Brakes – Inertia of damping mass dissipates motion
Reexamination Certificate
2002-04-30
2004-03-16
Lavinder, Jack (Department: 3683)
Brakes
Inertia of damping mass dissipates motion
C188S267100, C188S268000, C188S381000, C267S136000, C174S042000
Reexamination Certificate
active
06705440
ABSTRACT:
FIELD OF INVENTION
The present invention is directed generally to a cable stay damper band and to its method of use. More specifically, the present invention is directed to a cable stay damper band that is usable with both new cables and as a retrofit to existing cables. Most particularly, the present invention is directed to cable stay damper bands that are securable to cable stays in an application pattern which significantly reduces fluid current induced, or other induced, vibrations in the cable. The cable stay damper bands are structured to be attached to or placed about both new cables as well as existing cables in a particular pattern or array. These cable stay damper bands can also be incorporated into the cable stay at the time of manufacture in order to eliminate the need for a later retrofit. Vibrations can be induced in a cable by the passage of any fluid, such as air or water, over the surface of a cable. The use of damper bands in accordance with the present invention has been very effective in the substantial reduction and near elimination of wind/rain induced vibrations in cable stays in air. Similarly, damper bands in accordance with the present invention can have a significant effect in the reduction of vibrations or oscillations induced in an underwater cable as a result of relative movement between the cable and the fluid; i.e. water in which the cable is placed. The damper bands, if intended to be placed on the exterior of the cable, have a circular, or ringed shape that will counteract these fluid passage induced vibrations in the cable stay generated by the relative movement of the cable and the fluid which surrounds it.
The damper bands can be either passive or active. Passive damper bands will function without any mechanical or electrical input. Active damper bands can be reactive or proactive and include movable masses. These movable masses can be caused to move in reaction to cable induced vibrations and are thus reactive. They can also be caused to shift by either mechanical or electrical devices and are thus proactive. The proactive damper bands with actuating devices can be considered to be computer-controlled devices. In the case of active damper bands, these can either form the generalized ring or ribbed shape on the cable stay exterior surface, or they can be embedded within the cable stay, thus, leaving a smooth outer cable stay surface. Typically, the distributed bands or rings will be placed along the full length of the cable stay. It is also possible for only a partial length of the cable, e.g. the top third or top quarter of cable stay length, to have the distributed damping devices attached.
The implementation of an active, smart underwater cable vibration damping system is included in the present invention. The active underwater system of the present invention employs distributed bands or rings together 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 depths at which underwater cables, which can receive the damper bands of the present invention, are mounted, efforts in active smart control are focused on low-maintenance damping techniques and low-cost cable modifications.
DESCRIPTION OF THE PRIOR ART
The use of cable stays in the construction of a wide variety of structures is well known. Any number of types of bridges use various cables to support bridge decks, to hold bridge towers steady and to generally form the support for the bridges. Suspension bridges are one example of a bridge structure that uses a large number of elongated cables as stays and supports. In a somewhat similar manner, cables are frequently used as guy wires or as stays in connection with tall antenna towers and the like. A large number of these towers are used to support various receivers, repeaters and other similar assembles. One need not look far without seeing such a tower. A plurality of elongated cables are typically run from various elevations on these towers to suitable ground anchors. These cable stays or guy wires are used to stabilize the tower.
Elongated cables are also utilized in the underwater stabilization of off-shore structures such as floating oil drilling installations. These cables are subjected to hydrodynamic forces that are very similar to the aerodynamic forces which above ground stay cables and guy lines experience. A much slower fluid flow speed in water is capable of producing cable stay vibrations found generally only with very high wind speeds, i.e. low water speeds generally correspond to fluid flow in high air speeds.
In all of these cable applications, the passage of a fluid, such as air or water, over the surface of the cable, can induce vibrations or oscillations in the cable. If the fluid velocity is sufficient, the cable can be seen to vibrate at node points with sufficient amplitude that the structure with which the cable is associated may be damaged. In the case of cable stays for use with off-shore structures, the off-shore structural stays may be caused to vibrate or in extreme situations to shake sufficiently that the structural integrity of the off-shore structure may be compromised. Such vibrations can also cause fatigue in the cables. It is relatively common knowledge that fatigue in off-shore oil platforms, due primarily to underwater currents, is a problem. Such 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. Such fatigue problems can lead to the need for early replacement of the cables. In the situation involving sub-sea cables, the position of the anchored platform can be affected with a resultant possible misalignment of platform supported drill strings and other similar down-hole implements.
For cable stays in air, it has been proposed to provide various mechanical vibration dampers for elongated cables. In one configuration, these vibration dampeners have taken the form of shock absorber-like devices that may be interposed between an end of the cable and an anchoring or attachment site for the cable. Other similar spring-biased connections have been used in the past in an effort to compensate for or to counteract wind induced vibrations and oscillations.
Fairings and streamlining devices have been applied to overhead cables, to sub-sea cables and to guy wires and cable stays. These attempt to altar the shape of the generally cylindrical cable to create an airfoil or flow-smoothing shape.
Various forms of underwater surface treatments have been sought to serve as solutions to the vibrations of the smooth-surfaced, circular cable. While some of these treatments can be adopted only at the cable design stage, others are feasible for retrofitting of the cables. Fluid dynamic countermeasures usually modify the surface of the cable cross section to improve its fluid dynamic performance in terms of reducing the excitation from the moving fluid, e.g. water, or increasing the fluid dynamic damping. Two examples of generally known types of underwater cable surface/cross section modifications are surface dimpling and parallel axial protuberances.
It is also known in the art to fabricate structures with integrally formed annular rings and with various projections and protrusions. In these structures, the rings are formed during the fabrication of the structure, which may be a mast of an outdoor antenna, a smokestack, transmission lines or pipelines. These rings are intended to reduce or to eliminate the vortex shedding which affects structures of these types. The elimination of this vortex shedding will greatly reduce the oscillating lateral forces which smokestacks, antennas, transmission lines and other cylindrical structure have been plagued by due to this periodic shedding of vortices.
The prior art has appreciated the use of various vibration dampers and integrall
Gardner Thomas B.
Mehta Kishor C.
Phelan R. Scott
Sarkar Partha P.
Zhao Zongshan
Jones Tullar & Cooper PC
Lavinder Jack
Sy Mariano
Texas Tech University
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