Investigation of air-core vortex at hydraulic intakes

Hydrodynamic properties of the surface vortex have been investigated. Based on the Navier-Stokes equations, three sets of the new formulations for the tangential velocity distributions are derived, and verified against the experimental measurements in the literature. It is shown that one modification greatly improves the agreement with the experimental data. Physical model experiments were carried out to study the intake vortex related to the Xiluodu hydropower project. The velocity fields were measured using the Particle Tracking Velocimetry (PTV) technique. The proposed equation for tangential velocity distribution is applied to the Xiluodu project with the solid boundary being considered by the method of images. Good agreement has been observed between the formula prediction and the experimental observation. © 2010 Publishing House for Journal of Hydrodynamics.

Specifying a hydraulic regenerative braking system for an articulated urban delivery vehicle

Previous research has shown that hydraulic systems offer potentially the lightest and smallest regenerative braking technology for heavy goods vehicles. This paper takes the most practical embodiment of a hydraulic system for an articulated urban delivery vehicle and investigates the best specification for the various components, based on a simulated stop-start cycle. The potential energy saving is quantified. © 2011 IEEE.

Eliminating discharge imbalances in predicting shallow water flows with shocks

The shallow water equations are widely used in modelling environmental flows. Being a hyperbolic system of differential equations, they admit shocks that represent hydraulic jumps and bores. Although the water surface can be solved satisfactorily with the modern shock-capturing schemes, the predicted flow rate often suffers from imbalances where shocks occur, eg the mass conservation is violated by failing to maintain a constant discharge rate at every cross-section in a steady open channel flow. A total-variation-diminishing Lax-Wendroff scheme is developed, and used to demonstrate how to achieve an exact flux balance. The performance of the proposed methods is inspected through some test cases, which include 1- and 2-dimensional, flat and irregular bed scenarios. The proposed methods are shown to preserve the mass exactly, and can be easily extended to other shock-capturing models.

Development of a servo-hydraulic earthquake actuator for the Cambridge Turner beam centrifuge

Dynamic centrifuge modelling has been carried out at Cambridge since the late 1970s. Over this period, three different mechanical earthquake actuators were developed. In this paper the development of a new servo-hydraulic earthquake actuator is described. The basic design principles are explained along with the need to carry out these designs to match the existing services and systems of the 35 year old Turner beam centrifuge at Cambridge. In addition, some of the features of the Turner beam centrifuge are exploited in the design of this new earthquake actuator. The paper also explains the mechanical fabrication of the actuator and the control systems that were developed in order to generate real earthquake motions. Finally, the performance of this new servo-hydraulic earthquake actuator is presented and assessed based on a wide range of earthquake input motions.

Pneumatic and hydraulic microactuators: A review

The development of MEMS actuators is rapidly evolving and continuously new progress in terms of efficiency, power and force output is reported. Pneumatic and hydraulic are an interesting class of microactuators that are easily overlooked. Despite the 20 years of research, and hundreds of publications on this topic, these actuators are only popular in microfluidic systems. In other MEMS applications, pneumatic and hydraulic actuators are rare in comparison with electrostatic, thermal or piezo-electric actuators. However, several studies have shown that hydraulic and pneumatic actuators deliver among the highest force and power densities at microscale. It is believed that this asset is particularly important in modern industrial and medical microsystems, and therefore, pneumatic and hydraulic actuators could start playing an increasingly important role. This paper shows an in-depth overview of the developments in this field ranging from the classic inflatable membrane actuators to more complex piston-cylinder and drag-based microdevices. © 2010 IOP Publishing Ltd.

Microsized piston-cylinder pneumatic and hydraulic actuators fabricated by lithography

Future microrobotic applications require actuators that can generate a high actuation force in a limited volume. Up to now, little research has been performed on the development of pneumatic or hydraulic microactuators, although they offer great prospects in achieving high force densities. In addition, large actuation strokes and high actuation speeds can be achieved by these actuators. This paper describes a fabrication process for piston-cylinder pneumatic and hydraulic actuators based on etching techniques, UV-definable polymers, and low-temperature bonding. Prototype actuators with a piston area of 0.15 mm2 have been fabricated in order to validate the production process. These actuators achieve actuation forces of more than 0.1 N and strokes of 750 μm using pressurized air or water as driving fluid. © 2009 IEEE.

Development of a hybrid ferrofluid seal technology for miniature pneumatic and hydraulic actuators

Future microrobotic applications require actuators that can generate a high actuation force and stroke in a limited volume. Up to now, little research has been performed on the development of pneumatic and hydraulic microactuators, although they offer great prospects in achieving high force densities. One of the main technological barriers in the development of these actuators is the fabrication of powerful seals with low leakage. This paper presents a seal technology for linear fluidic microactuators based on ferrofluids. A design and simulation method for these seals has been developed and validated by measurements on miniaturized actuator prototypes. These actuators have an outside diameter of 2 mm, a length of 13 mm and have been tested using both pressurized air and water. Our current actuator prototypes are able to operate at pressures up to 1.6 MPa without leakage. At these pressures, forces up to 0.65 N have been achieved. The stroke of the actuators is 10 mm. © 2009 Elsevier B.V. All rights reserved.

Design and characteristion of a hydraulic microactuator fabricated by lithography

To improve the force output of microactuators, this work focuses on actuators driven by pressurized gasses or liquids. Despite their well known ability to generate high actuation forces, hydraulic actuators remain uncommon in microsystems. This is both due to the difficulty of fabricating these microactuators with the existing micromachining processes and to the lack of adequate microseals. This paper describes how to overcome these limitations with a combination of anisotropic micromachining, UV definable polymers and low temperature bonding. The functionality of these actuators is proven by extensive measurements which showed that actuation forces of 0.1 N can be achieved for actuators with an active cross-section of 0.15 mm2. This is an order of magnitude higher than what is reported for classic MEMS actuators of similar size.

A hybrid surface tension seal for pneumatic and hydraulic microactuators

Recent research revealed that microactuators driven by pressurized fluids are able to generate high power and force densities at microscale. One of the main technological barriers in the development of these actuators is the fabrication low friction seals. This paper presents a novel scalable seal technology, which resists the actuation pressure relying on a combination of a clearance seal and a surface tension seal. This approach allows to seal pressures of more than 800 kPa without leakage. The seal is tested on an actuator with a bore of 0.8 mm2 and a length of 13 mm, which was able to generate forces up to 0.32 N. © 2008 Springer-Verlag.

Comparison of two seal technologies for hydraulic microactuators

In order to improve the power density of microactuators, recent research focuses on the applicability of fluidic power at microscale. One of the reasons that hydraulic actuators are still uncommon in micro system technology is due to the difficulty of fabricating powerful microseals. This paper presents two seal technologies that are suitable for sealing small-scale hydraulic actuators. Measurements on prototype actuators show that force densities up to 0,45 N/mm2 (0,025 N/mm3) and work densities up to 0,2 mJ/mm3 can easily be achieved with the developed seal technology. These characteristics can still be improved as the maximum driving pressures of the actuators have not yet been determined. © 2005 IEEE.