Numerical estimation of shallow water effect on multipurpose amphibious vehicle resistance

This research paper investigated the hydrodynamic resistance of Multipurpose Amphibious Vehicles (MAV) due to navigate in low water depth numerically. This type of vehicle and other coastal floating vehicles encounter the problem of a small under keel clearance with river bed. The proper estimation of ship resistance and squat is influence largely on the power calculation in the design stage. The present work describes the effect of shallow water on the Multipurpose Amphibious Vehicles (MAV) resistance at different speed using Computational Fluid Dynamics (CFD) techniques. A comparison in the drag on the hull is illustrated between depth restriction and infinite depth water. This paper provides a wide introduction into the problems of modelling of the restricted water depth effects on the ship behaviour, specifically hydrodynamic resistance and squat using CFD which is applied by ANSYS-CFX14.0.

Recent foraminifera from inter-reef channels, nearshore North Rarotonga, Cook Islands, South Pacific

The Avatiu and Avarua sand-covered channels within the fringing reef of north Rarotonga, Cook Islands, contain foraminiferal assemblages considered to be predominantly derived from the adjacent reef platform. Benthonic species which display a depth restriction include Melonis affinis, Cassidulina delicata, Clavulina pacifica and Bolivina alata. Small (less than 200 μm), rare planktonic species, including Globigerina bulloides, are recovered from sediments as shallow as 8 m, but an increase in species diversity and abundance is noted at 30 m in Avarua channel and 48 m in Avatiu channel.No clear depth, substrate nor symbiont-associated restriction of species is evident, and this may result from mixing of primary microfaunal assemblages by sediment transport in this exposed part of the island.

The Photic Environment of a Salmontd Nursery Lake

The spectral characteristics of Lake Cowichan (Vancouver Island) were examined using a LiCor underwater spectroradiometer. The results were analyzed in terms of salmonid vision with special emphasis placed on the ultraviolet part of the spectrum. Irradiance measurements were taken by SCUBA divers every 3 m from 18m to the surface at each of seven locations. The measurements at each depth consisted of four scans from 300 to 850 nm of downwelling, upwelling and horizontal light in the sun and antisun directions. The study covered different times of day and variable atmospheric conditions. According to predictions from the absorptive properties of water molecules and scattering by these and suspended particulates, it was found that the ultraviolet part of the spectrum was the least transmitted. The light field varied in intensity and dominant wavelengths depending on direction and time of day. The relative proportion of ultraviolet, short and middle wavelengths with respect to the entire spectrum peaked during crepuscular periods; the opposite was true for long wavelengths. An analysis of the irradiance values with respect to salmonid vision showed that there was enough light to stimulate all the photoreceptor mechanisms found in juvenile salmonid retinae (sensitive to ultraviolet, short, middle and long wavelengths) at all depths studied. Nevertheless, 18 m was found to be the limiting depth for stimulation of the ultraviolet cone mechanism, which is required for perception of ultraviolet polarized light. This depth restriction may be linked to the observed salmonid movements close to the surface during crepuscular periods.