58 research outputs found
Modal analysis of violin bodies viewed as three-dimensional structures
No full textModal analyses of violins show several strong modes in the low frequency range. Holographic interferograms suggest that four strong modes can be interpreted as doublets having two and three nodal planes that intersect a cylinder with a roughly elliptical cross section at the bridge [A. Runnemalm, N.-E. Molin, and E. Jansson, J. Acoust. Soc. Am. 107, 3452-3459 (2000); M. Roberts and T. D. Rossing, Catgut Acoust. Soc. J. 3, 9-15 (1998)]. This is especially clear when the instrument is viewed simultaneously from three sides using mirrors, and the holographic system is made sensitive to in-plane motion as well. These doublets are not unlike those observed in cylindrical vibrators such as bells, and they remind us that a violin is a 3-dimensional object.</p
Model based compensation of systematic errors in an inductive gap measurement method
No full textA model-based correction of systematic errors to improve the measurement of gap dimensions in a recently presented method is described. Using one inductive coil on each side of the gap to measure distance and liftoff, the method detects zero width gaps and shows position error less than 0.1 mm. The correction model relies on observations of experimental data, and is calibrated to a small set of measurements. From the initial measurement of gap dimensions, the model estimates errors in each coil to calculate new values for gap width, alignment and height. The errors in the compensated results are within 0.1 mm except for gap width, which still suffers from the effect of combined gap width and misalignment. The method is intended for gap measurement in laser keyhole welding, where the laser beam and the resulting weld seam are very narrow, requiring high precision in alignment and gap preparation.CC BY-NC-ND 4.0Corresponding author at: University West, Nohabgatan 18A, SE-461 53 Trollhättan, Sweden. E-mail address: [email protected] (E. Svenman).The authors gratefully acknowledge the financial support from the Research School SiCoMaP, funded by the Knowledge Foundation, and GKN Aerospace Engine Systems.</p
Sound and vibrations in structures with air enclosures
No full textVibrations in thin shell structures and sound fields in enclosures are investigated as well as the interaction between such structures and the enclosed sound field. Optical, non-contacting methods as TV holography, shearography and laser scanning vibrometry are used to investigate vibrations of thin shell structures with air enclosures. The sound radiation from vibrating structures is also measured with more traditional sound intensity techniques. The techniques used are briefly presented and compared in this thesis. Structural vibrations in organ pipes made of different materials are investigated as well as the sound distribution from the pipes. Operating deflection shapes of a complete violin are investigated, and the effect of enclosed air on structural vibrations is measured on a violin model. Aerial standing waves inside three cavities are measured and visualised with an optical technique. The response of the shell structures due to aerial standing waves is also measured. From the investigations it is found that the enclosed air has a significant effect on, above all, the lowest eigenmodes. It is also shown that non-contacting measuring techniques have advantages in that they do not to disturb the measured object and in that they are field methods. In numerical comparisons to the measurements it is found that the enclosed air should be included in the numerical model to predict correct results. Two different finite element models of the enclosed air are tested.Godkänd; 1999; 20061117 (haneit)</p
Sound and vibrations in structures with air enclosures [Elektronisk resurs]
No full textVibrations in thin shell structures and sound fields in enclosures are investigated as well as the interaction between such structures and the enclosed sound field. Optical, non-contacting methods as TV holography, shearography and laser scanning vibrometry are used to investigate vibrations of thin shell structures with air enclosures. The sound radiation from vibrating structures is also measured with more traditional sound intensity techniques. The techniques used are briefly presented and compared in this thesis. Structural vibrations in organ pipes made of different materials are investigated as well as the sound distribution from the pipes. Operating deflection shapes of a complete violin are investigated, and the effect of enclosed air on structural vibrations is measured on a violin model. Aerial standing waves inside three cavities are measured and visualised with an optical technique. The response of the shell structures due to aerial standing waves is also measured. From the investigations it is found that the enclosed air has a significant effect on, above all, the lowest eigenmodes. It is also shown that non-contacting measuring techniques have advantages in that they do not to disturb the measured object and in that they are field methods. In numerical comparisons to the measurements it is found that the enclosed air should be included in the numerical model to predict correct results. Two different finite element models of the enclosed air are tested.</p
Effects of material choice and tooling methods on structural modes of open organ pipes
No full textHow are wall vibrations of organ pipes influenced by material choice and tooling methods ? Six groups of three equally made diapason organ pipes (tuned to C4 at 260 Hz) fabricated out of two different alloys and with three tooling methods are investigated. All experiments are performed with the pipes mounted in an experimental organ. Results from the following experiments are compared: Modes of vibration for external sinusoidal excitation of the walls, so called free structural eigenmodes, are measured using TV holography, a non contact, optical, full field measuring method. These measurements are performed both before and after voicing of the pipes. The pipes are externally excited, sinusoidal, at the fundamental frequency and five higher harmonics (n*260 Hz where n = 1, 2, ..., 6) of the blown pipe. Forced structural modes of vibration at those frequencies are measured, again using TV holography. Structural modes of vibration of the blown pipes are measured. This time shearography is used, another optical non contact measuring method.The results show that structural vibrations are affected by the choice of material and tooling; a pipe with higher tin contents have higher eigenfrequencies. It is also shown that the voicing process selects certain modes of vibration in the pipes.</p
Vibrations and sound from structures with air enclosures
No full textGodkänd; 1997; 20070418 (ysko)</p
Vibration Induced Disturbances in Automatic Non-destructive Testing
No full textThe interest in automatic inspection of welds has increased during the last decade. An automatic inspection cell is self-acting both by scanning the inspected test piece and by evaluation of the resulting images. For automatic evaluation, high quality of the resulting images is essential. The non-smooth movement of the NDT-sensor when mounted on a robot-arm will have influence on the results. This paper focus on evaluation of the vibration induced disturbances due to the mounting of the sensor and the movement of the robot in an automatic cell. A thermography system detecting the geometry of welds is used in this study and both stationary and continuous movement of the IR camera are studied. The vibration due to the mounting on a robot arm are quantified and compared.</p
Standing waves in a rectangular sound box recorded by TV holography
No full textA simple but informative whole-field method to visualize standing waves in air enclosures is presented. The integrated sound pressure field distribution of standing-wave patterns inside a rectangular, air-filled transparent box is measured using ordinary TV holography (also called ESPI or DSPI). The phase distribution of the sound pressure is measured by using the more complicated, phase-modulated TV holography technique. Standing waves in the box are excited by a loudspeaker. The structural vibration amplitude distribution of the walls of the same box (operational deflection shapes, ODSs) are measured at the same frequencies as the standing waves with the same optical technique. The pressure maps obtained and the corresponding structural ODSs are of great pedagogical value and can be used to verify numerical models, etc. Standing-wave patterns in non-rectangular enclosures, as the sound box of a guitar, illustrates the usefulness of the method.</p
Evaluation of non-destructive testing methods for automatic quality checking of spot welds
No full textCar bodies are today more often made of high strength steel. In high strength steel spot welds are more friable and it is necessary to have higher demands on the inspections of spot welds. Quality control of spot weld can be either destructive or non-destructive. Destructive testing is still the most common method to test spot weld. The non-destructive methods that are investigete in this project are visual inspektion (VT), penetrant testing (PT), eddy current testing (ET), ultrasonic testing (UT), magnetic paticle testing (MT) and X-ray testing (RT). Other NDT methods are acoustic emission (AE), digital sheargraphy and IR-termography (IRT). These methods are investigated with focus on the possibility to detect Lens Diameter, stick welds, expulsions, porosity and cracks. And the possibility to automation of the method with focus on size and weight of the system, protection equipment, contact or contactless, one or two sided, position accuracy, and result in real-time. Only tree NDT methods, UT, RT and IRT, can detect all discontinuities that we looking for in RSW. The thermography system has the largest potential to be a NDT system for spot weld in the future, mainly because the method is non-contact, which helps when you have the opportunity to searching on a surface instead of a specific position. The main problem with this method is that there is no software for analysing the results to obtain lens diameter.SpotLigh
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