Visualization study of the flow processes and phenomena in the external gear pump

The article describes the flow rates of mineral oil and water flowing, as working media, through the commutation unit of a hydraulic satellite motor. It is demonstrated that geometrical dimensions of commutation unit clearances change as a function of the machine shaft rotation angle. Methods for measuring the rate of this flow and the pressure in the working chamber are presented. The results of pressure measurements in the working chamber during the transition from the filling cycle to the emptying cycle are included. The pressure in the motor’s working chamber changes linearly as a function of the shaft rotation angle, which has a significant effect on the leakage in the commutation unit clearances. The paper presents new mathematical formulas in the form: Q=f(Δpγ ) to calculate the flow rate of water and mineral oil in the commutation unit clearances. The γ factor is described as a function of fluid viscosity and clearance length (the motor shaft rotation angle). The coefficients used in these formulas were determined based on the results of laboratory tests of a motor supplied with water and mineral oil.

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Influence of water and mineral oil on the leaks in satellite motor commutation unit clearances

In this paper mechanical losses in a positive displacement pump supplied with water and mineral oil (two liquids having significantly different viscosity and lubricating properties) are described and compared. The experimental tests were conducted by using a prototype satellite pump of a special design. The design of the satellite pump is presented in the article. The pump features and a non-circular tooth working mechanism was developed to work with both water and mineral oil. The sources of mechanical losses in such pump are also characterized in this paper. On this basis, a mathematical model of the losses has been developed and presented. The results of the calculation of mechanical losses according to the model are compared with the results of the experiment. The experimental studies have shown that the mechanical losses in the water pump are even 2.8 times greater than those in the oil pump. It has been demonstrated that the mathematical model well describes the mechanical losses both in the water pump and the oil pump. It has been found that the results from the loaded pump simulation (at Δp=25MPa) differ from the results of the experiment by no more than 5% both for oil and water.

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The Influence of Water and Mineral Oil On Mechanical Losses in the Displacement Pump for Offshore and Marine Applications

In this article, the second method of determination of the theoretical and actual working volume of a hydraulic motor is described. The proposed new method is based on the characteristics of effective absorbency of the motor. The effective absorbency has been defined as the ratio of flow rate in a motor to the rotational speed of the motor’s shaft. It has been shown that the effective absorbency is a nonlinear function of the rotational speed and nonlinear function of the pressure drop in the motor’s working chambers. Furthermore, it has been proven that the actual working volume of a motor is a function of a third degree of pressure drop in the motor’s working chamber. The actual working volume should be taken to assess the mechanical and volumetric energy losses in the motor. Furthermore, the influence of the flowmeter location in the measurement system and the compressibility of liquid on the result of the theoretical and actual working volume calculation was also taken into account and is described in this article. The differences in the assessment of the volumetric efficiency assuming the theoretical and actual working volume was also shown.

Determination of the Theoretical and Actual Working Volume of a Hydraulic Motor—Part II (The Method Based on the Characteristics of Effective Absorbency of the Motor)

It is widely accepted that vortex-induced vibration (VIV) is a major concern in the design of deep sea top-tensioned risers, especially when the riser is subjected to axial parametric excitations. An improved time domain prediction model was proposed in this paper. The prediction model was based on classical van der Pol wake oscillator models, and the impacts of the riser in-line vibration and vessel heave motion were considered. The finite element, Newmark-β and Newton‒Raphson methods were adopted to solve the coupled nonlinear partial differential equations. The entire numerical solution process was realised by a self-developed program based on MATLAB. Comparisons between the numerical calculation and the published experimental test were conducted in this paper. The in-line and cross-flow VIV responses of a real size top-tensioned riser in linear sheared flow were analysed. The effects of the vessel heave amplitude and frequency on the riser VIV were also studied. The results show that the vibration displacements of the riser are larger than the case without vessel heave motion. The vibration modes and frequencies of the riser are also changed due to the vessel heave motion.

Prediction of Vortex-Induced Vibration Response of Deep Sea Top-Tensioned Riser in Sheared Flow Considering Parametric Excitations

The paper presents the results of numerical calculations of stress distributions in the gear micropump body for applications in hydraulic systems, especially in the marine sector. The scope of the study was to determine the most favorable position of bushings and pumping unit in the gear pump body in terms of stress and displacement distribution in the pump housing. Fourteen cases of gear pump bushings and pumping unit locations were analyzed: starting from the symmetrical position relative to the central axis of the pump, up to a position shifted by 2.6 mm towards the suction channel of the pump. The analysis of the obtained calculation results has shown that the most favorable conditions for pump operation are met when the bushings are shifted by 2.2 mm towards the suction channel. In this case the maximal stress was equal to 109 MPa, while the highest displacement was about 15μm. Strength and stiffness criteria in the modernized pump body were satisfied.

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The influence of gear micropump body asymmetry on stress distribution

The results of verification performed on the numerical models of liquid flow in the chambers of a hydraulic cylinder, as reported in this paper, constitute a part of a larger research and development project carried out by the Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, in cooperation with WM Engineering S.A. The project involved designing an innovative experimental set-up for testing hydraulic cylinders. The new test stand significantly improved the research potential of Research and Development Center of PONAR Wadowice S.A. – a company which cooperates with the above mentioned project leaders. The original test program and the new test equipment allowed the verification of the accuracy of the numerical model which was generated in the Ansys CFX environment and which describes the process of mixing fluid from two different domains, having different initial temperatures, during the operation of the cylinder. The data obtained during the tests confirmed that it is reasonable to modify the cylinder supply system in accordance with the patent application filed by Wroclaw University of Science and Technology. This paper presents sample results of both actual tests and computational simulations performed on the analyzed phenomenon of liquid exchange in the piston chamber of the hydraulic cylinder. It also describes the proposed method for the comparative analysis of the results. The obtained results fully confirm that research in this area was justified and provide a basis for further research, development and deployment works on the design of hydraulic cylinders and their power supply systems.

Modeling of Liquid Exchange Process in a Hydraulic Cylinder Chamber in the Aspect of Power System Design

The amount of energy losses in hydraulic systems, determined directly by the efficiency parameter, becomes one of the basic aspects related to the design of these systems. Recently, reducing the energy consumption of hydraulic drives has become one of the most important factors in, and sometimes even the main reason for, development works focused on hydrostatic drive systems in newly designed and already deployed types of machines. The article presents an approach to improve the efficiency of such a hydraulic system based on the analytical model and also includes a case study of redesigning a hydrostatic drive system in a stationary rock breaking machine. The analysis of the calculation results showed benefits resulting from two different concepts of modifying hydraulic systems with an aim at reducing their energy consumption.

Improving the efficiency of a rock breaker hydraulic working system by changing the structure of the hydraulic system

The analysis of problems occurring in work machines operated in particularly difficult conditions is an irreplaceable source of knowledge about the degradation processes of their individual components or entire systems. The article presents a part of the results of research and development works carried out at the Faculty of Mechanical Engineering of Wrocław University of Science and Technology in the area of identification, analysis and development of new solutions for hydraulic cylinders. The basis for undertaking the work was the analysis of operational problems occurring in the machines operated in Polish underground mines of KGHM Polska Miedź S.A. The environment of machines operation in underground mines is usually characterized by a high ambient temperature, which is the result of the impact of a rock mass temperature and a difficult process of air exchange. At high ambient temperatures in machines equipped with hydrostatic systems, a significant phenomenon of accelerated degradation of hydraulic cylinders may be observed. The results of the analysis of this issue made it possible to develop a new technical solution for hydraulic cylinders. The research and development work of a new solution is being carried out in a very wide range of problems, and one of them is the analysis of the influence of the angular position of the nozzles on the obtained degree of liquid exchange in the cylinder chambers. The results of the conducted research in this area together with the discussion are contained in this article and are in the opinion of the authors an important stage in the process of designing and implementing the new cylinder solution.

Numerical simulations of the liquid exchange process in a chamber of a new hydraulic cylinder solution in the aspect of the angular nozzle arrangement

A pressure pulsation phenomenon in positive displacement machinery and resulting from that noise and vibration problems are well-known and still unsolved issues. The article concerns modeling pressure pulsation dampers used for fluid machinery, in particular in gas systems. The currently used mathematical models based on the plane wave theory are verified in the special laboratory conditions with no flow and no wave reflections at the system outlet. The use of a compressor as an excitation source significantly influences the characteristics of a damper installed in a system. In this study, a measurement of common type dampers transmission loss characteristics with the use of pressure transducers is proposed. The article discusses the influence of boundary conditions in analytical models based on the plane wave theory on the accuracy of dampers characteristics. Basing on the measurements results some improvements in the analytical model are proposed.

Urszula Warzyńska

Papers

The influence of gear micropump body asymmetry on stress distribution

Modeling of Liquid Exchange Process in a Hydraulic Cylinder Chamber in the Aspect of Power System Design

Improving the efficiency of a rock breaker hydraulic working system by changing the structure of the hydraulic system

Numerical simulations of the liquid exchange process in a chamber of a new hydraulic cylinder solution in the aspect of the angular nozzle arrangement

Influence of Boundary Conditions on the Accuracy of Pulsation Dampers Characteristics in Analytical Models