Helicopter landing load analysis method based on model test

Abstract

The invention belongs to the technical field of helicopter landing, and particularly relates to a helicopter landing load analysis method based on a model test. Comprising the following steps: S1, determining a scaling ratio of a helicopter scaling model; testing the installation position of the test equipment; s2, under the conditions of a static water surface and regular waves, collecting and recording angles and angular velocities in pitching and rolling directions of the model, accelerations in three directions of an airframe shaft system at the gravity center, and a load on a buoy airframe joint balance of the model, and taking the collected and recorded data as dampening test data of the helicopter scaled model; s3, respectively analyzing the working conditions of the first 10% of the buoy load and the first 10% of the helicopter overload under the static water surface and the regular wave condition, and recording the dampening load test data under the corresponding working conditions; s4, establishing a dampening load calculation model of a corresponding working condition, and correcting the dampening load calculation model; and S5, carrying out dampening load calculation of the full-size helicopter.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of helicopter ditching, and particularly relates to a helicopter ditching load analysis method based on model test. BACKGROUND

[0002] The helicopter ditching structural integrity requirement is one of important design requirements of a ship-borne helicopter and a helicopter applying for water operation. The first problem faced by the helicopter when the helicopter has to be ditched due to failure during water flight is how to make the helicopter land on the water surface without overturning, while ensuring the integrity of the fuselage structure and maximizing the survival probability of passengers and pilots. In order to ensure that the helicopter does not overturn during ditching, the helicopter applying for ditching will usually install an emergency floatation device on the helicopter, and carry out a scaled-down model ditching test to verify whether the helicopter will overturn during ditching. Meanwhile, a balance is installed at the float joint position of the model, a pressure sensor is installed at the bottom, and an attitude and acceleration sensor is installed in the cabin to test the float load, the pressure distribution at the bottom of the fuselage and the motion of the helicopter during ditching.

[0003] The existing helicopter scaled-down model ditching test is difficult to simulate the rotor lift during ditching of the helicopter due to the limitation of test conditions, it is difficult to simulate the most severe sea conditions, and the fuselage structure and the float structure are difficult to be scaled down according to the similarity criterion, so the load data of the helicopter measured by the scaled-down model test cannot be directly converted into the load borne by the full-size ditching process. The method for calculating the ditching load of the full-size helicopter considers the rotor lift during ditching of the helicopter, the most severe sea condition level and the real structure characteristics of the float / fuselage, and can more reasonably give the water load borne by the helicopter during ditching.

[0004] The helicopter ditching load belongs to the fluid-structure coupling problem of two-phase flow, which not only needs to consider the force of water and air on the solid during ditching, but also needs to consider the elastic deformation of the float and the contact relationship with the fuselage, the problem has high complexity, and the reliability of calculation is poor. Before the method is verified, the ditching load calculation result is directly used for the design of the fuselage and the float structure, and the risk is high. SUMMARY

[0005] The application provides a helicopter ditching load analysis method based on model test, which solves the problem that the scaled-down model ditching load test of the helicopter cannot simulate the real load bearing condition of the helicopter during ditching, and the calculation reliability of the conventional ditching load calculation method is low, and the real load during the helicopter ditching process cannot be accurately calculated.

[0006] The application provides a helicopter ditching load analysis method based on model test, which solves the problem that the scaled-down model ditching load test of the helicopter cannot simulate the real load bearing condition of the helicopter during ditching, and the calculation reliability of the conventional ditching load calculation method is low, and the real load during the helicopter ditching process cannot be accurately calculated. S1, determine the scale ratio of the helicopter scale model; determine the installation position of the test equipment, the test equipment at least including: a pontoon force balance, an acceleration sensor, a body bottom pressure measuring element, an attitude sensor; and plan the water-landing state of the helicopter; S2, in the case of a still water surface and regular waves, the helicopter scale model uses the attitude sensor installed in the helicopter scale model to collect and record the angles and angular velocities in the pitch and roll directions of the model, the acceleration sensor collects and records the accelerations in three directions of the body shaft at the center of gravity, and the pontoon force balance collects and records the load on the pontoon body joint balance as the test data of the water-landing of the helicopter scale model; S3, analyze the test data of the water-landing of the helicopter scale model, analyze the working conditions of the front 10% of the pontoon load and the front 10% of the helicopter overload in the case of a still water surface and regular waves respectively, and record the water-landing load test data in the corresponding working conditions; S4, according to the water-landing load test data obtained in S3, establish a water-landing load calculation model corresponding to the working conditions, and develop a water-landing load calculation model correction; S5, according to the corrected water-landing load calculation model obtained in S4, develop the water-landing load calculation of the full-size helicopter.

[0007] Further, S1 determines the scale ratio of the helicopter scale model, specifically: The scale ratio of the helicopter scale model satisfies: Wave height required by the full-size test / pool regular wave making ability>model scale ratio And the model scale ratio> .

[0008] Further, the arrangement of the pontoon force balance; When the left-rotor helicopter flies at low speed, the helicopter rolls to the right, the left limit center of gravity is used, and the pontoon force balance is arranged on the left pontoon; when the right-rotor helicopter flies at low speed, the helicopter rolls to the left, the right limit center of gravity is used, and the pontoon force balance is arranged on the right pontoon.

[0009] Further, S2 is specifically: First, carry out the test of the most prone to roll condition to determine whether the floating system scheme can meet the water-landing stability requirements, if not, stop the test and adjust the floating system scheme; the prone to roll condition usually appears in the most extreme combination of the extreme lateral and longitudinal center of gravity, the 15-degree sideslip water-landing condition, and the maximum roll angle condition; Carry out repetitive tests in still water conditions, and if there is no abnormality, carry out formal tests; The longitudinal center of gravity selection test and the best water entry attitude selection test are carried out, the load on the float force balance is taken as the selection principle, the helicopter longitudinal center of gravity is selected, and the best water entry attitude of the helicopter is selected according to the helicopter overload and attitude response; According to the water landing state of the helicopter, other tests are carried out after the helicopter longitudinal center of gravity is selected and the best water entry attitude of the helicopter is selected.

[0010] Further, before S2, the method further comprises: The pressure retention capability of the float of the helicopter scale model is checked to prevent the abnormal change of the float pressure from affecting the test result during the test; The installation of the bottom pressure test element of the helicopter scale model is checked, and it is required to be flat with the fuselage without protrusions or depressions.

[0011] Further, S4 is specifically: According to the fuselage shape, the float material, the inflation pressure, the weight center of gravity and the moment of inertia of the helicopter scale model, the initial water landing speed, the wave height and the wave height wavelength ratio, a water landing load calculation model is established; According to the float load selected by S3 and the working condition of the helicopter overload, water landing load calculation is carried out, the float load and the helicopter overload during water landing are output, and the calculation values are compared with the water landing load test data under the working condition; By adjusting the fluid-structure coupling relationship of the bottom of the water landing load calculation model, the error between the calculated value and the test value of the helicopter overload under most working conditions is within a small range; the fluid-structure coupling relationship of the contact between the float and the water and the contact relationship between the float and the fuselage are adjusted, so that the error between the calculated value and the test value of the float load under most working conditions is within a small range, and a corrected model is obtained; more than 80% of all working conditions under most working conditions, the error within a small range is within 15% of the test value; Based on the calculated load, the corrected model is obtained according to the calculation results of the corrected model, and the float load correction coefficient and the helicopter overload correction coefficient of the corrected model are obtained.

[0012] Further, according to the shape of the full-size helicopter, the grid size of the water landing load calculation model is scaled according to the scale size, and the full-size water landing load calculation model is drawn; The fluid-structure coupling relationship and the solid-structure contact relationship determined by S4 are used, the full-size float material properties, the inflation pressure, the weight center of gravity and the moment of inertia of the fuselage, and the initial speed are used to assign values to the full-size water landing load calculation model; The node force is replaced by the rotor lift, the node force is 2 / 3 of the helicopter gravity, and the node force direction is upward through the center of gravity; Only two phases of head wave and wave crest are considered in water landing load calculation; The load calculation for the corresponding working condition is performed using a full-size water load calculation model, and the corresponding load is output. The float load is corrected using the float load correction coefficient obtained from S4, and the bottom pressure of the entire aircraft is corrected using the obtained helicopter overload correction coefficient.

[0013] Furthermore, when using a full-scale water-load calculation model to calculate the load for the corresponding working condition, The corresponding operating conditions should ensure that the water-landing load conditions required for seaworthiness are covered. Based on the severe load conditions tested in the water-landing test, and considering that the test float balance is installed on one side, the left and right sideslip conditions should also be considered to ensure that no severe load conditions are missed. The corresponding operating conditions should also consider the full immersion condition.

[0014] In summary, the beneficial effects of the present invention are as follows: The beneficial effects of the present invention are as follows: Through the process described above, the preparation of the scaled-down model test task book, the scaled-down model water landing test, the scaled-down model test data analysis, the correction of the water landing load calculation model based on the test, and the calculation of the full-size water landing load based on the corrected model are coordinated and unified, ensuring the reliability of the helicopter water landing load calculation and solving the problem that it is difficult to give a reliable helicopter water landing load due to insufficient test conditions and insufficient calculation accuracy. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating a helicopter water load analysis method based on model testing. Figure 2 A schematic diagram of the sensor installation positions for a scaled-down helicopter model, 1-center of gravity acceleration sensor, 2-inertial measurement unit; Figure 3 Distribution of pressure measurement points on the bottom of a scaled-down helicopter model; Figure 4 For the comparison of repeatability test data of the water landing test, the following comparisons are made in order: pitch angle data comparison, acceleration data comparison, and bottom measuring point pressure data comparison. Figure 5 A schematic diagram showing the selection of test overload data for the water entry attitude angle in the water landing test of the model of this invention; Figure 6 A schematic diagram of the test load of the float joint in the water landing test of the model of the present invention for selecting the center of gravity; Figure 7 This is a schematic diagram of a two-dimensional wave model; Figure 8 This is a schematic diagram of projecting a two-dimensional wave onto a three-dimensional wave. Figure 9 This is a schematic diagram comparing the calculated and experimental values ​​of normal acceleration. Figure 10 This is a schematic diagram comparing the calculated and experimental values ​​of the load on the pontoon joint. Figure 11 This is a schematic diagram comparing the calculated and experimental values ​​of the pontoon joint load. Figure 12 A schematic diagram comparing the scaled full-size load for the model water immersion test similarity criterion with the full-size load calculated in this invention. Detailed Implementation

[0016] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] This invention provides a method for analyzing helicopter water landing loads based on model experiments, such as... Figure 1 As shown, it includes the following steps: Step 1: Compilation of the scaled-down model test task specification; The scaling ratio of the helicopter scale model; Installation locations of testing equipment; float force balance, acceleration sensor, pressure measuring element at the bottom of the fuselage, attitude sensor; Plan the helicopter's water landing configuration; The scaled-down model test task specification defines the model test conditions and the test data. It must include the most likely capsizing conditions and the most severe load conditions in water, and the data must effectively verify the water load calculation model. The water test task specification must meet the following conditions: (1) Determine the model scaling ratio based on the wave generation capacity of the pool, the sea state requirements for helicopter landing, and the weight of the helicopter scale model, so as to avoid the model exceeding the design weight after adding test equipment due to improper selection of scaling ratio, or the scale ratio being insufficient to simulate the required sea state.

[0018] Formula for the model scaling ratio.

[0019] Wave generation capability of the pool for regular waves / wave height required for full-scale testing > model scale-up Model scaling ratio >

[0020] (2) For helicopters with symmetrically arranged floats, the installation location of the float force balance should be determined based on the helicopter's lateral center of gravity range, fuselage roll angle during hovering and low-speed forward flight, and whether it is on the left or right side of the fuselage. This measure can be used to test the maximum load on the float joint during the helicopter's water landing test by only testing the load on one side of the float joint. When a left-handed rotor helicopter is flying at low speed, it rolls to the right, using the left extreme center of gravity and placing the float balance on the left float. When a right-handed rotor helicopter is flying at low speed, it rolls to the left, using the right extreme center of gravity and placing the float balance on the right float.

[0021] (3) If the float is installed on the left side, the left extreme center of gravity of the helicopter will be used during the test; otherwise, the right extreme center of gravity of the helicopter will be used. The advantage of this is that it can reduce the additional weight that the model needs to add due to the counterweight.

[0022] (4) Install the acceleration sensor at the normal center of gravity of the helicopter and arrange the pressure measuring element at the bottom of the fuselage in a flat position to reduce the interference of water waves caused by other components. The plan for the helicopter's water landing state must include both the most severe attitude response and the most severe load conditions. The load mainly serves the model verification, so it is mainly based on regular waves.

[0023] Step 2: Water immersion test of the scaled-down model; According to the requirements of the test task, the test design, model manufacturing, and installation of test equipment were carried out. Under conditions of still water and regular waves, the scaled-down helicopter model was tested using attitude sensors installed within the model to collect and record the pitch and roll angles and angular velocities. Accelerometers collected and recorded the accelerations in three directions along the fuselage axis at the center of gravity. A float-mounted force balance collected and recorded the load on the balance at the float-fuselage joint. Images of the model during its water landing process were recorded as supporting data for the landing position. The following sequence was followed during the water landing test to improve the test's effectiveness and reduce risk: (1) Check the pressure holding capacity of the model float to prevent abnormal changes in float pressure during the test from affecting the test results; (2) Check the installation of the bottom pressure test element. It should be flat with the machine body and without any protrusions or dents.

[0024] (3) First, conduct the test of the most likely to overturn condition to determine whether the floating system scheme can meet the water stability requirements. If it does not meet the requirements, stop the test and adjust the floating system scheme. The most likely to overturn condition usually occurs in the extreme combination of extreme lateral and longitudinal center of gravity, the 15-degree side slip into the water, and the maximum roll angle.

[0025] For example, the left front extreme center of gravity, roll 5 degrees to the left, slide 15 degrees to the right, and landing in still water and maximum sea conditions.

[0026] (4) Conduct repeatability tests under static water conditions. If the repeatability is good, formal tests can be carried out. (5) Conduct longitudinal center of gravity selection test and optimal water entry attitude selection test. The longitudinal center of gravity is selected based on the principle of large load on the float force balance. The optimal water entry pitch attitude is selected based on the helicopter overload and attitude response.

[0027] (6) Conduct other tests after selecting the longitudinal center of gravity and the optimal water entry pitch attitude according to the helicopter landing state planned in the test mission statement.

[0028] Step 3: Scaled-down model test data analysis; The test data were analyzed, specifically for still water and regular waves, with a focus on the conditions of high buoy load and helicopter overload. The water load test data under these conditions were recorded. Any anomalies discovered during data analysis should be addressed promptly, as follows: (1) If the test condition is found to be overloaded by the helicopter or the load of the float force balance is significantly higher than that of similar working conditions, and there is any doubt, this condition should be repeated. (2) Compare the phases of the waves hitting the water to distinguish between wave crests, wave troughs, waves facing the water, and waves away from the water. If the data does not cover the above states, additional tests should be conducted.

[0029] Step 4: Correction of the water load calculation model based on the experiment; Based on the water-bearing load test data obtained in step three, a water-bearing load calculation model for the corresponding working condition is established, and the water-bearing load calculation model is corrected, as follows: (1) The calculation was performed using software with fluid-structure interaction calculation function that has an airbag model.

[0030] (2) Based on the fuselage shape, float material, inflation pressure, fuselage weight, center of gravity and moment of inertia, initial water-landing velocity, wave height and wave height-to-wavelength ratio of the scaled-down model test, establish a water-landing load calculation model. It is recommended to use the ALE method or Euler method for the water body model, which can simulate the Bernoulli effect of the water body and is more conducive to simulating the motion of the helicopter during the water-landing process; (3) Regular wave: Two-dimensional waves can be created first, and three-dimensional waves can be generated through projection function.

[0031] (4) Based on the pontoon load and helicopter overload conditions selected in step three, perform water landing load calculation, output the pontoon load and helicopter overload during the water landing process, and compare them with the water landing load test data under this condition. (5) By adjusting the fluid-structure interaction relationship at the bottom of the fuselage of the water load calculation model, the error between the calculated and experimental values ​​of helicopter overload under most working conditions is kept within a small range; by adjusting the fluid-structure interaction relationship between the float and the water and the contact relationship between the float and the fuselage, the error between the calculated and experimental values ​​of float load under most working conditions is kept within a small range; under most working conditions, it is more than 80% of all working conditions, and the error is kept within 15% of the experimental value. (6) Based on the principle of correcting the test load by calculating the load, the float load correction coefficient and helicopter overload correction coefficient between the model and the measured load are obtained according to the calculation results of the corrected model. Since the maximum overload of the helicopter when it touches the water occurs at the moment when the fuselage comes into contact with the water, the overload at this moment is basically determined by the water pressure at the bottom of the fuselage. Therefore, the overload correction coefficient can be used to correct the full-size overload and the pressure at the bottom of the fuselage.

[0032] Step 5: Calculation of full-scale water load based on the modified model; Based on the corrected calculation model obtained in step four, a full-scale calculation of the water-receiving load is performed, as follows: (1) Based on the overall shape of the machine and referring to the mesh size of the water load calculation model, scale the model according to the scaling ratio to draw a full-size water load calculation model; (2) Using the fluid-structure interaction relationship and solid-solid contact relationship determined in step four, the full-size float material properties, inflation pressure, fuselage weight center of gravity and moment of inertia, and initial velocity are used as values ​​for the full-size water load calculation model. (3) The rotor lift is replaced by nodal force, the magnitude of which is 2 / 3 of the helicopter's weight, and the direction of the nodal force is upward through the center of gravity; (4) Considering the influence of 2 / 3 of the rotor lift, the vertical velocity of the real helicopter when it touches the water at the trough is less than that when it touches the water in the model test. In reality, the maximum water load of the helicopter occurs when it is facing the waves. When calculating the water load, it is usually only necessary to consider the two phases of facing the waves and the wave crest.

[0033] (5) Use the established model to calculate the load for the corresponding working condition, output the corresponding load, use the float load correction coefficient obtained in step four to correct the float load, and use the obtained helicopter overload correction coefficient to correct the bottom pressure of the whole aircraft.

[0034] (6) The corresponding working conditions can cover the water load conditions required for seaworthiness. Usually, based on the severe load conditions tested in the water landing test, the test float balance is installed on one side. In order not to miss the severe load conditions, the left and right sideslip conditions should also be considered.

[0035] (7) The calculation time for water load is usually very short, and it fails to calculate the stable floating of the helicopter, loss of rotor lift, and the load on the float joint under buoyancy due to fuselage damage. Therefore, the corresponding working conditions also need to consider the full immersion working conditions.

[0036] To provide a reliable method for analyzing helicopter water landing loads, this invention establishes an experimental-based water landing load analysis method based on existing helicopter water landing load test conditions and the computational analysis capabilities of existing fluid / structure interaction analysis software. This method is used to provide reliable helicopter water landing load analysis based on existing technical conditions.

[0037] As attached Figure 1The diagram shown is a flowchart of the helicopter floating stability verification method of the present invention. The helicopter water-landing load analysis method based on model testing of the present invention includes: preparation of a scaled-down model test task book, scaled-down model water-landing test, scaled-down model test data analysis, correction of the water-landing load calculation model based on the test, and full-scale water-landing load calculation based on the corrected model. This method, which uses a test-corrected calculation model followed by full-scale load calculation, addresses the current situation where existing model test conditions are difficult to simulate real water-landing conditions and the accuracy of unverified calculation models is low, thus achieving reliable helicopter water-landing load calculation.

[0038] As attached Figure 2 and attached Figure 3 The diagram shown illustrates the sensor installation on the scaled-down helicopter model used in the water landing test of this invention. Before conducting the scaled-down model water landing test, sensors need to be installed on the model. Figure 2 The added sensor 1 is an acceleration sensor that records the acceleration of the helicopter shaft system during the water landing process; the added sensor 2 is an inertial measurement element used to collect and record the pitch, roll and yaw angle and angular velocity data of the model. Figure 3 The added sensor is a pressure measurement sensor at the bottom of the machine body, used to measure the impact pressure of water during water overload.

[0039] As attached Figure 4 As shown in the comparison of repeatability test data for the water contact test, the repeatability is good, and the next step of the test can be carried out.

[0040] As attached Figure 5 The figure shows the overload data for selecting the water entry attitude angle in the water entry test of the model of the present invention. By carrying out water entry tests under different water entry attitude angles, the influence of different water entry attitude angles on overload is analyzed. The water entry attitude angle with smaller overload is selected as the optimal water entry attitude angle and is used as the selected water entry attitude angle for the next test.

[0041] As attached Figure 6 The figure shows the test load of the float joint in the center of gravity selection test of the model landing test of the present invention. By carrying out landing tests with different centers of gravity under the same conditions, the influence of different centers of gravity on the load of the float joint is analyzed, and the center of gravity with a larger load on the float joint is selected as the selected center of gravity for the next test.

[0042] Based on the parameters of the water-landing test, a water-landing load calculation model was developed. When calculating the water-landing load under wave conditions, the following method was used: Figure 7 A two-dimensional wave model is established as shown, and the two-dimensional wave model is projected onto the attached image using a projection method. Figure 8 The three-dimensional computational water model shown.

[0043] As attached Figure 9As shown, the key parameters of the fluid / structure interaction of the body / water in the calculation model were repeatedly adjusted, and the acceleration of the calculation model under large load conditions was adjusted to more than 90% of the experimental acceleration; as attached. Figure 10 and Figure 11 As shown, the key parameters of the fluid / structure interaction between the pontoon and the water, and the key parameters of the pontoon / fuselage contact were repeatedly adjusted to ensure that the water load at the front and rear pontoon joints was slightly greater than the experimental value. The adjusted fluid / structure interaction key parameter settings and pontoon / fuselage contact key settings were recorded. Based on the comparison of overload and pontoon load, the calculated normal overload and bottom pressure correction coefficients were set to 1.1, and the correction coefficient for the pontoon joint load was set to 1.0.

[0044] The model's mesh can be scaled up to obtain a full-size mesh for calculating the water-landing load. By adjusting the center of gravity, water-landing velocity, material properties, and adding an upward lift force of 2 / 3 of the weight at the center of gravity, the water-landing load can be calculated on still water. A full-size two-dimensional wave is then created and projected onto a three-dimensional water body for calculating the water-landing load under sea conditions. The calculation result is multiplied by a correction factor to obtain the water-landing load calculation result used for strength verification.

[0045] As attached Figure 12 As shown, comparing the full-size water-landing load scaled according to the similarity criterion through model tests with the water-landing load of the front pontoon joint calculated based on the present invention, the load calculated based on the present invention is much smaller than the water-landing load scaled according to the similarity criterion based on model tests.

[0046] The beneficial effects of this invention are as follows: Through the process described above, the compilation of the scaled-down model test task book, the scaled-down model water landing test, the analysis of scaled-down model test data, the correction of the water landing load calculation model based on the test, and the calculation of the full-size water landing load based on the corrected model are coordinated and unified, ensuring the reliability of helicopter water landing load calculation. This solves the problem that it is difficult to provide reliable helicopter water landing load due to insufficient test conditions and insufficient calculation accuracy. Its specific advantages include: Using model water landing tests to provide water landing model verification data reduces the dependence on water landing test conditions, such as maximum wave energy and helicopter rotor generating 2 / 3 of the lift, and can lower the technical threshold for testing.

[0047] The lateral center of gravity for the experiment was selected when the task description was written, and the balance was installed on one side of the lateral center of gravity. This has two advantages: first, it can reduce the number of water-based test conditions and save on test costs; second, installing the balance on the same side as the lateral center of gravity can reduce the difficulty of balancing the weight of the model helicopter, reduce the minimum gravity of the design model, and allow the model to be designed to be smaller, simulating larger wave heights with the same wave-generating capacity.

[0048] The purpose of the test task preparation stage was to provide data support for the water-landing calculation. Therefore, the water-landing under wave conditions was mainly based on regular waves to avoid using a large number of irregular waves in the test, which would make it impossible to obtain test data that can be used to verify the water-landing load calculation model.

[0049] Before the test, the airtightness of the model pontoon should be checked to avoid large deviations in the test data of the pontoon joint load due to pressure decay during the pontoon landing process.

[0050] The installation of the pressure measuring element at the bottom of the machine body needs to be checked to improve the accuracy of pressure measurement at the bottom of the machine body. If the pressure measuring element protrudes from the bottom, the measured pressure will be greater, and if the pressure measuring element is recessed from the bottom, the measured pressure will be less.

[0051] Conducting tests before identifying the dangerous overturning conditions can verify in advance whether the floating system design meets the requirement of not overturning upon contact with water, thus avoiding invalid tests caused by discovering that the floating system design does not meet the requirements in the later stages of the test.

[0052] By selecting the center of gravity and the optimal entry posture through experiments, detailed experiments can be conducted under selected conditions, reducing the number of experimental conditions and costs.

[0053] In data analysis, select the data states used for model correction in water load calculation to reduce the number of calculation states that need to be verified by the model.

[0054] A wave generation method based on projection from two-dimensional waves to three-dimensional waves is proposed to improve the speed of wave generation and the efficiency of wave state calculation.

[0055] Providing targeted key parameters for model water overload correction and model pontoon load correction can improve the efficiency of model correction.

[0056] A dual correction method based on model correction and calculation result correction coefficients is adopted to reduce the difficulty of water load model correction without reducing the reliability of the final calculation results.

[0057] Based on the analysis of experimental data, a method is presented to determine the full-scale calculation to be carried out, taking into account possible omissions in the calculation process and supplementing the calculation conditions for full immersion load.

[0058] A method is presented for extending the validated model to the full-size model, establishing the relationship between the validated model and the full-size model to ensure the accuracy of the water load calculation for the full-size model.

[0059] This method takes into account the difference between the model test state and the full-scale water-based state. The most severe load in the full-scale calculation state usually occurs in the wave-facing water-based condition, focusing on the severe state of the water-based load calculation.

[0060] The helicopter water-landing load calculated using this method is significantly lower than the water-landing load calculated directly from the model water-landing test, which can reduce the structural weight increase required to ensure the integrity of the water-landing structure.

Claims

1. A method for analyzing helicopter water load based on model tests, characterized in that, The method includes: S1. Determine the scaling ratio of the helicopter scale model; determine the installation location of the test equipment, which should include at least: float-mounted force balance, acceleration sensor, pressure measuring element on the bottom of the fuselage, and attitude sensor; and plan the helicopter's landing conditions. S2. Under conditions of still water and regular waves, the helicopter scale model uses attitude sensors installed inside the helicopter scale model to collect and record the pitch and roll angles and angular velocities of the model, acceleration sensors to collect and record the accelerations of the body axis system in three directions at the center of gravity, and float force balances to collect and record the loads on the float fuselage joint balances, as test data for the helicopter scale model landing on water. S3. Analyze the test data of the helicopter scale model landing on water, and analyze the working conditions of the first 10% of the float load and the first 10% of the helicopter overload under the conditions of still water surface and regular waves, and record the water landing load test data under the corresponding working conditions. S4. Based on the water load test data obtained in S3, establish a water load calculation model for the corresponding working condition and carry out the correction of the water load calculation model. S5, based on the modified water-landing load calculation model obtained in S4, performs water-landing load calculations for a full-size helicopter.

2. The helicopter water load analysis method based on model test according to claim 1, characterized in that, S1, determine the scaling ratio of the helicopter scale model, specifically: The scaling ratio of the helicopter scale model satisfies: Wave generation capability of the pool for regular waves / wave height required for full-scale testing > model scale-up And the model scaling ratio is greater than .

3. The helicopter water load analysis method based on model test according to claim 2, characterized in that, Arrangement of the float-mounted force balance; When a left-handed rotor helicopter is flying at low speed, it rolls to the right, using the left extreme center of gravity and placing the float balance on the left float. When a right-handed rotor helicopter is flying at low speed, it rolls to the left, using the right extreme center of gravity and placing the float balance on the right float.

4. The helicopter water load analysis method based on model test according to claim 2, characterized in that, S2 specifically refers to: First, conduct tests under the most likely capsizing conditions to determine if the floating system can meet the water stability requirements. If it does not meet the requirements, stop the test and adjust the floating system. The most likely capsizing conditions usually occur in extreme lateral and longitudinal center of gravity situations, 15-degree sideslip into the water, and the extreme combination of the maximum roll angle. Conduct repeatability tests under static water conditions; if no abnormalities are found, proceed with formal testing. The longitudinal center of gravity selection test and the optimal water entry attitude selection test were carried out. The longitudinal center of gravity of the helicopter was selected based on the principle of large load on the float force balance, and the optimal water entry pitch attitude of the helicopter was selected based on the principle of small overload and attitude response of the helicopter. Further tests were conducted based on the helicopter's water landing condition, after selecting the helicopter's longitudinal center of gravity and the optimal water entry pitch attitude.

5. The helicopter water load analysis method based on model test according to claim 4, characterized in that, Prior to S2, the method further includes: Check the pressure holding capacity of the floats of the scaled-down helicopter model to prevent abnormal changes in float pressure during the test from affecting the test results; Check the installation of the pressure test element at the bottom of the scaled-down helicopter model. It should be flush with the fuselage and free from protrusions or dents.

6. The helicopter water load analysis method based on model test according to claim 4, characterized in that, S4 specifically refers to: Based on the fuselage shape, float material, inflation pressure, fuselage weight, center of gravity and moment of inertia, initial water-landing velocity, wave height and wave height-to-wavelength ratio of the helicopter scaled-down model test, a water-landing load calculation model is established. Based on the pontoon load and helicopter overload conditions selected by S3, water load calculation is carried out, the pontoon load and helicopter overload during the water landing process are output, and compared with the water landing load test data under this condition. By adjusting the fluid-structure interaction relationship at the bottom of the helicopter body in the water load calculation model, the error between the calculated and experimental values ​​of helicopter overload under most operating conditions is kept within a small range. By adjusting the fluid-structure interaction relationship between the float and the water and the contact relationship between the float and the fuselage, the error between the calculated and experimental values ​​of the float load under most operating conditions is kept within a small range, resulting in a corrected model. Under most operating conditions, the error is more than 80% of all operating conditions, and the error is kept within 15% of the experimental value. Based on the principle that the calculated load covers the test load after correction, the float load correction factor and helicopter overload correction factor are obtained according to the calculation results of the corrected model and the water-landing load test value.

7. The helicopter water load analysis method based on model test according to claim 6, characterized in that, Based on the overall shape of the helicopter and referring to the mesh size of the water load calculation model, the model is scaled down to create a full-size water load calculation model. The fluid-structure interaction relationship and solid-to-solid contact relationship determined by S4 are used, and the full-size float material properties, inflation pressure, fuselage weight, center of gravity and moment of inertia, and initial velocity are used to assign values ​​to the full-size water-landing load calculation model. The rotor lift is replaced by nodal force, the magnitude of which is 2 / 3 of the helicopter's weight, and the direction of the nodal force is upward through the center of gravity. When calculating the water load, only the wave front and wave crest phases are considered. The load calculation for the corresponding working condition is performed using a full-size water load calculation model, and the corresponding load is output. The float load is corrected using the float load correction coefficient obtained from S4, and the bottom pressure of the entire aircraft is corrected using the obtained helicopter overload correction coefficient.

8. The helicopter water-landing load analysis method based on model test according to claim 7, characterized in that, When using a full-size water-load calculation model to calculate the load for the corresponding working condition, The corresponding operating conditions should ensure that the water-landing load conditions required for seaworthiness are covered. Based on the severe load conditions tested in the water-landing test, and considering that the test float balance is installed on one side, the left and right sideslip conditions should also be considered to ensure that no severe load conditions are missed. The corresponding operating conditions should also consider the full immersion condition.

9. A helicopter water load analysis system based on model testing, characterized in that, The system is used to implement the method as described in any one of claims 1-8.

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