Conventionally, transfer‐length strain measurements are performed using mechanical gauges such as the Whittemore gauge, or demountable mechanical (DEMEC) strain gauges, and others devices using ‘contact’ measuring principles. These methods involve tedious surface preparation, and are also prone to significant human errors and inaccuracies. Furthermore, these mechanical sensors can only detect lateral displacements. This paper presents a new optical sensor of measuring prestress concrete surface strains. It makes use of the laser‐speckle displacement that is detected by cross correlating the associated optical signals from a Charged‐Coupled Device (CCD) sensor. The sensor was designed to be able to measure the surface displacement components without being affected by other surface motions that are generally present during the concrete detensioning process. Experiments were conducted on a compressed concrete beam and a real prestressed concrete member during the manufacturing process. The results from the optical strain sensor showed good consistency with contact measurements made by using both a foil strain gauge and a Whittemore gauge.
For several years at Kansas State University, as part of the annual Engineering and Science Summer Institute (ESSI) Program, participating high school students have been assigned the task of designing, constructing and testing streamlined rocket models of their own design. The rocket models are constructed from readily available construction materials consisting of hardwood dowel rods for the rocket body and rectangular block balsa wood for the fins. Their assignment is to modify (streamline) and assemble their rocket in such a manner as to minimize the aerodynamic drag. They are not allowed to alter the overall length of the rocket body (rod), the front view profile area, or the planform area of the fins. The students work in teams of two and the first of two class periods is devoted to the design/construction phase of the assignment. They are given a "kit" consisting of an assortment of materials and "tools" to assist them in the streamlining and assembly task. During the second class period each design group is assigned the task of testing their design using the wind tunnel in the Mechanical and Nuclear Engineering Department. The rocket models are mounted on an electronic balance in the wind tunnel and the measured drag force for each of the designs is compared against a "poor" rocket design with virtually no streamlining, and against designs from the other competing design groups. This paper describes the authors' experience with high school students involved in this hands-on design/build/test activity, as a means of introducing them to the principles of aerodynamic streamlining, along with a presentation of some of the typical quantitative results. I.
A typical refrigeration loop is composed of an evaporator, compressor, condenser, and an expansion valve. There are many possible refrigerants that can be used, but the physical properties of water make it ineffective in the traditional refrigeration loop. But if water could be used it would have many advantages as it is abundant, cheap, and is safe for the environment. As part of development of a new refrigeration loop using water, flow visualization and cavitation of water through nozzles are being investigated. Cavitation is generally defined as creating vapor from liquid, not through adding heat, but by decreasing the pressure. In a converging/ diverging nozzle as the cross sectional area is constricted the velocity of the flow will increase, decreasing the pressure. Therefore, by flowing water through the nozzle it will cavitate. Transforming liquid into gas requires a certain amount of energy, defined as the latent heat. When a liquid is turned to vapor by an increase in the temperature the latent heat is provided by the heat transfer to the system. As no energy is being added in the nozzle to cause the cavitation, the heat to create the vapor comes from the liquid, effectively causes a temperature drop. This article presents results for the flow visualization of the water cavitating as it goes through the nozzle. Under different flow conditions and nozzle geometries the cavitation manifested itself in different formations. When gasses were entrained in the water they formed bubbles, creating a nucleation site and moving through the nozzle, called travelling bubble cavitation. In venturi nozzles the cavitation nucleated off of the wall, forming attached wall cavitation. When water flowed out of an orifice, a turbulent water jet was formed which caused vapor to form around it, causing shear cavitation. When the water was rotated prior to the throat of an orifice, the orifice jet expanded radially and formed swirl cavitation.
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