Karachun V.V., Trivailo M.S., Mel’niсk V. N., Kovalets O.Ya.

National Technical University of Ukraine «KPI»

The NOISE-PROTECTIVE CASe

This device attributes to Mechanical engineering and can be used in aviation and rocket-cosmic technics for protection facilities and pressure cells from noise of high power.

There is a known noise-protective case (NPC), which includes a body and an inflatable elastic casing, hermetically connected to the body. This casing is filled in with gas, the velocity of sound propagation in this gas transcends the velocity of sound propagation in the air (look, e.g., the patent of France № 2852938, G10 К11/16, 1991, or its summary on the page 11 in the magazine “Изобретения стран мира”, МКИ G10, “Музыкальные инструменты и акустика”, Москва, вып. 97, № 1 ).

The drawback of this NPC consists in a low reliability: when the tightness breaks, the NPC loses its working capacity.

There is also a well-known NPC, which includes a rigid body of glass shape, put on the protected object, a cylindrical screen, that is allocated with an air gap, from outside of the body, and also a thickening washer (see, e.g., В.С.Дидковский, В.В.Карачун, В.И.Заборов, Проектирование ограждающих конструкций с оптимальными звуко– и виброизоляционными свойствами. – К.: Будівельник, 1991, С. 91, рис.ІV. 1).

This NPC is the most suitable, because of its technical essence and the attainable effect.

The drawback of the NPC consists in its deficient sound resistance, consequently, the acoustic protection efficiency reduces.

Mentioned drawback can be explained, by fact, that case sidewalls possess a small inflexibility, and propagation of sound waves, in the air gap between screen and body passes without barriers.

At the root of proposal there is a problem of the NPC improvement, by selecting the optimal screen aperture sidewalls form. This will secure the growth of proposal’s inflexibility and the accessory energy dissipation of sound waves. Consequently, the sound resistance raises, then the acoustic protection efficiency increases.

This problem can be solved, by improving the NPC. The NPC includes a cylindrical body of glass shape, a screen, which is allocated with an air gap, outside the body, with rectangular elongated apertures in sidewalls, and also a washer. The screen is equipped with ledges that overlap the air gap in width.

The screen rigging with radial ledges increases a sound energy dissipation, due to the rising of inflexibility and the accessory braking of sound waves in the air gap. All above mentioned promotes growing of the NPC sound resistance, so the efficiency of acoustic protection raises.

The NPC is introduced on the fig.1.2(а), general form; on the fig.1.2(b) – look from the top of the fig. 1.2(a); on the fig.(c,d) – the variants of forming (location) of ledges.

The NPC includes the cylindrical body of glass shape 1, outside it there is the air gap 2 and the screen 3 with rectangular elongated apertures 4 on the lateral surface, and apertures 5 on the end surface. The body 1 and the screen 3, allocated in alignment, and linked with each other with the help of damping, for example, rubber cushion 6. The screen 3 is equipped with radial ledges 7, 8, that are situated on its cylindrical and front sidewalls and overlap the air gap 2 in width “ d ”. Ledges 7, 8 can be derived, when apertures 4, 5 are forming, by the way of flanging (bending) along one 9 (fig.1.2(c)), or along both 9, 10 (fig.1.2 (d) long borders of each aperture of tabs 11, 12, which are made after gashes 13, 14 are done. The implementation of ledges 7, 8 of flanging shape simplifies their making and secures the growth of screen inflexibility, and, in such way, it is used for supplemental sound energy dissipation in the air gap 2.

When in use the NPC is installed on the protected object 15, for example, gyroscopic mechanism, and is fastened to the basic 16.

The principle of the NPS operation is following.

When there is an influence of the floor P in sidewalls of screen 3 on the NPC, then compound forms of bending vibrations appear (see, e.g., Карачун В.В., Лозовик В.Г., Потапова Е.Р., Мельник В.Н. Многомерные задачи нестационарной упругости поплавкового гироскопа. – К.: “ Корнейчук ”, 2000, C.98). As the result of it, one part of sound energy absorbs at the expense of internal friction, the other passes through sidewalls of screen and body, and considerably weakened reaches the protected object 15. In connection with the fact, that ledges 7, 9 are made of flanging shape and can be deformed together with sidewall, they even a part of, emerging in sidewalls, bending efforts (deformations). This sets conditions for growing of sound energy propagation (absorption) that, in addition, raises the general sound resistance of screen walls (see, e.g. Шендеров Е.Л. Волновые задачи гидроакустики.– Л.: Судостроение, 1972, C. 288).

Besides mentioned higher, part of sound energy, that influences the NPC, penetrates through the apertures 4, 5, and obtains the outside surface of the body 1, for example, in the form of the sound wave 17 beam. After the reflection of the sound wave from the body surface, a part of this energy conveys along the air gap 2 and, obtaining the ledges 7, 8, partially, absorbs by them. This generates an accessory sound resistance of the NPC.

Thus, the rise of the NPC sound resistance by the screen inflexibility growing and, in addition, the sound energy dissipating by radial ledges, increases the sound protection efficiency.

The invention can be used for the protection from the aerodynamic noise of pressure cells and gyroscopes in the hydro stabilized platforms, and the integrators of lengthwise rocket accelerations, in aerospace complexes (systems), for multiple use MACS or SVITYAZ’ , on the heavy aircrafts A-225 etc.