For farmed fish, the breeding pond is its most important living space, is its "home" for the whole life process, so what kind of "home" to build is the fish love and suitable for actual production? Fish prefer to move in areas where the flow rate is more comfortable, and the flow rate in the area is too low or too fast, which is not conducive to their growth. However, in the current culture ponds, there are very few comfortable areas that are preferred by the fish, which leads to the aggregation and crowding of fish in a small vantage space, which greatly limits the range of fish movement. How to make the water flow rate in the aquaculture pond more uniform, and how to make the activity range of the farmed fish larger through simple and efficient tank type modification, are scientific problems worthy of research and optimization.
A common type of pond where flaws and yogs are seen - square breeding ponds
The square culture pond has the advantage of relatively high space utilization. However, due to the restriction of the geometry of the pool wall, the water flow will turn sharply at right angles and collide with the pool wall, resulting in a large energy loss, and the remaining energy in the pool is difficult to maintain the rotational motion of the water body at a higher velocity, resulting in the increase of the low flow velocity area in the pool. In addition, poor hydraulic mixing conditions lead to the generation of "dead zones", which makes it difficult to remove solid waste in time, which increases the oxygen consumption in the pond, which in turn leads to uneven distribution of fish and deterioration of fish quality.
Square breeding ponds.
A common type of pond where flaws and yogs are seen - circular ponds
Due to the uniform water quality and stable flow pattern of the circular culture pond, it can provide relatively good hydrodynamic conditions for the farmed fish, and the higher flow rate in the pond can also make the solid waste quickly move out of the culture tank and achieve self-cleaning. However, compared with the square pond, the circular pond has the obvious defect of low space utilization, which affects the cost and economic benefit of aquaculture.
Circular breeding ponds.
Complement each other's strengths and weaknesses of the pool type change - square arc angle breeding pond
In order to improve the flow field characteristics in the breeding pond under the premise of maintaining the space utilization rate as much as possible, the square arc angle breeding pond came into being. By changing the geometric structure of the breeding pond, the arc angle is used instead of the right angle of the square aquaculture pond, and the flow field is optimized by the combination of the arc angle and the straight edge of the pond wall, so as to realize the effective combination of the advantages of the square and circular aquaculture ponds, and provide better aquaculture equipment for the circulating aquaculture industry.
Square arc angle breeding pond.
Determination of the optimal arc width ratio
To design a square arc angle culture tank, a key problem needs to be solved - the value range of the optimal arc width ratio (r b, r is the radius of the arc angle, b is the length of the pond wall).
Schematic diagram of pool type optimization.
In this study, a three-dimensional numerical calculation model was established by computational fluid dynamics (CFD) to analyze the influence of the relative arc width ratio on the flow field characteristics of the two-channel aquaculture pond under the condition of different underflow diversion ratios, and the flow field performance of different volumes of the aquaculture pond under the same water exchange rate was compared by correcting the average velocity in the aquaculture pond, and the uniformity coefficient UC50 was used to quantitatively evaluate R B Effect on the uniformity of the flow field in the cell.
Model buildingAverage speed
From the perspective of improving the efficiency of aquaculture, reducing input and increasing income are the top priorities for the sustainable development of aquaculture. Therefore, achieving a higher velocity in the pond with a lower energy cost is a key issue in the hydrodynamic study of the pond. 
The change trend of the correction speed with the relative arc width ratio, the average speed in the breeding pond showed a trend of first increasing greatly and then basically stable with the increase of r b. 0.2≤r/b＜0.4 square arc angle culture ponds maintain a high average speed. where r b=02 square arc angle culture pond and circular culture pond (r b=0.).5) Only 6% 11% reduction compared to the average speed and 42% 49% increase compared to the square tank (r b=0).
It follows from this that 02≤r/b＜0.The average velocity in the square arc angle breeding pond of 4 has a small change compared with the circular breeding pond, and the increase is larger than that of the square breeding pond, which realizes the "low energy and high speed" of breeding demand.
Uniformity factor
Improving the uniformity of the flow field is the primary problem to improve the effective utilization rate of aquaculture water space. In order to quantitatively evaluate the uniformity of the flow field in the breeding pond, the uniformity coefficient UC50 was used as the discriminant parameter to evaluate the influence of the relative arc width ratio on the uniformity of the flow field in the dual-channel breeding pond. The closer UC50 is to 1, the closer the average value of the low flow rate area and the high flow rate area is, and the better the overall flow field uniformity in the breeding tank.
The trend of uniformity coefficient with the relative arc width ratio.
The uniformity of the flow field in the breeding pond was affected by R b, and showed a trend of first increasing and then decreasing. When r b=02. At 2, the uniformity of the flow field of the square arc angle breeding pond was significantly improved due to the existence of the arc angle, and its UC50 was increased by 40% and 46% compared with the square breeding pond. It follows from this that 02≤r/b<0.The square arc angle aquaculture pond of 4 realizes the flow regime similar to that of the circular aquaculture pond, and the flow field in the pond is more uniform, which can make the aquaculture fish evenly distributed, and improves the effective utilization rate of the aquaculture water space. Space utilization
The space utilization rate decreases with the increase of r b, and the space utilization rate of the circular culture pond is only 78 of that of the square culture pond5%。And 02≤r/b＜0.The space utilization rate of the square arc angle breeding pond of 4 is 86% and 97% of the square aquaculture pond; Compared with the circular breeding pond, its space utilization rate has been significantly improved. where r b is 020 (97% space utilization) and 025 (space utilization rate 95%), both good flow field uniformity and space utilization.
Velocity distribution contour map
Summary
To sum up, 02≤r/b＜0.The hydrodynamic characteristics of the double-channel square arc angle aquaculture pond of 4 are significantly better than those of other aquaculture ponds with relative arc width ratio, and maintain a high space utilization rate, effectively combine the advantages of square and circular aquaculture ponds in terms of space utilization rate and flow state in the aquaculture pond, and have a good promotion and application prospect in the field of aquaculture.
Corresponding author
Ren Xiaozhong, professor and master's tutor of the Key Laboratory of Facility Fisheries of the Ministry of Education (Dalian Ocean University), was selected into the municipal talent plan. He is mainly engaged in the research and application demonstration of efficient aquaculture engineering and engineering hydrodynamics of facility fisheries, and has presided over 8 projects such as the key special project of "Intelligent Agricultural Machinery Equipment" of the National Key Research and Development Program and the National Natural Science ** General Project. He has won the first prize of Liaoning Provincial Science and Technology Progress Award (the 8th end) and has obtained more than 30 achievements such as patents, monographs and textbooks. Zhang Qian, Gui Jinsong, Ren Xiaozhong, Xue Boru, Bi Chunwei, Liu Ying. Research on flow field optimization of two-channel square culture pond with relative arc width ratio[J].South China Fisheries Science, 2022, 18(4): 119-125
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Written by |Zhang Qian.
Edit |Jiang Rui.