A method for measuring the hydrodynamic pressure of the bilge keel of a surface ship

Abstract

A method for measuring the hydrodynamic pressure of a bilge keel on a surface ship includes: 1. Determining the main structure and bilge keel structure of a ship model, with a scale ratio of λ, and determining the positions of n measurement nodes located on the lower surface of the bilge keel; 2. Modeling the ship model from step 1 and comparing the strain at each measurement node with the strain at the lower surface of the bilge keel by applying water pressure, and calculating the strain transfer coefficients C1 to C2 corresponding to the n measurement nodes. n 3. Construct the boat model from step 1, and conduct a water immersion test in the test tank to obtain the water velocities V1 to V at n measurement nodes. n The micro-strain με1~με at n measurement nodes was measured. n 4. Obtain the hydrodynamic pressure P at the measurement node of the ship model. i :P i =με i / C i , i = 1, 2, 3…n; V. Obtain the actual ship hydrodynamic pressure SP at the corresponding measurement node positions of the bilge keel on the actual ship. i And the actual ship's entry speed SV i SP i =λ×P i This allows us to obtain hydrodynamic pressure data for the bilge keel under different working conditions, which can be used to assist in bilge keel design and improve the reliability of the bilge keel structure.

Description

Technical Field

[0001] This invention relates to the field of ship design technology, and in particular to a method for measuring the hydrodynamic pressure of the bilge keel of a surface ship. Background Technology

[0002] For seakeeping purposes, surface vessels are generally equipped with appendages such as bilge keels. When a vessel is sailing at a relatively high speed in medium to high waves, the bilge keel is very likely to emerge from the water, resulting in slamming loads, which can cause damage. Slamming loads are an important parameter in local structural design, and how to reasonably determine the design load is a concern for ship designers, researchers, and major classification societies.

[0003] Generally, when ships sail at high speeds in rough seas, wave slamming is severe, with significant impact pressure on structures such as the bow hull and flare. Severe slamming can also cause strong vibrations in the hull beams, potentially damaging local and overall structures. While general specifications address wave slamming of the bow hull and flare, they often neglect the impact of water ingress and egress on the bilge keel. Designing the bilge keel using existing structural calculation methods may result in a weak bilge keel structure, making it highly susceptible to damage. This has been confirmed in numerous vessels; statistics show that the bilge keels of ships sailing in rough seas generally suffer varying degrees of damage.

[0004] Currently, directly measuring the hydrodynamic pressure (slamming pressure) of the bilge keel is quite difficult. It is hard to implement through actual ship tests, and it is also not easy to carry out model tests directly. There is a need to develop a measurement method to obtain hydrodynamic pressure data of the bilge keel under different working conditions, so as to assist in the design of the bilge keel structure and improve the reliability of the ship's bilge keel structure. Summary of the Invention

[0005] To address the shortcomings of existing production technologies, the applicant provides a method for measuring the hydrodynamic pressure of bilge keels on surface ships, thereby obtaining hydrodynamic pressure data of the bilge keels under different operating conditions. This data is used to assist in the design of bilge keel structures and improve the reliability of ship bilge keel structures.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for measuring the hydrodynamic pressure of the bilge keel of a surface ship includes the following steps:

[0008] Step 1: Determine the main structure and bilge keel structure of the ship model. The scale ratio of the ship model is λ, and determine the positions of n measurement nodes located on the lower surface of the bilge keel.

[0009] Step 2: Model the ship model from Step 1 and compare the strain at each measurement node by applying water pressure to the lower surface of the bilge keel. Calculate the strain transfer coefficients C1 to C2 corresponding to the n measurement nodes.n ;

[0010] Step 3: Construct the boat model from Step 1 and conduct a water immersion test in the test tank to obtain the immersion velocities V1 to V at n measurement nodes. n And the micro-strain με1~με at n measurement nodes was measured. n ;

[0011] Step 4: Obtain the hydrodynamic pressure P at the measurement nodes of the ship model. i :

[0012] P i =με i / C i , i = 1, 2, 3…n;

[0013] Step 5: Obtain the actual ship hydrodynamic pressure SP at the corresponding measurement node position of the bilge keel on the actual ship. i And the actual ship's entry speed SV i :

[0014] SP i =λ×P i

[0015]

[0016] Its further technical solution lies in:

[0017] The water ingress velocity V1~V at the measuring node n The relative speed was measured by a relative speed sensor mounted on the bilge keel.

[0018] The modeling in step two uses ABQUS for calculation, selecting 3D solid elements of type C3D4. By rigidly constraining the contact surface between the bilge keel and the hull, the rigidity of the bilge keel and the hull is ensured. It is assumed that water pressure is uniformly distributed on the lower surface of the bilge keel, and that the water pressure is a force perpendicular to the lower surface of the bilge keel. Boundary conditions are set. The strain at n measurement nodes under unit water pressure is obtained, which are the strain transfer coefficients C1 to C2. n The value.

[0019] In step three, the bilge keel is subjected to hydrodynamic pressure from waves in the test pool at each measurement node, and the micro-strain με1 to με at each measurement node is measured by strain sensors installed at n measurement nodes. n Based on step four, the hydrodynamic pressures P1 to P2 at the n measurement nodes are calculated. n .

[0020] Based on the water entry velocity V of each measurement node of the ship model obtained in step three. i And the hydrodynamic pressure P at each measurement node obtained in step four.i The hydrodynamic pressure coefficient k at each measurement node can be calculated. i :

[0021] k i =P i / V i 2 , i = 1, 2, 3...n.

[0022] For the water inlet velocity V1~V n and hydrodynamic pressure P1~P n The data were statistically processed to obtain the mean, maximum, and triplet values ​​of the ingress velocity and the mean, maximum, and triplet values ​​of the hydrodynamic pressure.

[0023] Without changing the main structure and bilge keel structure of the model boat, change the water wave parameters in the test tank and / or the sailing speed of the model boat, and repeat steps three to five.

[0024] Without changing the main structure of the ship model, change the bilge keel structure and repeat steps one to five to obtain multiple sets of data on the relationship between different bilge keel structures and hydrodynamic pressure.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention features a compact and reasonable structure and is easy to operate. By using the constantly changing water entry velocity as the working condition, and combining ship model tests and numerical calculations, it indirectly obtains the hydrodynamic pressure of each measuring node on the bilge keel under different water entry velocities. Based on the scale ratio, it obtains the actual hydrodynamic pressure and water entry velocity of the actual ship's bilge keel, which is used to guide the structural design of the ship's bilge keel and select a suitable and safe bilge keel structural form. This method can support ship structural designers in designing the bilge keel and ensuring its safety.

[0027] Furthermore, the present invention also has the following advantages:

[0028] Based on the experimental ship model and bilge keel drawings, a finite element model was established to calculate the ratio of strain change at the measurement node to the unit external load. The strain data of the measurement node was obtained in the ship model test, and the hydrodynamic pressure load on the bilge keel was inverted. This method is simple and the obtained hydrodynamic pressure data is scientific and accurate.

[0029] After calculating the hydrodynamic pressure coefficient based on the water entry velocity and hydrodynamic pressure, the water entry velocity of the bilge keel measurement node is calculated by modeling the ship model and using software. The hydrodynamic pressure on the measurement node is obtained by estimation method. More data on water entry velocity and hydrodynamic pressure can be obtained by modeling alone. This eliminates the need for model testing, ensuring data accuracy while improving efficiency. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention.

[0031] Figure 2 A finite element model was established based on the bilge keel parameters.

[0032] Figure 3 Boundary conditions for the bilge keel finite element model

[0033] Figure 4 A schematic diagram showing the placement of strain gauges at the measurement nodes of the bilge keel.

[0034] Figure 5 This is a schematic diagram of a typical hydrodynamic pressure (micro-strain) signal for a bilge keel. Detailed Implementation

[0035] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0036] Example 1:

[0037] like Figure 1 As shown in this embodiment, the method for measuring the hydrodynamic pressure of the bilge keel of a surface ship includes the following steps:

[0038] Step 1: Determine the main structure and bilge keel structure of the ship model. The scale ratio of the ship model is λ, and determine the positions of n measurement nodes located on the lower surface of the bilge keel.

[0039] Step 2: Model the ship model from Step 1 and compare the strain at each measurement node by applying water pressure to the lower surface of the bilge keel. Calculate the strain transfer coefficients C1 to C2 corresponding to the n measurement nodes. n .

[0040] Step 3: Construct the boat model from Step 1 and conduct a water immersion test in the test tank to obtain the immersion velocities V1 to V at n measurement nodes. n And the micro-strain με1~με at n measurement nodes was measured. n .

[0041] Step 4: Obtain the hydrodynamic pressure P at the measurement nodes of the ship model. i .

[0042] P i =με i / C i , i = 1, 2, 3…n;

[0043] Step 5: Obtain the actual ship hydrodynamic pressure SP at the corresponding measurement node position of the bilge keel on the actual ship. i And the actual ship's entry speed SV i :

[0044] SPi =λ×P i

[0045]

[0046] Specifically, in the above steps:

[0047] A ship model is a scaled-down model of the surface ship to be measured, which facilitates pool testing.

[0048] Bulch keel is a continuous profile installed on the bilge of a ship (the linear part where the hull and bottom plate connect). It is generally installed on ships with a small block coefficient to enhance seakeeping and stability. When designed properly, it can greatly reduce roll and pitch.

[0049] In step one, n measuring nodes are spaced apart along the length of the ship on the lower surface of a single bilge keel; during the water entry test, the water entry velocities V1 to V at the n measuring nodes are obtained in real time. n and micro-strain με1~με n All data are time-history data. The water entry velocity corresponding to the measurement node at the same moment is the microscopic working condition of that measurement node at a certain moment, which is related to the wave particle motion law and the ship motion characteristics.

[0050] In step three, strain sensors are installed on the lower surface of the bilge keel of the ship model corresponding to the measurement node position. The strain sensors are used to measure the micro-strain of the bilge keel at the node when it is subjected to waves.

[0051] In step three, the bilge keel is subjected to hydrodynamic pressure from waves in the test pool at each measurement node, and the micro-strain με1 to με at each measurement node is measured by strain sensors installed at n measurement nodes. n Based on step four, the hydrodynamic pressures P1 to P2 at the n measurement nodes are calculated. n ;

[0052] The water entry velocity of the measuring nodes is the relative velocity between each measuring node of the bilge keel and the waves. It can be measured by a relative velocity sensor installed on the bilge keel. The relative velocity sensor is an externally purchased component and can be installed near the strain sensor. The water entry velocity can also be calculated by simplifying the stress conditions of the bilge keel.

[0053] Using the constantly changing water entry velocity as the operating condition, this method indirectly obtains the hydrodynamic pressure at various measurement nodes on the bilge keel under different water entry velocities through a combination of ship model tests and numerical calculations. Based on the scale ratio, the actual hydrodynamic pressure and water entry velocity of the actual ship's bilge keel are obtained, which can be used to guide the structural design of the ship's bilge keel and select a suitable and safe bilge keel structural form. This method can support ship structural designers in designing the bilge keel and ensuring its safety.

[0054] Example 2:

[0055] Further details of the methods and measures in Example 1:

[0056] Furthermore, in step two, modeling was performed using Abqus with 3D solid elements of type C3D4. The contact surfaces between the bilge keel and the hull were rigidly constrained to ensure the bilge keel was rigidly fixed to the hull. It was assumed that water pressure was uniformly distributed on the lower surface of the bilge keel, and that the water pressure was a force perpendicular to the lower surface of the bilge keel. Boundary conditions were set. The unit water pressure was uniformly distributed on the lower surface of the bilge keel, and the strain at n measurement nodes under unit pressure was obtained, which are the strain transfer coefficients C1 to C2. n The value.

[0057] Specifically, the strain transfer coefficient C is the ratio of the strain change on the upper surface of the bilge keel to the unit external load after a one-unit change in external pressure. This value can be obtained in the software used for modeling and calculation. The strain transfer coefficients C1 to C2 are also mentioned. n The numerical value is the same as the strain value in the modeling calculation, but the units are different.

[0058] Based on the experimental ship model and bilge keel drawings, a finite element model was established to calculate the ratio of strain change at the measurement node to the unit external load. The strain data of the measurement node was obtained in the ship model test, and the hydrodynamic pressure load on the bilge keel was inverted. This method is simple and the obtained hydrodynamic pressure data is scientific and accurate.

[0059] Furthermore, such as Figure 1 As shown, based on the water entry velocity V of each measurement node of the ship model obtained in the third step... i And the hydrodynamic pressure P at each measurement node obtained in step four. i The hydrodynamic pressure coefficient k at each measurement node can be calculated. i :

[0060] k i =P i / V i 2 , i = 1, 2, 3...n.

[0061] After obtaining the hydrodynamic pressure coefficient, the hydrodynamic pressure on the measurement node is obtained by modeling the ship model and calculating the water entry velocity of the bilge keel measurement node through software. More data on water entry velocity and hydrodynamic pressure can be obtained by modeling alone, so that model testing can be avoided, ensuring data accuracy while improving efficiency.

[0062] Furthermore, regarding data processing, due to the water inlet velocity V1~V n and hydrodynamic pressure P1~P nAll data are time-history data, covering inlet velocities V1 to V2. n and hydrodynamic pressure P1~P n The data were statistically processed to obtain the mean, maximum, and triplet values ​​of the inflow velocity and the hydrodynamic pressure. This method facilitates faster data processing.

[0063] Specifically, since the water ingress velocity and hydrodynamic pressure are directly proportional, the data of water ingress velocity and hydrodynamic pressure can be sorted to obtain the mean, maximum, and third-order values ​​of water ingress velocity and the mean, maximum, and third-order values ​​of hydrodynamic pressure. Theoretically, there is a one-to-one correspondence. The third-order value refers to the average value of the largest 1 / 3 of the data in a series of data sorted from largest to smallest. This makes the data under study more targeted and facilitates comparative analysis of the data.

[0064] Furthermore, such as Figure 1 As shown, regarding the operating conditions, without changing the water wave parameters in the test tank and / or the sailing speed of the ship model, the measured entry velocities V1 to V2 are... n For microscopic working conditions, if macroscopic working conditions are to be changed, steps three to five need to be repeated after changing the water wave parameters in the test tank and / or the sailing speed of the model without changing the main structure of the ship model and the bilge keel structure.

[0065] Specifically, changing the water wave parameters in the test pool and / or the sailing speed of the ship model alters the motion patterns of wave particles and the characteristics of ship motion.

[0066] By macroscopically altering the entry speed of the ship model into the water, multiple sets of bilge keel impact pressure and entry speed data under the same structural conditions are obtained. This data can be used to guide the structural design of the bilge keel and select a suitable and safe bilge keel structural form.

[0067] Furthermore, such as Figure 1 As shown, without changing the main structure of the ship model, steps one to five are repeated by changing the bilge keel structure to obtain multiple sets of data on the relationship between different bilge keel structures and hydrodynamic pressure.

[0068] After changing the bilge keel structure, multiple sets of slamming pressure and water entry velocity data of bilge keels under different structural conditions were obtained to guide the structural design of the bilge keel and select a suitable and safe bilge keel structure.

[0069] Example 3:

[0070] Based on the methods in Examples 1 and 2, this method is applied to the hydrodynamic pressure measurement of the bilge keel of a specific surface ship.

[0071] The ship model in this embodiment has a total length of 4.6m, a waterline length of 4.4m, and a beam of 64.0cm.

[0072] The bilge keel is 2.0m long, with a 1.0m range between the midships and the bow and stern, and a width of 20.0mm. The specific arrangement is shown in Table 1. The specific details can be calculated by modeling based on the actual drawings.

[0073] Table 1 Detailed parameters of bilge keel

[0074] X Y(mm) Z(mm) 5 230.10 89.06 6 250.40 74.44 7 277.26 47.34 8 291.30 23.82 9 296.88 12.82 9.5 298.88 12.38 10 300.46 15.02 11 298.32 25.64 12 287.38 37.04 13 271.36 46.60 14 253.12 54.52 14.5 243.64 58.10

[0075] In Table 1, X represents the station number of the ship model, Y represents the distance of different positions of the bilge keel from the longitudinal section of the ship model, and Z represents the vertical distance of different positions of the bilge keel from the bottom of the ship model.

[0076] A finite element model of the bilge keel is established using the provided data file (ship model structural dimensions and specific dimensions of the bilge keel), such as... Figure 2 As shown.

[0077] The model was calculated using Abqus with 3D solid elements of type C3D4. The bilge keel was rigidly fixed to the hull by imposing full rigid constraints on the contact surfaces. It was assumed that water pressure was uniformly distributed on the lower surface of the bilge keel, and boundary conditions were set as follows: Figure 3 As shown.

[0078] The unit pressure is evenly distributed on the lower surface of the bilge keel, and the strain at the measuring nodes under the unit pressure is calculated. This strain transfer coefficient is the strain transfer coefficient between the unit external load pressure and the upper surface of the bilge keel. Strain transfer coefficients: C1 = 2.61 με / Pa; C2 = 2.95 με / Pa; ...; C n = ...με / Pa. (Taking the data from the first two measurement nodes as an example, the same applies below.)

[0079] The measurement node locations are consistent with those used in calculating the strain transfer coefficient. Measurement node BS1 is located 50mm forward of station 6 (forward towards the bow), and BS2 is located at station 6. Strain gauges are attached to each measurement node, as follows: Figure 4 As shown.

[0080] The positions for attaching strain gauges to the bilge keel are shown in the table below.

[0081] Table 2. Bilge Keel Model Patch Locations

[0082] Bike keel patch placement X Y Z BS1 6 stations 25cm 7.44cm BS2 6 stations + 5cm 25cm 7.50cm BS3 …… …… …… …… …… …… …… BSn …… …… ……

[0083] The time-history data of microstrain at each measurement node obtained from the ship model test can be used to deduce the hydrodynamic pressure load on the bilge keel at a specific moment by dividing the microstrain data at each measurement node by the aforementioned strain transfer coefficient. Figure 5 The figure shows the time history data of microstrain measured by the BS1 strain gauge under high wave height conditions.

[0084] The time-history data of hydrodynamic pressure on the bilge keel under different working conditions (macro-level working conditions) were processed, and the mean, maximum, and three-dimensional values ​​of the hydrodynamic pressure were recorded as shown in Table 3 below. Table 3 lists the hydrodynamic pressure on the bilge keel of the model ship under several top-wave working conditions (wave direction angle of 180 degrees) with relatively large slamming values.

[0085] Table 3 Examples of hydrodynamic pressure on bilge keel of ship model

[0086]

[0087]

[0088] The time-history data of the bilge keel's water entry velocity under different working conditions (macro-level working conditions) were processed, and the mean, maximum, and three-dimensional values ​​of the water entry velocity are recorded as shown in Tables 4 and 5 below. Tables 4 and 5 show the statistical results under the same working conditions as Table 3.

[0089] Table 4. Example of bilge entry speed of model boat at BS1

[0090] Typical operating conditions Average value (m / s) Triad value (m / s) Maximum value (m / s) Operating Condition 1 1.18 1.25 1.24 Operating Condition 2 1.20 1.32 1.40 Operating Condition 3 2.67 2.83 3.11

[0091] Table 5. Examples of bilge entry speeds for model boats at various locations in BS2.

[0092] Typical operating conditions Average value (m / s) Triad value (m / s) Maximum value (m / s) Operating Condition 1 0.90 1.17 1.27 Operating Condition 2 1.32 1.32 1.40 Operating Condition 3 2.67 2.81 3.09

[0093] Tables 3-5 show the processed hydrodynamic pressure and entry velocity of the ship model at measurement nodes BS1 and BS2. The hydrodynamic pressure and entry velocity of the actual ship can be obtained based on the scale ratio.

[0094] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A method for measuring the hydrodynamic pressure of the bilge keel of a surface ship, characterized in that: Includes the following steps: Step 1: Determine the main structure and bilge keel structure of the ship model. The scale ratio of the ship model is λ, and determine the positions of n measurement nodes located on the lower surface of the bilge keel. Step 2: Model the ship model from Step 1 and compare the strain at each measurement node by applying water pressure to the lower surface of the bilge keel. Calculate the strain transfer coefficients C1~C1 corresponding to the n measurement nodes. n ; Step 3: Construct the boat model from Step 1 and conduct a water immersion test in the test tank to obtain the immersion velocities V1~V at n measurement nodes. n And the micro-strain με1~με at n measurement nodes was measured. n ; Step 4: Obtain the hydrodynamic pressure P at the measurement nodes of the ship model. i : P i =with i / C i ,i=1、2、3…n; Step 5: Obtain the actual ship hydrodynamic pressure SP at the corresponding measurement node position of the bilge keel on the actual ship. i And the actual ship's entry speed SV i : SP i =λ×P i SV i = ×V i ; The modeling in step two uses ABQUS for calculation, selecting 3D solid elements of type C3D4. By rigidly constraining the contact surface between the bilge keel and the hull, the rigidity of the bilge keel and the hull is ensured. It is assumed that water pressure is uniformly distributed on the lower surface of the bilge keel, and that the water pressure is a force perpendicular to the lower surface of the bilge keel. Boundary conditions are set accordingly. The strain at n measurement nodes under unit water pressure is obtained, which are the strain transfer coefficients C1~C1. n The value; Based on the water entry velocity V of each measurement node of the ship model obtained in step three. i And the hydrodynamic pressure P at each measurement node obtained in step four. i The hydrodynamic pressure coefficient k at each measurement node can be calculated. i : k i =P i / V i 2 ,i=1、2、3…n。 2. The method for measuring the hydrodynamic pressure of the bilge keel of a surface ship as described in claim 1, characterized in that: The water ingress velocity V1~V at the measurement node n The relative speed was measured by a relative speed sensor mounted on the bilge keel.

3. The method for measuring the hydrodynamic pressure of the bilge keel of a surface ship as described in claim 1, characterized in that: In step three, the bilge keel is subjected to hydrodynamic pressure from waves in the test pool at each measurement node, and the micro-strain με1~με at each measurement node is measured by strain sensors installed at n measurement nodes. n Based on step four, the hydrodynamic pressures P1~P at the n measurement nodes are calculated. n .

4. The method for measuring the hydrodynamic pressure of the bilge keel of a surface ship as described in claim 1, characterized in that: For the water inlet velocity V1~V n and hydrodynamic pressure P1~P n The data were statistically processed to obtain the mean, maximum, and triplet values ​​of the ingress velocity and the mean, maximum, and triplet values ​​of the hydrodynamic pressure.

5. The method for measuring the hydrodynamic pressure of the bilge keel of a surface ship as described in claim 1, characterized in that: Without changing the main structure and bilge keel structure of the model boat, change the water wave parameters in the test tank and / or the sailing speed of the model boat, and repeat steps three to five.

6. The method for measuring the hydrodynamic pressure of the bilge keel of a surface ship as described in claim 1, characterized in that: Without changing the main structure of the ship model, change the bilge keel structure and repeat steps one to five to obtain multiple sets of data on the relationship between different bilge keel structures and hydrodynamic pressure.

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