A method for measuring the center of gravity height of a small underwater unmanned vehicle

Abstract

This invention provides a method for measuring the epicenter height of a small underwater unmanned vehicle (UUV). The method accurately measures the actual epicenter height of the UUV through experimentation. Specifically, by changing the position of the counterweight on the horizontal plane, the UUV's center of gravity and center of buoyancy are altered, as well as the attitude angle during the natural ascent to the surface without power, thus obtaining the epicenter height. This method is simple to operate, highly practical, and low-cost. Accurate epicenter height can be obtained through simple operating steps and common measuring tools, making it applicable to most small underwater unmanned vehicles.

Description

Technical Field

[0001] This invention relates to the field of underwater unmanned submersible technology, specifically a method for measuring the center-of-gravity height of a small underwater unmanned submersible. Background Technology

[0002] An unmanned underwater vehicle (UUV) is a device that is unmanned and can navigate underwater via wireless or automatic control. It can carry various sensors, specialized equipment, or devices to perform underwater tasks. Underwater stability is one of the important overall performance characteristics of a UUV, and the magnitude of the epicenter height is closely related to the maneuverability and safety of the UUV. The epicenter height, which is the vertical distance between the UUV's center of gravity and its center of buoyancy, can be used to measure the stability of a UUV.

[0003] The epicenter height of a typical UUV can be theoretically calculated during the design phase using the shape, weight, and installation location of each section and component. However, errors occur during actual manufacturing and assembly, and these accumulated errors lead to a deviation between the actual epicenter height and the theoretical value.

[0004] There is currently no effective method for measuring the actual center-of-gravity height of a UUV. Summary of the Invention

[0005] In view of this, the present invention provides a method for measuring the epicenter height of a small underwater unmanned vehicle, which can accurately measure the actual value of the epicenter height of the UUV through experiments. The specific method is as follows:

[0006] A method for measuring the epicenter height of a small underwater unmanned vehicle (UUV) involves changing the position of the counterweight on the UUV in the horizontal plane, altering the position of the UUV's center of gravity and center of buoyancy, and changing the attitude angle of the UUV when it is in a stable state as it naturally rises from underwater to the surface without power.

[0007] Furthermore, the specific steps are as follows:

[0008] 1) Obtain the buoyancy force B on the UUV when it is completely submerged in water using a counterweight while it is at rest;

[0009] 2) After the UUV is powered to descend beyond the depth threshold, all power is set to zero, and the attitude angles when the UUV is stable during the natural ascent to the surface are obtained. The attitude angles include pitch angle and roll angle.

[0010] 3) Change the position of any counterweight on the UUV in the horizontal plane while keeping the longitudinal height unchanged, and obtain its weight m0 and buoyancy b0 by weighing the counterweight in the air and in the water.

[0011] 4) Repeat step 2) to obtain the attitude angle when the UUV is stable as it naturally floats to the surface of the water after the position of the counterweight changes;

[0012] 5) Using the weight and buoyancy B of the UUV, the weight m0 and buoyancy b0 of the counterweight that changes position, and the displacement of the counterweight, the displacement of the center of gravity and the displacement of the center of buoyancy of the UUV caused by the change in the position of the counterweight are obtained.

[0013] 6) The center of gravity and center of buoyancy of the UUV are shifted due to the change in the position of the counterweight, and the change in attitude angle during the natural ascent to the water surface is used to obtain the center of gravity height of the UUV.

[0014] Furthermore, the specific method for 1) is as follows:

[0015] Step 1.1: After assembling the UUV, place it in the water tank. By adding or removing counterweights, ensure that all parts of the UUV are completely submerged in the water when it is stationary.

[0016] Step 1.2: Remove the counterweight from the UUV and use a crane scale to suspend the counterweight in the water. At this time, the reading of the crane scale is the positive buoyancy force ΔB of the UUV.

[0017] Step 1.3: Adjust the position of the remaining breeding blocks on the UUV and adjust the attitude angle of the UUV to meet the requirements for underwater navigation;

[0018] Step 1.4: Weigh the UUV in the air using an electronic crane scale to obtain its weight M. Then, the buoyancy of the UUV is B = M + ΔB.

[0019] Furthermore, the formula for calculating the UUV's center of gravity height is: GM1 = (Δx G -Δx B ) / (tanα1-tanα2), where Δx G Δx represents the distance the UUV's center of gravity shifts in the x-axis due to the change in the position of the counterweight. B α1 is the distance the UUV's center of buoyancy moves in the x-direction due to the change in the position of the counterweight; α2 is the pitch angle of the UUV when its attitude is stable during the natural ascent to the surface of the water before the change in the position of the counterweight; α3 is the pitch angle of the UUV when its attitude is stable during the natural ascent to the surface of the water after the change in the position of the counterweight.

[0020] Furthermore, the formula for calculating the UUV's center of gravity height is: GM 2=(Δy B -Δy G ) / (tanβ1-tanβ2), where Δy G Δy represents the distance the UUV's center of gravity shifts in the y-axis due to the change in the position of the counterweight. Bβ1 is the distance the UUV's center of buoyancy moves in the y-direction due to the change in the position of the counterweight; β2 is the roll angle when the UUV's attitude is stable during its natural ascent to the surface before the counterweight position changes; β3 is the roll angle when the UUV's attitude is stable during its natural ascent to the surface after the counterweight position changes.

[0021] Furthermore, the formula for calculating the UUV's center height is: GM = (GM1 + GM2) / 2.

[0022] The following beneficial effects can be achieved by using the present invention:

[0023] 1. The method of the present invention is simple to operate, highly practical, and low in cost;

[0024] 2. Accurate centering height can be obtained through simple operating steps and common measuring tools;

[0025] 3. This invention is applicable to most small underwater unmanned vehicles. Attached Figure Description

[0026] Figure 1 Method Flowchart

[0027] Figure 2a A schematic diagram showing the displacement of the counterweight in the horizontal plane after the position of the counterweight changes.

[0028] Figure 2b A schematic diagram showing the longitudinal displacement of the counterweight after its position changes.

[0029] Figure 3a A schematic diagram illustrating the principle of the first method for calculating the stationary height of a UUV;

[0030] Figure 3b A schematic diagram illustrating the principle of the second method for calculating the UUV's center of gravity.

[0031] Where G represents the center of gravity of the UUV before the counterweight position changes, G' represents the center of gravity of the UUV after the counterweight position changes, B represents the center of buoyancy of the UUV before the counterweight position changes, and B' represents the center of buoyancy of the UUV before the counterweight position changes. Detailed Implementation

[0032] Step 1.1: After assembling the UUV, place it in the water tank. By adding or removing counterweights, make the UUV reach a zero buoyancy state, that is, in a static state, all parts of the UUV are just completely submerged in the water.

[0033] Step 1.2: Remove a counterweight from the UUV (the value depends on the UUV's tonnage, etc.), and use a crane scale to suspend the counterweight in the water. The reading on the crane scale at this time is the positive buoyancy ΔB of the UUV. The magnitude of the positive buoyancy ΔB = buoyancy - gravity. If multiple counterweights need to be removed, simply add up the readings of these counterweights.

[0034] Step 1.3: Adjust the position of the remaining breeding blocks on the UUV without adding or removing any additional counterweights, and adjust the attitude angle of the vehicle to meet the final state for underwater navigation.

[0035] Step 1.4: Weigh the UUV in the air using an electronic crane scale to obtain its weight M. Then, the buoyancy of the vehicle is B = M + ΔB.

[0036] Step 2: After the UUV descends beyond the depth threshold using propulsion, all propulsion is reduced to zero. The attitude angles, including pitch and roll angles, are obtained during the natural ascent to the surface. Specifically, the UUV is placed in open water, and its descent is accelerated beyond the depth threshold. Then, all propulsion is reduced to zero, allowing the vehicle to naturally rise to the surface. The depth threshold refers to a depth sufficient for the UUV to naturally rise to a stable attitude. The attitude data recorded by the UUV's inertial navigation system or other sensors is examined to read the pitch angle α during the ascent when the attitude is stable. 11 (Heaving up is positive) and roll angle β 11 (Right tilt is positive), n sets of data α were obtained through repeated trials. 11 ~α 1n β 11 ~β 1n The average value is taken to obtain the pitch angle α1 in the water under this state. 11 +α 12 +……+α 1n ) / n, roll angle in water β1=(β 11 +β 12 +……+β 1n ) / n;

[0037] Step 3: Remove a counterweight from the aircraft and mark its position 1. Measure its weight m0 in air and its buoyancy b0 by weighing it in water. Move the counterweight to position 2, keeping the horizontal height of positions 1 and 2 constant. Measure the longitudinal distance Δx (positive when moving from stern to bow) and the lateral distance Δy (positive when moving from port to starboard) between positions 1 and 2. Figure 2a As shown, the arrows indicate the direction of movement;

[0038] Step 4: Repeat step 2. After the counterweight position changes, during the process of the UUV naturally rising to the water surface, the UUV's pitch angle in the water is α2 = (α 21 +α 22+……+α 2n ) / n, roll angle in water β2=(β 21 +β 22 +……+β 2n ) / n;

[0039] Step 5: The measured weight M, buoyancy B, weight m0 of the moving counterweight, buoyancy b0 of the moving counterweight, pitch angle α1 before the counterweight moves, roll angle β1 before the counterweight moves, pitch angle α2 after the counterweight moves, and roll angle β2 after the counterweight moves can be used to calculate the center-of-field height GM of the UUV.

[0040] When a UUV floats naturally under a state of slight positive buoyancy, its speed is very small, and its hydrodynamic influence can be ignored. Only the static balance of gravity and buoyancy needs to be considered. There are three ways to calculate the height of the center of gravity: 1. Calculate using longitudinal calculation; 2. Calculate using lateral calculation; 3. Averaging the first two methods.

[0041] 1) Vertical calculation:

[0042] Calculate the longitudinal shift of the center of gravity using existing methods: Δx G =Δx*m0 / M;

[0043] Calculate the longitudinal movement distance of the center of buoyancy using existing methods: Δx B =Δx*b0 / B;

[0044] use Figure 3a The quantitative relationship shown allows us to obtain the relationship before and after the counterweight is moved, i.e., GM1*tanα1+Δx B -Δx G -GM1*tanα2=0;

[0045] From this, we can deduce that the stationary height of the UUV is GM1 = (Δx) G -Δx B ) / (tanα1-tanα2);

[0046] 2) Horizontal calculation:

[0047] Calculate the lateral movement distance of the center of gravity using existing methods: Δy G =Δy*m0 / M;

[0048] Calculate the lateral movement distance of the center of buoyancy using existing methods: Δy B =Δy*b0 / B;

[0049] use Figure 3b The quantitative relationship shown allows us to obtain the relationship before and after the counterweight is moved, i.e., GM*tanβ1+Δy G -Δy B -GM*tanβ2=0;

[0050] Therefore, we can deduce that the steady-state height of the UUV is GM2 = (Δy B -Δy G ) / (tanβ1-tanβ2).

[0051] When the difference between the longitudinal and transverse gyroscope heights GM1 and GM2 is very small, the experiment can be considered successful.

[0052] 3) To improve accuracy, the stable high GM can be reduced to the average value GM = (GM1 + GM2) / 2.

Claims

1. A method for measuring the center-of-gravity height of a small underwater unmanned vehicle, characterized in that: By changing the position of the counterweight on the submersible in the horizontal plane, the displacement of the submersible's center of gravity and center of buoyancy can be obtained. The attitude angle of the submersible when it is in a stable state during the process of naturally rising from underwater to the surface without power can also be changed, thereby obtaining the submersible's epicenter height. 1) Obtain the buoyancy force B on the UUV when it is completely submerged in water using a counterweight while it is at rest; 2) After the UUV descends beyond the depth threshold by power, all power is set to zero, and the attitude angles when the UUV is stable during the natural ascent to the surface are obtained. The attitude angles include pitch angle and roll angle. 3) Change the position of any counterweight on the UUV in the horizontal plane while keeping the longitudinal height unchanged, and obtain its weight m0 and buoyancy b0 by weighing the counterweight in the air and in the water. 4) Repeat step 2) to obtain the attitude angle when the UUV is stable as it naturally floats to the surface of the water after the position of the counterweight changes; 5) Using the weight and buoyancy B of the UUV, the weight m0 and buoyancy b0 of the counterweight that changes position, and the displacement of the counterweight, the displacement of the center of gravity and the displacement of the center of buoyancy of the UUV caused by the change in the position of the counterweight are obtained. 6) The center of gravity and center of buoyancy of the UUV are shifted due to the change in the position of the counterweight, and the change in attitude angle during the natural ascent to the water surface is used to obtain the center of gravity height of the UUV. There are three methods for calculating the UUV's center of gravity: (1) Using the x-axis for calculation, the formula for calculating the UUV's center height is: GM1=(Δx G -Δx B ) / (tanα1-tanα2), where Δx G Δx represents the distance the UUV's center of gravity shifts in the x-axis due to the change in the position of the counterweight. B α1 is the distance the UUV's center of buoyancy moves in the x-direction due to the change in the position of the counterweight; α2 is the pitch angle when the UUV's attitude is stable during the process of the UUV naturally rising to the surface before the change in the position of the counterweight; α3 is the pitch angle when the UUV's attitude is stable during the process of the UUV naturally rising to the surface after the change in the position of the counterweight. (2) Using the y-axis calculation, the formula for calculating the UUV's center height is: GM 2=(Δy B -Δy G ) / (tanβ1-tanβ2), where Δy G Δy represents the distance the UUV's center of gravity shifts in the y-axis due to the change in the position of the counterweight. B β1 is the distance the UUV's center of buoyancy moves in the y-direction due to the change in the position of the counterweight; β2 is the roll angle when the UUV's attitude is stable during its natural ascent to the surface before the change in the position of the counterweight; β3 is the roll angle when the UUV's attitude is stable during its natural ascent to the surface after the change in the position of the counterweight. (3) The average of the first two is used to calculate the UUV's center height. The formula is: GM = (GM1 + GM2) / 2.

2. The method for measuring the center-of-gravity height of a small underwater unmanned submersible according to claim 1, characterized in that: The specific method for 1) is as follows: Step 1.1: After assembling the UUV, place it in the water tank. By adding or removing counterweights, ensure that all parts of the UUV are completely submerged in the water when it is stationary. Step 1.2: Remove the counterweight from the UUV and use a crane scale to suspend the counterweight in the water. At this time, the reading of the crane scale is the positive buoyancy force ΔB of the UUV. Step 1.3: Adjust the position of the remaining breeding blocks on the UUV and adjust the attitude angle of the UUV to meet the requirements for underwater navigation; Step 1.4: Weigh the UUV in the air using an electronic crane scale to obtain its weight M. Then, the buoyancy of the UUV is B = M + ΔB.

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