JP2007131201A - Underwater impact-absorbing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an underwater impact-absorbing method absorbing an underwater explosion impact to a hull caused by a bubble impact wave generated by the underwater explosion of a mine and a torpedo by utilizing a bubble for absorbing the energy of the bubble impact wave in a marine vessel or the like. <P>SOLUTION: The impact to an impact receiving body 1 caused by underwater explosion is absorbed by covering a part or the whole of the impact receiving body 1 with an energy absorption body A for absorbing transmission energy in the underwater of the bubble impact wave W generated by underwater explosion. The energy absorption body A is made to serve as an energy absorption body for absorbing the energy of the bubble impact wave W by making it resonate with the vibration of the bubble impact wave W. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

    The present invention relates to an underwater impact mitigation method for mitigating underwater explosion impact on a hull due to bubble shock waves generated by underwater explosions such as mines and torpedoes in a ship.

  In an attack by a mine or torpedo on a ship, there is a method of destroying with a bubble shock wave generated by a close explosion near the ship, in addition to an explosion after directly colliding with the ship.

  In particular, in recent torpedoes and mines, close-up explosions are becoming mainstream, and when torpedoes and mines explode in locations close to the hull, explosion bubbles (detonation gas spheres) are generated in addition to explosion shock waves generated by glaze.

  Since this explosive bubble has a gas body in the bubble, if the bubble contracts due to an external fluid pressure (water pressure) after the bubble expands rapidly, the internal gas pressure increases and expands again. Shrink due to external fluid pressure. As this rebound is repeated, the bubbles vibrate as they become smaller and larger with time, but eventually decay and disappear. The pressure amplitude and period in the bubble decrease with time.

  When a large explosion bubble grown by this underwater explosion contracts most into a donut shape, a high-speed jet flow of 100 m / s generated by deformation of the bubble, that is, a so-called jet flow is generated. When this jet stream hits the hull, it gives a very high pressure locally, so the hull will suffer tremendous damage, such as a hole in a part of the hull and the collapse of the hull. .

  In addition, in the case of an underwater explosion at a distance far from the hull, the jet flow attenuates before reaching the hull, so that damage caused by the jet flow can be avoided, but even in this case, the process of the bubble moving from contraction to expansion Since the bubble shock wave called “bubble pulse” generated in the sea is transmitted to the seawater and damages the hull, the hull is damaged by the bubble shock wave.

  As for the bubble kinetics (bubble dynamics) problem, the impact generated by this underwater explosion is simulated by numerical calculation using the following Rayleigh bubble equation (Equation (1)). It is becoming possible.

  Here, R is the bubble radius, R0 is the initial bubble radius, ρ is the density of the external fluid, Pa0 is the initial bubble internal pressure, γ is the specific heat ratio of the internal gas body, P1 is the bubble ambient pressure, μ is the viscosity of the external fluid, T is the surface tension of the external fluid, and dots are time derivatives. Strictly speaking, there are also effects of compressibility of the internal gas body and thermal effects.

  In the case of an underwater explosion, the inside of the bubble is filled with the gas generated by the explosion.

  FIG. 2 shows the result of simulating the impact pressure due to bubble shock waves during an underwater explosion when a 0.25 kg (0.55 lb [lb]) TNT glaze explodes at a water depth of 91 m (300 ft [ft]). In this case, the maximum bubble diameter generated by the explosion was about 0.6 m, the bubble rebound period was about 30 ms, and the frequency was about 33 Hz. In the example of FIG. 2, when an explosion shock wave is received at the time point E, as shown by point B, the bubble interface pressure suddenly rises at a period of about 30 ms (milliseconds), and the bubbles expand rapidly. It can be seen that the bubble interface pressure and the bubble diameter at that time gradually attenuate with the passage of time.

  On the other hand, it is known that underwater sound that is a pressure wave can be shielded by fine bubbles such as microbubbles. This is because bubbles such as bubbles resonate with the frequency of the underwater sound and absorb the energy of the underwater sound.

  For example, in the case of the bubble distribution of FIG. 3 in which the horizontal axis indicates the diameter of bubbles (bubbles whose inside is air) and the vertical axis indicates the number of bubbles, the sound pressure attenuation when passing through a 1 cm-thick bubble layer The quantity (A) is shown in decibel (dB) in FIG. According to FIG. 4, it can be seen that when microbubbles having a bubble diameter of about 30 microns (μ) are included in the fluid, the sound pressure at a high frequency of 50 kHz or more is almost attenuated.

  The relationship between the bubble resonance frequency f and the bubble diameter R at this time can be calculated by Minato's formula (Formula (2)).

  Here, R is the bubble radius, ρ is the density of the external fluid, γ is the specific heat ratio of the internal gas body, and P1 is the bubble ambient pressure.

  The present inventors have obtained the above knowledge, and have considered to use the principle of sound insulation by bubbles for relaxation of shocks against bubble shock waves caused by underwater explosions.

  For example, since the frequency in the underwater explosion of FIG. 2 is 33 Hz, the radius of a bubble (bubble having air as an internal gas body) resonating at this frequency of 33 Hz is about 10 cm from Equation (2). Therefore, by disposing a bubble with a radius of about 10 cm around an impact receptor such as a hull and enclosing it, the energy of the bubble shock wave generated by the underwater explosion is absorbed and the bubble shock wave reaching the impact receptor is attenuated. It is considered possible.

  Therefore, by immediately covering the impact receptor such as the hull with a bubble that attenuates the bubble shock wave generated by the underwater explosion immediately before the explosion, damage due to the bubble shock wave of the impact receptor can be reduced or avoided.

  In addition, as a torpedo defense system, a torpedo defense net is fired from a ship, the net is deployed vertically in the sea, and a torpedo is sent to the net with a noise transmitter built in the weight to capture the torpedo on the net. A net-type torpedo defense system has been proposed (see, for example, Patent Document 1).

In addition, as a method and apparatus for generating bubbles around the hull, although the purpose of foaming, the effect of bubbles and the bubble diameter are different, many bubble generating devices have been proposed for reducing the frictional resistance of ships (for example, (See Patent Documents 2 to 5.) However, these bubbles often use microbubbles such as microbubbles, and the diameter of the bubbles and characteristics to be used are greatly different from those of the present invention.
JP-A-6-135382 JP 2003-160091 A JP 2000-168673 A JP-A-11-321775 JP-A-9-328095

  The present invention has been made to solve the above problems by obtaining the above knowledge, and its purpose is to underwater explosion to the hull due to bubble shock waves generated by underwater explosions such as mines and torpedoes in ships. An object of the present invention is to provide an underwater impact mitigation method for mitigating an impact by utilizing a bubble that absorbs energy of a bubble shock wave.

  The underwater impact mitigation method of the present invention for achieving the above object is an energy absorber that absorbs propagation energy of a bubble shock wave generated by underwater explosion in water, and covers the impact receptor by covering part or all of the impact receptor. It is a method to reduce the impact of underwater explosions on the body.

  As this energy absorber, a bubble or an elastic body can be considered. According to this underwater shock mitigation method, the energy of bubble shock waves can be absorbed, so that shock receivers such as hulls can be protected from bubble shock waves.

  When the energy absorber is an energy absorber that absorbs the energy of the bubble shock wave by resonating with the vibration of the bubble shock wave in the above-described underwater shock mitigation method, according to this method, the shock wave energy is efficiently absorbed by the resonance. Since it can, it can relieve the impact of underwater explosions very effectively.

  In the above-described underwater shock mitigation method, if an energy absorber that resonates at a frequency of about 10 Hz to 100 Hz is used as the energy absorber, bubble shock waves generated by underwater explosions of mines and torpedoes that are considered to be currently used. Since the period enters this period, it is remarkably effective.

  The period of the bubble shock wave generated by this underwater explosion varies depending on the amount of glaze and the water depth at the time of the explosion, but since the amount of glaze (explosive power) and usage depth of mines and torpedoes can be estimated, the Rayleigh equation (formula ( 1)) and can be estimated by simulation calculation.

  When the energy absorber is formed with bubbles by the underwater impact mitigation method, a large amount of energy absorber can be easily generated.

  In addition, a bubble here has a gas body inside, and means that the volume as a whole can expand | swell and shrink | contract by the fluctuation | variation of ambient pressure. The bubble may be liquid or solid as long as it is a substance that can allow expansion and contraction of the volume of the internal gas body.

  This bubble may be other than the one containing air, engine exhaust gas, etc., but in the case of a bubble containing air inside, the bubble diameter is about 10 cmφ to 100 cmφ for reducing frictional resistance. Since it is very large compared to bubbles, it has a large buoyancy and is easy to break up into small diameter bubbles, so it is difficult to keep it around the impact receptor for a long time.

  For this reason, it is possible to enclose bubbles with a thin film or thick film made of a substance having a high density (ρ) and viscosity (μ), such as a polymer, or to form a bubble that contains the whole with a polymer (gel) or the like. If they are formed, or a bubble enveloping a gas such as ether (γ = 1) whose specific heat ratio (γ) is smaller than air (γ = 1.4) is released into water or sea The impact relaxation effect can be obtained even with a small diameter bubble that has a small buoyancy and can be kept around the impact receptor for a relatively long time.

  In addition, the use of thin metal film spheres containing gas makes it possible to produce spheres with relatively freely selected energy absorption characteristics, and it is easy to adjust the balance of weight, buoyancy, and so on. Can be made relatively easy, and can be kept around the impact receptor for a relatively long time, so that a large impact relaxation effect can be obtained.

  When a substance other than air is contained inside, the resonance frequency can be obtained by performing numerical simulation using the basic equation (Equation (1)) of Rayleigh's bubble motion equation. Parameters governing this basic formula (Formula (1)) include external fluid density, internal gas body density, ambient pressure, radius, external fluid viscosity, internal gas body viscosity, surface tension, specific heat ratio, and bulk elasticity. It is possible to handle the rate, diffusion coefficient, etc., obtain a value that increases vibration energy by parameter study, create a database, and find the bubble that resonates with the vibration of the bubble shock wave generated by the target underwater explosion and its diameter.

  And the big impact relaxation effect can be acquired by generating the bubble of the diameter of this diameter and the periphery of this diameter.

  Further, in the underwater impact mitigation method, when the impact receptor is a ship or a submarine, the ship or submarine can be protected from an underwater explosion of a mine or a torpedo.

  According to the underwater shock mitigation method of the present invention, an impact receptor such as a ship is covered with an energy absorber that absorbs energy of a bubble shock wave generated by an underwater explosion such as a mine or a torpedo, and a bubble shock wave that reaches the impact receptor. Therefore, the impact due to the underwater explosion on the impact receptor can be mitigated by using the energy absorber.

  In addition, by forming this energy absorber with bubbles, such as bubbles that resonate at the frequency of the bubble shock wave, it efficiently absorbs the energy of impacts caused by underwater explosions and mitigates impacts caused by underwater explosions on impact receptors. be able to.

  Hereinafter, an embodiment of the underwater impact mitigation method according to the present invention will be described in the case where bubbles are adopted as an energy absorber when the impact receptor is a ship.

  FIG. 1 shows a state of relaxation of an impact caused by an underwater explosion on a ship due to bubbles. As shown in this figure, a shock wave (pressure wave) W generated by vibration of an explosion bubble B generated by an underwater explosion is protected by a bubble A around the ship 1. That is, the energy of the shock wave propagating from the explosion bubble B is absorbed by the bubble A that resonates with the vibration of the shock wave, and the shock wave energy reaching the hull of the ship 1 is reduced.

  The bubble A also absorbs energy and repeats expansion and contraction, but the energy absorbed by each bubble A is smaller than the impact energy radiated from the explosion bubble B, and the energy of the bubble A is the surrounding energy. Since it is transmitted to the fluid side due to the vibration of the fluid and attenuates, it can be said that there is almost no damage to the ship 1 compared to the damage by the shock wave energy.

  A bubble generating device 20 as shown in FIG. 1 is provided in the protection portion of the ship. The bubble generating device 20 is a bubble generating device that foams bubbles that attenuate the bubble shock wave B generated by the underwater explosion. The generated bubbles A generate bubbles that resonate with the frequency of the bubble shock wave B.

  This bubble generating device 20 is configured by connecting a bubble generating chamber 21 to an atmosphere release pipe 22 having a pump 23 and an opening / closing valve 24. The bubble generating chamber 21 is a bubble generating box provided in the ship and communicates with a slit-like bubble blowing device 25 provided on the hull surface 1f or a pipe-like bubble blowing device 25 piped on the hull surface 1f.

  When the torpedo 2 is expected to explode, when the on-off valve 24 is opened and the pump 23 is operated, air is sucked from the atmosphere and sent into the bubble generation chamber 21 via the pipe 22. In the bubble generation chamber 21, a bubble A that resonates with a frequency of about 10 Hz to 100 Hz of the bubble shock wave B is generated by an indoor nozzle (not shown) or by a slit-like opening or a pipe-like opening of the bubble blowing device 25. Then, the bubble A is discharged from the bubble blowing device 25 to the hull surface 1f.

  The diameter of the bubble A that resonates with the frequency of the bubble shock wave B can be calculated by the Rayleigh equation (formula (1)) when the bubble is not a bubble. In the case of bubbles, the inside of the bubble A is air, and the external fluid is seawater, which can be calculated by Minato's formula (Formula (2)).

  Here, R is the bubble radius, R0 is the initial bubble radius, ρ is the density of the external fluid, Pa0 is the initial bubble internal pressure, γ is the specific heat ratio of the internal gas body, P1 is the bubble ambient pressure, μ is the viscosity of the external fluid, T is the surface tension of the external fluid, and dots are time derivatives.

  The diameter of the bubble A is about 10 cmφ to 100 cmφ when air is included. The bubble diameter is determined by the shape, size, and type of opening (shape change, size) of the nozzle opening in the bubble generating chamber 21 or the slit-like opening or the pipe-like opening of the bubble blowing device 25. The distribution density of the opening, the position of the opening, the opening direction, etc., the supply amount of air supplied to the bubble generation chamber 21, the pressure, the air temperature, the surrounding seawater temperature, the water depth, the ship It depends on the relationship with speed etc.

  Therefore, for a ship 1 to be protected, a range in which an appropriate amount of bubble A is obtained and an appropriate amount of bubble A is obtained with respect to these parameters is obtained in advance through experiments and simulation calculations. Provide an opening with an appropriate shape, size, distribution density, and arrangement, and select appropriate parameters such as the amount of air when bubbles A are generated, and have an appropriate diameter distribution that suits the situation. A large amount of bubble A is generated.

  The bubble A discharged to the outside of the ship covers the hull surface 1 f while rising and wraps an important part of the ship 1 with the bubble A.

  When the torpedo 2 or the like explodes in water and an explosion bubble B is generated to generate a bubble shock wave W, the bubble A enveloping the hull resonates with the frequency of the bubble shock wave W and absorbs the impact energy. Thereby, the impact to a hull is relieve | moderated and the important part of the ship 1 is protected.

  The parameters governing bubble dynamics equation (1) include density, ambient pressure, radius, viscosity, surface tension, specific heat ratio, bulk modulus, diffusion coefficient, and so on. By doing and specifying and using bubbles that can absorb vibration energy, a greater impact mitigating effect can be obtained, and a more efficient underwater impact mitigating method can be provided.

  Particularly, in the case of bubbles containing air, since the bubble diameter becomes large, a polymer having a high density or a gas having a small specific heat ratio, for example, a gas body of ether having γ = 1.0 instead of water vapor having γ = 1.4. If the bubbles are formed by, for example, an impact relaxation effect can be obtained even with bubbles having a small bubble diameter. In addition, although recovery is necessary, a metal sphere containing gas is also possible in principle.

It is a figure which shows typically the mitigation method of the impact by the underwater explosion which concerns on this invention. It is a figure which shows the time series of the pressure change of the underwater explosion of a numerical simulation result. It is a figure which shows bubble distribution. It is a figure which shows the shielding effect of the underwater sound by the bubble group which has the bubble distribution of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ship 1f Hull surface 2 Torpedo 20 Bubble generator 21 Bubble generation chamber 22 Piping 23 Pump 24 On-off valve 25 Bubble blowing device A Bubble B Explosion bubble W Bubble shock wave

Claims (4)

  An underwater impact mitigation method for mitigating an impact caused by an underwater explosion on an impact receptor by covering a part or all of the impact receptor with an energy absorber that absorbs propagation energy of bubble shock waves generated by underwater explosion in water.   2. The underwater impact mitigation method according to claim 1, wherein the energy absorber is an energy absorber that absorbs energy of a bubble shock wave by resonating with vibration of the bubble shock wave.   The underwater impact mitigation method according to claim 1, wherein the energy absorber is formed of bubbles. The underwater impact mitigation method according to claim 1, wherein the impact receptor is a ship or a submarine.

Images