Piston Displacement Research Articles

Experimental study on impact coupling characteristics of high-pressure accumulator for unconstant-pressurized chamber rock drills

In order to improve the efficiency of unconstant-pressurized chamber rock drills in large-hole and hard-rock conditions, the coupling characteristics of high-pressure accumulator and the impact system were analyzed. The multi-parameter mechanism experiment was designed. Piston displacement, oil return flow, main input-oil, and internal chamber pressure were obtained. Combining the structural characteristics and working principles of rock drills, the experiment-based accumulator volume calculation methods was proposed. According to the phase plane analysis of the accumulator diaphragm and the time series analysis of impact performance parameters, which indicate that the high-pressure accumulator and impact system have typical non-contact nonlinear structures. The dynamic performances also present complex nonlinear characteristics. With the increase of gas pre-charge pressure, the bifurcation points were developed from period-one motions to period-two motions, the coupling degree of flow coupling between the accumulator and the impact piston was gradually enhanced, and the impact performance was gradually improved. With the formation of the period-one motions and the increase of bifurcation strength, the diaphragm became more susceptible to fatigue damage. The optimum choice of high-pressure accumulator gas pre-charge pressure is 80–90 bar, which provides a reference for the application and parameter setting of high-pressure accumulators in unconstant-pressurized chamber rock drills.

High Speed Particle Image Velocimetry in a Large Engine Prechamber

Abstract Planar velocity measurements using the particle image velocimetry technique have been performed at a repetition rate of 10 kHz in the prechamber of a large bore gas engine mounted on a rapid compression machine (RCM), to visualize the velocity fields in the non-reacting gas flow during a compression stroke. The prechamber investigated in this work is a prototype with modifications made to facilitate optical access, and it is mounted axially on the RCM combustion chamber. The parameters of the compression stroke in the RCM are set to achieve a compression ratio of 10. After removing outlying data based on pressure and piston displacement curves, PIV data from compression strokes were analyzed. The time-resolved velocity fields capture the formation and motion of a tumble vortex in the imaged plane. Mean flow fields obtained by phase averaging across the datasets are presented, showing the development of the flow field in the prechamber throughout the compression stroke. The data obtained will be used to validate CFD simulations.

Phase behavior of the carbon dioxide/toluene/poly(ethylene glycol) ternary system

The phase behavior of a carbon dioxide (CO2)/toluene (Tol)/poly(ethylene glycol) (PEG) ternary system was investigated in this study to consider the effect of the polymer species on the phase diagram. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurements. Bubble points (vapor–liquid phase separation) were determined from changes in the piston displacement and cloud points (liquid–liquid (LL) phase separation) were determined from changes in the turbidity. The phase boundaries of the CO2 mass fractions ranging from 0.113 to 0.496 were measured by varying the Tol/PEG mass ratio. The homogeneous phase area decreased when the mass ratio of PEG to Tol increased and/or the temperature decreased. These changes in the LL phase-separation behavior were explained by referring to the free volume fraction and solubility parameter estimated using the Sanchez–Lacombe equation of state. The free volume integral fraction could explain the phase diagram, but not the solubility parameter; the effect of polymer species on the Px phase diagram of the ternary system was explained by considering specific interactions between dissimilar components. These results could promote a comprehensive understanding of the phase diagram of CO2/organic solvent/polymer systems and aid the prediction of phase behavior.

Fabrication and high-power testing of an X-band high-power phase shifter for the very compact inverse Compton scattering gamma-ray source.

This paper proposed an X-band phase shifter for the very compact inverse Compton scattering gamma-ray source program at Tsinghua University and conducted its structure design, numerical simulation, fabrication, cold test, and high-power testing. This phase shifter is composed of a polarizer, circular waveguide, and a piston with a choke structure. The simulation results show that the reflection coefficient of the phase shifter is under -40 dB and the insertion coefficient exceeds -0.06 dB at the operating frequency of 11.424GHz. The phase variation is 20°/mm, and a linear phase change from 0° to 360° can be achieved with a piston displacement of 18mm. The manufactured phase shifter has exhibited good performance in the cold test by using the vector network analyzer. After 16h conditioning in the Tsinghua X-band high-power test stand, the phase shifter reached a peak power of 72MW at 230ns pulse width and a peak power of 82MW at 130ns pulse width. After processing signals from the high-speed oscilloscope, it was found that the transmission phase variations were in good agreement with the simulation results.

A Large-Scan-Range Electrothermal Micromirror Integrated with Thermal Convection-Based Position Sensors.

This paper presents the design, simulation, fabrication, and characterization of a novel large-scan-range electrothermal micromirror integrated with a pair of position sensors. Note that the micromirror and the sensors can be manufactured within a single MEMS process flow. Thanks to the precise control of the fabrication of the grid-based large-size Al/SiO2 bimorph actuators, the maximum piston displacement and optical scan angle of the micromirror reach 370 μm and 36° at only 6 Vdc, respectively. Furthermore, the working principle of the sensors is deeply investigated, where the motion of the micromirror is reflected by monitoring the temperature variation-induced resistance change of the thermistors on the substrate during the synchronous movement of the mirror plate and the heaters. The results show that the full-range motion of the micromirror can be recognized by the sensors with sensitivities of 0.3 mV/μm in the piston displacement sensing and 2.1 mV/° in the tip-tilt sensing, respectively. The demonstrated large-scan-range micromirror that can be monitored by position sensors has a promising prospect for the MEMS Fourier transform spectrometers (FTS) systems.

Effect of Piston Displacement on Performance of an MR Damper for Structural Application

Effect of Piston Displacement on Performance of an MR Damper for Structural Application

Study on the key parameters of closed-loop free-piston Brayton generator

The escalating energy crisis and environmental issues have compelled countries worldwide to advance energy transitions and vigorously develop green and clean energy technologies. External combustion devices can effectively utilize hydrogen-based fuels, biomass, solar energy, and other sources, playing a critical role in achieving carbon reduction. As a type of external combustion device, the free-piston Brayton generator, with its strong energy adaptability, stands as a highly promising power generation device. Therefore, the design optimization methods and operational characteristics of the free-piston Brayton generator system are worthy of thorough investigation. This paper introduces a novel method for constructing and structurally optimizing a free-piston Brayton generator model. Sage software is utilized to construct a closed-loop free-piston Brayton generator system in the time domain, followed by numerical analysis. The results show that within the frequency range of 35 ∼ 80 Hz, the system maintains a thermal-to-electric efficiency exceeding 40.00 %, demonstrating the system’s ability to operate efficiently at high frequencies. The piston diameter influences the dynamic behavior of the system’s piston, emphasizing the necessity of gradually adjusting the piston diameter to achieve optimal efficiency during structural parameter optimization. System efficiency and power can be balanced by adjusting the compressor inlet pressure. Under design conditions, the system can output 2046 W of electrical power. The thermal efficiency and thermal-to-electric efficiency are 46.84 % and 41.36 %, respectively. Additionally, an innovative analysis of the temperature distribution of the system and the distribution of exergy losses in major components under conditions of high frequency and small piston displacement is conducted. This work provides a new method and guidance for the subsequent design and optimization of free-piston Brayton generators.

In situ observation of the multistep process of cold sintering

AbstractA compact cold sintering stage was constructed to densify ceramic samples in capillary tubes for the purpose of conducting in situ experiments designed to elucidate fundamental cold sintering mechanisms. The stage was used to successfully densify samples composed of ZnO/CH₃COOH mixtures under a range of pressures (25–175 MPa) over a modest temperature range (room to 150°C) in capillary tubes (0.75 mm inner diameter). The progression of the cold sintering process of ZnO was monitored by both piston displacement and a camera. These measurements allowed the strain rate and fluid extraction during densification to be recorded. The results of these measurements are compared to existing models of cold sintering and pressure solution creep, and direct correlations are observed between abrupt changes to the densification rate during constant heating rate experiments and the observation of solvent extraction from the powder compact.

Performance improvement of a Stirling-type two-stage pulse tube cooler by using stepped displacer plus bypasses phase shifter

Stirling-type pulse tube cooler (SPTC) is the most prospective thermoacoustic refrigerator due to its long lifetime, high reliability and low vibration, and the phase shifter significantly affects the energy conversion efficiency of SPTC. A novel phase shifter of the stepped displacer plus bypasses (SD-B) is proposed in this paper. Thermoacoustic impedance characteristics of the stepped displacer (SD) and the stepped displacer plus bypasses (SD-B) are analyzed. Based on a two-stage SPTC, the effect of additional combined DC flows in the system is first investigated. Results indicate that the cooling capacity could be improved through introducing additional DC flows in the positive direction from the hot end of regenerator to pulse tube. While for SD, negative DC flows are induced due to the clearance seal gaps between the displacer piston and cylinder shell. Thus, SD-B is explored to improve energy conversion efficiency through naturally introducing DC flows by bypasses. The influence of the opening diameter of two bypasses is investigated, and comparisons between the SD and SD-B are performed. Results indicate that with SD-B, the cooling capacity at 20 K achieves a maximum of 2.04 W with a relative Carnot efficiency of 13.0 %, 56.9 % higher than that of SD.

Phase behavior of the carbon dioxide/toluene/poly(methyl methacrylate) ternary system

Carbon dioxide/organic polymer/solvent systems have several industrial applications, including supercritical polymerization. Various process parameters affect the phase behavior of these systems, thereby influencing the process design. Accordingly, the phase behavior of a carbon dioxide (CO2)/toluene (Tol)/poly(methyl methacrylate) (PMMA) ternary system was investigated in this study. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurement. Bubble points (vapor–liquid phase separation) were determined from changes in the piston displacement, whereas cloud points (liquid–liquid (LL) phase separation) were determined from changes in the turbidity The phase boundaries of CO2 mass fractions ranging from 0.098 to 0.577 were measured by varying the Tol/PMMA ratio. The homogeneous phase area decreased when the ratio of PMMA to Tol increased, molecular weight of PMMA increased, and/or temperature decreased. These changes in the LL phase separation behavior were explained with reference to the free volume (vf) and solubility parameter (δ) estimated using the Sanchez–Lacombe equation of state. The estimation of vf and δ is expected to be helpful in comprehensively understanding the phase diagram and in predicting the phase behavior of CO2/organic solvent/polymer systems.

Optimizing Accumulator Performance in Hydraulic Systems through Support Vector Regression and Rotational Factors

The piston-type accumulator is an energy storage device in hydraulic–pneumatic systems, playing a significant role in industries such as petrochemicals, heavy machinery, and steel metallurgy. The displacement parameters of the piston-type accumulator are vitally important for fault diagnosis and early warning in hydraulic systems. Traditional displacement measurement methods cannot meet the requirements of the internal testing environment of the accumulator. Therefore, this paper proposes an accumulator piston displacement signal compensation method based on rotational factors and support vector regression. Firstly, empirical mode decomposition is utilized to denoise the signal. Then, rotational factors are used to generate a delay compensation module to compensate for the signal attenuation and time delay caused by metallic reflection and scattering within the cylinder of the radar signal. The support vector regression model is improved based on a hash table to enhance its computational efficiency and achieve radar displacement signal compensation. Finally, a simulation experiment is designed to verify the effectiveness of the proposed method.

Operating characteristics study of a dual-opposed free-piston Stirling generator

Dual-opposed Free-piston Stirling generators (dual-opposed FPSGs) offer advantages of reduced vibration and increased power density, making them promising candidates for space and distributed energy applications. So far, operational characteristics of the dual-opposed FPSG have yet to be completely understood. This study focuses on a 3 kW dual-opposed FPSG prototype designed to integrate heat pipes. Through computational fluid dynamics and thermoacoustic analysis, a novel hot end heat exchanger with evenly-distributed heat pipe bore was discovered to deliver 12 kW heating power with a gas–solid temperature difference of 21 K. Subsequently effort combined thermoacoustically-based calculations with experiments to investigate the impact of two electrical connection methods of linear alternators on FPSG performance. Experimental results validated the numerical model, showing heat-to-electricity efficiency deviations within 5 % under different electrical connection modes. The FPSG consistently achieved its rated power in both series and parallel connection modes, exhibiting a thermal-to-electric efficiency of 25.2 %. Notably, the series connection mode demonstrates superior sensitivity and consistency compared to parallel connection. Further experiments revealed that charge pressure, load resistance and external capacitance all exerts limited impact on the consistency, while external capacitance significantly influenced acoustic impedance. This resulted in an enhancement in both hot-end wall temperature and heat-to-electricity efficiency, while minimizing power piston displacement and damping temperature when resonating with the inductance.

Multi-Objective Optimization of Absorber Piston Rod Design Parameter using Response Surface Methodology

Car absorbers provide a comfortable ride and improve ride handling by delivering road wheel contact. The typical car absorber problems are oil leakage and piston rod wear-out due to the lateral friction between the shell case and piston rod. The piston rod can bend and rupture when exposed to higher vibration exerting high impact force. This study focuses on optimizing car absorber piston rod design parameters via finite element analysis. The response surface methodology (RSM) was utilized to create the design of the numerical experiment. The piston rod parameters (i.e., length of the piston rod, the piston rod diameter #1, and the piston rod diameter #2) were optimized to reduce the stress and displacement of the piston rod. The optimization results revealed that the optimum parameters were 254 mm in piston length, 24.79 mm in diameter #1, and 15 mm in diameter #2. With the optimized piston rod parameters, the stress and displacement of the piston were 1.65048E+007 and 0.007569 mm, respectively. The most significant factors that influence the responses were also studied. The suggested optimized factors and responses were validated in the finite element simulation.

Flow pulsation characteristics of variable displacement piston pump considering coupling effects cavitation bubble and swash plate inclination angle vibration

Variable-displacement piston pumps, in comparison with quantitative pumps, offer high volumetric efficiency, energy savings, and variable displacement advantages. The outlet flow pulsation of these pumps is influenced by several factors, including swash plate inclination angle vibration, cavitation bubbles, flow distribution structure, and valve control structure. This complexity poses challenges in accurately predicting the flow pulsation at the outlet of variable-displacement piston pumps. In response to this challenge, a novel outlet flow pulsation model for variable-displacement piston pumps is proposed, taking into account the coupling effects of cavitation bubbles and swash plate inclination angle vibration, building upon an existing model. Initially, the effects of cavitation bubbles and swash plate inclination vibrations on flow pulsation were analyzed. Subsequently, a comprehensive flow pulsation model for variable-displacement piston pumps was developed, considering the coupling effects of cavitation bubbles and swash plate inclination angle vibrations. This model was compared with three other existing flow pulsation models. The accuracy of the results was validated using a constructed test bench, with an accuracy improvement of approximately 12% compared to traditional theoretical models. Finally, an optimization model for outlet flow pulsation was proposed. The structural parameters of the valve plate, aimed at minimizing flow pulsation, were determined using the multi-agent particle swarm optimization algorithm. These findings underscore the importance of considering the coupled effects of cavitation bubble and swash plate inclination angle vibration in the design optimization process for reducing low-flow pulsation. This study provides a theoretical foundation for the design of variable-displacement piston pumps with minimized vibration and noise levels.

Investigation of an efficient high cooling-capacity Stirling-type pulse tube refrigerator with passive rod displacer operating at 173 K

Pulse tube refrigerator (PTR) with passive rod displacer is of great potential to realize high-efficiency refrigeration and can be a feasible substitute for the vapor compression system in ultra-low temperature cold storage. However, PTRs with passive rod displacer in that application require high efficiency and substantial cooling capacity, which still need to be developed in previous research. In this paper, a high cooling-capacity PTR with passive rod displacer operating at 173 K was designed, fabricated, and investigated. The special property of acoustic power recovery was exhibited based on an electrical circuit analogy model and energy flow analysis. The structural parameters of PTR with passive rod displacer were optimized by one-dimensional numerical software. The experimental results showed that a cooling capacity of 157.5 W at 173 K was obtained with an input electric power of 500 W. The corresponding relative Carnot efficiency reached 21.8 %. The phase difference between the displacer and piston decreased slightly from 58.1° with the increase of cooling temperature when charging pressure and operating frequency were 2.8 MPa and 65 Hz, respectively. The phase difference was determined by the operating frequency and was slightly affected by charging pressure, cooling temperature, and input electric power. Based on the validated numerical models, PTR with passive rod displacer and inertance-tube-type PTR were compared. The numerical results showed that both enthalpy and PV power enlarged at the T-junction in the PTR with passive rod displacer due to acoustic power recovery. According to the acoustic-mechanical–electrical coupling phasor diagram, the phase difference between pressure and piston displacement decreased because of the mass flow superposition at the T-junction, affecting the output capability of the linear compressor. The efficient high cooling-capacity prototype verifies that PTR with passive rod displacer has a bright future in ultra-low temperature engineering applications.

Experimental and simulation investigation on the impact performance of pneumatic hammer under varied drilling conditions

It is of great significance to reveal the influence on the output performance of pneumatic hammers under different drilling condition parameters to improve their impact efficiency used in drilling applications. In this study, Computational fluid dynamics (CFD) wisth dynamic mesh method was utilized to simulate dynamic airflow and piston movement within the hammer. User-Defined Functions (UDFs) are modified to introduce friction and varying well deviation angles. Meanwhile, a test bench of pneumatic hammer performance is designed and built to record real-time data on the piston displacement and chamber pressure within the hammer, validating the simulation results. The results show that the simulated and experimental data exhibit similar values and trends, with a maximum error of 10.92% for the impact velocity, 9.5% for the impact frequency, 8.36% for the maximum piston displacement, and 10.81% for the pressure drop, respectively. In addition, the piston motion mechanism was analyzed and the effects of well deviation angle, mass-flow rate, backpressure, restitution coefficient, and friction coefficient on the hammer's performance were investigated in detail. The results indicate that the mass-flow rate and restitution coefficient have a positive effect on increasing the piston's impact velocity and impact frequency, as well as pressure drop. In the context of directional drilling, the hammer's impact energy varies with the well deviation angle. At lower values of the friction coefficient, a clear positive correlation emerges between impact energy and deviation angle. Conversely, at larger values of the friction coefficient, a distinct biphasic behavior is observed, with the impact energy first decreasing before subsequently increasing. Furthermore, the backpressure, and friction coefficient adversely affect the hammer performance, with the backpressure being the dominant factor.

Importance of Water‐Clay Interactions for Fault Slip in Clay‐Rich Rocks

AbstractClay‐rich rocks are integral to subduction zone dynamics and of practical importance, for example, as barriers in nuclear waste and CO2 repositories. While the effects of swelling strain on the self‐sealing capabilities of these rocks are relatively well‐established, the implications of polar fluids interacting with charged clay particles on the frictional behavior, and the role of swelling stress in initiating slip in critically stressed faults, remain ambiguous. To address these uncertainties, we conducted triaxial friction experiments using saw‐cut samples, with the upper half composed of Opalinus claystone (OPA) and the lower half of Berea sandstone (BER). The frictional strength of the non‐wetted OPA‐BER interface was estimated based on experiments at confining pressures of 4–25 MPa and constant axial loading rate (0.1 mm/min). Fluid injection friction experiments were performed using decane (non‐polar fluid) or deionized water (polar fluid) at 10 and 25 MPa confining pressures and constant piston displacement control. Macroscopic mechanical data were complemented by distributed strain sensing on the sample surface. Compared to decane, the frictional strength of the OPA‐BER interface tended to decrease when injecting water, which is attributed to phyllosilicate lubrication and the transition of the OPA from a solid rock to an incohesive mud near the saw‐cut surface. When injecting water, slip was initiated during initial hydration of the OPA‐BER interface, although the apparent stress state was below the yield stress. To explain this behavior, we propose that the swelling stress is a crucial factor that should be integrated into the effective stress model.

Performance investigation of an active free-piston Stirling engine using artificial neural network and firefly optimization algorithm

The aim of this study is to explore the characteristics of an active Free-Piston Stirling Engine (AFPSE) through the use of machine learning methods. Due to the time-intensive nature of extracting simulation results from complex thermal equations, an Artificial Neural Network (ANN) is utilized to expedite the process. To construct a nonlinear model, 5000 samples are extracted from simulation results. Input parameters included in the model are the hot and cold source temperatures, the voltage given to the DC motor, spring stiffness, and the mass of the power piston, while output parameters are the amplitude and frequency of power piston displacement. The proposed ANN model structure comprises two hidden layer with 10 and 20 neurons, respectively, indicating the applicability of the ANN model in estimating significant parameters of AFPSE in a shorter amount of time. The firefly optimization algorithm is utilized to determine the unknown input parameters of ANN and maximize the output power. Results indicate that a maximum output power of 23.07 W can be attained by applying 8.5 V voltage on the DC motor. This study highlights the potential of machine learning techniques to explore the primary features of AFPSE.

Regional scale evaluation of nitrate fluctuations in groundwater using cluster analysis and standardised hydrometeorological indices

Temporal fluctuations in nitrate in groundwater can result in concentrations temporarily exceeding drinking water standards. This can bring about the need for costly water treatment or blending. Despite this, the extent and potential controls on these fluctuations are poorly understood, particularly at regional to national scales. Applied to Southeast England (UK), here we develop the first application of cluster analysis and standardised hydrometeorological indices to evaluate nitrate fluctuations in groundwater at the regional scale. Hierarchical and K-means cluster analysis of 96 groundwater nitrate time series for the period 1995–2022 showed that nitrate time series can be divided into 4 clusters: (1) long term increasing trends (n = 23, mean trend = 0.26 mg NO3/l/a), (2) long term decreasing trends (n = 19, mean trend = − 0.65 mg NO3/l/a), (3) long term increasing trends with seasonal fluctuations (n = 24, mean trend = 0.29 mg NO3/l/a) and (4) long term increasing trends superimposed on near-decadal scale fluctuations (n = 30, mean trend = 0.22 mg NO3/l/a). Boreholes in cluster 1 appear to be deeper than boreholes in cluster 2. In comparison to shallower boreholes, deeper boreholes are likely to be intersecting longer groundwater flow systems where nitrate concentrations are affected by historic “legacy nitrate” leaching. There is weak spatial coherence in the clustering, with clusters 3 and 4 present in the South and North Downs respectively. Cross-correlation analysis between groundwater nitrate time series with precipitation and groundwater level indices showed that rapid seasonal fluctuations in nitrate concentrations in cluster 3 in the South Downs are associated with rapidly responding groundwater level fluctuation. This is likely due to the highly fractured and faulted nature of the Chalk aquifer in this area. This is in contrast with the slower near-decadal fluctuations in cluster 4 in the North Downs. The strongest correlations between groundwater levels and nitrate concentrations in cluster 3 occurred when cross-correlating at a lag of zero months, which would suggest that matrix diffusion is unlikely to be a significant control on nitrate seasonality. Seasonal fluctuations in nitrate concentrations are likely to be associated with a combination of piston displacement at the water table and changing groundwater flow paths to the borehole. Future climate change may change the magnitude and timing of seasonal fluctuations caused by these processes. The methodology developed here is generic and can be applied wherever there is a large body of groundwater nitrate time series data.

The effects of design parameters on the dynamic performance, in-cylinder pressure and electrical power generation of a free piston linear engine

Operation of a free piston linear engine is modeled based on the combination of three mathematical models, including a piston dynamic model, a linear alternator model and a thermodynamic model. The simulated in-cylinder pressure, piston velocity, and electric power output are compared with the corresponding experimental results to validate the models mentioned above. The influences of the design parameters, including cylinder dimension ( Le), number of coil turns ( N), and air gap ( g) between the translator and stator, on the dynamic performance, in-cylinder pressure and electric power generation of the free piston linear engine are studied. The study results show that the reduction of Le has a benefit for improving the piston dynamic performance and output electric power, however it also reduced the cylinder pressure. The increase of number of coil turns N results in the reduction of the peak piston velocity, displacement, acceleration, and pressure in the cylinder, however, it increases the output electric power of the free piston linear engine. The peak piston velocity, displacement, acceleration, and pressure in the cylinder are considerably decreased when g is reduced. However, the reduction of g has a benefit to improve the output electric power of the free piston linear engine. The energy conversion efficiency can be maximized when g and Le are reduced, and N is increased.