Structure of turbulence in three-dimensional boundary layers

This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by a 'sink flow' in a fully developed two dimensional turbulent boundary layer. Also, the mean and turbulence field measurement procedure using a three component laser Doppler velocimeter is described

Device and method for measuring thermal conductivity of thin films

A device and method are provided for measuring the thermal conductivity of rigid or flexible, homogeneous or heterogeneous, thin films between 50 .mu.m and 150 .mu.m thick with relative standard deviations of less than five percent. The specimen is sandwiched between like material, highly conductive upper and lower slabs. Each slab is instrumented with six thermocouples embedded within the slab and flush with their corresponding surfaces. A heat source heats the lower slab and a heat sink cools the upper slab. The heat sink also provides sufficient contact pressure onto the specimen. Testing is performed within a vacuum environment (bell-jar) between 10.sup.-3 to 10.sup.-6 Torr. An anti-radiant shield on the interior surface of the bell-jar is used to avoid radiation heat losses. Insulation is placed adjacent to the heat source and adjacent to the heat sink to prevent conduction losses. A temperature controlled water circulator circulates water from a constant temperature bath through the heat sink. Fourier's one-dimensional law of heat conduction is the governing equation. Data, including temperatures, are measured with a multi-channel data acquisition system. On-line computer processing is used for thermal conductivity calculations

Temperature Distribution in Different Materials Due to Short Pulse Laser Irradiation

The purpose of this study is to analyze the heat-affected zone in materials such as meat samples, araldite resin-simulating tissue phantoms, and fiber composites irradiated using a mode-locked short pulse laser with a pulse width of 200 ps. The radial surface temperature profiles are compared with that of a continuous wave (CW) laser of the same average power. The short pulse laser results in a more localized heating than a continuous laser with a corresponding high peak temperature. A parametric study addressing the effect of pulse train frequency, material thickness, and amount of scatterers and absorbing agent in the medium and different initial sample temperatures is performed, and the measured temperature profiles are compared with the theoretical non-Fourier hyperbolic formulations and Fourier parabolic heat conduction formulations for both CW and pulsed laser cases

Experimental and Computational Performance Analysis of a Multi-Sensor Wireless Network System for Hurricane Monitoring

A wireless sensor network system was developed at Florida Institute of Technology to monitor wind induced pressure on low-rise residential building roofs during hurricane events. The system was tested to evaluate the performance of the sensors and their reliability to measure accurate pressure variations. The reliability of the pressure sensors is established by comparing measurements with secondary references and basic Bernoulli theory. The effects of sensor case, wind gusts, wind direction and structural vibration on the measured pressure are also presented. The system was tested in a wind tunnel, on top of a van on a highway road test, and at the University of Florida hurricane simulator. These tests revealed that the pressure readings were sensitive to mechanical vibrations and the sensor case shape, only when facing the windward direction. Some computational fluid dynamics analysis was also employed to verify the sensors performance and to develop reliable computational tools to simulate hurricane effects

Hybrid control system for spacecraft antenna boom

Sensitive equipment utilized in aerospace applications experience vibrations from mechanical and thermal disturbances. Without proper vibration suppression systems, the delicate equipment can be severely damaged. A comparison between passive, active and hybrid control of light weight boom structure for space vehicles is carried out. Numerical and experimental analyses using NASTRAN finite element software are performed. Different control methods are applied, and a PID controller is implemented in the experiment. The main target of this research is to study the dynamic response of sensitive and light spacecraft structure like a boom antenna. In this experiment, the source of vibration disturbance is the force applied to one end of the structure and the response signal is captured by an accelerometer sensor at the free end of the beam. Piezoelectric Translator (PTS30 nanopositioning stage) (which is a linear actuator suitable for static and dynamic applications) is used for the reducing the vibration characteristics and thus damping out the vibrations. The maximum displacement provided by this actuator is +/- 15 mm and they provide pushing or pulling force of up to 30 N. The linear speed range of the PTS30 is 0 to 500 micrometer per second. The input to the actuator is provided by the accelerometer sensor through a power amplifier which is connected through a computer. The measured acceleration is integrated to obtain the corresponding velocities. Effectiveness of the control system highly depends on the position of the actuators. The average energy level taken over a frequency bandwidth of 4 Hz to 8 Hz will be considered as a parameter to be minimized. This research focuses on the reduction of vibration behavior of satellite boom structures over a wide frequency bandwidth using hybrid vibration control system. Here we present the results of damping effectiveness for different excitation amplitudes. Copyright © 2010 by ASME