JPH037816B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dynamic vibration absorber used to reduce vibrations of a structure. Taking a ship as an example, the ship's hull vibrates due to the operation of its engine, making the inside of the ship extremely noisy. To eliminate this, various dynamic vibration absorbers have been conventionally attached to the ship's hull and used. The reason why ship hull vibrations are eliminated by a dynamic vibration absorber is based on the following principle of dynamic vibration absorption. That is, when a periodic external force θsinωt acts on a vibration system as shown in Figure 1 (mass of the vibrated body = m ₁ , spring constant = k ₁ ), if the natural frequency of this vibration system p ₁ = √ ₁ When ₁ is close to ω, it resonates. However, at this time, by adding a vibration system as shown in Figure 2 (mass of the vibrated body = m ₂ , spring constant = k ₂ ), ω = P ₂
= √ _{2 2} , the added vibration system will vibrate, as shown by the formula below, but
It is possible to stop the vibration of the original vibration system. The equations of motion of both vibrating systems are: m ₁ d ₂ x ₁ /dt ² =k ₁ k ₁ +k ₂ (x ₂ −x ₁ ) + θsinωt …(1) m ₂ d ² x ₂ /dt ² =−k ₂ ( x ₂ −x ₁ ) …(2) Assuming that x ₁ = A ₁ Sinωt, x ₂ = A ₂ Sinωt, and substituting the solution into equations (1) and (2), we get (−m ₁ ω ² +k ₁ +k ₂ )A ₁ −K ₂ A ₂ =0 …(3) −k ₂ A ₁ +(−m ₂ ω ² +K ₂ )A ₂ =0 …(4) From this equation, A ₁ and A ₂ When calculated as a function of ω, the result is as shown in FIGS. 3 and 4. Here, the amplitude is expressed as an amplitude multiplier for the static deflection of K ₁ due to θ. As is clear from this figure, A ₁ =0 for a certain ω. That is, as can be seen from equation (4), A ₁ =0 for ω ₀ =√ _{2 2} . At this time, A ₂ =-θ/k ₂ is obtained from equation (3). Therefore, if a vibration system with a natural frequency equal to the external force frequency is added, the original vibration system will no longer vibrate. However, the range in which vibration can be stopped using the above principle is limited to a certain ω as shown in Figure 3.
Moreover, there are resonance points on both sides of this ω, where there is a risk that the original vibration system will resonate with an infinite amplitude. Therefore, when a dynamic vibration absorber is used to stop vibrations of a ship's hull, the limit of the natural frequency of the dynamic vibration absorber must be able to accurately follow changes in the frequency of the ship's engine. However, since conventional dynamic vibration absorbers have poor ability to follow changes in the frequency of the ship's engine, none of them has been satisfactory in practice. The present invention has been made in order to eliminate the drawbacks of the conventional system, and it is possible to make the natural frequency accurately follow the change in the frequency of the ship's engine, thereby suppressing the vibration of the ship, which is the body to be vibrated, that is, the structure. It is an object of the present invention to provide a dynamic vibration reducer that can be stopped reliably. The present invention provides a support fixed to a vibrated body to which forced vibration is applied, a support handle made of a long rigid body attached in a cantilever manner to the support via a hinge, and a support handle and the support handle fixed to a vibrated body. A coil spring is interposed between the vibrating body and holds the support handle so that it can vibrate; a heavy plow that changes the frequency P2; a motor that moves the heavy plow via the screw mechanism;
an accelerometer that detects the frequency ω of the vibrated body;
Based on the frequency ω detected by the accelerometer, the motor moves the heavy peg to determine the natural frequency of the support handle.
The gist of the present invention is a dynamic vibration absorber comprising a control means for automatically controlling P2 to a detected frequency ω. An embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 denotes a ship body which is a body to be vibrated, and the ship body 1 is subjected to forced vibration by an engine 2 while sailing.
Reference numeral 3 denotes a long support handle attached to the hull 1 in a cantilevered state. A spring 5 is inserted between the support handle 3 and the support handle 3 so that the support handle 3 can vibrate. Reference numeral 6 denotes a heavy peg which is movably attached to the support handle 3 and whose natural frequency P ₂ can be increased or decreased as the distance from the fulcrum of the hinge 41 changes. 7 is a motor for moving the heavy plow 6, and the motor 7 is connected to the heavy plow 6 via a screw mechanism 61. 8 is an accelerometer for detecting the vibration frequency of the engine 2, and the output side of the accelerometer 8 is connected to a control device 9 for controlling the motor 7. Next, the operation of the present invention will be explained with reference to FIG. 6. First, the frequency ω of vibrations generated from the engine 2 is detected using an accelerometer 8 attached to or near the engine 2, which is the vibration source. The control device 9 rotates the motor 7 based on the vibration frequency detected by the accelerometer 8 so that P ₂ =ω, and moves the heavy plow 6. Note that the natural frequency P ₂ of the dynamic vibration absorber is given by the following formula. When the support handle 3 of the dynamic vibration absorber is rotated by an angle θ, the change in the weight = lmθ, the extension of the spring =
lkθ At this time, the reaction force = −Klkθ, and the equation of motion is
Mlm ² θ¨=-Klk ² θ holds Now, if y=lmθ, My¨=-K・(lk/lm ²・lmθ=−K・(lk/lm) ²・y
Therefore, the effective spring constant is K・(lk/lm) ² , and if this is Ke, the natural frequency is

It is given by [Formula]. As explained above, in the present invention, the control device automatically controls the position of the heavy plow so that P ₂ = ω, so the natural frequency P ₂ of the dynamic vibration absorber can be easily controlled, and the dynamic The natural frequency P ₂ of the vibration absorber can be made to accurately match the frequency ω of the periodic external force, and as a result, the vibration of the structure that is the vibrated body can be reliably stopped.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a 1-degree-of-freedom vibration system, and Figure 2 is an explanatory diagram of a 1-degree-of-freedom vibration system.
An explanatory diagram of a vibration system with degrees of freedom. Figure 3 shows the relationship between the amplitude and frequency of the vibrated system in a vibration system with two degrees of freedom. Figure 4 shows the relationship between the amplitude and frequency of the added vibration system in a vibration system with two degrees of freedom. FIG. 5 is an explanatory diagram of the installation of the dynamic vibration absorber of the present invention, and FIG. 6 is an explanatory diagram of the relationship between the length from the fulcrum to the heavy shaft and the natural frequency. 1... Vibrated body, 2... Vibration source, 3... Support handle, 4... Support tool, 5... Spring, 6... Heavy peg, 7
... Motor, 8 ... Accelerometer, 9 ... Control device.

Claims (1)

[Claims] 1. A support fixed to a vibrated body to which forced vibration is applied, a support handle made of a long rigid body attached in a cantilever manner to the support via a hinge, and a support handle and the vibrated body connected to each other. A coil spring is interposed between the coil springs and holds the support shaft so that it can vibrate, and a coil spring is movably attached to the support shaft via a screw mechanism to adjust the natural frequency P2 of the vibration system of the support shaft by changing the distance from the fulcrum. a motor that moves the heavy plow through the screw mechanism; an accelerometer that detects the vibration frequency ω of the vibrated body; control means for automatically controlling the natural frequency P2 of the support handle to the detected frequency ω by moving the heavy peg.