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Testing full-scale mechanical systems, such as trawl systems (bottom and midwater) is connected with great economic costs, therefore, it is advisable to carry out the study of dynamic processes on the models in laboratories. The paper describes special features, advantages and weak points of units for physical modelling fishing gears and processes (testing sites, experimental tanks, water flumes, water channels), which use two different modelling principles: modelling straight motion of a fishing tool model (towing) in still fluid and modelling reversed motion when a static model is washed by the moving water. There have been given detailed specifications and capacities of a model basin under Kaliningrad State Technical University, which is an instrument for studying model fishing gears and processes (seine hauling, trawl hauling, purse seine setting, etc.), as well as of a hydraulic channel in Kaliningrad, which is one of the largest construction of such type in the world. It is noted that during investigation of dynamic processes it is necessary to follow the rules of dynamic similarity. These rules have been developed at the Department of industrial fishing in Kaliningrad State Technical University. There has been determined the base scale for setting the problem of dynamic similarity of a trawl system, substantiation of which is primary in the model developing and testing at a selected unit. There was given the formula for taking the only one and correct decision in determining the base scale. In terms of the determined value of the base scale, there are calculated all the other scales of dynamic similarity given in the table of general scales of physical characteristics of hydrodynamic, ground dynamic and tribological processes, which occur in the trawl systems under dynamic similarity.

STATEMENT OF THE PROBLEM OF DYNAMIC SIMILARITY OF THE TRAWL SYSTEM