Dynamic Behavior of Sand Bed under Oscillating Water Pressure

Under the attack of storm waves, there are many destructions of coastal structures in the forms of sinking and sliding. These types of destructions will be in close relation to the dynamic behavior of sand bed around the structures. From this point of view, in this paper, we investigate the characteristics of the pore water pressure and effective stresses in the highly saturated sand bed under oscillating water pressure theoretically. The results indicate that the oscillating water pressure induce the notable drop of strength of sand bed around the structure under certain condition

Granular size segregation in underwater sand ripples

We report an experimental study of a binary sand bed under an oscillating water flow. The formation and evolution of ripples is observed. The appearance of a granular segregation is shown to strongly depend on the sand bed preparation. The initial wavelength of the mixture is measured. In the final steady state, a segregation in volume is observed instead of a segregation at the surface as reported before. The correlation between this phenomenon and the fluid flow is emphasised. Finally, different ``exotic'' patterns and their geophysical implications are presented.Comment: 8 page

Assessing Deep-Water Culture and Sand-Bed Aquaponics Systems for Lettuce (Lactuca sativa) Yield and Water Consumption

Agriculture and aquaculture play an important role in food security and water withdrawals. Agriculture and aquaculture contribute to over 70% of global water consumption. Aquaponics provides a solution for both sectors to reduce the combined water consumption and pollution and increase food production. The goal of the present study was to assess two aquaponics systems Deep-Water Culture (DWC) and Sand-Bed lettuce (Lactuca sativa variety capitata Type Batavia) production and water consumption. Each system contained a fish tank, plant bed, collection bed, three replicates per system and a mechanical filter; whereas, DWC contained an additional biological filter after the mechanical filter. The main differences assumed between DWC and Sand-Bed are Sand-Bed uses less water and does not require biological filter as sand media acts like a biological filter. Both systems had similar nitrate and ammonium concentration over 35 days period. PH, temperature, EC, SAR and DO in both systems remained within acceptable ranges compared to literature. Sand-Bed nitrifying bacteria counts were also higher than DWC\u27s bacteria by end of study period. Results showed that the lettuce root length in DWC were nearly two-fold the root length in Sand-Bed which provides larger surface area for nutrients uptake and enhance nitrification rate by bacteria. Calcium, phosphorous, zinc, copper, magnesium and boron concentrations in lettuce samples harvested form the DWC were nearly two-times the concentrations in lettuce samples growing in Sand- Bed. The DWC Lettuce yields per m2 were 27% higher than the Sand-Bed system\u27s lettuce of 1.42 kg/m2 in DWC and 1.04 kg/m2 in Sand-Bed system. However, the daily water consumption in DWC system was higher than Sand-Bed system. Overall, DWC system performed better by producing higher lettuce yield with higher nutritional content while consuming more water compared to Sand bed system. Therefore, the Sand-Bed system requires further research to reach productive yields like the DWC system and benefit from its reduced water consumption and the potential of growing larger variety of crops

Dynamics of a slowly-varying sand bed in a circular pipe

The long wave-length dynamics and stability of a bed of sand occupying the lower segment of a circular pipe are studied analytically up to first-order in the small parameter characterizing the slope of the bed. The bed is assumed to be at rest, with at most a thin sand layer (the bedload) moving at the sheared interface. When the sand bed is plane, with depth independent of position z along the axis of the pipe, the velocity of the liquid is known from previous studies of stratified laminar flow of two Newtonian liquids (the lower one with infinite viscosity representing the sand bed). When the depth of the sand bed varies with z, secondary flows develop in the cross-sectional (x, y) plane, and these are computed numerically, assuming that the sand bed remains a straight horizontal line in the cross-sectional plane. The mean shear stress acting on the perturbed sand bed is then determined both from the computed secondary flows and by means of the averaged equations of Luchini and Charru. The latter approach requires knowledge only of the flow over the unperturbed, flat sand bed, combined with an accurate approximation of the distribution of the perturbed stresses between the pipe wall and the sand bed. The perturbed stresses determined by the two methods agree well with each other. Using these stresses, it is then possible to apply standard theories of bed stability to determine the balance between the destabilizing effect of inertial (out-of-phase) stresses and the stabilizing effects of gravity and relaxation of the particle flux, and various examples are considered

Dynamic Behavior of Sand Bed around Structure under Wave Motion

Under the attack of storm waves, there are many destructions of coastal structures due to scouring, sinking and sliding. These types of destructions are considered to be in close relation to the dynamic behavior of sand bed around the structures. In this study the characteristics of pore water pressure and stresses in the sand bed around a breakwater under the attack of superposed waves are treated theoretically. The results show that during the crest or the trough being in front of the structure the strength of sand bed around the structure decreases notably and the unstable zone will occur

FILTRATION: EFFECT OF SAND PARTICLES ARRANGEMENT ON WATER QUALITY

Water filtration is aprocess for separating suspended or colloidal impurities from water by passage through aporous medium, usually aband of sand or others. Water fills the pores (open spaces) between the sand particles and the impurities are left behind either clogged in the open spaces or attached to the sand itself. It is well known that the arrangement ofthe sand bed determines the quality ofthe water filtered. In this research, the equipment use is the Filterability Index Unit (FIU). Different types of sand bed arrangement with various sand particles sizes will be used to remove impurities or suspended solids. The first experiment using paddy field sample water and the second experiment using UTP River sample water. In general, the main objective of this experiment is to propose the best sand bed arrangement for water filtration process. During the filtration, the data for volumetric and the flowrate is taken into account in order to calculate its specific cake filter resistance and filter medium resistance. The filtrate is tested for its quality measurement. From the result obtained, the first sand bed arrangement (larger particles to small particles, from top to bottom) is proposed as the best sand bed arrangement for sand filtration due to the lowest COD and smallest specific filtercakeresistance

Pore Water Pressure in Sand Bed under Oscillating Water Pressure

In this paper the theoretical method to analyse the pore water pressures in the sand bed under the oscillating water pressure is developed. In the former researchs the validity of the theoretical treatment for the one-dimensional problem has been verified. However, the one-dimensional treatment is not sufficient to obtain the precise informations concerning the many practical problems. From this point of view, in this study, we derive the fundamental equations for the general three-dimensional sand layer under the oscillating water pressure. The validity of this theoretical method is verified by experiments for the twodimensional problems

A Multiphase First Order Model for Non-Equilibrium Sand Erosion, Transport and Sedimentation

Three phenomena are involved in sand movement: erosion, wind transport, and sedimentation. This paper presents a comprehensive easy-to-use multiphase model that include all three aspects with a particular attention to situations in which erosion due to wind shear and sedimentation due to gravity are not in equilibrium. The interest is related to the fact that these are the situations leading to a change of profile of the sand bed