Vibration Of Fluid Research Articles

ABOUT THE INFLUENCE OF VIBRATIONS OF THE CONVEYED LIQUID ON THE AREA OF STABILITY OF A CLOSED SYSTEM AUTOMATIC VEHICLE COURSE CONTROL

The existing publications that investigate vehicle course stability optimization were analyzed. A mathematical model, which describes the disturbed movement of a car with a tank, was compiled. This model allows to consider the liquid free surface oscillations and determine their effect on the car course stability during constant motion or emergency braking. There was described the main information regarding the car that was used to perform mathematical calculations. An algorithm was developed for deriving the characteristic equation for a complex system of differential equations describing dynamic changes in the movement parameters of a car, oscillations of partial layers of liquid in a tank and the operation of an electromagnetic drive of the control valve and an electronic PID controller for a two-circuit system for ensuring course stability. Based on the developed mathematical model, the influence of forced oscillations of the fluid on the stability area of the system built in the plane of variable parameters of the controller is investigated. It is shown that low-frequency oscillations of the free surface of a liquid lead to a significant reduction in the stability area, which indicates the need to consider such oscillations when solving problems of analysis and synthesis of this system. It was found that for a car with a tank, where low-frequency transverse oscillations of the liquid occur, which are accompanied by a redistribution of mass and disturb the movement, an increase of the speed unambiguously leads to a deterioration in directional stability. That enables exclusion of speed from the number of variable parameters and significantly simplify the problem being solved. The calculations for cases with different loading levels were performed. It was found out that the level of liquid in the tank, considering its relationship with the speed, has an ambiguous effect on the car course stability, and it is unacceptable to limit the research calculations to the case with 50 % load. Instead of this, it is necessary to find a line that bends from above the stability boundaries that correspond to many liquid levels.
 Keywords: fluid vibrations; exchange rate stability system; area of stability; tank; PID-controller; parameters.

Exploring the underlying mechanism of acoustic radiation force on a sphere in a fluid-filled rigid tube

The propagation of sound waves in a fluid-filled rigid tube has potential application in acoustic particle-positioning, valuable reagent recovery, and noninvasive manipulation of targets. The interaction between sound waves and targets causes momentum transport, and the acoustic radiation force is motivated to move and rotate the targets. Generally, acoustic radiation force is related to sound scattering of the target. The relationship between acoustic radiation force and the scattering pattern will play a positive role in better explaining the phenomenon of and changed trend in acoustic radiation force acting on a particle in a tube and in predicting the acoustic control system in a tube. This paper studies the interactions between a plane sound wave and a sphere in a fluid-filled rigid tube and tries to explore the relationship between acoustic radiation force and the dimensionless complex scattering pattern. The spherical particle with different materials is studied for Rayleigh scattering and Mie-like scattering. Simulation results show that there is a certain relationship between the acoustic radiation force and the scattering pattern for a spherical particle. At the resonance frequency, which corresponds to the natural frequencies of the vibration of fluid filled in the cavity with the rigid wall, both acoustic radiation force and the backscattering form function show identical resonance characteristics. At Rayleigh scattering and Mie-like scattering regimes, when the backscattering is greater than the forward scattering, acoustic radiation forces show an increasing trend compared with the dimensional frequency. However, with the increase in dimensionless frequency, the acoustic radiation force does not respond to the forward scattering except the resonance positions in the transition region from Mie-like scattering regimes to the geometric scattering regimes. When a negative force occurs near the resonance position, the scattering in the back hemisphere is weaker than that of the front hemisphere. This study will help predict the various behaviors of radiation force using the measured backscattering echo and the forward scattering wave, and it can provide reference to the control of the acoustic manipulation system effectively and precisely.

Analysis of vibration and sound characteristics of fluid conveying pipeline considering the effect of acoustic-solid coupling

Objectives In order to accurately grasp the vibration and sound characteristics of pipelines, a numerical simulation is carried out. Methods Based on the theory of acoustic-solid coupling, a numerical model of a pipeline is established. The dispersion curve of the vibration and acoustic modes of the pipeline is solved by parametric scanning. The dispersion characteristics of the elastic wall pipeline with air, water and crude oil, as well as the absolute pressure stress distribution in the pipeline, are analyzed, and the effects of wall thickness, elastic wall and hard sound field wall on the dispersion characteristics of the pipeline are studied. Results The results show that wall thickness has little effect on the propagation mode of elastic waves in the pipeline, and the dispersion curve is shifted to high frequency with the increase in wall thickness, mainly influencing the cut-off frequency. Due to the effects of acoustic-solid coupling, the number of modes of the elastic pipeline increases, and the increased mode number is mainly the deformation mode of the pipeline wall. The absolute sound pressure distribution in the elastic wall is basically the same as that in the hard sound field wall. The dispersion characteristics of liquid or gas inside are different, while the dispersion characteristics of water or oil inside are similar, but the direct modes of the two are different. Conclusions The results of this study can provide a theoretical basis for the pipeline acoustic detection of ships.

Mathematical Modelling and Dynamic Analysis of a Direct-Acting Relief Valve Based on Fluid-Structure Coupling Analysis

To explain the sudden jump of pressure as the variation of water depth for a direct-acting relief valve used by torpedo pump as the variation of water depth, a 2-DOF fluid-structure coupling dynamic model is developed. A nonlinear differential pressure model at valve port is applied to model the axial vibration of fluid, and a nonlinear wake oscillator model is used to excite the valve element in the vertical direction; meanwhile, the contact nonlinearity between the valve element and valve seat is also taken into consideration. Based on the developed dynamical model, the water depths for the sudden jumps of pressure can be located precisely when compared with the experimental signals, and the corresponding vibration conditions of the valve element in both the axial and vertical directions are explored. Subsequently, in order to eliminate the sudden jumps of pressure, different pump inlet pressure was tested experimentally; when it was decreased to 0.4 MPa, the pressure jumps ever appeared during the dropping and lifting processes were removed, and the numerical simulation based on the developed mathematical model also verified the experimental measurements.

Investigation of Fluid Vibration of a Cross-flow Turbine

Investigation of Fluid Vibration of a Cross-flow Turbine

ВИМУШЕНІ КОЛИВАННЯ ПАЛИВНИХ БАКІВ ПРИ РІЗНИХ УМОВАХ ЕКСПЛУАТАЦІЇ

Дослідження коливань рідини у паливних баках космічних апаратів є необхідним для забезпечення їх стійкості під час польоту. Рідинні ракети-носії мають на борту значні запаси рідких компонентів. В паливних баках та баках окисників виникають коливання вільної поверхні рідини, на характер яких впливають також і зовнішні чинники, такі як гравітація, рівень заповнення баків, їх форма тощо. Виникає необхідність визначення форм та частот коливань вільної поверхні рідини для забезпечення стійкого стану літального апарату під час польоту. Для вирішення цієї задачі застосовано методи математичного моделювання. Розглянуто дослідження задачі малих коливань у резервуарах, частково заповнених рідиною, що стосуються космічної галузі. Також розглянуті роботи вітчизняних та закордонних авторів щодо розв’язання задач коливань рідини в нелінійній постановці. У даній роботі проведено аналіз форм та частот коливань рідини в умовах перевантаження при різних рівнях заповнення. Виконано дослідження малих коливань (лінійне формулювання). Прийнято, що рідина є нестисливою та однорідною, а її рух безвихровий. Існує потенціал швидкості руху, що задовольняє рівнянню Лапласа. Виконуються кінематична та динамічна граничні умови на вільній поверхні. Для врахування впливу низької гравітації виконано узагальнення граничних умов. В динамічній умові на вільній поверхні враховано поверхневий натяг, що моє визначальне значення в умовах мікрогравітації. Отримано співвідношення, що має виконуватись на вільній поверхні. Отримане рівняння дозволяє проводити дослідження вимушених коливань жорсткої оболонки обертання, що частково заповнена рідиною. Отримано числові результати для циліндричної оболонки обертання. Прийняті нульові початкові умови. Виконані розрахунки при різних рівнях заповнення для циліндричної оболонки. Отримані найнижчі частоти коливань. Також досліджені коливання рідини, що знаходиться під дією вертикального навантаження. Отримані фазові портрети для різних значень частот вертикальної сили збудження. Отримані результати дозволяють дослідити амплітуди коливань вільної поверхні.

Acoustic impedance regulation of Helmholtz resonators for perfect sound absorption via roughened embedded necks

Acoustic impedance regulation of a neck embedded Helmholtz resonator is realized by introducing surface roughness to the neck so as to convert the initially non-perfect sound absorber to a perfect sound absorber. The proposed roughened-neck embedded Helmholtz resonator (R-NEHR) achieves perfect sound absorption (α>0.999) at 158 Hz across a deep subwavelength thickness of λ/42. Theoretical predictions of the R-NEHR's performance are validated against experimental measurements. Physically, surface roughness triggers the periodic concentration effect of fluid vibration in the neck, thereby improving its acoustic mass and acoustic resistance and altering the resonant damping state of the absorber. As a result, the absorption peak position of the R-NEHR shifts by 16.0% to lower frequency, together with a peak value increase of 19.6%. This work provides an approach for perfect sound absorber design and impedance regulation of acoustic metamaterials.

On the tympanic membrane impedance of the katydid Copiphora gorgonensis (Insecta: Orthoptera: Tettigoniidae).

Katydids (bush-crickets) are endowed with tympanal ears located in their forelegs' tibiae. The tympana are backed by an air-filled tube, the acoustic trachea, which transfers the sound stimulus from a spiracular opening on the thorax to the internal side of the tympanic membranes (TM). In katydids the sound stimulus reaches both the external and internal side of the membranes, and the tympanal vibrations are then transferred to the hearing organ crista acustica (CA) that contains the fluid-immersed mechanoreceptors. Hence the tympana are principally involved in transmitting and converting airborne sound into fluid vibrations that stimulate the auditory sensilla. Consequently, what is the transmission power to the CA? Are the TM tuned to a certain frequency? To investigate this, the surface normal acoustic impedance of the TM is calculated using finite-element analysis in the katydid Copiphora gorgonensis. From this, the reflectance and transmittance are obtained at the TM. Based on the impedance results obtained from the pressure recordings at TM and the velocity field calculations in the AT, in the frequency range 5-40 kHz, it is concluded that the tympana have considerably higher transmission around 23 kHz, corresponding to the dominant frequency of the male pure-tone calling song in this species.

Dynamics Analysis and Numerical Simulation of Large-Scale Hydraulic Cylinder Actuators

This research presents a dynamic analysis of a large-scale hydraulic cylinder actuator via numerical simulation. A model of the actuator built with dynamically parameters is implemented basing on fluid mechanics and vibration theories. In which, coefficients of viscous damping and stiffness generated by compressibility and viscous characteristics of hydraulic oil are considered. Hence, the large-scale hydraulic cylinder actuator can be investigated via an equivalent model of mass-spring-damper. In order of obtaining the system response, numerical simulation is done with some realistic actuator parameter sets. The results are consistent with reality and can be used as valuable fundamental for large-scale hydraulic cylinder actuator design.

Nonlinear vibration of full-filled fluid corrugated sandwich functionally graded cylindrical shells

This article proposes a semianalytical approach for the nonlinear free and forced asymmetric vibration of corrugated sandwich functionally graded cylindrical shells containing fluid under harmonic radial load. The corrugation is considered with two types: trapezoidal corrugation and round corrugation. By using the Donnell shell theory, taking into account the geometrical nonlinearity of von Kármán and an equivalent model for corrugated structures, the governing equations of shell are established. The nonlinear motion equations are reduced to nonlinear differential equation in terms of time by applying the Galerkin procedure. The numerical investigations for the nonlinear dynamic response of cylindrical shells are obtained by using the fourth-order Runge–Kutta method. Numerical results show the very large effects of corrugation and fluid on the natural frequency and nonlinear vibration behavior of shells.

Resonant frequencies analysis and vibration control of fluid in three-dimensional (3D) moonpool: Analytical modeling and experimental study

Moonpool widely exists in the fields of offshore oil and gas resources drilling, marine energy development and so on, and also has important applications in special ships and surface ships. The aim of this paper is to present an accurate three-dimensional modeling method and analyze resonant frequencies of fluid in three-dimensional moonpool. Based on the three-dimensional potential flow theory, the governing equations and boundary conditions of the fluid in the three-dimensional moonpool are established. According to the characteristics of the governing equations and boundary conditions of the fluid in the moonpool, the velocity potential of the fluid in the moonpool is expanded into the form of the sum of three-dimensional Fourier series and smooth auxiliary functions. Then, the velocity function is introduced into the governing equations and boundary conditions, so that the complex partial differential equations can be transformed into a set of simple linear equations, and the resonance frequency of the fluid vibration in the moonpool can be obtained by solving the linear equations. In order to verify the validity of the three-dimensional accurate model proposed in this paper, numerical examples and experimental verification are carried out, and then the numerical and experimental results show that the proposed solution has good convergence accuracy and calculation accuracy. On this basis, the effects of the length, width and water depth of the moonpool on the resonant frequencies and modes are discussed, and the natural vibration behavior control of the fluid in the three-dimensional moonpool are analyzed in detail. In this work, the three-dimensional analytical solution is proposed for the first time to study the natural vibration characteristics of the fluid in the three-dimensional moonpool, and its correctness is verified by the model experiment. At the same time, some bright research results are also given, which is of great engineering significance for understanding the resonant frequencies and modes of the fluid in the complex moonpool structure.

Nonlinear Behavior of High-Intensity Ultrasound Propagation in an Ideal Fluid

In this paper, nonlinearity associated with intense ultrasound is studied by using the one-dimensional motion of nonlinear shock wave in an ideal fluid. In nonlinear acoustics, the wave speed of different segments of a waveform is different, which causes distortion in the waveform and can result in the formation of a shock (discontinuity). Acoustic pressure of high-intensity waves causes particles in the ideal fluid to vibrate forward and backward, and this disturbance is of relatively large magnitude due to high-intensities, which leads to nonlinearity in the waveform. In this research, this vibration of fluid due to the intense ultrasonic wave is modeled as a fluid pushed by one complete cycle of piston. In a piston cycle, as it moves forward, it causes fluid particles to compress, which may lead to the formation of a shock (discontinuity). Then as the piston retracts, a forward-moving rarefaction, a smooth fan zone of continuously changing pressure, density, and velocity is generated. When the piston stops at the end of the cycle, another shock is sent forward into the medium. The variation in wave speed over the entire waveform is calculated by solving a Riemann problem. This study examined the interaction of shocks with a rarefaction. The flow field resulting from these interactions shows that the shock waves are attenuated to a Mach wave, and the pressure distribution within the flow field shows the initial wave is dissipated. The developed theory is applied to waves generated by 20 KHz, 500 KHz, and 2 MHz transducers with 50, 150, 500, and 1500 W power levels to explore the effect of frequency and power on the generation and decay of shock waves. This work enhances the understanding of the interactions of high-intensity ultrasonic waves with fluids.

Nonlinear vibration of fluid conveying cantilever nanotube resting on visco‐pasternak foundation using non‐local strain gradient theory

Frequency analysis and forced vibration response of fluid conveying viscoelastic nanotubes that resting on nonlinear visco-pasternak foundation under magnetic field using size-dependent non-local strain gradient theory are considered in this study. It is supposed that the nanotube is modelled as cantilever type beam and subjected to a harmonic load. The material property of the nanotube is modelled by Kelvin-Voigt viscoelastic constitutive relation and slip boundary conditions of nanotube conveying fluid are taken into account. Extended Galerkin method is used to obtain the nonlinear differential equation of the motion and the multiple time-scales method is utilised to investigate the primary vibration resonance of the nanotube. Firstly, the frequency analysis is performed on the linear system and the effects of foundation coefficients on the natural frequency are investigated at several flow velocities. Moreover, the resonance properties of the system are solved in closed form and analysed from the frequency-response curves, and then the effects of the non-local parameter, length scale parameter and magnetic field are fully investigated. In this case, non-local parameter, length scale parameter and foundation coefficients are highly influential on the frequency response of the considered system.

Study on Gap Phenomena Before and After the Breakout Event of Fast Electrical Discharge Machining Drilling

Abstract Fast electrical discharge drilling is broadly used to manufacture small holes on molds, dies, filters, and automobile and aerospace components. Breakout is the event when the tool electrode reaches the opposite surface of the workpiece. When a breakout happens, the machining efficiency drops sharply and the process becomes unstable. To gain a deep understanding of the breakout process, this paper observed the gap phenomena before and after the breakout with cameras through a quartz glass flake. Experiments were conducted on the workpiece tilted to 45 deg. From the observation, it was found that the deformation of the electrode was not negligible. The electrode would vibrate or shake before and after the breakout. Side-gap sparks were common in the process, and even more were observed after the breakout. The fluid flow in the discharge gap and the side gap did not vanish immediately when a breakout happened and could still evacuate debris for a short period. The debris gradually accumulated as the fluid flow in the gap vanished. A series of simulations were conducted to study the fluid flow and debris movement after the breakout. And simulations were also performed to find the influence on electrode vibration of high-pressure flush fluid and discharge location. The results of simulations agreed well with the observed phenomena. From the observation and simulation results, the deformation or vibration of the electrode and the accumulation of debris were found to be the main factors that led to the low machining efficiency after the breakout.

Об одной начально-краевой задаче, возникающей в динамике вязкой стратифицированной жидкости

An initial-boundary value problem is considered, which describes the linear vibrations of a viscous stratified fluid in a bounded vessel with elastic membrane. We find sufficient existence conditions for a strong (with respect to the time variable) solution of the initial-boundary value problem describing the evolution of the specified hydrodynamics system.

Damped Natural Vibrations of Fluid in a Well Interfaced with a Reservoir

Damped Natural Vibrations of Fluid in a Well Interfaced with a Reservoir

Analysis of the phase structure of fluid vibrations with floating longitudinally compressed elastic plate in nonlinear interaction of the surface progressive waves

Based on the asymptotic expansions obtained by the multi-scale method up to the third order of smallness for the potential velocity of liquid particles and the plate-fluid surface elevation, the dispersion properties of the vibrations generated by the interaction of progressive surface wave harmonics of finite amplitude are analyzed in the article. The effect of nonlinearity of acceleration of vertical displacements of an elastic plate on the dispersion characteristics of wave disturbances is studied. The dependence of the vibration frequency is estimated by taking into account the nonlinearity of the first and second approximations values, the plate thickness, and the longitudinal compressive force. It is shown that the sign of the amplitude of the second interacting harmonic and the nonlinearity of the acceleration of vertical displacements of the longitudinally compressed elastic plate affect the vibration phase. It was found that with a decrease in the wavelength of the initial harmonic, the influence of the plate’s nonlinearity vertical acceleration is enhanced. The presence of compressive force is manifested in a decrease in the frequency of vibrations of the wave disturbance in comparison with the frequency obtained in the absence of longitudinal compression, both with a positive and negative sign of the second interacting harmonic amplitude.

Hybrid adaptive method for finding the roots of a nonsmooth function in the problem of determining the natural frequencies of fluid vibrations in reservoirs

The article proposes a hybrid adaptive method for finding the roots of a non-smooth function of a single variable. The algorithm of adaptive root search method for non-smooth functions is presented. It assumes both adaptive reduction of a search step, and changing the search direction. It is found that the proposed approach allows us to detect the root even in the presence of a point of inflection. That is, for example, is impossible for the Newton method. The accuracy of finding the root using the proposed algorithm does not depend on the type of functions, the choice of the initial approximation; the method in any case will find the root with the given accuracy. Comparison of the results of the root calculations is performed using the dichotomy method, the "3/5" method and the proposed algorithm. It is established that the effectiveness of the developed method exceeds the efficiency of both methods - hybrids, when they have applied separately. The developed method is applied to the solution of the characteristic equation in the problem of determining the natural frequencies of oscillations of a liquid in a rigid tank having the form of a shell of revolution. The fluid in the tank is assumed to be perfect and incompressible, and its motion caused by the action of external loads is eddy. Under these assumptions, there exists a velocity potential to describe the fluid motion. The formulation of the problem is given and the method of its reducing to the solution of a nonlinear equation is given. This equation is a characteristic one for the corresponding problem of eigenvalues. The methods of integral singular equations and the boundary element method for their numerical solution are applied. The problem of fluid oscillation in a rigid cylindrical tank is considered. The results of numerical simulation of the fluid oscillation frequencies obtained by different methods for different number of nodal diameters are compared. It is noted that if the root of the characteristic equation is localized using approximate methods, then its refinement can be carried out using the proposed approach.

Physical Principles of the Method of Low-Frequency Piezothromboelastography for Studying Rheological Properties of Whole Blood

The paper expounds physical principles of the low-frequency piezothromboelastography method for studying viscous properties of whole blood and diagnosis of the hemostatic potential. A mathematical model of ultrasonic vibrations in a viscous fluid has been developed. An ARP-01M “Mednord” piezothromboelastograph is used to carry out a numerical experiment to study the operational modes of a piezoelectric sensor and its applicability for measuring the dynamics of the viscous properties of whole blood. It is shown that the piezoelectric sensor reaches the optimal operational mode with the configuration of the needle-resonator in the form of a rectilinear rod with a loop. The maximum sensitivity in measuring the amplitude-frequency signal characteristics with a recording piezoelement is observed at 2.95 kHz. A numerical experiment studying the influence of a viscous medium on changes in the amplitude-frequency characteristics of vibrations of the needle-resonator of the piezoelectric transducer with allowance for the viscous friction force magnitude has been performed. The viscous properties of water and glycerin are used as an example. Calculations have been performed for two limiting magnitudes of the viscous force encompassing the interval of changes of the whole blood viscosity in the process of coagulation. It is demonstrated that the method has sufficient sensitivity to changes in the viscous characteristics of blood and to the dynamics of changes of these characteristics during coagulation and hence, has high measurement accuracy.

Study of the hydraulic disturbance suppression of a vibrator under high-frequency vibration based on experiments and numerical simulations

Hydraulic disturbance of a vibrator is the main cause of distortion of the vibroseis geophysical exploration signal that is caused by high-frequency fluid vibration during servo valve cavity commutation. This disturbance is closely related to the structure, size, and arrangement of the hydraulic flow path of the vibrator reaction mass. In this work, a vibrator disturbance–suppression mechanism was examined, an experimental study was carried out on an improved design of the hydraulic flow channel, and the source of the hydraulic disturbance of the horizontal channel vibrator was determined. The vibrator hydraulic flow channel was changed to a vertical flow channel in the piston rod. In addition, the structure of the track was designed, and the angle of the oil inlet of the piston rod was tested at 0°, 45°, and 90°. Then, the fluid flow state and fluid–solid coupling analysis method were used to improve the vibration-suppression effect of the vibrator. The results showed that the optimal oil inlet angle is 90°, for which the turbulent intensity of the oil inlet is the smallest, the pressure drop loss is reduced, and the influence of the oil flow on the piston rod deformation is minimal. The vibration reaction mass test of the vibrator showed that the disturbance inhibition rate of the piston rod with a 90° inlet structure design reaches 64.087%; the hydraulic disturbance had the best suppression effect and effectively reduced the distortion of the seismic prospecting signals with this oil inlet angle, improving the quality and efficiency of oil and gas exploration.