Hubertus Murrenhoff

Piston Slippers for Robust Water Hydraulic Pumps

Liu et al. /6/ developed a test bench for experiments in search for materials for water hydraulic axial piston pumps. The test bench consisted of a turning swash plate (wobble plate) which actuated a piston and its slipper. Therefore the slipper/swash plate contact as well as the piston/cylinder contact could be tested. Liu et al. experimented with slippers made up of PEEK running against metal and ceramic coating. The wear value of the slipper is reduced to 38 % for the ceramic coating (stainless steel 32 μm, ZrO2 11.9 μm).

Influence of transient effects on the behaviour of translational hydraulic seals

In the FE-simulation hyperand viscoelastic material properties are taken into account in order to model the dynamic behaviour of the material at different frequencies and temperatures. The calculation is performed dynamic implicit. For a physically based calculation of the solid contact, the FE-model is coupled with Persson’s theory of rubber friction and contact mechanics /5/, /6/, /7/. For the numerical calculation of the fluid film and its influences on the seal deformation, the FE simulation is coupled with an implementation of the transient Reynold’s equation (1):

Validation of a thermo- and a hydromechanical model of a brake system for high-speed rail applications

This research deals with a numerical and experimental investigation of the vibratory frequency and the thermal response of a railway brake disc and pad under varying conditions. Railway brake systems play a vital role in passenger safety and comfort. The performance of disc brakes with regard to the dynamic effects like brake torque oscillations and brake judder depends on the contact properties and wear surfaces. Brake fading occurs due to accumulated frictional heat thereby reducing the stopping power. For an improved understanding of the complex processes of a brake system during long-term braking, a comprehensive numerical investigation is performed initially using the finite element software Abaqus for a thermomechanical and modal analysis. While the thermomechanical analysis based on the calculations of frictional heat is used to investigate the increase of temperature during braking, the contact pressure is a crucial parameter that influences the distribution of temperature both on the brake disc and on the pads. The modal analysis is used to investigate the frequency behaviour of the vibrations. Then, a simulation model of a self-energised electrohydraulic brake provides the results of brake force oscillations with regard to the observed topologies of the brake disc’s wear surface, which is measured at a full-scale test rig by an enlarged experimental set-up. In addition to the dynamic brake force, the set-up contains the online measurement of the side face run-out and the temperature of one side of a ventilated brake disc. By comparing the results of our experimental and numerical investigations, the simulation models are validated. Future research should focus on a thermomechanical analysis that considers heating, cooling, and the wear effects. A detailed implementation of the contact pressure distribution between the brake pads and disc can lead to a more precise prediction of brake torque oscillations. The achieved results can be used to improve riding comfort and resolve safety critical problems in high-speed trains.

Pressure Loss in Unsteady Annular Channel Flow

expression for the pressure loss is known, see e.g. IDELCHIK [1]. For unsteady laminar flow with a given temporal distribution of the flow rate, a reasonable first guess would be to take the instantaneous value ?̅?u(tt) and calculate the unsteady pressure loss based on this value. This method is referred to as the quasi steady approach and is a common practice not only for annular channels but for pipe flows in general. The quasi steady approach gives exact results for unsteady flows with relatively low frequencies. For highly dynamic flows like water hammer problems, the experiments conducted by HOLMBOE and ROULEAU [2] (performed with cylindrical pipes without an inner cylinder) could demonstrate that the quasi steady approach fails to predict the correct shape of the pressure transients, see Figure 2:

Transient simulation of a pneumatic sharp edged L-shaped pipe

To allow the occurrence of shocks and other discontinuities which, for instance, can be caused during the opening process of a valve it is necessary to use the conservative formulation of Eulerian Equations. If the time integration is done numerically and the computational domain is discretised (figure 1 a) the numerical scheme is given by Equation (7). Herein, i is the local index of a cell and n is the index of the current time step.

An energy efficiency evaluation method based on least squares combination weight in refrigeration system

Refrigerant [ammonia, R717 is refrigerant grade high purity ammonia (NH3). The product typically is 99.98% pure with minimal levels of moisture (<200 ppm) and other impurities (<5 ppm oil), making it ideal for use in all types of refrigeration systems] flows through the compressor firstly, which raises the pressure of ammonia. Subsequently, ammonia flows through the condenser, where it condenses from vapour form to liquid form, giving off heat in the process. After the condenser, it goes through the expansion valve, where it experiences a pressure drop. Finally, the ammonia goes to the evaporator. It draws heat from the evaporator which causes ammonia to vaporize. The evaporator draws heat from the region that is to be cooled. The vaporized ammonia goes back to the compressor to restart the cycle.

Development of a rotary pneumatic transformer

Most boosters offer the possibility to reduce the driving pressure in the driving chambers. Due to the force equilibrium at the piston the output pressure is decreased. As the air in the outer driving chambers is exhausted to the environment at the end of each cycle, a lower driving pressure in these chambers also increases the efficiency of the booster because less air is filled into the chamber. Standard double piston boosters emit a lot of noise due to the nearly undamped end stops of the piston. The efficiency of an exemplary piston booster is examined in chapter 4 of the paper.