Toshiharu Kazama

A thermohydrodynamic lubrication (THL) model of hybrid (hydrostatic and hydrodynamic) thrust bearings, which is applicable to slippers of swashplate type axial piston pumps and motors, was validated by experimental results. The model consisted fundamentally of the generalised Reynolds equation, three-dimensional energy equation, and the heat conduction equation. The numerical calculation was performed in fluid film lubrication under the experimental conditions and the solutions were compared with the data. Reverse flow and oil mixing were considered in solving the energy equation. The comparison of the temperature distributions and centre clearances was made at supply pressures up to 35 MPa and rotational speeds up to 26.7 s<SUP align="right">−1</SUP>. The simulation showed good agreement with the experiment and the theoretical model was validated.]]>

Pawan Panwar; Paul Michael

The effectiveness of orthogonal and Latin hypercube (LHS) experimental design strategies was compared in axial piston pump and radial piston motor testing. Stratified sampling via LHS was used to create test plans of varying sample size. Pump flow and motor torque-loss models were derived from the experimental results based on a comprehensive list of physically significant terms. The effectiveness of the sampling plans was evaluated by tracking the evolution of model errors using progressively sequenced regression. Progressively sequenced regression identified the minimum sample size required to achieve data saturation by incrementally increasing the number of data points included in the regression analysis. It was found that LHS produced higher fidelity models but reached data saturation no sooner than the orthogonal method. These results demonstrate the merit of combining LHS with progressively sequenced regression to improve empirical model fidelity and determine minimum sample-size requirements in hydraulic pump and motor testing.]]>

Shuce Zhang; Hiromu Iwashita; Kazushi Sanada

Real gas that considering intermolecular force and molecular volume shows difference compared with the assumption as ideal. While designing accumulator or quantitatively evaluating working state of accumulator in hydraulic circuit, charged in gas-loaded accumulator, the gas properties involves pressure, temperature and stored energy are assumed by the first law of thermodynamics and gas equation of state. The discrepancy of thermodynamic behaviours of real gas from ideal gas should be highlighted. In this paper, the well-known van der Waals equation was employed as real gas model to compare with ideal gas model. The gas behaviours have shown different trends during compression and expansion by mathematically analysis and being confirmed in both isothermal and adiabatic operations. A detailed pressure deviation between ideal gas model and van der Waals model was displayed.]]>

Jack L. Johnson

The number of samples needed to create mathematical models is an issue as manufacturers see benefits to customers. Testing to acquire scores or hundreds of samples in a production environment is costly. This paper explains a method for verifying minimum sample size. Latin hypercube experiment design strategy (LHC sampling) is used along with a new method, progressively sequenced regression (PSR) analysis. The number of samples becomes, essentially, an independent variable, which the user has control over. PSR analysis provides efficacy verification. Specific steps must be followed to prevent false positives and negatives, but no new technology is used. This paper presents the principles, the procedures that are required, and shows empirical flow model results using a typical variable displacement piston pump. It is an empirical paper and is presented as an introduction to a technique that has the potential for other uses.]]>

Viacheslav Stetsyuk; John Chai Chee Kiong

Particle image velocimetry was used to obtain the mean axial <span style="text-decoration: overline"><i>u</i></span> and radial <span style="text-decoration: overline"><i>v</i></span> velocities and the Reynolds stress statistics ‹<i>u'<SUB align="right">iu'<SUB align="right">j</i>› in an isothermal swirling jet. The flow Reynolds number was 29,000. The effects of the swirl number on the behaviours of the Reynolds stresses, and their gradients are analysed. The results show pronounced asymmetry in the mean and the fluctuating quantities for all swirl numbers. The flow asymmetricity is found to be related to the radial velocity fluctuations. The ratio of <span style="text-decoration: overline"><i>u'</i></span><SUP align="right">2</SUP>√<span style="text-decoration: overline"><i>v'</i></span><SUP align="right">2</SUP> was found to be circa 0.5 and was independent of the flow swirl number. The values of <span style="text-decoration: overline"><i>u'v'</i></span> were circa 5%-10% of <span style="text-decoration: overline"><i>v'</i></span><SUP align="right">2</SUP>. It was postulated that for swirling flows with constant Reynolds number the change in the flow swirl number only, does not necessary result in increase of turbulent intensity. An 'effective' turbulent viscosity was shown to be independent of the flow swirl number for constant Reynolds number.]]>

Yutaka Tanaka

In the field of marine construction, traffic ships are used to board the floating structures. However, the position of a traffic ship can be fluctuated because of tidal waves, and workers face the risk of an accident such as falling into the water or a collision with the vessel. Due to such potential hazards, we focus our attention on the safety and workability of such ship fluctuations. In this study, an active vibration compensator with a Stewart platform has been proposed and developed. The platform is supported on the main hull by means of a six-degrees-of-freedom hydraulic parallel mechanism that absorbs the motion of the main hull in accordance with the control signal from an on-board computer and motion sensors. Results of the simulation models confirm the design of the motion range that is required for the actual active vibration compensation system. Trial results depict that 66%-84% of the heave, roll, and pitch motion of the main hull is absorbed.]]>