A fixed-frequency pump selection device and selection method for a ship central cooling system

Abstract

A fixed-frequency pump selection device for a ship's central cooling system, the fixed-frequency pump selection device for the ship's central cooling system includes a first cooling water pump, a second cooling water pump, a third cooling water pump, a control mechanism and a fresh water pipeline system; the control mechanism is signal-connected to a first heat exchanger, the first heat exchanger is arranged on the fresh water pipeline system, the water inlet end of the fresh water pipeline system is communicated with the seawater area through a second heat exchanger, two flow sensors and a temperature sensor are arranged on the pipeline between the fresh water pipeline system and the seawater area, a flow sensor is arranged on the pipeline between the fresh water pipeline system and the control mechanism, and a first cooling water pump, a second cooling water pump and a third cooling water pump are sequentially arranged on the fresh water pipeline system. This design can select the fixed-frequency pump according to the actual situation of the seawater temperature and flow rate, and reduces the error of estimating the size of the optimal low-temperature fresh water flow rate.

Description

Technical Field

[0001] The present invention relates to an improvement in the selection technology of fixed-frequency pumps in a ship's central cooling system, belonging to the field of ship central cooling systems, and particularly relates to a fixed-frequency pump selection device and a selection method for a ship central cooling system. Background Art

[0002] Most current ship main engine cooling systems are central cooling systems, which are used to cool the main engine and other auxiliary equipment; the ship main engine cooling system consists of a high-temperature fresh water cooling system, a low-temperature fresh water cooling system, and a seawater cooling subsystem. The cooling water pump is the main energy-consuming component of these three subsystems. Since variable-frequency pumps are expensive, most ships choose fixed-frequency pumps as cooling water pumps during design and manufacturing. Although this approach reduces the initial construction cost, because fixed-frequency pumps can only provide a fixed amount of flow, a pump with a relatively large surplus flow is usually selected in ship design, and it is impossible to select a fixed-frequency pump according to the actual seawater temperature and flow conditions, resulting in a relatively high actual operating energy consumption of the pump and increasing the operating cost of the ship.

[0003] Chinese patent application with the application number CN201921170017.6 and the application date of July 24, 2019, discloses a hybrid variable-frequency central cooling system for polar ships; it includes a seawater cooling system, a fresh water cooling system, and an electrical control system; the seawater cooling system is used to pump and cool the seawater area to cool the fresh water in the fresh water cooling system. The seawater cooling system includes a seawater area main pipe, a cooling seawater area inlet pipe, a central cooler, a seawater area outlet pipe, and a cooling seawater area return pipe; a seawater area cooling pump is provided on each cooling seawater area inlet pipe; the fresh water cooling system is used to supply water to the ship and transport the hot water after heat exchange and temperature rise to the seawater cooling system for heat exchange and temperature reduction; the fresh water cooling system includes a cooling fresh water outlet pipe and a cooling fresh water inlet pipe; the electrical control system is used to control the entire hybrid variable-frequency central cooling system; however, the comparative document still does not solve the problem of being unable to select a fixed-frequency pump according to the actual seawater temperature and flow conditions.

[0004] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of this patent application, and should not be regarded as an admission or any form of suggestion that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0005] The object of the present invention is to overcome the problem in the prior art that it is impossible to select a fixed-frequency pump according to the actual seawater temperature and flow conditions, and provides a fixed-frequency pump selection device and a selection method for a ship central cooling system that can select a fixed-frequency pump according to the actual seawater temperature and flow conditions.

[0006] To achieve the above object, the technical solution of the present invention is a fixed-frequency pump selection device for a ship's central cooling system. The fixed-frequency pump selection device for the ship's central cooling system includes a cooling water pump, a second cooling water pump, a third cooling water pump, a control mechanism and a fresh water pipeline system;

[0007] The control mechanism is signal-connected to a heat exchanger. The first heat exchanger is arranged on the fresh water pipeline system. The water inlet end of the fresh water pipeline system is communicated with the seawater area through a second heat exchanger. Two flow sensors and a temperature sensor are arranged on the pipeline between the fresh water pipeline system and the seawater area. A flow sensor is arranged on the pipeline between the fresh water pipeline system and the control mechanism. A cooling water pump, a second cooling water pump and a third cooling water pump are sequentially arranged on the fresh water pipeline system.

[0008] The fresh water pipeline system includes a main pipeline, a first branch pipeline and a second branch pipeline. The first cooling water pump is arranged on the main pipeline. The second cooling water pump is arranged on the first branch pipeline. The third cooling water pump is arranged on the second branch pipeline.

[0009] The first cooling water pump, the second cooling water pump and the third cooling water pump are not communicated with each other.

[0010] A selection method for a fixed-frequency pump selection device of a ship's central cooling system. The selection method for the fixed-frequency pump selection device of the ship's central cooling system includes the following steps:

[0011] Step 1: Obtain the flow data of the total low-temperature fresh water flow Q1, the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 at the control mechanism and the seawater area;

[0012] Step 2: After generating a database according to the flow data and the data under normal operating conditions of the control mechanism, establish a database of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5;

[0013] Step 3: According to the established database, establish a mathematical model of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 of the seawater area side heat exchanger through a neural network;

[0014] Step 4: Input the preset temperature of the seawater area in the navigation environment into the mathematical model to obtain the low-temperature fresh water inlet flow Q21 at the current seawater area temperature;

[0015] Step 5: After comparing and analyzing the low-temperature fresh water inlet flow Q21 and the total low-temperature fresh water flow Q1, obtain the selection result.

[0016] The specific method for obtaining the flow data at the control mechanism and the seawater area is as follows:

[0017] A flow sensor obtains the total low-temperature fresh water flow Q1 during the operation of the control mechanism;

[0018] Two flow sensors obtain the low-temperature fresh water inlet flow rate Q2 at the two heat exchangers;

[0019] A temperature sensor obtains the seawater area inlet temperature T5 at the two heat exchangers.

[0020] After generating the database according to the flow data and the data under normal operating conditions of the control mechanism, it further includes: A low-temperature fresh water subsystem and a seawater area cooling subsystem are provided in the control mechanism, and the control mechanism monitors the data of the low-temperature fresh water subsystem and the seawater area cooling subsystem.

[0021] The comparison and analysis specifically are:

[0022] If Q21 is less than Q1, the selection of the first cooling water pump, the second cooling water pump, and the third cooling water pump is too large;

[0023] If Q21 is greater than Q1, the performance of the cooling system decreases or the selection of the first cooling water pump, the second cooling water pump, and the third cooling water pump is too small;

[0024] If Q21 is equal to Q1, the selection of the first cooling water pump, the second cooling water pump, and the third cooling water pump is reasonable.

[0025] If Q21 is less than Q1, it means that a part of the low-temperature fresh water passes through the pipeline of the two heat exchangers, that is, the flow rate of this part of the low-temperature fresh water does not need to be cooled, and the selection of the cooling water pump can be made according to the data result of Q21.

[0026] The specific establishment of the neural network is as follows: Determine the number of network layers and the number of neurons in each layer. The input layer and the output layer are both 1 layer, and the corresponding number of neurons are the data dimensions of the input and output variables. The input variable in the model is the low-temperature fresh water inlet flow rate Q2 at the two heat exchangers, and the output variable is the total low-temperature fresh water flow rate Q1. Therefore, the data dimensions are both 1;

[0027] In the model, the Log-sigmoid function is selected as the transfer function of the middle layer to map the data to the range of (0, 1) for processing. The purelin function is selected as the transfer function of the output layer, the LM algorithm is selected as the training function of the neural network model, and the learngdm function is selected as the learning function;

[0028] Select seven-tenths of the data in the database for training using Matlab. After training is completed, select the remaining data in the database to verify the generalization ability of the model;

[0029] After verification, the model establishment is completed.

[0030] The number of middle layers and the number of neurons in each layer can be determined by trial and error through continuous changes, and the numbers are different for different ship data.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. In the fixed-frequency pump selection device and its selection method for a ship's central cooling system of the present invention, the control mechanism is signal-connected to a heat exchanger. A heat exchanger is arranged on the fresh water pipeline system. The water inlet end of the fresh water pipeline system is communicated with the seawater area through a second heat exchanger. A second flow sensor and a temperature sensor are arranged on the pipeline between the fresh water pipeline system and the seawater area. A first flow sensor is arranged on the pipeline between the fresh water pipeline system and the control mechanism. A first cooling water pump, a second cooling water pump, and a third cooling water pump are sequentially arranged on the fresh water pipeline system. The low-temperature fresh water flow is measured by the first flow sensor and the second flow sensor, and the seawater inlet temperature is measured by the temperature sensor. The first cooling water pump, the second cooling water pump, and the third cooling water pump are selected by the main control mechanism according to the measurement results. The fixed-frequency pump can be selected according to the actual situation of the seawater temperature and flow, reducing the error in estimating the size of the optimal low-temperature fresh water flow. Therefore, the selection of this design is convenient and highly accurate.

[0033] 2. In the fixed-frequency pump selection device and its selection method for a ship's central cooling system of the present invention, according to the established database, a mathematical model of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 of the seawater area side heat exchanger is established through a neural network. The preset temperature of the seawater area in the navigation environment is input into the mathematical model to obtain the low-temperature fresh water inlet flow Q21 at the current seawater area temperature. After obtaining the optimal low-temperature fresh water flow, it can not only provide a scientific reference for the pump selection, thereby reducing energy waste caused by over-selection, but also evaluate the performance of the cooling system. Therefore, this design saves energy and has accurate evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic structural diagram of the present invention.

[0035] In the figure: a first flow sensor 1, a second flow sensor 2, a first cooling water pump 3, a second cooling water pump 4, a third cooling water pump 5, a temperature sensor 6, a control mechanism 7, a seawater area 8, a first heat exchanger 9, a second heat exchanger 10, a fresh water pipeline system 11, a main pipeline 111, a first branch pipeline 112, a second branch pipeline 113. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0037] See Figure 1 , a fixed-frequency pump selection device for a ship's central cooling system. The fixed-frequency pump selection device for the ship's central cooling system includes a first cooling water pump 3, a second cooling water pump 4, a third cooling water pump 5, a control mechanism 7, and a fresh water pipeline system 11;

[0038] The control mechanism 7 is connected to a heat exchanger 9 by signal. A heat exchanger 9 is arranged on the fresh water pipeline system 11. The water inlet end of the fresh water pipeline system 11 is communicated with the seawater area 8 through a second heat exchanger 10. A second flow sensor 2 and a temperature sensor 6 are arranged on the pipeline between the fresh water pipeline system 11 and the seawater area 8. A first flow sensor 1 is arranged on the pipeline between the fresh water pipeline system 11 and the control mechanism 7. A first cooling water pump 3, a second cooling water pump 4 and a third cooling water pump 5 are sequentially arranged on the fresh water pipeline system 11.

[0039] The fresh water pipeline system 11 includes a main pipeline 111, a first branch pipeline 112 and a second branch pipeline 113. The first cooling water pump 3 is arranged on the main pipeline 111. The second cooling water pump 4 is arranged on the first branch pipeline 112. The third cooling water pump 5 is arranged on the second branch pipeline 113.

[0040] The first cooling water pump 3, the second cooling water pump 4 and the third cooling water pump 5 are not communicated with each other.

[0041] A selection method for a fixed-frequency pump selection device of a ship central cooling system. The selection method for the fixed-frequency pump selection device of the ship central cooling system includes the following steps:

[0042] Step 1: Obtain the flow data of the total low-temperature fresh water flow Q1, the low-temperature fresh water inlet flow Q2 at the control mechanism 7 and the seawater area 8, and the seawater area inlet temperature T5.

[0043] Step 2: After generating a database according to the flow data and the data under normal working conditions of the control mechanism 7, establish a database of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5.

[0044] Step 3: According to the established database, establish a mathematical model of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 of the seawater area side heat exchanger 2 through a neural network.

[0045] Step 4: Input the preset temperature of the seawater area in the navigation environment into the mathematical model to obtain the low-temperature fresh water inlet flow Q21 at the current seawater area temperature.

[0046] Step 5: After comparing and analyzing the low-temperature fresh water inlet flow Q21 and the total low-temperature fresh water flow Q1, obtain the selection result.

[0047] The specific method for obtaining the flow data at the control mechanism 7 and the seawater area 8 is as follows:

[0048] The first flow sensor 1 obtains the total low-temperature fresh water flow Q1 during the operation of the control mechanism 7.

[0049] The second flow sensor 2 obtains the low-temperature fresh water inlet flow Q2 at the second heat exchanger 10.

[0050] The temperature sensor 6 obtains the inlet temperature T5 of the seawater area at the second heat exchanger 10.

[0051] After generating the database according to the flow data and the data under normal operating conditions of the control mechanism 7, it further includes: a low-temperature fresh water subsystem and a seawater area cooling subsystem are provided in the control mechanism 7, and the control mechanism 7 monitors the data of the low-temperature fresh water subsystem and the seawater area cooling subsystem.

[0052] The comparison and analysis specifically is:

[0053] If Q21 is less than Q1, the selected types of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 are too large;

[0054] If Q21 is greater than Q1, the performance of the cooling system decreases or the selected types of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 are too small;

[0055] If Q21 is equal to Q1, the selected types of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 are reasonable.

[0056] If Q21 is less than Q1, it indicates that a part of the low-temperature fresh water passes through the pipeline of the second heat exchanger 10, that is, the flow rate of this part of the low-temperature fresh water does not need to be cooled, and the type selection of the cooling water pump can be carried out according to the data result of Q21.

[0057] The specific establishment of the neural network is as follows: determine the number of network layers and the number of neurons in each layer. The input layer and the output layer are both 1 layer, and the corresponding number of neurons are the data dimensions of the input and output variables respectively. The input variable in the model is the low-temperature fresh water inlet flow rate Q2 at the second heat exchanger 10, and the output variable is the total low-temperature fresh water flow rate Q1. Therefore, the data dimensions are both 1;

[0058] In the model, the Log-sigmoid function is selected as the transfer function of the middle layer to map the data to the range of (0, 1) for processing. The purelin function is selected as the transfer function of the output layer, the LM algorithm is selected as the training function of the neural network model, and the learngdm function is selected as the learning function;

[0059] Select seven-tenths of the data in the database for training using Matlab. After the training is completed, select the remaining data in the database to verify the generalization ability of the model;

[0060] After verification, the model is established.

[0061] The number of middle layers and the number of neurons in each layer can be determined by trial and error through continuous changes, and their numbers are different for different ship data.

[0062] Embodiment 1:

[0063] A fixed-frequency pump selection device for a ship's central cooling system, the fixed-frequency pump selection device for the ship's central cooling system includes a cooling water pump 3, a second cooling water pump 4, a third cooling water pump 5, a control mechanism 7 and a fresh water pipeline system 11; the control mechanism 7 is signal-connected to a heat exchanger 9, the heat exchanger 9 is arranged on the fresh water pipeline system 11, the water inlet end of the fresh water pipeline system 11 is communicated with the seawater area 8 through a second heat exchanger 10, and a second flow sensor 2 and a temperature sensor 6 are arranged on the pipeline between the fresh water pipeline system 11 and the seawater area 8, and a first flow sensor 1 is arranged on the pipeline between the fresh water pipeline system 11 and the control mechanism 7, and a first cooling water pump 3, a second cooling water pump 4, and a third cooling water pump 5 are arranged on the fresh water pipeline system 11 in sequence.

[0064] A selection method for a fixed-frequency pump selection device of a ship's central cooling system, the selection method for the fixed-frequency pump selection device of the ship's central cooling system includes the following steps:

[0065] Step 1: Obtain the flow data of the total low-temperature fresh water flow Q1, the low-temperature fresh water inlet flow Q2, and the seawater area inlet temperature T5 at the control mechanism 7 and the seawater area 8;

[0066] Step 2: After generating a database based on the flow data and the data under normal working conditions of the control mechanism 7, establish a database of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5;

[0067] Step 3: According to the established database, establish a mathematical model of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 of the seawater area side heat exchanger 2 through a neural network;

[0068] Step 4: Input the preset temperature of the seawater area in the navigation environment into the mathematical model, the preset temperature is 32 °C, and obtain the low-temperature fresh water inlet flow Q21 at the current seawater area temperature;

[0069] Step 5: After comparing and analyzing the low-temperature fresh water inlet flow Q21 and the total low-temperature fresh water flow Q1, obtain the selection result.

[0070] Example 2:

[0071] Example 2 is basically the same as Example 1, and the difference is as follows:

[0072] A fixed-frequency pump selection device for a ship's central cooling system, the fresh water pipeline system 11 includes a main pipeline 111, a first branch pipeline 112 and a second branch pipeline 113, a first cooling water pump 3 is arranged on the main pipeline 111, a second cooling water pump 4 is arranged on the first branch pipeline 112, a third cooling water pump 5 is arranged on the second branch pipeline 113, and the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 are not connected to each other.

[0073] Example 3:

[0074] Example 3 is basically the same as Example 1, and the difference lies in:

[0075] A selection method for a fixed-frequency pump selection device of a ship's central cooling system. The specific process of obtaining the flow data at the acquisition control mechanism 7 and the seawater area 8 is as follows: A flow sensor 1 obtains the total low-temperature fresh water flow Q1 during the operation of the acquisition control mechanism 7; a second flow sensor 2 obtains the low-temperature fresh water inlet flow Q2 at the second heat exchanger 10; a temperature sensor 6 obtains the seawater area inlet temperature T5 at the second heat exchanger 10. After generating a database based on the flow data and the data under normal operating conditions of the acquisition control mechanism 7, it further includes: There is a low-temperature fresh water subsystem and a seawater area cooling subsystem in the acquisition control mechanism 7, and the acquisition control mechanism 7 monitors the data of the low-temperature fresh water subsystem and the seawater area cooling subsystem. The comparison and analysis are specifically as follows: If Q21 is less than Q1, the selection of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 is too large; if Q21 is greater than Q1, the performance of the cooling system decreases or the selection of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 is too small; if Q21 is equal to Q1, the selection of the first cooling water pump 3, the second cooling water pump 4, and the third cooling water pump 5 is reasonable; If Q21 is less than Q1, it means that a part of the low-temperature fresh water passes through the pipeline of the second heat exchanger 10, that is, the flow of this part of the low-temperature fresh water does not need to be cooled, and the selection of the cooling water pump can be carried out according to the data result of Q21.

[0076] Example 4:

[0077] Example 4 is basically the same as Example 1, and the difference lies in:

[0078] A selection method for a fixed-frequency pump selection device of a ship's central cooling system. The specific process of establishing the neural network is as follows: Determine the number of network layers and the number of neurons in each layer. The input layer and the output layer are both 1 layer, and the corresponding number of neurons is the data dimension of the input and output variables. The input variable in the model is the low-temperature fresh water inlet flow Q2 at the second heat exchanger 10, and the output variable is the total low-temperature fresh water flow Q1, so the data dimensions are both 1; in the model, the Log-sigmoid function is selected as the transfer function of the middle layer to map the data to the range of (0,1) for processing, the purelin function is selected as the transfer function of the output layer, the LM algorithm is selected as the training function of the neural network model, and the learngdm function is selected as the learning function; Select seven-tenths of the data in the database for training using Matlab. After the training is completed, select the remaining data in the database to verify the generalization ability of the model; After verification, the model is established; The number of middle layers and the number of neurons in each layer can be determined by trial and error by constantly changing, and the numbers are different for different ship data.

[0079] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those of ordinary skill in the art according to the disclosure of the present invention shall fall within the protection scope recorded in the claims.

Claims

1. A fixed-frequency pump selection device for a ship's central cooling system, characterized in that : The fixed-frequency pump selection device of the ship's central cooling system includes a first cooling water pump (3), a second cooling water pump (4), a third cooling water pump (5), a control mechanism (7) and a fresh water pipeline system (11); The control mechanism (7) is signal-connected to a first heat exchanger (9). The first heat exchanger (9) is arranged on the fresh water pipeline system (11). The water inlet end of the fresh water pipeline system (11) is communicated with the seawater area (8) through a second heat exchanger (10). Two flow sensors (2) and a temperature sensor (6) are arranged on the pipeline between the fresh water pipeline system (11) and the seawater area (8). A flow sensor (1) is arranged on the pipeline between the fresh water pipeline system (11) and the control mechanism (7). A first cooling water pump (3), a second cooling water pump (4), and a third cooling water pump (5) are successively arranged on the fresh water pipeline system (11); The fresh water pipeline system (11) includes a main pipeline (111), a first branch pipeline (112) and a second branch pipeline (113). The first cooling water pump (3) is arranged on the main pipeline (111). The second cooling water pump (4) is arranged on the first branch pipeline (112). The third cooling water pump (5) is arranged on the second branch pipeline (113); The first cooling water pump (3), the second cooling water pump (4), and the third cooling water pump (5) are not connected to each other.

2. A selection method for a fixed-frequency pump selection device of the ship central cooling system according to claim 1, characterized in that: The selection method of the fixed-frequency pump selection device of the ship's central cooling system includes the following steps: Step 1: Obtain the flow data of the total low-temperature fresh water flow Q1, the low-temperature fresh water inlet flow Q2, and the seawater area inlet temperature T5 at the control mechanism (7) and the seawater area (8); Step 2: After generating a database based on the flow data and the data under normal working conditions of the control mechanism (7), establish a database of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5; Step 3: According to the established database, establish a mathematical model of the low-temperature fresh water inlet flow Q2 and the seawater area inlet temperature T5 of the second heat exchanger (10) in the seawater area through a neural network; Step 4: Input the preset temperature of the seawater area in the navigation environment into the mathematical model to obtain the low-temperature fresh water inlet flow Q21 at the current seawater area temperature; Step 5: After comparing and analyzing the low-temperature fresh water inlet flow Q21 and the total low-temperature fresh water flow Q1, obtain the selection result.

3. The selection method of a fixed-frequency pump selection device for a ship's central cooling system according to claim 2, characterized in that: The specific method for obtaining the flow data at the control mechanism (7) and the seawater area (8) is as follows: A flow sensor (1) obtains the total low-temperature fresh water flow Q1 during the operation of the control mechanism (7); Two flow sensors (2) obtain the low-temperature fresh water inlet flow Q2 at the second heat exchanger (10); The temperature sensor (6) obtains the seawater area inlet temperature T5 at the second heat exchanger (10).

4. The selection method of a fixed-frequency pump selection device for a ship central cooling system according to claim 3, characterized in that: After generating a database based on the flow data and the data under normal working conditions of the control mechanism (7), it further includes: The control mechanism (7) is provided with a low-temperature fresh water subsystem and a seawater area cooling subsystem, and the control mechanism (7) monitors the data of the low-temperature fresh water subsystem and the seawater area cooling subsystem.

5. The selection method of a fixed-frequency pump selection device for a ship's central cooling system according to claim 2, characterized in that: The comparison and analysis are specifically as follows: If Q21 is less than Q1, the selection of the first cooling water pump (3), the second cooling water pump (4), and the third cooling water pump (5) is too large; If Q21 is greater than Q1, the performance of the cooling system deteriorates or the selected models of the first cooling water pump (3), the second cooling water pump (4), and the third cooling water pump (5) are too small. If Q21 is equal to Q1, the selected models of the first cooling water pump (3), the second cooling water pump (4), and the third cooling water pump (5) are reasonable.

6. The selection method of a fixed-frequency pump selection device for a ship central cooling system according to claim 5, characterized in that: If Q21 is less than Q1, it indicates that a part of the low-temperature fresh water passes through the pipeline of the second heat exchanger (10), that is, the low-temperature fresh water flow in this part does not need to be cooled. The model selection of the cooling water pump can be carried out according to the data result of Q21.

7. The selection method of a fixed-frequency pump selection device for a ship's central cooling system according to claim 2, characterized in that: The establishment of the neural network is specifically as follows: Determine the number of network layers and the number of neurons in each layer. The input layer and the output layer are both 1 layer, and the corresponding number of neurons are the data dimensions of the input and output variables. In the model, the input variable is the low-temperature fresh water inlet flow Q2 at the second heat exchanger (10), and the output variable is the total low-temperature fresh water flow Q1. Therefore, the data dimensions are both 1. In the model, the Log-sigmoid function is selected as the transfer function of the middle layer to map the data to the range of (0, 1) for processing. The purelin function is selected as the transfer function of the output layer. The LM algorithm is selected as the training function of the neural network model, and the learngdm function is selected as the learning function. Select seven-tenths of the data in the database for training using Matlab. After the training is completed, select the remaining data in the database to verify the generalization ability of the model. After verification, the model is established.

8. The selection method of the fixed-frequency pump selection device for a ship central cooling system according to claim 7, characterized in that: The number of middle layers and the number of neurons in each layer can be determined by continuous trial and error, and the numbers are different for different ship data.

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