Piston Model Research Articles

Fault Diagnosis Research on Impact System of Hydraulic Rock Drill Based on Internal Mechanism Testing Method

In the production and manufacturing process of hydraulic rock drill, there are small impact energy and low impact frequency, and a fault diagnosis method based on the internal mechanism testing and testing of the hydraulic rock drill is proposed. This method is used to test the change law of hydraulic oil in the rock drill, by retaining the test holes on the cylinder body and other important components of the hydraulic rock drill. At the same time, the mathematical method is used to deal with the test curve, and the influence of pressure pulsation characteristics of the front and rear chambers of the impact piston and the left and right valve chambers of the reversing valve on the impact performance of the rock drill is analyzed. Based on Newton’s law, the model of the impact piston and reversing valve is established. According to the velocity and other parameters of the impact piston, the size of the impact piston switch point is calculated. The coupling between the movement of the impact piston and the movement of the reversing valve is analyzed according to the model established. Comparing the results of the experimental data, the correctness of the fault diagnosis analysis method and model is verified. The effect of the fault rock drill and the improved model is compared, and the theoretical basis is provided for the fault diagnosis of the rock drill and the design of a new type of rock drill.

Calculation of Volumetric Sound Field of Pulsed Air-Coupled Ultrasound Transducers Based on Single-Plane Measurements.

Quantitative and reproducible air-coupled ultrasound (ACU) testing requires characterization of the volumetric pressure fields radiated by ACU probes. In this paper, a closed-form reradiation method combining the Rayleigh-Sommerfeld integral and time-reversal acoustics is proposed, which allows calculation of both near- field and far-field based on a single-plane measurement. The method was validated for both 3-D (circular, square) and 2-D (rectangular) planar transducers in the 50-230 kHz range. The pressure fields were scanned with a calibrated microphone. The measurement window was at least four times the size of the transducer area and the grid step size was one third of the wavelength. Best results were observed by acquiring the measurement plane at near-field distance. The method accurately reproduces pulsed ultrasound waveforms and pressure distributions (RMSE <2.5% in far field and <5.5% in near field), even at the transducer radiation surface. The effects of speed of sound drifts during the scan in the pressure were negligible (RMSE <0.3%). The reradiation method clearly outperforms conventional baffled piston models. Possible applications are transducer manufacture control (imperfections at radiation surface) and calibration (on-axis pressure, side lobes, and beamwidth) together with generation of accurate source functions for quantitative nondestructive evaluation inverse problems.

Tongue-driven sonar beam steering by a lingual-echolocating fruit bat.

Animals enhance sensory acquisition from a specific direction by movements of head, ears, or eyes. As active sensing animals, echolocating bats also aim their directional sonar beam to selectively “illuminate” a confined volume of space, facilitating efficient information processing by reducing echo interference and clutter. Such sonar beam control is generally achieved by head movements or shape changes of the sound-emitting mouth or nose. However, lingual-echolocating Egyptian fruit bats, Rousettus aegyptiacus, which produce sound by clicking their tongue, can dramatically change beam direction at very short temporal intervals without visible morphological changes. The mechanism supporting this capability has remained a mystery. Here, we measured signals from free-flying Egyptian fruit bats and discovered a systematic angular sweep of beam focus across increasing frequency. This unusual signal structure has not been observed in other animals and cannot be explained by the conventional and widely-used “piston model” that describes the emission pattern of other bat species. Through modeling, we show that the observed beam features can be captured by an array of tongue-driven sound sources located along the side of the mouth, and that the sonar beam direction can be steered parsimoniously by inducing changes to the pattern of phase differences through moving tongue location. The effects are broadly similar to those found in a phased array—an engineering design widely found in human-made sonar systems that enables beam direction changes without changes in the physical transducer assembly. Our study reveals an intriguing parallel between biology and human engineering in solving problems in fundamentally similar ways.

Piston temperature model oriented to control applications in diesel engines

In this paper, the development of a control-oriented piston temperature model for diesel engines is discussed. Using the underlying energy balance at the piston, a one-state piston temperature model was developed based on a thermal resistance concept. The model is composed of five sub-models: an engine model, a heat distribution model, a piston temperature model, an initial piston temperature model, and a maximum piston temperature model. In the engine model, the combustion heat transferred to the engine is calculated based on the energy balance in the cylinder chamber. The heat distribution model, which is a main feature in this model, determines the heat transferred to the piston using two maps as a function of engine speed and fuel depending on the piston cooling jet (PCJ) operation. The energy balance at the piston is applied to calculate the mean piston temperature, and the initial piston temperature is determined by the arbitration between the piston and the oil temperatures. The maximum piston temperature is estimated using a simple linear correction to the mean piston temperature. Integrating all sub-models in the Simulink platform, the model was identified and validated using piston temperature measurements under steady-state fuel steps as well as transient tests. There is a good agreement between the modeled and the measured piston temperatures with less than 4.1°C of root-mean-square-error (RMSE) over transient emissions cycles (FTP-75, LA92, and HWEFT). The modeled piston temperature can be used as an input to the control strategy of variable cooling devices, such as a variable displacement oil pump.

Asymptotics of linear water waves generated by a localized source near the focal points on the leading edge

Consider a liquid in a uniform gravitational field in a horizontally infinite basin of variable finite depth. Assume that the liquid performs a potential motion and its state at the initial time is characterized by a given free surface elevation decaying at infinity and by the zero vertical velocities of the free surface (which, for example, corresponds to the so-called piston model of tsunami generation [1, 2]). The problem is to determine the free surface elevation at the subsequent times.

Modelling of the multi-chamber oscillating water column in regular waves at model scale

This paper studies the reliability of numerical models used for estimating multi-chamber oscillating water column (MC-OWC) response in the time-domain. The model for the internal water surface level and instantaneous pressure inside the chamber at regular waves conditions using a hybrid system of hydrodynamic and thermodynamic rigid piston models without power take-off. Reliability is assessed using experimental data obtained from a wave tank used in the model concept validation. The results show the method could be extended to describe the hydrodynamics of the MC-OWC in regular and irregular wave conditions.

Fracture mechanism of air percussive rotary bit matrix based on impact stress wave theory

An air percussive rotary bit is a key component of air percussive rotary drilling technology, and its fracture failure seriously affects the safe operation and economic efficiency of drilling. This paper presents (1) theoretical analysis of the impact stress wave propagating in the air percussive rotary bit and effect of the stress wave on bit fracture and (2) finite element simulation study based on the stress wave theory which builds a model of the air hammer piston, drill and rock, defines material parameters, meshes and defines boundary conditions, clarifies propagation characteristics of the impact stress wave, analyzes stress characteristics of the bit matrix under different conditions (same drilling pressure and same piston speed, different drilling pressure and same piston speed and same drilling pressure and different piston speed) and determines the main factors of bit matrix fracture. The correctness of the theoretical analysis was verified with simulation results and fundamental ways of preventing bit fracture failure were proposed to provide a theoretical basis for the structural optimization design of a new bit. The results show that a bit section mutation is the root cause for the shock of the impact wave and the change in nature of the wave during propagation. The tensile wave is the root cause for bit matrix fracture, and a breakage is the most serious at stomatal interchanges. With increasing drilling pressure and piston speed, the rate of increase in the peak stress of the bit matrix increases, leading to early fatigue fracture of the bit matrix. The fracture of the bit matrix can be reduced, and the bit life can be extended by rationally designing the bit sectional structure parameters, ensuring that the bit withstands the effects of the compression wave so as to reduce the formation of a tensile wave, and rationally choosing drilling process parameters (such as drilling pressure and air pressure).

Squeal simulation and analysis of brake system with pressure and speed dependent friction model and exerting process of pressure

In this paper, a complete finite element model of disc brake considering the ventilated brake disc, pads, back-plate, caliper, bracket, piston, rubber bushes and simplified fluid model driving piston is established. The pressure and speed dependent friction model and temperature field are considered. The results of complex eigenvalue analysis (CEA) show consistence with the existing achievements, thus the feasibility of the established model is verified. Subsequently, the transient dynamic analysis of the brake system is carried out for different exerting process of the pressure which represents the operation of different drivers. Besides, the vibration responses of different brake pressure and different speed are also investigated. The evolution process of the stability is studied by time-frequency analysis (STFT method). Both CEA and time-frequency analysis show the squeal tends to appear in the case of high friction coefficient, low speed and low brake pressure. It can also be found that the vibration frequency and its energy are not constant but fluctuate in a certain range. The results of different pressure exerting processes with simplified fluid model driving piston show that vibration response of disc brake not only depends on the value of brake pressure but also depends on the pressure exerting process. It is supposed that brake pressure and rotational speed determine the frequency of squeal while the process of exerting pressure determines the existing duration of brake squeal.

Vibration of a baffled piezoelectric ceramic circular disk in lower radial modes, with near- and farfield sound radiation

Accurate knowledge of the sound field generated by an ultrasonic transducer is important in certain applications, such as custody transfer oil and gas flow measurement. Near- and farfield diffraction effects may influence on the measurement result, demanding a need for control of magnitude and phase influences. In many situations, the simplified model of a planar and uniformly vibrating baffled piston is used to approximate the transducer’s sound field. The Rayleigh distance of the piston model is often used as a measure of the near- and farfield transition range. Real transducers typically exhibit a non-uniform vibration distribution at the front, with significant side and rear vibration. It is of interest to investigate the accuracy of the traditional piston and Rayleigh distance approaches for real transducer sound fields. A circular and baffled Pz27 piezoelectric ceramic disk with diameter 12.7 mm and thickness 2.0 mm is studied, operating in air. Finite-element modeling, supported by analytical and numerical modeling, is used to investigate the near- and farfield sound pressure field over the 0-500 kHz range, including radiation at the two lowest radial modes of the piezoelectric disk. Significant nearfield effects are observed well beyond the Rayleigh distance, both on and off the acoustic axis.

Optimised intake stroke analysis for flat and dome head pistons

This research exerts are suitable for the automobile industry in understanding the performance characteristics optioned between flat head and dome head pistons in engine design. This study was carried out to analyze the optimization parameters for effective and efficient flow characteristics of air-fuel mixture at the intake port of the combustion chamber of an internal combustion engine. A unique and industrial standard CFD software, STAR-CCM V8, was used to model both geometry for flat head and dome head pistons which was developed with precise dimensions of a 1.8L gasoline engine. A planar 3-D model approach was adopted for simplified static CAD modeling and also to reduce the solver processing time. The piston models were meshed using tetrahedral mesh of base size 0.001m. The boundary and physics conditions were applied to simulate the actual intake stroke process for normal operating conditions and initial conditions. The extracted results were validate and comparisons developed to analyze the various optimization parameters for performance characteristics of the two pistons. http://dx.doi.org/10.4314/njt.v36i1.1 5

Heating in ultraintense laser-induced shock waves

AbstractThis paper considers the heating of a target in a shock wave created in a planar geometry by the ponderomotive force induced by a short laser pulse with intensity higher than 1018 W/cm2. The shock parameters were calculated using the relativistic Rankine–Hugoniot equations coupled to a laser piston model. The temperatures of the electrons and the ions were calculated as a function of time by using the energy conservation separately for ions and electrons. These equations are supplemented by the ideal gas equations of state (with one or three degrees of freedom) separately for ions and electrons. The efficiency of the transition of the work done by the laser piston into internal thermal energy is calculated in the context of the Hugoniot equations by taking into account the binary collisions during the shock wave formation from the target initial condition to the compressed domain. It is shown that for each laser intensity there is threshold pulse duration for the formation of a shock wave. The explicit calculations are done for an aluminum target.

A Study on Force and Lubrication Characteristics of Ball Piston in Eccentric Ball Piston Pump

Ball piston is an essential design element in eccentric ball piston pump. The objective of this paper is to investigate the dynamic force and lubrication characteristics of the ball piston. In this study, a tribodynamic model of the ball piston is proposed. The model couples the elastohydrodynamic lubrication model of ball–ring pair and the elastohydrodynamic model of ball–cylinder pair with the dynamic model of the ball piston. The interaction between tribological behavior and dynamic performance and the effects of centrifugation and structural deformation of the ball piston are considered. The pressure distributions and film profiles of the ball–ring pair and ball–cylinder pair are calculated. The dynamic normal contact forces and friction forces are analyzed. The friction torque loss and mechanical efficiency of the whole pump are obtained by combing the tribodynamic model of the ball piston with a simplified friction torque model of cylinder-valve shaft pair. A test bench is established for validating the simulation results. The results show that the normal contact force of the ball–ring pair waves in each stroke, and in discharge stroke, the contact force is much bigger than that in suction stoke because of loading force, while the friction force changes very little for the ball sliding in the outer ring. Comparing with the average friction force of the ball–ring pair, the average friction force of the ball–cylinder pair is small, which reflects that the ball–ring pair is more prone to wear. For the ball–ring friction pair, when the load increases, the secondary contact pressure peak appears, the profile of film presents a horseshoe shape, and the classical shrinkage appears at the outlet of contact region. For the ball–cylinder pair, the film pits and the contact pressure jumps at the entrance of contact region for the heavy load and the high shear stain of film. In addition, the friction torque presents a nonlinear growth trend with the increasing working pressure

Finite element analysis of thermo-mechanical conditions inside the piston of a diesel engine

In this paper, we present our theoretical investigations on thermo-mechanical conditions inside the piston of a diesel engine. For the theoretical analysis, the operational parameters of such piston, semi-empirical formula and empirical model were employed to determine the boundary conditions such as temperature and stress fields. Using the finite element method (FEM), the stress loading and fatigue life were calculated. Based on the available experiment data, the used empirical formula and models can be improved well. Furthermore, the harsh conditions were simulated using the FEM, and the results were verified using the accelerated life testing. Moreover, the relationships between the piston life and stress under the thermal load, mechanical load, and thermal-mechanical coupling conditions were established based on the above simulated data. The results showed that in different thermal, mechanical, and thermal-mechanical coupling conditions, their relationships obeyed Arrhenius model, Inverse power law model, and Generalized Eyring model, respectively.

First Principle-Based Control Oriented Model of a Gasoline Engine

A first principle based-control oriented gasoline engine model is proposed that is based on the mathematical model of the actual piston and crankshaft mechanism. Unlike conventional mean value engine models (MVEMs), which involve approximating the torque production mechanism with a volumetric pump, the proposed model obviates this rather over-simplistic assumption. The alleviation of this assumption leads to the additional features in the model such as crankshaft speed fluctuations and tension in bodies forming the mechanism. The torque production dynamics are derived through Lagrangian mechanics. The derived equations are reduced to a suitable form that can be easily used in the control-oriented model. As a result, the abstraction level is greatly reduced between the engine system and the mathematical model. The proposed model is validated successfully against a commercially available 1.3 L gasoline engine. Being a transparent and more capable model, the proposed model can offer better insight into the engine dynamics, improved control design and diagnosis solutions, and that too, in a unified framework.

Modeling of Oil Film Thickness in Piston Ring/Liner Interface

The correct understanding of piston ring/liner lubrication condition has a primary importance in order to improve internal combustion engine efficiency in terms of oil consumption and friction losses. Analytical and numerical investigation of piston ring-pack becomes then a reliable tool for evaluating piston ring/liner interface lubrication mechanism. Main aim of this paper is to examine the effects of technical aspects, such as ring geometry and operating condition on modeling of piston ring/liner lubrication. An analytical model based on lubrication theory under hydrodynamic regime is here presented and discussed. The model can represent a useful tool for designing low friction engine components and it can be applied to develop reliable friction models to predict actual engine output.

Analiza i izbor metodologije za određivanje kinetike sagorevanja poljoprivredne biomase

The paper presents results of experimental investigation performed in order to examine kinetics of loose biomass combustion in vertical tube reactor. The investigation conducted included continuous measurement of the fuel mass loss rate, with two biomass combustion models (piston and batch model) proposed, each relying on appropriate theoretical postulates. Results obtained indicated that piston combustion model had shown better agreement between theoretical and experimental data and was therefore used to further analyse effects of excessair on the combustion kinetics. Experiments were conducted on specially designed and constructed apparatus that enabled kinetic parameters to be determined for the combustion of different types of biomass. Results obtained have indicated that quantity of air affects kinetics of biomass combustion. Experiments were conducted with two different types of agro-biomass, namely wheat straw and corn stalks, which are most commonly used for energy generation. Results achieved are deemed particularly important when it comes to design of new plants that utilize 'cigar' firing combustion system, but also for development of numerical models used to simulate combustion of biomass bales.

Analysis of thermal temperature fields and thermal stress under steady temperature field of diesel engine piston

With the improvement of the diesel engine power and performance, the piston in the combustion chamber is subjected to higher thermal load and the thermal stress decreases its working life. Therefore, it is necessary to analyze the subsequent thermal stress on the piston during design process to reach the optimum one. This paper tries to present a new calculation method for the theoretical design of the piston. In this study, the 3D solid model of piston in 16V280 diesel engine was developed and the simulation calculation of the steady-state and the transient-state temperature field is carried out. Based on calculation results, the maximum temperature fluctuation of the piston temperature field is less than 20°, so the steady-state temperature field was used as boundary condition for the thermal stress calculation and the thermal mechanical decoupling method was used to calculate the thermal stress caused only by the uneven temperature distribution. The results show that the maximum temperature is 354°C, which appears at the edge of the combustion chamber. The steady-state temperature field of finite element simulation shows a good agreement with the experimental results. The thermal stress obtained from thermal mechanical decoupling method was within the allowable range, since the maximum value is 270MPa. Danger zone appears at the combustion chamber throat, the contact area of piston head and skirt.

Gravitational waves generated by laser accelerated relativistic ions

The generation of gravitational waves by laser accelerated relativistic ions is investigated. The piston and light sail models of laser plasma acceleration are considered, and analytical expressions for space-time metric perturbation are derived. For both models, the dependence of gravitational wave amplitude on the laser and plasma parameters as well as gravitational wave spectrum and angular distribution is examined.

Structural Analysis of the Ligand-Binding Domain of the Aspartate Receptor Tar from Escherichia coli.

The Escherichia coli cell-surface aspartate receptor Tar mediates bacterial chemotaxis toward an attractant, aspartate (Asp), and away from a repellent, Ni(2+). These signals are transmitted from the extracellular region of Tar to the cytoplasmic region via the transmembrane domain. The mechanism by which extracellular signals are transmitted into the cell through conformational changes in Tar is predicted to involve a piston displacement of one of the α4 helices of the homodimer. To understand the molecular mechanisms underlying the induction of Tar activity by an attractant, the three-dimensional structures of the E. coli Tar periplasmic domain with and without bound aspartate, Asp-Tar and apo-Tar, respectively, were determined. Of the two ligand-binding sites, only one site was occupied, and it clearly showed the electron density of an aspartate. The slight changes in conformation and the electrostatic surface potential around the aspartate-binding site were observed. In addition, the presence of an aspartate stabilized residues Phe-150' and Arg-73. A pistonlike displacement of helix α4b' was also induced by aspartate binding as predicted by the piston model. Taken together, these small changes might be related to the induction of Tar activity and might disturb binding of the second aspartate to the second binding site in E. coli.

An extension to the methodology for characterization of thermal properties of thin solid samples by photoacoustic techniques

The paper presents a study of possibilities to extend the present methodology for thermal characterization of thin solid samples by photoacoustic techniques. The present methodology consists of linear fitting of the experimental data to approximate the expressions derived from the composite piston model of photoacoustic response and it is mainly used for calculation of thermal diffusivity of thin samples. The study has shown that the methodology may be extended to calculation of thermal diffusivity, thermal conductivity and thermal expansion coefficients of thin samples by linear fitting in multiple frequency ranges and by analysis of the intersection frequency, which is the frequency where the magnitudes of two components of photoacoustic response in the composite piston model are equal. The analysis of numeric errors of the methodology has revealed the dominant sources and magnitude of the errors, leading to the conclusion that photoacoustic techniques should be carefully used as a tool for extensive thermal characterization of thin samples in the cases when other techniques are not applicable or have larger errors.