Computational and experimental analysis of elastic deformation in impact
thesisposted on 10.09.2013, 13:24 authored by Alan Hocknell
This thesis presents new developments in the computational analysIs of sculptured surface products and in non-contacting vibration measurements based on the laser Doppler technique. The work is applied to the study of elastic deformation during impact where a detailed measurement and analysis capability is demonstrated using the golf impact as a principal example. A study of quadrilateral finite element mesh generation on sculptiired surface product families has shown that the versatility of an existing paving mesh generation algorithm can be improved significantly by dividing the product geometry into an anatomy of features and further subdividing primary features into smaller areas with four curvilinear sides. The hollow golf club head is an example of a sculptured surface product and is used to demonstrate the mesh generation difficulties which are overcome using the proposed approach. A computational analysis of a hollow golf club head under steady state dynamic conditions and in impact with a golf ball is presented which is of greater accuracy and superior detail to any previously reported. These tools are necessary for the development of a greater understanding of the detailed mechanical behaviour during impact in terms of energy transfer and 'feel' characteristics and are of importance to the golf equipment industry. Experimental validation of impact models is achieved through the introduction of a system of measurements which is suited to the analysis of high-speed, short duration impacts between lightweight bodies in which large elastic deformation occurs. A wealth of short duration golf impact data is captured efficiently using laser Doppler vibrometers and piezo-electric accelerometers. When using remote, non-contacting transducers such as the vibrometer, whole body translation of the target body causes the point on the target interrogated by the laser beam to change during the impact. A displacement compensation technique is introduced which permits close approximation of the vibration of fixed points on bodies undergoing whole body translation using data recorded from remote transducers. The technique is of additional importance in matching the available experimental data to points of interest in a computational model of the body. The improvement in data quality, relative to a single remote measurement, is quantified by reference to both simulated and actual experimental data in the case of steady state vibration and transient pulse propagation in impact. The golf impact is one of an increasing number of applications to exceed the measurement range of the available non-contacting instrumentation. Accordingly, the first practical demonstration of the laser Doppler accelerometer, a new non-contacting laser transducer which is directly sensitive to the acceleration of a target surface, is reported. The instrument has several advantages including an easily adjustable working range with effectively no upper measurement limit, straightforward operation and use of low cost optical components. Practical issues in the successful isolation of the particular optical beat frequency which carries the acceleration signal are descnbed and recommendations for the future development of this important new instrument are discussed.
- Mechanical, Electrical and Manufacturing Engineering