Method for calculating jet thrust of water jet propulsion ship

Abstract

The invention discloses a method for calculating the jet thrust of a water jet propulsion ship, and the method comprises a ship model which comprises a naked ship and a ship body with water jet propulsion. The relation among the rotating speed, the pressure difference and the flow of the ship body with water jet propulsion is obtained; based on the obtained relation among the rotating speed, the pressure difference and the flow of the ship body with the water jet propulsion function, a water jet propulsion ship jet thrust hydrodynamic model of the ship body with the water jet propulsion function is constructed; and based on the jet thrust hydrodynamic model of the water jet propulsion ship, jet thrust and steering force of the ship body with water jet propulsion are obtained through calculation. According to the method, a momentum impulse method is adopted, the water jet propulsion flow and the inlet and outlet flow speed are obtained, and the water jet propulsion force and the steering force are obtained by considering the thrust derating fraction, the steering induction factor and the like in the control process.

Description

Technical Field

[0001] The invention relates to a method for calculating the thrust of a water jet propulsion ship, and belongs to the technical field of water jet propulsion ships. Background Art

[0002] Waterjet propulsion ships have the advantages of good maneuverability, low vibration and noise, and are suitable for near-shore shallow water operations. Especially in high-speed military ships, waterjet propulsion systems have obvious advantages over propeller propulsion and have been widely used. Therefore, in-depth research on the hydrodynamic performance of waterjet propulsion systems is particularly important.

[0003] In the early stage of the study of waterjet propulsion performance, due to the limitation of technical conditions, most of the research focused on the evaluation of the hydrodynamic performance of a single waterjet propulsion unit. Since the operating conditions of a single waterjet propulsion unit are quite different from the actual working conditions behind the ship, the influence between the hull and the waterjet propulsion unit cannot be ignored. More and more scholars have carried out research on the hydrodynamic performance of the waterjet propulsion unit behind the ship and the mutual interference between the ship and the waterjet propulsion system. However, so far, related research has mainly focused on the field of rapidity of waterjet propulsion ships, and there are few related studies in the field of maneuverability of waterjet propulsion ships. In terms of maneuvering motion modeling, it is ignored that when the waterjet propulsion system is turned on, the suction effect causes the flow field at the stern of the hull to change, which in turn leads to the hull posture and the hydrodynamic changes of the hull. On the other hand, it is not considered that the waterjet flow rate changes when the speed, heading, and angular velocity of the bow turn change during the maneuvering motion of the waterjet propulsion ship, which in turn leads to changes in the thrust of the waterjet propulsion unit.

[0004] Therefore, it is necessary to develop a jet thrust calculation method that takes into account the changes in waterjet flow caused by changes in speed, heading, and bow angular velocity during the maneuvering of waterjet ships. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for calculating the jet thrust of a waterjet ship, which adopts the momentum impulse method to obtain the flow rate of the waterjet propulsion and the flow rate of the inlet and outlet, and considers the thrust reduction fraction, steering induction factor, etc. during the maneuvering process to obtain the waterjet propulsion force and steering force.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a method for calculating the jet thrust of a water jet propulsion ship, comprising a ship model, wherein the ship model comprises a naked ship and a ship hull with a water jet propulsion, and is characterized in that the method comprises the following steps:

[0008] Obtain the relationship between the rotation speed, pressure difference and flow rate of a hull with water jet propulsion;

[0009] Based on the obtained relationship between the rotation speed, pressure difference and flow rate of the water jet propulsion ship, a water jet thrust hydrodynamic model of the water jet propulsion ship with water jet propulsion hull is constructed;

[0010] Based on the hydrodynamic model of waterjet propulsion ship, the jet thrust and steering force of the waterjet propulsion ship are calculated.

[0011] Preferably, the relationship between the rotational speed, pressure difference and flow rate of the water jet propulsion hull includes determining the flow rate of the water jet propulsion through model tests, installing multiple pressure sensors on a single water jet propulsion, monitoring the pressure of two sections of the nozzle contraction section, and obtaining the relationship between the rotational speed, pressure difference and flow rate.

[0012] Furthermore, the model test includes:

[0013] The water inlet and the water outlet of the bare hull are blocked, and the resistance and attitude of the bare hull at the required speed are measured when the bare hull moves in straight and oblique directions respectively;

[0014] The straight-line motion of the water jet propulsion hull is constrained, and the pressure of two sections of the nozzle contraction section and the ship model posture are measured at the required speed of the water jet propulsion hull, so as to obtain the straight-line nozzle flow rate when the water jet propulsion hull is in straight-line motion, and the flow velocity of the straight-line flow-gaining area is determined based on the straight-line nozzle flow rate, and then the thrust of the water jet propulsion and the thrust reduction are determined based on the flow velocity of the straight-line flow-gaining area;

[0015] The oblique navigation motion of the hull with water jet propulsion is constrained, and the pressure of two sections of the nozzle contraction section and the ship model attitude are measured at the required speed of the hull with water jet propulsion, so as to obtain the oblique navigation nozzle flow rate when the hull with water jet propulsion is in oblique navigation, and the flow velocity of the oblique navigation gaining flow area is determined based on the oblique navigation nozzle flow rate, and then the thrust of water jet propulsion and the thrust reduction are determined based on the flow velocity of the oblique navigation gaining flow area;

[0016] The thrust and thrust reduction under different drift angles are obtained by converting the thrust and thrust reduction during straight flight and the thrust and thrust reduction during oblique flight.

[0017] Furthermore, the thrust of the waterjet propulsion of the waterjet-propelled hull is calculated by the momentum impulse difference between the nozzle and the inlet of the acquisition area; the thrust reduction of the waterjet propulsion of the waterjet-propelled hull is calculated by the thrust obtained by the waterjet-propelled hull and the resistance of the bare hull.

[0018] Furthermore, the control equation of the water jet propulsion hull in the x direction is as follows:

[0019]

[0020] Among them, A1, A2, A3, A4, A5, and A6 are six physical surfaces of the waterjet propulsion hull under the action of the waterjet propulsion system. A1 is the water inlet surface of the waterjet propulsion system flow area, A2 is the physical surface of the inlet flow pipe, A3 is the physical surface of the waterjet propulsion flow channel that is not in the flow field control body, A4 is the inner surface of the waterjet propulsion system flow channel, A5 is the body force physical surface of the waterjet propulsion, and A6 is the physical surface of the nozzle. i is the velocity component in any direction, u is the flow field velocity, n is the control surface normal vector, σ i is the component of stress acting on the control surface in the i direction, F pi is the component of the water jet propulsion body force in the i direction, Fi is the component of the control body force in the i direction, V is the control force volume contained in the A1, A2, A3, A4, A5 surfaces; the total thrust on the hull with water jet propulsion in the x direction is defined as:

[0021]

[0022] Furthermore, the actual physical surface of the water jet propulsion hull and the hull includes the physical surface A3 of the water jet propulsion flow channel that is not in the flow field control body, the inner surface A4 of the water jet propulsion system flow channel and the body force physical surface A5 of the water jet propulsion. The force transmitted to the hull by the water jet propulsion system is defined as the net thrust, and its expression is:

[0023]

[0024] The relationship between the gross thrust and the net thrust is as follows:

[0025] T net =(1-t j )T gross ;

[0026] Among them, t j is the momentum deduction fraction. When the nozzle is completely in the air or underwater, the momentum deduction fraction is usually 0, that is, the total thrust is equal to the net thrust.

[0027] Furthermore, when maneuvering the oblique navigation motion, the position and size of the inlet surface of the oblique navigation flow acquisition area of ​​the water jet propulsion hull change, and the net thrust transmitted to the hull by the water jet propulsion system of the water jet propulsion hull is calculated by CFD with the aid of model test, and then the position and size of the flow acquisition area are determined, and the total thrust is calculated by the momentum difference. Based on the thrust relationship, the jet thrust hydrodynamic model of the water jet propulsion ship with the water jet propulsion hull is obtained as follows:

[0028]

[0029] Where Q is the flow rate of the waterjet propulsion. When the impeller speed is fixed, the flow rate Q is related to the ship speed U, the distance b between the centerline of the jet pump and the center of the ship, and the lateral velocity vx at the entrance of the waterjet propulsion channel. p Function between r, x p is the distance from the center section of the flow channel inlet to the center of gravity; the functional relationship of the flow rate Q of the water jet propulsion system is derived through the measurement of the straight-line test and the oblique-line test;

[0030] U6 is the nozzle flow rate, specifically:

[0031]

[0032] U6 is obtained by the flow rate Q, c is the inflow momentum coefficient, the c coefficient of the self-propelled condition is only related to the speed, the c coefficient of the hull with water jet propulsion is related to the distance b from the centerline of the jet pump to the middle of the ship and the lateral speed at the entrance of the water jet propulsion channel. The coefficient c is related to (U, b, vx p The expression of r) is obtained through CFD simulation of the oblique ship test.

[0033] Furthermore, when calculating the steering force of the waterjet-propelled hull, the nozzle rotates at equal intervals within a preset angle range when the waterjet-propelled hull moves in straight and oblique directions, and the force on the hull at each interval is converted into the steering induction factor during straight and oblique directions.

[0034] Furthermore, the water jet propulsion hull is driven by the steering mechanism at an inlet speed of U i , the exit speed is U o , where U i The water jet is ejected from the nozzle of the water jet propulsion hull, that is:

[0035] Q i =Q6,U i =U6;

[0036] According to the momentum theorem, the force on the steering mechanism is:

[0037] F R =ρQ i U i -ρQ o U o ;

[0038] Among them, Q i is the inlet flow rate, Q i =Q6,Q o is the outlet flow rate. From the law of conservation of mass, we know that Q i =Q o , so the force on the steering mechanism is:

[0039] F R =ρQi (U i -U o ).

[0040] Furthermore, the directions in which the steering mechanism with water jet propulsion hull is subjected to force include:

[0041]

[0042] Among them, δ is the rudder angle, X R A is the projection of the distance from the force center of the steering mechanism to the center on the x-axis; i is the nozzle area, A0 is the outlet area, and since Q i =Q6, Q6 is obtained through model test, a is the proportional coefficient between the induced lateral force of the steering mechanism on the hull and the force on the steering mechanism, X H is the distance from the center of force of the lateral force induced by the steering mechanism to the center of gravity of the ship, a, X H The value of the coefficient is determined by steering tests during straight and oblique navigation.

[0043] The method for calculating the thrust of a water jet propulsion ship provided by the present invention has the following advantages:

[0044] (1) The method for calculating the thrust of a waterjet-propelled ship of the present invention takes into account the influence of waterjet propulsion on the hull posture, is closer to the actual operating conditions of the waterjet-propelled ship, and has higher accuracy.

[0045] (2) The method for calculating the jet thrust of a waterjet ship of the present invention takes into account the influence of the hull drift angle on the waterjet flow rate, and the jet thrust analysis of the waterjet propulsion is more accurate.

[0046] (3) The method for calculating the jet thrust of a waterjet-propelled ship of the present invention takes into account the influence of the hull drift angle on the thrust reduction and the steering induction factor, and the steering force analysis of the waterjet propulsion is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a calculation flow chart of a method for calculating the thrust of a water jet propulsion ship according to the present invention;

[0048] Figure 2 A coordinate system of a method for calculating the jet thrust of a water jet propulsion ship according to the present invention;

[0049] Figure 3 It is a schematic diagram of a force control body of a water jet propulsion system in a method for calculating the jet thrust of a water jet propulsion ship according to the present invention;

[0050] Figure 4 The present invention provides a schematic diagram of the steering force of a water jet propulsion system in a method for calculating the jet thrust of a water jet propulsion ship. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technical personnel in this field without creative work are within the scope of protection of the present invention.

[0052] Reference Figure 1 The present application provides a method for calculating the jet thrust of a water jet propulsion ship, which is assisted by a ship model. The ship model includes a naked ship and a hull with a water jet propulsion, and includes the following steps:

[0053] S1, obtain the relationship between the rotation speed, pressure difference and flow rate of the hull with water jet propulsion;

[0054] The flow rate of water jet propulsion is measured by a model test of a hull with water jet propulsion. The pressure of two sections of the contraction section of the nozzle of the hull with water jet propulsion is monitored. Four pressure sensors are evenly installed on a single section of water jet propulsion, and there are eight pressure sensors in total for two water jet propulsion sections. The water sprayed from the water jet propulsion nozzle is collected and weighed in a rectangular box with an upper opening, and the measured time is recorded at the same time. The speed is measured by a speed encoder, and the flow rate is the ratio of the weight of the measured water to the recorded time. The average of the values ​​measured by the four pressure sensors is used to obtain the pressure of a certain section, and the relationship between the pressure difference between the two sections, the speed and the flow rate is obtained.

[0055] S2, reference Figure 2 and Figure 3 , based on the obtained relationship between the rotation speed, pressure difference and flow rate of the water jet propulsion ship, a water jet thrust hydrodynamic model of the water jet propulsion ship with water jet propulsion hull is constructed;

[0056] Hull model test with water jet propulsion includes:

[0057] The water inlet and outlet of the bare hull are blocked, and the resistance and attitude of the bare hull at the required speed are measured when the bare hull moves in straight and oblique directions, including trim, heave, etc.;

[0058] Constrain the straight-line motion of the hull with water jet propulsion, measure the pressure of the two sections of the nozzle contraction section and the ship model attitude (trim, heave, etc.) at the required speed of the hull with water jet propulsion, obtain the straight-line nozzle flow rate when the hull with water jet propulsion is in straight-line motion, and determine the flow velocity in the straight-line flow-gaining area based on the straight-line nozzle flow rate, and then determine the thrust of water jet propulsion and thrust reduction based on the flow velocity in the straight-line flow-gaining area;

[0059] Constrain the oblique motion of the hull with water jet propulsion, measure the pressure of the two sections of the nozzle contraction section and the ship model attitude at the required speed of the hull with water jet propulsion, obtain the oblique nozzle flow rate when the hull with water jet propulsion moves obliquely, and determine the flow velocity in the oblique flow area based on the oblique nozzle flow rate, and then determine the thrust of water jet propulsion and thrust reduction based on the flow velocity in the oblique flow area;

[0060] Finally, the thrust and thrust reduction under different drift angles are obtained by converting the thrust and thrust reduction during straight flight and the thrust and thrust reduction during oblique flight.

[0061] In a further embodiment, the thrust of the waterjet propulsion of the waterjet-propelled hull is calculated by the momentum impulse difference between the nozzle and the inlet of the acquisition area; the thrust reduction of the waterjet propulsion of the waterjet-propelled hull is calculated by the thrust obtained by the waterjet-propelled hull and the resistance of the bare hull.

[0062] The control equation of the hull with water jet propulsion in the x direction is as follows:

[0063]

[0064] Among them, A1, A2, A3, A4, A5, and A6 are six physical surfaces of the waterjet propulsion hull under the action of the waterjet propulsion system. A1 is the water inlet surface of the waterjet propulsion system flow area, A2 is the physical surface of the inlet flow pipe, A3 is the physical surface of the waterjet propulsion flow channel that is not in the flow field control body, A4 is the inner surface of the waterjet propulsion system flow channel, A5 is the body force physical surface of the waterjet propulsion, and A6 is the physical surface of the nozzle. i is the velocity component in any direction, u is the flow field velocity, n is the control surface normal vector, σ i is the component of stress acting on the control surface in the i direction, F pi is the component of the water jet propulsion body force in the i direction, Fi is the component of the control body force in the i direction, V is the control force volume contained in the A1, A2, A3, A4, A5 surfaces; the total thrust on the hull with water jet propulsion in the x direction is defined as:

[0065]

[0066] The surface of the waterjet-propelled hull affected by the waterjet propulsion system also includes the jet section A7.

[0067] Furthermore, the actual physical surfaces acting on the hull with water jet propulsion are only the physical surface A3 of the water jet propulsion channel that is not in the flow field control body, the inner surface A4 of the water jet propulsion system flow channel and the physical surface A5 of the water jet propulsion volume force. Therefore, the force transmitted to the hull by the water jet propulsion system is defined as the net thrust, and its expression is:

[0068]

[0069] The relationship between the total thrust and the net thrust on a waterjet propulsion hull is as follows:

[0070] T net =(1-t j )T gross (4);

[0071] Among them, t j is the momentum deduction fraction. When the nozzle is completely in the air or underwater, the momentum deduction fraction is usually 0, that is, the total thrust is equal to the net thrust.

[0072] Furthermore, when maneuvering oblique navigation, the flow acquisition area of ​​the water jet propulsion ship will change greatly relative to the self-propulsion condition. The position and size of the inlet surface may be different from those of the straight navigation condition, and the position and size of the inlet surface are the determining factors of the thrust measurement accuracy. The force measurement is completed by the CFD calculation method assisted by the model test. The net thrust can be obtained through CFD calculation, and the position and size of the "flow acquisition area" can also be determined. Then, the total thrust is calculated through the momentum difference. Based on the thrust relationship, the jet thrust hydrodynamic model of the water jet propulsion ship with a water jet propulsion hull is obtained as follows:

[0073]

[0074] Where Q is the flow rate of the waterjet propulsion. When the impeller speed is fixed, the flow rate Q is related to the ship speed U, the distance b between the centerline of the jet pump and the center of the ship, and the lateral velocity vx at the entrance of the waterjet propulsion channel. p Function between r, x p is the distance from the center section of the flow channel inlet to the center of gravity; the functional relationship of the flow rate Q of the water jet propulsion system is derived through the measurement of the straight-line test and the oblique-line test;

[0075] U6 is the nozzle flow rate, specifically:

[0076]

[0077] Therefore, as long as the flow rate Q is obtained, U6 can be obtained, c is the inflow momentum coefficient. The c coefficient of the self-propelled condition is only related to the speed. The c coefficient of the maneuverability problem involved in the present invention is also related to the distance b from the centerline of the jet pump to the middle of the ship and the lateral speed at the entrance of the water jet propulsion flow channel. The coefficient c is related to (U, b, vx p The expression of r) is obtained by CFD simulation of the oblique navigation test. So far, the water jet propulsion force model used in the present invention is given. The model directly predicts the performance of the water jet propulsion system behind the ship, taking into account the influence of the hull on the water jet propulsion.

[0078] S3, refer to Figure 2-Figure 4 , based on the hydrodynamic model of waterjet propulsion, the jet thrust and steering force of the waterjet propulsion ship are calculated;

[0079] When calculating the steering force of a hull with water jet propulsion, the nozzle is rotated at equal intervals within a preset angle range when the hull with water jet propulsion moves in straight sailing and oblique sailing respectively, and the force on the hull at each interval is converted into the steering induction factor during straight sailing and oblique sailing. In this embodiment, preferably, the steering induction factor is converted based on the force on the hull when the nozzle rotates 0-30° at every 5° interval.

[0080] like Figure 4 As shown, the water jet propulsion hull is driven by the steering mechanism, and the inlet speed is U i , the exit speed is U o , where U i The water jet is ejected from the nozzle of the water jet propulsion hull, that is:

[0081] Q i =Q6,U i =U6 (7);

[0082] According to the momentum theorem, the force on the steering mechanism is:

[0083] F R =ρQ i U i -ρQ o U o (8);

[0084] Among them, Q i is the inlet flow rate, Q i =Q6,Q o is the outlet flow rate. From the law of conservation of mass, we know that Q i =Q o , so formula (8) can be rewritten as:

[0085] F R =ρQ i (U i -U o )(9).

[0086] The directions of the forces acting on the steering mechanism of a water jet propulsion vessel include:

[0087]

[0088] Wherein, δ is the rudder angle. In this embodiment, it is positive with respect to the left rudder, and X R A is the projection of the distance from the force center of the steering mechanism to the center on the x-axis; i is the nozzle area, A0 is the outlet area, and since Q i =Q6, Q6 is obtained through model test, the relationship between Q6 and motion parameters such as speed, a is the proportional coefficient between the induced lateral force of the steering mechanism on the hull and the force on the steering mechanism, X His the distance from the center of force of the lateral force induced by the steering mechanism to the center of gravity of the ship, a, X H The value of the coefficient is determined by steering tests during straight and oblique sailing. So far, the method for calculating the jet thrust of a water jet ship in the present invention is given, which is based on the momentum flux method to give the force of the steering mechanism, while considering the influence of the steering mechanism on the hydrodynamic force of the hull.

[0089] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the jet thrust of a water jet propulsion ship, comprising a ship model, wherein the ship model comprises a naked ship and a ship with a water jet propulsion hull, characterized in that: The method comprises the following steps: Obtain the relationship between the rotation speed, pressure difference and flow rate of a hull with water jet propulsion; Based on the obtained relationship between the rotation speed, pressure difference and flow rate of the water jet propulsion ship, a water jet thrust hydrodynamic model of the water jet propulsion ship with water jet propulsion hull is constructed; Based on the hydrodynamic model of waterjet propulsion ship, the jet thrust and steering force of the waterjet propulsion ship are calculated.

2. A method for calculating the jet thrust of a water jet ship according to claim 1, characterized in that: The relationship between the rotation speed, pressure difference and flow rate of the water jet propulsion hull includes determining the flow rate of the water jet propulsion through model tests, installing multiple pressure sensors on a single water jet propulsion, monitoring the pressure of two sections of the nozzle contraction section, and obtaining the relationship between the rotation speed, pressure difference and flow rate.

3. A method for calculating the jet thrust of a water jet ship as claimed in claim 2, characterized in that: The model test includes: The water inlet and the water outlet of the bare hull are blocked, and the resistance and attitude of the bare hull at the required speed are measured when the bare hull moves in straight and oblique directions respectively; The straight-line motion of the water jet propulsion hull is constrained, and the pressure of two sections of the nozzle contraction section and the ship model posture are measured at the required speed of the water jet propulsion hull, so as to obtain the straight-line nozzle flow rate when the water jet propulsion hull is in straight-line motion, and the flow velocity of the straight-line flow-gaining area is determined based on the straight-line nozzle flow rate, and then the thrust of the water jet propulsion and the thrust reduction are determined based on the flow velocity of the straight-line flow-gaining area; The oblique navigation motion of the hull with water jet propulsion is constrained, and the pressure of two sections of the nozzle contraction section and the ship model attitude are measured at the required speed of the hull with water jet propulsion, so as to obtain the oblique navigation nozzle flow rate when the hull with water jet propulsion is in oblique navigation, and the flow velocity of the oblique navigation gaining flow area is determined based on the oblique navigation nozzle flow rate, and then the thrust of water jet propulsion and the thrust reduction are determined based on the flow velocity of the oblique navigation gaining flow area; The thrust and thrust reduction under different drift angles are obtained by converting the thrust and thrust reduction during straight flight and the thrust and thrust reduction during oblique flight.

4. A method for calculating the jet thrust of a water jet ship as claimed in claim 3, characterized in that: The thrust of the water jet propulsion of the water jet propulsion hull is calculated by the momentum impulse difference between the nozzle and the inlet of the flow acquisition area; the thrust reduction of the water jet propulsion of the water jet propulsion hull is calculated by the thrust obtained by the water jet propulsion hull and the resistance of the bare hull.

5. A method for calculating the jet thrust of a water jet ship as claimed in claim 4, characterized in that: The control equation of the water jet propulsion hull in the x direction is as follows: Among them, A1, A2, A3, A4, A5, and A6 are six physical surfaces of the waterjet propulsion hull under the action of the waterjet propulsion system. A1 is the water inlet surface of the waterjet propulsion system flow area, A2 is the physical surface of the inlet flow pipe, A3 is the physical surface of the waterjet propulsion flow channel that is not in the flow field control body, A4 is the inner surface of the waterjet propulsion system flow channel, A5 is the body force physical surface of the waterjet propulsion, and A6 is the physical surface of the nozzle. I is the velocity component in any direction, u is the flow field velocity, n is the control surface normal vector, σ i is the component of stress acting on the control surface in the i direction, F pi is the component of the water jet propulsion body force in the i direction, Fi is the component of the control body body force in the i direction, and V is the control force volume contained in the A1, A2, A3, A4, and A5 surfaces; The total thrust in the x direction on the hull with water jet propulsion is defined as:

6. A method for calculating the jet thrust of a water jet ship as claimed in claim 5, characterized in that: The actual physical surface of the water jet propulsion hull and the hull includes the physical surface A3 of the water jet propulsion flow channel that is not in the flow field control body, the inner surface A4 of the water jet propulsion system flow channel and the physical surface A5 of the water jet propulsion body force. The force transmitted to the hull by the water jet propulsion system is defined as the net thrust, and its expression is: The relationship between the gross thrust and the net thrust is as follows: T net =(1-t j )T gross (4); Among them, t j is the momentum deduction fraction. When the nozzle is completely in the air or underwater, the momentum deduction fraction is usually 0, that is, the total thrust is equal to the net thrust.

7. A method for calculating the jet thrust of a water jet ship as claimed in claim 6, characterized in that: When maneuvering the oblique navigation motion, the position and size of the inlet surface of the oblique navigation flow acquisition area of ​​the water jet propulsion hull change. The net thrust transmitted to the hull by the water jet propulsion system of the water jet propulsion hull is calculated by CFD with the aid of model test, and then the position and size of the flow acquisition area are determined, and the total thrust is calculated by the momentum difference. Based on the thrust relationship, the jet thrust hydrodynamic model of the water jet propulsion ship with the water jet propulsion hull is obtained as follows: Where Q is the flow rate of the waterjet propulsion. When the impeller speed is fixed, the flow rate Q is related to the ship speed U, the distance b between the centerline of the jet pump and the center of the ship, and the lateral velocity vx at the entrance of the waterjet propulsion channel. p Function between r, x p is the distance from the center section of the flow channel inlet to the center of gravity; the functional relationship of the flow rate Q of the water jet propulsion system is derived through the measurement of the straight-line test and the oblique-line test; U6 is the nozzle flow rate, specifically: U6 is obtained by the flow rate Q, c is the inflow momentum coefficient, the c coefficient of the self-propelled condition is only related to the speed, the c coefficient of the hull with water jet propulsion is related to the distance b from the centerline of the jet pump to the middle of the ship and the lateral speed at the entrance of the water jet propulsion channel. The coefficient c is related to (U, b, vx p The expression of r) is obtained through CFD simulation of the oblique ship test.

8. A method for calculating the jet thrust of a water jet ship as claimed in claim 7, characterized in that: When calculating the steering force of the waterjet-propelled hull, the nozzle rotates at equal intervals within a preset angle range when the waterjet-propelled hull moves in straight and oblique directions, and the force on the hull at each interval is converted into the steering induction factor when sailing straight and oblique directions.

9. A method for calculating the jet thrust of a water jet ship as claimed in claim 8, characterized in that: The water jet propulsion hull is driven by the steering mechanism, and the inlet speed is U i , the exit speed is U o , where U i The water jet is ejected from the nozzle of the water jet propulsion hull, that is: Q i =Q6,U i =U6 (7); According to the momentum theorem, the force on the steering mechanism is: F R =ρQ i U i -ρQ o U o (8); Among them, Q i is the inlet flow rate, Q i =Q6,Q o is the outlet flow rate. From the law of conservation of mass, we know that Q i =Q o , so formula (8) is: F R =ρQ i (U i -U o ) (9).

10. A method for calculating the jet thrust of a water jet ship according to claim 9, characterized in that: The directions in which the steering mechanism with water jet propulsion hull is subjected to force include: Among them, δ is the rudder angle, X R A is the projection of the distance from the force center of the steering mechanism to the center on the x-axis; i is the nozzle area, A0 is the outlet area, and since Q i =Q6, Q6 is obtained through model test, a is the proportional coefficient between the induced lateral force of the steering mechanism on the hull and the force on the steering mechanism, X H is the distance from the center of force of the lateral force induced by the steering mechanism to the center of gravity of the ship, a, X H The value of the coefficient is determined by steering tests during straight and oblique navigation.

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