Bulk Modulus Of Oil Research Articles

An investigation on the dynamic characteristics of a two-dimensional piston flowmeter

The immediate measurement of dynamic flow rate is of importance in the modern hydraulic system. Following a brief review and analysis on measuring methods of dynamic flow rate, authors introduced the structure and working principle of a two-dimensional piston dynamic flowmeter. Consequently, a mathematical model was carefully established based on its unique mechanical properties due to the two degrees of working freedom. Meanwhile, the transform function is obtained to describe the dynamic characteristics and used to discuss influences from various design parameters. Finally, a 3D printed prototype was designed and fabricated to measure the sinusoidal flow rate with the frequency range of 1–7 Hz on a calibration test rig. The discrepancy between the experimental and the simulated date is quite foreseeable considering the major influence of low oil bulk modulus due to air bubbles. Although the magnitude reaches −3 dB at 4 Hz, the dynamic characteristics are acceptable and can verify the feasibility of applying the two-dimensional piston flowmeter on the dynamic measurement field. The shortcomings of this prototype are well discussed in the conclusion part to provide guidance to enhance the design ability of next-generation prototypes.

Novel Methods for Modeling and Online Measurement of Effective Bulk Modulus of Flowing Oil

Oil is a key medium for transmitting power and coupling information in the hydraulic transmission system. Accurate calculation and measurement of the dynamic compressibility of the oil have profound significance to the system performance analysis. The present study primarily focuses on the effect of steady pressure on the bulk modulus of static oil. However, changing pressure and flowing oil are the general working conditions in most of hydraulic apparatus. There are few researchers paying attention to the influence of pressure on the compressibility of flowing oil. Considering the log-normal distribution of bubble size in oil, an improved static oil model (Model B) is developed to calculate the bulk modulus of the motionless oil under the dynamic pressure. Then, by deriving Model B, this paper proposes an original flowing oil model (Model C) to determine the effective bulk modulus of flowing oil. Finally, based on the inherent pressure pulsation of the axial piston pump, an innovative online method for measurement of the bulk modulus of flowing oil is presented as it has the advantage of avoiding interference with flow stability. It has been proved that the changes in the flow velocity corresponds to the crucial effect on the effective bulk modulus of flowing oil, especially under the low-flow and low-pressure operation conditions. Those results and analysis provide promoting support for identifying and determining the effective bulk modulus of oil, analyzing the system stiffness, improving the control accuracy, as well as optimizing the mathematical models.

Integrated design of a novel force tracking electro-hydraulic actuator

Conventional hydraulic actuators in which the output force is regulated through servo-valves or variable pumps usually suffer from great noise and low efficiency. To overcome this hurdle, a novel force tracking electro-hydraulic actuator based on Pascal's principle is developed. The novel device uses an electric cylinder to change the volume of enclosed fluid and generate the desired loading pressure. In order to further improve the performance of the novel actuator, an integrated design procedure in which the mechanisms and control structure are designed simultaneously is studied. Firstly, the complete mathematical model of the novel actuator is established. The nonlinear system is translated into a linear time-varying model by replacing the effective bulk modulus of hydraulic oil with a time-varying coefficient. The feasibility of the semi-closed control structure with pressure feedback is analyzed on frequency domain and a compound controller is given. Secondly, performance indexes such as stability criteria, bandwidth, control errors and continuous operation capability of the novel actuator are presented in detail. Interactions of the design variables are analyzed through numerical simulations. Afterwards, a nonlinear constrained multi-objective optimization problem including both mechanical and control parameters is formulated. To prevent the optimization progress from falling into local minimum point, a particle swarm algorithm is employed to carry out the optimization design. Experiment results demonstrate the effectiveness of the proposed integrated design method. And simulations are executed to verify the higher efficiency of the proposed novel electro-hydraulic actuator which is compared with the valve-controlled counterpart.

Oscillatory Yaw Motion Control for Hydraulic Power Steering Articulated Vehicles Considering the Influence of Varying Bulk Modulus

In this investigation, a detailed hydraulic steering system of articulated steer vehicles (ASVs) and a 12-DOF ASV model are developed for vehicle dynamics performance research. The real-time changing characteristic of oil bulk modulus is considered. Field test and multibody dynamics model by Adams/View software are compared with the established mathematical model, respectively, to verify the correctness of the model at low speed and high speed. The snaking and oscillatory area is confirmed to reveal the influence of varying bulk modulus on the stability of ASV. To improve the stability of ASV, the direct yaw moment control system and driving force distribution system are designed with the application of the optimal control theory. The upper level controller calculates the expected yaw moment by feedforward and feedback compensatory strategies. Different from zero-sideslip control in most studies, an Ackermann-based sideslip angle is used for feedforward compensatory gain derivation and reference model design. The lower level controller distributes the driving force for each wheel aiming at the optimal utilization rate of tires. High-speed weave test by sinusoidally steering for loaded ASV is simulated to verify the effectiveness of the control algorithms.

Research on Theoretical Model of Dynamic Bulk Modulus of Gas-Containing Hydraulic Oil

The bulk modulus of the gas-containing hydraulic oil is an important indicator reflecting its compressibility, directly affecting the stability, accuracy, rapidity, and reliability of the fluid transmission system. In the time-varying system with high speed and pressure, since the gas release rate differs from the gas dissolution rate, there exists a large difference between the static and dynamic values of the bulk modulus of hydraulic oil. Therefore, it is necessary to research the dynamic bulk modulus of the gas-containing hydraulic oil. Based on the improvement of Henry's law and gas-polytropic-process equation, a modified model of dynamic bulk modulus of the gas-containing hydraulic oil was proposed. Through the analysis of parameter influence, the influence of initial gas content and pressure on the dynamic bulk modulus of the gas-containing hydraulic oil during compression and expansion was discussed. Comparing the modified model and the Zhou model with the experimental results, the goodness of fit between the Zhou model and the experimental results during compression and expansion was 0.9936 and 0.9864, respectively. And the goodness of fit between the modified model and the experimental results during compression and expansion was 0.9937 and 0.9936, respectively. The prediction precision of the dynamic bulk modulus was improved while verifying the accuracy of the modified model. This research can provide a reference for optimizing the theoretical model of the dynamic bulk modulus of the gas-containing hydraulic oil.

Non-linear analysis of a quarter-car model with stroke-dependent twin-tube shock absorber

Abstract The work presents results of the analysis of a quarter-car model with a modified twin-tube hydraulic shock absorber. In comparison with a classical damper, this shock absorber possesses an additional double-chamber cylinder. The flow of oil into these chambers is controlled by relative displacement of the auxiliary piston and by pressure difference in the adjacent chambers. The introduced nonlinear spring element – bumper – protects the shock absorber against damage in the case of large amplitudes of excitations. Performance efficiency of the shock absorber model within the range of both large amplitudes and high excitation frequencies ensures that the change of the oil bulk modulus resulting from a change in pressure is accounted for. The introduction of additional chambers into the shock absorber leads to a change in the characteristics of the damping force. Within the range of small amplitudes and high frequencies the system acts like a shock absorber with a soft characteristic, which improves the driving comfort. In resonance ranges the increase in the damping force ensures higher driving safety. The analysis of the system response to the harmonic excitation of variable frequency and amplitude as well as to the random excitation permits to examine the impact of excitation parameters and construction parameters on the indicators characterizing the driving comfort and safety. The results of numerical simulations are illustrated with the graphs of time histories, spectral analyses, characteristics of the damping force, and others, illustrating the processes of controlling oil flow.

Nonlinear model of a servo-hydraulic shaking table with dynamic model of effective bulk modulus

Abstract In this paper, based on fluid mechanical expressions and a new modified effective bulk modulus model of hydraulic oil built upon IFAS model (developed at the Institute fur Fluidtechnische Antriebe und Steuerungen, RWTH Aachen university), an empirical nonlinear model for a servo-hydraulic uni-axial shaking table is developed. This new model can precisely simulate the acceleration, velocity and position outputs of the system with respect to different kinds of inputs such as pulse and sinusoidal signals for a wide range of frequencies and different weights of the specimen. Therefore, it can be helpful for designing and optimizing the parameters of a model-based controller for tracking reference force or acceleration signals, which is the goal of the shaking table with only position sensor. In the new modified IFAS model, the effective bulk modulus of hydraulic oil on both sides of the piston has been considered as two nonlinear springs, which are connected serially. The minimum stiffness of the spring effect of the hydraulic oil in a symmetric double-acting hydraulic cylinder occurs, when the piston is in the center of its travel, which can be characterized with differential pressure on its both sides. When the differential pressure is less than a specific threshold pressure, these springs have the minimum stiffness and reserve energy in themselves. Based on the experimental observations, this effect has been modeled with a function, which multiplies the IFAS model. The experimental acceleration output of the system demonstrates the dynamic behaviors of the effective bulk modulus of hydraulic oil, which occurs in the center of the piston travel. The parameters of the simulated model are estimated with the nonlinear least square method in MATLAB. Finally, the accuracy of the proposed model for simulating the motion states of the shaking table, by comparing the experimental and simulated results in different ranges of amplitudes and frequencies with respect to the new and the previous model of the hydraulic servo-systems have been shown.

Study on Precise Displacement Control of a Miniature Hydraulic System via RBF-DOB

For compact and efficient actuation, miniature hydraulic system has overwhelming superiority in power to weight ratio. However, it always involves nonlinear interferences like variable hose volume or oil bulk modulus, which greatly restricts control performance for the actuation. In this paper, a miniature hydraulic volume-controlled actuation system is introduced and the problem of precise displacement control of the system in presence of variable hose volume caused by uncertain external load is investigated. A radical basis function-disturbance observer (RBF-DOB) hybrid control strategy based on back-stepping theory is proposed. The system and the controller are mathematically modeled and simulation to demonstrate the validity of the RBF-DOB. Comparison to proportion-integral-differential and sliding model control (SMC) methods indicates that, the system using RBF-DOB has highest displacement precision and best dynamic performance. SMC is inclined to exhibit the best robustness but inferior jitter in control command output. As far as anti-disturbance capacity is concerned, RBF-DOB control strategy falls between other two counterparts. RBF-DOB hybrid control strategy can substantially solve the problems of nonlinear interferences resulted from uncertain system parameters and different load states in miniature hydraulic actuation systems.

Analyses of Influential Factors of Dynamic Characteristics of Hydraulic Pump Test System

A set of hydraulic pump test system was designed according to national test standard. The simulation model of the test system was built in hydraulic simulation software AMESim. Through setting and adjusting simulation parameters, groups of simulation results were obtained and graphed with different pipeline diameter, pipeline length, elastic modulus of pipeline material, oil temperature and oil bulk modulus. The description about the influences of the above factors on system dynamic characteristics and the analyses about the reasons were given. The advices on optimizing design of hydraulic test system were presented contraposing different parameters and design requirement.

Modeling Study on Stiffness Characteristics of Hydraulic Cylinder under Multi-Factors

For a complex mechanical system driven by hydraulic cylinders, the dynamic response characteristics of the mechanical system are significantly affected by the stiffness characteristics of hydraulic cylinders. This paper comprehensively studies the impacts of various factors on the stiffness characteristics of the hydraulic cylinders, including the oil bulk modulus, the air content in the hydraulic oil, the axial deformation of the piston rod, the volume expansion of the cylinder barrel, the volume expansion of the metal pipes and the flexible hoses, and the deformation of the hydraulic cylinder sealing. By combining the theoretical analysis and the experimental results, the level of each impacting factor was quantified, and the stiffness model of the hydraulic cylinder was established. Finally, comparative analysis of the stiffness was conducted by taking the experimental hydraulic cylinder as an example; it was verified that the calculated results of the proposed hydraulic cylinder stiffness model approximated the experimental results. Compared with stiffness models presented in current literature, the average accuracy was improved by more than 15 %.

Simulation of dynamics of hydraulic system with proportional control valve

Dynamics of a hydraulic system is influenced by several parameters, in this case mainly by proportional control valve, oil bulk modulus, oil viscosity, mass load etc. This paper will be focused on experimental measurement and mathematical simulation of dynamics of a hydraulic system with proportional control valve, linear hydraulic cylinder and mass load. The measurement is performed on experimental equipment that enables realization of dynamic processes of the hydraulic system. Linear hydraulic cylinder with mass load is equipped with position sensor of piston. The movement control of piston rod is ensured by the proportional control valve. The equipment enables to test an influence of parameter settings of regulator of the proportional control valve on position and pressure system responses. The piston position is recorded by magnetostrictive sensor that is located in drilled piston rod side of the linear hydraulic cylinder. Pressures are measured by piezoresistive sensors on the piston side and the piston rod side of the hydraulic cylinder. The measurement is performed during movement of the piston rod with mass load to the required position. There is realized and verified a mathematical model using Matlab SimHydraulics software for this hydraulic system.

Determination of Undissolved Air Content in Oil by Means of a Compression Method

This article describes a combination of experimental and mathematical methods for determination of undissolved air content in hydraulic oil. The experimental part consists in determination of oil bulk modulus considering an influence of undissolved air by means of a volume compression method in steel pipe. A multiphase model of an oil/undissolved air mixture is subsequently defined using Matlab SimHydraulics software. The multiphase model allows to include volume compression of oil and air bubbles independently of each other. Furthermore, time dependencies of pressures are mathematically simulated during compression of the multiphase mixture of oil and undissolved air for different concentrations of undissolved air. The undissolved air content is determined by comparing of mathematically simulated and experimentally measured time dependencies of pressure increases.

Non-Destructive Experimental Method for Determination of Modulus of Elasticity of Hydraulic Hoses

This article deals with a non-destructive experimental method for determination of modulus of elasticity of hydraulic hoses. There is described experimental equipment for determination of the modulus of elasticity of hydraulic hoses by expansion method. The modulus of elasticity is determined for several hydraulic hoses of different parameters on basis of combined hydraulic capacity of oil and hose. Furthermore it is necessary to know oil bulk modulus. The modulus of elasticity of hoses is very important during design of a hydraulic system. It is necessary to take into account the modulus of elasticity of hoses in a mathematical simulation model of dynamic parameters of a given hydraulic system. A designer can subsequently utilize maximal flexibility, maximal stiffness or required ratio of the mentioned hose properties. The measured hose isn't destructed and can be subsequently used in hydraulic systems. It is a big advantage of this method.

Fluid Air Content Affecting the Power Shift Performance of the Hydro-mechanical Variable Transmission

The influence rules about fluid air content affecting dynamic behavior of the hydro-mechanical variable transmission during power shift is researched. The theoretical analysis about oil bulk modulus is carried out, and the experimental research of oil bulk modulus with different air content is done. The theoretical curves of the fluid secant bulk modulus are in accord with the experimental results, which shows its mathematical model can be used in power shift simulation analysis of the hydro-mechanical variable transmission closed hydraulic circuit. The power shift mathematical model of the closed hydraulic circuit in hydromechanical variable transmission is built with the method that the closed hydraulic circuit is equivalent to a loop consisting of two double-acting hydraulic cylinders, and it is simulated in Matlab/Simulink. The results show that the more air in fluid, the lower bulk modulus and the greater speed fluctuation of the fixed displacement hydraulic component during the power shift, so the power shift quality is worse; control of the hydraulic component's displacement and extension of load torque reverse time can effectively reduce the fixed displacement component speed and pressure fluctuation of the closed hydraulic circuit.

Mathematical model for bulk modulus of hydraulic oil containing air bubbles

Mathematical model for bulk modulus of hydraulic oil containing air bubbles

가변 용적형 사판식 피스톤 펌프의 회전 속도 조절에 의한 정압 제어 소비 동력 절감

This paper proposes a control scheme to reduce the power consumption of a variable displacement swash-plate type piston pump supplying oil to a valve-controlled hydraulic cylinder at constant pressure. Whenever flow rate demand was absent, the swash plate angle and the pump speed were changed to the minimum values required to compensate for the internal leakage flow. In response to command signals, the pump speed was changed in proportion to the absolute mean value of the speed component for position commands. At the same time, a pressure regulator was activated to maintain constant system pressure by precisely adjusting the pump speed with the swash plate angle fixed at the maximum. The conventional system consisting of a pressure-compensated variable displacement type pump is driven at a constant speed of 1,800rpm. By comparison, computer simulation and experimental results showed that idling power at stand-by status could be reduced by up to 70% by reducing the pump speed from 1,800rpm to 300rpm and the swash plate angle to the minimum. * Corresponding author: yshong@kau.ac.kr 1 Aerospace & Mechanical Engineering, Graduate School, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea 2 Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea Copyright C 2014, KSFC This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 기호 설명  : Position Command Signal, mm  : Reference System Pressure, bar  : Accumulator Pressure, bar  : Pump Flow Rate, l/min  : Cylinder Flow Rate, l/min  : Accumulator Flow Rate, l/min  : Gas Pre-charge Pressure, bar  : Effective Gas Volume, m 3  : Oil Volume in the Accumulator, m 3  : Volumetric Displacement, cc/rev  : Cross Sectional Area of Cylinder, mm 2  : Pitch Circle Diameter of Barrel, mm  : Piston Diameter, mm  : Number of Pistons  : Swash Plate Angle, deg  : Bulk Modulus of Oil, MPa

Analysis and experiment of HMT stationary shift control considering the effect of oil bulk modulus

In order to improve the shift quality of hydro-mechanical continuously variable transmission, the effect of tangent bulk modulus and different control methods on the shift quality were analyzed. Theoretical analysis and experimental study on the tangent bulk modulus of oil were carried out to obtain the effect law of air content on the tangent bulk modulus of oil. A four-cavity model of a closed hydraulic circuit was established based on a two-stage arithmetic type hydro-mechanical transmission. By means of simulation analysis and experimental study, the effect of the tangent bulk modulus of oil on the shift quality is studied. The lean control method of reasonably controlling displacement ratio and prolonging the reverse time of load torque is put forward. The results show that this method can reduce the fluctuations of the speed of the fixed displacement motor and the oil pressure of the original low-pressure side. This method can also improve the shift quality and provide reference for the study of the shift process of hydro-mechanical continuously variable transmission.

Modeling and Experimental Validation of the Effective Bulk Modulus of a Mixture of Hydraulic Oil and Air

It is well known that the presence of entrained air bubbles in hydraulic oil can significantly reduce the effective bulk modulus of hydraulic oil. The effective bulk modulus of a mixture of oil and air as pressure changes is considerably different than when the oil and air are not mixed. Theoretical models have been proposed in the literature to simulate the pressure sensitivity of the effective bulk modulus of this mixture. However, limited amounts of experimental data are available to prove the validity of the models under various operating conditions. The major factors that affect pressure sensitivity of the effective bulk modulus of the mixture are the amount of air bubbles, their size and the distribution, and rate of compression of the mixture. An experimental apparatus was designed to investigate the effect of these variables on the effective bulk modulus of the mixture. The experimental results were compared with existing theoretical models, and it was found that the theoretical models only matched the experimental data under specific conditions. The purpose of this paper is to specify the conditions in which the current theoretical models can be used to represent the real behavior of the pressure sensitivity of the effective bulk modulus of the mixture. Additionally, a new theoretical model is proposed for situations where the current models fail to truly represent the experimental data.

Research on the Influence of Oil Bulk Modulus on Performance of the Hydraulic System Coupling

With closed hydraulic transmission system at Step condition as the research object,the dynamic model of variable pump driving variable motor is established under the AMESim software to study the influence of the effective bulk modulus of fluid on coupling characteristics of the hydraulic system. The simulation results show that the greater the bulk modulus is, the smaller the pressure fluctuations and the power loss are, and the faster the motor response speed is, which instructions that reasonable choice of fluid the bulk modulus can improve the stability of the hydraulic system. This paper provides theoretical guidance for the hydraulic system design and analysis of the dynamic quality of hydraulic equipment.

2D22 Experimental investigation of effective bulk modulus of oil with entrained air bubbles(The 12th International Conference on Motion and Vibration Control)

Although hydraulic systems are compact and have high output power, the demand for further downsized systems with increased output power has been on the rise in recent years. The operating pressures of hydraulic systems have recently been increasing, and condition monitoring of the properties of hydraulic fluid has been one of the most important technical issues. Bulk modulus is a property that indicates the compressibility of a hydraulic fluid. Hydraulic fluids typically become aerated during use, and a certain amount of air is always present in a hydraulic fluid. Aeration strongly influences the bulk modulus of hydraulic fluid because air is significantly more compressible than oil. Entrained air in the form of bubbles reduces the effective bulk modulus. Furthermore, air bubbles entrained in hydraulic fluids cause numerous problems in hydraulic systems. Active bubble elimination devices that use swirl flow capable of eliminating air bubbles from hydraulic fluid have been proposed and developed by the authors. We focus on the relationship between the change in bulk modulus and the elimination of air bubbles from hydraulic fluid. Hydraulic fluid from which bubbles have been eliminated is sampled in a vessel and experimentally pressurized by a servo piston. The volume and pressure change of the sampled oil is measured, and bulk modulus change is calculated to evaluate the bubble elimination. We conclude that the change in bulk modulus of the bubble-eliminated oil influences system performance with respect to positioning, power loss, response time, and stability in hydraulic systems.