A method for analyzing the hydroelastic response of a water surface vehicle

Abstract

The present invention belongs to the structural dynamic response analysis technology of water surface aircraft, and specifically relates to a method for analyzing the hydrodynamic elastic response of water surface aircraft. The method of the present invention performs finite element modeling of the whole aircraft structure according to the overall shape, structural form and mass distribution of the aircraft; calculates the waterline position of the aircraft according to the weight center of gravity state and water surface sliding parameters of the aircraft; calculates the additional mass generated by water on the fuselage according to the structural parameters below the waterline of the aircraft using the added mass theory; superimposes the additional mass and the whole aircraft mass, solves the whole aircraft dynamics equation, and analyzes the various wet modes of the aircraft; based on the results of the wet modal analysis, simplifies the hydrodynamic loads during the use of the aircraft and applies them to the structural model, and uses the modal superposition method to solve the response history of the fuselage overload, deformation, shear force, bending moment, and torque. The method of the present invention can obtain the elastic response characteristics of the fuselage structure of the water surface aircraft when it moves on the water surface, provide a basis for the structural strength design of the water surface aircraft, and improve the safety and reliability of the water surface aircraft.

Description

Technical Field

[0001] The present invention mainly relates to a water surface aircraft structure dynamic response analysis technology, and in particular to a water surface aircraft hydrodynamic elastic response analysis method. Background Art

[0002] Water surface aircraft, especially water / amphibious aircraft, are often disturbed by water surface airflow, waves, etc. during takeoff and landing and taxiing on the water surface, which can easily cause additional vibration of the airframe structure, affecting the ergonomics of personnel and equipment and the life of the airframe structure. Analyzing the dynamic response characteristics of water surface aircraft can provide a basis for preventing resonance damage and vibration fatigue of the airframe structure.

[0003] However, when a surface aircraft is sailing on the water, the movement of the hull structure will induce the movement of the surrounding water, and the water will react to the hull surface in the form of additional movement. When conducting hydrodynamic analysis of surface aircraft, it is necessary to consider the coupling between the water and the structure, take into account the elastic effect of the body, and conduct structural hydrodynamic elastic response analysis. In the past, when designing surface aircraft, engineering algorithms were generally used to design rigid aircraft water loads, without considering the influence of structural elastic deformation, and it was impossible to evaluate the elastic response characteristics of the body structure when moving on the water. There is little attention paid to the hydrodynamic elastic response characteristics of surface aircraft at home and abroad, and there is no complete analysis method. Summary of the invention

[0004] The purpose of the present invention is to provide a hydrodynamic elastic response analysis method which can effectively guide the structural strength design of a surface aircraft and improve the structural safety and reliability.

[0005] The technical solution of the present invention is: a method for analyzing the hydrodynamic elastic response of a surface aircraft, which performs finite element modeling of the entire structure of the surface aircraft, calculates the additional mass and the total mass of the surface aircraft, substitutes them into the solved dynamic motion equations of the surface aircraft, obtains the wet mode of the surface aircraft, and then applies the hydrodynamic loads during the use of the aircraft to the finite element model based on the wet modal parameters of the surface aircraft to solve the transient response characteristics of the model.

[0006] The method for analyzing the hydrodynamic elastic response of a water surface vehicle comprises the following steps:

[0007] Step 1: Conduct finite element modeling of the entire aircraft structure based on the overall shape, structural form and mass distribution of the surface aircraft;

[0008] Step 2: Calculate the waterline position of the surface aircraft according to the loading state and water gliding parameters of the surface aircraft;

[0009] Step 3, using the structural parameters of the surface aircraft below the waterline to calculate the additional mass of the surface aircraft caused by water;

[0010] Step 4: Substitute the additional mass and the total aircraft mass into the motion equation for solution to analyze the wet modal characteristics of the surface aircraft;

[0011] Step 5: Based on the results of wet modal analysis, solve the hydroelastic response characteristics of the fuselage structure.

[0012] In step 2, the water planing parameters include but are not limited to weight center of gravity, planing speed, flap angle, and elevator angle.

[0013] In step 2, the gravity, lift and required buoyancy of the surface aircraft are calculated, and the waterline position of the surface aircraft is calculated based on the buoyancy and geometric shape.

[0014] In step 3, according to the waterline position of the surface aircraft, the structural units in contact with water are defined in the finite element model, and then the added mass theory is used to calculate the additional mass generated by water on the surface aircraft.

[0015] The additional mass is expressed as:

[0016] [M a ]=[D] -1 ·[E]

[0017] Among them, M a is the additional mass matrix generated by water on the body, D is the coefficient matrix obtained by numerical integration of the node velocity vector and the flow velocity vector of the finite element model, and E is the coefficient matrix obtained by numerical integration of the node force and the flow velocity vector of the finite element model.

[0018] In step 4, considering that water is an isotropic, incompressible ideal fluid and the additional inertial force, the additional mass and the total machine mass are superimposed and substituted into the inherent modal motion equation:

[0019]

[0020] In the formula, M is the body mass matrix, C is the damping matrix, K is the stiffness matrix, and x is the displacement vector. The characteristic roots and eigenvectors of the equation are solved to obtain the wet mode of the surface aircraft.

[0021] In step 5, based on the wet modal analysis results of the surface aircraft, the hydrodynamic loads during the use of the surface aircraft are simplified and applied to the finite element model, and the transient response equation of the model is solved to obtain the hydrodynamic elastic response history of the surface aircraft.

[0022] The transient response equation is as follows:

[0023] [φ] T [M+M a ][φ]·{ξ(t)}+[φ] T[C][φ]·{ξ(t)}+[φ] T [K][φ]·{ξ(t)}=[φ] T {P(t)}

[0024] Where φ is the wet mode shape, ξ is the modal coordinate, and P(t) is the transient excitation load in the time domain, which is a function of time t.

[0025] The hydrodynamic elastic response parameters include but are not limited to overload, stress, deformation, shear force, bending moment, and torque.

[0026] Beneficial effects of the present invention:

[0027] The hydrodynamic elastic response analysis method of a water surface aircraft of the present invention is mainly aimed at water / amphibious aircraft, and considers the mutual influence between the body structure movement and the additional movement of the water body and the elastic effect of the body structure, analyzes the wet modal and dynamic response characteristics of the aircraft structure, obtains the body wet modal parameters and the response history of overload, deformation, shear force, bending moment, torque, etc., fills the design gap of the dynamic load and structural response of water / amphibious aircraft, and is beneficial to improving the safety and reliability of water surface aircraft.

[0028] The present invention mainly solves the following technical problems:

[0029] To address this problem, this method takes into account the elastic effect of the fuselage structure, conducts structural dynamic response analysis of the aircraft under the influence of hydrodynamic elasticity, solves the response history of the fuselage structure such as overload, deformation, and load during movement on the water surface, and guides the structural strength design of water / amphibious aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a partial schematic diagram of a finite element model in an example of the present invention,

[0031] Among them, 1-mass element, 2-beam element, 3-rigid element, 4-shell element.

[0032] Figure 2 It is the calculation result of dry mode and wet mode frequency of an amphibious aircraft in the example of the present invention. For the convenience of comparison, the calculation results are normalized.

[0033] Figure 3 It is the acceleration response history of a typical part of the fuselage of an amphibious aircraft in the example of the present invention.

[0034] Figure 4 The load response history of a typical part of an amphibious aircraft wing in an example of the present invention. DETAILED DESCRIPTION

[0035] All features disclosed in this specification, or all methods disclosed, or steps in a process, except mutually exclusive features and / or steps, can be combined in any manner.

[0036] The method for analyzing the hydrodynamic elastic response of a water surface aircraft provided by the present invention takes an amphibious aircraft as a typical water surface aircraft as an example to analyze its hydrodynamic elastic response characteristics. The specific implementation process is as follows:

[0037] Step 1: Based on the basic form of the main load-bearing structure of amphibious aircraft, take the sections of the wing and tail ribs and the fuselage frame, consider the influence of longitudinal structural parts such as skin, long stringers, beams, etc., and use the closed-chamber section theory to calculate the section stiffness distribution of the fuselage, wing, and tail;

[0038] Step 2: Use variable-section beam elements to model the structural stiffness of the entire machine, simulate the bending stiffness and torsional stiffness distribution of the entire machine, and the nodes of the beam elements are located at the rigid center to improve the calculation efficiency;

[0039] Step 3: Based on the overall shape of the amphibious aircraft, the finite element modeling of the geometric shape of the main parts of the whole aircraft is carried out using shell elements. The thickness value of the shell element is very small, generally set to ≤0.001mm, which will not produce obvious additional stiffness and will not affect the stiffness distribution of the model;

[0040] When finite element modeling of geometric shapes, the water contact form of amphibious aircraft must be considered. The outer surface of the fuselage that touches or may touch water must be fully modeled, and other parts that do not touch water can be simplified to improve calculation efficiency;

[0041] Step 4: Use rigid connection elements to connect the beam unit nodes in step 2 and the shell unit nodes in step 3 according to the principle of longitudinal proximity, ensuring that the displacement of the shell unit nodes at each station is consistent with the displacement of the beam unit nodes, so as to simulate the complete shape of the aircraft, especially accurately simulate the shape of the hull of the surface aircraft;

[0042] Step 5: Based on the calculation results of the mass distribution of the aircraft, the beam unit nodes are selected as the loading nodes of the concentrated mass according to the principle of spatial proximity, and the mass distribution of the aircraft is simulated with the concentrated mass unit to improve the calculation efficiency and simulation accuracy;

[0043] Step 6: Combine the stiffness model, shape model and all mass units into a finite element model of the whole machine structure. A local form of the model is as follows: Figure 1 As shown, it more accurately reflects the structural characteristics of water surface powered aircraft;

[0044] Step 7: Use the finite element model of the whole aircraft structure in step 6 to perform natural modal analysis to solve the natural frequency and vibration mode of each mode of the aircraft;

[0045] In the natural mode analysis, the equation of motion is:

[0046]

[0047] The equation of motion is solved using the eigenvalue method, where M is the mass matrix, C is the damping matrix, K is the stiffness matrix, and x is the displacement vector;

[0048] Step 8: Use the full-aircraft ground resonance test results to correct the stiffness distribution calculation results in step 1, so that the main natural modal analysis results of the aircraft are basically consistent with the test results, thereby improving the effectiveness of the analysis model;

[0049] If there is no full-aircraft ground resonance test result, you can skip step 8 and complete it later;

[0050] Step 9: Calculate the lift generated by the aircraft based on the aircraft's water taxiing parameters, including taxiing speed, flap deflection angle, elevator deflection angle, etc., and calculate the aircraft's attitude angle according to the trim state;

[0051] Step 10: Calculate the gravity of the aircraft according to the weight loading state of the aircraft. The difference between the gravity and the lift in step 9 is the buoyancy that the aircraft should have when gliding on the water surface.

[0052] Step 11, based on the geometric shape and pitch attitude of the aircraft, and in accordance with the requirement that the volume of the aircraft below the waterline is equal to the displacement, calculate the aircraft waterline position that meets the buoyancy requirements of step 10;

[0053] Step 12: Based on the calculated aircraft waterline position, define all shell elements in contact with water in the finite element model of the entire aircraft structure, and the outer surfaces of the shell elements below the waterline position are all in contact with water;

[0054] Step 13: Based on the added mass theory, calculate the added mass M generated by water on all shell elements below the waterline in the finite element model of the entire aircraft. a For underwater structures, the added mass describes the hydrodynamic force per unit acceleration acting on the surface of the object, which is in phase with the acceleration of the object, which is equivalent to adding a new mass to the surface of the object.

[0055] When calculating the additional mass of water on an object, the Helmholtz boundary integral method is used to solve the Laplace equation based on the continuity equation and energy equation of fluid mechanics, and the velocity potential and pressure field at any point on the fluid boundary are obtained as follows:

[0056]

[0057]

[0058] In the formula, is the velocity vector at node i of the finite element model, σ i is the velocity vector at node i, e ij is the unit vector from point i to point j, s i is the area of ​​the microelement on the surface of the structure, p i is the pressure on the surface of the microelement, and ρ is the fluid density.

[0059] Integrating the velocity potential and pressure field separately yields:

[0060]

[0061]

[0062] Where F is the force acting on the node, and D and E are the coefficient matrices obtained by numerical integration.

[0063] According to the relationship between the force matrix, mass matrix, and acceleration matrix:

[0064]

[0065] Solving the problem, we can get the additional mass matrix as:

[0066] [M a ]=[D] -1 ·[E]

[0067] Step 14: Consider the effect of the additional mass, add the additional mass to the total mass of the aircraft, and calculate the overall mass M of the aircraft when it moves on the water surface. total :

[0068] [M total ]=[M]+[M a ]

[0069] Step 15, ignoring the influence of the additional elastic force and the additional damping force of water, substituting the overall mass of the aircraft into the modal motion equation, solving the characteristic roots and characteristic vectors of the equation, the wet modal characteristics of the aircraft can be obtained. In this embodiment, the wet modal analysis results of the amphibious aircraft are as follows: Figure 2 As shown, it can be seen that the wet modal frequencies of different states are obviously different from the dry modal frequencies.

[0070] In wet modal analysis, the equation of motion is transformed into:

[0071]

[0072] Step 16: Simplify the hydrodynamic loads during the use of the aircraft and apply them to the structural finite element model. The load loading nodes are selected according to the principle of longitudinal proximity.

[0073] The hydrodynamic load used for loading can be the transient load obtained by numerical calculation or by test. When simplifying, the total load and load distribution must be kept unchanged, including pressure and overload.

[0074] Step 17: Use transient response analysis theory to solve the elastic response characteristics of the model. The equation of motion is:

[0075] [φ] T [M+M a ][φ]·{ξ(t)}+[φ] T [C][φ]·{ξ(t)}+[φ] T [K][φ]·{ξ(t)}=[φ] T {P(t)}

[0076] Where φ is the wet mode shape, ξ is the modal coordinate, and P(t) is the transient excitation load, which is a function of time t;

[0077] Step 18: Use the numerical integration method to solve the transient response motion equation according to the time step, and superimpose the modal responses of each order to obtain the analysis results, including the elastic response history of overload, deformation, shear force, bending moment, torque, etc. In this embodiment, the response history of the typical parts of the amphibious aircraft is as follows: Figure 3 As shown, the front and rear of the fuselage have different accelerations with respect to time, such as Figure 4 As shown, shear force, bending moment and torque also change with time.

[0078] Step 19: Analyze the extreme values ​​of overload, deformation, shear force, bending moment, torque and other responses of the fuselage, wings, tail wing and other parts for use in aircraft structure design.

[0079] The hydrodynamic elastic response analysis method of a water surface aircraft provided by the present invention considers the coupling effect between the water body and the structure, uses the overall shape, structural form and mass distribution of the water surface aircraft to perform finite element modeling of the whole aircraft structure, uses the added mass theory to calculate the additional mass generated by water on the aircraft body, and then solves the various wet modes of the water surface aircraft, and solves the elastic response characteristics of the aircraft body based on the wet mode results. The hydrodynamic elastic response analysis method of a water surface aircraft can be used to obtain the elastic response characteristics of the aircraft body when it moves on the water surface, guide the structural strength design, and improve the safety and reliability of the water surface aircraft.

[0080] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. For example, it can also be applied to other water surface aircraft, such as seaplanes. Any changes or substitutions that can be easily thought of by technicians familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims, and the parts not detailed in the description are conventional technologies.

Claims

1. A method for analyzing the hydroelastic response of a surface vehicle, characterized in that: Conduct finite element modeling of the entire structure of the surface aircraft, calculate the additional mass and the total mass of the surface aircraft, substitute them into the dynamic motion equation of the surface aircraft to solve, obtain the wet mode of the surface aircraft, and then apply the hydrodynamic loads during the use of the aircraft to the finite element model based on the wet mode characteristics of the surface aircraft to solve the transient response characteristics of the model; The steps include: According to the basic form of the main load-bearing structure of amphibious aircraft, the cross-sections of the wing and tail ribs and the fuselage frame are taken, and the cross-section stiffness distribution of the fuselage, wing and tail is calculated using the closed-chamber cross-section theory; The variable section beam element is used to model the structural stiffness of the whole aircraft, simulating the bending stiffness and torsional stiffness distribution of the whole aircraft. The node of the beam element is located at the rigid center. According to the overall shape of the amphibious aircraft, the finite element modeling of the geometric shape of the main parts of the whole aircraft is carried out using shell elements, and the thickness of the shell elements is ≤0.001mm; Rigid connection elements are used to connect the beam unit nodes and shell unit nodes together according to the principle of longitudinal proximity, ensuring that the shell unit node displacement at each station is consistent with the beam unit node displacement to simulate the complete shape of the aircraft; According to the calculation results of the mass distribution of the aircraft, the beam unit nodes are selected as the loading nodes of the concentrated mass according to the principle of spatial proximity, and the concentrated mass unit is used to simulate the mass distribution of the aircraft; Combine the stiffness model, shape model and all mass units into a finite element model of the whole aircraft structure; Use the finite element model of the entire aircraft structure to perform natural modal analysis and solve the natural frequency and vibration shape of each mode of the aircraft; The results of the ground resonance test of the whole aircraft are used to correct the calculation results of the stiffness distribution, so that the main natural modal analysis results of the aircraft are basically consistent with the test results; The lift generated by the aircraft is calculated based on the aircraft's water taxiing parameters, including taxiing speed, flap deflection angle, and elevator deflection angle, and the aircraft's attitude angle is calculated according to the trim state; The gravity of the aircraft is calculated based on the weight loading status of the aircraft. The difference between gravity and lift is the buoyancy that the aircraft should have when gliding on the water surface. Based on the geometric shape and pitch attitude of the aircraft, and the requirement that the volume of the aircraft below the waterline is equal to the displacement, calculate the aircraft waterline position that meets the buoyancy requirements; According to the calculated aircraft waterline position, all shell elements in contact with water are defined in the finite element model of the whole aircraft structure, and the outer surfaces of the shell elements below the waterline position are in contact with water; Calculate the additional mass of water on all shell elements below the waterline in the finite element model of the entire aircraft; Substitute the overall mass of the aircraft into the modal motion equation, solve the characteristic roots and eigenvectors of the equation, and obtain the wet modal characteristics of the aircraft; The hydrodynamic loads during the use of the aircraft are simplified and applied to the structural finite element model. The load loading nodes are selected according to the principle of longitudinal proximity. The elastic response characteristics of the model are solved. The transient response motion equation is solved by numerical integration method according to the time step, and the modal responses of each order are superimposed to obtain the analysis results, including the elastic response history of overload, deformation, shear force, bending moment and torque.

2. The method for analyzing the hydrodynamic elastic response of a water surface vehicle according to claim 1, characterized in that: The additional mass is expressed as: [M a ]=[D] -1 ·[E] Among them, M a is the additional mass matrix generated by water on the structure, D is the coefficient matrix obtained by numerical integration of the node velocity vector and the flow velocity vector of the finite element model, and E is the coefficient matrix obtained by numerical integration of the node force and the flow velocity vector of the finite element model.

3. The method for analyzing the hydrodynamic elastic response of a water surface vehicle according to claim 1, characterized in that: Considering that water is an isotropic, incompressible ideal fluid and the additional inertial force of water, the additional mass and the total machine mass are superimposed and substituted into the inherent modal motion equation. In the formula, M is the mass matrix of the whole aircraft, C is the damping matrix, K is the stiffness matrix, and x is the displacement vector. The characteristic roots and eigenvectors of the equation are solved to obtain the wet mode of the surface aircraft.

4. The method for analyzing the hydrodynamic elastic response of a water surface vehicle according to claim 1, characterized in that: The transient response equation of motion is as follows: [f] T [M+M a ][φ]·{ξ(t)}+[φ] T [C][φ]·{ξ(t)}+[φ] T [K][φ]·{ξ(t)}=[φ] T {P(t)} Where φ is the wet mode shape, ξ is the modal coordinate, and P(t) is the transient excitation load in the time domain, which is a function of time t.

Images