CN114077770A - Direct wave generation method for simulating water forced landing SPH (flying wave height) of aircraft - Google Patents
Direct wave generation method for simulating water forced landing SPH (flying wave height) of aircraft Download PDFInfo
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Abstract
The invention provides a direct wave making method for simulating an SPH (forced landing on water) of an aircraft, which solves the speed, the acceleration and the like of each mass point in a wave water field according to a hydrodynamic potential flow theory, and gives wave conditions and motion parameters to water area particles in an initial state when a calculation field is initialized before calculation of the SPH flow field. The method does not need time-consuming wave-making calculation in advance, and provides convenience for SPH calculation and analysis of the helicopter forced landing problem under the wave condition.
Description
Technical Field
The invention relates to the field of aircraft dynamics, in particular to a direct wave generation method for simulating an SPH (flying wave height) of an aircraft on water forced landing.
Background
The forced landing performance on water for an aircraft operating in a particular river, lake or marine environment is a design and manufacturing consideration. From the viewpoint of crash resistance, the load applied to an airplane by water forced landing during impact is completely different from the ground crash. Therefore, it is necessary to develop special research on the mechanical problems of load, motion and the like of forced landing on water of the aircraft. In the simulation numerical simulation analysis of the aircraft, simulating the overwater forced landing characteristic under different sea conditions is an important guarantee for testing the reliability and the practicability of the design scheme. It is therefore important to use an efficient wave generation method in the numerical simulation program.
Meanwhile, compared with Any Lagrange Eulerian (ALE) method based on grids, the smooth Particle dynamics method (SPH) adopts a large number of smooth particles to describe the flow field, does not need to perform spatial dispersion on the grids, and can avoid the problems of grid deformation or entanglement and the like caused by large deformation of a free surface on the grid method, so that the method has natural advantages when the flow problem of large deformation of the free surface such as water impact is treated.
The basis of the SPH method is the theory of integral interpolation. The material of the whole flow field is dispersed into a series of particles, and the particles have parameters of speed, internal energy, mass and the like. The parameters at any position in the flow field can be obtained by integrating the parameters of each particle through a 'kernel function'. Finally, the fluid mechanics basic equation is converted into an equation set for calculating the SPH value, and the particles can flow freely according to the calculated motion parameters. The SPH method has shown high accuracy and efficiency in strong nonlinear fluid problems of attack on free surfaces, collapse of dams, gas explosion, etc.
The forced landing mechanics problem of the aircraft under the wave condition is investigated by utilizing SPH numerical simulation, and firstly, how to generate a wave water body is solved.
Disclosure of Invention
The invention provides a direct wave generation method for simulating the forced landing SPH of an aircraft, aiming at solving the problems in the prior art.
The invention provides a direct wave generation method for simulating an SPH (flying wave height) of an aircraft on water forced landing, which comprises the following steps of:
1) establishing an aircraft model;
2) carrying out mesh division on the surface of the aircraft model, wherein the size of a mesh is consistent with that of a particle to be subjected to SPH simulation, and generating two layers of virtual particles by adhering the surface of the mesh on the basis of a surface mesh;
3) and (3) importing the configuration parameters of the SPH solver and the aircraft grid model, solving the speed, acceleration and pressure parameters of the water area fluid particles under the wave condition by using a direct wave-making method, and initializing the water area particles to obtain the initial flow field of the water area with waves.
4) And starting an inner core by the SPH module to solve and operate, simulating a six-degree-of-freedom motion process of the aircraft under the action of gravity and water body impact force, and obtaining hydrodynamic force and a motion response rule of the aircraft.
5) And (4) analyzing and collating data by using post-processing software, and providing reference for the design of the aircraft.
Further improvement, in the step 1), simplified models of the designed aircraft are established by adopting CATIA software.
Further improved, the direct wave-making method in step 3) makes waves by means of direct wave-giving mode, and considers two typical wave conditions of forward traveling wave and standing wave: wherein the wave form of the forward wave
Horizontal velocity
Vertical velocity
Pressure intensity
Standing wave shape
Horizontal velocity
Vertical velocity
Pressure intensity
Where H is the wave height, i.e. the height difference from the peak to the trough, and σ is the angular frequency σ2Gktanhkh, t is the wave travel time, k is the wave number,
l is the wavelength and h is the average water depth.
The invention has the beneficial effects that: according to the hydrodynamics law, the motion and dynamics parameters of water particles at each position of a wave water area are directly given without time-consuming wave-making calculation in advance, and convenience is brought to SPH calculation analysis of the forced landing problem of the aircraft under the wave condition.
Drawings
Fig. 1 is a definition of waveforms and hydrodynamic motion parameters of forward traveling waves and standing waves.
Fig. 2 is an example of the SPH calculation domain for generating forward traveling waves by the direct wave-making method.
Fig. 3 is an example of the SPH calculation domain for generating standing waves by the direct wave-making method.
FIG. 4 is a scheme and a flow of SPH simulation calculation for forced landing on water under a wave condition of a helicopter applying a direct wave-making method.
FIG. 5 is a schematic view of the landing attitude of the helicopter in the presence of regular waves on the water surface.
Figure 6 is a comparison of the forced landing characteristics of a helicopter on water in the case of a regular wave on the water surface and in the case of no wave.
Detailed Description
The invention will be further explained with reference to the drawings.
The direct wave making method and the flow and scheme for carrying out numerical simulation calculation on the SPH of the helicopter overwater forced landing by applying the direct wave making method are as follows:
the first step is as follows: and establishing a helicopter model. Simplified models of the designed helicopter were built using CATIA software.
The second step is that: and (5) dividing the grids. And carrying out mesh division on the surface of the helicopter model, wherein the size of the mesh is consistent with the size of the particle to be subjected to SPH simulation, and generating two layers of virtual particles by adhering the surface of the helicopter model to the surface based on the surface mesh.
The third step: and (3) importing the configuration parameters of the SPH solver and the helicopter grid model, solving the speed and pressure parameters of the water area fluid particles under the wave condition by using a direct wave-making method, and initializing the water area particles to obtain the initial flow field of the water area with waves.
The fourth step: the SPH module starts an inner core to solve and operate, simulates the six-degree-of-freedom motion process of the helicopter under the action of gravity and water impact force, and obtains hydrodynamic force and motion response rules of the helicopter.
The fifth step: and analyzing and collating data by using post-processing software, and providing reference for the design of the helicopter.
Fig. 1 shows the waveforms of the forward wave and the standing wave and the definition of the hydrodynamic motion parameters. According to the hydrodynamic potential flow theory, the motion parameters and the pressure of each particle in the water area can be deduced.
Taking the former traveling wave as an example, the wave surface displacement equation can be expressed as:
where H is the wave height, i.e. the height difference from the peak to the trough, and σ is the angular frequency σ2Gktanhkh, t is the wave travel time, k is the wave number,
l is the wavelength and h is the average water depth. The corresponding velocity potentials are:
the horizontal direction velocity in the water area below the wave surface can be obtained by solving a partial derivative according to a velocity potential function:
the acceleration is as follows:
the vertical direction speed in the water area below the wave surface is obtained by solving a partial derivative through a speed potential function:
the acceleration is as follows:
the pressure field of a body of water is determined by the unsteady bernoulli equation, as shown below:
substituting the boundary condition to obtain the following results after simplification:
similarly, the parameters associated with the standing wave may also be calculated. The expressions for the relevant physical parameters of the forward wave and the standing wave are summarized in table 1.
Wherein: h is the wave height, i.e. the height difference from the crest to the trough, σ is the angular frequency σ2＝gktanhkh, t is wave propagation time, k is wave number,
l is the wavelength and h is the average water depth.
According to the wave mechanics theory, when the SPH numerical simulation is used for initializing the calculation domain particles, the calculated water area particle motion and pressure parameters under the wave condition can be given to the SPH particles, the water area waves are directly created, and the simulation method is ready for simulating the forced landing numerical value of the helicopter water under the wave condition.
Fig. 2 and 3 show a simple example of the SPH calculation domain for generating the forward traveling wave and the standing wave by the direct wave-making method, and the motion and pressure parameters of the water mass point of the SPH calculation domain meet the hydrodynamic rules, so that the requirements of the simulation of the SPH numerical value of the forced landing problem on water of the helicopter under the wave condition can be met.
The SPH simulation calculation scheme and flow of forced landing on water under the condition of waves of a helicopter applying a direct wave-making method are shown in figure 4. To illustrate the utility and reliability of this method, the direct wave generation method was validated using specific examples. Simulating a working condition: the pitch angle of the helicopter is 6 degrees, the wave height is 1.25m, the wavelength is 6.4m, the landing position is a wave crest, the advancing speed of the helicopter is 15.4m/s, and the vertical speed is 1.5 m/s.
Fig. 5 shows the landing attitude (0.1 s to 0.4s state after landing) of the helicopter on the regular wave water surface and the impact effect of the helicopter on the water body, which are generated by the method, the method well simulates the water surface wave condition of the actual condition and captures the impact characteristic of the helicopter on the regular wave water surface.
FIG. 6 is a comparison of the forced landing characteristics of the helicopter on water under the condition of regular waves on the water surface and under the condition of no waves, wherein (a) is the working condition of regular waves, and (b) is the working condition of a hydrostatic surface.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (3)
1. A direct wave generation method for simulating the water forced landing SPH of an aircraft is characterized by comprising the following steps:
the first step is as follows: establishing a three-dimensional model of the aircraft;
the second step is that: carrying out mesh division on the surface of the aircraft model, wherein the size of a mesh is consistent with that of a particle to be subjected to SPH simulation, and generating two layers of virtual particles by adhering the surface of the mesh on the basis of a surface mesh;
the third step: and (3) importing the configuration parameters of the SPH solver and the aircraft grid model, solving the speed and pressure parameters of the water area fluid particles under the wave condition by using a direct wave-making method, and initializing the water area particles to obtain the initial flow field of the water area with waves.
The fourth step: the SPH module starts an inner core to solve and operate, simulates the six-degree-of-freedom motion process of the helicopter under the action of gravity and water impact force, and obtains hydrodynamic force and motion response rules of the helicopter.
The fifth step: and analyzing and collating data by using post-processing software, and providing reference for the design of the helicopter.
2. The direct wave generation method for aircraft forced landing SPH simulation of claim 1, wherein: and step 1), adopting CATIA software to establish a simplified model of the designed aircraft.
3. The direct wave generation method for aircraft forced landing SPH simulation of claim 1, wherein: the direct wave-making method in the step 3) makes waves by a direct wave-giving mode, and considers two typical wave conditions of a forward traveling wave and a standing wave: wherein the wave form of the forward wave
Horizontal velocity
Vertical velocity
Pressure intensity
Standing wave shape
Horizontal velocity
Vertical velocity
Pressure intensity
Where H is the wave height, i.e. the height difference from the peak to the trough, and σ is the angular frequency σ2Gktanhkh, t is the wave travel time, k is the wave number,
l is the wavelength and h is the average water depth.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115600316A (en) * | 2022-10-17 | 2023-01-13 | 中国船舶科学研究中心（Cn） | Ship bottom gas-liquid layering two-phase flow fluctuation form numerical simulation method |
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|---|---|---|---|---|
| CN108846225A (en) * | 2018-06-27 | 2018-11-20 | 中国直升机设计研究所 | A kind of SPH wave simulation method applied to helicopter ditching |
| CN111339658A (en) * | 2020-02-25 | 2020-06-26 | 河海大学 | Hydraulic transient simulation method and device based on Lagrange mesh-free particle method |
| CN113515805A (en) * | 2021-04-07 | 2021-10-19 | 南京航空航天大学 | Method for simulating numerical value of two-phase flow of water and gas generated during taking off and landing on wave water surface of seaplane |
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- 2021-10-25 CN CN202111240711.2A patent/CN114077770A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108846225A (en) * | 2018-06-27 | 2018-11-20 | 中国直升机设计研究所 | A kind of SPH wave simulation method applied to helicopter ditching |
| CN111339658A (en) * | 2020-02-25 | 2020-06-26 | 河海大学 | Hydraulic transient simulation method and device based on Lagrange mesh-free particle method |
| CN113515805A (en) * | 2021-04-07 | 2021-10-19 | 南京航空航天大学 | Method for simulating numerical value of two-phase flow of water and gas generated during taking off and landing on wave water surface of seaplane |
Non-Patent Citations (1)
| Title |
|---|
| 陆召严: "基于SPH的飞行器水上迫降数值模拟方法与应用", 《国优秀硕士学位论文全文数据库工程科技Ⅱ辑》, no. 03, 15 March 2017 (2017-03-15), pages 031 - 81 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115600316A (en) * | 2022-10-17 | 2023-01-13 | 中国船舶科学研究中心（Cn） | Ship bottom gas-liquid layering two-phase flow fluctuation form numerical simulation method |
| CN115600316B (en) * | 2022-10-17 | 2023-05-12 | 中国船舶科学研究中心 | Ship bottom gas-liquid layered two-phase flow fluctuation morphology numerical simulation method |
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