Browsing by Subject "storm surge"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item An Analysis of Self-similarity, Momentum Conservation and Energy Transport for an Axisymmetric Turbulent Jet through a Staggered Array of Rigid Emergent Vegetation(2013-05-29) Allen, Jon ScottMarsh vegetation is widely considered to offer protection against coastal storm damage, and vegetated flow has thus become a key area of hydrodynamic research. This study investigates the utility of simulated Spartina alterniora marsh vegetation as storm protection using an ADV measurement technique, and is the first to apply jet self-similarity analysis to characterize the overall mean and turbulent flow properties of a three-dimensional axisymmetric jet through a vegetated array. The mean axial flow of a horizontal axisymmetric turbulent jet is obstructed by three configurations of staggered arrays of vertical rigid plant stems. The entire experiment is repeated over five sufficiently high jet Reynolds number conditions to ensure normalization and subsequent collapse of data by nozzle velocity so that experimental error is obtained. All self-similarity parameters for the unobstructed free jet correspond to typical published values: the axial decay coefficient B is 5:8 +/- 0:2, the Gaussian spreading coefficient c is 85 +/- 5, and the halfwidth spreading rate eta_(1/2) is 0:093 +/- 0:003. Upon the introduction of vegetation, from partially obstructed to fully obstructed, B falls from 5:1+/- 0:2 to 4:2 +/- 0:2 and finally 3:7 +/-0:1 for the fully obstructed case, indicating that vegetation reduces axial jet velocity. Cross-sectionally averaged momentum for the unobstructed free jet is M=M0 = 1:05 +/- 0:07, confirming conservation of momentum. Failure of conservation of momentum is most pronounced in the fully obstructed scenario ? M=M0 = 0:54 +/- 0:05. The introduction of vegetation increases spreading of the impinging jet. The entrainment coefficient alpha for the free jet case is 0.0575; in the fully obstructed case, alpha = 0:0631. Mean advection of mean and turbulent kinetic energy demonstrates an expected reduction in turbulence intensity within the vegetated array. In general, turbulent production decreases as axial depth of vegetation increases, though retains the bimodal profile of the free jet case; the fully vegetated case, however, exhibits clear peaks behind plant stems. Turbulent transport was shown to be unaffected by vegetation and appears to be primarily a function of axial distance from the jet nozzle. An analysis of rate of dissipation revealed that not only does the cumulative effect of upstream wakes overall depress the magnitude of spectral energy density across all wavenumbers but also that plant stems dissipate large anisotropic eddies in centerline streamwise jet flow. This study, thus, indicates that sparse emergent vegetation both reduces axial flow velocity and has a dissipative effect on jet flow. Typically, however, storm surge does not exhibit the lateral spreading demonstrated by an axisymmetric jet; therefore, the results of this study cannot conclusively support the claim that coastal vegetation reduces storm surge axial velocity.Item An evaluation of the potential of coastal wetlands for hurricane surge and wave energy reduction(2009-05-15) Loder, Nicholas MasonGiven the past history and future risk of storm surge in the United States, alternative storm protection techniques are needed to protect vital sectors of the economy and population, particularly within southeastern Louisiana. It is widely hypothesized that coastal wetlands offer protection from storm surge and wave action, though the extent of this protection is unknown due to the complex physics behind vegetated flow dynamics. This thesis presents numerical modeling results that estimate the relative sensitivity of waves and storm surge to characteristics embodied by coastal wetlands. An idealized grid domain and 400 km2 (20 km by 20 km) marsh feature provide a controlled environment for evaluating marsh characteristics, including bottom friction, elevation, and continuity. Marsh continuity is defined as the ratio of healthy marsh area to open water area within the total wetland area. It is determined that increased bottom friction reduces storm surge levels and wave heights. Through the roughening of the bottom from sandy to covered with tall grass, it is estimated that waves may be dampened by up to 1.2 m at the coast, and peak surge may be reduced by as much as 35%. The lowering of marsh elevation generally increases wave heights and decreases surge levels, as expected. A 3.5 m decrease in marsh elevation results in as much as a 2.6 m increase in wave height, and up to a 15% decrease in surge levels. Reductions in marsh continuity enhance surge conveyance into and out of the marsh. For storms of low surge potential, surge is increased by as much as 70% at the coast due to decreasing marsh continuity from 100% to 50%, while for storms of high surge potential, surge is decreased by 5%. This indicates that for storms of high surge potential, a segmented marsh may offer comparable surge protection to that of a continuous marsh. Wave heights are generally increased within the marsh due to the transmission of wave energy through marsh channels. Results presented in this thesis may assist in the justification of coastal wetland mitigation, and optimize marsh restoration in terms of providing maximum storm protection.Item Storm surge analysis using numerical and statistical techniques and comparison with NWS model SLOSH(Texas A&M University, 2005-11-01) Aggarwal, ManishThis thesis presents a technique for storm surge forecasting. Storm surge is the water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level by almost 20 feet. Numerical modeling is an important tool used for storm surge forecast. Numerical model ADCIRC (Advanced Circulation model; Luettich et al, 1992) is used in this thesis for simulating hurricanes. A statistical technique, EST (Empirical Statistical Technique) is used to generate life cycle storm surge values from the simulated hurricanes. These two models have been applied to Freeport, TX. The thesis also compares the results with the model SLOSH (Sea, Lake, and Overland Surges from Hurricanes), which is currently used for evacuation and planning. The present approach of classifying hurricanes according to their maximum sustained winds is analyzed. This approach is not found to applicable in all the cases and more research needs to be done. An alternate approach is suggested for hurricane storm surge estimation.