International Journal of Hydromechatronics (7 papers in press)
Thermohydrodynamic lubrication model of a slipper in swashplate type axial piston machines--validation through experimental data
by Toshiharu Kazama
Abstract: 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 generalized 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^-1. The simulation showed good agreement with the experiment and the theoretical model was validated.
Keywords: tribology; fluid power systems; hydraulics; piston pumps and motors; slipper; hybrid bearings; thermohydrodynamic lubrication; simulation; experiment; validation.
EMPIRICAL MODELLING OF HYDRAULIC PUMPS AND MOTORS BASED UPON THE LATIN HYPERCUBE SAMPLING METHOD
by Paul Michael, Pawan Panwar
Abstract: 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.
Keywords: Latin Hypercube sampling; hydraulic pump testing; hydraulic motor testing; modelling.
Thermal performance difference of ideal gas model and van der Waals gas model in gas-loaded accumulator
by Shuce ZHANG, Hiromu Iwashita, Kazushi Sanada
Abstract: 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.
Keywords: Hydraulic; Gas-loaded accumulator; Thermal properties; Equation of state; van der Waals model; Gas pressure; Isothermal; Adiabatic; Energy; Control.
Design of Experiments and Progressively Sequenced Regression are Combined to Achieve Minimum Data Sample Size
by Jack Johnson
Abstract: The number of samples needed to create useful mathematical models becomes a growing issue as more manufacturers may choose to supplyrna mathematical model with each product. It is prohibitively expensive to test, for example, a hydraulic pump, to acquire scores or hundredsrnofsamples in the production line environment. The proposed testingmethodology consists of verifiable procedure for reducing the numberrnof samples needed to create useful models for hydraulic pumps. The method that has evolved consists of applying latin hypercubernexperiment design strategy(LHC Sampling) alongwitha newmethod which has been named Progressively SequencedRegressionAnalysisrn(PSR Analysis). The result is that the number of samples becomes, essentially, an independent variable, which the user has substantialrncontrol over. Also, the experiment is designed to produce optimized sampling using the proven LHC sampling algorithm, and then PSRrnAnalysis is used to verify the efficacy of the experiment as designed. Specific steps must be followed to prevent both false positives and/orrnfalse negatives, but no new technology is needed, only a new way to applywell-known tools. This paper presents the principles that guidernthe method, the procedures that are required, and shows empirical results using a typical variable displacement piston pump for the pumprnoutput flow model. It is a totally empirical paper and is presented as an introduction to a technique that has the potential for other uses.rnBecause of the newness of this method, this paper is written with a tutorial emphasis.
Keywords: Progressively Sequenced Regression; PSR Analysis; latin hypercube sampling; LHC Sampling; residual; residual analysis; information saturation; efficacious sampling; hyperspace; design of experiments; experiment design; catalyst regression function; convergence zone.
Reynolds stress statistics in the near nozzle region of coaxial swirling jets
by Viacheslav (Slava) Stetsyuk, John Chai
Abstract: Particle image velocimetry (PIV) was used to obtain the mean axial velocity , the mean radial velocity and the Reynolds stress statistics in an isothermal flow formed by discharging a central jet in an annular stream of swirling air flow. This is a typical geometry used in swirl-stabilised burners, where the central jet is the fuel. The flow Reynolds number was 29000, based on the area-averaged velocity of 8.46 m/s at the exit and the diameter of swirling co-flow of 50.8 mm. Three swirl numbers, S, of 0.3, 0.58, and 1.07 of the annular swirling stream were considered. The effects of the swirl number on the behaviours of the Reynolds stresses, and their gradients, which appear in the Reynolds-averaged Navier-Stokes (RANS) equations 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. 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.
Keywords: Reynolds stress; swirling jet; RANS; coaxial.
A Lumped Parameter Vane Pump Model for System Stability Analysis
by Ryan Jenkins, Monika Ivantysynova
Abstract: This paper presents a semi-empirical lumped parameter model developed for analysing the dynamic stability and performance limitations of a pressure compensated vane pump for an automotive application with low-cost components. The model calculates continuous displacement chamber pressure profiles and inertial effects for the determination of the internal forces acting on the vane pumps pivoting cam. Measurements conducted on a custom test stand were used to define a nonlinearly progressive bias spring model and a black-box representation of the pump control system valves. Analysis of the complete model reveals that the performance limitations imposed by the control system valves, in terms of system stability and achievable controller bandwidth, are more restrictive than the limitations imposed by the low-cost vane pump and limit the that bandwidth to 1.84Hz. The control system also imposes limitations to the system performance based on resonance phenomena which may be significant in some applications.
Keywords: pressure compensation; vane pumps; pivoting cam; internal forces; stability analysis; lumped parameter models; black-box models; resonant behaviour; progressive spring rate; nonlinear simulation models; experimental validation; automatic transmission.
Active Vibration Compensator on Moving Vessel by Hydraulic Parallel Mechanism
by Yutaka Tanaka
Abstract: 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.
Keywords: inverse kinematics; motion simulation; motion-stabilized platform; offshore wind power; offshore access; parallel mechanism; prototype scale model; six-degrees-of freedom; Stewart Platform; vibration compensator; work space.