Nam Woong Kim

Experimental study on active vibration control of a flexible cantilever using an artificial neural-network state predictor

Active control of flexible structures is crucial for the successful operation of large aerospace structures. One of the predominant difficulties in the active control of flexible structures is that such structures have a number of vibratory modes within or beyond the bandwidth of the controller. In the active control of flexible structures, spillover can occur because only a few vibratory modes are dealt with by the control. Although modal-space-based optimal control is known to avoid spillover, it requires a large number of sensors and actuators. In this study the modified independent modal space control (MIMSC) algorithm proposed by Baz et al is adopted to minimize the number of actuators. An artificial neural network is also proposed to identify the system characteristics and to reduce the number of sensors. Experiments are performed for the active vibration control of a flexible aluminum cantilever beam employing a piezoactuator. It is experimentally found that active control with the proposed artificial neural-network state predictor is able to suppress vibration successfully without spillover.

Finite element analysis investigating thermal stress characteristics and weight reduction design for perfectly flat CRT

For the perfectly flat CRT (PFCRT), corner cracking of the panel while passing through the exhaust furnace has been a long standing problem. These cracks frequently occur during the heat-up cycle for the evacuation in the exhaust furnace and originate on the corner of the inner surface of the panel. The transient stresses for the perfectly flat CRT during the heat-up cycle for the evacuation in the exhaust furnace in which both thermal and vacuum loads are applied are analyzed by the finite element method. From the results, the transient stress states and the crack propagation are clearly explained. Also by using the numerical analysis, a design aimed at the weight reduction is investigated. For the PFCRT with 1 mm reduced panel glass, the thermal stresses are calculated with consideration of vacuum load taken into account.

Measurements of the temperature distribution of a shadow mask in a cathode-ray tube by use of a radiation thermometer

This paper presents an experimental study of non-contact temperature measurements for the shadow mask in a cathode-ray tube (CRT) by use of a radiation thermometer. As the demand for large and flat CRTs and high resolution increases, it becomes more important to design the shadow mask assembly precisely, even for the Invar shadow mask CRT that brings about a shift of the landing site of the order of a few micrometres. To do this, first of all knowledge about the temperature distribution of the shadow mask is needed. However, up to now most researchers could not measure the temperature distribution of a shadow mask. We studied a method for measuring the temperature distribution of a shadow mask for a 17 CRT. Considering the energy and the wavelength passing through the face plate, we equipped the radiation thermometer with an indium antimonide (InSb) photo-sensor. Experiments using the thermocouple were performed to validate the results of non-contact measurement. The results agree well with those of a non-contact method using an InSb sensor.