Noise and Vibration Characteristic Studies of Twin Screw Compressor in Different Operating Conditions

The tonal noise or vibration of air-cooled or water-cooled chillers with rotary twin screw compressors is crucial for environmental concerns. This work aims to perform the receiver tests regarding the radiated noise and structural vibration due to the compressor in different operating conditions. The sound pressure near the compressor is recorded by the one-third octave and narrow band frequency analyzers, respectively. For environmental concern, the one-third octave band spectrum is frequently adopted to evaluate the radiated noise, while the narrow band spectrum can be used to characterize the noise sources. The axial, vertical and horizontal accelerations on the compressor shell at the motor and oil-injection locations are also monitored to correlate the structure-borne noise. Other than the comparison of spectral content between radiated noise and compressor shell vibration, the frequency response functions and the coherence functions are examined to further characterize the relation between noise and vibration. This work lays out the general steps and measurement procedures for noise and vibration evaluation in primary stage for receiver tests considering different load capacities. The vibration energy transmission path tests as well as the refrigerant pulsation effects on the compressor noise and vibration can then be carried out accordingly

Vibration modes and sound characteristic analysis for different sizes of singing bowls

The singing bowl is used not only for the instrument of Buddhism but also for musical therapy. This work aims to investigate the correlation of vibration modes and percussion sound for singing bowls. A typical singing bowl is first selected to perform finite element analysis (FEA) for theoretical modal analysis (TMA) as well as experimental modal analysis (EMA). Modal parameters of singing bowl, including natural frequencies and mode shapes, can be obtained from analysis and experiment, respectively. Singing bowl FE model can then be updated and verified by adjusting material properties and used to predict structural vibration modes. The percussion sound of singing bowl is also measured to obtain its sound spectrum. The peak frequency response of singing bowl sound can be interpreted and contributed from circular vibration modes of the bowl. With the knowledge of sound generation mechanism for the singing bowl, this work also studies the percussion sound characteristics of seven different sizes of singing bowls. Results show the fundamental frequency and overtone frequencies of singing bowl percussion sound are higher for the smaller size. Interestingly, that the peak resonant frequencies have near the integer ratio relationship makes the singing bowl revealing harmony sound effects. The radiated sound spectrum can be well calibrated and predicted for different sizes of singing bowls. This work shows the analytical and experimental approaches in studying the singing bowl percussion sound that strongly correlated to structural vibration modes and can be adopted for future development of singing bowls

Vibration modes and sound characteristic analysis for different sizes of singing bowls

The singing bowl is used not only for the instrument of Buddhism but also for musical therapy. This work aims to investigate the correlation of vibration modes and percussion sound for singing bowls. A typical singing bowl is first selected to perform finite element analysis (FEA) for theoretical modal analysis (TMA) as well as experimental modal analysis (EMA). Modal parameters of singing bowl, including natural frequencies and mode shapes, can be obtained from analysis and experiment, respectively. Singing bowl FE model can then be updated and verified by adjusting material properties and used to predict structural vibration modes. The percussion sound of singing bowl is also measured to obtain its sound spectrum. The peak frequency response of singing bowl sound can be interpreted and contributed from circular vibration modes of the bowl. With the knowledge of sound generation mechanism for the singing bowl, this work also studies the percussion sound characteristics of seven different sizes of singing bowls. Results show the fundamental frequency and overtone frequencies of singing bowl percussion sound are higher for the smaller size. Interestingly, that the peak resonant frequencies have near the integer ratio relationship makes the singing bowl revealing harmony sound effects. The radiated sound spectrum can be well calibrated and predicted for different sizes of singing bowls. This work shows the analytical and experimental approaches in studying the singing bowl percussion sound that strongly correlated to structural vibration modes and can be adopted for future development of singing bowls

A knowledge-based parametric design system for drawing dies

[[abstract]]The design of drawing dies is a very complex and knowledge-intensive process. This paper describes a knowledge-based parametric design system for drawing dies which requires only a minimum set of parameters to be set before it is able to complete the design of the main components of a die, such as upper dies, lower dies, and blank holders. This minimum set of parameters includes blank sizes, die faces, punch open lines, drawing strokes, and press data. This design system implemented on top of the Pro/E CAD software consists of a drawing die knowledge base, a subcomponent inferencer, a dimension calculator, a subcomponent generator, a system coordinator, and a user interface. We use the design of drawing dies for inner wheel house as a concrete example to show that our system can greatly improve the design quality while reducing the development time and cost

Computer-aided structural design of drawing dies for stamping processes based on functional features

[[abstract]]This paper describes a structural design system for 3D drawing dies based on functional features using a minimum set of initial information. In addition, it is also applicable to assign the functional features flexibly before accomplishing the design of a solid model for the main parts of a drawing die, such as upper die, lower die, and blank holder. The initial information includes blank sizes, work strokes, die faces, punch open lines, and press data. The proposed system integrated the design knowledge of drawing die into functions of 3D computer-aided design (CAD) software to automate design and to shorten design time. This design system is constructed on a PC and integrated with a Pro/ENGINEER CAD system including feature selector, shape calculator, model generator, design coordinator, and user interface. The proposed system is demonstrated using the example of designing a drawing die for the roof panel of a vehicle within 1 h. The results reveal that it can dramatically improve the design quality and can save both time and costs with excellent design quality