A METHOD AND A DEVICE FOR NOISE REDUCTION

A method and a device for noise reduction

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a method and a device for reducing noise from a gun.

When firing with heavy guns, such as for instance high-pressure canons, strong sound impulses arise, which may be very annoying to those living or being near to the firing spot. In order to avoid such noise disturbances, large protective distances between firing spots and houses are generally used, often in com- bination with fixed noise reducing appliances in the form of embankments or noise reducing screens. The noise reducing ability of the latter is strongly affected by meteorological conditions and the noise reducing effect is periodically low, which results in strong noise disturbances. Modern research has shown that the noise disturbances are mainly caused by the components of lowest frequency in the noise, which constitutes another aggravating circumstance for noise reduction by means of noise reducing screens and similar screening appliances, since the noise reducing characteristic of these is such that the low- frequency noise is reduced to a smaller extent than the high- frequency noise. Furthermore, the screening methods will not offer any satisfying solution in connection with mobile guns firing from different firing spots. OBJECT OF THE INVENTION

The object of the present invention is to achieve a method and a device which in a practical manner make possible a reduction of the noise when firing with a gun.

SUMMARY OF THE INVENTION

According to the invention, said object is achieved by means of a method having the features defined in claim 1 and a device having the features defined in claim 6.

The inventive solution implies that propellant gases escaping through the muzzle of the gun's barrel in connection with a firing are cooled by means of a coolant in liquid or crystalline state to such an extent that a noise reducing pressure reduction of the propellant gases is obtained. The invention is based on the thermodynamic principle that a gas that is being cooled also is subjected to a pressure reduction. By cooling the propellant gases immediately when they escape through the muzzle of the barrel, the pressure of the propellant gases is consequently reduced, whereby the noise caused by the propellant gases is reduced. By the inventive solution, it will be possible to efficiently reduce the noise in question without requiring any ex- pensive and bulky fixed screening appliances.

Preferred embodiments of the inventive method and the inventive device will appear from the dependent claims and the subsequent description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be more closely described by means of embodiment examples, with reference to the appended drawings. It is shown in: Fig 1 a schematical illustration of a device according to a first embodiment of the invention in section,

Fig 2 a schematical illustration of a device according to a second embodiment of the invention in section,

Fig 3 a cross-section according to A-A in Fig 2,

Fig 4 a schematical illustration of a device according to a third embodiment of the invention in section, and

Fig 5 a cross-section according to A-A in Fig 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to the inventive solution, a coolant in liquid or crystalline state is applied at the muzzle of the gun's barrel so that at least some of the propellant gases escaping through the muzzle of the barrel in connection with a firing are cooled by said coolant for achieving a reduction of the noise caused by the propellant gases.

Fig 1 illustrates a device 1 according to a first embodiment of the invention. The coolant 2, preferably in the form of water, is here applied at the muzzle 3 of the gun's barrel 5 by jetting. The device 1 comprises several nozzles 4 for jetting the coolant, which nozzles are arranged about the barrel 5 of the gun. The coolant is carried to the respective nozzle 4 via a distribution channel 6 extending about the barrel 5, to which distribution channel the coolant is supplied via a conduit 7 from a not shown coolant supply. The coolant supply may consist of a suitable container. When the coolant is water the conduit may of course be arranged to carry the water to the respective nozzle 4 from a lake or other pool of water. The nozzles 4 are distributed about the periphery of the barrel, preferably at regular mutual distances, and are pointed forward in the firing direction. The nozzles 4 are suitably arranged to jet the coolant 2 in the longitudinal direction of the barrel in several jets 8 together forming an essentially tubular configuration about the longitudinal axis of the barrel. In this way a tubular "body" of coolant will surround a projectile fired through the muzzle 3 of the barrel. The projectile is in this case intended to pass in the middle 9 of the tubular "body", which is essentially free from coolant. In this embodiment, the coolant is consequently applied at the barrel 5 freely in the air in the form of a series of jets 8 surrounding the muzzle 3 of the barrel and extending forward past the barrel in its longitudinal direction. When the hot propellant gases reach the muzzle area in connection with a firing, they expand strongly and are mixed with the coolant applied at the muzzle of the barrel so that they are cooled by the coolant, whereby a pressure reduction of the propellant gases is achieved. The pressure reduction will in its turn result in that the explosion sound is reduced.

The coolant is according to the invention applied at the muzzle of the barrel in such a manner that the propellant gases together with the coolant is allowed to expand essentially freely in all directions as soon as the propellant gases have left the muzzle of the barrel. With the inventive solution, the propellant gases are cooled immediately when they escape through the muzzle of the barrel in that the propellant gases are mixed with the coolant applied at the muzzle of the barrel.

When a projectile is fired, a combined heat and pressure wave is radiated from the muzzle of the barrel immediately following the exit of the projectile from the muzzle of the barrel. By applying a coolant at the muzzle in accordance with the invention, the gradient and amplitude of this heat and pressure wave is reduced. When the coolant is hit by the wave front of the heat and pressure wave, a transfer of energy from the wave front to the coolant takes place, which causes the coolant to evaporate. By the evaporation of the coolant, the heat and pressure of the wave front is reduced very rapidly so that a substantial reduction of the sound pressure and infra sound pressure and thereby a substantial reduction of the noise caused by the heat and pressure wave, i.e. of the noise caused by the propellant gases, is obtained.

A device 1 ' according to a second embodiment of the invention is illustrated in Fig 2 and 3. The coolant 2, preferably in the form of water, is here applied at the muzzle 3 of the barrel enclosed in several envelopes 12, preferably of plastic, which are designed to break by the pressure from the propellant gases. The envelopes 12 are suitably design as elongated bags of thin plastic or other suitable material. The device 1 ' comprises a holder 13 arranged to support the envelopes 12. This holder 13 may either be detached from the gun or arranged to be supported by the gun, for instance by being attached to the barrel 5 of the gun. The holder 13 is arranged to support the envelopes 12 in such a manner that they together surround the muzzle 3 of the barrel and extend forward past the barrel 5 in its longitudinal direction. When the pressure from the propellant gases reaches the muzzle 3 of the barrel, the envelopes 12 break so that the coolant is released and thereby achieves the desired cooling and pressure reduction of the propellant gases. The holder is designed to allow an essentially free expansion of the propellant gases and the coolant in all directions as soon as the propellant gases have exited the muzzle of the barrel and caused the envelopes 12 to break.

In the embodiment illustrated in Fig 2 and 3, the holder 13 com- prises a ring-shaped mounting member 14 arranged to surround the barrel 5 so as to make the holder supported by the barrel. A number of supporting arms 15 are attached to the mounting member 14. The supporting arms 15 bind together and support a set of ring-shaped elements 16, which are arranged at a dis- tance from each other in the longitudinal direction of the barrel. The respective element 16 has an upper semi-circular section 17 with an inner radius essentially corresponding to or being somewhat larger than the outer radius of the barrel and a lower semi-circular section 18 with a radius considerably larger than the radius of the upper section 17. Shelves are hereby formed, onto which the envelopes 12 containing the coolant can be placed and supported. A gap is left in the middle of the holder, through which gap a fired projectile is intended to pass.

A device 1 " according to a third embodiment of the invention is illustrated in Fig 4 and 5. The coolant 2 is here in crystalline state, preferably in the form of snow, and at least partly self- supporting. The crystalline coolant 2 is formed into a tubular body 20, which is arranged to surround the front part of the barrel and extend forward past the barrel 5 in its longitudinal direc- tion. In this manner a tubular body 20 of coolant will surround a projectile fired through the muzzle 3 of the barrel. The projectile is in this case intended to pass in the cavity 21 in the middle of the tubular body. The device 1 " comprises a holder 22 arranged to support the body 20. This holder 22 may either be detached from the gun or arranged to be supported by the gun, for instance by being attached to the barrel 5 of the gun.

In the embodiment illustrated in Fig 4 and 5, the holder 22 comprises a ring-shaped mounting member 23 arranged to surround the barrel 5 so as to make the holder supported by the barrel. Supporting arms 24 are attached to the mounting member 23. The supporting arms 24 are intended to support the body 20 in that the body rests on these supporting arms.

The invention is particularly intended for reducing noise from large-calibred guns. These large-calibred guns comprise inter alia different types of artillery guns, such as for instance mortars, canons and howitzers.