Conventional Hydraulic Systems Research Articles

A Full-Scale Tidal Blade Fatigue Test using the FastBlade Facility

Fatigue testing of tidal turbine blades requires the application of cyclic loads without the ability to match the natural frequency of the blade due to their high stiffness and the associated thermal issues of testing composite materials at those frequencies (i.e., 18–20 Hz). To solve this, loading the blades with an auxiliary system is necessary; in most cases, a conventional hydraulic system tends to be highly energy-demanding and inefficient. A regenerative digital displacement hydraulic pump system was employed in the FastBlade fatigue testing facility, which saved up to 75 % compared to a standard hydraulic system. A series of equivalent target loads were defined using Reynolds-Averaged Navier Stokes (RANS) simulations (based on on-site collected water velocity data) and utilised in FastBlade to demonstrate an efficient way to perform fatigue testing. During the test, a series of measurements were performed on the blade response and the Fastblade test structure itself, providing novel insights into the mechanical behaviour of a blade, and enabling improved testing practice for FastBlade. Without catastrophic failure, the blade withstood the principal tidal loading for 20 years (equivalent). This test data will enable FastBlade to identify improvements to the testing procedures, i.e., control strategies, load introduction, instrumentation layout, instrument calibration, and test design.

A full-scale composite tidal blade fatigue test using single and multiple actuators

In order to perform fatigue testing on tidal turbine blades, it is necessary to apply cyclic loads that do not match the blade’s natural frequency. This is due to the high stiffness of the blades and the thermal challenges associated with testing composite materials at frequencies typically around 18–20 Hz. To overcome this challenge, auxiliary systems are used to load the blades. However, conventional hydraulic systems commonly used for this purpose are known to be energy-intensive and inefficient. In this work, we present results obtained at the FastBlade fatigue testing facility, which utilises a regenerative digital displacement hydraulic pump system to address these issues. This innovative system has proven to be highly efficient, resulting in up to 75% energy savings compared to standard hydraulic systems. To perform these tests, we first performed a series of Reynolds-Averaged Navier–Stokes (RANS) simulations using on-site water velocity data to determine equivalent target hydrodynamic loads. These target loads are applied to the blades using initially a single contact point and, later, three load contact points. The FastBlade facility showcases an effective approach to fatigue testing during these tests. Throughout the testing process, comprehensive measurements are taken to evaluate the response of the blades and the FastBlade test structure itself. These measurements provide valuable insights into the mechanical behaviour of the blades when a single or multi-actuator setup is used to match the root bending moment and contribute to the refinement of testing practices. Notably, the blades successfully endured the equivalent of 20 years of tides in an accelerated fatigue loading test without experiencing catastrophic failure. The data obtained from these tests will enable the identification of improvements in testing procedures, including control strategies, load introduction methods, instrumentation layout, instrument calibration, and test design. This knowledge will lead to enhanced performance and reliability of the FastBlade facility, further advancing the field of tidal turbine blade testing.

Degradation Identification of an EHA Piston Pump by Analysis of Load-Holding States

In pursuit of advancing the development of more electric aircraft, the present research explores the forefront capabilities of electro-hydrostatic actuators (EHAs) as potential replacements for conventional hydraulic flight control systems. EHAs are currently used primarily as backup options due to their limited durability. As of now, the high dynamic axial piston pump is the main cause of the limited longevity of the EHA, due to strong tribological wear. The primary objective of this investigation is the identification of parameters and pump behavior to determine the current wear of the pump, as well as providing valuable insights into run-ins, temperature dependencies, and wear-related efficiency losses for future pump improvements. In the scope of this paper, the design of EHAs is explained in detail and the impact of challenging working conditions on the health status of the pump by comprehensive analysis of load-holding modes is examined. The experimental data for analysis is conducted on a longevity test bench with test profiles specifically designed to simulate real-world operational scenarios.

Digital Hydraulic Technology: Applications, Challenges, and Future Direction

Digital hydraulic technology has emerged as a promising alternative to conventional hydraulic systems, offering several advantages such as improved energy efficiency, more precise control, and reduced complexity. In recent years, digital hydraulic technology applications have been widely researched in various engineering sectors, including aerospace, biomedical and industrial. The aim of this paper is to provide an overview of the recent advancements in digital hydraulic technology, focusing on the various applications and their benefits. The paper begins by introducing the two different branches of this innovative technology. Subsequently, it presents an overview of digital hydraulic technology applications, highlighting their specific advantages, particularly in biomedical, industrial and aeronautical sectors, when compared to conventional hydraulic technology. Finally, the paper addresses the challenges and limitations associated with digital hydraulic technology and discusses potential areas for future research and development.

The Development and Challenges of More Electric Aircraft

The development of electrical and electronic engineering makes the replacement of conventional hydraulic, mechanic, and pneumatic system into electrical system become much more possible. That means the secondary power of aircraft will be dominated by electricity, rather than hydraulic oil or bleed air from the engine. The Boeing 787 and Airbus A380 has applied these technologies significantly and their fuel consumption and noise level during flight are also get improved by comparison with their counterpart which has traditional hydraulic and pneumatic system. On the other side, the mass application of electrical driven components on board will lead to various new challenges to aircraft design when concerning the weight and flight safety due to the characteristics of those components. In this paper, technologies implemented, and challenges will be introduced through reviewing literatures. The benefit and drawbacks will be concluded by comparing electrical and hydraulic and pneumatic system.

Numerical Analysis of Energy Recovery of Hybrid Loader Actuators Based on Parameters Optimization

The conventional loader actuator hydraulic system suffers from the potential energy waste problem of the boom arm. This study proposes a hydraulic control method and control strategy for the energy recovery and regeneration of a hybrid loader arm. When the boom arm drops, the piston side of the boom cylinder charges the accumulator, and the system achieves energy recovery. When the boom arm rises, the accumulator releases hydraulic energy to drive the energy regeneration hydraulic motor to provide energy for the system, and the system achieves energy regeneration. The system’s principle analysis and the mathematical model are completed based on Boyle’s, Newton’s second law, and the flow continuity principle. The simulation model is established using AMESim 2D mechanical library, HCD library, and signal library. Under the typical working condition, 50-type wheel loader numerical simulation research is conducted, and the system cylinder motion characteristics, accumulator charging and discharging performance, system energy recovery, and regeneration performance are obtained. On this basis, energy recovery and regeneration efficiency are selected as optimization objectives. The optimal designs of accumulator and energy regeneration hydraulic motor parameters are carried out to obtain the influence law of accumulator and hydraulic motor parameters on system energy recovery and regeneration, and the energy-saving effect of the system is analyzed. The results show that the optimized parameters effectively improve the system energy recovery and regeneration efficiency and reduce engine fuel consumption. The system provides a reference for designing an energy recovery system and researching the energy-saving technology of loaders.

Sensotronic Brake Control System

Abstract: Sensotronic Brake Control (SBC™) works electronically, and thus faster and more precisely, than a conventional hydraulic braking system. As soon as you press the brake pedal and the sensors identify the driving situation in hand, the computer makes an exact calculation of the brake force necessary and distributes it between the wheels as required. This allows SBC™ to critically reduce stopping distances. SBC™ also helps to optimise safety functions such as ESP®, ASR, ABS and BAS. Keywords: SBC, ABS. BAS, TCS, ESP

Characteristic investigation of a flow-dependent inertia hydraulic converter driven by an equivalent fast switching valve

To acquire a linear load pressure with the potential of energy-saving compared with conventional throttling hydraulic systems, a switched hydraulic circuit (referred to as a flow-dependent inertia hydraulic converter) featuring a flow-dependent inertial effect was proposed. In this device, the flowing fluid modulated by an equivalent fast switching valve allows the fluid inertance at the connection pipe and rotation inertia incorporated in the flywheel to be combined. The theoretical and simulation models of the flow-dependent inertia hydraulic converter were established, and then the flow-dependent inertia was discussed and quantified. The predictions of the load pressure, flywheel speed and system efficiency were confirmed by experimental measurements. Results indicated that the theoretical and simulation predictions match well with the experiments for this configuration. The pressure wave propagation effect within the connection pipe is responsible for the variation in the transient load pressure and flywheel speed that is initially modulated by the rotation inertia theoretically, which seriously questions the predecessor's hypothesis of using a compressible volume to model the upstream connection pipe. The parabolic mean suction flow induced by the flow-dependent inertia draw our attention to the available supply flowrate and duty cycle. Finally, the throttling loss and system efficiency that varies with the desired characteristics is superior to that of conventional throttling hydraulic systems theoretically, and an acceptable system efficiency was obtained under the premise of ignoring friction experimentally.

Commercial Aircraft Electrification—Current State and Future Scope

Electric and hybrid-electric aircraft propulsion are rapidly revolutionising mobility technologies. Air travel has become a major focus point with respect to reducing greenhouse gas emissions. The electrification of aircraft components can bring several benefits such as reduced mass, environmental impact, fuel consumption, increased reliability and quicker failure resolution. Propulsion, actuation and power generation are the three key areas of focus in more electric aircraft technologies, due to the increasing demand for power-dense, efficient and fault-tolerant flight components. The necessity of having environmentally friendly aircraft systems has promoted the aerospace industry to use electrically powered drive systems, rather than the conventional mechanical, pneumatic or hydraulic systems. In this context, this paper reviews the current state of art and future advances in more electric technologies, in conjunction with a number of industrially relevant discussions. In this study, a permanent magnet motor was identified as the most efficient machine for aircraft subsystems. It is found to be 78% and 60% more power dense than switch-reluctant and induction machines. Several development methods to close the gap between existing and future design were also analysed, including the embedded cooling system, high-thermal-conductivity insulation materials, thin-gauge and high-strength electrical steel and integrated motor drive topology.

Analysis of the Effect of the Wedged Type Brake Caliper Piston on Brake Drag

<div class="section abstract"><div class="htmlview paragraph">Recently, there’s a massive flow of change in the automotive industry with the coming era of electric vehicles and self-driving (autonomous) vehicles. The automotive braking system field is not an exception for the change and there are not only lots of new systems being developed but also demands for researches for optimizations of conventional brake systems fitting to the newly appeared systems such as E-Booster and Electric Motor Brake (EMB) Caliper. Taking the Electric Motor Brake Caliper for example, it is considered as a very important and useful system for autonomous vehicles because the motor actuator of the caliper is much easier to control with ECUs compared to the conventional hydraulic pressure system. However, easy of control is not the only thing that excites brake system engineers. Since the whole actuating mechanism of the brake systems has been changed, engineers now can see some new ways to solve chronic problems in conventional brake systems such as brake residual drag, brake fade and so forth. Brake residual drag can be possibly solved by simply connecting the motor actuator of the caliper to the brake piston so that ECUs can actually control the whole life cycle of brake torque creation and extinction. However, there have to be a few more components needed on top of the fact that its structure inside the brake piston could be much more complex than it used to be and this could cause some side effects as well. With the reasons above, this study illuminates the concept for a way of reducing brake residual drag in the new systems by enhancing the capability of piston roll-back of the caliper without any complex structures. Several test results and CAE analysis are presented and discussed to get a better understanding of the concept.</div></div>

Investigation of suction flow characteristic in the inertance hydraulic converters for efficiency improvement

The inertance hydraulic converter relies on fluid inertance to modulate flow or pressure and is considered to be a competitive alternative to the conventional proportional hydraulic system due to its potential advantage in efficiency. As the quantification of fluid inertance, the suction flow characteristic is the crucial performance indicator for efficiency improvement. To explore the discrepancy between the passive inertance hydraulic converter featured by the check valve and the active inertance hydraulic converter driven by an equivalent 2/3 way fast switching valve in regard to suction flow characteristics, analytical models of the inertance hydraulic converters were established in MATLAB/Simulink. The validated models of the respective suction components were incorporated in the overall analytical models and their suction flow characteristics were theoretically and experimentally discussed. The analytical predictions and experimental measurements for the current configurations indicated that the active inertance hydraulic converter yields a larger transient suction flow rate than that of the passive inertance hydraulic converter due to the difference of the respective suction components. The suction flow characteristic can be modulated using the supply pressure and duty cycle, which was confirmed by experimental measurements. In addition, the suction flow characteristics are heavily affected by the resistance of the suction flow passage and switching frequency. There is a compromise between the resistance and switching frequency for inertance hydraulic converters to achieve large suction flow rate.

Experimental study on the behaviour of an electrorheological double miniature valve

In many hydraulic systems, actuators are controlled by conventional valves that require a lot of installation space. They consist of many moving parts which make them prone to errors. Miniature valves with high power densities using the electro-rheological technology can help to reduce the space requirement and possible defects. They can generate a local and reversible viscosity increase to realize higher usable pressure drops. Until now, some valves using this working principle are macro-scaled for the use in conventional hydraulics and needed too much space. Others are microvalves for microfluidics and therefore could not generate a sufficiently high pressure drop. Intermediary sizes such as miniature valves combined with conventional hydraulics have not yet been developed satisfactorily. For this reason, a medium-sized valve was designed to be used in conventional hydraulics but requires considerably less space. Furthermore, it is manufacturable using conventional production methods. The proof of function of this new miniature valve confirmed the concept. Experiments showed that the measured ER behaviour is similar to previous results of macro scale ER valves. The valve reproducibly generated pressures of more than 5 bar without any leakage. This proved that a valve with this novel design is usable in conventional hydraulic systems.

Retraction: Experimental investigation of the vacuum-actuated brake system compared with hydraulic brake system in a vehicle

In this study, a new vacuum brake system has been designed in the place of conventional hydraulic braking system for a Light Commercial Vehicle (LCV). An attempt has been made to reduce the braking...

Development and Application of a Hydraulic Loading Test System That Provides Continuous and Stable Hydraulic Pressure

To accurately determine the stress characteristics of underground rock masses subjected to hydraulic pressure and reveal the crack-initiation, crack-propagation, and macromechanical characteristics of fractured rock masses under long-term hydraulic pressure, a hydraulic loading system that can deliver continuous and stable hydraulic pressure was developed. The system is composed of a device that supplies a stable hydraulic pressure, flowmeter, pressure gauge, acoustic emission instrument, loading device, and control system. The main innovation of the test system lies in the stabilization of the hydraulic pressure, which distinguishes the new system from traditional hydraulic loading devices and provides several advantages. First, in the new system, air pressure serves as the driving force, and water and gas coexist in the same cavity. Given the high compressibility of gas, the hydraulic pressure can still reach the relative stability during crack initiation and propagation in the specimen. Second, the device is capable of long-term operation with low energy consumption. In contrast to conventional hydraulic loading systems based on servo control, the hydraulic pressure of the new device can be maintained for a long time with little energy consumption. Finally, the device is simple to operate, low cost, convenient to assemble, and can be used in single-, double-, and triple-axis tests. The accuracy and reliability of the test system were verified through its application in the uniaxial compression test of a fractured body under the action of stable hydraulic pressure. The test system provides the foundation for the study of the physical mechanisms of deep underground rock masses subjected to long-term, stable seepage pressure.

Effect of Energy Recovery on Efficiency in Electro-Hydrostatic Closed System for Differential Actuator

This paper investigates energy efficiency and dynamic behavior through simulation and experiments of a compact electro-hydrostatic actuator system (EHA) consisting of an electric motor, external gear pump/motors, hydraulic accumulator, and differential cylinder. Tests were performed in a stand-alone crane in order to validate the mathematical model. The influence and importance of a good balance between pump/motors displacement and cylinder areas ratios is discussed. The overall efficiency for the performed motion is also compared considering the capability or not of energy recovery. The results obtained demonstrate the significant gain of efficiency when working in the optimal condition and it is compared to the conventional hydraulic system using proportional valves. The proposed system presents the advantages and disadvantages when utilizing components off-the-shelf taking into account the applicability in mobile and industrial stationary machines.

Modelling and energy efficiency analysis of a hybrid pump-controlled asymmetric (single-rod) cylinder drive system

A conventional valve-controlled cylinder drive system is not energy efficient, and a pump-controlled cylinder system can be unstable in some particular conditions. For drive systems not requiring fast response, a hybrid pump-controlled system, that combines the advantages of both valve and pump-controlled systems, is proposed. As nonlinear behaviours are inevitable in most asymmetric cylinder drive systems, the hybrid pump-controlled system also suffers from such problems, and extra nonlinear behaviours are identified, for example, stall when the cylinder change its direction of motion. A simulation model of the hybrid pump-controlled asymmetric cylinder drive system is developed and used to investigate the system's simulation behaviours which are analysed and compared with the experimental test results. The energy efficiency of the hybrid pump-controlled system is compared with a comparable valve-controlled hydraulic system with the same hydraulic cylinder sizing. The outcome is to demonstrate the advantage of the hybrid pump-controlled system in energy-saving aspect, and the efficiency of the hybrid system is up to five times more than a conventional hydraulic system. Suggestions are given to improve the performance and stability of the hybrid pump-controlled system.

Modelling and energy efficiency analysis of a hybrid pump-controlled asymmetric (single-rod) cylinder drive system

A conventional valve-controlled cylinder drive system is not energy efficient, and a pump-controlled cylinder system can be unstable in some particular conditions. For drive systems not requiring fast response, a hybrid pump-controlled system, that combines the advantages of both valve and pump-controlled systems, is proposed. As nonlinear behaviours are inevitable in most asymmetric cylinder drive systems, the hybrid pump-controlled system also suffers from such problems, and extra nonlinear behaviours are identified, for example, stall when the cylinder change its direction of motion. A simulation model of the hybrid pump-controlled asymmetric cylinder drive system is developed and used to investigate the system's simulation behaviours which are analysed and compared with the experimental test results. The energy efficiency of the hybrid pump-controlled system is compared with a comparable valve-controlled hydraulic system with the same hydraulic cylinder sizing. The outcome is to demonstrate the advantage of the hybrid pump-controlled system in energy-saving aspect, and the efficiency of the hybrid system is up to five times more than a conventional hydraulic system. Suggestions are given to improve the performance and stability of the hybrid pump-controlled system.

High-response electrorheological servo valve

The demand of more powerful and high-dynamic hydraulic actuators gives the servo valve as a control member an increasingly important role. The valve should provide the hydraulic actuator with sufficient volume flow over wide frequency range to achieve large strains at high operating frequencies. Here, the electrorheological effect as an electrohydraulic valve drive offers great potential. It converts the electrical input signal directly into a controlling mechanical quantity within a few milliseconds and provides theoretically unlimited strain. Thus, the electrorheological effect has the ability to increase the performance of conventional hydraulic systems. This work presents a two-stage servo valve with an electrorheological pilot stage. Furthermore, it introduces a model to describe the static and dynamic properties of the system. The model is validated on the basis of measurement results.

A novel experimental method to investigate the plugging characteristics of diversion agents within hydro-fracture

Temporary plugging and diverting fracturing (TPDF) technique has been widely used in exploiting hydrocarbon resources in conventional/unconventional formations. The key to ensuring the success of this technique lies in the efficient plugging of the previously created fractures. However, the plugging characteristics of diversion agents influenced by the fracture geometry have not been efficiently investigated through experiments. In this study, the conventional true tri-axial hydraulic fracturing system was modified, then a series of investigative experiments were carried out and a novel experimental method was proposed to systematically investigate the plugging characteristics of diversion agents within the fracture. This method can not only investigate the effects of fracture geometry on the diversion agent distribution, plugging capacity, and plugging speed within fracture, but also optimize the diversion agent recipe for plugging various geometries fracture with different apertures, thus saving the dosage of diversion agents and fracturing fluids. Moreover, under certain conditions, as for the common four types of fractures i.e., distorted (type-Ⅰ) fracture, inclined and flat (type-Ⅱ) fracture, longitudinal and flat (type-Ⅲ) fracture, and transverse and flat (type-Ⅳ) fracture, the required ratio of diversion agent dosage for plugging is approximately 1:7:15:3.

Combined velocity and position control of large inertial hydraulic swing mechanism considering energy balance of supply and demand

Abstract The position of a conventional large inertial hydraulic swing system is controlled by the operator-in-loop, the production efficiency of which is poor, and the repetitive positioning precision is low owing to slow human reactions. To address this problem, this study proposes a combined velocity and position control strategy based on the independent metering control system. In this method, it is not necessary to change the conventional operation mode. If the required rotary angle is the same in each swing process, a precise desired position is provided as the input signal for closed-loop position control. If the required rotary angle is random, in order to be compatible with the handle operation mode used in mobile machines, a handle signal integral control method is proposed. Moreover, velocity feedback is used to improve the control accuracy, while differential pressure feedback is used to reduce the position overshoot. Meanwhile, to improve the system dynamic characteristics during the braking process, an energy balance principle is applied. The proposed strategy is verified with simulation and a 6 t hydraulic excavator. The simulation and experimental results demonstrate that a higher positioning accuracy can be achieved with different desired angular displacements. Furthermore, the position overshoot, and velocity and pressure fluctuation are avoided, while the dynamic characteristics are clearly improved.