Oscillations Of Piston Research Articles

Аналитическая модель одномерной нестационарной динамики одиночной частицы в акустическом и электрическом полях

This paper presents the results of calculations of the dynamics of an electrically neutral and electrically charged particle in a closed channel. A mathematical model of the dynamics of a single particle in an acoustic field is presented, in which the potential of the acoustic field is given by a one-dimensional linear wave equation. The dynamics of the particle was described by a differential equation that puts the dependence of the particle velocity on the forces applied to it - the Stokes force acting from the side of the acoustic field, and the Coulomb force acting from the side of the electric field. It is revealed that the amplitude of oscillations of an electrically neutral particle is less than the amplitude of oscillations of an electrically charged particle in an electric field. It is determined that at a small amplitude of the piston oscillations, the amplitude of the change in the speed of an electrically charged particle under the action of electric field forces exceeds the amplitude of the change in the speed of an electrically neutral particle. In this paper, we analyzed the influence on the dynamics of an electrically charged particle in an acoustic field for stationary and nonstationary distributions of the electric field potential. The paper presents calculations of the dynamics of an electrically charged particle in a periodic electric field with different frequencies of electric field variation. It was found that when a particle is exposed to an alternating electric field that is in phase with the gas velocity field, the particle velocity increases, if the frequency of the alternating electric field is in antiphase with the gas velocity, then the particle velocity decreases. It is determined that if a stationary electric field acts on a particle, then the particle drifts to that part of the channel to which a potential is applied, the sign of which is opposite to the sign of the particle charge.

Numerical simulation of forced acoustic gas oscillations with large amplitude in closed tube

Nonlinear acoustic oscillations with large amplitude created in gas-filled closed tube by piston oscillating according to the harmonic law near three natural resonant frequencies are numerically studied. The movement of the medium is described by the Navier–Stokes equations for viscous compressible fluid, which are approximated through the control volume method using the OpenFoam library. The influence on the maximum pressure drop of the excited piston oscillation frequency at large amplitudes near the first resonant frequency is studied. The used numerical model allows to achieve good agreement with the experimental data for intensive gas oscillations with breaking waves. The dynamics of changes in pressure and velocity during a single period of oscillations at different natural frequencies are studied in detail. Nonlinear features for intensive shock oscillations of viscous gas in a closed tube at higher harmonics have been detected. In particular, oscillations in the pressure nodes with a frequency equal to the doubled frequency of forced oscillations of the piston at the first and higher modes resonance frequencies were found. For non-linear gas oscillations with a shock front of pressure changes in the nodes for the velocities of gas particles inside the tube, the large amplitudes of the change in particle velocities over a very short period of time are observed. The received results show that the used numerical approach is a suitable method for modeling highly nonlinear acoustic oscillations and related problems.

Modeling, Simulation, and Analysis of a Variable-Length Pendulum Water Pump

Due to the long-term problem of electricity and potable water in most developing and undeveloped countries, predominantly rural areas, a novelty of the pendulum water pump, which uses a vertically excited parametric pendulum with variable-length using a sinusoidal excitation as a vibrating machine, is presented. With this, more oscillations can be achieved, reducing human effort further and having high output than the existing pendulum water pump with the conventional pendulum. The pendulum, lever, and piston assembly are modeled by a separate dynamical system and then joined into the many degrees-of-freedom dynamical systems. The present work includes friction while studying the system dynamics and then simulated to verify the system’s harmonic response. The study showed the effect of the pendulum length variability on the whole system’s performance. The vertically excited parametric pendulum with variable length in the system is established, giving faster and longer oscillations than the pendulum with constant length. Hence, more and richer dynamics are achieved. A quasi-periodicity behavior is noticed in the system even after 50 s of simulation time; this can be compensated when a regular external forcing is applied. Furthermore, the lever and piston oscillations show a transient behavior before it finally reaches a stable behavior.

Development and experimental investigation of a novel solar-powered cooling system

The development of novel and improvement of existing technologies for utilising solar thermal energy for cooling purposes traditionally attracts increased attention in both industry and academia. This work presents the development of a novel cooling system with a simple design and direct utilisation of solar thermal energy. The cooling system combines a liquid piston engine and cooling machine and is driven by an evacuated tube solar collector. A prototype of such the system was designed, built and tested in laboratory conditions using a solar radiation simulator. Variations in pressures, temperatures, and the fluid piston oscillation amplitudes in the system during its operation were recorded, and the indicated power of the engine and cooling capacity of the system were determined for a range of operation and design parameters. For the heat input range of 700–900 W and the constant temperature of the cooling water equal to 26.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–88.0 and 51.0–61.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–9.7 and 7.2–6.7%. The temperature in the cooling chamber was registered in the range of 20.0–18.2 °C at an ambient temperature of 24.0 °C. The COP of the cooling machine decreased from 0.71 to 0.69. The system performance improved in tests with a constant heat input (700 W) and reducing cooling water temperature. For cooling water temperature reduction from 26.0 to 18.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–111.9 and 51.0–72.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–16.0 and 7.2–10.3%. The COP of the cooling machine decreased from 0.71 to 0.64. The temperature in the cooling chamber was registered in the range of 20.0–14.4 °C at an ambient temperature of 24.0 °C. Experimental results obtained using the system's initial design demonstrate that the engine has efficiency comparable to low-temperature steam and Organic Rankine Cycle turbines. The Coefficient of Performance of the system is similar to that of single-stage absorption chillers.

Analytical and experimental research of nonlinear resonant gas oscillations in a cube

The gas pressure in a cubic resonator is studied experimentally and numerically at the first resonant frequency. Lagrange’s approach is used to analytical study of problem. Comparison of the pressure oscillations obtained experimentally and numerically at different amplitudes of piston oscillation is carried out.

Research of transverse dynamic oscillation for the piston in labyrinth compressor

In labyrinth compressor, non-contact labyrinth sealing clearance was designed between piston and cylinder wall to process oil-free gas containing fine particles. To prevent the collision between piston and cylinder wall, this labyrinth clearance was usually set bigger than 2‰ of the piston diameter. Such a big clearance seriously increased the leakage rate and reduced the volume efficiency of the compressor. Thus, it was necessary to investigate the piston transverse oscillation, and find a way to minimize the oscillation amplitude to reduce the labyrinth clearance set. In this paper, a dynamic model was established to predict the piston transverse oscillation based on inertia mass vibration analysis and finite difference method. Experiments investigation of the piston transverse oscillation track showed high prediction accuracy of the proposed model. Then, structure parameters optimization of the compressor was carried out to reduce piston oscillation amplitude. It was found that ratio of the crank shaft radius to connecting rod length and the position of the guide bearing were two key parameters determining the oscillation amplitude. Finally, a case study showed that the oscillation amplitude could be reduced by 53% by adopting optimized parameters.

Estimation of shear rate change in vertically oscillating non-Newtonian fluids: Predictions on particle settling

This study investigates the effect of oscillatory motion on velocity and shear rate change within different non-Newtonian, slightly viscoelastic fluids oscillated in a vertical U-shaped circular pipe. An estimation to quantify the influence on particle settling in an oscillatory environment is also presented. Flow visualization using particle image velocimetry (PIV) technique was deployed to compare the two-dimensional velocity field in the vertical plane of the U-tube axis and the resulting shear rate change in three different non-Newtonian fluids. The experiments were performed in a 1.2 m high, 50 mm diameter transparent test section, at room temperature (21 ± 0.5 °C) and atmospheric pressure.A piston was driven at harmonic motion via a gas buffer, to provide the driving force for the test fluids at four different low frequencies ranging from 0.1 – 0.75 Hz and at three different piston oscillation amplitude ratios of A = a/D = 0.3, 0.4 and 0.5, where a is the displacement amplitude of the piston and D is the pipe diameter. Oscillatory Reynolds number (Reδ) based on Stokes layer thickness was used as the criteria for determining the specific flow regime. 36 different experimental cases were tested within the range of 2 < Reδ < 34, and all the experimental cases exhibited the laminar flow regime.The study reveals that the axial velocity amplitude along the pipe centerline increases with the increasing frequency and with increasing oscillation amplitude irrespective of the non-Newtonian fluid type. The thickness of the shear region decreases with the increase of frequency. The change of shear rate is maximum near the wall region of the pipe and that is achieved at the maximum position of the phase cycle, where the axial velocity also possesses its highest magnitude. The most viscous and the least elastic fluid have reported a maximum reduction of viscosity as an effect of the oscillatory motion and the viscosity reduction becomes insignificant when the non-Newtonian fluids become less viscous.

Моделирование инфразвукового пистонфона

There are presented the results of numerical simulation of an applied acoustic problem – modeling of gas processes occurring in the measuring chamber of the infrasound pistonphone 3202 at different frequencies of piston oscillation (0.1 – 1000 Hz) and characterized by extremely small Mach numbers (9.1·10-7÷9.1·10-3). The simulation was performed using quasi-gas-dynamic (QGD) and quasi-hydrodynamic (QHD) equations of a viscous compressible heat-conducting gas with the use of a time-explicit difference scheme, all spatial derivatives was approximated by central differences. It is shown that QGD and QHD models can be used for a simulation of applied acoustics and, in particular, to the simulation of infrasonic pistonphone: the stability limits of the QGD and QHD algorithms in this problem were determined, the dependence of sound pressure on the tuning parameter α is investigated and it is shown that this dependence is quite small. The spectra of sound pressure at the control point calculated by QGD and QHD are given, their dependence on the tuning parameter α is shown, both models equally predict the value of the sound pressure amplitude at the fundamental frequency oscillations. At the end of the article, the sound pressure at the control point at the fundamental frequency oscillations obtained by using QGD and QHD is compared with the values calculated by using semi-empirical formula of sound pressure at closed volume for a case of small oscillations using the polytropic index obtained by Henry Gerber instead of the adiabatic coefficient.

Scrutinizing the sources of inefficiencies in the piston-cylinder clearance of an oil-free linear compressor

The piston of linear compressors is subjected to low side loads and metal contact can be avoided by feeding high-pressure refrigerant gas from the discharge system into the piston-cylinder clearance. This paper reports a thorough study on the inefficiencies associated with leakage and viscous friction brought about by the transient compressible fluid flow in the piston-cylinder clearance of an oil-free linear compressor. The main objective is to understand the effect of design parameters, such as compressor speed, piston oscillation amplitude, pressure ratio and radial clearance, on the volumetric and isentropic efficiencies. The compressor efficiency was found to be mainly affected by the clearance and pressure ratio. A reduction of 2.5% in the volumetric efficiency and 4.2% in the isentropic efficiency, for instance, were predicted when the radial clearance was varied from 2.5 to 10.0 µm.

Particularities of the Dynamics of Linear Domains in Liquid Crystals under a Binary Acoustic Action

The dynamical properties of a system of linear domains induced by shear oscillations in a planar layer of a nematic liquid crystal under the joint action of shear and piston oscillations at frequencies in the audio range, have been studied experimentally. The phenomenon of spatial modulation of the domains of an initial system along their axis under the piston oscillations producing periodic layer compression is investigated for the case where the directions of the director in a mesophase layer and the shear oscillations coincide. A relationship between the period of secondary two-dimensional structures at the effect threshold and the layer thickness as well as oscillation frequency is established. It is shown that the formation mechanism of these structures can be interpreted on the basis of a known phenomenological model, according to which the instability of the initial system of these linear domains is caused by the “mismatch” between the real period of domains and its optimal value, which varies jointly with the variations in the thickness of a periodically compressed layer.

Rayleigh-Taylor instability in oscillating liquid pistons

In this study, an experimental apparatus is used to excite four U-tube-shaped liquid pistons connected in series, and to study their behaviour. Some of the gas spaces are heated to induce piston oscillations; in others, gas expansion is utilised to produce a refrigeration effect. It was discovered that the liquid piston surface would become unstable and turbulent at relatively low gas charge pressures (2 bar–3 bar). Cylindrical polyethylene floats were employed at each piston surface in order to reduce the area of the free surface of each piston and allow experiments to be conducted over a wide range of operating conditions. Experiments were carried out using gas charge pressures in the range of 1 bar–6 bar. The resulting liquid piston oscillations were measured and analysed to assess the impact of any developing piston instability. Evidence of a liquid piston acceleration limit, likely resulting from the Rayleigh-Taylor instability phenomenon, is consistently observed during the experiments. The use of submerged polyethylene piston floats is found to increase the surface stability and enable maximum accelerations of 25 ms−2 to 30 ms−2.

Mathematical simulation of a gas flow in the vicinity of the open end of a tube for harmonic oscillations of a piston at the resonance frequency at the other end of the tube

The structure of the gas flow in the vicinity of the open end of a tube for the oscillating gas flow caused by piston oscillations at the first resonance frequency at the other end of the tube has been determined by numerical integration of the Navier–Stokes equations using the ANSYS FLUENT program package. For the variant of the tube with an infinitely long flange and a sharp edge, the influence of the piston displacement amplitude on the gas flow rate in the tube is investigated, and the phases of gas inflow and outflow during the period of oscillation have been determined.

Dynamics of Linear Hydraulic Cylinder with Mass Load

The paper deals with examination of dynamics of linear hydraulic cylinder with mass load. The hydraulic cylinder is placed in vertical position. There is experimentally simulated a system state. In this case a higher piston velocity is achieved due to the mass load compared to the piston velocity that corresponds to a supplied flow. A piston oscillation of the hydraulic cylinder is caused by rapid stop of movement in a desired position. There are experimentally evaluated eigenfrequencies of the linear hydraulic cylinder depending on the piston position and the mass load. Mineral oil was used as the working liquid. Time dependencies of pressures are measured on sides of the piston and the piston rod. Furthermore there are measured time dependencies of the piston position and the oil temperature. A mathematical model is created for this hydraulic system. This model is realized by Matlab SimHydraulics software. There are simulated time dependencies of the piston position and the pressure on the side of the piston rod. The mathematically simulated time dependencies of the pressure and the piston position are compared with the experiment.

A Decoupled Design Parameter Analysis for Free-Piston Engine Generators

The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25–35% reported in conventional reciprocating engines. This paper seeks to address a major challenge in the development of new and complex technologies—how do we effectively communicate and understand the influence of key design parameters on its operating performance? In this paper, the FPEG is described using a simple numerical model, a model which is reduced to a forced mass-spring vibration system under external excitation, enabling all the major input parameters to be decoupled. It proved that the engine piston position as a function of time and output power could be predicted directly from the input parameters with acceptable accuracy. The influence of the key FPEG design parameters on the piston oscillation characteristics and electric power output can be characterised with respect to one another and summarised. Key design parameters include piston mass, compression stroke length, piston cross sectional area, and electric load. Compared with previous and more complex numerical models, the presented methods can be used to simply describe the sensitivity of key design parameters on the FPEG performance. It will provide useful general guidance for the FPEG hardware design process.

Damped oscillations of a frictionless piston in an adiabatic cylinder enclosing an ideal gas

Suppose that a piston of nonzero mass encloses an ideal gas in a vertical cylinder. The piston and cylinder are thermally insulated so that no energy is lost by heat transfer to the surroundings. If the piston is set into motion, it oscillates like a block on a spring. However, the motion is damped because the gas density and pressure immediately adjacent to the piston are higher or lower than the bulk values, depending on whether the piston is compressing or expanding the gas, respectively. That automatically gives rise to a drag force linear in the velocity of the piston. It is not necessary to add extra dissipative terms such as kinetic friction between the piston and cylinder, or viscosity of the gas, to damp out the motion of the piston. The ideas should thus be helpful to undergraduate students performing a Rüchardt experiment to measure the ratio of the heat capacities of a gas.

Resonant oscillations of a gas in an open tube in the shock-free wave mode

Nonlinear gas oscillations excited in an open tube by a flat piston at one of the tube ends are studied. The sinusoidal piston oscillations in the shock-free wave mode are created by a vibration exciter near the first eigenfrequency. Expressions for gas pressure oscillations are obtained for a tube with a nonrounded end without a flange and secondary flow velocity components. The influence of the piston displacement amplitude on the pressure range and secondary flow velocity of gas is studied. The theoretical calculations of the gas pressure are compared with experimental data. An estimate for the velocity of particle motion along the tube axis is presented with calculated values of the secondary flow velocity.

Testing and Modeling of an Acoustic Instability in Pilot-Operated Pressure Relief Valves

Pressure relief valves (PRVs) are included as an essential element of many compressor piping systems in order to prevent overpressurization and also to minimize the loss of process gas during relief events. Failure of the valve to operate properly can result in excessive quantities of vented gas and/or catastrophic failure of the piping system. Several mechanisms for chatter and instability have been previously identified for spring-loaded relief valves, but pilot-operated relief valves are widely considered to be stable. In this paper, pilot-operated PRVs are shown to be susceptible to a dynamic instability under certain conditions where valve dynamics couple with upstream piping acoustics. This self-exciting instability can cause severe oscillations of the valve piston, damaging the valve seat, preventing resealing, and possibly causing damage to attached piping. Two case studies are presented, which show damaging unstable oscillations in a field installation and a blowdown rig, and a methodology is presented for modeling the instability by coupling a valve dynamic model with a 1D transient fluid dynamics simulation code. Modeling results are compared with measured stable and unstable operation in a blowdown rig to show that the modeling approach accurately predicts the observed behaviors.

A novel small dynamic solar thermal desalination plant with a fluid piston converter

An innovative small dynamic water desalination plant was developed and tested under laboratory conditions. The system is a combination of a heat pipe evacuated tube solar collector, conventional condenser and novel fluid piston converter. Saline water is boiled and turned into vapour in the manifold of the solar collector. A small fraction of the solar energy supplied to the plant is used to drive the fluid piston converter. Oscillations of the fluid piston periodically change the volume and pressure in the plant. For the duration of approximately half of the periodic cycle the pressure in the plant drops below the atmospheric level causing flash boiling of saline water in the manifold of the solar collector. Generated vapour is turned into fresh water in the condenser which is surrounded by a cooling jacket with saline water. The flash boiling effect improves the fresh water production capacity of the plant. Additionally, the fluid piston converter drives a pump which provides lifting of saline water from a well and pumps this through the cooling jacket of the condenser to a saline water storage tank. This tank replenishes saline water in the manifold of the solar collector. Experimental investigations demonstrated the saline water self-circulation capability of the plant and increase in the fresh water production compared to the static mode of operation. Experimental data was also used to calibrate the mathematical model of the plant. Comparison of theoretical and experimental information demonstrates that the model accurately predicts the performance of the plant. The proposed novel system with greater fresh water production capacity has a simple design and is easy to manufacture using low cost materials and therefore can be mass deployed for small scale saline water pumping and desalination across different regions with the relatively high solar radiation and shortage in the drinking water supply.

Nonlinear oscillations of gas in an open tube near the resonance frequency in the shock-free mode

The forced oscillations of gas in an open tube, excited by harmonical oscillations of piston in the shock-free mode were investigated near the first first eigenfrequencies. An expression for the pressure oscillations of gas was obtained for the tube with unrounded end without flange. The amplitude impact of piston displacement on the oscillations of pressure and velocity of the secondary flow of gas was investigated. The comparison of theoretical calculations with experimental data was executed. The effect of secondary flow on the particle drift along the tube axis with acoustic oscillations of gas was shown.

Semi-analytical modelling of a hydraulic free-piston engine

The hydraulic free-piston engine is a hybrid of a hydraulic plunger pump and a free-piston engine. This paper presents a semi-analytical method for the hydraulic free-piston engine parameter design. An oscillation function described the piston oscillation were established. The piston oscillation characteristics were analysed. The parameter sensitivity and the limit cycle stability of the piston oscillation were investigated. The results show that the single piston free-piston engine system is a hard self-oscillation with variable damping and stiffness. External energy is required to start the piston oscillation. The piston oscillation has an unsymmetrical oscillation characteristic. The dead centres of the piston motion are determined by the energy balance. The energy supply and the energy consumption are determined by the generalised damping in the piston oscillation function. The piston oscillation frequency should satisfy the minimum compression ratio requirement for the compression ignition. In the steady operation, the piston motion is a self-excitation oscillation. The trajectory stability is mainly determined by the fuel combustion energy supply. The scavenging affected by the BDC should be paid special attention to ensure the trajectory stability.