U.S. patent application number 10/831161 was filed with the patent office on 2004-12-23 for retractable strake and method.
Invention is credited to Butts, James C., Steinkamp, Jeffrey H..
Application Number | 20040258485 10/831161 |
Document ID | / |
Family ID | 32107506 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040258485 |
Kind Code |
A1 |
Steinkamp, Jeffrey H. ; et
al. |
December 23, 2004 |
Retractable strake and method
Abstract
A retractable strake is disclosed that includes an assembly of
flexible finger elements or flexible faces. The assembly, when
coupled to a structure, deflect at wind speeds greater than
approximately twenty mph or wind pressures greater than
approximately one psf. Accordingly, the strakes' retractable or
flexing feature does not contribute to the wind load when the wind
load is overly severe, while providing vortex shedding benefits
within a wind speed profile range.
Inventors: |
Steinkamp, Jeffrey H.;
(Quincy, IL) ; Butts, James C.; (Casco,
ME) |
Correspondence
Address: |
Baker & Hostetler LLP
Washington Square, Suite 1100
1050 Connecticut Avenue, N.W.
Washington
DC
20036
US
|
Family ID: |
32107506 |
Appl. No.: |
10/831161 |
Filed: |
April 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10831161 |
Apr 26, 2004 |
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10283202 |
Oct 30, 2002 |
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6726407 |
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Current U.S.
Class: |
405/211 ;
172/44 |
Current CPC
Class: |
H01Q 1/005 20130101;
H01Q 1/42 20130101; F15D 1/10 20130101 |
Class at
Publication: |
405/211 ;
172/044 |
International
Class: |
E02D 005/60 |
Claims
What is claimed is:
1. A system for reducing vortex shedding on an object, comprising:
a strake having a substantially polygonal shape; and flexible
attachment feet, wherein the strake is attached to the feet and the
feet are attached to the object.
2. The system of claim 1, wherein the strake deflects at wind
pressures greater than approximately one psf.
3. The system of claim 1, wherein the strake deflects at wind
speeds greater than approximately twenty mph.
4. The system of claim 1, wherein the strake's inner edge is
notched.
5. The system of claim 1, wherein the strake is attached to the
object by a single foot.
6. The system of claim 1, wherein the strake is substantially
rectangular.
7. The system of claim 1, further comprising: a plurality of
strakes, the plurality of strakes being arranged about the object
in a semi-helical form.
8. The system of claim 1, wherein the plurality of strakes are
arranged about the object in a plurality of semi-helical forms.
9. The system of claim 1, wherein the strake is molded to the
feet.
10. The system of claim 1, wherein the feet are molded into the
object.
11. The system of claim 1, wherein the strake is less than five
inches wide.
12. The system of claim 1, wherein a maximum height of the strake
is approximately 10 percent of an overall diameter of the
object.
13. The system of claim 1, wherein a surface of the strake is
patterned.
14. The system of claim 1, wherein the object is a radome.
15. The system of claim 1, wherein the object is a chimney.
16. The system of claim 1, wherein the object is a mast.
17. The system of claim 7, wherein the strakes of the plurality of
strakes are displaced from each other by approximately {fraction
(1/2)} inches.
18. An apparatus for reducing vortex shedding on an object,
comprising: vortex shedding means for shedding vortices about the
object, wherein the shedding means is flexibly retractable; and
attachment means for attaching the vortex shedding means to the
object, wherein at least one of the vortex shedding means or the
attachment means flexs when at least one of wind speeds are greater
than approximately twenty mph and wind pressures are greater than
approximately one psf.
19. The apparatus of claim 17, wherein the shedding means and the
attachment means are positioned in a semi-helical arrangement about
the surface of the object.
20. The apparatus of claim 18, wherein the attachment means is an
adhesive.
21. The apparatus of claim; 18, wherein the shedding means is
primarily a truncated flat surface.
22. The apparatus of claim 18, wherein the object is a radome.
23. A method for manufacturing an apparatus for reducing vortex
shedding on an object, comprising: arranging a plurality of
truncated two-side strake elements into an assembly of attachment
elements; and coupling the assembly of attachment elements to the
object, such that the assembly of strake elements deflects when at
least one of wind speeds are greater than approximately twenty mph
and wind pressures are greater than one psf.
Description
[0001] This non-provisional Continuation-in-Part application claims
the benefit and priority of pending U.S. patent application Ser.
No. 10/283,202 filed Oct. 30, 2002, titled, "RETRACTABLE RADOME
STRAKE AND METHOD," by Jeffrey H. Steinkamp and James C. Butts, the
contents of which are incorporated by reference in its
entirety.
FIELD OF THE FIELD OF THE INVENTION
[0002] The present invention relates generally to methods and
devices for reducing vortex shedding. More particularly, the
present invention is directed to a retractable strake for reducing
the susceptibility of an object to vortex shedding.
BACKGROUND OF THE INVENTION
[0003] It is well known that antenna structures or other tall
cantilevered cylindrical structures are subject to vibration caused
vortex shedding from wind forces. Vortex shedding refers to the
phenomenon that occurs when wind forces exert an unbalanced
crosswind pressure on opposite sides of the object. Vortex shedding
occurs as the air moving over the surface of a cylinder separates
from its hind quarters at about the four to five and seven to eight
o'clock positions forming a regular train of downwind swirling
eddies or vortices. The separation of the vortices for a given size
cylinder is periodic over a range of windspeeds. The pressure
exerted by the air is reduced as it separates from the cylinder.
Thus the separating vortices cause unbalanced pressure fluctuations
on the sides of the cylinder. If the frequency of the pressure
fluctuations is near or at the natural frequency of the structure,
large amplitude, potentially damaging cross wind vibrations can
occur.
[0004] For example, an antenna structure is typically surrounded by
a radome. A radome is a hollow cylindrical mast, typically made
from fiberglass, that is placed around an antenna structure to
protect it from elements, such as snow and ice, that could affect
the performance of the antenna. When a radome enclosed antenna
structure is erected and subjected to wind, the wind flows around
the circumference of the radome.
[0005] As shown in FIG. 1, when wind 10 flows around the radome it
separates on the downwind surface. As the air separates from the
cylinder a vortex is created. This typically occurs on one side at
a time. As the newly created vortex moves away downwind another
vortex is forming as the air separates from the opposite side of
the cylinder. Each time this occurs the side to side pressure on
the cylinder is unbalanced. FIG. 1 shows a possible pattern of
vortices created. The frequency of the shedding vortices is
dependent on the kinematic viscosity of the fluid (in this case
air), the wind speed, and the geometry of the object. The frequency
of vortex shedding can be either random or periodic. For a fixed
geometry (ie radome or smoke stack) the frequency is most strongly
dependent upon windspeed.
[0006] Antenna structures are designed to withstand established
maximum expected wind speeds as the local and national standards
dictate. The antenna structures are designed to withstand the
expected maximum wind speeds, which are measured from a reference
point location at or near ground level, occurring over a given time
period of fifty years or so. Typically, the maximum design wind
speeds are in excess of seventy mph. The wind pressure at the
antenna is scaled up to account for the increase in wind speed that
occurs as with the increased height of the structure.
[0007] Vortex shedding frequencies are either random or
significantly higher than any of the potentially damaging modes of
structural vibration at the expected maximum windspeed used for
structural design. The greatest vortex shedding problem occurs at
low wind speeds. The frequency of vortex shedding is periodic at
low wind speeds. A vortex will shed off of one side and then the
other at regular intervals, producing a periodic oscillating side
to side force. This can be damaging if the frequency of vortex
shedding is slightly above the first structural mode and the wind
speed driving the structure is greater than ten mph. This will
cause resonance, a condition where there is very little resistance
to oscillatory motion. Large displacements can develop causing
damage or failure. As shown in FIG. 1, the vortices 14, 16, 18 are
spiraling circles of wind that tend to increase the pressure
exerted on the radome 12.
[0008] When the pressure on one side of a structure differs from
the pressure on the opposite side of the structure, at a point in
time, the structure may move in a direction toward the side that is
lower in pressure. As the wind traverses the structure, the
pressure exerted on opposite sides of the structure may continue to
fluctuate, and cause the structure to vibrate, i.e., sway in
response to the alternating low pressure sides. For example, as
shown in FIG. 1, vortex 14 will cause radome 12 to move downward,
while vortex 16 will cause the radome 12 to move upward.
[0009] Several approaches have been used to eliminate or alleviate
vortex shedding. One of the most common is to use Scruton Windings,
which are helical rigid strakes added to the upper third of the
structure to disrupt the formation of the vortices. The rigid
strakes disrupt and diffuse the flow of wind around the radome,
such that the development of periodic vortices, which may cause the
antenna structure to resonate, is reduced. The negative side of
using helical rigid strakes is a large amount of windload is added
since the overall projected area has increased as well as the shape
is changed from a lower drag full cylinder to more flattened
cross-section.
[0010] Typically, radome enclosed antenna structures, such as a
television broadcasting antennas, experience vortex shedding at
wind speeds in the range of ten to twenty mph and/or at wind
pressures at or below one pound per square foot (psf). Thus,
strakes are mostly needed at wind speeds below approximately twenty
mph and/or wind pressures below one psf.
[0011] However, since the addition of the strakes to a radome
increases the cross-sectional area of the radome, the radome is
susceptible to greater wind loads that could affect the stability
of the antenna. Thus, components of the antenna structure, such as
an antenna mast and a supporting tower structure, have to be built
stronger to withstand the increased wind loads. As a result of the
added strakes, the cost to manufacture the antenna structure, or
any structure that endures wind forces, increases.
[0012] Accordingly, it would be desirable to provide a strake that
may reduce the susceptibility of wind-bearing structures such as
towers, chimneys, smoke stacks, masts, etc. to vortex shedding,
while reducing the contribution of the strake to the wind load of
the structure.
[0013] Further, it would be desirable to provide a strake that
helps to prevent vortex shedding without significantly increasing
the costs of associated structures, such as in the case of an
antenna, the antenna masts and supporting tower structures.
SUMMARY OF THE INVENTION
[0014] In various embodiments of the present invention, system(s)
for reducing vortex shedding on an object are provided. In one
aspect of the present invention, the system comprises a strake
having a substantially polygonal shape, and flexible attachment
feet, wherein the strake is attached to the feet and the feet are
attached to the object.
[0015] In another aspect of the present invention, the system
comprises vortex shedding means for shedding vortices about the
object, wherein the shedding means is flexibly retractable, and
attachment means for attaching the vortex shedding means to the
object, wherein at least one of the vortex shedding means or the
attachment means flexs when at least one of wind speeds are greater
than approximately twenty mph and wind pressures are greater than
approximately one psf.
[0016] In another aspect of the present invention, a method is
provided for manufacturing the present invention, comprising a
method for manufacturing an apparatus for reducing vortex shedding
on an object, comprising arranging a plurality of truncated
two-side strake elements into an assembly of attachment elements,
and coupling the assembly of attachment elements to the object,
such that the assembly of strake elements deflects when at least
one of wind speeds are greater than approximately twenty mph and
wind pressures are greater than one psf.
[0017] There has thus been outlined, rather broadly, the more
important features of the invention in order that the detailed
description thereof that follows may be better understood, and in
order that the present contribution to the art may be better
appreciated. There are, of course, additional features of the
invention that will be described below and which will form the
subject matter of the claims appended hereto.
[0018] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein, as well as the
abstract, are for the purpose of description and should not be
regarded as limiting.
[0019] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 illustrates a radome subjected to vortex
shedding.
[0021] FIG. 2 is a top view of a retractable strake in accordance
with the present invention.
[0022] FIG. 3 is a front elevation view of a retractable strake in
accordance with the present invention.
[0023] FIG. 4 is a front view and side views of another retractable
strake in accordance with the present invention.
[0024] FIG. 5 is a series of perspective views of the retractable
strake of FIG. 4 arranged about an antenna radome and a smoke
stack, in accordance with the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0025] Referring now to the figures, wherein like reference
numerals indicate like elements, there is shown in FIG. 2, a
retractable strake 20, 22 in accordance with the present invention,
that may be utilized to reduce vortex shedding. For purposes of
example, the present invention is described with respect to a
radome 12. However it should be understood by one of ordinary skill
in the art that a strake 20, 22 in accordance with the present
invention may have other applications, for towers, chimneys, smoke
stacks, masts, etc.
[0026] In an exemplary embodiment of the present invention, the
strake 20, 22 is constructed from an assembly of finger elements
24, 26, 28. The individual finger elements 24, 26, 28 are bristle
elements manufactured from a non-metallic material, for example, a
plastic, a nylon material, or a polyethylene material. In another
exemplary embodiment of the present invention, the finger elements
24, 26, 28 are formed from strips of a plastic material, for
example polyethylene.
[0027] It should be understood by one of ordinary skill in the art
that a strake 20, 22, when utilized in connection with an antenna
system, is made from a non-metallic material to prevent
interference with the transmission of signals from the antenna.
However, a strake 20, 22 of the present invention, when utilized
for other applications, such as preventing the occurrence of vortex
shedding on, for example, metal chimney stacks, may be manufactured
alternately from a metallic material.
[0028] Shown in FIG. 2, the assembly of finger elements 24, 26, 28
are arranged according to a predetermined pattern. The pattern is
designed such that the maximum height of the assembly of finger
elements 24, 26, 28 is approximately ten percent of the overall
diameter of the radome 12. In an exemplary embodiment of the
present invention, the diameter of the radome 12 is forty inches
and the maximum height of the assembly of finger elements is
approximately four inches.
[0029] In an exemplary embodiment of the present invention, at
least one side of the assembly of finger elements 24, 26, 28 is
curved, such that the strake 20, 22 can be curvedly positioned
about the radome 12.
[0030] Shown in FIG. 3, strakes 20, 22, in accordance with present
invention, are positioned on an exterior surface of a radome 12. In
an exemplary embodiment of the present invention, the strakes 20,
22 are positioned about the exterior surface of the radome, such
that they form a helical or nearly helical pattern about the
exterior surface of the radome.
[0031] By positioning the strakes 20, 22 in a helical-like type of
pattern about the radome 22, instead of straight out from the
radome 12, the strakes 20, 22 cover more surface area of the radome
12, and are able to diffuse the wind flow, and prevent the
development of vortices, such as vortices 14, 16, 18 shown in FIG.
1. Also, by configuring the strakes in a semi-helical manner, the
strakes are able to disrupt the air flow from any direction.
[0032] During operation, a strake 20, 22, in accordance with the
present invention, is retractable. For example, at wind speeds of
approximately twenty mph or less and/or wind pressures of
approximately one pound psf or less, when vortex shedding typically
occurs, the strake 20, 22 is erect, stiff and/or stable.
Accordingly, the strake 20, 22 creates the necessary turbulence to
avoid the development of vortices that could affect the stability
of, for example, a radome enclosed antenna structure.
[0033] However, the strake 20, 22 is designed such that, at wind
speeds above approximately twenty mph and/or wind pressures greater
than approximately one psf, when vortex shedding typically does not
occur, the strake 20, 22 deflects in the direction of airflow, as
the wind speeds and/or wind pressures increase. Thus, the
cross-sectional area of the radome 12, with the added strake,
decreases. Accordingly, the amount of wind load that the radome 12
is susceptible to also decreases. The deflection serves to retract
the strake.
[0034] In an exemplary embodiment of the present invention, at wind
speeds of approximately twenty miles per hour, and/or wind
pressures of twelve and one-half psf, the assembly finger elements
24, 26, 28 of a strake 20, 22 completely deflect, and lay along the
surface of the radome 12.
[0035] In an exemplary embodiment of the present invention, a
strake 20,22 is coupled to the radome via an adhesive. In an
exemplary embodiment of the present invention the radome 12 has
openings/ports through which the finger elements 24, 26, 28 are
inserted, and secured with adhesive, such as an epoxy. In a second
exemplary embodiment of the present invention, the individual
finger elements 24, 26, 28, of a strake 20, 22, are secured to the
exterior surface of the radome 12 with an adhesive.
[0036] FIG. 4 is a front view and side views of an exemplary
retractable strake 41. The retractable strake 41 is illustrated in
the front view as being upright and having a generally rectangular
shape. The retractable strake 41 is a preferably, but not
necessarily, made from a UV resistant elastomer and is fabricated
in relatively short sections. In this example, the retractable
strake 44 is of approximately 5 inches in length or less. The
retractable strake 41 employs a notch running along the edge
adjacent to the surface of the structure 43 to help elevate the
strake 41, to add flexibility to the strake 41, and also to provide
an alternate flow path around the strake 41, and is attached to the
surface via mounts 45. The mounts 45, shown here for illustrative
purposes, as bolts or hex head screws secure the strake 41 and
joined to the strake 41 through the feet 47, which are attached to
the strake 41 at its perimeter. The feet 47 are made from a
material that is pressure sensitive, specifically wind loads, to
result in the strake 41 having a bent configuration as shown in the
high speed illustration. The feet 47 serve as both the hinge point
and spring tension to return the strake 41 to its original low
vortex shedding position.
[0037] FIG. 5 is a series of perspective views of an exemplary
embodiment of this invention arrayed about an antenna radome 50 and
a smoke stack 60, respectively. The individual strakes 41 are
placed around the antenna radome 50 and smoke stack 60 in an
overlapping helical pattern to provide vortex shedding from any
angle of wind impingement. The strakes 41 are positioned with a
slight gap between adjacent strakes 41 to enable the adjacent
sections to fold without interference. The gap in the exemplary
embodiments is about 0.50 inches, however, the gap may be changed
according to design preferences. Similar to the benefits afforded
to the antenna radome 50, the smoke stack 60 can be protected from
oscillatory vibrations caused by vortex shedding.
[0038] While FIG. 5 shows the exemplary retractable strakes
according to this invention being placed about an antenna radome 50
and a smoke stack 60, it should be appreciated that the exemplary
retractable strakes may be placed about other structures, such as
sailing masts, towers, buildings, etc., to provide vortex shedding.
Also, while the exemplary retractable strakes are shown in FIGS. 4
and 5 as having a predominantly rectangular shape, alternate shapes
may be used as deemed appropriate. Additionally, alternate
positioning of the exemplary feet on the strake may be facilitated
based on the choice of materials used or the type of application.
For example, instead of using two feet, one foot may be used either
at a midpoint of the strake edge or at another desired location.
Furthermore, it should be appreciated that while the exemplary
embodiments illustrated the use of flexible feet to accomplish a
retractable function of the invention, other mechanisms may be used
without departing from the spirit and scope of this invention. For
example, mechanical springs may be attached to the strake to enable
the strake to retract under a given wind load. Alternatively,
portions of a section of the face of the strake may be made of a
material that allows the strake to flex when subject to a given
wind load rather than the entire face of the strake.
[0039] Furthermore, while the surface of the strake in FIGS. 4-5 is
shown as having a smooth face, alternative strake face designs may
be used utilizing any one of holes, grooves, dimples, patterns,
etc. that result in a distinct wind drag attribute to the strake.
Thus, strakes aligned about a structure may have an assortment of
wind effect profiles. For example, alternate strakes in the helical
pattern may flex at different wind speeds, according to design
preference. Additionally, it should be appreciated that a
non-helical arrangement of strakes may be implemented, or a
non-continuous arrangement, as desired.
[0040] In various exemplary embodiments of the present invention, a
strake may be assembled on a non-metallic support structure and/or
base that is molded into the structure of, or coupled to the
wind-bearing object with non-metallic hardware. In various other
exemplary embodiments of the present invention, the strake is
assembled within a non-metallic frame structure that is coupled to
the wind-bearing object with non-metallic hardware. It should be
understood by one of ordinary skill in the art that there may be
various other methods for coupling the strake to a wind-bearing
object.
[0041] The many features and advantages of the invention are
apparent from the detailed specification, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention which fall within the true spirit and scope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described, and accordingly, all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *