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Hurricane Wind Data Collection and Simulation
Every year Florida residents endure the costly effects of hurricanes. 1999 was the first time on record in which
four category four storms occurred in the same season. Experts expect that the current trend of increasing
quantity and intensity of storms will continue for the next decade. As the population in Florida's coastal
regions continues to grow, more Florida residents will be experiencing hurricanes. Aggressive efforts are
now underway to reduce the effects of this natural disaster on life and property. Improvements in storm
path prediction models, evacuation procedures, and construction methods and building materials will
collectively leave us better prepared to survive the storm.
ENGINEERING HURRICANE SAFE STRUCTURES
It is an engineer's responsibility to design structures with enough strength to resist the forces applied to them,
while still providing a useful and affordable structure. Design codes set acceptable standards to define the
most severe forces a structure might reasonably expect to experience during its lifetime. To avoid mishap, factors
of safety are applied to provide a margin of error in this estimation. Another factor is applied to account for
the dynamic effects of fluctuating loads such as winds. These forces, safety, and amplification factors are
generally based on experience and some fundamental understanding of the nature of the loads.
Hurricane winds are one type of loading about which very little is known. Are engineers grossly underestimating
or overestimating hurricane loads, or misunderstanding the way they attack a structure? The only way to find out
is to measure the most extreme winds that impinge upon man made structures during hurricane landfall. With
the rapidly increasing capabilities of computers and instrumentation, this is now an achievable goal. This
project involves the collection of hurricane data, its analysis, and its application to design improvements
for residential structures.
HURRICANE WIND DATA COLLECTION
Millions of dollars are spent each year collecting wind speed data throughout the United States. These systems
almost exclusively cater to the needs of normal weather prediction, operation of aircraft and airports,
and identification of severe weather conditions. Unfortunately, very little focus has been placed on collecting
data close to the ground. This is the data needed by the civil engineers building structures which can survive
extreme winds. Ground level hurricane wind speeds are typically extrapolated from measurements made higher
in the atmosphere, providing only a rough guess of the wind speed, and no real information on the
turbulence structure of the gusts that cause damage to homes. The goal of my project is to directly measure
this important low elevation wind data in as many landfalling hurricanes as possible in order to establish a
better understanding of just how hurricane winds behave near the ground where structures are built. With
this information in hand, a rational approach to strengthening houses will be pursued through improved
construction methods, materials, and testing procedures.
I am a part of a team that remains on standby throughout the hurricane season.
'When a storm approaches land, the team heads out from Gainesville to meet it
vvith specially designed portable equipment in tow on two 25-foot long trailers.
These trailers are placed in the hurricane's path approximately 8 hours before
impact, and the systems are then readied. After about 30 minutes of work, each
trailer unfolds into a very stiff 10-meter tall tower able to withstand 200 MPH
winds. Each tower is outfitted with multiple sensors at three elevations along its height. This equipment gathers
wind speed and direction at 5 and 10-meter elevations as well as temperature, rainfall, barometric pressure,
and relative humidity data. The equipment can be set to run for up to 24 hours, providing a detailed record of
the storm's behavior as it approaches, passes over, and leaves the area. All data is stored in digital form on two
hard disks in the tower's computer system. The units are operated at a sampling rate of 50 hertz, providing
excellent resolution of high-speed wind field dynamics.
The deployment of these mobile units is coordinated with the NOAA Hurricane Research Division. My team sends
the GPS location of the towers to NOAA, which uses this information to arrange for GPS drop sondes to be
dropped near the tower positions. These devices are dropped from hurricane hunter aircraft, and transmit
wind information as they drift to the earth's surface. Subsequent analysis will allow correlation between the
upper level winds and the surface wind speeds, thus providing, for the first time, a complete profile of
wind characteristics from upper atmosphere to ground level.
In the event that the approaching hurricane is headed for southeast Florida, the wind data collection towers
are complimented by a separate set of sensors that directly measure the wind force on residential structures. A
series of sophisticated pressure sensing packages are placed on 10 pre-selected homes along the southeast coast
of Florida. Each home had been pre-bracketed to allow quick installation of up to 28 pressure sensors on the roof
and sides of the house. These pressure devices will provide the needed full-scale information on how the
hurricane wind gust structure imparts forces to structures near ground level. A video camera is set up at each
home to provide a visual record of any damage as it occurs.
This simultaneous measurement of wind velocity and pressure will fill a significant void in the current extreme
wind data bases, namely a comprehensive real time display of the wind speed - wind load - accumulated
damage chain at low elevations typical of residential housing and human exposure.
The project is a joint effort between UF, FIU, and Clemson University. Each university has a team of students and
a faculty member who conduct the deployments and participate in the data analysis. Dr. Tim Reinhold of
Clemson University initiated the project and developed the equipment. Dr. Kurt Gurley heads the UF effort in
the Department of Civil Engineering. The Florida Department of Community Affairs sponsored the project using
FEMA Stafford Act funds. Florida Sea Grant also provides funds for the UF team.
Two different deployment strategies are possible. The mobile towers operate independently of the
house pressure sensing packages. Any hurricane likely to make landfall from Texas to the
Carolinas is targeted for possible deployment of the mobile towers at optimal locations to measure
eye wall wind velocity. Deployment of the pressure instruments takes place only for hurricanes
with a high probability of landfall along the southeast coast of Florida where the pre-selected
homes are located. The speed of the storm's development and movement determines the distance
that the UF team is able to travel to safely deploy the towers and retreat to shelter.
The deployment strategy is to anticipate the storm's movement and locate the towers in the general area 24
hours before landfall. The National Hurricane Center provides timely updates directly to the deployment teams in
the field. As the track predictions become more precise, the units will be setup on appropriate public lands
with permission of the local authorities. About 8 hours before landfall, the units are positioned and activated.
The teams then withdraw to shelter and the instrumentation runs unattended for up to 24 hours collecting
a continuous record of wind speeds from the anemometer arrays.
During the 1999 season, the mobile towers were deployed to measure Dennis, Floyd, and Irene, taking the UF
team from southern Florida to North Carolina. The pressure sensors were also installed for Floyd in the Juniper
area. The data collected during these deployments are now being analyzed.
DATA ANALYSIS AND APPLICATION
The next phase of my work is the analysis of the collected data. Empirical wind field
models are being developed to describe wind speeds, turbulence intensity, and
the correlation structure of gusts as a function of upper atmosphere wind
measurements, storm size and intensity, and the effects of localized parameters such
as terrain and proximity to the coast. These wind turbulence models will provide a
more realistic baseline with which to approach future computational and wind tunnel
studies of wind damage mitigation strategies.
Computer models of wind and structural response, and wind tunnel studies on the effects of wind on structures
are only beginning to address extreme winds and structural survivability. These methods are dependent upon
the collected full-scale wind data to derive detailed empirical models of the true behavior of the wind field.
Advanced wind load computer simulation techniques being developed for computational evaluation of
design improvements in the most damage prone area in the structural envelope are currently being calibrated
using the collected hurricane data. With this tool, multiple storms from various directions and intensities can
be applied to structures to evaluate survivability.
Recommendation of appropriate retrofits to existing homes, higher standards for construction of new
homes, hurricane resistant fastening systems, and new materials will quickly follow a better understanding of
the fundamental wind damage mechanisms.
Photos by John Elderkin and Forrest Masters
Back to the Journal of Undergraduate Research
College of Liberal Arts and Sciences I University Scholars Program I University of Florida I
ï¿½ University of Florida, Gainesville, FL 32611; (352) 846-2032.
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