Compressibility Of Hydraulic Oil Research Articles

A novel system identification method for servo-hydraulic shaking table using physics-guided long short-term memory network

Effective system identification is critical to realize the high-performance control of shaking table, however, the common reduced-fidelity models can rarely capture the practical dynamics of the system over a wide frequency range. To address this issue, this study adopts the latest advances in deep learning to develop a physics-guided long short-term memory (PhyLSTM) network for system identification of the shaking table. The basic idea is to embed the physical laws describing the system into the network, which can prompt the model to converge quickly to the right solution and constrain the output to a rational solution space in the case of poor data quality. To give insight into the operating mechanism of the shaking table, a series of tests were designed to reveal the flow properties of servovalve and the compressibility of hydraulic oil. Based on the above cognition, a testing program including various signals and specimens was conducted to complete data collection. After detailed hyperparameters testing, PhyLSTM exhibited far superior performance to traditional transfer function model, which indicated that PhyLSTM is a promising approach for shaking table modeling.

Effect of hydraulic oil compressibility on the volumetric efficiency of a diaphragm compressor for hydrogen refueling stations

The low volumetric efficiency of the diaphragm compressor under hydrogen refueling process, which hereby results in poor energy efficiency and high cost of hydrogen applications, should be paid attention to. This paper presents theoretical analysis and experimental investigation of the factors affecting the volumetric efficiency of the diaphragm compressor for hydrogen refueling process, focusing on the influence of hydraulic oil compressibility. A mathematical model was established to estimate the volumetric efficiency of diaphragm compressors, in which the effects of clearance volume, superheating of suction gas and pressure loss were taken into account and the emphasis was focused on the compressibility of hydraulic oil. A test rig was built to validate the theoretical model and further experimental investigations were carried out to identify the factors influencing the oil compressibility and hereby the volumetric efficiency. The volumetric efficiency was measured and compared under varied oil compressibility conditions by varying elastic modulus, oil overflow pressure and oil volume. The results indicated that the measured volumetric efficiency agrees well with the calculated value. The compression and expansion of hydraulic oil have a dominant influence on the volumetric efficiency, resulting in a loss of 37% of volumetric efficiency as compared to 2.4%, 18% and 1%, respectively for losses associated with clearance volume, superheating of suction gas and pressure loss, for a diagram compressor under refueling conditions with suction pressure of 30 MPa and discharge pressure of 90 MPa. The volumetric efficiency reduced rapidly with the increased oil overflow pressure, at a rate of 5% decrease with every 10 MPa rise in oil overflow pressure. As the oil volume increased by 100% of the stroke volume, the volumetric efficiency droped by 5.5%. • A volumetric efficiency model with oil compressibility effects was established. • Oil compressibility had a major effect on the volumetric efficiency. • Major factors on oil influencing volumetric efficiency were quantitatively estimated. • Oil volume should be designed less than 3 times stroke volume.

Study on key performance parameters of hydro-pneumatic tensioner for top tensioned riser

In this paper an improved mathematical model of a hydro-pneumatic tensioner (HPT) system for top tensioned riser (TTR) is derived by consideration of friction, mass of piston and piston rod, tension loss in hydraulic oil piping, and compressibility of hydraulic oil. The vertical motion of the riser string is also considered. Subsequently, the proposed detailed model and the conventional simplified model are comparatively studied. Finally, the tension characteristic and performance parameters of the HPT are analyzed based on the proposed model. Results show that the conventional simplified model indeed overestimates the tension of tensioner as it neglects some performance parameters resulting in tension loss. The diameters of piston and piston rod and the initial pressure of high pressure (HP) gas have the most significant influence on the tension of the tensioner. The initial volume of HP gas and the initial pressure of low pressure (LP) gas also have some impact. The influence of the initial volume of LP gas and the inner diameter and length of the piping is relatively small. The research has some reference value for HPT and TTR design.

THEORETICAL ANALYSIS OF INFLUENTIAL PARAMETERS TO COMPRESSION AND DECOMPRESSION PROCESS OF COMPRESSED OIL IN HYDRAULIC SYSTEMS OF THE PRESS

Compressibility of hydraulic oil is very significant for large diameter cylinder presses, especially if they are exposed to high pressures. The paper presents a theoretical analysis of the process of compression and decompression of oil in the cylinders with and without the presence of air presenting an analog model. Although considerations are relating to the ideal conditions of the process of compaction, the paper defines the basic mathematical processes depending on compression and discharge of the same. They refer to the definition of the time discharge and elimination of adverse effects in the same.

THEORETICAL ANALYSIS OF INFLUENTIAL PARAMETERS TO COMPRESSION AND DECOMPRESSION PROCESS OF COMPRESSED OIL IN HYDRAULIC SYSTEMS OF THE PRESS

Compressibility of hydraulic oil is very significant for large diameter cylinder presses, especially if they are exposed to high pressures. The paper presents a theoretical analysis of the process of compression and decompression of oil in the cylinders with and without the presence of air presenting an analog model. Although considerations are relating to the ideal conditions of the process of compaction, the paper defines the basic mathematical processes depending on compression and discharge of the same. They refer to the definition of the time discharge and elimination of adverse effects in the same.

Piecewise model and experiment of power chuck’s gripping force loss during high speed turning

High speed power chucks are important function units in high speed turning. The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks. This paper proposes a piecewise model considering the difference of wedge transmission’s radial deformation between low-speed stage and medium-to-high-speed stage, the friction forces of chuck transmission, and the compressibility of hydraulic oil in rotary hydraulic cylinders. A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness. The model is verified by experiment results. It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages. Besides, the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed. For wedge power chucks with small wedge angel (α 0.06), the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage. For wedge power chucks with larger wedge angel (α>20°) or low friction coefficient (μ0<0.06), the wedge transmissions cannot self-lock at high speed stage, and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder; the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage. This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks. high speed turning, power chuck, gripping force loss, rotary hydraulic cylinder, model, experiment

Flow Ripple of Axial Piston Pump with Computational Fluid Dynamic Simulation Using Compressible Hydraulic Oil

The flow ripple, which is the source of noise in an axial piston pump, is widely studied today with the computational fluid dynamic(CFD) technology development. In the traditional CFD modeling, the fluid compressibility, which strongly influences the accuracy of the flow ripple simulation results, is often neglected. So a compressible sub-model was added with user defined function(UDF) in the CFD model to predict the flow ripple. At the same time, a test rig of flow ripple was built to study the validity of simulation. The flow ripple of pump was tested with different working parameters, including the rotation speed and the working pressure. The comparisons with experimental results show that the validity of the CFD model with compressible hydraulic oil is acceptable in analyzing the flow ripple characteristics. In this paper, the improved CFD model increases the accuracy of flow ripple rate to about one-magnitude order. Therefore, the compressible model of hydraulic oil is necessary in the flow ripple investigation of CFD simulation. The compressibility of hydraulic oil has significant effect on flow ripple, and the compression ripple takes about 88% of the total flow ripple of pump. Leakage ripple has the lowest proportion of about 4%, and geometrical ripple leakage ripple takes the remnant 8%. Besides, the influence of working parameters was investigated through the CFD simulations and experimental measurements. Comparison results show that the amplitude of flow ripple grows with the increasing of rotation speed and working pressure, and the flow ripple rate is independent of the rotation speed. However, flow ripple rate of piston pump grows with the increasing of working pressure, because the leakage ripple will increase with the pressure growing. The investigation on flow ripple of an axial piston pump using compressible hydraulic oil provides a more validity simulation model for the CFD analyzing and is beneficial to further understanding of the flow ripple characteristics in an axial piston pump.

A Study on Design Techniques for Control System of an Electrohydraulic Servo Mechanism Based on .MU. Synthesis.

Design techniques for a control system of an electrohydraulic servo mechanism are discussed with emphasis on modeling error and structure of an uncertainty block. As a typical modeling error, compressibility of hydraulic oil, servo valve dynamics and linearized parameters are considered. Classification of the modeling errors is proposed, where errors are classified into those caused by order-reduction and those caused by linearization. Techniques for building an uncertainty block which represents the errors are discussed. Robust controllers which are designed based on μ synthesis using the techniques are examined experimentally.