On the effect of circulatory flow around objects in marine medium and atmosphere

Analytical expressions of the hydrodynamic reaction of a point dipole in two-layer circulatory fluid flow around it are obtained. The dependence of the wave resistance and the lift force on the flow velocity, the density jump, the circulation and the depth of the sea is investigated. It is shown that the influence of the velocity circulation leads to a change in the lift force acting on the dipole. Moreover, such changes are reversible in a relatively narrow range of the velocity of flow around the pipeline. Along with the pipeline, such features in the nature of the effect of circulation on the lift force can be manifested for self-propelled underwater objects and aerial vehicles.

Influence of Critical Flow Rates on Characteristics of Enforced and Shear Flows in Circular Convergent-Divergent Channels

Analysis of the reasons of critical flow rate occurrence in hydraulic tracts of cryogenic machines has been carried out. Theoretical expressions have been derived to calculate critical velocities in a boiling multiphase medium. Applied to hybrid fluid-film bearings with throttles for lubricant supply, a mathematical model has been developed to calculate pressure distribution and hydrodynamic reaction forces of a lubricant considering the influence of steam content and critical flows in throttle devices. Numerical results of phase state and load capacity calculations of a hybrid fluid-film bearing under lubricant’s critical flow rates condition have been presented.

Application of the IMO Maneuvering Criteria for Pod-Driven Ships

The fundamental objective of this paper is to make qualified assessment of the validity of the International Maritime Organization (IMO) maneuvering criteria "Resolution MSC.137(76)," when applied to pod-driven ships. The performance limits given by the criteria provide an adequate benchmark to compare all ships, regardless of propulsion type. However, the application of specific helm angle is less well defined as azimuthing pod drives, like any vectoring thrusters, can be turned to any helm angle, with no specific definition for the angle of maximum force. To address this problem, new methods for modeling the hydrodynamic reaction for both the ship hull and pod drive are identified. Then, a dedicated numerical tool is developed and simulation study conducted exploring systematic variation of applied helm angles with comparison of time-and frequency-domain responses. The study reaches the definitive conclusion that the criteria provides equivalent information about the maneuvering response of pod-driven ships as for conventionally propelled ships and can thus be applied directly.

HYDRODYNAMIC COEFFICIENTS AND FORCES ON MULTIHULLS IN SHALLOW WATER WITH CONSTANT OR VARIABLE DEPTH

Numerical and hydro dynamical procedures are developed to compute bidimensional hydrodynamic coefficients and forces on multihulls associated with harmonic oscillations in shallow water with constant or variable depth. The forces are composed of two parts and include the sum of incident and diffracted forces and hydrodynamic reaction. The latter one is used to determinate the hydrodynamic coefficients (added mass and damping). The numerical method used is the Boundary Element Method. We can compute flow around multihulls sections. An application to cylindrical, right triangular and rectangular hull forms is presented.

UNDULATED BOTTOM PROFILES AND ONSHORE-OFFSHORE TRANSPORT

Underwater bars, the characteristic features of oceans and lakes occur singly or in a series along the coast. Nearest bar to the shore, namely the break-point bar moves shoreward in summer, joins the coast and is replaced by another bar in its original place. The other seaward bars are storm bars, more or less permanent though they may shift slightly in orientation, position and shape depending upon the wave climate and state of the coastal processes. With the sediment and bottom profiles changing constantly with differing wave characteristics and beach exposure, a rigorous mathematical analysis for long range variability of profiles and therefore coastal processes in not possible. Therefore, the concept of medium depth and steepness characteristics is introduced to distinguish the profiles and their major dimensions. Onshore-offshore sediment motion is sometimes far in excess of longshore transport mostly confined in the breaker zone. When submarine bars are present, such motion is considerable mainly as a result of the hydrodynamic reaction between the rotating eddies generated over the bars and the bar surface. By means of dimensional analysis, it is possible to relate the quantity of onshore-offshore motion to the bar dimensions, wave period, water depth and transport direction by profile steepness characteristics. The above two concepts are then applied to the Nile Delta coastal processes with satisfactory results.