A circadian rhythm-based mechanism modeling method and regulation method for a dissolved oxygen machine in a recirculating aquaculture pond

Abstract

The present application relates to a kind of circadian rhythm-based circulating water aquaculture fish pond dissolved oxygen mechanism modeling method, including the influence of fish respiration consumption, water surface atmospheric reoxygenation, circulating water flow, mechanical aeration factor on dissolved oxygen dynamic change;According to oxygen transfer equation, considering the influence of the above four factors on fish pond dissolved oxygen, the dissolved oxygen mechanism model of circulating water aquaculture fish pond is established;Combined with oxygen transfer equation and the characteristics of fish respiratory activity changes between day and night, the influence of fish respiratory circadian rhythm on the model is analyzed, and the model is verified.The present application can more accurately reflect the high and low peak value in different time periods and also capture the dynamic changes presented in the whole cycle, and effectively avoid the loss and risk caused by the inaccurate model description to the aquaculture industry in extreme breeding environment or abnormal environment.

Description

Technical Field

[0001] This invention relates to the field of aquaculture, specifically to a method for modeling and regulating dissolved oxygen mechanisms in recirculating aquaculture fish ponds based on diurnal rhythms. Background Technology

[0002] China is a major aquaculture country. Compared with traditional aquaculture methods, recirculating aquaculture systems (RAS) can save more than 90% of water consumption and 99% of land occupation. It can achieve high-density aquaculture, with high controllability of the aquaculture environment, good quality of farmed aquatic products, and environmental friendliness. It is more in line with the requirements of national sustainable development and will be the main production method of factory farming in the future.

[0003] In the operation and production of recirculating aquaculture systems (RAS), good water quality is a prerequisite for stable fish production. Among the various water quality parameters, dissolved oxygen (DO) is the soul of the RAS, directly determining the respiration and growth of fish. Dissolved oxygen refers to the oxygen content dissolved in water. Sufficient dissolved oxygen is an important factor in maintaining the normal growth of aquatic animals. For fish in RAS, the dissolved oxygen concentration should be greater than 60% of the oxygen saturation concentration in water or maintained at... Therefore, aeration devices are commonly used in recirculating aquaculture systems to provide sufficient dissolved oxygen. Low dissolved oxygen levels lead to reduced fish feeding, increased feed conversion ratios, rapid breathing, and in severe cases, surface-gazing, causing fish mortality. High dissolved oxygen levels can cause gas bubble disease in juvenile fish, leading to their death and ultimately disrupting the balance of the recirculating aquaculture system. During the day, increased light intensity and water temperature lead to increased fish activity, feeding frequency, and metabolic rate, all of which increase oxygen consumption. Conversely, at night, altered environmental conditions reduce activity, feeding frequency, and metabolic rate, resulting in decreased oxygen consumption. This clear and periodic variation indicates a distinct diurnal rhythm that can be incorporated into established models. Therefore, precise modeling and regulation of dissolved oxygen in aquaculture water is crucial for precise production in recirculating aquaculture systems, possessing significant strategic, theoretical, and practical value.

[0004] Mechanistic models explain phenomena or predict system behavior by describing the fundamental principles and relationships within the system. They provide in-depth understanding and explanation, offering insights into the system's internal mechanisms to support optimization, control, and design decisions. Mechanistic models exhibit high predictive accuracy because they are based on the system's internal mechanisms, thus typically predicting system behavior more accurately. The parameters of mechanistic models have very clear physical meanings, making the models easier to understand and use. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies and proposes a modeling method for dissolved oxygen mechanisms in recirculating aquaculture ponds based on the diurnal rhythms of fish, tailored to actual aquaculture production needs. The method then optimizes and regulates this model using PID control theory, thereby reducing the workload of aquaculture workers and improving work efficiency. Simultaneously, it effectively avoids losses and risks to aquaculture caused by inaccurate model descriptions leading to extreme or abnormal environmental conditions.

[0006] This invention proposes a method for modeling the dissolved oxygen mechanism in recirculating aquaculture fish ponds based on diurnal rhythms, comprising the following steps:

[0007] The effects of fish respiratory consumption, atmospheric reoxygenation at the water surface, circulating water flow, and mechanical aeration reoxygenation on the dynamic changes of dissolved oxygen were analyzed.

[0008] Based on the oxygen mass transfer equation, and considering the effects of the above four factors on dissolved oxygen in fish ponds, a dissolved oxygen mechanism model for recirculating aquaculture fish ponds is established.

[0009] Combining the oxygen mass transfer equation with the characteristics of fish respiratory activity changing between day and night,

[0010] The influence of fish respiratory diurnal rhythm on the model was analyzed, and the model was validated.

[0011] Furthermore, based on the influence of dynamic changes in dissolved oxygen, a differential equation model is established to describe the dynamic changes in dissolved oxygen concentration in water:

[0012] ;

[0013] in For circulating water flow rate, For mechanical aeration, To reoxygenate the atmosphere at the water surface. It is consumed by fish respiration.

[0014] Furthermore, the circulating water flow rate The effect of water flow on dissolved oxygen concentration in the aquaculture pond is expressed by the following expression:

[0015] ;

[0016] The dissolved oxygen concentration in the effluent reflects the actual dissolved oxygen concentration in the tank, and the effluent flow rate equals the influent flow rate; that is:

[0017] ;

[0018] Therefore, equation (2) can be written as follows:

[0019] ;

[0020] In the formula:

[0021] V, volume of water in the aquaculture pond, in meters. 3 ;

[0022] Q in Inlet flow rate, unit: m³ 3 / h;

[0023] Q out Water flow rate, unit: m³ 3 / h;

[0024] C, Real-time dissolved oxygen concentration in the fishpond, in mg / L.

[0025] C in Dissolved oxygen concentration in influent, unit: mg / L;

[0026] C out Dissolved oxygen concentration in effluent, in mg / L.

[0027] Furthermore, the aforementioned According to the ASCE oxygen mass transfer model, the equation for the change of dissolved oxygen during mechanical aeration is as follows:

[0028] ;

[0029] Integrating both sides of equation (5) simultaneously, we obtain the equation for the change of dissolved oxygen over time:

[0030] ;

[0031] And:

[0032] ;

[0033] The change in saturated dissolved oxygen concentration with water temperature is shown in the following formula:

[0034] ;

[0035] In the formula:

[0036] C satSaturated dissolved oxygen concentration in water, unit: mg / L;

[0037] K La Oxygen volumetric mass transfer coefficient, unit ;

[0038] C 0 The initial concentration of dissolved oxygen at the start of aeration, in mg / L;

[0039] T Aeration time, in hours (h).

[0040] Q， Aeration flow rate, unit m 3 / h;

[0041] t d Delay time, in hours (h).

[0042] T w Current water temperature, in °C;

[0043] k 1 、k 2 、k 3 、β The constant is obtained by fitting experimental data.

[0044] Furthermore, the aforementioned The atmospheric reoxygenation process at the water surface is described by the following formula:

[0045] ;

[0046] In the formula: Regeneration coefficient, unit .

[0047] Furthermore, the aforementioned The oxygen consumption of fish respiration is described by the following formula:

[0048] ;

[0049] In the formula:

[0050] R Oxygen consumption per unit mass of respiratory energy, per unit ;

[0051] M , which represents the total mass of cultured organisms, in kg.

[0052] RIt was treated as a constant.

[0053] Furthermore, the model can be obtained by curve fitting as follows:

[0054] ;

[0055] That is, the expression of the fish diurnal rhythm mechanism model (11) is obtained, and finally the dissolved oxygen mechanism model of the recirculating aquaculture fish pond in relation to the diurnal rhythm is obtained:

[0056] ;

[0057] in ,and It is a constant, and its value is obtained by fitting experimental data.

[0058] On the other hand, this invention proposes a control method based on the diurnal rhythm of dissolved oxygen mechanism modeling in recirculating aquaculture ponds. A PID controller with a control algorithm is used in the recirculating aquaculture process to obtain the yield of fish in recirculating aquaculture.

[0059] Furthermore, the control algorithm assumes a certain time t, at which point the input quantity is... The output is Therefore, the calculated deviation is... Therefore, the basic control law of PID is expressed as:

[0060] ;

[0061] In the formula:

[0062] K p , Proportional band;

[0063] T I Integral time;

[0064] T D , where is the differential time.

[0065] The beneficial effects of this invention are:

[0066] 1. This invention can more accurately reflect the peak and trough values ​​in different time periods and can also capture the dynamic changes that occur throughout the entire cycle.

[0067] 2. This invention can effectively avoid losses and risks to the aquaculture industry caused by inaccurate model descriptions leading to extreme or abnormal aquaculture environments. Attached Figure Description

[0068] The present invention includes the following figures:

[0069] Figure 1 This is a schematic diagram of the dissolved oxygen dynamic equilibrium of the present invention;

[0070] Figure 2 This is a structural diagram of the recirculating aquaculture system of the present invention;

[0071] Figure 3 This is a diagram showing the actual comparative experimental setup of the present invention;

[0072] Figure 4 This invention compares experimental results and fitting results;

[0073] Figure 5 This is a structural diagram of the PID control system based on the diurnal rhythm dissolved oxygen model of this invention;

[0074] Figure 6 This is a response diagram of the present invention based on the diurnal rhythm dissolved oxygen model under three aeration flow rates;

[0075] Figure 7 This is a PID control diagram based on the diurnal rhythm dissolved oxygen model of this invention. Detailed Implementation

[0076] To make the objectives, advantages and features of the present invention more apparent, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments.

[0077] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0078] To simulate the dynamic behavior of dissolved oxygen in aquaculture ponds, we assume the following conditions:

[0079] 1) Throughout the aeration process, the airflow changes ideally over time, resulting in uniform mixing of the water and thus achieving uniform distribution of dissolved oxygen in the aquaculture water.

[0080] 2) The effect of photosynthesis on dissolved oxygen concentration in the pond is ignored, and the increase in biomass generated during the growth process is considered negligible;

[0081] 3) Only consider the oxygen consumed by fish respiration;

[0082] 4) At the same time, the exchange with the atmosphere and the changes in fish oxygen consumption with the diurnal rhythm should be considered.

[0083] Based on these conditions, we use ordinary differential equations to express the dynamic changes in dissolved oxygen. According to the principle of mass conservation, dissolved oxygen in water is always in a dynamic equilibrium process, meaning that the increase in dissolved oxygen equals the consumption of dissolved oxygen. Given the complexity of recirculating aquaculture systems, we comprehensively evaluated the main factors affecting the dynamic fluctuations of dissolved oxygen in the culture tank. These include the recirculating water flow rate. Mechanical aeration Atmospheric reoxygenation of water surface and the energy consumed by fish respiration .like Figure 1 As shown.

[0084] Subsequently, we established a differential equation model to describe the dynamic changes in dissolved oxygen concentration in water:

[0085] ;

[0086] Under normal circumstances, the dissolved oxygen concentration in recirculating aquaculture systems is mainly affected by the four factors mentioned above. Therefore, equation (1) can be used as a difference equation model to describe the dynamic changes of dissolved oxygen in most recirculating aquaculture systems.

[0087] In a recirculating aquaculture system, water discharged from the aquaculture pond undergoes preliminary filtration, sterilization, and aeration before being returned to the pond, facilitating water recycling. Therefore, water flow affects the dissolved oxygen concentration within the aquaculture pond, a relationship that can be expressed by the following formula:

[0088] ;

[0089] It is generally believed that the dissolved oxygen concentration in the effluent reflects the actual dissolved oxygen concentration inside the tank, and the effluent flow rate is equal to the influent flow rate. That is:

[0090] ;

[0091] Therefore, equation (2) can be written as follows:

[0092] ;

[0093] In the formula:

[0094] V Volume of water in aquaculture pond, in m³ 3 ;

[0095] Q in Inlet flow rate, unit: m³ 3 / h;

[0096] Q out Water flow rate, unit: m³ 3 / h;

[0097] C Dissolved oxygen concentration in the fishpond in real time, in mg / L.

[0098] C in Dissolved oxygen concentration in influent, unit: mg / L;

[0099] C out Dissolved oxygen concentration in effluent, unit: mg / L;

[0100] The aeration flow rate of the blower is the main manipulated variable for controlling dissolved oxygen. According to the ASCE oxygen mass transfer model, the equation for the change in dissolved oxygen during aeration is as follows:

[0101] ;

[0102] Integrating both sides of equation (5) simultaneously, we obtain the equation for the change of dissolved oxygen over time:

[0103] ;

[0104] And:

[0105] ;

[0106] The change in saturated dissolved oxygen concentration with water temperature is shown in the following formula:

[0107] ;

[0108] In the formula:

[0109] C sat Saturated dissolved oxygen concentration in water, unit: mg / L;

[0110] K La Oxygen volumetric mass transfer coefficient, unit ;

[0111] C 0 The initial concentration of dissolved oxygen at the start of aeration, in mg / L;

[0112] T Aeration time, in hours (h).

[0113] Q， Aeration flow rate, unit m 3 / h;

[0114] t d Delay time, in hours (h).

[0115] T w Current water temperature, in °C;

[0116] k 1 、k 2 、k 3 、β The constant is obtained by fitting experimental data.

[0117] Surface reoxygenation refers to the phenomenon of atmospheric oxygen molecules naturally dissolving from the water surface into the water body. When the dissolved oxygen in the water body is below saturation, oxygen diffuses from the atmosphere into the water. Conversely, when dissolved oxygen reaches saturation, oxygen escapes from the water body. Therefore, atmospheric reoxygenation capacity is inversely proportional to the difference between the saturated dissolved oxygen concentration and the instantaneous dissolved oxygen concentration. The atmospheric reoxygenation process can be described by the following equation:

[0118] ;

[0119] In the formula: Regeneration coefficient, unit .

[0120] Fish require oxygen and energy for movement, growth, and food digestion. Therefore, fish respiration reduces the concentration of dissolved oxygen in the water. The oxygen consumption of fish respiration can be described by the following formula:

[0121] ;

[0122] In the formula:

[0123] R Oxygen consumption per unit mass of respiratory energy, per unit ;

[0124] M , which represents the total mass of cultured organisms, in kg.

[0125] In previous studies, R It was treated as a constant.

[0126] Regarding experimental design and model analysis methods for fish circadian rhythms, we propose an effective experimental analysis method to determine the circadian rhythm of fish. By combining the oxygen mass transfer equation and considering the characteristics of fish respiratory activity changes between day and night, we can more accurately analyze and predict significant differences in fish physiological processes. To verify the reliability of the proposed model, we collected a large amount of data on fish oxygen consumption and other relevant parameters at different time periods. This data was then applied to the established model.

[0127] The structure of a recirculating aquaculture system is as follows: Figure 2As shown, IoT devices and data terminal devices (mainly dissolved oxygen sensors and aerators in this paper) are deployed in the recirculating aquaculture system to achieve data transmission. The actual comparative experiment setup is shown in the diagram below. Figure 3 As shown, the culture conditions in fishpond 1 and fishpond 2 are exactly the same, the only difference being that fishpond 2 is stocked with fish, while fishpond 1 is not. Through this comparative experiment, the oxygen consumption of the cultured fish can be obtained, and their diurnal rhythm can be calculated.

[0128] Dissolved oxygen concentration values ​​in two fish ponds were obtained using sensors, such as... Figure 4 As shown, the following formula can be obtained through curve fitting:

[0129] ;

[0130] The expression for the fish diurnal rhythm mechanism model (11) can be obtained, and finally the dissolved oxygen mechanism model of the recirculating aquaculture fish pond in relation to the diurnal rhythm is obtained:

[0131] ;

[0132] in ,and It is a constant, and its value is obtained by fitting experimental data.

[0133] Comparison with traditional models revealed that the model based on fish diurnal rhythms is significantly superior in describing and predicting observations. It not only more accurately reflects peak and trough values ​​across different time periods but also captures the dynamic changes throughout the entire cycle. This result demonstrates that our proposed experimental analysis method is feasible and effective in understanding and predicting dissolved oxygen concentrations.

[0134] The platform is built by combining hardware and software. Figure 2 The designed PID control algorithm runs on the platform to optimize and regulate the dissolved oxygen concentration in the recirculating aquaculture system. The PID algorithm best embodies the concept of feedback control. The system inputs the calculated error between the input and output values ​​into the PID controller for feedback adjustment, repeating the cycle continuously.

[0135] Assume there is a certain time t, and the input quantity is... The output is Therefore, the calculated deviation is... Therefore, the basic control law of PID can be expressed as:

[0136] ;

[0137] In the formula:

[0138] k p , Proportional band;

[0139] T I Integral time;

[0140] T D , where is the differential time.

[0141] Based on the diurnal rhythm-based dynamic mechanism model of dissolved oxygen obtained above, PID control was applied to conduct control experiments. The structure diagram of the designed control system is shown below. Figure 5 As shown.

[0142] This invention proposes a dynamic mechanism model of dissolved oxygen based on diurnal rhythms and its corresponding PID control, which was experimentally tested at the aquaculture base of the National Digital Fisheries Innovation Center of China Agricultural University. We conducted model analysis on recirculating aquaculture ponds and performed 70-hour simulation experiments in MATLAB under three different aeration flow rates. The results are as follows: Figure 6 After considering diurnal rhythms, the overall trend of dissolved oxygen concentration remained consistent across the three different aeration flows, exhibiting a clear fluctuation pattern with periodic increases and decreases. This variation significantly impacts fish growth in recirculating aquaculture systems, and the model allows for more precise control based on diurnal rhythm analysis.

[0143] A dissolved oxygen regulation strategy designed using a PID algorithm was implemented, setting the dissolved oxygen reference value to 6 mg / L and regulating the dynamic mechanism model of dissolved oxygen based on diurnal rhythms. The output response curve is shown below. Figure 7 As shown.

[0144] The response curves show that the dissolved oxygen concentration oscillated between approximately 5.6 and 6.4 mg / L, and the control variable also exhibited oscillating changes. This is because dissolved oxygen changes are lag-dependent and periodic, consistent with the regulation requirements of a circadian rhythm-based dissolved oxygen model. During the daytime, increased light intensity and water temperature lead to increased fish activity, feeding frequency, and metabolic rate, all of which increase oxygen consumption. Therefore, the control variable is increased to enhance oxygen supply. Conversely, at night, altered environmental conditions result in decreased activity, feeding frequency, and metabolic rate, leading to reduced oxygen consumption. Therefore, the control variable is decreased to reduce oxygen supply. This effectively avoids losses and risks to aquaculture caused by inaccurate model descriptions of extreme or abnormal environments.

Claims

1. A method for modeling the dissolved oxygen mechanism in recirculating aquaculture fish ponds based on diurnal rhythms, characterized in that, The method comprises the following steps: analyzing the influence of different environmental factors on the dynamic change of dissolved oxygen; According to the oxygen transfer equation, considering the influence of different environmental factors on the dissolved oxygen in the fish pond, a mechanism model of dissolved oxygen in the recirculating aquaculture fish pond is established; The different environmental factors include four factors of recirculating water flow, mechanical aeration, atmospheric reoxygenation on the water surface, and fish respiration consumption; Combined with the oxygen transfer equation and the characteristics of fish respiration activity changing between day and night, the influence of fish respiration diurnal rhythm on the mechanism model is analyzed, and the mechanism model is verified; The analysis of the influence of fish respiration diurnal rhythm on the mechanism model specifically includes the analysis of the influence of fish respiration diurnal rhythm on the dynamic change of the dissolved oxygen concentration.

2. The circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond of claim 1, wherein, The influence of the dynamic change of the dissolved oxygen is established by a differential equation model to describe the dynamic change of the dissolved oxygen concentration in water: ; wherein, C is the real-time dissolved oxygen concentration in the fish pond, t is the simulation time interval, is the recirculating water flow rate, is the mechanical aeration, is the atmospheric reoxygenation of the water surface, is the fish respiration consumption.

3. A circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond aerator as claimed in claim 2, wherein, The circulating water flow rate The water flow has an impact on the dissolved oxygen concentration in the culture pond, and the expression is ； The outlet dissolved oxygen concentration reflects the actual dissolved oxygen concentration in the water tank, and the outlet flow rate is equal to the inlet flow rate; that is: ； Therefore, formula (2) can be written as the following formula: ； In the formula, V , volume of the water body of the breeding pond, unit m 3 ; Q in , inlet water flow rate, unit m 3 / h; Q out , m3 / h 3 / h; C in , inlet water dissolved oxygen concentration, unit mg / L; C out , effluent dissolved oxygen concentration, in mg / L.

4. The circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond according to claim 3, wherein, The Mechanical aeration, according to the ASCE oxygen transfer model, the change equation of dissolved oxygen during aeration process is as follows: ； Integrating both sides of formula (5) simultaneously, the change equation of the dissolved oxygen with time is obtained: ； Also, ； The change of the saturated dissolved oxygen concentration with water temperature is shown in the following formula: ； In the formula, C sat , the saturated dissolved oxygen concentration value in water, unit: mg / L; K La , oxygen volumetric mass transfer coefficient, units ; C 0 initial concentration of dissolved oxygen at the beginning of aeration, in mg / L; T , aeration time, in h; Q， Aeration flow, units m 3 / h; t d , delay time, unit h; T w current water temperature, in °C; k 1 、k 2 、k 3 、β , constants, obtained by fitting experimental data.

5. A circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond aerator as claimed in claim 4, wherein, The The atmospheric reoxygenation of the water body surface is described by the following equation: ； In the formulae: regeneration coefficient, unit .

6. A circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond aerator as claimed in claim 5, wherein, The Fish respiration consumption is described by the following equation: ； In the formula, R , for the oxygen consumption of respiration per unit mass, unit ; M for the total mass of the cultivated organisms, in kg; R are treated as constants.

7. A circadian rhythm-based modeling method of a dissolved oxygen mechanism of a recirculating aquaculture pond aerator as claimed in claim 6, wherein, The mechanism model can be obtained by curve fitting as the following formula: ； That is, the fish diurnal rhythm mechanism model expression (11) is obtained, and finally the dissolved oxygen mechanism model of the recirculating aquaculture fish pond based on diurnal rhythm is obtained: ； wherein R m is the average daily consumption rate of dissolved oxygen, A m is the amplitude of the circadian model, f is the frequency of the model, is the phase of the model, P k is the temperature coefficient, wherein , and is a constant whose value is obtained from experimental data fitting.

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