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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
16.06.2005, Faculty of Mechanical Engineering
Candidate:
mr. sc. Nedim Hodžić
Mentor:
prof. dr. Nermina Zaimović-Uzunović

Thesis title:

Numerical Analysis of Oil Flow Process through Distribution Elements in Hydraulic Systems

Summary:
One of the most important hydraulic distribution elements is a distribution valve which belongs to a group of steering and regulating components of a hydraulic system. In classical hydraulics, the main function of distribution valve is to direct fluids in a certain course and direction, whereas in proportional and servo hydraulics, this valve, apart from its aforementioned basic function, affects both kinematic characteristics and pressure features. In oil hydraulic systems for steering and regulation of oil flow or pressure level, different distribution valve designs are used. One of the most frequently used valves is a spool valve because a vast number of different shapes of a valve body and movable pistons within it allows different effects on the flow of oil in the system as well as different pressure levels, which results in a better quality of steering in hydraulic system performance as a whole.
In classical hydraulics, the task of distribution valve is to stop or enable the oil flow in certain course and direction. The loss of energy occurring within a valve should be minimal. If the distribution valve is designed as a proportional or servo valve, a continuous displacement of a piston can be obtained, so that a flow cross-section is gradually changed. Thus, characteristics of oil flow and change of pressure in hydraulic system is affected, which in turn influence the work of a machine or a plant in which a hydraulic system is built. In addition, these valves facilitate the connection between electronic components and hydraulic flow, which closes the course of automatization and steering of a certain process. Building in the hydraulic oil systems with classical, proportional and servo hydraulic valves is very common and important in industrial processes, so that the distribution valves are a subject of many expertized and scientific investigations.
This thesis presents an application of numerical analysis, based on finite volume method (FVM), within an analysis of hydraulic oil flow through the channels and chambers of a spool valve. It is for the first time that the finite volume method is applied in simulation and analysis of stationary and non-stationary flow of hydraulic oil on a 3D model of channels and chambers in a spool valve.
The applied mathematical model is based on basic equations of fluid mechanics defined in an integral form. Equations related to maintenance of mass, movement quantity, energy and space, which define the mathematical model, are closed by corresponding constitutive relations. The basic equations are discretized and transformed into subsystems of non-linear algebraic equations in which unknown variables such as velocity components, pressure, temperature, turbulence kinetic energy and velocity of its dissipation are present. Due to non-linearity these subsystems of equations were solved by iterative method based on an algorithm of separate equation solving. A particular attention was paid to defining boundary conditions.
Verification of possibilities for application of numerical analysis, based on finite volume method, for analysis of stationary and non-stationary hydraulic oil flow through 3D model of channels and chambers in a spool valve was performed by comparing results of numerical calculation with results achieved by experiments, analytical calculation and by application of some other methods. Besides, the verification of the method was carried out by simulating hydraulic oil flow through channels and chambers of the both alternate irreversible valve and irreversible valve, which is, considering the aim of the investigation, only partially presented in the thesis. A good concord of results has been found between the results of numerical simulation and the ones achieved by other methods, which proves the applicability of finite volume method to analysis of fluid flow through channels and chambers of spool valve on the 3D model.

Key words :
Numerical analysis, numerical simulation, finite volume method, spool valve, hydraulic oil


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