Hydraulic Lines Research Articles

スティフな断片線形系の時刻歴応答解析に関する研究

We present a characteristic improvement method for time historical analysis of stiff piecewise-linear system by adding mass. Hydraulic power lines with check valves and control valves for construction machinery exhibit piecewise-linear characteristics for hydraulic flow rate and spool stroke. The proposed method involves no time delay in determining the mass by considering both eigenvalue distortion of the system and time response. This method is useful for time historical analysis of hydraulic power lines including stiff piecewise-linear elements such as check valves, relief valves and control valves.

Energy loss at surcharged manholes — Model experiment

This study aims to evaluate the energy loss at manhole. Experimental model with straight pipes (D=0.2 m for diameter, 18.S m for length) and four rectangle-shaped manholes (0.26 m for width, Dm=0.12 m for length) was used. Energy losses at manholes, ΔH, were determined as the difference of hydraulic gradient lines at the center of the manhole extended from both upper and lower side of pipes. The energy loss coefficient was given as K=(ΔH)(2g)/v2. Obtained coefficients converged their range from 0.02–0.12 to 0.04–0.06, according to the increase of the water velocity. We concluded that the reason of this comparatively smaller K values was due to the smaller diameter ratio; Dm (manhole diameter or length)/D(pipe diameter), compared to the results of other experiments.

Study of Unsteady Orifice Flow Characteristics in Hydraulic Oil Lines

A technique to measure fluctuating differential pressures with high fidelity has been developed first. When applied to detecting differential pressures generated by an accelerated or decelerated liquid column, the technique turned out to be effective in finding unsteady flow rates. An experimental study has been carried out on periodically changing hydraulic oil flows through an orifice. The results support the validity of the traditional standpoint that characteristics of an unsteady orifice flow can be approximately represented by those of a steady-state one. When inspected in detail, however, a net pressure loss across an orifice in a periodical flow is delayed against a change of the flow rate. The resulting relation between the pressure loss and the flow rate describes a loop with a counter-clockwise hysteresis and a nonlinear twist along the steady-state one. Pressure recovery in a pulsating orifice flow varies with the flow rate almost along the steady-state relation, which is confirmed when the change is not fast.

Simulation and Experimental Studies of Gear Backlash and Stick-Slip Friction in Hydraulic Excavator Swing Motion

Inherent to any heavy-duty hydraulic machine operation with a large number of interconnected components are nonidealities such as gear backlash, friction and leakage. The swing motion of the operator’s cabin in an excavator is a typical example. In this paper we conduct a study comprising experimental, mathematical and simulation components to determine the degree to which these nonlinearities affect the performance of such machines. The inclusion of the conventional model of backlash in the simulation of the excavator swing motion is shown to be inefficient and unnecessary in terms of computation time and the final results. A new model which combines the fluid-flow and the gear train dynamics is developed. The study of contact and non-contact cases brings about proper sets of static and dynamic equations which efficiently simulate this phenomenon for the class of excavator machines under consideration. The inclusion of stick-slip friction model in the simulation shows two effects. Firstly, it causes a noticeable time-delay at the beginning of the swing motion. Secondly, it results in an overshoot during velocity control experiments. It is also shown that dry friction and leakage (cross-port or external) are as significant as gear backlash in determining the pressure patterns in the connecting hydraulic lines and, therefore, should not be overlooked, especially when the excavator cabin is brought to a stop. Often, this is the most important state event when accurate positioning is crucial. The simulation results are qualitatively supported by the experimental evidence. The experiments were performed on an instrumented teleoperated Caterpillar 215B excavator.

Design and effectiveness of in‐line tuning cables for quieting hydraulic power units.

The use of hydraulic units to power tools, lifts, and other industrial equipment in both indoor and outdoor settings is widespread. The noise radiated by these units and the hydraulic lines used to convey the fluid continues to be a problem. The dominant noise components arise from pressure fluctuations in the hydraulic fluid ocurring at harmonics of the pump vane or piston passage frequency. In this study, the effectiveness of in‐line tuning cables (after a patent by Klees 1967) for quieting the harmonic noise from these hydraulic lines is determined. This approach, which combines ease of installation with relative economy, amounts to the insertion of a quarter‐wavelength side branch into the acoustical circuit. Critical to effective design is the determination of the wave speeds in the flexible hosing. Theoretical predictions and measurements are applied to determine the wave speeds in the fluid‐loaded hydraulic line. Multiple PVDF sensors measure wave speeds and the wave amplitude insertion loss achieved by the device. Experiments performed on a full‐scale 60 h.p., 1500 p.s.i. unit will be compared to the theory. Sound pressure levels determine design effectiveness.

Condition of hydraulic jump and pressure in a steep slope conduit

Hydraulic gradients in a circular conduit with a hydraulic jump were investigated by experiments. It was made to confirm the results presented by Kalinske et. al. on closed conduit flow, and to establish a set of formula in determining the location and height of the jump. The experimental observations were conducted in three cases, i. e. 1) steady hydraulic jumps with different lengths, 2) moving hydraulic jumps due to pressurized flow coming from the inlet of the conduit and 3) the alternate flow of full flow and partly-full flow. Observation results on the hydraulic grade line of flows in the conduit, which are different from the previous researches, are discussed

Measurement of Transiently Changing Flow Rates in Oil Hydraulic Column Separation.

Column separation and subsequent rejoining in an oil hydraulic line usually result in tensile waves and consequent ruptures in an oil column. In order to investigate these phenomena in more detail, it is essential to precisely measure transient flow rates in column separation and rejoining. The aim of the present work is to attain this objective : a method based on the theoretical relation of the flow rate change in a pipe with a kinetically induced pressure difference between the two separate sections. Instead of a conventional differential pressure transducer, two individual pressure gauges are used to measure pressures at the two sections and find the difference between them by subtraction. Theoretically predicted stepwise decreases of the flow rate until the column rejoining have been accurately measured, showing the effectiveness of the method. It is also pointed out that the successive calculus proposed by Zhao et al., which is expected to substantially economize the procedure to obtain flow rates from differential pressure data, may give unrealistic results.

Combined Piezoelectric-Hydraulic Actuator Based Active Vibration Control for Rotordynamic System

Previous research by the authors concentrated on using piezoelectric actuators for active vibration control (AVC) of rotating machinery. The current work extends this by positioning the piezo-actuator remotely from the controlled structure and transmitting the control force via a hydraulic line and two pistons. Liquid plastic (LP) is employed as a transmission “fluid” to obtain a high bulk modulus and low leakage. The paper presents results for bulk moduli measurement, and bench and rig tests for the entire actuator system. These results show the high effectiveness of the hybrid actuator for controlling vibrations on a laboratory rotor test rig.

Studies on corrosion behaviour of Cu‐Si alloys in Sulphide and Chloride media

Introduction It is well established that Si in silicon bronzes imparts high strength and corrosion resistance which are essential requirements for applications in hydraulic pressure lines, heat exchangers, propeller shafts, storage tanks and other equipments for chemical industries. They have high corrosion resistance towards marine environments, but possess inferior corrosion resistance in sulphide bearing atmosphere although more resistant to stress corrosion cracking and season cracking than brass on exposure to polluted atmospheres. In general, corrosion resistance of alloys depends on alloy chemistry, heat treatment schedule, presence of second phase, precipitation morphology and specific environment. However, studies on influence of heat treatment and variation of silicon content in (Binary) Cu‐Si alloys with particular reference to their corrosion resistance in chloride and sulphide bearing environments are scanty in literature. The present work has been designed to study the corrosion behaviour and to generate data on three types of commercially important Cu‐Si alloys in 3.5 per cent sodium chloride and 1 per cent sodium sulphide solutions.

Hydraulics of corrosive gas pockets in force mains

ABSTRACT: Hydrogen sulfide corrosion can occur in sewage force mains in places where the sewage does not continuously contact the top of the pipe. This situation can occur because air is drawn into the pipe when the hydraulic grade line is below the pipe, or a gas pocket cannot be dragged down a downward slope because of the buoyancy of the pocket. This paper presents and verifies methods for predicting when each of these situations can occur and applies the results to an existing force main.

The influence of thermo-mechanical processing on the hardness and microstructure of Beta-C titanium

Beta-C is a metastable titanium alloy with an alpha to beta transition temperature of 802 C and the high temperature beta phase readily retained at room temperature. The beta phase has a body centered cubic (bcc) structure and the alpha phase has a hexagonal close packed (hcp) structure. This alloy has a combination of good strength, ductility and fracture toughness as well as good corrosion resistance and low density. This has resulted in an interest in this alloy for use in a variety of industries. The Navy is investigating the use of this alloy as a replacement material for the steam catapults on aircraft carriers. The oil industry has found use for this alloy in tis transport piping systems, and a whole production schedule has been created for manufacturing Beta-C titanium for aircraft hydraulic lines. However, these properties are extremely sensitive to the thermo-mechanical processing (TMP) of the alloy. A study was undertaken in order to elucidate the effects of solution heat treatment, cold rolling and aging on the phase morphology, microstructure and hardness of Beta-C titanium. Preliminary results on the effects of solution heat treatment and cold rolling of this alloy are presented.

Resolved-Mode Teleoperated Control of Heavy-Duty Hydraulic Machines

This paper addresses the control problem for a class of heavy-duty hydraulic machines in order to achieve coordinated motion control of the implement. A model and sensor-based control algorithm is proposed which is applied in conjunction with closed-loop components. The algorithm is basically a feedforward load compensating scheme which uses the measured hydraulic line pressures along with the appropriate portion of the hydraulic model to control the joint velocities. The effects of nonlinear dynamic coupling between the links, loading, coupled actuation and power limitations are compensated in this technique. The closed-loop part consists of PD components. A knowledge of some hydraulic parameters is the only requirement of this control scheme. The proposed approach has been examined through simulation and is supported by experimental evidence. The experiments were performed on a Caterpillar 215B excavator. The control program is written in the C language, running on a computer system which is interfaced between the human operator and the machine.

A transfer matrix model for analysis of noise and vibration in automotive power steering systems

Noise and vibration generated in automotive power steering systems significantly influence the sound pressure level measured in the passenger compartment and other disturbances such as steering wheel shudder. To address these problems, a distributed parameter, transfer matrix model of a complete power steering hydraulic transmission line was developed and implemented on a personal computer. The model includes not only the axisymmetric viscous fluid mechanics, but also the fluid–structure interaction created by the three-dimensional nature of the bends and twists in the tubing, and structural supports. The computations account for 14 state variables throughout the line. Computational results show that the effectiveness of devices such as expansion hoses with or without coaxial tuning cables, employed to reduce structurally transmitted noise and vibration, is limited by the complex coupling between fliud and structure. In fact, proper use of hoses, bends, and structural supports can attenuate noise and vibration and potentially eliminate the need for special devices. Use of this computational model could reduce the amount of experimental testing required to evaluate these systems. [Work supported in part by NSF.]

Describing function-based analysis of a nonlinear hydraulic transmission line

This paper presents an analytical method of predicting and eliminating limit cycle conditions in hydraulic drive systems, where backlash in the actuator seal is the dominant nonlinearity. It is shown that limit cycle conditions are a strong function of certain plant parameters. The elimination of limit cycle conditions may thus be achieved by the alteration of certain inherent plant parameters. Fluid flow in a hydraulic pipe is modeled using transmission line theory. The sinusoidal-input describing function is used to indicate which values of the plant parameters would result in limit cycle conditions. The analytical results were verified on an experimental test bench.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wave propagation with different pressure signals: An experimental study on the latex tube

To have deeper insight into the main factors affecting wave propagation in real hydraulic lines, we measured the true propagation coefficient in two latex rubber tubes via the three-point pressure method. The measurements were performed using both sinusoidal pressure signals of different amplitudes and periodic square waves as well as aperiodic pressure impulses. The results obtained were then compared with those predicted by a classic linear model valuable for a purely elastic maximally tethered tube. Our measurements demonstrate that the three-point pressure method may introduce significant errors at low frequencies (below 1 Hz in the present experiments) when the distance between two consecutive transducers becomes much lower than the wavelength. The pattern of phase velocity in the range 2-20 Hz turns out to be about 10 per cent higher than the theoretical one computed using the static value of the Young modulus. This result supports the idea that the dynamic Young modulus of the material is slightly higher than that measured in static conditions. The experimental attenuation per wavelength is significantly higher than the theoretical one over most of the frequencies examined, and settles at a constant value as frequency increases. Introduction of wall viscoelasticity in the theoretical model can explain only a portion of the observed high frequency damping and wave attenuation. Finally, increasing the amplitude of pressure changes significantly affects the measured value of the propagation coefficient, especially at those frequencies for which direct and reflected waves sum together in a positive fashion. In these conditions we observed a moderate increase in phase velocity and a much more evident increase in attenuation per wavelength.

Evaluation of an electrohydraulic forge valve behavior using a CAD package

An electrohydraulic system of the type used to control the position of a forging press cylinder is studied analytically and experimentally. The main control component is a flow bypass valve that controls flow rate into and out of the main hydraulic line and is of the poppet-following type. The steady-state pressure/flow characteristic of the bypass valve with an existing seated poppet is compared with a new vee notch poppet design intended to improve the steady-state characteristic and hence the closed-loop press cylinder position response characteristic. Dynamic modelling of the flow bypass valve is then considered and the transient performance is assessed for the two poppet designs and with the valve in an idealized circuit. The complete system dynamic model is then established and a recently developed CAD package is used to simulate the position response of the press cylinder. Both poppet designs are studied, and it is deduced that there is a negligible difference in transient performance, attributable to unique features of the control system. Good comparisons between simulation and experimental results were achieved.

Fast and Convenient Method for Simulation of Hydraulic Transmission Lines.

In order to simulate transient phenomena of hydraulic transmission lines with high accuracy, we are usually forced to adopt a mathematical model of a distributed parameter system, in which the effect of frequency-dependent friction is taken into account. This exact model, however, is considerably troublesome to developing a simulation program, and too time-consuming to be suited to simulation. The purpose of this study is to propose a fast and convenient method for the simulation of transmission lines. The method is based on a technique for formulating rational polynomial approximations for both Bessel functions and hyperbolic functions.

インラインアキュムレータを用いた自己調節形油圧脈動抑制装置

In order to suppress pressure pulsation in hydraulic lines, bladder type accumulators are used widely. Especially, in-line accumulators whose bladder gas pressure is adjusted appropriately show outstanding performances. The effective range of the bladder gas pressure, however, is quite narrow and the performances drastically reduce according to even a slight change of mean hydraulic pressure, length and diameter of pipe, etc. In the present paper, firstly, the fundamental characteristics of the in-line accumulator have been investigated in detail by using frequency analysis. Secondly, a self-adjustable hydraulic pulsation suppressing system has been developed by attaching pressure transducers, a board computer with a universal pulse processor, hydraulic to pneumatic converter, etc. to the accumulator. As the result, it has been confirmed that the developed system is remarkably effective in suppression of the pulsation when mean hydraulic pressure changes frequently.

High Frequency Pressure Propagation in Viscoelastic Tubes: A New Experimental Approach

A new method for estimating the high-frequency characteristics of wave propagation (phase velocity and attenuation per wavelength) in hydraulic lines is presented in this work. It consists of measuring the ratio of pressure amplitudes at two distinct sections of an occluded tube at different frequencies, and minimizing the difference between the experimental pattern and the theoretical one predicted on the basis of the transmission line theory. In this work the method is used for estimating the high frequency propagation characteristics of two different latex tubes. The values obtained are then compared with those provided by the more traditional three-point pressure method. The results of our trials demonstrate that the new method furnishes reliable estimations of the asymptotic values of phase velocity and attenuation per wavelength, provided the frequencies used during the experiment are sufficiently high. Moreover, the method turns out quite robust as to the influence of noise and possible measurement errors. For this reason it seems particularly suitable for studying wave propagation under difficult experimental conditions, such as those met with when measurements are performed on blood vessels in vivo. Finally, some discrepancies between our experimental results and the predictions of the transmission line theory are pointed out, and their possible origin examined.

Computer program to compute pressure forces in pipe flow junctions

A frequently occurring and difficult to solve problem in civil engineering and water resources analysis is the analysis of hydraulic phenomena in storm flow pipe systems. In the design of storm drain flood control systems, the analysis of energy losses in pipeflow junction structures is of key interest. The general practice is to use a pressure-plus-momentum balance analysis in order to estimate the change in water surface (or hydraulic grade line) elevations through the pipe structure, from which an energy loss is subsequently estimated. A computer program is presented for the evaluation of pressure forces within a pipe junction structure. The water profile or HGL is assumed to be a straight line between endpoint conditions. The program provides estimates of force for both a complete mathematical formulation as well as a popular estimate of the complete formula. The program can be substituted for other estimates in the analysis of storm drain systems.