CN110738420A - method for solving additional mass in aircraft free surface crossing process - Google Patents

method for solving additional mass in aircraft free surface crossing process Download PDF

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CN110738420A
CN110738420A CN201910983880.1A CN201910983880A CN110738420A CN 110738420 A CN110738420 A CN 110738420A CN 201910983880 A CN201910983880 A CN 201910983880A CN 110738420 A CN110738420 A CN 110738420A
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李永利
吴虎胜
李博敏
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Engineering University of Chinese Peoples Armed Police Force
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Abstract

The invention discloses an additional mass solving method in a crossing process of free surfaces of aircrafts, which comprises the steps of obtaining the relation between each additional mass item and the action force and moment of ideal fluid through theoretical derivation, establishing a flow field numerical model for the crossing process of the free surfaces of the aircrafts, setting two groups of motion laws with the same speed and opposite acceleration for respective calculation, integrating the pressure on the surfaces of the aircrafts to obtain the surface stress condition, and finally obtaining the additional mass by adopting a derived solving formula, so that novel additional mass solving methods suitable for the crossing process of the free surfaces are provided.

Description

method for solving additional mass in aircraft free surface crossing process
Technical Field
The invention relates to the field of unmanned aerial vehicles, in particular to an additional mass solving method in a free surface crossing process of aircrafts.
Background
With the rise of ocean engineering, people have more and more intensive research on hydrodynamic force borne by ships and ocean structures when the ships and the ocean structures move in water, a large number of fluid-solid coupling problems exist in the actual engineering, and when the response and the stability of a fluid-solid coupling system are solved, the solution of additional mass is often involved.
The object moves in the fluid at variable speed, and the principle of pushing the object does not only do work to increase the kinetic energy of the object but also do work to increase the kinetic energy of the surrounding fluid, so that the object with mass obtains acceleration, the force applied to the object is greater than the product of the mass of the object and the acceleration, and the added mass is the additional mass.
At present, the solution of the additional mass is mainly achieved by three methods: 1) the method is used for solving by using the hypothesis of the elongated body and the slicing theory, but the method has great limitation and is only suitable for objects with large length-diameter ratio and simple appearance. 2) The numerical method based on the potential flow theory is adopted for solving, and although the method is high in precision, the calculation is complex and time-consuming. 3) The additional mass is obtained through an experimental method, the result obtained through the experiment is more real, but the requirement on experimental conditions is higher, and the experiment about the additional mass of the aircraft crossing the free liquid level is difficult to implement at present.
Disclosure of Invention
The invention aims to provide additional mass solving methods in the process of crossing the free surface of an aircraft, so as to provide novel additional mass solving methods suitable for the process of crossing the free liquid surface.
additional mass solving methods in the crossing process of the free surface of the aircraft are adopted, the relation between each additional mass item and the action force and moment of ideal fluid is obtained through theoretical derivation, a flow field numerical model is established for the crossing process of the free surface of the aircraft, two groups of motion laws with the same speed and opposite acceleration are set for respective calculation, the pressure on the surface of the aircraft is integrated to obtain the stress condition of the surface, and finally the derived solving formula is adopted to obtain the additional mass.
, the concrete implementation method comprises the following steps:
step 1, according to a potential flow theory of fluid, only considering the motion of an aircraft on an xOy plane, and by setting different specific initial motion states, jointly deducing a solving formula of the additional mass and the change rate of the additional mass in the process of crossing the medium of the aircraft:
wherein, Fix、FiyThe components of the ideal fluid acting force in the x-axis and y-axis directions of the elastic coordinate system, MizFor ideal hydrodynamic rotary moment about the z-axis, λ11、λ22、λ26、λ66For the purpose of adding to the mass,
Figure BDA0002236090410000022
for additional mass rate of change, vx、vy、The speed and the acceleration in the directions of an x axis and a y axis respectively; fix+、Fix-The components of the ideal fluid acting force in the positive and negative directions of the elastic coordinate system along the x-axis direction are adopted; fiy+、Fiy-The component of the ideal fluid acting force in the positive and negative directions of the elastic body coordinate system along the y-axis direction is adopted; miy+、Miy-The moment is generated by the motion of the vehicle along the positive and negative directions of the y axis in the elastic coordinate system under the action force of ideal fluid; miz+、Miz-The moment is generated by the counterclockwise and clockwise rotation of the ideal fluid acting force around the z axis in the missile coordinate system vehicle;
step 2, constructing a flow field numerical model of the aircraft in the process of crossing the free liquid level;
step 3, arbitrarily setting two groups of initial calculation conditions with the same speed and opposite acceleration, namely [ upsilon, upsilon ', omega' ] and [ upsilon, -upsilon ', omega, -omega' ], and respectively carrying out simulation calculation by adopting the numerical model constructed in the step 2 to obtain the surface pressure of the aircraft;
step 4, integrating the aircraft surface pressure obtained by calculation in the step 3 to obtain the following parameter Fix+、Fix-、Fiy+、Fiy-、Miy+、Miy-、Miz+And Miz-Substituting the value into the formula (1) in the step 1, and calculating to obtain the additional mass and the additional mass change rate.
Compared with the prior art, the invention has the following remarkable advantages: the method can be used for solving the additional mass and the additional mass change rate of the aircraft in the process of crossing the free liquid level, does not need to solve potential functions and immersion volumes, considers the influence of the free liquid level, can be used for solving the additional mass of objects with complex shapes, meets the requirement of engineering precision, and is quick and convenient to calculate.
Drawings
FIG. 1 is a comparison graph of the additional mass change in the process of crossing the free surface into the water when the inclination angle of a certain -shaped aircraft is 90 degrees, which is obtained by respectively adopting the method and the thin body slice theory solution.
FIG. 2 is a comparison graph of additional mass change during water production across the free surface at 90 tilt angle for an configuration aircraft solved using the present invention and slice theory, respectively.
Detailed Description
The invention combines calculation methods of numerical simulation on the basis of theoretical derivation, and solves the problems of defects in the prior method for solving the additional mass.
The invention relates to a method for solving additional mass in a free surface crossing process, which comprises the following concrete steps:
step 1, considering that the additional mass is only related to the shape and the movement direction of the aircraft, and is not related to the movement state of the aircraft. According to the potential flow theory of the fluid, if only the motion of the aircraft in the xOy plane is considered, different specific initial motion states can be set, and then a solving formula of the additional mass and the change rate of the additional mass in the crossing process of the medium of the aircraft can be obtained through combined derivation:
Figure BDA0002236090410000031
wherein, Fix、FiyThe components of the ideal fluid acting force in the x-axis and y-axis directions of the elastic coordinate system, MizFor ideal hydrodynamic rotary moment about the z-axis, λ11、λ22、λ26、λ66For the purpose of adding to the mass,
Figure BDA0002236090410000032
for additional mass rate of change, vx、vy、
Figure BDA0002236090410000033
Velocity and acceleration in the x-axis and y-axis directions, respectively, ax、ayAcceleration in the x-axis and y-axis directions, ωz、
Figure BDA0002236090410000041
Angular velocity and acceleration for the rotation of the vehicle about the z-axis; fix+、Fix-The components of the ideal fluid acting force in the positive and negative directions of the elastic coordinate system along the x-axis direction are adopted; fiy+、Fiy-The component of the ideal fluid acting force in the positive and negative directions of the elastic body coordinate system along the y-axis direction is adopted; miy+、Miy-The moment is generated by the motion of the vehicle along the positive and negative directions of the y axis in the elastic coordinate system under the action force of ideal fluid; miz+、Miz-The moment is generated by the counterclockwise and clockwise rotation of the ideal fluid acting force around the z axis in the missile coordinate system vehicle;
and 2, adopting numerical simulation software to construct a flow field numerical model of the aircraft in the process of crossing the free liquid level.
The method comprises the steps of establishing a CAD model of the aircraft by adopting three-dimensional modeling software, introducing the CAD model into ICEM software through a corresponding interface to establish a numerical calculation domain, dividing discrete grids, adopting unstructured grids to improve calculation accuracy, carrying out grid encryption around the aircraft and in the moving direction of the aircraft, stretching on a normal surface to generate a three-dimensional prism grid, setting the grid area around the three-dimensional prism grid as a moving grid, updating by adopting a spring fairing method and a local reconstruction method, selecting time step length according to the ratio of the minimum size of the divided grids to the initial speed, respectively using air and ideal fluid with the temperature of 25 ℃ as gas phases and liquid phases, using the reference pressure of atmospheric pressures and using the air with the lower density as a reference, setting boundary conditions of the aircraft as rigidbody, setting external field boundary adjustment as openning, setting multiple models as standard free surface models, and calculating the modelsHeat transfer is not considered in the calculation process, namely the temperature is constant; the fluid buoyancy model is a density difference model, and the air-phase turbulence model and the water-phase turbulence model are SST models; the convection mode is high precision; the transient format is a second-order backward Euler format; residual type is RMS, precision is 10-5(ii) a The volume force average type is Harmonic; the initial volume fraction fairing of the multiphase control is controlled by a volume weighting method.
Step 3, arbitrarily setting two groups of initial calculation conditions ([ upsilon, upsilon ', omega' ], [ upsilon, -upsilon ', omega, -omega' ]) with the same speed and opposite acceleration, and respectively carrying out simulation calculation by adopting the numerical model constructed in the step 2;
step 4, integrating the aircraft surface pressure obtained by calculation in the step 3 respectively to obtain Fix+、Fix-、Fiy+、Fiy-、Miy+、Miy-、Miz+、Miz-And substituting the formula (1) in the step 1 to calculate the additional mass and the change rate of the additional mass. Wherein the result of the integration is directly available by the CFD software.
The invention is further illustrated in the following description with reference to the figures and examples.
According to an embodiment, the invention is applied to calculate the additional mass of the process across the free surface at an angle of inclination of an aircraft of 90 ° and to compare it with the results obtained by the theoretical solution using slices of elongated bodies.
The results of the calculations are shown in tables 1 and 2. Each table gives additional mass values for the aircraft at 10 different penetration depths. x is the number ofaFor the distance of the head of the navigation device from the water-air interface, for the sake of convenience, it is dimensionless, i.e.
Figure BDA0002236090410000052
L is the aircraft length.
TABLE 1 comparison of additional mass solution results for crossing free surface water entry process of aircraft
Figure BDA0002236090410000051
Figure BDA0002236090410000061
TABLE 2 comparison of additional mass solution results for aircraft crossing free surface water outlet process
Figure BDA0002236090410000062
FIG. 1 shows a comparison graph of additional mass change in the process of entering water by crossing a free surface of an aircraft, which is calculated by adopting two algorithms, FIG. 2 shows a comparison graph of additional mass change in the process of exiting water by crossing a free surface of an aircraft, which is calculated by adopting two algorithms, wherein a solid line in the graph is a result calculated by adopting an elongated body slicing theory, discrete data points of a circle, a diamond and a triangle are results calculated by adopting the method of the invention, and the solid line is a result calculated by adopting the elongated body slicing theory.
As can be seen by comparing the attached drawings 1 and 2, the method has better goodness of fit with the result obtained by theoretical calculation of the slice of the elongated body, and the correctness of the method for calculating the additional mass in the process of crossing the free surface of the object is verified. The existing error is mainly caused by the fact that the influence of the free surface on the additional mass is not considered when the slender body slicing theory is adopted. When the method of the invention is used for obtaining the fluid information of the surface of the object, the influence of the free surface on the fluid information is fully considered, and the method is closer to the real situation, so that the additional mass obtained by the method is more accurate, and the method is more convenient for solving the additional mass and the change rate thereof in the process of crossing the free surface.
It should be noted that the above-mentioned description is not intended to limit the present invention, and the present invention is not limited to the above-mentioned examples, and those skilled in the art should make modifications and changes within the spirit of the present invention, which fall within the scope of the appended claims.

Claims (2)

  1. The method is characterized in that the relation between each additional mass item and the action force and moment of ideal fluid is obtained through theoretical derivation, a flow field numerical model is established for the process that the aircraft crosses the free liquid level, two groups of motion laws with the same speed and opposite acceleration are set for respective calculation, the pressure on the surface of the aircraft is integrated to obtain the surface stress condition, and finally the derived solving formula is adopted to obtain the additional mass.
  2. 2. The method for solving the additional mass in the crossing process of the free surfaces of types of aircrafts as recited in claim 1, wherein the method comprises the following steps:
    step 1, according to a potential flow theory of fluid, only considering the motion of an aircraft on an xOy plane, and by setting different specific initial motion states, jointly deducing a solving formula of the additional mass and the change rate of the additional mass in the process of crossing the medium of the aircraft:
    Figure FDA0002236090400000011
    wherein, Fix、FiyThe components of the ideal fluid acting force in the x-axis and y-axis directions of the elastic coordinate system, MizFor ideal hydrodynamic rotary moment about the z-axis, λ11、λ22、λ26、λ66For the purpose of adding to the mass,
    Figure FDA0002236090400000012
    for additional mass rate of change, vx、vy、
    Figure FDA0002236090400000013
    The speed and the acceleration in the directions of an x axis and a y axis respectively; fix+、Fix-The components of the ideal fluid acting force in the positive and negative directions of the elastic coordinate system along the x-axis direction are adopted; fiy+、Fiy-The component of the ideal fluid acting force in the positive and negative directions of the elastic body coordinate system along the y-axis direction is adopted; miy+、Miy-For ideal fluid acting force, the vehicle moves along the positive and negative directions of the y axis in a missile coordinate systemThe moment of (a); miz+、Miz-The moment is generated by the counterclockwise and clockwise rotation of the ideal fluid acting force around the z axis in the missile coordinate system vehicle;
    step 2, constructing a flow field numerical model of the aircraft in the process of crossing the free liquid level;
    step 3, arbitrarily setting two groups of initial calculation conditions with the same speed and opposite acceleration, namely [ upsilon, upsilon ', omega' ] and [ upsilon, -upsilon ', omega, -omega' ], and respectively carrying out simulation calculation by adopting the numerical model constructed in the step 2 to obtain the surface pressure of the aircraft;
    step 4, integrating the aircraft surface pressure obtained by calculation in the step 3 to obtain the following parameter Fix+、Fix-、Fiy+、Fiy-、Miy+、Miy-、Miz+And Miz-Substituting the value into the formula (1) in the step 1, and calculating to obtain the additional mass and the additional mass change rate.
CN201910983880.1A 2019-10-16 2019-10-16 method for solving additional mass in aircraft free surface crossing process Pending CN110738420A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114323552A (en) * 2021-11-18 2022-04-12 厦门大学 Method for judging stability of water entering and exiting from cross-medium navigation body

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
张晓强等: "跨介质运动物体的附加质量", 《北京航空航天大学学报》 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114323552A (en) * 2021-11-18 2022-04-12 厦门大学 Method for judging stability of water entering and exiting from cross-medium navigation body

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