Introduction Directory UMM :Data Elmu:jurnal:A:Aquacultural Engineering:Vol23.Issue1-3.Sept2000:

1. Introduction

This paper presents the results of computational fluid dynamics CFD simula- tions of the aerator driven circulation and sediment shear stress in an intensively aerated shrimp growout pond. Such physical processes strongly affect the biological productivity of a pond. Understanding and controlling these processes may help to mitigate some of the problems which plague the aquaculture industry: electrical power load; bank erosion; anoxic pond sediment conditions; wasteful feed-conver- sion; and high water exchange rates. CFD is the generic term for numerical schemes which account for the flow of mass and momentum throughout a fluid continuum. CFD has the advantage that it does not generally require calibration, because it is derived from universal equations which govern fluid flow. To the authors’ knowledge, CFD has not been applied in research on aquaculture ponds. The method has only recently been applied to wastewater treatment ponds. Wood et al. 1995 simulated water exchange through wastewater oxidation ponds using a commercially available CFD code. They first attempted to model the problem in two-dimensions for laminar flow, neglecting the effects of bottom friction. Wood et al. 1997 published results of simulations of three-dimensional water exchange through an effluent retention pond, using the standard k – o turbu- lence model. This simulation was validated with observations of hydraulic retention time in a real pond, using a tracer dye. The present paper introduces a methodology to build CFD simulations of aerator driven aquaculture ponds and interprets the effect of these machines on the banks and sediments. Methods and computer source code are detailed in the thesis by Peterson 1999a, which are referred to collectively as the automatic pond simulation methodology, AUTOPOND. The methodology works with the fluid dynamics analysis package, FIDAP, to build computer simulations of aerated ponds. The methodology is capable of simulating a wide variety of pond geometries and aerator specifications, given access to a high performance computer running FIDAP. Details of FIDAP were published by FDI 1993, 1995. Simulation results presented herein are interpreted in the context of the theory of Peterson 1999b, whereby water currents are assessed with regard to the underlying shear stress exerted in the particular pond of interest. The magnitude of the bottom shear stress is related to the sediment condition, and the pond bottom is classified into six zones on that basis. Results of simulations have been compared with the experimental data obtained by Peterson 2000 from an intensive shrimp aquacul- ture pond.

2. Mathematical model