Browsing by Subject "Hurricane"
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Item Analysis of performance and reliability of offshore pile foundation systems based on hurricane loading(2011-05) Chen, Jiun-Yih; Gilbert, Robert B. (Robert Bruce), 1965-; Stokoe, II, Kenneth H.; Manuel, Lance; Bickel, J. Eric; Murff, James D.Jacket platforms are fixed base offshore structures used to produce oil and gas in relatively shallow waters worldwide. Their pile foundation systems seemed to perform better than what they were designed for during severe hurricanes. This observation has led to a common belief in the offshore oil and gas industry that foundation design is overly conservative. The objective of this research is to provide information to help improve the state of practice in designing and assessing jacket pile foundations to achieve a consistent level of performance and reliability. A platform database consisting of 31 structures was compiled and 13 foundation systems were analyzed using a simplified foundation collapse model, supplemented by a 3-D structural model. The predicted performance for most of the 13 platform foundations is consistent with their observed performance. These cases do not preclude potential conservatism in foundation design because only a small number of platform foundations were analyzed and only one of them actually failed. The potential failure mechanism of a foundation system is an important consideration for its performance in the post-hurricane assessment. Structural factors can be more important than geotechnical factors on foundation system capacity. Prominent structural factors include the presence of well conductors and jacket leg stubs, yield stress of piles and conductors, axial flexibility of piles, rigidity and strength of jackets, and robustness of foundation systems. These factors affect foundation system capacity in a synergistic manner. Sand layers play an important role in the performance of three platform foundations exhibiting the largest discrepancy between predicted and observed performance. Site-specific soil borings are not available in these cases. Higher spatial variability in pile capacity can be expected in alluvial or fluviatile geology with interbedded sands and clays. The uncertainties in base shear and overturning moment in the load are approximately the same and they are slightly higher than the uncertainty in the overturning capacity of a 3-pile foundation system. The uncertainty in the overturning capacity of this foundation system is higher than the uncertainty in shear capacity. These uncertainties affect the reliability of this foundation system.Item Characterization of hurricane gust factors using observed and analytical data(Texas Tech University, 2009-05) Edwards, Rebecca Paulsen; Schroeder, John L.; Gilliam, Kathleen; Smith, Douglas A.The nature of turbulence in the hurricane boundary layer has been the subject of much discussion. Two questions in particular continue to be the source for debate and ongoing research. The first question is whether or not hurricane GFs exhibit the same behavior as GFs from winds generated by extratropical systems (thunderstorms excluded). The second question is whether the structure of the wind, and the resulting gust factors, change at high wind speeds. This study seeks to address those two questions using a variety of data sources and analysis techniques. Observational data were collected from both landfalling tropical cyclones and synoptically generated extratropical wind. Analytical data at a variety of wind speeds were created using an inverse fast Fourier Transform of the universal spectrum for wind in the perturbed terrain. Gust factors and other parameters were computed for both types of data and the results assimilated in a data base. Analysis of these data yielded interesting results. A strong dependence on surface roughness was noted for gust factors from both observed and analytical data. However, once efforts were made to control for this dependency by stratifying the data into roughness regimes using the roughness length, slight differences between the tropical and extratropical gust factor data remained. Analysis of the artificial data, suggest spectral differences between the tropical and extratropical regimes due to the presence of additional low-frequency energy in the tropical regime. A slight decrease of the gust factor with increasing wind speed was noted in the high-speed analytical data. A similar decrease was suggested in the tropical data. It was concluded that the low-frequency spectral differences between the two regimes have less of an effect on the resulting gust factors as the wind speed increases, resulting in better agreement between the two distributions.Item Examination of the Coastal Transition Zone in Hurricane Frances (2004)(2011-05) Hirth, Brian D.; Schroeder, John L.; Weiss, Christopher C.; Smith, Douglas A.Understanding the structure of the coastal internal boundary layer (IBL) during the landfall of a tropical cyclone has important ramifications on operational forecasting, structural design, and post-storm damage assessment. Despite these important issues, it is unclear how the structure of the IBL evolves at the coastline on micro- and meso-scales during a landfalling hurricane. Knowledge of the vertical kinematic structure within tropical cyclones over water has improved greatly through aircraft reconnaissance missions and the advent of GPS dropsondes and the Stepped Frequency Microwave Radiometers. Unfortunately, reconnaissance and research aircraft are limited to over-water missions resulting in a poor understanding of vertical kinematic structure near the coastal interface where changes in IBL structure are expected due to changes in coastal geometry and surface roughness. Additionally, IBL structure may evolve due to the passage of convective precipitation and associated downdrafts. A unique observational dataset was collected from the coastal transition zone in the onshore flow region of Hurricane Frances (2004) over Cape Canaveral, FL. Single- and dual-Doppler radar data collected by the Shared Mobile Atmospheric Research and Teaching radars provide the ability to discern horizontal and vertical mean IBL structure over a complex coastal interface while assessing the influence of a variable underlying surface and the passage of transient convective wind gusts. Additional wind speed data were collected by a meso-network of surface towers operated by the Cape Canaveral Air Force Station and Kennedy Space Center along with a portable surface tower deployed by Texas Tech University. Radar and tower data analyses reveal that IBL mean structure over the Cape Canaveral remains quite consistent during the landfall of Hurricane Frances, though IBL growth is suppressed when compared to empirical growth models. Additionally, transient convective gusts commonly perturb the mean structure at the top of the IBL, though the higher momentum associated with these gusts is typically not able to descend to the surface within an established IBL.Item Extreme wave height estimation for ocean engineering applications in the Gulf of Mexico(2012-07-16) Jeong, Chan KwonRecent hurricanes in the Gulf of Mexico (e.g., Ivan, Dennis, Katrina, Rita and Ike) were observed to develop wave conditions that were near or exceeded the predicted 100-year conditions. As a result, many offshore facilities, as well as coastal infrastructure, which were designed to withstand the 100-year condition, were damaged. New estimates of extreme conditions, which incorporate recently observed maxima, are needed to provide better guidelines for design of coastal and offshore structures. Berek et al. (2007) have used modeled data to develop new criteria, but these estimates can be very sensitive to the data and to the statistical methods used in the development. Berek's estimates also do not cover the entire Gulf of Mexico. We have developed updated estimates of the 100-year extreme wave conditions for the entire Gulf of Mexico using a more comprehensive approach. First, the applicability of standard parametric wind models was examined and appropriate adjustments to the Rankine vortex model were developed to reduce the wind field errors during hurricane conditions. The adjusted winds reduced the error by up to 25 percent compared to the original Rankine vortex model. To obtain reliable wave data, merged wind fields were generated using the NCEP/NCAR Reanalysis 1 project modeled wind data for background wind and the parametric wind model for hurricane conditions. Next, the SWAN wave model was used for the 51-year period from 1958 to 2008 along with multiple statistical methods (Gumbel, Weibull and GEV-Generalized Extreme Value distribution). The effect of the recent hurricane season (2004-2008) shows that maximum 100-year wave height values and their distribution changes. A resampling technique (bootstrap) is used to evaluate and select the optimum statistical method to estimate more appropriate extreme wave conditions.Item Model for estimating damages on power systems due to hurricanes(2010-05) Krishnamurthy, Vaidyanathan; Kwasinski, Alexis; Baldick, RossHurricanes are a threat to power and telecommunication infrastructure. This work summarizes a method for hurricane characterization using the proposed Localized Tropical Cyclone Intensity Index(LTCII) as a model for estimating damages to Electric power infrastructure. The model considers the effect of storm surge, maximum sustained wind speeds, the duration of time for which the system has been under tropical storm conditions and the area swept by hurricane over land. The measurements focus on major load centers in the system. The validation of the outage data is discussed. The model is evaluated for hurricanes from 2004, 2005 and 2008 hurricane seasons. The degree of influence of various hurricane parameters on the damages suffered by electric power systems are discussed using case studies. The maximum outages are observed to follow a logistic regression curve with respect to log(LTCII), with a correlation of 0.85. The observed restoration times fit a 6th degree polynomial with an R2 = 0.6. The effects of time under tropical storm winds were observed to have great significance in the damage profile observed with the model.Item Remote-sensing applications to windstorm damage assessment(Texas Tech University, 2005-12) Womble, James A.; Mehta, Kishor C.The collection and study of windstorm damage information is critical for the understanding of wind effects on the built environment, for measuring progress in construction technologies and mitigation measures, and for (ultimately) helping to build disaster-resilient communities. Rapid and thorough documentation of damage is crucial but has not generally been possible in the past due to limited time (prior to cleanup and repair efforts), manpower, and access to affected areas. Modern remote-sensing technologies, including high-resolution satellite imagery, have proven effective for the documentation and study of damage caused by multiple hazards, such as earthquakes. In conjunction with traditional forensic damage assessments, these technologies also provide a means for enhancing the speed, thoroughness, coverage area, and consistency of windstorm damage documentation. Ongoing developments in the fields of remote sensing and digital image processing can eventually lead to the computer-automated detection of multi-hazards damage. Each individual hazard has unique damage mechanisms and, therefore, unique remote-sensing signatures that must be identified and quantified for use in eventual automation. This research examines the use of remote-sensing technologies for damage assessment in multiple hazards and presents a framework for the automated application of remote-sensing technologies specifically to the windstorm hazard. This study utilizes remote-sensing data and corresponding ground-truthing field data from recent significant windstorms to demonstrate the use of remote-sensing technologies in collecting windstorm damage data. This study also examines the remote-sensing signatures of windstorm damage to buildings and demonstrates the use of remote-sensing and digital-image-processing technologies for making quantitative assessments of windstorm damage to buildings. This research finally provides suggestions for future developments in the remote-sensing assessment of windstorm damage.Item Robust Hurricane Surge Response Functions(2012-11-30) Udoh, Ikpoto 1980-To adequately evaluate risk associated hurricane flooding, numerous surge events must be considered, and the cost associated with high resolution numerical modeling for several storms is excessive. The Joint Probability Method with Optimal Sampling (JPM-OS) has been recently shown to be a reliable method in estimating extreme value probabilities of hurricane flooding ? it relies heavily on a hurricane surge matrix comprised of surge values from several hurricane scenarios (with varying meteorological and climate change characteristics). Surge Response Functions (SRFs) are physics-based equations developed using scaling laws to adequately scale surge response in dimensionless space; they serve as surrogates to high resolution numerical models in estimating hurricane peak surge to populate the JPM-OS surge matrix. Research presented in this dissertation is primarily focused on the development of dimensionless formulations using physics-based scaling laws to account for the contribution of forward speed (v_f), approach angle (theta) and Sea Level Rise (SLR). These parameters are incorporated into pre-existing SRFs for open coast locations and bays. For the bays, in addition to accounting for the effects of v_f and theta in the SRFs, a new dimensionless formulation for the influence of storm size (R_p) is included in the SRFs. ? To account for the influence of v_f in the SRFs, the dimensionless formulations primarily consist of the time it takes for surge to build up (over the shelf, for open coast SRFs and within the bays, for bay SRFs). The formulation for the influence of theta primarily accounts for the rotation of the hurricane wind field as the storm makes landfall. For the influence of R_p in the bays, the new formulation scales R_p with the farthest distance through which water mass will move inside the bay, from its center of gravity. A simple correction based on a linear model is derived to account for the influence of SLR on surge response at open coast locations and in bays. The developed dimensionless formulations for v_f and theta (and R_p for bay SRFs) are incorporated into the SRFs to obtain revised versions of the response functions. For open coast locations, the revised SRFs estimate peak surge with an increased accuracy (based on root-mean-square errors of modeled versus SRF-estimated peak surge) of up to 12.5% reduction in root-mean-square errors. In addition, the new formulations improve the predictions of 65% of surge events of 2 m or greater. For the bays, the revised SRFs reduce the root-mean-square errors (by up to 54% in Matagorda Bay), when compared to the previous formulation. These results indicate that the new formulations, which include v_f and tehta (and R_p for bay SRFs), significantly improve the accuracy of the SRFs. Application of the revised open coast SRFs to the JPM-OS framework shows only minor impacts of v_f and theta variation on surge versus return period curves (about 5.2% maximum increase in surge for theta varying from -80 degrees to +80 degrees, and a maximum of 6.7% for fvvarying from 1.54 m/s to 10.8 m/s). Climate change parameters however show a much more significant impact on the surge versus return period curves. SLR variation from 0.5 m to 2.0 m yields a maximum of 42.4% increase in surge, while hurricane intensification from 0.5 degrees C to 1.5 degrees C yields an increase of up to 11.3% in surge.Item Simulation of windborne debris trajectories(2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.Item Simulation of windborne debris trajectories(Texas Tech University, 2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.Item The Evaluation of the Mechanical Strength of Epoxy-Based Resin as a Plugging Material, and the Development of a Novel Plug and Abandon Technique Using Vitrified Solid Epoxy-Based Resin Beads(2012-07-16) Abuelaish, AhmedOver the past several years, some of the platforms in the Gulf of Mexico have been damaged completely, such that conventional P&A operations may not be possible. In these cases, plugging fluid needs to be pumped through an intervention well and dropped several thousand feet in water to settle above a packer and seal the well. The current P&A material of choice is cement, but cement is miscible in water, which dilutes and contaminates the cement. Therefore, alternate plugging materials need to be used for these operations. This paper discusses the development of a cost-effective Epoxy P&A method and the challenges of using Epoxy. First, the impact of seawater, oil, and pipe dope on the curing process remains unknown. Secondly, the yield strength of Epoxy with and without the contaminating chemicals must be equal to or better than cement. Finally, previous tests have shown significant losses of Epoxy to the walls of the wellbore during the 7,000-ft drop. 2 High temperature curing and compression tests were performed on contaminated epoxy samples to determine the effectiveness of the epoxy plug. To reduce material losses, an improved method for introducing the epoxy into the target zone was developed. This method takes advantage of a narrow window in the cure process where the curing process can be suspended by quenching the partially cured liquid epoxy in water at room temperature, thereby changing the liquid epoxy into solid beads. The beads can then be pumped into the wellbore, where they liquefy at wellbore temperature, 200?F, then cure into a solid plug. Seawater was found to accelerate the cure time, while all contaminants tested reduced the fracture strength by more than 25% compared to pure resin. The yield strengths of contaminant mixtures, however, remained relatively constant, with the greatest drop being only 11%. The use of solid epoxy beads was found to have a compressive strength 50% greater than Portland cements I&II. In addition, the application mentioned herein eliminates the need to prepare the plug material on site. These advantages greatly contribute to reducing the costs of an epoxy P&A operation, to potentially being USD 0.7 million cheaper than a Portland cement operation.Item Water-Column Inertial and Sub-Inertial Oceanic Response to Hurricane Isaac in the Deepwater Gulf of Mexico(2014-11-14) Spencer, Laura JeanTropical Storm Isaac entered the Gulf of Mexico on 27 August 2012 and strengthened to become a Category 1 hurricane shortly before making landfall in southern Louisiana. Hurricane Isaac approached Southwest Pass near the mouth of the Mississippi River on August 29, 2012 at 00:00 UTC. The center of the storm then moved westward before making landfall eight hours later at Port Fourchon, LA. On August 28, 2012 at approximately 18:00 UTC, Hurricane Isaac passed directly over the center of a mooring array in a northwesterly trajectory. As part of the Gulf Integrated Spill Research Program, six deepwater moorings featuring upward-looking 75 kHz Acoustic Doppler Current Profilers were deployed in water depths between 836 m and 1690 m in the Mississippi Fan region of the northern Gulf of Mexico in July 2012. Each of the six moorings featured 3 Aanderaa RCM current meters. One current meter was located near the bottom, the next positioned approximately 180 m shallower, then the last positioned an additional 200 m shallower. One mooring featured four InterOcean S4A current meters positioned 100 m apart between 790 m and 1090 m. Maximum current speeds of 41.3 cm/s at 100 m, 35.5 cm/s at 300 m, and 32.7 cm/s at 500 m depth were observed during the passage of the Hurricane Isaac. Maximum bottom current speeds measured from Aanderaa RCMs ranged between 16.1 cm/s at 1645 m depth and 34.0 cm/s at 1020 m depth. Inertial band oscillations (1/2-2 days) are seen to 800 m depths, with energy propagation speeds on the order of 30 m/day vertically and 5.7 km/day horizontally. A blue shift in the effective frequency to 1.11f is observed in the near-inertial band in the wake of Hurricane Isaac. Wavelet analyses of the time-series records indicate two subinertial oscillations (2-5 days and 5-12 days) initiated throughout the water-column at the time of the storms closest approach that persist for approximately one week. Each sub-inertial band response was fundamentally different from the near-inertial response to Hurricane Isaac and showed a strong barotropic response.