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Dynamic analysis of hydraulic systems - Introduction


The dynamic analysis is the important stage at designing of hydraulic drives and transmissions of various machines and mechanisms (cars, self-propelled chassis, tractors, cranes, tractors, loaders, excavators, scrapers, machine tools, hydraulic stands, etc.) and allows to simulate long before creation of a pre-production model working processes and to obtain necessary data about dynamic properties of hydraulic system and features of passing of working processes, to pay attention to presence of weak places in hydraulic system, and before carrying out of tests to carry out optimization of the design decision on a basis of results of mathematical simulation and the alternative analysis.

Mathematical simulation of various modern technical systems of the certain class (mechanical, hydraulic, electric, etc.) is connected with construction of the models providing the formalized description of any such system of arbitrary structure.

For construction of formal dynamic model of hydraulic system as a whole the method based on representation of system in the form of finite element-node structure is used. In a basis of such approach the idea of a method of finite elements lays when the complex system on a configuration can be divided conditionally into separate functional elements which mathematical description is known and for which within the limits of considered system it is possible to define unequivocally conditions of communications of these elements with each other ( input – output ). Then for the description of system as a whole it is enough to specify a name ( identifier of type) of element , to number its nodes on an input and an output , to give necessary physical, geometrical and design data (constants) and to write down the equations, transforming variables on an input of an element in variables on an output.

As such base elements in hydraulic systems can be: pump , hydraulic motor , hydraulic cylinder , direct action valve , indirect action valve , local resistance ( throttle ), pipeline (including, deadlock site of pipeline or cavity ), tee ( divider or adder of flows ), power regulator , hydro pneumatic or spring accumulator , directional control valve , pilot operated check valve , diesel engine with centrifugal regulator , wheel carrier , linear dynamic links of automatic control systems (ACS).

Then the structure of any hydraulic circuit can be described by means of identification of elements, numbering of nodes (points of connection of elements in the circuit by a principle input – output ) and forming on a basis of it matrices of communications describing the circuit structure (topology). Thus, for simulation of dynamic processes in hydraulic systems of arbitrary structure the following things are necessary:

– algorithm of the structural description of arbitrary hydraulic circuits;

– library of base hydraulic elements and their mathematical models;

– ordering of input data, and a way of their forming and preparation;

– algorithm of automatic forming of system of equations describing the hydraulic circuit of arbitrary structure as a whole;

– method of solving of the generated system of equations;

– program realization of dynamic calculation of any hydraulic circuits;

– way of representation and analysis of the received results.

The program analyzes the input information and depending on set of elements and structures of the investigated hydraulic circuit chooses from library of base hydraulic elements and their mathematical models the necessary equations, forming the general mathematical model of hydraulic system and solving it at the given external influences.

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