U.S. patent application number 09/738346 was filed with the patent office on 2001-10-04 for distributed aerodynamic and mechanical damping of cables with active smart control.
Invention is credited to Gardner, Thomas B., Mehta, Kishor C., Phelan, R. Scott, Sarkar, Partha P., Zhao, Zhongshan.
Application Number | 20010026037 09/738346 |
Document ID | / |
Family ID | 22622499 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026037 |
Kind Code |
A1 |
Phelan, R. Scott ; et
al. |
October 4, 2001 |
Distributed aerodynamic and mechanical damping of cables with
active smart control
Abstract
A system for the mitigation of cable stay vibrations, typically
induced by wind and rain, utilizes a plurality of active damper
bands positioned along the cable stay. Each damper band includes a
shiftable mass and an energizing device for facilitating assisted
shifting of the mass. A control assembly can actuate all or
selected ones of the energizing devices in response to sensed
magnitudes of cable stay vibration.
Inventors: |
Phelan, R. Scott; (Lubbock,
TX) ; Sarkar, Partha P.; (Ames, IA) ; Mehta,
Kishor C.; (Lubbock, TX) ; Gardner, Thomas B.;
(Lubbock, TX) ; Zhao, Zhongshan; (Houston,
TX) |
Correspondence
Address: |
Douglas R. Hanscom
JONES, TULLAR & COOPER, P.C.
Eads Station
P.O. Box 2266,
Arlington
VA
22202
US
|
Family ID: |
22622499 |
Appl. No.: |
09/738346 |
Filed: |
December 18, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60171094 |
Dec 16, 1999 |
|
|
|
Current U.S.
Class: |
267/136 ;
188/378 |
Current CPC
Class: |
E01D 19/16 20130101;
F16F 7/1005 20130101 |
Class at
Publication: |
267/136 ;
188/378 |
International
Class: |
F16M 001/00 |
Claims
What is claimed is:
1. An active cable damping device comprising: a cable damper band
adapted to be positioned on a cable subject to oscillations; a
shiftable mass supported for movement in said cable damper band in
response to oscillations of the cable; and an energizing device
positioned in said cable damper band and being operable to effect
shifting of said shiftable mass in said cable damper band
independently of oscillations of the cable.
2. The active cable damping device of claim 1 wherein said cable
damper band includes a plurality of shiftable mass receiving
chambers.
3. The active cable damping device of claim 2 wherein each of said
shiftable mass receiving chambers includes at least one of said
energizing devices.
4. The active cable damping device of claim 1 wherein said
shiftable mass is a viscous fluid.
5. The active cable damping device of claim 2 wherein said
energizing device is a rotatable paddlewheel.
6. The active cable damping device of claim 1 wherein said
shiftable mass is at lease one pendulum.
7. The active cable damping device of claim 6 wherein each said at
least one pendulum is supported for movement by a pendulum support
shaft.
8. The active cable damping device of claim 7 further wherein said
energizing device includes means to rotate each said pendulum
support shaft.
9. The active cable damping device of claim 1 wherein said cable
damper band is provided with an aerodynamic outer shape.
10. A method for controlling cable oscillations including:
providing a cable oscillation damper band having a shiftable mass
and a shiftable mass energizing device; securing said cable
oscillation damper band to a cable subject to oscillations; sensing
oscillations in the cable; actuating said shiftable mass energizing
device in response to said sensed oscillations in the cable; and
using said energizing device to shift said shiftable mass in said
damper band to counteract the oscillations in the cable.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The subject patent application claims the benefit of U.S.
Provisional Application Ser. No. 60/171,094, which was filed on
Dec. 16, 1999. The disclosure of that provisional application is
hereby incorporated herein by reference. The subject patent
application is also related to U.S. application Ser. No.
09/643,754, filed Aug. 28, 2000. The disclosure of that patent
application is also hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention is directed generally to the
aerodynamic and mechanical damping of cable stays. More
specifically, the present invention is directed to the aerodynamic
and mechanical damping of cable stays by utilizing active devices.
Most particularly, the present invention is directed to the
structure and to the use and control of active aerodynamic damper
bands applied to cable stays for the purpose of mitigation of
wind/rain induced cable stay vibrations.
[0003] Current approaches to controlling large amplitude cable stay
vibrations are passive. No active sensing or control mechanisms are
utilized. The implementation of an active, smart cable vibration
damping system is presented in the subject invention. The system of
the present invention employs distributed aerodynamic rings along
with small, embedded mechanical dampers, such as shiftable media,
pendulums, and/or spring type inertial masses that may be energized
using active smart control when the cable vibration reaches a
threshold limit. Due to the extreme heights at which cables are
mounted, efforts in active smart control are focused on
low-maintenance damping techniques and low-cost cable
modifications.
DESCRIPTION OF THE PRIOR ART
[0004] In recent years, large-amplitude cable stay vibrations have
been observed on a number of bridges in the U.S. and abroad during
relatively low wind speeds in the range of 7 to 14 m/s (1530 mph),
with and without the presence of rain. Rain and wind-induced cable
stay vibration is an aerodynamic phenomenon that was relatively
unknown and did not receive adequate attention from bridge
designers thus resulting in the need for mitigation devices.
Excessive vibrations are detrimental to the fatigue life of the
cable stays and cause distractions to the passing motorists.
[0005] The vibration of cable stays is most prevalent during low
wind speeds, below 14 m/s (30 mph), and accompanying moderate to
heavy rain. In addition, vibrations may also occur at high wind
speeds, above 22 m/s (50 mph), without rain. The cause of the
vibration problem at low wind speeds with rain is believed to be
the change in cross-sectional shape of the cable or cable stay that
occurs when rain forms a rivulet along the cable. This modification
of the cross section of the cable stay affects the aerodynamics of
the cable stay, resulting in large vibrations at wind speeds well
below known vortex shedding speeds for cylindrical cable stays in a
specific vibration mode. Cable stay vibrations can be severe and
have led to concerns that they are contributing to significant
fatigue loads on the cables. At risk is the material that makes up
the cable stay itself, as well as the anchorage devices.
[0006] Investigations at the Fred Hartman Bridge located at
Baytown, Tex., and at the Veteran's Memorial Bridge located at Port
Arthur, Tex. have shown the existence of a large number of
rain/wind induced cable stay vibrations. Over 5000 five-minute
"triggered" events of cable stay accelerations have been recorded
in just over two years. "Triggered" events are recorded when a
predetermined acceleration and/or wind speed threshold is exceeded.
It has been noted that each individual cable seems to vibrate at a
particular lower-mode shape, but typically not the first mode. For
example, a long Fred Hartman stay cable, 183 m (601 ft) in length
with a fundamental frequency of 0.65 Hz, vibrates predominately in
the 3.sup.rd mode and not in the first two. Similarly, a mid-size
Fred Hartman stay cable, 87 m (286 ft) in length with a fundamental
frequency of 1.2 Hz, was found to vibrate predominately in the
2.sup.nd mode and not in the first.
[0007] Higher modes of vibration in the cables were also found on
both the Fred Hartman and the Veterans's Memorial bridges. It is
generally accepted, though unproven, that cables vibrating in lower
modes cause more damage than cables vibrating in higher modes,
since lower-mode vibrations generally cause larger displacements.
However, it is entirely possible that higher mode vibrations occur
often enough to produce significant fatigue loadings on the stay
cables due to cycles of reversed stressing.
[0008] Considering the physics of the rivulet formation, it is
difficult to conceive that the rivulet is consistently located at
the most critical location along the full cable length; there is
lack of full-scale information. It is possible that the rivulet
that primarily causes the vibration at the lower wind speeds forms
at the critical location only over a partial cable length. This
could explain why there is a preference for certain lower-modes to
vibrate.
[0009] Currently, cable stay oscillations caused by wind/rain
induced aerodynamic forces are controlled by one, or by a
combination, of the following methods: 1) single-point mechanical
dampers, typically at the base of each cable, 2) restraining cable
devices connecting adjacent cables at various locations along the
length of the cable, resulting in a reduced effective length for
each cable and/or 3) aerodynamic damping approaches such as
grooves, protuberances or circular rings. The former two methods
are considered concentrated damping mechanisms, while the latter is
considered distributive.
[0010] For a distributed mitigation device, such as the aerodynamic
rings, it is possible to completely solve the vibration problem by
installing the rings only on a partial length of the cable-and not
along the full cable length. A distributed aerodynamic ring system
will be effective in eliminating significant vibrations in all
vibration modes, unlike a linear mechanical damper (hydraulic) that
is optimized to be effective for a single mode.
[0011] Mechanical dampers generally are linear viscous mechanisms,
somewhat similar to an automobile shock absorber. However, they
also can be non-linear, computer-controlled mechanisms. Mechanical
dampers are a proven technology and are relatively easy to install.
However, they generally are: 1) expensive systems-and can be
expensive to install, 2) may need periodic maintenance, and 3)
typically require substantial cable stay displacements to occur
before the damping mechanism becomes functional.
[0012] Restrainers are employed to tie adjacent cable stays
together at discrete points along the cable. Restrainers generally
are effective solutions, as one cable adjacent to another
oscillating cable generally will not be oscillating. For cases when
adjacent cables do oscillate together, many times they will vibrate
out of phase or in different modes from each other. In these cases,
restrainers are able to utilize the stiffness of adjacent cables to
prevent a particular cable from oscillating. If the restrainer is
unable to prevent oscillations, it continues to be considered
beneficial in that it causes the cable stay to vibrate at higher
modes as it "fixes" intermediate nodal points. Again, though a
higher mode vibration is visually less dramatic, significant
fatigue loadings can occur. Restrainers also are a proven
technology. However, they are fairly difficult to
install-particularly at cable stay heights generally required.
Also, restrainers have had problems due to failure through
loosening of attachments to the cable stays.
[0013] Although mechanical dampers are more popular, aerodynamic
devices have certain advantages. They can be very effective over a
wide range of wind speeds, and perform even better at high wind
speeds, if properly designed. These aerodynamic devices are
generally cost-effective and demand little maintenance efforts,
thus they can function reliably. They can also be designed to be
aesthetically pleasing; and reduce the effect of the aerodynamic
forces before the cable begins to vibrate, where mechanical devices
must dissipate energy of the cables that are already vibrating.
[0014] Various forms of aerodynamic solutions to the vibrations of
smooth-surfaced, circular cable have been sought. While some can be
adopted only at the design stage, others are feasible for
retrofitting as well. Aerodynamic countermeasures usually modify
the surface of the cable cross section to improve its aerodynamic
performance in terms of reducing the excitation from the moving air
or increasing the aerodynamic damping. Three examples of generally
known types of cable surface/cross section modifications are
surface dimpling, parallel axial protuberances, and elliptical
plates. The elliptical plates were found to be the most effective
of the three types of cable modifications. A variation of the
elliptical plate is the helical strake, which has been used
successfully on chimneys to reduce vortex-induces vibrations.
[0015] While the prior art has utilized various so-called passive
devices to attempt to mitigate the effects of wind/rain induced
cable stay vibrations, a need still exists for additional
solutions. These new and different solutions will overcome the
limitation of the prior art devices.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide an
active system for cable stay vibration mitigation.
[0017] Another object of the present invention is to provide an
active smart control system for cable stay vibration mitigation
using distributed aerodynamic rings.
[0018] Still a further object of the present invention is to
provide a smart control system using aerodynamic rings with
embedded mechanical dampers.
[0019] Yet another object of the present invention is to provide
aerodynamic rings having embedded mechanical dampers that are
energized using active smart control when cable vibrations reach a
threshold value.
[0020] As will be set forth in greater detail in the description of
the preferred embodiment, which are presented subsequently, the
distributed aerodynamic and mechanical damping of cables with
active smart control, in accordance with the present invention
utilizes a plurality of aerodynamic damper bands or rings that are
positionable at spaced lengths along the cable stay to be dampened.
Each damper band has an outer, aerodynamic shape and a hollow or
partially hollow interior. The interior of the damper band is
provided with active mechanical dampers. These can take the form of
shiftable weights, pendulums, spring type inertial masses and other
movable or shiftable bodies. In one embodiment of the present
invention, these active, shiftable masses are characterized as
active, "smart" masses. This means that they are caused to shift by
a control system that senses cable vibrations or oscillations above
a threshold level and then activates the shiftable masses in a
manner which will effectively counteract the cable or cable stay
vibrations or oscillations.
[0021] The system of aerodynamic and mechanical damping of cables
with active smart control, in accordance with the present
invention, provides superior damping of cable stay vibration with
less cable fatigue. It also will reduce the number of required
aerodynamic damper bands or rings required for each cable. A
further benefit of the subject invention is its ability to
eliminate ice build-up on the cable stays. An additional benefit is
the provision of innovative aesthetic treatments to the overall
bridge structure.
[0022] The active smart control system of the present invention is
directed primarily for use with a distributed aerodynamic ring or
band system. It is also usable for a computer-controlled single
point mechanical damper system which could be used either by
itself, or in combination with an aerodynamic ring or damper band
system.
[0023] The distributed aerodynamic and mechanical damping of cables
with active smart control in accordance with the present invention
overcomes the limitations of the prior art device. It represents a
substantial advance in the field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] While the novel features of the distributed aerodynamic and
mechanical damping of cables with active smart control in
accordance with the present invention are set forth with
particularity in the appended claims, a full and complete
understanding of the invention may be had by referring to the
detailed description of the preferred embodiments, as will be set
forth subsequently, and by referring to the accompanying drawings,
in which:
[0025] FIG. 1 is a cross-sectional schematic view of a first
preferred embodiment of an aerodynamic ring with a shiftable mass
in accordance with the present invention;
[0026] FIG. 2 is a cross-sectional schematic view of a second
preferred embodiment of an aerodynamic ring with a shiftable
mass;
[0027] FIG. 3 is a block diagram of an active control system for a
shiftable mass dampening system in accordance with the present
invention;
[0028] FIG. 4 is a schematic side elevation view of a portion of a
bridge with active aerodynamic damping rings on one cable stay;
[0029] FIG. 5 is a block diagram of an active smart control system
for a shiftable mass damping system; and
[0030] FIG. 6 is a schematic side elevation view of a portion of a
bridge with a plurality of smart active aerodynamic damping rings
arranged on a plurality of cables.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] In our prior U.S. patent application Ser. No. 09/643,754,
filed Aug. 28, 2000, which prior patent application is referenced
previously in this patent application, and which is hereby
expressly incorporated by references herein, the structure and
useage of passive aerodynamic damper bands has been discussed in
detail. These bands are passive in nature since they are secured to
the cable stays of a bridge and depend on their aerodynamic shape
to mitigate cable stay vibrations which are caused by wind and
rain. The devices and systems of the present invention, while
incorporating and utilizing the benefits of the aerodynamic damper
bands of the previous invention, also provide active control
devices and systems that will even more effectively dampen wind and
rain induced cable stay vibrations.
[0032] Referring initially to FIG. 1, there may be seen generally
at 10 a first preferred embodiment of an active damper band in
accordance with the present invention. This active damper band 10
is similar in overall shape to the damper bands described in the
above-referenced prior U.S. patent application. A flexible ring or
band 12 is securable about the outer circumference of a cable stay
14. An integral securement strap or other suitable securement
device 16, which is depicted in dashed lines in FIG. 1, is
incorporated in, or is inserted through the hollow interior portion
18 of the flexible band 12. Ends of the securement straps 16 are
connected to each other as schematically depicted at 20 in FIG. 1.
It will be understood that the flexible ring 12 can be made of any
suitable plastic or similar flexible yet weather resistant material
and that the securement straps 16 could be a wire tie or another
similar type of quick connecting device that would lend itself to
quick field assembly, either by manual or by mechanical means.
[0033] The hollow interior 18 of the flexible ring 12 of the first
preferred embodiment of the active damper band in accordance with
the present invention, is preferably divided into several shiftable
mass receiving chambers, with three such chambers 22 being depicted
in FIG. 1. A pair of interior barriers 24 and two end barriers 26
are positioned in the interior 18 of the flexible band or ring 12
to define the separate shiftable mass receiving chambers 22.
[0034] Each shiftable mass receiving chamber 22 is partially filled
with a shiftable mass 28. This shiftable mass 28 is preferably a
viscous fluid or another flowable material that can shift locations
in its shiftable mass chamber 22 either passively; i.e. solely due
to movement of the damper band, or actively. The free space within
each chamber 22 can be either filled with air or can be maintained
under a vacuum. A suitable energizing device 30, or several such
energizing devices 30 can be placed in each of the shiftable mass
chambers 22, as may be seen in FIG. 1. Each such energizing device
30 could be a small impeller driven by an electrically powered
micro motor which is not specifically illustrated. As will be
discussed shortly, if the system is a smart system, the energizing
devices will be controlled for selective operation to shift the
shiftable mass 28 in each chamber 22 so as to counteract the
movement of the cable stay. If the shiftable mass 28 is moved
solely as a result of the shifting of the cable stay, it will still
tend to counteract the shifting or oscillating movement of the
cable stay. For example, if the cable stay 14 depicted in FIG. 1 is
caused by wind and rain, to shift to the right, the shiftable mass
28 in the upper chamber 22 will tend to travel to the left side of
the upper chamber 22. If the damping system is an active system,
the energizing device 30 at the right end of the upper chamber 22
can be activated to more rapidly shift the shiftable mass 28 from
the right side of the upper chamber 22 to the left side of the
upper chamber 22. If the system is an active smart system, only
selected ones of the energizing devices 30 may be operated with the
decision of which devices 30 to be operated depending on which
cables stays are vibrating, as well as the magnitude of each
vibration. The result, whether the shiftable mass is caused to move
either solely by reacting to the movement of the cable stay, or
also as a result of the operation of the energizing device 30, is
to dampen the cable stay oscillations. The energizing devices 30
will preferably be electrically powered through suitable electric
leads that are not specifically shown in FIG. 1 of the drawings.
Such electric power can also be used to operate small heating
elements, also not specifically shown, that could be incorporated
into the walls of the flexible rings 12. Such heating elements
would be effective in heating the damping rings 12 to eliminate
possible ice buildup on the outer surfaces of the flexible rings
12.
[0035] Turning now to FIG. 2 there is shown, generally at 40 a
second preferred embodiment of an active damper band or ring in
accordance with the present invention. This active damper band 40
is again secured about an outer surface of a cable stay 14 and has
an aerodynamic shape similar to the flexible ring 12 described in
connection with FIG. 1. This damper band 40 can be comprised of
several hinge-connected sections, or can be fabricated as a single
ring of a suitable metal or other material. The circular body 42 of
the damper band 40 is provided with at least one bulge or enlarged
area 44. In the depiction of the active damper band 40 shown in
FIG. 2, there is one bulge 44 and it is located at the lower
portion of the circular band body 42. Location of this bulge 44 at
other orientations, as well as the provision of more than a sole
bulge 44 is within the purview of the subject invention. A
shiftable mass is provided in the bulge or bulges 44 formed in the
band body 42 of the second preferred embodiment 40 of the active
damper band in accordance with the present invention. This
shiftable mass takes the form of one or a plurality of pendulums
46, each of which is supported for pivotable movement by a support
shaft 48. As was the case with the first embodiment 10 of the
active damper band described previously, the shiftable mass; i.e.
the pendulum or pendulums 46 placed in the bulge or bulges 44 of
the band body 42 of the second preferred embodiment 40 of the
active damper band can be excited either passively as a result of a
response to shifting of the cable due to wind and rain induced
oscillations, or can be excited actively. In the latter situation,
the pendulum supporting shaft or shafts 48 are the energizing
mechanism and can be caused to pivot by suitable electrically
operated devices, such as micro motors, that are not specifically
shown. If the system is an active smart system, again as will be
discussed shortly, the energizing mechanisms can be caused to shift
the pendulum or pendulums in advance of a shifting or a similar
movement that the cable or cable stay 14 is sensed to be about to
make. In this second embodiment, as in the first, the shiftable
mass is shifted in a direction in opposition to the movement of the
cable stay to which the active damper band is attached. Such an
opposing shifting of the shiftable mass 28 or 46 in the active
damper band 12 or 42, respectively, will dampen the oscillation of
the cable stay 14.
[0036] In both of the two embodiments of an active damper band
discussed above, the bands are placed on the exterior surface of
the cable or cable stay 14. This is primarily a retro-fit
arrangement, or one where an accomplishment of aerodynamic damping
is important in conjunction with the damping provided by the
shiftable mass. In new construction, the shiftable mass could be
placed interiorly of the cable stay. Since a cable stay is
typically a sheath that is placed about a group or bundle of
individual cables and in which void areas are filled with a
settable material, it will be possible to place the shiftable
masses typically still in the above-described bands, within the
cable stay. While this may lead to an increased overall cable stay
diameter, it preserves a smooth exterior surface that is less apt
to experience ice buildup. Of course, the location of the damper
bands inside the cable stay will eliminate any aerodynamic benefit
provided by exteriorly mounted bands. In such a situation of
interior bands and shiftable masses, active control of the
shiftable masses and particularly active smart control of the
shiftable masses becomes the mechanism by which oscillations of the
cable stay are counteracted.
[0037] The most effective damping of cable stay vibration and
oscillations may well entail some combination of the several
mechanical and aerodynamic device discussed above. For instance, it
may well be that a solution could include an exteriorly positioned
active damper band having an aerodynamic shape. The damper band
could include right and left chambers such as chambers 22 discussed
in connection with the damper band 10 of FIG. 1, with their
shiftable masses 28 and included paddle wheel type energizing
devices 30. A pendulum 46 or a plurality of pendulums 46, as shown
in FIG. 2 could also be incorporated into the same active damper
band. The shiftable masses 28 on the left and right sides of the
damper band would control vertical oscillations of the cable stay
14. It is quite possible that no operation of the energizing
devices such as the paddle wheels 30 will be required with
acceleration forces of .gtoreq.1 g. If the acceleration is
.ltoreq.1 g the energizing paddle wheels 30 may be used. Similarly,
if the pendulum is to be effective at accelerations .ltoreq.1 g, it
is quite likely that the energizing device for the pendulum, such
as the rotatable pendulum support shaft 48 may be required to be
operated.
[0038] Turning now to FIGS. 3 and 4 there is schematically depicted
what will be referred to an "active" or "active only" system that
is useable to counteract and to dampen wind and rain induced
vibrations and oscillations in the cable stays of a bridge.
Referring initially to FIG. 4, there is schematically depicted a
portion of a bridge, generally at 60. The bridge 60 is constructed
with generally well known towers 62 and a plurality of cable stays
64. An outer or upper one of these cable stays 64 is shown as being
provided with a number of active damper bands 66 spaced along its
length in accordance with the spacing parameters discussed in
detail in the inventors' prior application. This cable damper band
spacing is preferably three times the cable stay diameter or 3D.
Several of the active damper bands are also provided with embedded
accelerometers. These accelerometer bands are denoted at 68 in FIG.
4. The damper bands 66 and 68 are all electrically connected to a
remote processing station 70 by suitable leads which are not shown
in detail. The remote processing station 70 is joined to a central
power communication and processing station generally at 72 by
suitable power and communication lines 74. In operation in the
active mode, as shown in the schematic diagram of FIG. 3, the
accelerometer receiving bands 68 will sense oscillations,
vibrations or other movement in the cable stay 64 to which they are
attached. It will be understood that the damper bands 66 of the
present invention are typically attached to all or the bulk of the
cable stays 64, not merely to the outermost one, as depicted in
FIG. 4. The accelerometers provide their readings to the remote
processing station 70 which includes a suitable data acquisition
unit 76, as shown in FIG. 3. The data is received by the remote
processing station 70, and is transferred to the central processing
station 72. The particular cable stay or cable stays 64 which are
being caused to oscillate are identified. In response, all of the
active damper barrels 66 on the particular cable stay or cable
stays 64 are energized. This results in a shifting of the shiftable
masses in each of the damper bands 66. As discussed previously, the
operation of the energizing devices, either 30 or 48 may occur at
cable stay acceleration levels only within specific ranges. If the
cable stays are being subjected to acceleration forces above 1 g,
for example, the operation of the energizing devices may be
unnecessary. The forces imparted to the shiftable masses by these
high cable stay acceleration forces will be sufficient to properly
shift the shiftable masses to counteract the cable stay
oscillations without the assistance of the energizing devices. If
the cable stay oscillations, as measured by the accelerometer
carrying damper bands 68 is below, for example 1 g, then it may be
appropriate to operate the energizing devices 30 or 48 to aid in
the dampening movement of the shiftable masses 28 or 46.
[0039] A more sophisticated, smart active system of cable stay
oscillation damping, in accordance with the present invention, is
depicted in FIGS. 5 and 6 in which similar structures are
identified by the same reference numerals. In this smart active
system, the central power communication and processing station 72
is able to energize selected ones of the smart active rings on
individual cables, again based on readings provided by special
accelerometer bearing ones of the active damper bands 66 that are
mounted on the plurality of cable stays 64. Since the smart active
system is more effective in damping cable stay oscillations, it is
possible that the active damper bands will need to be placed on
only the lower third of the length of the longer cable stays and
only on the lower half of the length of the shorter cable stays, as
depicted schematically in FIG. 6. Similarly, since the smart active
system will be more effective than the active or active only
system, it is likely that a damper band spacing of four times the
cable stay diameter, or 4D may be sufficient.
[0040] As shown in the schematic diagram of FIG. 5, the cable stay
oscillations are sensed by the accelerometer carrying active damper
bands and the data is sent to the central processing station. In
the smart active system, a mitigation strategy processor 80 is
included in the central processing station. This processor 80
reviews the input from the accelerometer carrying active damper
bands and implements a strategy of activation of energizing devices
in selected ones of the active damper bands in a manner that will
be most effective in eliminating cable stay oscillations. It is a
requirement of such a smart active system that each damper band
would be specifically identifiable to the controlling system and
would be individually and particularly energized for damping, where
needed. As with the previously discussed active system, electrical
energy could be supplied to all of the damper bands for the purpose
of heating the damper bands to prevent ice buildup along the cable
stay.
[0041] A method for the distributed aerodynamic and mechanical
damping of cable stay oscillations using active devices has been
set forth fully and completely hereinabove. Both of the shiftable
masses are well suited for use with active control technology and
are effective in damping cable stay oscillations. Other
applications to other areas, such as the damping of elongated
supports situated in bodies of water, such as, for example, the
stabilization of offshore oil drilling rigs and production
platforms is also within the scope of the subject invention. It
will be apparent to one of skill in the art that various changes
in, for example the specific sizes and associated fluid densities
of the cable stays and damper bands, the particular bridge or
platform structure, and the like could be made without departing
from the true spirit and scope of the present invention which is
accordingly, to be limited only by the appended claims.
* * * * *