A method for assessing the heading stability of a ship

Abstract

This invention relates to a method for assessing ship heading stability, comprising the following steps: starting from the definition of ship heading stability, a model for applying ship disturbance forces is proposed; the ship's self-center thrust and disturbance torque are calculated; numerical methods are used to simulate the ship's disturbed motion; and based on the analysis of the time-history curve of the ship's yaw rate change after disturbance, the maximum yaw rate, the time for yaw rate to return to zero, and the amplitude parameters of yaw rate fluctuation can be extracted to systematically evaluate the ship's heading stability. This method solves the problem that current heading stability assessment methods are difficult to be simple, efficient, and able to precisely describe the ship's heading stability state. The assessment results are more reliable, the method is convenient and easy to use, and the assessment efficiency is high.

Description

Technical Field

[0001] This invention relates to a ship maneuvering technology, and more particularly to a method for calculating ship heading stability. Background Technology

[0002] A ship's course stability falls under the category of ship maneuverability, referring to its ability to return to its original steady state of motion after a minor external disturbance has disappeared. Ship maneuverability is one of the important navigational performance characteristics of a ship, mainly studying its ability to maintain and change its speed, course, and position, and is closely related to navigation safety and economy. With the increasing speed and size of ships and the increasing density of shipping traffic, the study of ship maneuverability is showing its growing importance.

[0003] Current methods for predicting ship heading stability include two approaches: judging the ship's straight-line stability criterion number based on constrained model simulation tests, and judging the turning angular velocity after rudder return based on ship rudder return motion simulation tests. The method based on the straight-line stability criterion number requires first obtaining the ship's maneuvering hydrodynamic derivative through a series of constrained model planar mechanism motion tests or simulations, and then calculating the ship's straight-line stability criterion number based on the hydrodynamic derivative. If the criterion number is greater than zero, it indicates that the ship has heading stability; otherwise, it does not. The ship rudder return motion involves steering the ship to a specified rudder angle for a period of time while sailing at a constant speed in a straight line, allowing the ship to enter a stable turning state. Then, the ship's turning angular velocity is monitored after rudder return. If the turning angular velocity returns to zero, it proves that the ship has heading stability; otherwise, it does not. In summary, both methods of judging heading stability require complex model tests or numerical simulations, resulting in relatively high evaluation costs. Furthermore, the evaluation results only determine whether the ship has heading stability; there are no quantitative indicators to further determine the degree of heading stability, making it difficult to effectively support the refined design of ship heading stability. Summary of the Invention

[0004] To address the shortcomings of current methods for assessing heading stability, which often lack simplicity, efficiency, and the ability to accurately describe a ship's heading stability state, a new method for evaluating heading stability is proposed. Starting from the definition of heading stability, a model for applying ship disturbance forces is introduced. Numerical methods are used to simulate the ship's disturbed motion. Based on the analysis of the time-history curve of the ship's yaw rate change after disturbance, parameters such as the ship's maximum yaw rate, the time for yaw rate to return to zero, and the amplitude of yaw rate fluctuations can be extracted to systematically assess the ship's heading stability.

[0005] The technical solution of this invention is as follows:

[0006] A method for assessing the heading stability of a ship includes the following steps:

[0007] Step 1: Model the ship's self-propulsion numerical motion: Import the target ship's geometric model into computational fluid dynamics software and set up a numerical simulation example of self-propulsion motion. During the setup process, an overlapping mesh method is used to ensure the hull can move freely in multiple degrees of freedom; a volume force model is used to simulate the operation of the propulsion device (propeller or jet pump) to ensure the model can perform numerical simulations of free self-propulsion motion. The completed example is the ship's self-propulsion numerical model.

[0008] Step 2: Calculate the ship's self-propulsion thrust: Based on the numerical model of the ship's self-propulsion motion, and according to the expected speed of the ship, set the PID adaptive adjustment method of the volume force thrust, and carry out numerical simulation of the ship's free straight-line motion; record the magnitude of the volume force thrust when the ship reaches the required preset speed and sails stably, which is the ship's self-propulsion thrust.

[0009] Step 3: Calculate the ship's disturbance moment: Multiply the ship's self-propulsion thrust by sin(δ), where δ is the reference disturbance rudder angle, and then multiply by the longitudinal distance from the center of the propeller to the center of the ship's weight. This gives the amplitude of the ship's disturbance moment. Substitute the amplitude of the disturbance moment into the disturbance moment distribution to obtain the disturbance moment.

[0010] Step 4: Perform numerical simulation of ship motion under disturbance: Based on the numerical model of ship self-propulsion motion, set the volume force thrust as the thrust at the ship's self-propulsion point, and carry out numerical simulation of ship free straight-line motion. After the speed stabilizes, apply the disturbance torque. After the disturbance ends and the ship's motion state stabilizes, record the time history of the ship's heading angular velocity change.

[0011] Step 5: Conduct a course stability assessment: Based on the ship's heading angular velocity change history, extract and assess the maximum yaw rate, yaw rate return to zero time, and yaw rate fluctuation amplitude.

[0012] Furthermore, the numerical modeling process for ship self-propulsion is as follows: the geometric model of the target ship is imported into computational fluid dynamics software, and an overlapping mesh and volume force model method are used to ensure that the hull can move freely in multiple degrees and effectively simulate the operation of the propulsion device, thus completing the numerical simulation model of the ship's free self-propulsion motion; the coordinate systems used include the geodetic coordinate system O-XYZ, the hull motion coordinate system o-xyz, and the background region motion coordinate system ox around the hull used for numerical simulation. b y b z b Among them, the ship's motion coordinate system o-xyz follows the ship's motion, and its motion law is obtained by solving the six-free motion model; the background region's motion coordinate system only performs translation in the xoy plane and rotation around the z-axis, and its motion law is obtained from the ship's motion data.

[0013] Furthermore, the numerical simulation of the ship's disturbed motion is as follows:

[0014] For numerical simulation of free straight-line motion of a ship, a volume force model is used to simulate the thrust of the propeller. If a uniformly distributed thrust volume force model is used, the expression for calculating the thrust applied to the water flow per unit volume is as follows:

[0015]

[0016] Among them, F vd V represents the thrust of the jet pump, n represents the number of propellers, and V represents the thrust of the jet pump. D This refers to the virtual disk volume; in self-propulsion mode, the thrust volume force is adaptively adjusted by PID based on the ship's speed; the specific adjustment rules are as follows:

[0017]

[0018] Where v is the real-time monitored ship speed, U is the expected ship speed, and F x (t) represents the real-time resistance experienced by the ship excluding the thrust from the jet pumps; after the ship reaches its design speed and stabilizes, the self-propulsion thrust F at this point is recorded. sp size;

[0019] A disturbance torque is applied to the numerical model of the ship's self-propulsion motion. The distribution of the disturbance torque is as follows:

[0020]

[0021] Where M(t) is the real-time disturbance torque, M dis Let t be the amplitude of the disturbance torque, t be the current numerical simulation time, t1 be the disturbance start time, t2 be the duration of the disturbance start, t3 be the disturbance start and end time, and t4 be the disturbance end time. The amplitude of the disturbance torque is calculated by the following formula:

[0022] M dis =F sp ·sin(δ)·L d (4)

[0023] In the formula, F sp L is the thrust at the ship's self-propelled point, δ is the reference disturbance rudder angle; d The longitudinal distance from the rudder centerline to the ship's center of gravity;

[0024] Based on the numerical model of ship self-propulsion, the ship's free straight-line motion is carried out using the self-propulsion point thrust. After the speed stabilizes, a disturbance torque is applied. After the disturbance ends and the ship's motion state stabilizes, the time history of the ship's heading angular velocity change is recorded. The parameters of the maximum yaw angular velocity, the time for the yaw angular velocity to return to zero, and the amplitude of the yaw angular velocity fluctuation are extracted.

[0025] Furthermore, the specific criteria for assessing heading stability are as follows: if there is a time for the deflection angle to return to zero, it proves that the ship has heading stability; the smaller the maximum deflection angular velocity, the better the heading stability, and vice versa; the shorter the time for the deflection angular velocity to return to zero, the better the heading stability, and vice versa; the smaller the amplitude of the deflection angular velocity fluctuation, the better the heading stability, and vice versa.

[0026] Furthermore, δ is set to 10° by default.

[0027] Furthermore, in step 1, the volume force model is as follows: the propeller propulsion adopts the Goldstein distributed volume force model, and the jet pump propulsion adopts the uniformly distributed equal thrust volume force model.

[0028] Furthermore, in step 3, the disturbance torque is applied to the ship's center of gravity, and the distribution is trapezoidal, going through the stages of initial linear change to maximum, continuous application of maximum torque, and linear change of maximum torque until the disturbance disappears.

[0029] Furthermore, in step 5, the maximum yaw rate is the maximum change in the heading angle of the ship after being subjected to a disturbance torque.

[0030] Furthermore, in step 5, the time for the deflection angular velocity to return to zero is the time from the occurrence of the maximum deflection angular velocity to the deflection angular velocity becoming zero.

[0031] Furthermore, in step 5, the amplitude of the yaw rate fluctuation is the magnitude of the change in the heading angular velocity during the ship's continued straight-line navigation after the disturbance torque disappears.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) The present invention is based on the definition of ship heading stability to formulate an evaluation process, and only selects the disturbance moment that affects the ship's heading as the disturbance source, eliminating the coupling effect of other disturbances such as lateral force on the ship's motion, and the evaluation results are more reliable.

[0034] (2) The ship heading stability method proposed in this invention does not involve complex maneuvering motion control in the numerical simulation process. The method is convenient and easy to use, and has high evaluation efficiency.

[0035] (3) The method proposed in this invention can obtain parameters related to heading stability, such as maximum yaw rate, yaw rate return time to zero, and yaw rate fluctuation amplitude, and can provide a more comprehensive assessment of the heading stability of the ship. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the calculation process of a ship heading stability assessment method according to the present invention.

[0037] Figure 2This is the coordinate system of the ship heading stability assessment method of the present invention;

[0038] Figure 3 This is a schematic diagram of the disturbance torque in a ship heading stability assessment method of the present invention;

[0039] Figure 4 This is a schematic diagram of the heading stability characteristic parameters in the ship heading stability assessment method of the present invention. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] A method for assessing the heading stability of a ship, the calculation process of which is as follows: Figure 1 As shown, this includes: importing the target ship's geometric model into computational fluid dynamics software, and using methods such as overlapping meshes and volume force models to ensure that the hull can move freely with multiple degrees of freedom and effectively simulate the operation of the propulsion device (propeller or jet pump), thus completing the numerical simulation model of the ship's free-propulsion motion. The coordinate system used is as follows: Figure 2 As shown, it mainly includes the geodetic coordinate system O-XYZ, the ship motion coordinate system o-xyz, and the motion coordinate system ox of the background flow field region (hereinafter referred to as the background region) around the ship used for numerical simulation. b y b z b The ship's motion coordinate system o-xyz follows the ship's motion, and its motion law is obtained by solving the six-free motion model. Since the background region needs to move with the ship, but the stability of the free surface capture must be ensured, the background region's motion coordinate system only performs translation in the xoy plane and rotation around the z-axis, and its motion law is obtained from the ship's motion data.

[0042] For numerical simulation of a ship's free-straight motion, a volume force model is used to simulate the thrust of the propeller. If a uniformly distributed thrust volume force model is used, the expression for calculating the thrust applied to the water flow per unit volume is as follows:

[0043]

[0044] Among them, F vd V represents the thrust of the jet pump, n represents the number of propellers, and V represents the thrust of the jet pump. D This refers to the virtual disk volume. During self-propulsion, the thrust volume force is adaptively adjusted using PID control based on the ship's speed. The specific adjustment rules are as follows:

[0045]

[0046] Where v is the real-time monitored ship speed, U is the expected ship speed, and F x (t) represents the real-time resistance experienced by the ship excluding the thrust from the jet pumps. After the ship reaches its design speed and stabilizes, the self-propulsion thrust F at this point is recorded. sp size.

[0047] An interference torque is applied to the numerical model of the ship's self-propulsion motion, and the distribution diagram of the interference torque is shown below. Figure 3 As shown, the distribution pattern is as follows:

[0048]

[0049] Where M(t) is the real-time disturbance torque, M dis Let t be the amplitude of the disturbance torque, t be the current numerical simulation time, t1 be the disturbance start time, t2 be the duration of the disturbance start, t3 be the disturbance start and end time, and t4 be the disturbance end time. The amplitude of the disturbance torque is calculated by the following formula:

[0050] M dis =F sp ·sin(δ)·L d (4)

[0051] In the formula, F sp The thrust at the ship's self-propelled point is δ, which is the reference disturbance rudder angle, defaulted to 10°; L d It is the longitudinal distance from the rudder centerline to the ship's center of gravity.

[0052] Based on the aforementioned numerical model of ship self-propulsion, a free straight-line motion of the ship is conducted using the self-propulsion point thrust. After the speed stabilizes, a disturbance torque is applied. Once the disturbance ends and the ship's motion stabilizes, the time history of the ship's heading angular velocity change is recorded. Common examples of heading angle change time histories of disturbed motion of ships with heading stability are shown below. Figure 4 As shown, the parameters of maximum angular velocity, angular velocity return to zero time, and angular velocity fluctuation amplitude are extracted.

[0053] The heading stability of a ship is assessed based on the three heading stability parameters mentioned above. If there is a time for the deflection angle to return to zero, it proves that the ship possesses heading stability. The smaller the maximum deflection angular velocity, the better the heading stability, and vice versa; the shorter the time for the deflection angular velocity to return to zero, the better the heading stability, and vice versa; the smaller the amplitude of the deflection angular velocity fluctuation, the better the heading stability, and vice versa. This presents a method for assessing ship heading stability in this invention. This method is based on numerical simulation of a ship's free-roaming motion under artificial interference, providing relevant characteristic parameters for ship heading stability and assessing the ship's heading stability.

[0054] The above-described embodiments are merely one implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A method for assessing the heading stability of a ship, characterized in that, Includes the following steps: Step 1: Model the numerical model of the ship's self-propulsion motion: Import the geometric model of the target ship into the computational fluid dynamics software and set up a numerical simulation case of self-propulsion motion; during the setting up process, the overlapping mesh method is used, and the volume force model is used to simulate the action of the propulsion device. The completed case is the numerical model of the ship's self-propulsion motion. Step 2: Calculate the ship's self-propulsion thrust: Based on the numerical model of the ship's self-propulsion motion, and according to the expected speed of the ship, set the PID adaptive adjustment method of the volume force thrust, and carry out numerical simulation of the ship's free straight-line motion; record the magnitude of the volume force thrust when the ship reaches the required preset speed and sails stably, which is the ship's self-propulsion thrust. Step 3: Calculate the ship's disturbance moment: Multiply the ship's self-propulsion thrust by sin(δ), where δ is the reference disturbance rudder angle, and then multiply by the longitudinal distance from the center of the propeller to the center of the ship's weight. This gives the amplitude of the ship's disturbance moment. Substitute the amplitude of the disturbance moment into the disturbance moment distribution to obtain the disturbance moment. Step 4: Perform numerical simulation of ship motion under disturbance: Based on the numerical model of ship self-propulsion motion, set the volume force thrust as the thrust at the ship's self-propulsion point, and carry out numerical simulation of ship free straight-line motion. After the speed stabilizes, apply the disturbance torque. After the disturbance ends and the ship's motion state stabilizes, record the time history of the ship's heading angular velocity change. Step 5: Conduct a course stability assessment: Based on the ship's heading angular velocity change history, extract and assess the maximum yaw rate, yaw rate return to zero time, and yaw rate fluctuation amplitude.

2. The method for assessing ship heading stability according to claim 1, characterized in that, The specific process of creating a numerical model for ship self-propulsion is as follows: The geometric model of the target ship is imported into computational fluid dynamics software, and an overlapping mesh and volume force model method are used to ensure that the hull can move freely in multiple degrees and effectively simulate the operation of the propulsion system, thus completing the numerical simulation model of the ship's free-propulsion motion. The coordinate systems used include the geodetic coordinate system O-XYZ, the hull motion coordinate system o-xyz, and the background region motion coordinate system ox around the hull used for numerical simulation. b y b z b Among them, the ship's motion coordinate system o-xyz follows the ship's motion, and its motion law is obtained by solving the six-free motion model; the background region's motion coordinate system only performs translation in the xoy plane and rotation around the z-axis, and its motion law is obtained from the ship's motion data.

3. The method for assessing ship heading stability according to claim 1, characterized in that, The numerical simulation of ship disturbance motion is as follows: For numerical simulation of free straight-line motion of a ship, a volume force model is used to simulate the thrust of the propeller. If a uniformly distributed thrust volume force model is used, the expression for calculating the thrust applied to the water flow per unit volume is as follows: Among them, F vd V represents the thrust of the jet pump, n represents the number of propellers, and V represents the thrust of the jet pump. D This refers to the virtual disk volume; in self-propelled mode, the thrust volume force is adaptively adjusted using PID control based on the ship's speed; the specific adjustment rules are as follows: Where v is the real-time monitored ship speed, U is the expected ship speed, and F x (t) represents the real-time resistance experienced by the ship excluding the thrust from the jet pumps; after the ship reaches its design speed and stabilizes, the self-propulsion thrust F at this point is recorded. sp size; A disturbance torque is applied to the numerical model of the ship's self-propulsion motion. The distribution of the disturbance torque is as follows: Where M(t) is the real-time disturbance torque, M dis Let t be the amplitude of the disturbance torque, t be the current numerical simulation time, t1 be the disturbance start time, t2 be the duration of the disturbance start, t3 be the disturbance start and end time, and t4 be the disturbance end time. The amplitude of the disturbance torque is calculated by the following formula: M dis =F sp ·sin(δ)·L d (4) In the formula, F sp L is the thrust at the ship's self-propelled point, δ is the reference disturbance rudder angle; d The longitudinal distance from the rudder centerline to the ship's center of gravity; Based on the numerical model of ship self-propulsion, the ship's free straight-line motion is carried out using the self-propulsion point thrust. After the speed stabilizes, a disturbance torque is applied. After the disturbance ends and the ship's motion state stabilizes, the time history of the ship's heading angular velocity change is recorded. The parameters of the maximum yaw angular velocity, the time for the yaw angular velocity to return to zero, and the amplitude of the yaw angular velocity fluctuation are extracted.

4. The method for assessing ship heading stability according to claim 1, characterized in that, The specific criteria for assessing heading stability are as follows: if there is a time for the deflection angle to return to zero, it proves that the ship has heading stability; the smaller the maximum deflection angular velocity, the better the heading stability, and vice versa; the shorter the time for the deflection angular velocity to return to zero, the better the heading stability, and vice versa; the smaller the amplitude of the deflection angular velocity fluctuation, the better the heading stability, and vice versa.

5. The method for assessing ship heading stability according to claim 1, characterized in that, δ is set to 10° by default.

6. The method for assessing ship heading stability according to claim 1, characterized in that, In step 1, the volume force model is used. The propeller propulsion adopts the Goldstein distributed volume force model, while the jet pump propulsion adopts the uniformly distributed equal thrust volume force model.

7. The method for assessing ship heading stability according to claim 1, characterized in that, In step 3, the disturbance torque is applied to the ship's center of gravity and is distributed in a trapezoidal pattern, going through stages from initial linear change to maximum, continuous application of maximum torque, and linear change of maximum torque until the disturbance disappears.

8. The method for assessing ship heading stability according to claim 1, characterized in that, In step 5, the maximum yaw rate is the maximum change in the heading angle of the ship after being subjected to a disturbance torque.

9. The method for assessing ship heading stability according to claim 1, characterized in that, In step 5, the time for the deflection angular velocity to return to zero is the time from the occurrence of the maximum deflection angular velocity to the deflection angular velocity becoming zero.

10. The method for assessing ship heading stability according to claim 1, characterized in that, In step 5, the yaw rate fluctuation amplitude is the magnitude of the change in the heading angular velocity during the ship's continued straight-line navigation after the disturbance torque disappears.

Images