Matti Vilenius

Effects of fluid-flow velocity and water quality on planktonic and sessile microbial growth in water hydraulic system

Water hydraulic systems use water instead of oil as a pressure medium. Microbial growth in the system may restrict the applicability this technology. The effects of fluid-flow velocity and water quality on microbial growth and biofilm formation were studied with a pilot-scale water hydraulic system. The fluid-flow velocities were 1.5-5.2 m/s and the corresponding shear stresses 9.1-84 N/m2. The fluid-flow velocity had an insignificant effect on the total bacterial numbers and the numbers of viable heterotrophic bacteria in the pressure medium. Microbial attachment occurred under high shear stresses. The fluid-flow velocity did not affect the biofilm formation in the tank. Increase in the flow velocity decreased the bacterial densities on the pipe surfaces indicating preferable biofilm formation on areas with low flow velocity. Using ultrapure water as the pressure medium decreased the total cell numbers and resulted in slower growth of bacteria in the pressure medium. Lowering the nutrient concentration retarded biofilm formation but did not affect the final cell densities. The decreasing pressure medium nutrient concentration favoured microbial attachment in the tank instead of the pipelines. In conclusion, microbial growth and biofilm formation in water hydraulic systems cannot be controlled by the fluid-flow velocity or the quality of the pressure medium.

Improved Digital Hydraulic Tracking Control of Water Hydraulic Cylinder Drive

Abstract A position tracking control system is implemented by utilizing parallel-connected on/off valve series. The pulse code modulation method is used to achieve stepwise flow control and four valve series, each having four two-way solenoid valves, are used. A cost function based controller is used to control simultaneously and independently flow paths from supply to cylinder chambers and from chambers to tank. It is shown that controllability can be improved especially at low velocities by allowing three or four valve series to be open simultaneously instead of using classical inflow-outflow control.

Water hydraulic actuators for ITER maintenance devices

The characteristic advantages of hydraulics (high power density, simple construction and reliability) together with the characteristics of water as the pressure medium (fire and environmentally safe, chemically neutral, not activated nor affected by radiation) are highlighted in critical applications such as remote handling operations in international thermonuclear experimental reactor (ITER). However, lack of commercial selection of water hydraulic components, common design expertise and known application experiences prevents wide use of water hydraulics. Since 1994, IHA has designed and manufactured water hydraulic tools for ITER divertor maintenance and experiences have been good. Therefore, IHA is developing water hydraulic component selection to be applied in coming systems where water hydraulics is foreseen to provide an advantage. Aim of the still on going project is to develop a set of components like power units, control components and actuators. By that way designers are able to apply water hydraulics where advantageous. In the paper the component types, their design and characteristics and results obtained so far are presented.

Effect of Cavitation in Water Hydraulic Poppet Valves

Abstract In this paper, cavitation in water hydraulic poppet valves is investigated by an experimental method with a half cut test model. The situation of cavitation appearance, the effects of cavitation on the characteristics of flow rate, noise level, pressure distributions and the boundary of inception of the cavitation are investigated. Comparison between a poppet valve with sharp edged seat and another, which has a length on the seat, is made. The effects of change in the shape of the seat are discussed as well as the effect of cavitation appearance. As a result, it is revealed that the sharp edged seat valve is less influenced by the cavitation on its characteristics.

Accurate Trajectory Tracking Control of Water Hydraulic Cylinder with Non-Ideal on/off Valves

Abstract The aim of the work is to develop an on/off valve based trajectory tracking control solution without fast and/or continuous switching of valves. The pulse code modulation method is used to realise stepwise control of inflow and outflow of the actuator. Both inflow and outflow paths have five parallel-connected two-way solenoid valves, each having different flow capacity according to binary series, and a four-way on/off valve is used for changing direction of movement. Cost function based open-loop and closed-loop control solutions are developed and it is demonstrated how the cost function weights can be used to find a reasonable trade-off between tracking performance and pressure surges. Closed-loop results show accurate and reasonably smooth position tracking and simultaneous pressure level control. Achieved control performance is close to that of water hydraulic servo systems.

Jammed on/off Valve Fault Compensation with Distributed Digital Valve System

Abstract The digital valve system is an on/off valve based directional flow control valve capable of accurate control of hydraulic actuators. The presented system has good features concerning fault tolerance since it can detect, diagnose and compensate faults on-line. This paper concentrates on fault compensation when a valve has jammed in the open—position and the system has internal leakage. The system can adapt to the fault and continue operation with only a small degradation in performance. This feature is unique in the area of hydraulics since the system has no extra components added. The cost for this compensation is increased calculation in the controller and increased energy consumption if a fault occurs. If these downsides can be accepted the system can be considered fault-tolerant and it could be used even in critical applications where failing is not an option. Fault tolerance can also be introduced as standard in every modern hydraulic application where good performance and fault tolerance are needed.

Development of Water Hydraulic Remote Handling System for Divertor Maintenance of ITER

In hostile industrial environments where human access could be a health risk, a reliable and flexible teleoperation system is an eminent need. ITER is such an example where a dexterous teleoperation system is required for remote handling tasks in a nuclear environment. The compactness of space, high load capacity and reliability makes hydraulic manipulator an obvious choice. However, possible oil leakage from traditional hydraulic systems and the characteristics of water (fire and environmentally safe, chemically neutral, not activated, not affected by radiation) makes the use of water hydraulics the only choice. This paper describes the development of teleoperation system for ITER consisting of a water hydraulic manipulator as a slave, a commercial haptic device as a master, a human machine interface to assist the operator and a graphical system providing a virtual 3D view of the environment.

The Electro-Hydraulic Valve Actuation (EHVA) for Medium Speed Diesel Engines - Development Steps with Simulations and Measurements

Electro-Hydraulic Valve Actuation (EHVA) is one of the most promising ways to improve the performance and reduce the emissions of the diesel engines. The EHVA gives fully variable lift and event duration of the gas exchange valves and thus the combustion process can be better controlled in different operation points such as idle and partial load situation. Also totally new kind of gas exchange processes are possible to achieve. This paper consists of alternative solutions of EHVA systems, the comparison of them by means of simulation and measurements, the empirical tests of EHVA system in a laboratory and finally conclusion and future research activities. The developed EHVA system fulfills the requirements very well. The lift of the gas exchange valve is fast enough, and the seating velocity is under control. The system is able to run with open and closed loop control.

Utilization of virtual prototyping in development of CMM

The characteristic advantages of hydraulics (high power density, simple construction and reliability) together with the characteristics of water as the pressure medium (fire and environmentally safe, chemically neutral, not activated nor affected by radiation) are highlighted in critical applications such as remote handling operations in International Thermonuclear Experimental Reactor (ITER). However, component cost and lack of wide selection of water hydraulic components make it difficult to build and to test complex water hydraulic systems. The use of virtual prototyping for the development of water hydraulic tools can be used to address this problem. Rapidly increased computational power has created conditions for extensive numerical calculations, enabling computer aided virtual prototyping to replace physical prototype phases in product development.

ITER Divertor Maintenance: Development of a Control System for the Remote Handling of the Divertor Cassette Mover

Remote handling devices are being used to carry out the maintenance tasks in the divertor area of the ITER. One of the main challenging operations is the installation and transportation of Divertor Cassettes in and out from the vessel. This paper deals with the development of the control system for such remotely operated devices, with special emphasis on the tools, mock-ups and virtual prototypes employed to develop the high level control software and the water-hydraulics position servos controllers. Preliminary studies showing the effect of irradiation in hydraulic cylinder seals are also presented.