Time filter

Source Type

Iowa City, IA, United States

Egeberg T.F.,Norwegian Marine Technology Research Institute | Yoon H.,IIHR Hydroscience and Engineering | Stern F.,Dep. of Mechanical and Ind. Engineering | Pettersen B.,Norwegian University of Science and Technology | Bhushan S.,Center for Advanced Vehicular Systems
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

The onset and progression of vortices generated by the hull of a surface combatant has been investigated for drift angles of 0, 10 and 20 degrees by means of tomographic particle image velocimetry. Vortices are seen to form on the sonar dome and fore-body of the ship model, as well as on the bilge keels, and on the after-body. Two major streamwise vortex systems were identified: the vortices generated by the sonar dome and the vor- tices generated on the fore-body of the hull. Leading edge and crossflow vortices form on the bilge keels, and on the windward side, these vortices merge. Vortices are also seen to form on the afterbody of the hull at increased drift angles. Frequency anal- ysis of the sonar dome vortex at drift angle 20 degrees reveals a dominant frequency of approximately 3 Hz. Copyright © 2014 by ASME. Source

Michell F.,American Electric Power | Politano M.,IIHR Hydroscience and Engineering | Stallings J.,EPRI | Wang Y.,IIHR Hydroscience and Engineering
American Society of Mechanical Engineers, Power Division (Publication) POWER | Year: 2013

Ice blockage of a power plant's water intake is of paramount importance since it can lead to an unplanned shutdown of the intake compromising water supply and plant operation. American Electric Power's (AEP) Conesville Power Plant historically controlled ice accumulation at the river intake by routing to the intake a portion of the warm water return from the condenser on the only operating "once-through" unit's circulating water system. The unit operating with this oncethrough cooling system was retired at the end of 2012; thus, the plant lost the use of the condenser outlet/warm water return deicing flow at the river intake. A numerical study was conducted to evaluate design alternatives to alleviate ice accumulation at the river intake. A numerical model to predict the ice transport and accumulation at the river intake was developed and used to understand the main phenomenon leading to intake blockage. The effectiveness of mitigation measures was evaluated with the model. A mitigation plan consisting of intake modifications to be implemented during several phases is presented. In the first phase, large pipe openings are cut in the walls separating intake pump wells of previously retired units at the facility. In the second phase, a number of sediment control vanes previously placed in front of the intake are removed to facilitate downstream ice transport. A third phase, if needed to be implemented, involves removing additional sedimentation control vanes and cutting holes in the pump wells on the operating units. The paper describes the model, discusses numerical results and presents the field experience after implementation of phase one. Copyright © 2013 by ASME. Source

Persoon C.,IIHR Hydroscience and Engineering | Peters T.M.,University of Iowa | Kumar N.,University of Iowa | Hornbuckle K.C.,IIHR Hydroscience and Engineering
Environmental Science and Technology | Year: 2010

Passive samplers were deployed across Cleveland, OH and Chicago, IL to evaluate the spatial variability of airborne PCBs in urban areas. We measured ∑PCB concentrations, the sum of 151 congeners or congener groups quantified using tandem mass spectrometry, spatial distributions, and congener profiles in two urban areas in the Great Lakes region. Mean ∑PCB concentrations were significantly different between Cleveland (1.73 ± 1.16 ng m3) and Chicago (1.13 ± 0.58 ng m3) during the August 2008 sampling period. Mean congener profiles were compared with commercial Aroclor mixtures and found to be similar to Aroclor 1242 in Cleveland and similar to a mixture of 1242 and 1254 in Chicago. We observed large spatial variation in concentrations and weak or no significant autocorrelation between sites in both cities. "Hot spots" of high ∑PCB concentrations were identified in both urban areas and the congener profiles at these locations were most strongly correlated to that of PCB Aroclor mixtures. Congener profiles showed important differences including the enrichment of dioxin-like congeners in Chicago. © 2009 American Chemical Society. Source

De Moraes Frasson R.P.,IIHR Hydroscience and Engineering | Krajewski W.F.,IIHR Hydroscience and Engineering
American Society of Agricultural and Biological Engineers Annual International Meeting 2010, ASABE 2010 | Year: 2010

As rain falls on a canopy, it is redistributed and modified. While part of the rain will find a direct way through the canopy towards the ground, some will be redirected to the stem and then flow to the ground, some will accumulate on the leaves forming larger drops that will ultimately detach and fall and the remaining will eventually evaporate after the event is gone. This partitioning of rainfall into direct throughfall, stemflow and indirect throughfall modifies drop physical characteristics that are relevant to erosion studies, such as drop size and kinetic energy, while to stored water is relevant to remote sensing of soil moisture. With that in mind, we installed two modified tipping buckets to collect and measure the throughfall, two to measure the stemflow, one regular tipping bucket to measure the incoming rainfall, two compact weather stations to measure wind and to provide us with a redundant measurement of rainfall and two optical disdrometers, one underneath the canopy, one outside of the canopy, to measure the modification of the drop size distribution by the plants. The instruments were operational from 8 July 2009 until 30 September 2009, when we had the opportunity to record 17 events, from which 11 had accumulation of at least 10mm. We used the data to assess the partitioning of rainfall into stemflow and throughfall and to assess the modification of drop size distribution and kinetic energy caused by the plants. Source

Castro A.M.,IIHR Hydroscience and Engineering | Carrica P.M.,IIHR Hydroscience and Engineering
ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 | Year: 2011

Simulations of the two-phase bubbly flow around the research vessel Athena are presented. These are performed using a polydisperse model where several bubbles sizes are modeled. Intergroup transfer mechanisms such as breakup, coalescence and dissolution of air into water are considered. These simulations are performed on the fully appended Athena R/V including the rotating propeller. In this way the interaction of the stream of bubbles pushed down by the ship and the propeller is explicitly taken into account. Incoming regular waves are included in the simulations to mimic the observations of available data that show a pulsating entrainment of bubbles due to the waves. The effect of the several intergroup transfer mechanisms on the bubbly field around the ship is analyzed and discussed in depth. Simulations are performed in full scale to predict realistic turbulent structures and allow for a valid comparison with experiments. Copyright © 2011 by ASME. Source

Discover hidden collaborations