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This article is particularly interested in the numerical modeling of water hammer in a hydraulic circuit, taking into account the prevailing water temperature. The study concerns the propagation velocity of the wave and the amplitude of unsteady phenomena encountered in the circuit, as well as the severity and collapse of cavitations that are also considered as major risks. To conjecture the consequences of these phenomena, we were led to simulate a single-phase and two-phase transient flows in a hydraulic copper pipe system in a temperature range of 4–95 °C. To do this, we have developed a solver for the dynamic and continuity equations’ resolution. The method of characteristics is chosen for its capacities to solve these equations. Its application shows that it is robust and adapted to the problem studied. Two cavitations’ models and column separation have been incorporated; in this case, the Discrete Vapor Cavity Model (DVCM) and the Discrete Gas Cavity Model (DGCM). Moreover, in addition to the classic models of quasi-stable friction, of which the models of unsteady friction have been included, like the one based on the instantaneous acceleration proposed by Brunone and the one proposed by Vardy & Brown based on the convolution integral. Although single-phase and two-phase water hammers do not behave in the same way, the results obtained with these models show that the temperature produces a great effect on the hammer.

The pilot ratio is a critical parameter of the hydraulic system containing counterbalance valves, which has an important influence on the dynamic characteristics and energy consumption. Generally, these two aspects are contradictory. That is, a high pilot ratio is easy to cause the poor dynamic characteristics of the system, while a low pilot ratio leads to excessive energy consumption. Currently, there is still no effective method for determining the pilot ratio and analyzing the unstable dynamical behavior of the hydraulic system containing counterbalance valves. This paper establishes a dynamics model for the valve-controlled hydraulic cylinder system containing counterbalance valves and investigates the bifurcation in detail. Firstly, the mathematical model, in which the pilot chamber and the spring chamber of counterbalance valves are considered, is established for the segment erector of a tunnel boring machine. Regarding load mass as the bifurcation parameter, the central manifold theorem and normal form method are then introduced to analyze Hopf bifurcation. Simultaneously, the interval of periodic solutions is further determined by the 0–1 test method. Due to the limitation of the quantitative result, a novel homotopy-based method is finally proposed for solving the periodic solution at the above interval. In the case of a high pilot ratio (kx = 8), the supercritical Hopf bifurcation occurs when the load mass exceeds 2352.5 kg. Moreover, the periodic solution exists at the interval (2352.5 kg, 3583 kg). Compared with the numerical solution, the homotopy series solution gives an analytical expression and has a good approximation for the periodic solution. The qualitative results of bifurcation behaviors can be regarded as the basis for determining the pilot ratio of counterbalance valves. And the proposed method is adapted to analyze the unstable dynamical behavior introduced by counterbalance valves in a typical hydraulic circuit.

Leakage is one of the most important reasons for failure of hydraulic systems. The accurate positioning of leakage is of great significance to ensure the safe and reliable operation of hydraulic systems. For early stage of leakage, the pressure of the hydraulic circuit does not change obviously and therefore cannot be monitored by pressure sensors. Meanwhile, the pressure of the hydraulic circuit changes frequently due to the influence of load and state of the switch, which further reduces the accuracy of leakage localization. In the work, a novel Bayesian networks (BNs)-based data-driven early leakage localization approach for multi-valve systems is proposed. Wavelet transform is used for signal noise reduction and BNs-based leak localization model is used to identify the location of leakage. A normalization model is developed to improve the robustness of the leakage localization model. A hydraulic system with eight valves is used to demonstrate the application of the proposed early micro-leakage detection and localization approach.

Vegetable oils are well known for their potential applications in green chemistry, including use as hydraulic fluids. Among oilseed crops, Crambe abyssinica Hochst. EX R.E.Fr . gained attention for its low-input requirements during cultivation and for the properties of its oil, characterised by a high erucic acid content. This long-chain mono-unsaturated fatty acid provides appreciable features that make the oil suitable for interesting green chemistry sectors, as biolubricants and cosmetics. In the present work, Crambe oil was tested as a hydraulic fluid for sustainable agricultural applications. Crambe oil was partially refined through phospholipid removal and added with a food-grade antioxidant (tert-butylhydroquinone) at two different concentrations. The fluid efficiency tests were carried out using an experimental test rig, able to simulate a real hydraulic device, performing heavy work cycles at 40-MPa pressure and at 100 °C temperature, with the aim of strongly accelerating the ageing of the tested fluid. At a lower antioxidant concentration, 0.25 g kg−1, the oil underwent a very quick degradation process. However, increasing the additive dose to 2.0 g kg−1, the fluid maintained stable performances. Indeed, all parameters, referred to oil chemical-physical stability and technical performance, were constant along the entire work cycle, up to 290 h. Finally, the present work showed how Crambe seed cultivation, oil extraction and exploitation in the hydraulic circuit of farm machinery could be developed applying green chemistry approaches aiming at small-scale biorefineries linked to the local supply.

To enhance the operational reliability and maintainability of the manipulator for centering of a slab and measurement of its width in roughing mill stands, it is proposed to replace the electromechanical drive with a hydraulic one. The hydraulic circuit and design of the double-acting hydraulic cylinder with a pressure sensor are described. The sensor allows determining the position of the manipulator at any time and comparing the distance between the manipulators to the theoretical width of the slab.

The paper stresses on the designing and implementation of a nonlinear offline feed forward controller in association with a PID controller as a fault tolerant control measure for a closed loop hydraulic system. An off-line nonlinear feed forward control with proportional pressure relief valve (PRV) loading on the loading pump has been developed using the subsystem models without taking into considerations the oil compressibility, valve dynamics and leakages associated with various components of the hydraulic circuit. A PID feedback has been utilized in real-time to deal with the unmodeled features and the modelling approximations. The characteristics of the speed response are significantly influenced by the disturbances related to external torque, change in the input magnitude as well as system parameters like inertia load and supply pressure. The real-time control showed that the experimental and predicted closed–loop control performances justify each other quite well. Hence, the PID gains were estimated quite effectively with the help of the developed simulation tool here. The control model produced good agreement between the demanded and real-time speed response for various loading conditions such as step load, sinusoidal load, variable load, triangular load etc.

The hydraulic system is the control center of aircraft, the performance of which is critically dependent on the purity of the oil that flows through it. Contamination of hydraulic system oil has been known to be the primary cause of catastrophic failure and accidents. A review of literature in the area of hydraulic oil contamination reveals three facts: (i) there is a dearth of effective methods to prevent intrusion of external contaminants into the hydraulic oil, (ii) there are no effective purification methods for liquid and gaseous contaminants of oil, and (iii) there is an absence of real-time monitoring for major contaminants. This work systematically reviews the hazards, sources, and removal methods of major contaminants, especially of gaseous contaminants. An active method to control oil contamination is proposed instead of the existing passive maintenance techniques that are ridden with problems. In a case study of aviation hydraulic system, our active control system comprises (i) a closed hydraulic circuit and a closed oil tank to prevent the intrusion of external contaminants, (ii) a vacuum centrifuge to efficiently remove contaminants without creating consumption costs, and (iii) monitoring devices installed to actively monitor the contaminant content in oil during operation. The results from the purification experiments and three-dimensional modeling indicate that the active control of hydraulic oil contamination can effectively remove 98.4% solid contaminants and reduce the water content below 50 ppm, and in particular reduce the gas content below 2%. It is obvious that this method can improve the continuous operation capability of aviation hydraulic systems and extend the intermaintenance period of aircrafts by reducing the contaminant content in oil.

In this study, the effects of two piezo injectors operated by different mechanisms on multi-injection and Compression ignition (CI) combustion were investigated. High-pressure injectors for CI engines are divided into two categories according to the actuator: Solenoid and piezo injectors. It is commonly known that both injectors have a hydraulic circuit for fuel injection; thus, the performance of the injector is highly dependent on not only hydraulic characteristics such as volume of internal chambers and nozzle geometry, but also the actuation mechanism. Specially, the direct needle-Driven piezo injector (DPI) is introduced in this study and compared with the indirectacting Piezo injector (PI) to investigate the injection characteristics and influences on CI combustion performance by using spray visualization, injection rate measurement, and single cylinder diesel engine experiments, as well as numerical simulation for injection rate modeling of DPI. In the spray visualization experiment, a high-speed camera was used to examine spray tip penetration length and spray speed with respect to each injector. Also, in order to investigate injection rate information, which is a significantly dominant factor in combustion characteristics, the Bosch-tube method was adapted under the condition of a back pressure of 4.5 MPa, corresponding to engine motoring pressure. Also, a single-cylinder CRDi (Common-rail direct-injection) engine experiment was carried out to determine the effects of different piezo-acting mechanisms on two-stage fuel injection and CI combustion. From the key results obtained by this study, the direct needle-driven piezo injector has a faster SOI (Start of injection) and EOI (End of injection). In addition, the overall shape of the injection rate of DPI was narrow and the injection had a higher spray speed than that of PI. Also, DPI has a higher heat release rate and peak pressure, as verified by the engine experiment. In particular, it was found that DPI showed the possibility of combustion improvement when applying a pilot injection strategy.

Hydraulic turbines are operating at part load conditions depending on availability of hydraulic energy or to meet the grid requirements. The turbine experiences more fatigue during the part load operating conditions due to flow phenomena such as vortex breakdown in the draft tube and flow instability in the runner. The present paper focuses on the investigation of a high head model Francis turbine operating at 50% load. Pressure measurements have been carried out experimentally on a model Francis turbine. Total six pressure sensors were mounted inside the turbine and other two pressure sensors were mounted at the turbine inlet pipe. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space and the runner. Moreover, a standing wave is observed between the pressure tank outlet and the turbine inlet. Analysis of the data acquired by the pressure sensors mounted in the draft tube showed the presence of vortex breakdown co-rotating with the runner. The detailed analysis showed the rotating and plunging components of the vortex breakdown. The influence of the rotating component was observed in the entire hydraulic circuit including distributor and turbine inlet but not the plunging one.

The article presents the results of development and experimental studies of artificial ventricles used for modeling the cardiovascular system. The ventricle is divided into two hemispheres separated by a membrane, ensuring the necessary level of contractility of the artificial ventricle and separating its hydraulic and pneumatic components. The study considered two versions of the ventricle, with mechanical check valves (Vesta Trading, Shcherbinka, Moscow, Russia) and bicuspid artificial valves (ZAO NPP MedEng, Penza, Russia) as aortic and mitral valves. The designed ventricles were compared with a reference, which was represented by a Medos VAD membranous artificial ventricle (Medos Medizintechnik AG, Stolberg, Germany).

To increase the efficiency and reliability of the thermodynamics analysis of the spool valve, the precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke and thermal-hydraulic bond graph based on the conservation of mass and energy were introduced. Subsequently, the connection rule for the bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing the spool valve, the lumped parameter for mathematical model of the system was given. At last, the reliability of the mathematical model of the flow area and the thermal-hydraulic system for the sloping U-shape notch orifice on the spool were demonstrated by the test. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.

A simulator of the human cardiovascular system intended for testing circulatory assist devices is described. The device is a hydraulic circuit that simulates the greater and lesser circulation. It consists of two artificial ventricles, four closed reservoirs, a pneumatic control system, a flow sensor, ten liquid pressure sensors, and two inductors to provide vascular resistance. The device has hydrodynamic characteristics comparable to that of the human heart. It can be used for preclinical testing of circulatory assist devices of the left ventricle, right ventricle, or both ventricles of the heart, and of the completely artificial heart.

To increase the efficiency and reliability of the thermodynamics analysis of the hydraulic system, the method based on pseudo-bond graph is introduced. According to the working mechanism of hydraulic components, they can be separated into two categories: capacitive components and resistive components. Then, the thermal-hydraulic pseudo-bond graphs of capacitive C element and resistance R element were developed, based on the conservation of mass and energy. Subsequently, the connection rule for the pseudo-bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing a piston pump, the lumped parameter mathematical model of the system was given. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.

CFETR which stands for China Fusion Engineering Test Reactor is a superconducting Tokamak device. Remote handling (RH) has been proved to be an important way for maintenance of CFETR Blanket. The lifting mechanism of manipulator can remove or assemble blanket modular and then lift the blanket by use hydraulic drive system. However, the medium in traditional hydraulic system is mineral oil, in the nuclear environment they are dangerous in case of leakage and activate. While the characteristics of water is the inert medium, water hydraulic drive is best choice in the RH maintenance. This paper presents the technical and theoretical background of hydraulic component in the circuit of blanket maintenance manipulator. What is more, the hydraulic circuit will also be designed, which confirmed meets requirements in the work process.

Pump operating as turbine (PAT) is an effective source of reducing the equipment cost in small hydropower plants. However, the manufacturers provide poor information on the PAT performance thus representing a limit for its wider diffusion. Additional implementation difficulties arise under variable operating con- ditions, characteristic of water distribution networks (WDNs). WDNs allow to obtain widespread and globally significant amount of produced energy by exploiting the head drop due to the network pressure control strategy for leak reductions. Thus a design procedure is proposed that couples a parallel hydraulic circuit with an overall plant efficiency criteria for the market pump selection within a WDN. The proposed design method allows to identify the performance curves of the PAT that maximizes the produced energy for an assigned flow and pressure-head distribution pattern. Finally, computational fluid dynamics (CFD) is shown as a suitable alternative for performance curve assessment covering the limited number of experimental data.

Typical hydraulic system, although it is widely applied in industry because of its high energy density, its actual operational efficiency is only 23%–25% owing to very high energy losses, such as pressure loss and fluid dynamics loss, caused by the hydraulic system. An electro-hydrostatic actuator (EHA) system is a compact system in which an electric motor and hydraulic pump are incorporated into a cylinder, which results in greater energy efficiency than conventional hydraulic systems. The EHA system also suffers from relatively less leakage than valve-operated systems. This system consists of a bidirectional pump and a hydraulic cylinder operated by an electric motor, which adjusts the discharge flow rate of the pump by controlling the speed in both directions and changes the forward or backward direction and speed of the hydraulic cylinder accordingly. In this study, the characteristics of a single-rod cylinder load operation system, an EHA hydraulic circuit, and an electric motor are analyzed using mathematical models, and the performance of a closed-loop hydraulic control system incorporating an EHA with a rotation angle of a base plate controller is investigated.

A generalization of the singular spectral analysis (SSA) technique to ill-defined data is introduced in this paper. The proposed algorithm achieves tight estimates of the energy of irregular or aperiodic oscillations from records of interval or fuzzy-valued signals. Fuzzy signals are given a possibilistic interpretation as families of nested confidence intervals. In this context, some types of Supervisory Control And Data Analysis (SCADA) records, where the minimum, mean and maximum values of the signal between two scans are logged, are regarded as fuzzy constrains of the values of the sampled signal. The generalized SSA of these records produces a set of interval-valued or fuzzy coefficients, that bound the spectral transform of the SCADA data. Furthermore, these bounds are compared to the expected energy of AR(1) red noise, and the irrelevant components are discarded. This comparison is accomplished using statistical tests for low quality data, that are in turn consistent with the possibilistic interpretation of a fuzzy signal mentioned before. Generalized SSA has been applied to solve a real world problem, with SCADA data taken from 40 turbines in a Spanish wind farm. It was found that certain oscillations in the pressure at the hydraulic circuit of the tip brakes are correlated to long term damages in the windmill gear, showing that this new technique is useful as a failure indicator in the predictive maintenance of windmills.

The hydraulic circuit theory created to model hydraulic systems such as pipeline transportation systems usually considers the flow distribution problem with specified flow rates of the medium to be transported to and from the transportation system at individual nodes. This paper investigates the case of practical interest where the medium flow rates at individual nodes are not fixed but depend on the pressure at these nodes.

A way to measure flow rate inside a microchannel using a contactless optical technique is reported. The optofluidic device consists of a Bragg grating written on a soft wall, namely a Mylar stripe glued on the top of a microfluidic channel. Diffraction of a white-light probe beam is used to detect the small displacements of the grating caused by the liquid flowing inside the microchannel. A simple model of the hydraulic circuit gives theoretical expressions for the response time of the diffracted signal allowing to fit the experimental data and determine the applied flow rates.

A mathematical model was developed combining the dynamics of an Euler-Bernoulli beam, described by the assumed-mode method and hydraulic circuit dynamics. Only one matrix, termed drive Jacobian, was needed in the modeling of interaction between hydraulic circuit and flexible manipulator mechanism. Furthermore, a new robust controller based on mentioned above dynamic model was also considered to regulate both flexural vibrations and rigid body motion. The proposed controller combined sliding mode and backstepping techniques to deal with the non-linear system with uncertainties. The sliding mode control was used to achieve an asymptotic joint angle and vibration regulation by providing a virtual force while the backstepping technique was used to regulate the spool position of a hydraulic valve to provide the required control force. Simulation results are presented to show the stabilizing effect and robustness of this control strategy.

The work is suggested that represents a further extension of the methods related to the theory of hydraulic circuits of V.Ya. Hasilev and A.P. Merenkov in the direction of the substantiation, mathematical description, and statement of problems of regulation and control, which involve the nonstationary flow distribution in multiloop hydraulic circuits with lumped parameters. Consideration is given to a structural change in the diagram of a hydraulic circuit by way of a sequential exclusion of branches (edges) of the graph, which does not lead to its decomposition. The statement and description of this kind provide a model representation of the problem of structural control of actual piping systems, in particular, engineering systems of water and heat supply.

Water hydraulic systems use water as a pressure medium to minimize the adverse environmental impacts of oil-using hydraulics. Microbial growth in the systems may restrict the applicability of this technology. In this work, occurrence of bacteria in three different full-scale water hydraulic applications operating in different industries was studied. Bacteria were found from different parts of diesel engine direct water injection (DWI) systems in the range of 1.8×105–1.0×107 cells/ml. Filters designed for removal of mechanical particles released bacteria and particles into the pressure medium indicating that a more frequent change of filters was needed or better filters for microbial control should be developed. The microbiological quality of the pressure medium in the DWI systems did not significantly change during the hydraulic circuit indicating suitability for long-term operation. The DWI studies showed that tap water quality is sufficient to ensure the long-term operation of full-scale water hydraulic applications. The microbiological quality of the pressure medium in a nuclear power plant remained stable (1.4–2.1×105 cells/ml) over long-term operation. The results confirmed that water hydraulics, with demineralized water as a pressure medium, can be used in such demanding applications as nuclear power plants. In the pressure medium of the hydraulic system of a wood processing plant, microbial growth resulted in malfunction. Bacteria should be controlled by a better quality pressure medium rather than the use of a biocide.

Proper simulation of noise in hydraulic circuits requires reliable experimental data to be used in the simulations. In automotive power steering applications, obtaining reliable impedance data for both the pump and steering gear is critical for the success of any fluid-borne noise simulation program. Collecting data for power steering pumps has been the subject of various studies. Steering gears, on the other hand, have received little attention. The purpose of this paper is to present a comprehensive assessment of the need of such data and describe a test setup for obtaining the data according to recent ISO standards. This paper describes the results obtained and presents several studies. In particular, the effects of pressure, steering position, slave pump and steering fluid on rack impedance will be studied. Furthermore, repeatability and production variability of measured data will be addressed.

This paperdeals with the problem of water-level control for an array ofcells by means of an hydraulic circuit. An on-off valve fillsall the cells, while each cell is drained by a single on-offvalve, so the control is intrinsically coupled. An optimal controlwith PWM (pulse width modulation) valves is carried out. At theend, simulation and experimental results are presented. The arrayof cells may find application as compensator for radiotherapy(Total Body Irradiation), by interposing the cells between thex-ray source and the patient: on-line water-level variationsin the cells allow local radiation dose control.

Problems of numerical simulation of branched hydraulic systems are considered. Difference schemes in Riemann invariants are constructed for nonlinear equations of poorly compressed fluid that are prescribed on hydraulic networks. Results of numerical simulation of fluid flow in the hydraulic drive of a mechanism for lowering cargo are presented.

The aim of the present paper is to investigate the application of nickel foam electrodes in classical filter-press type electrochemical cells. For this purpose the ElectroSynCell®, commercialized by Electrocell AB, has been used. The interest of using metallic foams linked to a classical plane plate is to improve the performance of the electrochemical cell by increasing the electrode surface area. Moreover, for some industrial applications it is possible to use the cell without a membrane. In the proposed configuration, the working electrodes consist of metallic foam linked to a plane plate and the auxiliary electrode is simply a plane plate. The imbalance between the surface areas of working and auxiliary electrodes allows operation with a single hydraulic circuit. This paper, focuses on the study of residence time distribution and pressure drop in order to compare the flow behaviour with that in a classical configuration. A model for the reactive zone of the cell is also given.

A proportion of the damage sustained by potatoes at harvest time occurs during transfer from the potato harvester delivery conveyor to the trailer. A prototype delivery conveyor, designed to reduce this damage, was built and tested under commercial harvesting conditions. The conveyor has an automatic discharge height control consisting of a sensor ball mounted on the end of the conveyor and actuating an airswitch which causes a solenoid valve to operate a hydraulic lifting ram. The conveyor is in two parts, the distal part being capable of swinging sideways in the event of impact against the trailer tailboard. Results of tests show that the mean drop height can be held within the range 116–199 mm. This is an improvement on the mean drop heights of 390–780 mm measured under typical farm conditions on harvesters without automatic control of the delivery height of the discharge conveyor.