Showing papers on "Hydraulic machinery published in 2002"

Electrical generators for direct drive wave energy converters

Abstract: Wave power devices traditionally use conventional rotary electrical machines for power conversion. However hydraulic systems or air turbines are required to convert the low reciprocating motion of the wave device to rotation at 1500 rpm. The concept of a direct drive system is introduced, in which a reciprocating electrical machine is driven at the same speed as the device. A linear permanent magnet synchronous machine is compared to the transverse flux machine in a basic design study for this application. The latter machine is identified as offering the best potential. Electromagnetic and electric circuit models are developed to investigate the performance of the transverse flux machine in a wave energy converter. Measures are suggested to optimise the performance of the machine.

Power conversion mechanisms for wave energy

Abstract: It is easy to make a device that will respond vigorously to the action of sea waves. Indeed, it is quite hard to make one that will not. However, the conversion of the slow, random, reversing energy flows with very high extreme values into phase-locked synchronous electricity with power quality acceptable to a utility network is very much harder. This paper describes a range of different control strategies of varying degrees of sophistication and then describes possible conversion equipment for high-pressure oil and water and low-pressure air. Like many renewable energy sources, waves would benefit from some form of energy storage, particularly if they are to be used in weak island networks. Flywheels, gas accumulators, submerged oil/vacuum accumulators, thermal stores and reversible fuel cells are discussed, with emphasis on the coupling hardware. This leads on to a description of a new type of hydraulic machine with digital control which has been specially designed for high efficiency and flexible contr...

Impedance control of a teleoperated excavator

Abstract: Earth-moving machines such as hydraulic excavators are usually used for carrying out contact tasks. Impedance control can be employed as an approach for achieving compliant motion in such tasks. This paper describes a position-based impedance controller that has been developed in our laboratory for excavator-type manipulators, and presents the supporting experimental results. First, the problem of impedance control for a single hydraulic cylinder is addressed and a method is presented to analyze the system stability. The steady-state position and force tracking accuracy of the closed-loop system is also studied. Next, the problem of impedance control for a multi-link hydraulic excavator is addressed and the arm Jacobian and accurate estimates of the arm inertial terms are employed to map the desired impedance of the end-effector (bucket of the excavator) onto the hydraulic cylinders. Various contact experiments carried out using an instrumented mini-excavator demonstrate that the proposed impedance controller has very good performance for both single-link and multilink cases.

Forms of Hydraulic Fractures in Shallow Fine-Grained Formations

Abstract: Hydraulic fractures have been created in fine-grained formations at depths of 2–10 m to improve the performance of environmental remediation projects at dozens of locations and in a wide range of geologic conditions. The effectiveness of a hydraulic fracture during remediation will depend primarily on its form; that is, its shape, thickness, orientation, length, width, and location with respect to the borehole. The forms of many hydraulic fractures have been determined by mapping exposures in excavations and by compiling split-spoon sampling data. These observations indicate that a typical hydraulic fracture at shallow depths is gently dipping, slightly elongate in plan, and slightly asymmetric with respect to the parent borehole. Shallow hydraulic fractures lift the ground surface to produce gentle domes, and the pattern of uplift reflects the location and thickness of the fracture at depth. The forms of hydraulic fractures created over a narrow range of depths at the same site are similar, but the forms...

Mechanical analysis of idealized shallow hydraulic fracture

Abstract: The characteristics of hydraulic fractures created at shallow depths are known from excavations and borings, but this understanding has lagged behind the ability to predict fracture growth. This paper describes a simple analysis based on elasticity theory and fracture mechanics that will predict characteristics of shallow hydraulic fractures that are relatively flat lying. The analysis gives closed-form expressions for the injection pressure, fracture aperture, and radial length as functions of time, fracture toughness, and elastic modulus. The analysis is first used to estimate fracture toughness and elastic modulus of shallow formations from field tests of hydraulic fracturing. Those parameters are used to calibrate the model and predict the growth of fractures. The average relative error of the predictions is about 20% and increases with the dip and degree of asymmetry of the fracture.

Hydraulic circuit with a return line metering valve and method of operation

Abstract: A hydraulic system controls the flow of fluid to and from several functions on a machine. Each function has a valve assembly through which fluid is supplied under pressure from a source to an actuator and through which fluid returns from the actuator to a shared return line connected by a return line metering valve to the system tank. There are several regeneration modes of operation in which fluid exhausted from one port is supplied into the other port of the same actuator, which eliminates or reduces the amount of hydraulic fluid that must be supplied from the source. In some regeneration modes, input fluid for an actuator is obtained from another hydraulic function via the shared return line. In these regeneration modes an electronic controller operates the return line metering valve to restrict fluid from flowing into the tank from the shared return line, so that the fluid will be available to be supplied into an actuator port.

Combined drilling apparatus and method

Abstract: Method and apparatus for drilling, completion, well workovers and well control, combining an integrated lifting unit and a coiled tubing unit, the method and apparatus permit running jointed pipe and coil tubing in combination, and standing multiple joints of pipe near the unit. The invention combines a hydraulic pipe hoisting system, pipe handling systems and pipe racking containment apparatus. A hydraulic workover jack is combined with a multifunction injector head and a standpipe for fluid circulation. The invention may also include a rotary table for rotating pipe and/or a rotating power swivel to allow fluid circulation during pipe rotation. Also included are a gin pole, a winching system for jointed pipe, and a traveling head with traveling slips and stationary slips to allow pipe movement in the well. Hydraulic systems allow insertion and extraction of tools in a work string. The apparatus includes spoolable drill pipe including a connector, multi-section reel with core, connection to reel for fluid circulation, reel drive mechanism and a pipe pulling capability.

Mixed flow pump

Abstract: The present invention relates to propulsion and hydraulic systems having a co-axial design wherein the inlet section, impeller section, and outlet section of a mixed flow pump system all have a common centerline axis or axis of rotation. The mixed flow pump system includes an outer casing and a central body disposed co-axially within the outer casing. A pump impeller is rotatably connected to the central body for imparting hydraulic energy to the fluid flowing through the mixed flow pump system. The mixed flow pump system may also include inlet flow conditioning vanes for conditioning an inlet flow of fluid to the mixed flow impeller for improving the cavitation performance and/or acoustic performance of the pump module. Stator vanes are provided for connecting the central body to the outer casing and to remove any swirl velocity from the fluid flow exiting the mixed flow pump impeller. The mixed flow pump system exhibits improved resistance to cavitation due to the use of one or more of inlet flow conditioning vanes and low RPM motors for rotating the mixed flow pump impeller. The invention has applications in a variety of applications, including propulsion and hydraulic applications. For example, the invention may be used for the propulsion of marine vehicles, such as submerged crafts, weapons and unmanned underwater vehicles (UUVs) of various sizes and speed requirements. The mixed flow pump may also be applied to non-marine applications such as hydraulic applications, chemical distribution systems, and medical devices.

Electrohydraulic control system for implement lift cylinders

Abstract: Different sections of an agricultural implement can be raised and lowered independently and by varying amounts by a unique hydraulic system. That system incorporates a three-position, four-way primary control valve which selectively connects a supply line and a tank return line to first and second hydraulic lines. A plurality of double acting hydraulic cylinders are provided to produce movement of lift assemblies with respect to a frame of the implement. A separate electrohydraulic lift control valve for each hydraulic cylinder couples one cylinder chamber to the first hydraulic line and the other cylinder chamber is connected directly to the second hydraulic line. Operation of the primary control valve determines the movement direction and selective activation of the lift control valves determines whether the associated section of the implement moves and the amount of such movement.

Piezoelectric direct drive servovalve

Abstract: A single-stage servovalve using direct piezoelectric actuator drive is described. The single-stage servovalve design offers higher bandwidth than conventional two-stage valves. It takes advantage of the high energy density in piezoelectric materials while addressing the need for internal amplification of stroke. When used alone, the valve can regulate pressure, and when used in combination with a hydraulic output device it forms part of an effective servohydraulic actuator. Development of a direct drive prototype valve is described. Discussion includes design issues related to low stroke smart material actuators such as piezoelectrics. Component and subsystem testing and results are reviewed. Electronic drive and control of the piezoelectric and overall device along with performance in the control of fluid flow is discussed. The value of the new servovalve is shown in the combination of the valve with a hydraulic output device. Data are supplied for this servohydraulic actuator. The new actuator shows promise for a motion simulator application and more generally for motion control at higher bandwidth than is possible with currently available servohydraulics.

Unsteady flow in hydraulic networks with polymeric additional pipe

Abstract: This paper presents results of an experimental and theoretical study on the use of a high density polyethylene (HDPE) additional pipe inserted downstream of a pump in a hydraulic network as a surge suppressor. The experiments consistently show a reduction of the oscillations with respect to the case without a HDPE device, while in the case of a single pumping pipeline the oscillations can be amplified for small volumes of the additional pipe. Previously calibrated mechanical parameters are considered in the mathematical models whose results are compared with experimental results. Both linear elastic and Kelvin-Voigt viscoelastic behavior of the pipe material and both one-dimensional (1D) and quasi-2D flow models are taken into account. The numerical results show that the viscoelastic model better describes the phenomenon, but the elastic model adequately estimates the maximum and minimum oscillations. Furthermore, the results of the quasi-2D model are in better agreement with the experimental maximum and minimum oscillations than those of the 1D model, but the differences are less important than in the case of networks without a HDPE device.

Estimation technique of air content in automatic transmission fluid by measurign effective bulk modulus

Abstract: It is well known that the entrained air in oil causes appreciable reduction in the stiffness of hydraulic systems. It makes the response delay of the systems and sometimes destroys the stability. Because the hydraulic systems of automatic transmissions are operated in relatively low pressure and high temperature, it is very important to analyze the effects of the air included in automatic transmission fluid. However, it is difficult to derive the generalized model to describe the effective bulk modulus theoretically or measure it in actual operating conditions of automatic transmissions. This paper reviews previous studies of the air effects in hydraulic systems and the measurement techniques of the effective bulk modulus in operating conditions. Based on this work, the theoretical model with moderate complexity and the measurement technique of the effective bulk modulus considering entrained air effect at real operating conditions are suggested. Our paper also shows that the quantity of the entrained air in the automatic transmission fluid can be estimated from the experimental results.

Experimental evaluation of position control methods for hydraulic systems

Abstract: Presents a unified and systematic assessment of ten position control strategies for a hydraulic servo system with single-ended cylinder driven by a proportional directional control valve. We aim at identifying those methods that achieve better tracking, have a low sensitivity to system uncertainties, and offer a good balance between development effort and end results. A formal approach for solving this problem relies on several practical metrics, which is introduced herein. Their choice is important, as the comparison results between controllers can vary significantly, depending on the selected criterion. Apart from the quantitative assessment, we also raise aspects which are difficult to quantify, but which must stay in attention when considering the position control problem for this class of hydraulic servo systems.

System and apparatus for noise suppression in a fluid line

Abstract: Apparatus for reducing fluid-borne noise in a hydraulic system that includes a housing that defines a hollow chamber, and inlet and outlet connections for in-line connecting the apparatus in a hydraulic fluid flow system. A resilient member is disposed within the housing and effectively divides the housing chamber into a first portion adjacent to the fluid inlet and outlet for receiving hydraulic fluid, and a second portion remote from the fluid inlet and outlet for containing gas under pressure. Pressure pulsations in the hydraulic fluid are reduced and at least partially absorbed by the combined effect of resiliency of the elastic member and compressibility of the contained gas.

Energy-saving control of hydraulic systems with novel programmable valves

Abstract: The paper studies the energy-saving adaptive robust motion control of a single-rod hydraulic cylinder through the use of programmable valves-a unique combination of five proportional cartridge valves. The programmable valves decouple the meter-in and meter-out flows and provide true cross port regeneration flow which in turn allows tremendous control flexibility. Although at the expense of controller complexity, if well utilized, the added control flexibility can be used to significantly reduce the fluid power energy usage in a number of motion and loading conditions to meet the society's need for energy conservation while without sacrificing the achievable motion control accuracy.

Analysis of critical hydraulic gradient for particle movement in filtration

Abstract: The objective of this paper is to propose an explicit solution for the critical hydraulic gradient required to move a base particle within a pore channel. The particle is assumed to displace when the applied hydrodynamic forces exceed this critical hydraulic gradient. The current analysis is an extension of a previous study (Indraratna and Vafai 1997), where the limit equilibrium analysis was modified to include the effect of drag in the hydrodynamic force component. The theoretical model was examined in the laboratory using fine gravel filters and a cohesionless base soil consisting of very fine river sand.

Velocity based method of controlling an electrohydraulic proportional control valve

Abstract: An actuator is part of a hydraulic circuit branch that has a first electrohydraulic proportional valve connecting the actuator to a supply line containing pressurized fluid and a second electrohydraulic proportional valve connecting the actuator to a tank return line. A method for operating the valves includes requesting a desired velocity for the hydraulic actuator and sensing a parameter which varies with changes of a force on the actuator. The desired velocity and the parameter are used to derive an equivalent flow coefficient which characterizes fluid flow in the hydraulic circuit. From the equivalent flow coefficient, first and second valve flow coefficient are derived and then employed to activate each of the first and second electrohydraulic proportional valves. The coefficients may characterize either conductance or restriction in the respective part of the hydraulic system.

Experimental evaluation of position control methods for hydraulic systems

Abstract: Presents a unified and systematic assessment of ten position control strategies for a hydraulic servo system with single-ended cylinder driven by a proportional directional control valve. We aim at identifying those methods that achieve better tracking, have a low sensitivity to system uncertainties, and offer a good balance between development effort and end results. A formal approach for solving this problem relies on several practical metrics, which is introduced herein. Their choice is important, as the comparison results between controllers can vary significantly, depending on the selected criterion. Apart from the quantitative assessment, we also raise aspects which are difficult to quantify, but which must stay in attention when considering the position control problem for this class of hydraulic servo systems.

Hydraulic circuit of construction machinery

Abstract: A hydraulic circuit of construction machinery, wherein, when three hydraulic pumps are used, the displacement volumes of first and second hydraulic pumps are controlled based on the discharge pressures P1 and P2 of the first and second hydraulic pumps and a discharge pressure P3' obtained by reducing the discharge pressure P3 of a third hydraulic pump by a pressure reducing valve (14) and the displacement volume of the third hydraulic pump (3) is controlled only by the discharge pressure of the third hydraulic pump (3) so that one of the three hydraulic pumps is not affected by the variation of torque of the other hydraulic pumps, whereby a stable flow can be assured by preventing the pressure oil discharged from the third hydraulic pump (3) from being affected by the variation of the discharged flow from the first and second hydraulic pumps (1) and (2), i.e., by the variation of a torque consumption.

Plow system including a hydraulic fluid diverter

Abstract: A snow plow system for use with a skid steer loader includes a V-plow blade that is repositionable by a hydraulic actuator operated by pressurized hydraulic fluid supplied to the actuator from the auxiliary hydraulic output of the skid steer loader A normally open valve diverts hydraulic fluid away from the actuator whenever the plow blade is not being repositioned, enabling the auxiliary hydraulic system to be maintained actuated The valve is operated to a closed condition by a wireless remote control receiver which receives coded radio frequency signals transmitted by a wireless, portable, battery-powered transmitter locatable within or outside of a cab of the vehicle, or by a voice-actuated control A mounting panel of the snow plow system includes an anti-slip surface, providing footing for an operator upon entering or exiting the cab of the vehicle

Stochastic Variability of Fluvial Hydraulic Geometry: Mississippi and Red Rivers

Abstract: Major reasons for uncertainty in engineering predictions of river flows are the spatial variability and measurement error associated with depicting channel geometry. This paper develops a descriptive spatial stochastic model of depth-based hydraulic geometry in application to four dense data sets from the Mississippi and Red Rivers. To represent the irregularity in flow area and hydraulic radius as functions of flow depth, at-a-station cross-section geometry is defined using regressed power functions, accompanied by random residuals. More than 1600 surveyed cross sections are analyzed to describe trends in the spatial variance, and gradual (large-scale) and periodic (medium-scale) trends in the spatial mean of cross-sectional geometry parameters and channel bed slope. Also described are the probability distribution and correlation structure of each parameter’s random component. The relationships between spatial statistics of hydraulic geometry and bankfull width, channel sinuosity (meander patterns), bed elevation and riffle-pool spacing, and bank composition are explored. Conclusions and implications are discussed regarding the variable nature of fluvial hydraulic geometry and regarding the incorporation of geometric parameter uncertainty into prescriptive models of river processes.

Hydraulic actuator piston measurement apparatus and method

Abstract: A method and device for use with a hydraulic system is adapted to measure a position, velocity and/or acceleration of a piston of a hydraulic actuator based upon differential pressure measurement. The device of the present invention utilizes a differential pressure flow sensor to establish a flow rate of a hydraulic fluid flow traveling into and out of a cavity of the hydraulic actuator, from which the position, velocity and acceleration of the piston can be determined.

Torque transfer clutch with linear piston hydraulic clutch actuator

Abstract: A power transfer system is provided and equipped with a torque transfer coupling which includes a clutch and a ball-screw actuator. The ball-screw actuator functions to axially translate an apply plate via a closed hydraulic system to operatively engage the clutch and vary the frictional engagement thereof.

Internal-combustion engine with hydraulic system for variable operation of the valves and means for compensating variations in volume of the hydraulic fluid

Abstract: In an internal-combustion engine with a hydraulic system for variable operation of the engine valves, there is envisaged at least one supplementary reservoir bled off to the atmosphere, communicating with the low-pressure circuit for compensating for the variations in volume of the hydraulic fluid that derive from the variations in temperature and for thus preventing air bubbles from forming in the circuit.