Failure of Flawed Utility Poles in Wind Gusts

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
James F. Wilson
Keyword(s):  
Transmission Lines ◽  
Point Load ◽  
Electrical Safety ◽  
Wind Gust ◽  
Stress Concentrations ◽  
Wind Gusts ◽  
Utility Poles ◽  
Cantilevered Beam ◽  
Normal Mode Calculations ◽  
Proportional Limit Stress

The purpose of this study is to account for failures of wood utility poles in wind storms based on dynamic analysis and pole imperfections. The utility pole supporting multiple overhead transmission lines is modeled as a uniform Bernoulli–Euler cantilevered beam fixed at the base and subjected to three types of suddenly applied transverse loads that simulate a wind gust: a uniform pole pressure, a point load at the tip accounting for line and transformer drag, and another point load near midlength, accounting for drag on lines strung from that location. The dynamic pole moments are based on normal mode calculations rather than static calculations with a dynamic impact factor, and the critical flexural stresses include stress concentrations arising from pole imperfections such as holes, knots, and surface gouges. A case study illustrates the results for one of about 400 failed wood poles downed in a single New Jersey storm in 2003 with 107 km/h (67 m/h) wind gusts. Here, the critical pole stress based on the dynamic model and a hole imperfection exceeded the proportional limit stress of the wood. The predicted dynamic stresses are higher than those based on the National Electrical Safety Code.

scholarly journals Wind Gust Measuring at Low Altitude Using An Unmanned Aerial System

2021 ◽  
Author(s):  
Alton Yeung
Keyword(s):  
Turbulence Models ◽  
Satellite System ◽  
Data System ◽  
Measurement Unit ◽  
Wind Gust ◽  
Wind Gusts ◽  
Low Altitude ◽  
And Performance ◽  
Global Navigation Satellite ◽  
Aerial Platform

A small unmanned aerial vehicle (UAV) was developed with the specific objective to explore atmospheric wind gusts at low altitudes within the atmospheric boundary layer (ABL). These gusts have major impacts on the flight characteristics and performance of modern small unmanned aerial vehicles. Hence, this project was set to investigate the power spectral density of gusts observed at low altitudes by measuring the gusts with an aerial platform. The small UAV carried an air-data system including a fivehole probe that was adapted for this specific application. The air-data system measured the local wind gusts with an accuracy of 0.5 m/s by combining inputs from a five-hole probe, an inertial measurement unit, and Global Navigation Satellite System (GNSS) receivers. Over 20 flights were performed during the development of the aerial platform. Airborne experiments were performed to collect gust data at low altitudes between 50 m and 100 m. The result was processed into turbulence spectrum and the measurements were compared with the MIL-HDBK-1797 von K´arm´an turbulence model and the results have shown the model underpredicted the gust intensities experienced by the flight vehicle. The anisotropic properties of low-altitude turbulence were also observed when analyzing the measured gusts spectra. The wind and gust data collected are useful for verifying the existing turbulence models for low-altitude flights and benefit the future development of small UAVs in windy environment.

scholarly journals Characterizing wind gusts in complex terrain

2019 ◽  
Vol 19 (6) ◽  
pp. 3797-3819 ◽  
Author(s):  
Frederick Letson ◽  
Rebecca J. Barthelmie ◽  
Weifei Hu ◽  
Sara C. Pryor
Keyword(s):  
Wind Turbines ◽  
Complex Terrain ◽  
Probability Distributions ◽  
Wind Loading ◽  
Wind Gust ◽  
Wind Gusts ◽  
Sonic Anemometers ◽  
Vertical Displacements ◽  
Structural Loading ◽  
Good Agreement

Abstract. Wind gusts are a key driver of aerodynamic loading, especially for tall structures such a bridges and wind turbines. However, gust characteristics in complex terrain are not well understood and common approximations used to describe wind gust behavior may not be appropriate at heights relevant to wind turbines and other structures. Data collected in the Perdigão experiment are analyzed herein to provide a foundation for improved wind gust characterization and process-level understanding of flow intermittency in complex terrain. High-resolution observations from sonic anemometers and vertically pointing Doppler lidars are used to conduct a detailed study of gust characteristics with a specific focus on the parent distributions of nine gust parameters (that describe velocity, time, and length scales), their joint distributions, height variation, and coherence in the vertical and horizontal planes. Best-fit distributional forms for varying gust properties show good agreement with those from previous experiments in moderately complex terrain but generate nonconservative estimates of the gust properties that are of key importance to structural loading. Probability distributions of gust magnitude derived from vertically pointing Doppler lidars exhibit good agreement with estimates from sonic anemometers despite differences arising from volumetric averaging and the terrain complexity. Wind speed coherence functions during gusty periods (which are important to structural wind loading) are similar to less complex sites for small vertical displacements (10 to 40 m), but do not exhibit an exponential form for larger horizontal displacements (800 to 1500 m).

The Impact of Wind Gusts on the Ocean Thermal Skin Layer by Capillary-Gravity Waves

2020 ◽  
Author(s):  
Christopher J Zappa ◽  
Nathan Laxague ◽  
Sophia Brumer ◽  
Steven Anderson
Keyword(s):  
Infrared Imaging ◽  
Wind Waves ◽  
Ocean Surface ◽  
Skin Layer ◽  
Wind Gust ◽  
Thermal Infrared Imaging ◽  
Wind Gusts ◽  
Transient Forcing ◽  
The Impact ◽  
Depth Water

<p><span>The thermodynamic and emissive properties of the ocean thermal skin layer are crucial contributors to air-sea heat flux. In order to properly observe ocean surface temperature without disturbing any delicate fluid mechanical processes, thermal infrared imaging is often used. However, wind impacting the ocean surface complicates the extraction of meaningful information from thermal imagery; this is especially true for transient forcing phenomena such as wind gusts. Here, we describe wind gust-water surface interaction through its impact on skin layer thermal and emissive properties. Two key physical processes are identified: (1) the growth of centimeter-scale wind waves, which increases interfacial emissivity and (2) microscale wave breaking and shear, which mix the cool skin layer with warmer millimeter-depth water and increase the skin temperature. As more observations are made of air-sea interaction under transient forcing, the full consideration of these processes becomes increasingly important.</span></p>

Two-Dimensional Input Shaping for One-Dimensional Continua

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Amir Lotfi-Gaskarimahalle ◽  
Christopher D. Rahn
Keyword(s):  
Closed Form ◽  
Boundary Control ◽  
Position Control ◽  
Discrete Systems ◽  
Point Load ◽  
Input Shaping ◽  
Beam Model ◽  
Residual Vibration ◽  
One Dimensional ◽  
Cantilevered Beam

This paper extends input shaping control to one-dimensional continua. Unlike discrete systems where the input is shaped only in the temporal domain, temporal and spatial input shaping can produce zero residual vibration in setpoint position control of distributed strings and beams. For collocated and noncollocated boundary control of strings and domain control of strings and pinned beams, the response to step inputs is solved in closed form using delays. For a clamped beam model, a closed form infinite modal series is used. The boundary controlled string can be setpoint regulated using two-pulse zero vibration (ZV) and three-pulse zero vibration and derivative (ZVD) shapers but ZVD is not more robust to parameter variations than ZV, a unique characteristic of second-order partial differential equations systems. Noncollocated ZV and ZVD boundary control enables rigid body translation of a string with zero residual vibration. Domain controlled strings and pinned beams with spatial input distributions that satisfy certain orthogonality conditions (e.g., midspan point load or uniformly distributed load) can be setpoint regulated with shaped inputs. For the cantilevered beam, modal shaping of the input distribution and ZV or ZVD temporal shaping drives the tip to the desired position with zero residual vibration.

Effect of wind gusts on the dynamics of railway vehicles running on a curved track

2017 ◽  
Vol 232 (4) ◽  
pp. 1103-1120 ◽  
Author(s):  
Wonhee You ◽  
Hyukbin Kwon ◽  
Joonhyuk Park ◽  
Yujeong Shin
Keyword(s):  
Dynamic Characteristics ◽  
Wind Tunnel Test ◽  
Simulation Software ◽  
Scale Model ◽  
Railway Vehicle ◽  
Wind Gust ◽  
Railway Vehicles ◽  
Wind Gusts ◽  
Pitch Moment ◽  
Curved Track

Due to global warming, there is an increasing number of wind gusts that affect the stability of railway vehicles. A railway vehicle running on a curved track during a wind gust is subjected to multiple forces simultaneously, which include the centrifugal force and forces exerted by the wind gust and cant, and they significantly affect the vehicle’s dynamic characteristics as well as its safety. The forces increase the vibration of carbodies and the risk of derailment and overturning of cars; the effect is worse on irregular tracks. In order to review the phenomenon in detail, a 1/20 scale model of a railway vehicle was built to measure the aerodynamic coefficients in five directions—side force, lift force, roll moment, pitch moment, and yaw moment—through a wind tunnel test. The data collected were applied as external forces to a full-scale railway vehicle model traveling on a curved track. Using a multibody simulation software program, SIMPACK, a railway vehicle was modeled, which was then used in the simulation of the dynamic characteristics and safety of vehicles while traveling on a curved track during a wind gust. Using the actual measured track data from the curved zone, a comparison was made on the dynamic characteristics of the car traveling, with and without a wind gust, on a curved track with a railway curve radius of 599 m; also, the difference was analyzed with the direction of the wind gust blowing from inside and toward the center of curvature. The results showed that in the presence of a wind gust blowing from outside the curvature with an average speed of 25 m/s it is advisable to stop train services on grounds of safety.

Electrical safety of suppressing wildfires near high-voltage transmission lines using water mist

2018 ◽  
Vol 36 (4) ◽  
pp. 295-314 ◽  
Author(s):  
JiaZheng Lu ◽  
Bao-Hui Chen ◽  
Zhen Fang ◽  
Jianping Hu ◽  
Bowen Wang ◽  
...  
Keyword(s):  
Electric Conductivity ◽  
Leakage Current ◽  
High Voltage ◽  
Transmission Lines ◽  
Efficient Method ◽  
Power Transmission ◽  
Water Solution ◽  
Water Mist ◽  
Electrical Safety ◽  
Electrical Transmission

Wildfires near transmission lines are important disasters that affect power transmission. Water mist is a highly efficient method for suppressing wildfires near electrical transmission lines, where it avoids line-tripping to ensure the safety of the grid. However, few studies have investigated the electrical safety during the water mist extinguishing process, including the risk of tripping transmission lines and the shock hazard for users. In this study, we systematically studied the influence of the gap distance and the electric conductivity of the water solution on the insulation characteristics of water mist with a Dv0.99 diameter of the droplets of ca. 500 µm, including the breakdown voltage and leakage current. Furthermore, we investigated the effect of water mist on the development of a long-gap discharge, and the insulation mechanism of water mist was also considered. Finally, water mist with multi-component additives was employed for suppressing wildfires near transmission lines in China, and we demonstrated the effectiveness of this method based on the reduction of line-tripping accidents caused by wildfires near transmission lines.

Radar-Based Comparison of Thunderstorm Outflow Boundary Speeds versus Peak Wind Gusts from Automated Stations

2021 ◽  
Author(s):  
Keith D. Sherburn ◽  
Matthew J. Bunkers ◽  
Angela J. Mose
Keyword(s):  
Surface Wind ◽  
Thermodynamic Characteristics ◽  
Time Of Day ◽  
Wind Gust ◽  
Severe Thunderstorm ◽  
Wind Gusts ◽  
Thunderstorm Outflow ◽  
Versus Peak ◽  
Outflow Boundary ◽  
Lapse Rates

AbstractStraight-line winds are arguably the most challenging element considered by operational forecasters when issuing severe thunderstorm warnings. Determining the potential maximum surface wind gust prior to an observed, measured gust is very difficult. This work builds upon prior research that quantified a relationship between the observed outflow boundary speed and corresponding measured wind gusts. Though this prior study was limited to a 30-case dataset over eastern Colorado, the current study comprises 943 cases across the contiguous United States and encompasses all times of day, seasons, and regions while representing various convective modes and associated near-storm environments.The wind gust ratios (WGRs), or the ratio between a measured wind gust and the associated outflow boundary speed, had a nationwide median of 1.44, mean of 1.68, and 25th–75th percentiles of 1.19–1.91, respectively. WGRs varied considerably by region, season, time of day, convective mode, near-storm environment, and outflow boundary speed. WGRs tended to be higher in the plains, Intermountain West, and southern coastal regions, lower in the cool season and during the morning and overnight, and lower in linear convective modes compared to supercell and disorganized modes. Environments with stronger mean winds and low-to-midlevel shear vector magnitudes tended to have lower WGRs, while those with steeper low-level lapse rates and other thermodynamic characteristics favorable for momentum transfer and evaporative cooling tended to have higher WGRs. As outflow boundary speed increases, WGRs—and their variability—decreases. Applying these findings may help operational meteorologists provide more accurate severe thunderstorm warnings.

Advantages of an Ornithopter against an Airplane with a Propeller

2012 ◽  
Vol 84 ◽  
pp. 66-71
Author(s):  
Shigeru Sunada
Keyword(s):  
High Performance ◽  
Aerodynamic Force ◽  
Micro Air Vehicle ◽  
Wind Gust ◽  
Aerodynamic Forces ◽  
Promising Candidate ◽  
Flapping Motion ◽  
Wind Gusts ◽  
Air Vehicle ◽  
Before And After

The goal of our research is to develop a micro air vehicle (MAV) that is strongly stable in a wind gust. After observation of flights of an insect and a bird, we conjectured that an ornithopter would be a promising candidate as a high-performance MAV. In this paper we demonstrate the clear advantage of an ornithopter over an airplane with propellers. The variations in the aerodynamic forces acting on the two aircrafts, which generate the same thrust under the condition of no wind gust, were compared when they encountered gusts of wind. The consumed power, or alternately the period of one cycle of flapping motion and that of one rotation of propeller(s), remained constant before and after they encountered a wind gust. The following results were obtained: The variations of the aerodynamic force of an ornithopter by vertical and frontal wind gusts were slightly smaller than those of an airplane with one or two propellers. The variation in the aerodynamic force of the former by a side wind gust was smaller than that of the latter when the tip speed of the propeller and the flapping amplitude of the ornithopter were small.

Development of Energy-Absorbing Composite Utility Pole

2003 ◽  
Vol 1851 (1) ◽  
pp. 149-157 ◽  
Author(s):  
Richard Foedinger ◽  
John F. Boozer ◽  
Maurice E. Bronstad ◽  
James W. Davidson
Keyword(s):  
Energy Absorption ◽  
Functional Performance ◽  
Weight Ratio ◽  
Safety Performance ◽  
Performance Criteria ◽  
Electrical Safety ◽  
Roadside Safety ◽  
Utility Pole ◽  
Utility Poles ◽  
Energy Absorbing

The serious hazard presented by unforgiving timber utility poles installed along the nation’s roadways has long been recognized by the roadside safety community. However, relatively little attention has been devoted to the development of safer utility poles beyond breakaway timber pole designs. A new generation of utility pole designs that use energy-absorbing composite materials offers a solution to the development and implementation of safer utility poles that have a cost advantage over breakaway timber poles and can be tailored to achieve the desired functional performance and energy absorption characteristics inherently without the need for additional strength members or add-on energy absorption devices. This research has resulted in the development of an energy-absorbing fiberglass-reinforced composite (FRC) utility pole design that meets structural performance requirements for environmental loading in accordance with the National Electrical Safety Code for Class 4 poles and safety performance criteria in compliance with NCHRP Report 350 Test Level 2 conditions for utility poles. Developmental testing and analyses were performed to support the development of a prototype design for demonstration testing. Full-scale crash testing has demonstrated the ability of the composite pole to absorb the vehicle’s impact energy by progressive crushing and fracture propagation as the vehicle is brought to a controlled stop. In addition to offering improved safety performance, the energy-absorbing FRC pole provides significant functional advantages, such as reduced weight, an improved strength-to-weight ratio, increased longevity, ease of installation, low maintenance, and resistance to environmental degradation.

Sign in / Sign up

Export Citation Format

Share Document