.As a result of the isolator behavior under randomly selected earthquakes,the recorded motion and structural acceleration of the structure against any seismic vibration were examined,and the decrease in the damping capacity was estimated on a class basis.The performance loss of the isolators,which are separated according to their damping properties,has been tried to be determined,and the reductions in the amounts to be taken into account have been determined by class.In the developed prediction model,using various supervised machine learning classification algorithms,the classification algorithm providing the highest precision for the model has been decided.When the results are examined,it has been determined that the damping of the isolator structure with the machine learning method is predicted successfully at a level exceeding 96%,and it is an effective method in deciding whether there is a decrease in the damping capacity.

Microstructure and damping properties of LPSO phase dominant Mg-Ni-Y and Mg-Zn-Ni-Y alloys

This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.

Transient Damping of Virtual Synchronous Generator for Enhancing Synchronization Stability during Voltage Dips

Virtual synchronous generators(VSGs)are widely introduced to the renewable power generation,the variablespeed pumped storage units,and so on,as a promising gridforming solution.It is noted that VSGs can provide virtual inertia for frequency support,but the larger inertia would worsen the synchronization stability,referring to keeping synchronization with the grid during voltage dips.Thus,this paper presents a transient damping method of VSGs for enhancing the synchronization stability during voltage dips.It is revealed that the loss of synchronization(LOS)of VSGs always accompanies with the positive frequency deviation and the damping is the key factor to remove LOS when the equilibrium point exists.In order to enhance synchronization stability during voltage dips,the transient damping is proposed,which is generated by the frequency deviation in active power loop.Additionally,the proposed method can realize seamless switching between normal state and grid fault.Moreover,detailed control design for transient damping gain is given to ensure the synchronization stability under different inertia requirements during voltage dips.Finally,the experimental results are presented to validate the analysis and the effectiveness of the improved transient damping method.

基于PSD特征的FBCCA脑电信号识别方法

当前基于稳态视觉诱发电位(steady-state visual evoked potential,SSVEP)的脑机接口(brain-computer interfaces,BCIs)使用的都是单一识别算法,针对不同时间长度的识别准确率较低。提出了一种基于滤波器组的典型相关分析(filter bank canonical correlation analysis,FBCCA)与功率谱密度(power spectral density,PSD)分析相结合的SSVEP识别算法,可以提高SSVEP识别的普适性与准确率。该方法使用FBCCA寻找高相似度的参考频率信号,再通过多组PSD分析来锁定最终的响应频率,完成频率识别。该方法无需经过训练就能得到较高的识别准确率。实验结果表明:在刺激时长为1 s时,该方法能达到86.61%的准确率,比PSD分析方法提升了5.44%,比典型相关性分析方法(canonical correlation analysis,CCA)提升了10.38%的准确率,比FBCCA提升了8.86%的准确率。

Optimization on microstructure,mechanical properties and damping capacities of duplex structured Mg–8Li–4Zn–1Mn alloys

Optimizing the mechanical properties and damping capacity of the duplex-structured Mg–Li–Zn–Mn alloy by tailoring the microstructure via hot extrusion was investigated.The results show that the Mg–8Li–4Zn–1Mn alloy is mainly composed ofα-Mg,β-Li,Mg–Li–Zn and Mn phases.The microstructure of the test alloy is refined owing to dynamic recrystallization(DRX)during hot extrusion.After hot extrusion,the crushed precipitates are uniformly distributed in the test alloy.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of as-extruded alloy reach 156 MPa,208 MPa,and 32.3%,respectively,which are much better than that of as-cast alloy.Furthermore,the as-extruded and as-cast alloys both exhibit superior damping capacities,with the damping capacity(Q^(-1))of 0.030 and 0.033 at the strain amplitude of 2×10^(-3),respectively.The mechanical properties of the test alloy can be significantly improved by hot extrusion,whereas the damping capacities have no noticeable change,which indicates that the duplex-structured Mg–Li alloys with appropriate mechanical properties and damping properties can be obtained by alloying and hot extrusion.

基于PSD的火炮身管膛线精度测量数据补偿方法

针对火炮身管内部膛线测量技术及自动检测问题,提出一种精度测量数据补偿方法。搭建火炮内膛检测机器人测量系统。采用激光测距仪对火炮身管阴阳线内径进行测量,使用PSD激光位置传感器对火炮身管轴线与测量系统轴线的偏心距离进行测量,分析检测误差产生的原因,推导基于矢量三角法的测量数据精度补偿算法和误差补偿计算公式,通过补偿前后数据的对比分析,结果表明:该测量补偿方法是有效的,能够解决火炮内膛轴线与机器人旋转中心不重合产生误差的问题。

基于PSD传感器的炸点三维坐标测量方法研究

针对野外炸点空间三维坐标测量的问题,提出了基于二维PSD位置传感器的炸点位置测量方法,构建了基于二维PSD位置传感器的炸点三维坐标测量系统;基于双目视觉原理建立了炸点空间三维坐标测量数学模型;研究了被动探测系统在野外远距离下的标定技术;通过系统误差分解传递,分析了各参数的误差;在Matlab中分别绘制了炸点位置坐标3个维度的误差分布图,并分析了测量系统误差随炸点实际位置变化的分布情况;根据误差分布图得到了在理论100 m测试距离下X坐标最大测量误差约为0.292~0.303 m,Y坐标最大测量误差约为0.251~0.371 m,Z坐标最大测量误差0.270~0.336 m;最后通过静爆实验对测量方法正确性、被动探测系统标定技术可行性和测量系统功能性进行了验证,结果表明测量系统响应速度快且功能正常,被动探测系统标定技术具备可行性且操作方便,可适用于野外炸点位置的快速测量。

Damping performance of SiC nanoparticles reinforced magnesium matrix composites processed by cyclic extrusion and compression

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))

A Review of Influencing Factors of Damping Properties of High Manganese Steel

High manganese steel has wide prospects in industry due to their excellent mechanical and damping properties. The quenching structures of high manganese steel are ε-martensite, γ-austenite and α'-martensite. Researches show that the damping properties of high manganese steel are related to these microstructures. Besides, there are many ways to improve the damping property of damping alloys. This paper reviews the damping mechanism and the influences of the ad-dition of alloying elements, heat treatment, pre-deformation and other factors on their damping performance, hoping to provide methods and ideas for the study of damping properties of high manganese steel. .

A marine gravimeter based on electromagnetic damping and its tests in the South China Sea

A new gravity sensor based on electromagnetic damping for the JMGrav marine gravimeter is presented.The new gravity sensor considered the advanced construction methods of the electromagnetic damping system of the gravimeter.The design features of the new system are discussed and the research survey data in the South China Sea are shown.Numerical simulations are applied to model the magnetic and mechanical characteristics of the system using finite element analysis and to evaluate the force distribution and the resulting damping effects.The performance characteristics of the system were tested on a motion simulator in laboratory,and the gravimeter was subjected to vertical accelerations of up to 100 Gal in 1-1000 s.It was found that the amplitude reduction of vertical accelerations in 3-15 s is 30-45 dB,with a time lag of 2-5 s,while the effect on gravity in period greater than 600 s is less than 0.5 dB,with a time lag of less than 100 s.The accelerations cause discrepancies of approximately only 1 mGal between the static value and the mean dynamic value.The sea tests were conducted in September 2020.Gravity measurements were taken with a JMGrav marine gravimeter onboard the R/V Dongfanghong 3,and the effective survey line exceeded 2000 km.Completely irregular accelerations with peaks up to 100 Gal yielded a reduction of approximately 40 dB in amplitude.The survey data were evaluated using ocean gravity field models and grid line tests.The results show that the accuracy of the gravity measurements is better than 2 mGal.

Blowup of Solutions to the Non-Isentropic Compressible Euler Equations with Time-Dependent Damping and Vacuum

This paper mainly studies the blowup phenomenon of solutions to the compressible Euler equations with general time-dependent damping for non-isentropic fluids in two and three space dimensions. When the initial data is assumed to be radially symmetric and the initial density contains vacuum, we obtain that classical solution, especially the density, will blow up on finite time. The results also reveal that damping can really delay the singularity formation.

Resonance and Bifurcation of Fractional Nonlinear Systems with Power Damping Term for Robot Grinding

A fractional nonlinear system with power damping term is introduced to study the forced vibration system in order to solve the resonance and bifurcation problems between grinding wheel and steel bar during robot grinding.The robot,grinding wheel and steel bar are reduced to a spring-damping second-order system model.The implicit function equations of vibration amplitude of the dynamic system with coulomb friction damping,linear damping,square damping and cubic damping are obtained by average method.The stability of the system is analyzed and explained,and the stability condition of the system is proposed.Then,the amplitude-frequency characteristic curves of the system under different fractional differential orders,nonlinear stiffness parameters,fractional differential term coefficients and external excitation amplitude are analyzed.It is shown that the fractional differential term in the dynamic system is the damping characteristic.Then the influence of four kinds of damping on the vibration amplitude of the system under the same parameter is investigated and it is proved that the cubic damping suppresses the vibration of the system to the maximum extent.Finally,based on the idea that the equilibrium point of the system is the constant part of the Fourier series expansion term,the bifurcation behavior caused by the change of damping parameters in linear damping,square damping and cubic damping systems with different values of fractional differential order is investigated.

An abnormal carbody swaying of intercity EMU train caused by low wheel-rail equivalent conicity and damping force unloading of yaw damper

Low-frequency carbody swaying phenomenon often occurs to railway vehicles due to hunting instability,which seriously deteriorates the ride comfort of passengers.This paper investigates low-frequency carbody swaying through experimental analysis and numerical simulation.In the tests,the carbody acceleration,the wheel-rail profiles,and the dynamic characteristics of dampers were measured to understand the characteristics of the abnormal carbody vibration and to find out its primary contributor.Linear and nonlinear numerical simulations on the mechanism and optimization measures were carried out to solve this carbody swaying issue.The results showed that the carbody swaying is the manifest of carbody hunting instability.The low equivalent conicity and the decrease of dynamic damping of the yaw damper are probably the cause of this phenomenon.The optimization measures to increase the equivalent conicity and dynamic damping of the yaw damper were put forward and verified by on-track tests.The results of this study could enrich the knowledge of carbody hunting and provide a reference for solving abnormal carbody vibrations.

Nonlocal stress gradient formulation for damping vibration analysis of viscoelastic microbeam in thermal environment

An integral nonlocal stress gradient viscoelastic model is proposed on the basis of the integral nonlocal stress gradient model and the standard viscoelastic model,and is utilized to investigate the free damping vibration analysis of the viscoelastic BernoulliEuler microbeams in thermal environment.Hamilton's principle is used to derive the differential governing equations and corresponding boundary conditions.The integral relations between the strain and the nonlocal stress are converted into a differential form with constitutive constraints.The size-dependent axial thermal stress due to the variation of the environmental temperature is derived explicitly.The Laplace transformation is utilized to obtain the explicit expression for the bending deflection and moment.Considering the boundary conditions and constitutive constraints,one can get a nonlinear equation with complex coefficients,from which the complex characteristic frequency can be determined.A two-step numerical method is proposed to solve the elastic vibration frequency and the damping ratio.The effects of length scale parameters,viscous coefficient,thermal stress,vibration order on the vibration frequencies,and critical viscous coefficient are investigated numerically for the viscoelastic Bernoulli-Euler microbeams under different boundary conditions.

Laboratory investigation on damping characteristics of homogeneous and stratified soil-ash system

In this study,the damping responses of uniform soil,equi-proportional fly ash,and local soil as a single unit were investigated.The large-strain cyclic triaxial tests were performed for the specimen compacted at the desired density(95%e99%of maximum dry density).The compacted specimens were tested under the loading frequency of 0.3e1 Hz with medium confinement of 70e100 kPa.Also,the unsymmetrical behavior of the hysteresis loop was analyzed using three different damping estimation approaches,i.e.symmetric hysteresis loop(SHL),asymmetric hysteresis loop(ASHL),and the modified American Society for Testing and Materials(ASTM)method.The outcome of the study shows for fly ash,local soil,and layered soil-ash,the ASHL technique has the highest damping value,followed by ASTM and then the SHL approach.The specimens prepared under high density and subjected to high confinement show low damping values.However,the specimens tested at high frequency exhibits high damping behavior.Similarly,the damping value of fly ash determined using the SHL and ASHL methods has a similar profile and reaches a maximum at 1%shear strain value before decreasing.The composite stratified deposit exhibits more dependency on relative compaction,confining pressure,and less on loading frequency.Based on the results,it is highly recommended to use the ASHL approach,especially under large strain conditions irrespective of soil type.The maximum damping ratio of stratified deposits is always in between the damping ratio of local soil and fly ash.The damping ratio of stratified soil and local soil is slightly larger than that of the other soils,although the damping ratio of fly ash is equivalent to that of the sand and clayey soil.These results may be helpful in the accurate determination of the damping properties of the layered soil-ash system that is required in the seismic response analysis.

Design and analysis of a two-dimensional vibration control mechanism based on vibro-impact damping

The robotic drilling always generates the axial vibration along the drill bit and the torsional vibration around the drill bit,which will adversely affect the drilling precision.A vibration control mechanism fixed between the end-effector and the robot is proposed,which can suppress the axial and torsional vibrations based on the principle of vibro-impact(VI)damping.The energy dissipation of the system by vibro-impact damping is analyzed.Then,the influence of the structure parameters on the vibration attenuation effect is studied,and a semi-active vibration control method of variable collision clearance is presented.The simulation results show that the control method has effective vibration control performance.

A Review on Methods for Determining the Vibratory Damping Ratio

This article aims to popularize the methods for determining the vibratory damping ratio, to explain the various mathematical and physical theorems related to the establishment of literal expressions. Vibration damping is an essential parameter to reduce the dynamic responses of structures. The study aimed at its determination is necessary and essential for the safeguard of buildings and human lives during the earthquake. Among the main methods studied in this article, the free vibration attenuation method seems to be easy to implement but requires a state-of-the-art device to capture the responses. In addition to this device, the other methods require other equipment for the vibration of the system and the transformation of the responses in the frequency domain.

Design of Damping Damping Design of New Boring Head Drive Structure

This paper takes the boring head of 20 roll mill as the research object,optimizes the vibration inside the boring head through a differential damping structure,and then conducts the 3 d model inside the boring head through SolidWorks,and checks the interference of the boring head model.Finally,Ansys workbench finite element analysis software is used to analyze and verify the vibration damping characteristics of the differential damping structure.

Near resonance vibration isolation on a levered-dual response(LEDAR)Coulomb-damped system by differential preloads/offsets in linear springs

The levered-dual response(LEDAR)Coulomb-damped system attains near resonant vibration isolation by differential preloads/offsets in linear springs.It takes the advantages of both the preloads/offsets in linear springs and the guiderail friction for realizing different levels of vibration isolation.The isolation capacities are investigated on the strategies with both the horizontal and vertical guiderails,with the horizontal rail only,and without guiderails.The compressive preloads generally result in the consumption of most of the initial excitation energy so as to overcome the potential threshold.The isolation onsets at the frequency ratio of 1∓0.095 on the left-hand side(LHS)and the right-hand side(RHS)of the lever are relative to the load plate connector.The observed near resonant isolation thus makes the LEDAR system a candidate for the isolation of the mechanical systems about resonance while opening a path for simultaneous harvesterisolation functions and passive functions at extreme frequencies.