A high frequency vibration compensation approach for ultrahigh resolution SAR imaging based on sinusoidal frequency modulation Fourier-Bessel transform

Ultrahigh resolution synthetic aperture radar(SAR)imaging for ship targets is significant in SAR imaging,but it suffers from high frequency vibration of the platform,which will induce defocus into SAR imaging results.In this paper,a novel compensation method based on the sinusoidal frequency modulation Fourier-Bessel transform(SFMFBT)is proposed,it can estimate the vibration errors,and the phase shift ambiguity can be avoided via extracting the time frequency ridge consequently.By constructing the corresponding compensation function and combined with the inverse SAR(ISAR)technique,well-focused imaging results can be obtained.The simulation imaging results of ship targets demonstrate the validity of the proposed approach.

Vibration Frequency in Micro-Vibration Therapy in Nursing Care: A Cross-Sectional Study

This study investigated the vibration frequency in micro-vibration therapy (MVT) performed as a part of nursing care in Japan. We surveyed 31 nurses (25 women and 6 men) who performed MVT with accelerometers attached to the backs of their hands, and the data obtained were analyzed. The mean vibration frequency was 8.3 Hz (standard deviation [SD]: 1.9 Hz) bilaterally, with a left-right difference of 0.8 Hz (SD: 1.1 Hz, right > left). Furthermore, vibration frequency was correlated with duration of MVT use (rs = 0.5, P < 0.01). The vibration frequency was higher in men (9.2 Hz, SD: 2.4 Hz) than in women (8.1 Hz, SD: 1.8 Hz), but this difference was not significant (P = 0.34). The vibrations of MVT are of a lower frequency than those of other vibration therapies.

Research on modeling and self-excited vibration mechanism in magnetic levitation-collision interface coupling system

The modeling and self-excited vibration mechanism in the magnetic levitation-collision interface coupling system are investigated.The effects of the control and interface parameters on the system's stability are analyzed.The frequency range of self-excited vibrations is investigated from the energy point of view.The phenomenon of self-excited vibrations is elaborated with the phase trajectory.The corresponding control strategies are briefly analyzed with respect to the vibration mechanism.The results show that when the levitation objects collide with the mechanical interface,the system's vibration frequency becomes larger with the decrease in the collision gap;when the vibration frequency exceeds the critical frequency,the electromagnetic system continues to provide energy to the system,and the collision interface continuously dissipates energy so that the system enters the self-excited vibration state.

Ab initio potential energy surface and anharmonic vibration spectrum of NF_(3)^(+)

Potential energy surfaces(PESs), vibrational frequencies, and infrared spectra are calculated for NF_(3)^(+) using ab initio calculations, based on UCCSD(T)/cc-p VTZ combined with vibrational configuration interaction(VCI). Based on an iterative algorithm, the surfaces(SURF) program adds automatic points to the lattice representation of the potential function, the one-dimensional and two-dimensional PESs are calculated after reaching a convergence threshold, finally the smooth image of the potential energy surface is fitted. The PESs accurately account for the interaction between the different modes, with the mode q_(6) symmetrical stretching vibrations having the greatest effect on the potential energy change of the whole system throughout the potential energy surface shift. The anharmonic frequencies are obtained when the VCI matrix is diagonalized. Fundamental frequencies, overtones, and combination bands of NF_(3)^(+) are calculated, which generate the degenerate phenomenon between their frequencies. Finally, the calculated anharmonic frequency is used to plot the infrared spectra.Modal antisymmetric stretching ν_(5) and symmetric stretching ν_(6) exhibit a phenomenon of large-intensity borrowing. This study can provide data to support the characterization in the laboratory.

Effect of vibration frequency on primary phase and properties of grey cast iron fabricated by lost foam casting

The properties of gray cast iron(GCI)are affected by density of matrix,size of flake graphite and primary austenite.In this paper,the Y-type specimen of GCI was prepared by lost foam casting(LFC)with and without vibration,and the influence of vibration frequency on the density of matrix,size of primary phase,and properties of the GCI was studied.The results show that the length of the flake graphite and the size of the primary austenite in GCI firstly decrease and then increase with the increase of the vibration frequency.With a vibration frequency of 35 Hz,the length of the flake graphite is the shortest,the primary austenite is the finest and the density of the matrix is the highest.In addition,the tensile strength,elongation and hardness of the GCI firstly increase and then decrease with the increase of the vibration frequency,due to the refinement of the primary phase and the increase of the matrix density.In order to analyze the refinement mechanism of the primary phase of the GCI fabricated by the LFC with vibration,the solidification temperature fields of the GCI fabricated by the LFC with the vibration frequency of 0 and 35 Hz were measured.The results show that the vibration reduces the eutectic point of the GCI and increases the supercooling degree during the eutectic transformation.As a result,the length of the flake graphite and the size of the primary austenite in GCI fabricated by LFC with the vibration frequency of 35 Hz decrease.

On Frequency Sensitivity and Mode Orthogonality of Flexible Robotic Manipulators

This paper presents sensitivity analysis of vibration frequencies of flexible manipulators with respect to variations of systems parameters such as rotational inertia of hub,and mass,moment,and side of tip load.Both Euler-Bernoulli and Timoshenko dynamical models of flexible manipulators are discussed.By using variational method,sensitivity indices are obtained with explicit expressions for measuring the sensitivity of frequencies.Based on variational formulations,a novel method for deriving the orthogonal relations among vibration modal shape functions of flexible manipulators is introduced.With this method,the orthogonal relations can be derived easily without invoking the tedious process of differentiation and integration by part,as commonly used in their derivation.

Cascaded quasi-zero stiffness nonlinear low-frequency vibration isolator inspired by human spine

Human motion induced vibration has very low frequency,ranging from 2 Hz to 5 Hz.Traditional vibration isolators are not effective in low-frequency regions due to the trade-off between the low natural frequency and the high load capacity.In this paper,inspired by the human spine,we propose a novel bionic human spine inspired quasi-zero stiffness(QZS)vibration isolator which consists of a cascaded multi-stage negative stiffness structure.The force and stiffness characteristics are investigated first,the dynamic model is established by Newton’s second law,and the isolation performance is analyzed by the harmonic balance method(HBM).Numerical results show that the bionic isolator can obtain better low-frequency isolation performance by increasing the number of negative structure stages,and reducing the damping values and external force values can obtain better low-frequency isolation performance.In comparison with the linear structure and existing traditional QZS isolator,the bionic spine isolator has better vibration isolation performance in low-frequency regions.It paves the way for the design of bionic ultra-low-frequency isolators and shows potential in many engineering applications.

Experimental research and energy analysis of a new type of dry ice powder pneumatic rock breaking technology

When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We developed a supercritical CO_(2)true triaxial pneumatic rock-breaking experimental system,and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking.The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed.The fracturing mechanism of dry ice powder pneumatic rock breaking is studied.The research results show that:(1)The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2)The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz.Due to the dispersion effect,the dominant frequency of 10–30 Hz appears abnormally attenuated;(3)The traditional CO_(2)phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology,and the trinitrotoluene(TNT)equivalent of fracturing energy is applicable to the Sadovsky formula;(4)Dry ice powder pneumatic rock breaking is shock wave and highenergy gas acting together to fracture rock,which can be divided into three stages,among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.

Safety Assessment of Liquid Launch Vehicle Structures Based on Interpretable Belief Rule Base

A liquid launch vehicle is an important carrier in aviation,and its regular operation is essential to maintain space security.In the safety assessment of fluid launch vehicle body structure,it is necessary to ensure that the assessmentmodel can learn self-response rules from various uncertain data and not differently to provide a traceable and interpretable assessment process.Therefore,a belief rule base with interpretability(BRB-i)assessment method of liquid launch vehicle structure safety status combines data and knowledge.Moreover,an innovative whale optimization algorithm with interpretable constraints is proposed.The experiments are carried out based on the liquid launch vehicle safety experiment platform,and the information on the safety status of the liquid launch vehicle is obtained by monitoring the detection indicators under the simulation platform.The MSEs of the proposed model are 3.8000e-03,1.3000e-03,2.1000e-03,and 1.8936e-04 for 25%,45%,65%,and 84%of the training samples,respectively.It can be seen that the proposed model also shows a better ability to handle small sample data.Meanwhile,the belief distribution of the BRB-i model output has a high fitting trend with the belief distribution of the expert knowledge settings,which indicates the interpretability of the BRB-i model.Experimental results show that,compared with other methods,the BRB-i model guarantees the model’s interpretability and the high precision of experimental results.

A critical review of wheel/rail high frequency vibration-induced vibration fatigue of railway bogie in China

Purpose–This review aims to give a critical view of the wheel/rail high frequency vibration-induced vibration fatigue in railway bogie.Design/methodology/approach–Vibration fatigue of railway bogie arising from the wheel/rail high frequency vibration has become the main concern of railway operators.Previous reviews usually focused on the formation mechanism of wheel/rail high frequency vibration.This paper thus gives a critical review of the vibration fatigue of railway bogie owing to the short-pitch irregularities-induced high frequency vibration,including a brief introduction of short-pitch irregularities,associated high frequency vibration in railway bogie,typical vibration fatigue failure cases of railway bogie and methodologies used for the assessment of vibration fatigue and research gaps.Findings–The results showed that the resulting excitation frequencies of short-pitch irregularity vary substantially due to different track types and formation mechanisms.The axle box-mounted components are much more vulnerable to vibration fatigue compared with other components.The wheel polygonal wear and rail corrugation-induced high frequency vibration is the main driving force of fatigue failure,and the fatigue crack usually initiates from the defect of the weld seam.Vibration spectrum for attachments of railway bogie defined in the standard underestimates the vibration level arising from the short-pitch irregularities.The current investigations on vibration fatigue mainly focus on the methods to improve the accuracy of fatigue damage assessment,and a systematical design method for vibration fatigue remains a huge gap to improve the survival probability when the rail vehicle is subjected to vibration fatigue.Originality/value–The research can facilitate the development of a new methodology to improve the fatigue life of railway vehicles when subjected to wheel/rail high frequency vibration.

Analysis of Vibration Mode for H_2+F→HF+H Reaction Mechanism: Density functional Theory Calculation

Three density functional theory methods (DFT) have been used to investigate the H2+F?HF+H reaction comparing with the Hartree-Fock method and Moller-Plesset (MP2) perturbation theory method. Through the analysis of the vibrational mode and vibrational frequency in the reaction process, the reaction mechanism has been discussed. The activation energy, the reorganization energy and rate constant of the ET reaction are calculated at semi-quantitative level.

Effect of Train Carbody's Parameters on Vertical Bending Stiffness Performance

Finite element analysis(FEA) and modal test are main methods to give the first-order vertical bending vibration frequency of train carbody at present, but they are inefficiency and waste plenty of time. Based on Timoshenko beam theory, the bending deformation,moment of inertia and shear deformation are considered. Carbody is divided into some parts with the same length, and it's stiffness is calculated with series principle, it's cross section area, moment of inertia and shear shape coefficient is equivalent by segment length,and the fimal corrected first-order vertical bending vibration frequency analytical formula is deduced. There are 6 simple carbodies and1 real carbody as examples to test the formula, all analysis frequencies are very close to their FEA frequencies, and especially for the real carbody, the error between analysis and experiment frequency is 0.75%. Based on the analytic formula, sensitivity analysis of the real carbody's design parameters is done, and some main parameters are found. The series principle of carbody stiffness is introduced into Timoshenko beam theory to deduce a formula, which can estimate the first-order vertical bending vibration frequency of carbody quickly without traditional FEA method and provide a reference to design engineers.

Exploring the Efficiency of Experimental Construction of Sorting Ginned Cotton Seed Machine

In this paper, research has been conducted to increase the quantity of fiber produced in the enterprise by creating a sorting device for spun seeds, dividing them into fractions by geometric dimensions, and by re-ginning, separating those with long fibers. A new model was developed for geometric sorting of cotton seeds in the harvest, and experiments determined its effectiveness and the optimal values of the factors affecting the efficiency using mathematical modeling. Based on the results of the study, graphs of the influence of factors on device performance and on device efficiency were constructed.

Individual and combined influences of main loading parameters on granite damage development under ultrasonic vibration

Ultrasonic vibration technology has great potential to weaken hard rocks.Understanding the effect of ultrasonic vibration loading parameters is essential to accelerate the application of this technology in practical rock engineering.In the present work,three-factor mixed-level orthogonal ultrasonic vibration rock breaking tests were conducted to investigate the influence of the main loading parameters,including confining pressure,vibration frequency,and static force,on the damage of granite specimens.The individual and combined influences were analyzed according to the porosity increase and P-wave decrease of granite specimens using the variance analysis method.The results show that the combined effect of the static force and vibration frequency mainly promotes fatigue damage of specimens,that the confining pressure determines the damage behaviour and failure mode of specimens under ultrasonic vibration,and that the confining pressure and vibration frequency are the main factors that cause the fracture concentration in the upper part of specimens,an effect mechanistically driven by the obvious load energy attenuation.The research results provide theoretical guidance for the application of ultrasonic vibration technology.

Simulation and experimental study of fluid induced excitation mechanism for liquid rocket engine immerged rotor

Low frequency vibration has occurred in the turbine pump of one type of liquid-propellant rocket engine,which threatens the safety and reliability of the rockets and their engines seriously.To figure out the mechanism of the low frequency vibration faults,in this paper,a dynamical model of a immersion turbine pump rotor system was established for the consideration of the vibration caused by small gap annual flow excitation which properly happened in immersion turbine pump rotor.The Newmark directly integral method was used to simulate the vibration characteristics of turbine pump,and an experiment was also carried out to investigated this problem.Results showed that,the small gap annual flow excitation could induce large amplitude low frequency vibration on the turbine pump rotor bearing system.The amplitude and frequency of low frequency vibration had relation with the parameters of the turbine pump clearance structure,such as the clearance ratio,length-diameter ratio and the viscosity of the fluid medium.In order to avoid the vibration induced by the small gap annual flow excitation,sealing effect should be improved and length-diameter ratio should be decreased.

Graphene aerogel-based vibration sensor with high sensitivity and wide frequency response range

Compared with piezoresistive sensors,pressure sensors based on the contact resistance effect are proven to have higher sensitivity and the ability to detect ultra-low pressure,thus attracting extensive research interest in wearable devices and artificial intelligence systems.However,most studies focus on static or low-frequency pressure detection,and there are few reports on high-frequency dynamic pressure detection.Limited by the viscoelasticity of polymers(necessary materials for traditional vibration sensors),the development of vibration sensors with high frequency response remains a great challenge.Here,we report a graphene aerogel-based vibration sensor with higher sensitivity and wider frequency response range(2 Hz–10 kHz)than both conventional piezoresistive and similar sensors.By modulating the microscopic morphology and mechanical properties,the super-elastic graphene aerogels suitable for vibration sensing have been prepared successfully.Meanwhile,the mechanism of the effect of density on the vibration sensor’s sensitivity is studied in detail.On this basis,the sensitivity,signal fidelity and signal-to-noise ratio of the sensor are further improved by optimizing the structure configuration.The developed sensor exhibits remarkable repeatability,excellent stability,high resolution(0.0039 g)and good linearity(non-linearity error<0.8%)without hysteresis.As demos,the sensor can not only monitor low-frequency physiological signals and motion of the human body,but also respond to the high-frequency vibrations of rotating machines.In addition,the sensor can also detect static pressure.We expect the vibration sensor to meet a wider range of functional needs in wearable devices,smart robots,and industrial equipment.

Influence of High Frequency Vibration on Deep Drawing Process of AZ31 Sheet at Room Temperature

Quasi-ultrasonic vibration with a frequency of 15 kHz and a maximum output of 2 kW was imposed on the deep drawing process of AZ31 magnesium alloy sheet at room temperature,in order to reveal the effect of high frequency vibration on deformation behavior of AZ31 during the process.From the drawn results and the observation of the microstructure within the large deformation area,high frequency vibration has a great influence on the formability,the forming load and the failure mode of AZ31 sheet during the deep drawing process;the influence is a comprehensive result of so-called "volume effect" and "surface effect",and relies on the vibrating amplitude.Total forming load decreased significantly as soon as the vibration superimposed.According to the tensile test results of AZ31 bars under ultrasonic vibration,the formability of AZ31 sheet increases firstly with the increase of stimulating energy,then decreases and finally becomes brittle.Under the combined influence of "surface effect" and the "softening" in the "volume effect" near the relative low amplitude of 25%A in the experiment(A is the maximum amplitude),the formability of AZ31 reaches the largest value,and the samples possess the same distribution trend of cracks as those added with lubricating oil.With the increase of excitation energy,the "volume effect" gradually becomes apparent,and finally the "hardening" of the "volume effect" occupies a dominant position.

Low frequency vibration tests on a floating slab track in an underground laboratory

Low frequency vibrations induced by underground railways have attracted increasing attention in recent years. To obtain the characteristics of low frequency vibrations and the low frequency performance of a floating slab track (FST), low frequency vibration tests on an FST in an underground laboratory at Beijing Jiaotong University were carried out. The FST and an unbalanced shaker SBZ30 for dynamic simulation were designed for use in low frequency vibration experiments. Vibration measurements were performed on the bogie of the unbalanced shaker, the rail, the slab, the tunnel invert, the tunnel wall, the tunnel apex, and on the ground surface at distances varying from 0 to 80 m from the track. Measurements were also made on several floors of an adjacent building. Detailed results of low frequency vibration tests were reported. The attenuation of low frequency vibrations with the distance from the track was presented, as well as the responses of different floors of the building. The experimental results could be regarded as a reference for developing methods to control low frequency vibrations and for adopting countermeasures.

Discrimination of brownheart of Korla pear using vibration frequency spectrum technique

The purpose of this work was to use a nondestructive method for detecting the brownheart of Korla pear to reduce the chance of infection among pears without brownheart.A mechanical impulse method based on vibration testing system was used to excite the fruits.The consistent acquisition signal indicated that the test is repeatable at the same positions of fruit equator(cheek).A remarkable frequency signal was excited at 9-12 N force by a rubber tipped hammer.The dominant frequency was identified at the maximum response magnitude to assess the internal defect,and the result was not influenced by the distances between the defect borders and the excitation points.The sharp increase of defect mass could significantly affect the dominant frequency.Relationship between the dominant response frequency(fd)and the defect mass percentage(ω)was characterized by an equation fd=410.649e-0.0833ω+261.947 with a good correlation coefficient(R2=0.925).A defect mass of 2.281%was determined as a discrimination threshold.Once the threshold exceeded 2.281%,the defective pear could be classified with a high accuracy rate of 96.7%.This finding would provide guidance for determining the optimal detecting time to the brownheart of Korla pears,according to the specific storage conditions when the vibration frequency spectrum method is deployed.

Numerical prediction of ground vibrations induced by LPG boiling liquid expansion vapour explosion(BLEVE)inside a road tunnel

Accidental boiling liquid expansion vapour explosions(BLEVEs)caused by the bursting of liquified petroleum gas(LPG)tank inside a tunnel can induce vibrations of its surrounding geological media and threaten the stability of adjacent tunnels and structures.Therefore,it is essential to understand the characteristics of vibrations induced by LPG BLEVEs inside the tunnel for the safety design of its adjacent structures.Owing to the difficulty in effectively predicting the LPG BLEVE loads,the current practice usually employs equivalent methods,e.g.,the TNT-equivalency method,in LPG BLEVE load predictions for structural response analysis,which may lead to inaccurate response predictions.This study compares ground vibrations induced by a BLEVE inside an arched road tunnel with those induced by its equivalent TNT explosion via high-fidelity numerical simulations.The results demonstrate that the frequency of BLEVEinduced vibrations is lower than that induced by the TNT explosion at the same scaled distance.The intensity of LPG BLEVE-induced vibrations at relatively small-scaled distances is lower than that of TNT explosion-induced vibrations at the same scaled distance,but becomes higher after a certain scaled distance because of the relatively low attenuation rate.In addition,parametric analysis is conducted to evaluate the effects of various factors on the characteristics of LPG BLEVE-induced ground vibrations.It is found that the surrounding rock type,the rock porosity,and the cover depth of the tunnel have more significant influences than the concrete grade of the tunnel lining.The recommendation for the tunnel design is also given based on the intensity and frequency characteristics of BLEVE-induced vibrations.