对虾高位池中央排污口装置排污效果研究

高位池通常采用中央排污口排污,排污口上的排污装置是高位池的重要部件,其构造直接影响排污效果,是高位池养殖成败的重要因素。为解决传统排污口排污易堵塞和无法吸排底部沉积物的问题,研制了侧排式排污口装置SC-1、SC-2和顶排式排污口装置SD-1,在生产中应用并实测其排污效果。试验采用分时段测定排出口流速和总氮的方法,研究3种新型排污口的应用效果。结果显示,在养殖前期,SC-1型和SC-2型排污口装置的排污性能均优于SD-1,侧排式排污口装置的单次累计排氮量比顶排式的提高18.9%(P0.05)。通过改进中央排污口装置构造,可显著提高排污效率。研究表明,侧排式排污口装置对构建低换水率高位池对虾养殖模式、实现低换水量养殖,具有积极意义。     

方形圆弧角养殖池射流间距对流场特性的影响

为研究养殖池入射流间距对双管射流模式下(射流位置位于圆弧角,射流角度为30°)方形圆弧角养殖系统内流场特性的影响。采用流体动力学仿真技术,通过有限体积法和有限差分法构建三维数值计算模型,选取RNG k-ε湍流模型模拟工厂化循环水养殖池池内流场流动状态。结果显示:通过优化入射流间距可以有效提高养殖池整体流速、流场分布均匀性以及能量有效利用系数,减小入射流的能量损失,提高排污的经济效益。当入射流间距在0.05 m时,养殖池系统能够获得最佳水动力条件,此射流间距下,养殖池整体流速更高,污物移动时的向心趋势更加明显,流场运动状态最有利于养殖池内污物的排出。本研究结果可为方形圆弧角养殖池进水管布设方式提供理论参考。     

罗非鱼不同养殖系统对产出效果及异味物质含量的影响

对鱼菜共生系统、底排污系统、底排污+鱼菜共生3种养殖系统的水质变化和罗非鱼产出效果进行了分析,并利用微波蒸馏-吹扫捕集-气相色谱质谱联用技术检测了各系统水体中和罗非鱼肌肉中异味物质的含量变化。经过12周的养殖实验,对终重、生物量、特定生长率、饵料系数、增重率等指标进行测量比较,结果发现,罗非鱼的产出效果从优到差依次为:鱼菜共生组、底排污+鱼菜共生组、底排污组、对照组;底排污+鱼菜共生系统水体中溶解氧在各时期均最高,其亚硝氮、氨氮含量在各时期均最低;底排污或鱼菜共生系统均能有效降低养殖水体中异味物质2-MIB和GSM含量;对照组罗非鱼肌肉中异味物质含量最高,2-MIB和GSM分别达到(0.67±0.02)μg/kg和(0.870±0.018)μg/kg,而底排污+鱼菜共生组罗非鱼肌肉中异味物质含量在各时期最低,2-MIB和GSM分别为(0.31±0.02)μg/kg和(0.53±0.042)μg/kg。结果表明,在罗非鱼精养池塘中,可通过底排污和鱼菜共生结合,降低水体中和罗非鱼体内异味物质的累积,提高其经济价值。     

多营养级池塘养殖系统设计与试验

为有效解决水产养殖环境污染、提高水产品品质,本研究构建了一套1.33 hm~2的多营养级池塘养殖中试试验系统,主要包括草鱼养殖区、河蟹养殖区、螺蛳鲢鳙养殖区和水处理设施等。养殖的草鱼、河蟹作为饲料营养的Ⅰ级利用层级,投放的螺蛳、鲢鳙作为Ⅱ级利用层级,种植的沉水植物作为Ⅲ级利用层级,按时打捞水草、螺蛳作为草鱼、河蟹的生物饵料,从而提高饲料营养物质向鱼蟹等主养对象的转化比例。利用计算流体动力学(CFD)软件建立了试验系统水循环过程的1∶1比例计算模型,研究了全域水循环过程和单个草鱼养殖池的流动特性,并开展了水质调控试验,在试验系统内设置14个采样点,对一个养殖周期的水质参数进行监测。结果显示:草鱼养殖池壁附近的水体流度大于轴心区域的水体流速,有利于颗粒废物的沉淀,及时集排污;系统开启运行300 s后,水体在整个系统中的流态趋于稳定,营养物质在系统各个池塘中的分布基本均匀,保证物质能量的高效循环;系统对养殖水体氮、磷的去除效果显著,养殖全程的总氮质量浓度低于5 mg/L,总磷质量浓度低于1 mg/L,符合淡水养殖排放水标准,但对化学需氧量(COD)的控制效果不显著,应进一步改进系统结构,加强系统对有机污染物的处理能力。本研究为多营养级分隔池塘养殖系统的设计提供了参数参考。     

基于启发式Johnson算法优化BP神经网络的水产养殖产量预测模型

针对水产养殖产量预测难的现状,提出一种基于启发式Johnson算法优化的反向传播神经网络(BPNN)的产量预测模型。该模型在传统BP神经网络的基础上,针对网络训练时间长、易陷入局部最优的问题,通过启发式Johnson算法降低输入神经元维度,再结合试凑法确定神经网络隐层个数,构建启发式Johnson反向传播神经网络(HJA-BPNN)学习预测模型。实验结果表明,该模型在山东省对虾海水养殖产量预测中,预测的均方根误差小于传统BP神经网络和GM(1,1),且学习效率相比传统BP神经网络有所提升。研究表明,该学习预测模型在大量历史数据的模型构造上有更大的优势,能够缩短建模时间,同时获得良好的预测效果,为水产养殖产量预测提供了一种可行的新方法。     

折角比对养殖工船舱内流场特性的影响

为改善带有顶、底边舱且低径深比的养殖工船养殖舱内流场特性,以提高水产养殖动物福利与经济效益,提出一种结构优化参数折角比(a/B,a为角壁边长,B为养殖舱壁边长),以评估养殖舱内流场的改善效果。基于计算流体动力学(CFD)仿真技术,研究折角比参数a/B(0～0.4)和进水速度(0.8～1.2 m/s)对养殖舱内流场特性的影响。结果显示：不同进水速度下,养殖舱内流体特性的变化趋势一致;养殖舱水力停留时间一致的条件下,当折角比参数0.25≤a/B≤0.40时,养殖舱内流场均匀性较好,平均流速较原方形养殖舱提高35%,能量有效利用率提高70%;角壁附近低流速区域减少,养殖舱中间排水口区域有明显涡柱形成,有助于提高养殖舱系统的自清洁性能。研究表明,折角比参数a/B控制在0.25～0.40时,有助于提高养殖舱系统的能量有效利用率和养殖空间利用率。研究结果可为养殖工船养殖舱的结构设计和优化提供参考依据。     

近岸典型养殖海区潮流垂直结构的数值研究

采用改进的一维水动力模型对我国近岸典型筏式养殖海区的潮流垂直结构进行了数值研究。模型通过增加潮流上边界层来描述养殖活动与潮流垂直分布的关系。数值实验结果表明,高密度养殖对潮流的阻碍作用很强,使得海水表层流速显著减缓;当养殖密度达到临界值后,流速剖面出现变形,流速迅速减小。流速剖面随底应力的变化也会出现同样的变形。潮流流速及其垂直分布情况均受到上层养殖阻力和海底应力的共同作用,呈非线性变化趋势。潮流垂直结构就是对在外海传入潮波的驱动下,海水对上层养殖阻力和海底应力的适应与调整。这为进一步优化养殖设施布放、养殖品种安排等奠定了理论基础。生物生长与吊笼等因素对海水运动的阻力效应是需要进一步考虑的问题。     

影响池塘工业化生态养殖系统水槽集排污效果的因素与对策

正池塘工业化生态养殖系统与技术的核心是集排污,及时将鱼类养殖中的残饵和粪便排出池塘,是减轻池塘水净化处理压力和保障养殖水质达标的关键措施,是对传统池塘养殖做出革命性创新的精髓。因此必须对池塘工业化生态养殖系统的集排污区设计构建及运行管理予以足够的重视与优化,才能充分发挥该养殖系统的特点和优势,提高养殖绩效水平,实现产出高效、产品安全、资源节约、环境友好的目标。     

直壁双管结构射流角度对方形圆弧角养殖池流场的影响研究

为改善水产养殖池内的水动力条件,同时兼顾降低工厂化循环水养殖的能源消耗,采用计算流体力学(Computational Fluid Dynamics, CFD)技术,建立对直双管(两个进水管布设于不相邻的两个直壁中间位置)入流的养殖池三维数值计算模型,对不同射流角度的方形圆弧角养殖池内流场特性开展数值模拟。结果显示:射流角度对养殖池内平均流速和流场分布均匀性的影响明显;在同一循环次数设定条件下,当射流角度在0°～10°区间,有利于获得更高的水体流速和更均匀的流场,尤其以射流角度为0°时效果最优,养殖池内流场特性总体上优于其他工况,满足降低养殖能耗与兼顾营造养殖生物所需适宜流场的需求。本研究可为工厂化循环水养殖系统养殖池流场的设计建造提供参考。     

南美白对虾钢梁大棚养殖池塘建设技术要点

<正>近年来,浙江省兴起了一种新型设施养殖模式——南美白对虾大棚养殖,利用塑料大棚太阳能保温,在每年4-11月份进行养殖,可实现南美白对虾二茬养殖,甚至三茬养殖,避开了集中起捕时间,经济效益显著。现将南美白对虾钢梁大棚养殖池塘建设技术要点介绍如下,供水产养殖从业者参考。一、中央排污养殖池养殖池的面积约0.13公顷,一般呈长方形,长宽比约2∶1,池壁坡度为1∶(0.75~1),池壁四角呈弧形。池底     

进径比对矩形圆弧角养殖池水动力特性影响

为研究单管入流模式下,进径比(参数C/B,C为射流孔位置到养殖池壁的水平距离,B为养殖池短边边长)对单通道矩形圆弧角养殖池系统水动力特性的影响,实验运用计算流体动力学仿真技术构建单通道矩形圆弧角养殖池三维数值计算模型,应用平均流速、阻力系数和速度分布均匀系数等流体动力学特征量分析养殖池内(尤其是池底)的流场形态,并修正能量有效利用系数以评估养殖池系统的能量有效利用率。结果显示,将进径比参数C/B从0.00增大到0.05可有效改善养殖池内流场特性,进径比参数C/B设置在0.02～0.04之间有利于单通道矩形圆弧角养殖池系统获得最佳的流场条件。研究表明,进径比参数的较小优化可显著提高养殖池内平均流速与能量有效利用率,利于形成均匀稳定的流场。     

工厂化对虾养殖池管式射流集污水力特性

工厂化养殖池内水体的流场分布特性直接决定了其对残饵、粪便等的排污性能。本实验研究了管式射流驱动模式下,射流角度与射流流速对养殖池内水体流场与污物聚集特性的影响。养殖池流场特性采用点式流速仪进行布点测量,利用MATLAB软件对流场特性进行分析。采用相机采集的养殖池集污效果图像,并利用Photoshop软件与自行开发的不规则图形面积分析软件对图像进行分析。研究表明,流速从池心向外呈"V"型变化,在射流角度固定的情况下,射流速度越大,池心低流速区域越小,污物向池心的聚集效果越好;在流速固定的情况下,存在一个最佳的射流角度,本实验在24 cm/s流速条件下,射流角度为40°时,池内污物聚集效果最优。结论认为在保证养殖对象生长的前提下,可尽量提高射流流速;在24 cm/s流速条件下,最佳射流角度在40°左右。本研究成果可为工厂化养鱼池、养虾池等管式射流水力驱动系统的优化设计提供参考依据。     

基于流态的方形圆弧角养殖池进水系统优化数值研究

为研究进水系统优化对方形圆弧角养殖池内流场特性的影响,实验运用计算流体动力学仿真技术(CFD)构建方形圆弧角养殖池的三维数值湍流模型,单管进水系统设置在养殖池弧壁的中间位置(以下称弧壁单管),并主要对不同进径比(参数C/B,射流管中心位置到养殖池壁的水平距离C与养殖池短边边长B之比)和不同射流角度对养殖池系统内的流场特性开展研究。结果显示,不同进径比条件下,随射流角度增加养殖池水体平均速度均呈现先增大后减小的趋势,且最优射流角度不同。进径比为0.01且射流角度为45°时,养殖池内部流场平均流速最高。进径比为0.03时,最优射流角度为30°。当C/B=0.05～0.13时且射流角度为25°时,水体平均速度最高且流场均匀性较好。进径比C/B=0.07～0.09、射流角度为25°时,养殖池内部流态总体上优于其他工况。研究表明,养殖池流场特性与进水系统进径比和射流角度密切相关。研究结果可为工厂化循环水养殖进水系统设计和优化养殖池系统的流场特性提供理论依据。     

Comparative analysis of flow patterns in aquaculture rectangular tanks with different water inlet characteristics

The objective of the work is to improve the design rules of rectangular aquaculture tanks in order to achieve better culture conditions and improve water use efficiency. Particle tracking velocimetry techniques (PTV) are used to evaluate the flow pattern in the tanks. PTV is a non-intrusive experimental method for investigating fluid flows using tracer particles and measuring a full velocity field in a slice of flow. It is useful for analysing the effect of tank geometries and water inlet and outlet emplacements. Different water entry configurations were compared, including single and multiple waterfalls and centred and tangential submerged entries.

The appearance of dead volumes is especially important in configurations with a single entry. Configuration with a single waterfall entry shows a zone of intense mixing around the inlet occupying a semicircular area with a radius around 2.5 times the water depth. A centred submerged entry generates a poor mixing of entering and remaining water, promoting the existence of short-circuiting streams. When multiple waterfalls are used, the distance between them is shown to have a strong influence on the uniformity of the velocity field, increasing noticeably when the distance between inlets is reduced from 3.8 to 2.5 times the water depth. The average velocities in configurations with multiple waterfalls are very low outside the entrance area, facilitating the sedimentation of biosolids (faeces and non-ingested feed) on the tank bottom. The horizontal tangential inlet allows the achievement of higher and more uniform velocities in the tank, making it easy to prevent the sedimentation of biosolids.     

Effects of different layouts of fine-pore aeration tubes on sewage collection and aeration in rectangular water tanks

Sewage collection and dissolved oxygen (DO) management have always been the focus of industrialized recirculating aquaculture. However, there are still no reports on how to achieve efficient sewage collection and increase DO in rectangular water tanks. In the present study, the performance of sewage collection and aeration in rectangular water tanks were compared among three fine-pore aeration tubes (disc-type diffuser, four corner-type diffuser and distribute-type diffuser) layouts at three airflow rates, 6, 18, and 30 m³/h. The results of computational fluid dynamics (CFD) modeling and bait collection tests revealed that sewage collection using the four corner-type diffuser was better than using the disc-type diffuser and the distribute-type diffuser. Using the four corner-type diffuser, a strip-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an airflow rate of 18 m³/h and a disc-shaped sewage collector could be set up at the bottom of the tank to collect sewage at an air flow rate of 30 m³/h. In terms of aeration, volumetric oxygen transfer coefficient (K_La₂₀), standard oxygen transfer rate (SOTR), and standard oxygen transfer efficiency (SOTE) of the distribute-type diffuser were all the highest at the three airflow rates, followed by four corner-type diffuser, and finally the disc-type diffuser, indicating that the aeration performance in the distribute-type diffuser was optimal. However, there were no significant differences in K_La₂₀, SOTR, and SOTE between the four corner-type diffuser and the distribute-type diffuser at both 18 and 30 m³/h airflow rates. Therefore, four corner-type diffusers were the optimal choice for recirculating aquaculture, considering the sewage collection and aeration requirements. The results of the present offer novel insights on the application of CFD in recirculating aquaculture, in addition to basic data and theoretical guidance on how to achieve efficient sewage collection and aeration in recirculating aquaculture.     

An effective and practical method of net settings in rearing tank to suppress hypermelanosis in Japanese flounder

In Japanese flounder aquaculture, hypermelanosis occurs widely on the blind side. Rearing flounders in a net-lined tank was recently reported to prevent hypermelanosis. To effectively apply this method to larger tanks for aquaculture farming, the net setting method was examined. Juvenile flounders without darkened areas on the blind side [total length (TL) 13 cm] were selected, and reared for 6 months (TL 32 cm). In the control tank without a net, the median value of darkened area ratio (darkened area to blind side area) was 46%. By only covering the tank bottom with slack net, the darkened area ratio was suppressed to 8%, less than 1/5 of that in the control tank. At the end of experiment, bottom coverage ratios of 0%, 10%, 30%, 50%, and 100% revealed a negative correlation between bottom net coverage and darkened area ratio. In this experiment, the darkening area in the tank with 50% bottom net coverage decreased to 1/3 of the control. Although the occurrence of hypermelanosis differs depending on the production lot, these results are expected to serve as a reference for selecting the suitable net size to meet the level of clearness of the blind side.

     

Settling velocity and particle size bioengineering parameters gathered from solids generated by wild-caught premature punctuated snake-eels (Ophichthus remiger) reared in a marine prototype recirculating aquaculture system

This research reveals the applied engineering basis for determining the particle size and settling velocity distributions of solids generated while rearing wild-caught premature punctuated snake-eels (Ophichthus remiger) in a prototype recirculating aquacultural system. Settled solids were sampled from the bottom of the rearing tanks, and suspended solids were sampled before filtration within the drum filter and analyzed to characterize their settling velocity and particle size properties. These particle properties are considered bioengineering parameters since they will provide biological information to improve engineering solutions for RAS solids removal processes. The average settling velocity for the settleable solids in the rearing tanks was 2.89 ± 0.02 cm s⁻¹, and the average particle size ranged between 7.32 ± 3.41 and 19.44 ± 8.58 mm. Suspended solids within the drum filters before filtration had an average settling velocity of 0.35 ± 0.11 cm s⁻¹ and it was found that 69.93 % of the particles size was greater than 200 μm, 15.40 % were within the range of 120 μm and 90 μm sizes, and 6.53 % were between 70 μm and 40 μm sizes. The particle physical properties, settling curves, and particle sizes curves obtained from this experience represent valuable information to be used to improve engineering design of solids handling mechanisms, especially in marine land-based systems, and in this case, applied for rearing wild-caught punctuated snake-eels. The present investigation constitutes an advance in the knowledge of applied engineering to the design of a marine aquaculture fattening operation targeted to feed up wild-caught premature punctuated snake-eels to the point of sale or trade.     

Controlled hatchery production of Clarias gariepinus (Burchell 1822): an investigation of tank design and water flow rate appropriate for Clarias gariepinus in hatcheries

Circular tanks are appropriate for Clarias gariepinus (Burchell) culture. Wide/shallow tanks (with a diameter to depth ration of about 10) are preferable to narrow/deeper tanks. The optimal flow rate for larvae will be one which provides sufficient oxygen yet does not generate a current velocity fast enough to cause them to swim against it. However, current velocity, for a given type and orientation of inflow, will depend particularly upon tank diameter to depth ratio and flow rate and will be related to position within the tank. Therefore for a given circular tank design a theoretical maximum flow rate and concomitant biomass can be estimated for a given mean fish size. Once airbreathing begins the optimal flow rate for fry is simply that which does not elicit swimming.     

两种双通道圆形养殖池水动力特性的数值模拟与研究

为给养殖池的池型选择与设计提供理论依据,在相同的池体尺寸、进水速度和池底出水比例条件下,针对Cornell和Waterline两种经典双通道圆形养殖池,对其速度流场进行了计算流体动力学(CFD)仿真分析。仿真应用Ansys 15.0软件中的Fluent模块,采用RNG k-ε湍流模型对两种池型的内部速度流场进行了数值模拟,分析其流场特性并进行对比。结果显示:两种池型的水流速度向池中心方向在很短距离内随着径向距离的减少而急速增大,当达到某一径向距离时,速度达到最大值,然后速度随着径向距离的减小而减小,在池子中心轴线或附近处速度降到最小;在纵向上,与池心相同水平距离处的水体流转速度则随着高度增加而减小;在池底出水分流比小于10%时,Cornell池池底自清洁能力、池子整体流场均匀性均比Waterline池差。仿真结果从理论上验证了两种池型底流比例的经验设计值在10%以上。     

Analysis of sedimentation and resuspension processes of aquaculture biosolids using an oscillating grid

Sedimentation and resuspension processes of aquaculture biosolids (non-ingested feed and faeces) are analysed using vertically oscillating grids as a source of turbulence in fluid tanks. An oscillating grid system consists of a container in which a grid is stirred vertically generating a well-known turbulent field that is function of amplitude and frequency of oscillation, distance between grid and measurement point, and mesh spacing of the grid. The grid used in this study had a mesh spacing of 1.2 cm, and was calibrated using different amplitudes (1, 1.5 and 2 cm), frequencies (from 1 to 6 Hz) and distances (2.4, 2.7 and 3 cm). After calibration, the turbulence needed to resuspend biosolids and to maintain them in the water column following different times of consolidation, and with biosolids of different origin, was analysed. It was observed that the turbulence needed to resuspend aquaculture biosolids increased with the time of consolidation. When the turbulence was decreased after a resuspension process, the next sedimentation of biosolids showed a hysteretic behaviour: turbulence needed to resuspend a fixed percent of biosolids from the tank bottom is substantially higher than that needed to maintain the same percentage suspended in the water column. Differences in resuspension behaviour of biosolids originated in different tanks were also observed.

The method provides useful information that can be compared with turbulence generated by fish swimming activity, in order to determine the culture conditions, which can promote self-cleaning conditions in a particular tank.