Preventing Wind-Induced Oscillations of Structures of Circular Section.

Walshe, De; Wooton, Lr

doi:10.1680/iicep.1970.6689

Cited by 22 publications

(3 citation statements)

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“…According to full-scale observations reported in [102], for large vibration amplitudes (e.g., 3-5 % of the diameter) the vortices re-establish themselves and the strakes become ineffective. An alternative type of spoiler device is a perforated shroud placed over the top 25 % of the stack [6,103].…”

Section: Tall Chimneys and Stacksmentioning

confidence: 99%

Aeroelasticity in Civil Engineering

Simiu

2021

A Modern Course in Aeroelasticity

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Fluid-structure interaction occurs in civil engineering applications to flexible long span bridges and tall slender buildings. This chapter provides an authoritative account of current best practices and modeling methods.Certain types of civil engineering structures can be subjected to aerodynamic forces generated by structural motions. These motions, called self-excited, are in turn affected by the aerodynamic forces they generate. Behavior associated with selfexcited motions is called aeroelastic. The flutter of the Brighton Chain Pier Bridge (Fig. 1) and, more than one century later, the original Tacoma-Narrows Bridge (Fig. 2) are notorious examples of aeroelastic behavior. Tall chimneys and buildings may also respond aeroelastically and need to be designed accordingly. The John Hancock building in Boston, which has a relatively flat shape in plan (Fig. 3), has experienced across-wind and torsional motions of sufficient severity to warrant the installation of a large tuned-mass damper system at its top. These motions may have been due to aeroelastic effects. 1 Under certain conditions power lines experience aeroelastic behavior referred to as galloping.Aeroelastic phenomena of interest in civil engineering differ from those studied in aeronautical engineering in two important ways. First, civil engineering structures are typically bluff, although in modern suspended-span 2 bridge design streamlined box-like deck shapes are increasingly being used. Second, unlike flows typically considered in aeronautical engineering, the flows in which civil engineering structures are immersed are in most cases turbulent. Atmospheric turbulence depends upon the thermal stratification of the flow. At very high wind speeds mechanical turbulence is dominant and the air flow may therefore be assumed to be neutrally stratified.1 Recent research on tall buildings with relatively large ratio between depth and width suggests that this was indeed the case-see Sect. 2.2.2. To the writers' knowledge, for legal or other reasons, detailed technical reports on the wind-induced behavior of the John Hancock building are not available in the public domain. 2 The term "suspended-span bridge" covers both suspension bridges and cable-stayed bridges.

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Section: Tall Chimneys and Stacksmentioning

confidence: 99%

Aeroelasticity in Civil Engineering

Simiu

2021

A Modern Course in Aeroelasticity

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“…The negative impact of VIV on structures, including unsteady forcing as well as drag amplification, has led to the development of multiple means of VIV suppression, as reviewed in [144,133,35].…”

Section: Viv Suppression Mechanismsmentioning

confidence: 99%

Passive wake detection using seal whisker-inspired sensing

Beem¹

2015

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This thesis is motivated by a series of biological experiments that display the harbor seal's extraordinary ability to track the wake of an object several seconds after it has swum by. They do so despite having auditory and visual cues blocked, pointing to use of their whiskers as sensors of minute water movements. In this work, I elucidate the basic fluid mechanisms that seals may employ to accomplish this detection. Key are the unique flow-induced vibration properties resulting from the geometry of the harbor seal whisker, which is undulatory and elliptical in cross-section.First, the vortex-induced vibration (VIV) characteristics of the whisker geometry are tested. Direct force measurements and flow visualizations on a rigid whisker model undergoing a range of 1-D imposed oscillations show that the geometry passively reduces VIV (factor of > 10), despite contributions from effective added mass and damping. Next, a biomimetic whisker sensor is designed and fabricated. The rigid whisker model is mounted on a four-armed flexure, allowing it to freely vibrate in both in-line and crossflow directions. Strain gauges on the flexure measure deflections at the base. Finally, this device is tested in a simplified version of the fish wake -seal whisker interaction scenario. The whisker is towed behind an upstream cylinder with larger diameter. Whereas in open water the whisker exhibits very low vibration when its long axis is aligned with the incoming flow, once it enters the wake it oscillates with large amplitude and its frequency coincides with the Strouhal frequency of the upstream cylinder. This makes the detection of an upstream wake as well as an estimation of the size of the wake-generating body possible. A slaloming motion among the wake vortices causes the whisker to oscillate in this manner. The same mechanism has been previously observed in energy-extracting foils and trout actively swimming behind bluff cylinders in a stream. Dave, Jason, Gabe, Pablo, Remi, and Yahya were postdocs when we first met.Thank you for being approachable and sharing much needed advice all along the way.Your love of science has inspired me to be more inquisitive.Brandon, Chris, Matthew, and Patrick were undergrads or high school students who spent their summers working in the Tow Tank with me. Thanks for giving me the chance to practice being a mentor, moving this research forward a lot faster than I could do on my own, and helping me lift the mega-whisker in and out of the tank! May you all keep on building and exploring.Thanks to Kathy Streeter and the New England Aquarium staff for helping me understand more about real harbor seals. They graciously collected shed whisker specimens and allowed me to take many close-up pictures of their seals.Thanks to all the people who helped me prepare for and make it through research cruises: Eric Hayden, Terry Hammar, and Hanu Singh for contributing their expertise 5 to help me make my first ocean-ready sensor, all parties involved in the first UNOLS Chief Scientist Training Cruise se...

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“…Contrariwise, the passive control methods are also applied to suppress the FIV and VIVs. Some passive methods are focused on the natural frequency of the structure such, as employing wire ropes [18], tripping wires [19], and non-linear stiffness [20], while the others are concentrated on the fluid flow, such as adding hemispherical bumps on the cylinder to reduce the vortex shedding by Owen et al [21]. Passive methods, such as adding a non-linear dynamic absorber, have lower cost of maintenance, and are more interesting [22].…”

Section: Introductionmentioning

confidence: 99%

Positive Position Feedback Control of a Galloping Structure

Jamalabadi

2018

Acoustics

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In this study, the suppression of wind-induced oscillations of a D-shaped prism mounted on a cantilever beam by means of a positive position feedback (PPF) controller is investigated. The assumed mode method is applied to determine the stiffness, mass and non-linear force matrixes of a second order ordinary differential equation system. The positive position feedback control by use of a sensor-actuator piezoelectric is implemented on the galloping system to suppress the mechanical oscillations. The results show that the PPF controller is a powerful method to decrease the galloping amplitude of the D-shaped prism. The numerical results are in a good agreement with experimental results.

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Preventing Wind-Induced Oscillations of Structures of Circular Section.

Cited by 22 publications

References 0 publications

Aeroelasticity in Civil Engineering

Aeroelasticity in Civil Engineering

Passive wake detection using seal whisker-inspired sensing

Positive Position Feedback Control of a Galloping Structure

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