One of the main causes of pipeline systems' failure are sharp changes and fluctuations in pressure caused by various reasons. Pressure stabilizer is a modern and effective mean for damping of wave processes. The constructive scheme of the device is a pipeline with uniformly distributed perforation through which liquid can flow from the pipeline into a damping add-on above the perforated part of it. The article discusses the pipeline scheme, in which occurs water hammer. It is investigated the problem of optimal perforation area under the assumed constant parameters of the stabilizer. It was used a numerical method of characteristics. Index Terms-pressure stabilizer, water hammer, pipelines, unsteady flow, incompressible liquid, method of characteristics.

The strength criterion is the strength condition for a small element of the construction’s material. Strength criterion is analytical interpretation in stress space the allowable boundaries of stress state, within these boundaries the material can work under these conditions without breaking. Since analytical interpretation of the experimental data may be performed in different ways, therefore many different strength criteria exist. Properly chosen strength criterion allows determining the moment when the material is destroyed while it is working under various tense conditions. Also it gives an opportunity to assess the limit state of stress in the most loaded points of the structure. This paper suggests new modifications of some well-known strength criteria which are more comfortable for practical use and can help to achieve more exact results.

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The article deals with the issues related to the modelling of unsteady fluid flow in short and long pipelines, including various equipment: pumping stations (equipped with cen-trifugal or piston pumps), valves of different operating principle, pressure stabilizers, etc. Pres-sure stabilizers (especially in short pipelines) are able to protect the pipeline from sudden pres-sure surges. This is important not only in terms of the strength of the pipeline system, but also in short pipeline circuits for a uniform flow of liquid fuel supply. As a mathematical tool for numerical solution of differential equations of quasi-hyperbolic type, the method of character-istics is applied, which allows to consider the problems that develop over time. The program is written in C++ with graphical interpretation in Maple.

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