Mel’niñk V. N., Karachun V.V.
National Technical University
of Ukraine «KPI»
CONPENSATION
OF INFLUENCE OF DAY'S
MOVEMENT OF
THE EARTH
The invention relates to methods of excitation of sound vibrations
(MESV) of large capacity through dynamic sirens and could be used in the tests
on the acoustic fatigue of materials and constructions of ground objects and
space aircraft.
It is known a MESV using high dynamic siren, which is feeding compressed
air into the case of horizontally placed multirotor siren.
The disadvantage of this method is the complexity of maintaining
required parameters of sound vibrations due to rotating rotors of siren from
various engines and interaction of deformation of rotors on resistance of work
of siren.
It is also known a MESV using high dynamic siren, which is to feeding
compressed air into the case of horizontally placed monorotor siren.
This method is the most similar in technical essence and getting effect.
Defect of known method of excitation of sound vibrations is that for its
implementation a significant gyroscopic moment ÌÃ, which is due to
the impact of its work regarding the Earth's rotation of its axis influences,
that leads to the screw of siren disk of rotor against its stator, reducing
with this accuracy of reproduction of desired spectrum of fluctuations and
longevity of siren.
The basis of the invention is the task of development of the method of
excitation of sound vibrations through dynamic siren, in which the location of
the axis of the rotor of siren and giving her body forced rotary motion, would
reduce pressure on the gyroscopic rotor of siren. With this increased the
accuracy of set spectrum of sound vibrations and longevity of siren.
A task is solved by that in MESV using dynamic siren, which is feeding
compressed air in the case of horizontal siren, according to the invention,
before putting air into the case of siren, its axis locates along the
horizontal North-South line and body is provided with rotary motion around the
vertical of location of siren, which passes through the center of mass of rotor, with speed
where 
- angular velocity of rotation of the Earth around its axis, φ – geographic latitude
of location of siren, π =3,14 – constant.
Orientation of axis of rotor of siren parallel to the horizontal
North-South line and additional rotation of the case of siren allows to eliminate gyroscopic pressure on its
rotor and thereby to improve the accuracy of reproduction of the desired
spectrum of sound vibrations while increasing durability of siren.
In the fig. 2 it is shown the dynamic siren and diagrams that explain
the implementation of method, in the fig. it is shown the occurrence of
gyroscopic moment M due to rotation of Earth.
To do this it is used high-speed siren 1 with disk rotor 2 and the drive
3. The frame of the siren has a vertical shaft 4, which is held fixed on the
surface of the Earth 5, shown in reduced scale, base 6 and has the drive 7 for
forced rotation of siren, relatively vertical axis through the gear
transmission 8.
Method of excitation of sound vibrations through dynamic siren is as
follows. Siren 1 with horizontal rotor is set with 0-0 axis parallel to the
horizontal North-South line 0-0 and given the driving rotational movement
against the vertical axis. The drive 7 is being connected. At the same time
siren is being connected, pressurizing compressed air in it and siren stirs
excites sound vibrations of set structure.
In fig.2 in vector form, the angular
velocities of forced rotation of siren 
, its rotor 
and the Earth 
with its horizontal 
and vertical 
components are shown.
Because the horizontal component of angular velocity of rotation of the Earth 
is parallel to the
vector 
, it does not affect the dynamics of siren.
Influence of vertical component 
compensates with
forced rotation of case of siren in the opposite direction with angular
velocity
.
As it is known, under such conditions gyroscopic pressure on the
carriers of kinetic moments is missing. Thus, the proposed method allows to
release the rotor of siren because of gyroscopic effects of pressure and
therefore to reduce its screw during work.
In existent sirens excited motion of carrier of kinetic moment of
high-speed rotor of siren due to rotation of the Earth causes a gyroscopic
moment
,
here
I - axial moment of inertia of the rotor, which is trying to set the vector of
angular velocity of siren 
parallel to vector of angular speed of Earth 
leading thereby to unforeseen movement of axis of
rotor of siren (fig.1). This
is very significant, if take into account the fact that, to ensure best
performance siren must withstand gap δ between the disk of rotor and
stator within 10 ÷ 40 microns. Under such conditions, even slight screw
of disc of rotor much impair work of siren: occurs the band of spectrum of
excited vibrations, the smoothing-out of discs happens, the efficiency decreases,
frequency range changes. This screw while implementation claimed method does
not occur.
Therefore, the release of the rotor using given way let to exclude the
influence of Earth's rotation on the siren work by reducing the additional
gyroscopic load of bearings, to improve the accuracy of reproduction of the
desired spectrum of sound vibrations and to extend longevity of siren.
