Method and device for contactless mechanical excitation of structures

Abstract

A method and device for contactless vibrational excitation of a specimen 1 using a rigid cylinder 3 near the specimen, an explosive material being supplied to the cylinder via a valve 7 and detonated using a spark to generate an explosive impulse which exits the cylinder through an opening 10. The method includes mounting microphones 17 to the specimen to measure the pressure of the explosive impulse which is used to calculate the excitation force. The device includes the explosive material being like oxyhydrogen gas supplied from a reservoir 6, the spark being generated using two wires 9 and a voltage supply 14, and a control unit 13 controlling the valve to control the amount and timing of the gas supplied to the cylinder and also controlling the voltage supply and timing for the spark. A material (11, figure 2) may be placed between the cylinder and specimen to act as a spacer and increase the excitation force as air pressure from the detonation cannot escape via a gap 2. An array of devices can produce several small detonations at the same time with the resulting air pressure summed to produce a high detonation to excite the specimen.

Claims

1. Method for non-contacting vibrational excitation of specimen 1, comprising following steps:Step 1: Mount single microphones 17 or 25-31 on surface of specimen 1,Step 2: Positioning of rigid cylinder 3 or array 23 near specimen 1,Step 3: Definition of inital values for amount of detonation material and timing of inflammation of a single device or an array 23 of the device,Step 4: Valve 7 open, a well defined amount of detonation material is led into rigid cylinder 3,Step 5: A spark is generated at position 8,Step 6: The explosive material detonates and an explosive impulse is flowing out of opening 10,Step 7: The pressure of the explosive impulse is measured at microphone 17 or 25-31,Step 8: The excitation force is calculated using the measured pressure at microphone 17 or 25-31,Step 9a: Procedure finished, if only one detonation impulse is needed,Step 9b: Procedure is started again, if several consecutive detonation impulses are needed.

2. Device for non-contacting vibrational excitation of specimen 1, comprisinga rigid cylinder 3 positioned with a gap 2 from the test specimen 1in the rigid cylinder 3, explosive material like oxyhydrogen gas is introduced from a reservoir 6 via a supply line 5 into an opening 4 via a valve 7,the boundary 12 of the rigid cylinder 3 is mounted on a rigid supporting structure, immediately after the introduction of the oxyhydrogen gas into the opening 4 a spark is generated in the rigid cylinder 3 at position 8 using two wires 9 with a well-defined distance and a voltage supply 14,the spark initiates a detonation of the oxyhydrogen gas,due to this detonation of the oxyhydrogen gas, a spontaneous, pulse-like increase in the air pressure in the rigid cylinder 3 occurs,the pressure escapes via the outlet opening 10 of the rigid cylinder 3 and induces a force excitation of the test specimen with a maximum in the downstream area of the outlet opening 10,a control unit 13 controls valve 7 and subsequently, the amount and timing of the gas that flows into the rigid cylinder 3,the control unit 13 controls the voltage supply 14 and subsequently the voltage and timing for inflammation of the oxyhydrogen gas.

3. The device according to claim 2, whereinoxyhydrogen, chlorine oxyhydrogen or other solid, liquid or gaseous material can be used as explosive material that allows inflammation,different frequency content and amplitude of the excitation can be reached, depending on the detonation speed, density, charge density, specific energy, of the used explosive.

4. The device according to claim 2-3, whereina material 11 is placed between rigid cylinder 3 and specimen 1the material 11 allows closing the gap 2 and acts as a spacer,the closing of the gap 2 result in an increased excitation force because the air pressure from the detonation cannot vanish via the gap 2,the material 11 is made of very soft material to avoid a retroactive effect on the vibration of the specimen 1, the material withstand the air pressure caused by the detonation forces.

5. The device according to claim 2-4, whereinthe device is arranged vertically to the specimen 1,the boundary 12 is not rigidly connected to a supporting structure, during detonation the rigid cylinder 3 can be moved in direction 15.

6. The device according to claim 2-5, whereinsound absorbing material 16 is placed in the interior part of the rigid cylinder 3 to avoid the generation acoustic standing waves.

7. The device according to claim 2-6, whereinan aperture 18 is placed at the opening 10 to vary the outgoing pressure after detonation, the aperture 18 has one opening 19 or several openings 20 distributed over its surface, the openings 20 allow a design of the area of excitation respectively pressure distribution as well as a design of the directivity pattern of the outflowing air pressure due to the detonation.

8. The device according to claim 2-7, whereina single or several detonations are generated to excite the structure 1, the valve 7 controls the amount of a portion of gas,a rotating disc 21 is placed in the opening 4,the rotating disc 21 has one or more openings 22, depending on the rotation speed the number of detonations per seconds and the amount of gas for a single detonation are variedthe rotation speed of disc 21, the valve 7 and the inflammation via voltage supply 14 and wires 9 are controlled via the controller 13,the openings 22 are on the surface of rotating disc 21 in a way that a certain time pattern of the detonations is produced.

9. The device according to claim 2-8, whereinan array 23 of the invention is used,several small detonations can be generated at the same time, the resulting air pressure is summed and one superimposed, high detonation is produced to excite the structure.

10. The device according to claim 9, whereinthe timing of the single small detonations is controlled via controller 13 in a way that interferences between the single detonations are generated, these interferences subsequently result in a defined directivity pattern that either changes the direction of the excitation from perpendicular to an angle 24, or the directivity pattern allows focusing a single spot at the surface of the specimen 1.

11. The device according to claim 2-10, whereina lightweight microphone 17 (e.g., MEMS microphone) is mounted on the surface of the specimen 1 directly at the position of the excitation. The measured sound pressure p (Pa) at microphone 17 can be used to determine the excitation force acting on the specimen 1.

12. The device according to claim 11, whereinan array of lightweight microphones 25-31 are mounted on the surface of a flat or uneven specimen, 1,an algorithm calculates the sound pressure distribution 33 and detects the areas 32 and 33, where the influence of the pressure can be neglected, this algorithm subsequently calculates the diameter d (m) of the effective spot of the excitation.

13. The device according to claim 2-12, wherein microphones are mounted in the opening 10, the opening 11 or the openings 20 to calculate the excitation force.

14. The device according to claim 2-13, whereininstead of steel cylinder 3 a very long steel cylinder 43 is used,steel cylinder 43 has a continuously enlarging shape 44 and a second opening 45,the enlarging shape 44 allows a reduction of potential wave reflections at the opening 45, the second opening 45 has to be far away from the specimen 1 to avoid a disturbing second excitation of the specimen.

15. The method according to claim 1, whereinthe outlet of the rigid cylinder 3 is automatically moved to several positions for automatic measurement procedures using a joint 35 instead of a fixed boundary 12, the rigid cylinder 3 is translationally moved in space at boundary 38 automatically to excite several positions of specimen 1.

16. The method according to claim 1, whereina periodic excitation of the specimen 1 at a single frequency is induced using several detonations 40 in a recurring time interval 41.

17. The method according to claim 16during an automated procedure, several detonations are induced for the first well-defined frequency,after this frequency is sufficiently measured, other frequencies are excited and measured in the same way.

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