STATEMENT OF THE PROBLEM OF DYNAMIC SIMILARITY OF THE TRAWL SYSTEM

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.

Second-Order Reversed Phi

A second-order reversed-phi stimulus is composed of moving features (areas filled with texture) whose overall amount of texture-contrast is reversed between successive frames. In peripheral vision, the stimulus is perceived as moving in the reversed direction (opposite to the feature displacement). In central vision, it is perceived in the forward direction at low temporal frequencies but in the reversed direction at high temporal frequencies. Moving the observer away from the displays has the same effect as changing from central to periphery vision: reversed motion becomes more dominant. The illusion demonstrates the different properties of the second- and third-order motion systems.

Multi-branching three-dimensional flow with substantial changes in vessel shapes

This theoretical investigation of steady fluid flow through a rigid three-dimensional branching geometry is motivated by applications to haemodynamics in the brain especially, while the flow through a tube with a blockage or through a collapsed tube provides another motivation with a biomedical background. Three-dimensional motion without symmetry is addressed through one mother vessel to two or several daughters. A comparatively long axial length scale of the geometry leads to a longitudinal vortex system providing a slender-flow model for the complete mother-and-daughters flow response. Computational studies and subsequent analysis, along with comparisons, are presented. The relative flow rate varies in terms of an effective Reynolds number dependence, allowing a wide range of flow rates to be examined theoretically; also any rigid cross-sectional shape and ratio of cross-sectional area expansion or contraction from the mother vessel to the daughters can be accommodated in principle in both the computations and the analysis. Swirl production with substantial crossflows is found. The analysis shows that close to any carina (the ridge separating daughter vessels) or carinas at a branch junction either forward or reversed motion can be observed locally at the saddle point even though the bulk of the motion is driven forward into the daughters. The local forward or reversed motion is controlled, however, by global properties of the geometry and incident conditions, a feature which applies to any of the flow rates examined.

Reversed Visual Motion and Self-Sustaining Eye Oscillations

A random-dot field undergoing counterphase flicker paradoxically appears to move in the same direction as head and eye movements, ie opposite to the optic-flow field. The effect is robust and occurs over a wide range of flicker rates and pixel sizes. The phenomenon can be explained by reversed phi motion caused by apparent pixel movement between successive retinal images. The reversed motion provides a positive feedback control of the display, whereas under normal conditions retinal signals provide a negative feedback. This altered polarity invokes self-sustaining eye movements akin to involuntary optokinetic nystagmus.