Synergy of Multiple Cylinders in Flow Induced Motion for Hydrokinetic Energy Harnessing.

Vortex Induced Vibrations for Aquatic Clean Energy (VIVACE) Converter is a converter of marine hydro-kinetic (MHK) energy invented in the Marine Renewable Energy Lab (MRELab). It harnesses MHK from ocean currents. Using passive turbulence control, VIVACE maximizes and utilizes flow induced motion in the form of vortex induced vibration (VIV) or interference/proximity/wake/soft/hard galloping. MRELab has achieved back-to-back VIV and galloping for a single cylinder with passive turbulence control thus more than doubling the range of synchronization of flow induced motion. The goal of this research is to maximize the synergy of multiple cylinders in flow induced motion (FIM) for MHK energy harnessing in order to increase the power volume density. In order to achieve this goal, the effects of tandem spacing, staggering, passive turbulence control, mass ratio, spring stiffness, damping, and number of cylinders in FIM of multiple cylinders are studied experimentally. All model tests were conducted at high Reynolds numbers in the range of 28,000<Re<120,000, which primarily covers the TrSL2 and TrSL3 flow regimes. The following observations and conclusions are drawn: (a) By introducing PTC, all cylinders (2,3,4 tandem configurations) achieve galloping increasing the range of FIM synchronization with high amplitudes regardless of other parameters. (b) For tandem spacing of 1.43D, FIM of two cylinders in tandem is distinct: galloping starts earlier, amplitude is higher for the 2nd cylinder, oscillation frequency is lower for both cylinders, and energy conversion is 60% higher. (c) For two cylinders in close tandem proximity (d/D<2.0), contrary to single cylinder studies, energy envelope points in galloping may not correspond to the highest spring stiffness (d) Higher mass ratio (m*) results in higher MHK energy conversion in galloping with practically no change in the VIV region. Increase by a factor of 2.5 was measured for 0.65<m*<1.66. (e) Multiple cylinders in tandem can be in synergistic FIM in close proximity of d/D<2.0. (f) 2, 3, and 4 cylinders in synergistic FIM can harness more MHK energy than the sum of the energy harnessed by each cylinder acting in isolation.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/100015/1/bblwith_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/100015/2/bblwith_3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/100015/3/bblwith_1.pd

Flow Characteristics Around Step-Up Street Canyons with Various Building Aspect Ratios

We investigate the flow characteristics around step-up street canyons with various building aspect ratios (ratio of along-canyon building length to street-canyon width, and upwind building height to downwind building height) using a computational fluid dynamics (CFD) model. Simulated results are validated against experimental wind-tunnel results, with the CFD simulations conducted under the same building configurations as those in the wind-tunnel experiments. The CFD model reproduces the measured in-canyon vortex, rooftop recirculation zone above the downwind building, and stagnation point position reasonably well. We analyze the flow characteristics, focusing on the structural change of the in-canyon flows and the interaction between the in- and around-canyon flows with the increase of building-length ratio. The in-canyon flows undergo development and mature stages as the building-length ratio increases. In the development stage (i.e., small building-length ratios), the position of the primary vortex wanders, and the incoming flow closely follows both the upstream and downstream building sidewalls. As a result, increasing momentum transfer from the upper layer contributes to a momentum increase in the in-canyon region, and the vorticity in the in-canyon region also increases. In the mature stage (i.e., large building-length ratios), the primary vortex stabilizes in position, and the incoming flow no longer follows the building sidewalls. This causes momentum loss through the street-canyon lateral boundaries. As the building-length ratio increases, momentum transfer from the upper layer slightly decreases, and the reverse flow, updraft, and streamwise flow in the in-canyon region also slightly decrease, resulting in vorticity reduction

Paratracheal Air Cysts: Sonographic Findings in Two Cases

We report two cases of paratracheal air cyst discovered incidentally at neck ultrasonography and confirmed at CT. The cysts were located at the inferoposterior aspect of the right lobe of the thyroid. Ultrasonography revealed an ill-defined hypoechoic mass containing hyperechoic foci which mimicked calcifications. Neck CT confirmed the presence of an ill-defined air pocket which communicated with the trachea through a slit

Friends matter. The relationship between Korean international students\u27 friendship networks and study abroad outcomes

This study examined the determinants of international students\u27 interactions with different friendship networks and the relationships of these interactions with study abroad outcomes, using data from 482 Korean college students who had participated in international student exchange programs. The results showed that students\u27 participation in extracurricular and off-campus activities while studying abroad was significantly related to their interactions with local and other international students. The results also showed that students\u27 interactions with co-national, local, and other international students while studying abroad were positively associated with their intercultural competence, personal development, and career development, even after controlling for other variables. We discuss the policy implications of these findings beyond the Korean context. (DIPF/Orig.

Development of Eco-VE Function for Construction

AbstractRecently accepted “Paris Agreement” has restricted the Earth temperature increase to be below 1.5 degrees Celsius contrast to previous industrialization. To follow this agreement, there should be efforts such as carbon emission reduction and eco design etc. One of these efforts is development of eco-VE function that applied eco-friendly concept on VE which is commonly used at design phase. Concept of this model includes carbon productivity concept and potential environment pollution index that reflects eco-VE function on original VE. The carbon productivity concept is a cause of production increase that offset production decrease factor depending on green-house gas reduction. The potential environment pollution index presents the possibility of environment pollution through construction phase. The carbon productivity is ‘Construction cost/Carbon emission’. The construction costs are consisted of material, equipment, labour cost and indirect expenses. Carbon emissions are calculated by emission for material production and equipment fuel consumption. The potential environment pollution index is composed of environmental pollution and conservation cost. The environmental pollution cost includes environmental damage and destruction cost. The environmental conservation cost includes environmental pollution prevention cost, waste treatment cost, environmental pollution compensation, environmental pollution test research funds and law cost