Abstract:
Embodiments of the invention relate generally to rotary devices and, more particularly, to systems, devices, and methods for shifting a torsional mode frequency of a rotary device. In one embodiment, the invention provides a system for shifting a torsional mode frequency of a rotary device, the system comprising: a plurality of mass rings, each of the plurality of mass rings comprising: a pair of radially-segmented half rings; and at least one channel through each of the radially-segmented half rings, the at least one channel oriented substantially perpendicular to the radial segmentation of the mass ring, whereby the plurality of mass rings may be aligned and secured through the at least one channel of each radially-segmented half ring such that the radial segmentation of each mass ring is staggered with respect to the radial segmentation of an adjacent mass ring.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Embodiments of the invention relate generally to rotary devices and, more particularly, to systems, devices, and methods for shifting a torsional mode frequency of a rotary device. 
         [0002]    Rotary devices are known to suffer from various vibration problems during their operation. One such vibration problem is torsional vibration. In all practical rotor systems there is no inherent ability to damper torsional vibration. 
         [0003]    When a power train torsional mode is near to a continuous forcing function, such as twice a line frequency of a power generating unit (e.g., a steam turbine-generator system), torsional vibration may be so severe that continuous safe operation of the unit is not possible. Typically, this results in activation of a tripping system and the unit is shut down. 
         [0004]    Currently, since the line frequency cannot be changed, torsional vibration is addressed by disassembling the device and shrink fitting a large number of rings on an outer surface of a rotor flange. The device is then reassembled and tested to confirm a reduction in torsional vibration. This process is both time consuming (typically 30-40 days) and consequently expensive, resulting in significant downtime for the device and a concomitant loss of revenue. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In one embodiment, the invention provides a system for shifting a torsional mode frequency of a rotary device, the system comprising: a plurality of mass rings, each of the plurality of mass rings comprising: a pair of radially-segmented half rings; and at least one channel through each of the radially-segmented half rings, the at least one channel oriented substantially perpendicular to the radial segmentation of the mass ring, whereby the plurality of mass rings may be aligned and secured through the at least one channel of each radially-segmented half ring such that the radial segmentation of each mass ring is staggered with respect to the radial segmentation of an adjacent mass ring. 
         [0006]    In another embodiment, the invention provides a device for shifting a torsional mode frequency of a rotary device, the device comprising: a first radially-segmented half ring; a second radially-segmented half ring; and at least one channel through each of the first radially-segmented half ring and the second radially-segmented half ring, the at least one channel oriented substantially perpendicular to the radial segmentation. 
         [0007]    In still another embodiment, the invention provides a method of shifting a torsional mode frequency of a rotary device, the method comprising: applying to a rotating member of a rotary device a plurality of mass rings, each of the plurality of mass rings comprising a pair of radially-segmented half rings, such that a segmentation between each pair of radially-segmented half rings is staggered with respect to a segmentation between an adjacent pair of radially-segmented half rings; and fastening together the plurality of mass rings using a plurality of fasteners extending through each of the plurality of mass rings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0009]      FIGS. 1 and 2  show perspective views of a mass ring according to an embodiment of the invention. 
           [0010]      FIGS. 3 and 4  show perspective views of a mass ring according to an embodiment of the invention being positioned on a rotating member. 
           [0011]      FIG. 5  shows a partial facing view of the mass ring of  FIGS. 3 and 4  positioned on the rotating member. 
           [0012]      FIGS. 6-8  show perspective views of additional mass rings positioned on a rotating member. 
           [0013]      FIG. 9  shows a cross-sectional side view of a plurality of mass rings positioned on a rotating member. 
           [0014]      FIG. 10  shows a flow diagram of an illustrative method according to one embodiment of the invention. 
       
    
    
       [0015]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  shows a perspective view of a mass ring  100  for shifting a torsional mode frequency of a rotary device. Mass ring  100  includes a first radially-segmented half ring  10  and a second radially-segmented half ring  40 . Each of the first and second radially-segmented half rings  10 ,  40  includes an inner circumferential surface  12 ,  42  and an outer circumferential surface  14 ,  44 . Each of the first and second radially-segmented half rings  10 ,  40  also includes a plurality of channels  18 ,  48 , the use of which will be explained in greater detail below. In some embodiments of the invention, channels  18 ,  48  comprise a bolt hole for receiving a threaded bolt (not shown). 
         [0017]    In some embodiments of the invention, each of first and second radially-segmented half rings  10 ,  40  may also include a plurality of radially-spaced slots  16 ,  46  along the inner circumferential surface  12 ,  42 . Each of the plurality of radially-spaced slots  16 ,  46  is operable to receive a radial guide post positioned along a circumference of a rotating member, as will be described below. 
         [0018]      FIG. 2  shows mass ring  100  with first and second radially-segmented half rings  10 ,  40  positioned as they would be when installed on a rotary device. In  FIG. 2 , the radial segmentation  30  of mass ring  100  can clearly be seen. 
         [0019]      FIG. 3  shows a perspective view of first radially-segmented half ring  10  positioned on a rotating member  800 . Rotating member  800  includes, along its circumference, a plurality of radial guide posts  816  operable to fit within the radially-spaced slots  16  ( FIGS. 1-2 ) of first radially-segmented half ring  10 . Radial guide posts  816  help ensure proper alignment of first radially-segmented half ring  10  along the circumference of rotating member  800 . 
         [0020]    Typically, radial guide posts  816  will be placed along and within a slot of rotating member  800  such as may be used for balancing rotating member  800 , as will be recognized by one skilled in the art. Radial guide posts  816  and radially-spaced slots  16  may employ a friction fit or similar mechanism for ensuring a snug fit of radial guide posts  816  within radially-spaced slots  16 . 
         [0021]    In some embodiments of the invention, and as shown in  FIG. 3 , radially-spaced slots  16  may be “hemi-slots,” operable to contain a portion, but less than all, of each radial guide post  816 . That is, as will be explained in greater detail below, each radial guide post  816  may be contained within the “hemi-slot” of a first radially-segmented half ring and the “hemi-slot” of an additional radially-segmented half ring stacked adjacent the first radially-segmented half ring, such that each guide post  816  is sandwiched between two adjacently-stacked mass rings. 
         [0022]      FIG. 4  shows second radially-segmented half ring  40  similarly positioned on rotating member  800 , such that a first mass ring  100  is formed. One end of radial segmentation  30  may be seen in  FIG. 4 , the other end being obscured by rotating member  800 .  FIG. 5  shows a partial facing view of first and second radially-segmented half rings  10 ,  40  positioned on rotating member  800 . Radial guide posts  816  can be seen disposed within radially-spaced slots  16 . 
         [0023]      FIG. 6  shows a perspective view of the positioning of a third radially-segmented half ring  110  on rotating member  800 . As can be seen in  FIG. 6 , third radially-segmented half ring  110  is positioned with respect to first mass ring  100  such that segmentation  30  of first mass ring  100  is staggered from a first end  111  of third radially-segmented half ring  110 . The details of such staggering, according to some embodiments of the invention, will be described in greater detail below. 
         [0024]    Third radially-segmented half ring  110  may be fastened to first mass ring  100 , and specifically to first and second radially-segmented half rings  10 ,  40 , respectively, using a first fastener  58  and a second fastener  68 . First fastener  58  may be passed through a channel  18  ( FIG. 1 ) of first radially-segmented half ring  10  and a corresponding channel  118  of third radially-segmented half ring  110 . Similarly, second fastener  68  may be passed through a channel  48  ( FIG. 1 ) of second radially-segmented half ring  40  and a corresponding channel (obscured by rotating member  800 ) of third axially-segmented half ring  110 . 
         [0025]      FIG. 7  shows fourth radially-segmented half ring  140  positioned on rotating member  800  and adjacent third radially-segmented half ring  110  to form a second mass ring  200  adjacent first mass ring  100 . As shown in  FIG. 7 , segmentation  130  of second mass ring  200  is staggered with respect to segmentation  30  of first mass ring  100 . Such staggering provides improved strength, particularly in an circumferential direction, of both first and second mass rings  100 ,  200 . 
         [0026]    Similar to the description above, as shown in  FIG. 7 , fourth radially-segmented half ring  140  may be fastened to first radially-segmented mass ring  10  and second radially-segmented half ring  40  through channels  18 ,  48  ( FIG. 1 ),  148  of first, second, and fourth radially-segmented mass rings  10 ,  40 ,  140 , respectively, using one or more fasteners  78 . 
         [0027]      FIG. 8  shows a total of seven mass rings  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  so stacked. Each mass ring is preferably staggered such that its radial segmentation  30 ,  130 ,  230 ,  430 ,  530 ,  630  (radial segmentation  330  of ring mass  400  being obscured from view in  FIG. 8 ) is staggered with respect to the radial segmentation of any adjacently stacked mass ring. For example, as shown in  FIG. 8 , the radial segmentation  130  of mass ring  200  is staggered with respect to radial segmentation  30  of mass ring  100  and radial segmentation  230  of mass ring  300 . 
         [0028]    Such stacking of adjacent mass rings may continue using any number of mass rings until a total mass of all mass rings is sufficient to shift a torsional mode frequency of the device. In some embodiments of the invention, the rotating member will be rotated clockwise between the installation of the first mass ring and the second mass ring, and will then be rotated counterclockwise between the installation of the second mass ring and the third mass ring. Such alternating clockwise/counterclockwise rotation may be repeated until all desired mass rings are installed. Whether the initial rotation between installation of the first mass ring and the second mass ring is clockwise or counterclockwise is of no importance. Alternating the clockwise and counterclockwise rotation of the rotating member, however, helps to ensure that the segmentations of each mass ring remain staggered. 
         [0029]    The total number of mass rings employed may vary, of course, depending upon, for example, the degree of torsional mode frequency shifting to be achieved, the size and composition of the mass rings employed, etc. In some embodiments, a total mass of the plurality of mass rings employed is sufficient to shift the torsional mode frequency downward by about 1.5-4 Hz or even lower from the original torsional mode frequency. For example, where the original, unshifted torsional mode frequency is very close to 120 Hz (i.e., double the standard US electrical line frequency of 60 Hz), the total mass of the plurality of mass rings may be sufficient to shift the torsional mode frequency to between about 118.5 Hz and about 116 Hz, or even lower frequencies depending on the sensitivity of the mode. 
         [0030]    In some embodiments, the total mass of the plurality of mass rings is sufficient to shift the torsional mode frequency of the device by 10 Hz. That is, continuing with the embodiment above, the total mass of the plurality of mass rings is sufficient to decrease the torsional mode frequency to about 110 Hz. Such a degree of shifting is more than sufficient to overcome the most significant effects of torsional vibration, since the effects of torsional vibration diminish as the continuous forcing function increases. 
         [0031]      FIG. 9  shows a cross-sectional side view of the mass rings  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  of  FIG. 8 . Fastener  58 , in this case a threaded bolt, fastens each mass ring. Radial guide pin  816 , shown in phantom between mass ring  100  and mass ring  200  may also be seen. As can be seen in  FIG. 9 , radial slots  16 ,  116  of mass rings  100  and  200 , respectively, are “hemi-slots,” which together form a unitary radial slot into which radial guide pin  816  may be fitted. Although radial guide pin  816  is shown between mass ring  100  and mass ring  200 , this is not essential. Radial guide pins may be positioned between any two adjacent mass rings or, in some embodiments, within a single mass ring. 
         [0032]      FIG. 10  shows a flow diagram of an illustrative method according to an embodiment of the invention. At S 1 , if not already in place, radial guide pins may optionally be installed along the rotating member, as shown, for example, in  FIG. 3 . At S 2 , a first radially-segmented half ring is positioned along a surface of the rotating member using the radial guide pins. At S 3 , a second radially-segmented half ring is positioned along the surface of the rotating member using the radial guide pins to form a first half ring. 
         [0033]    At S 4 , the rotating member is rotated, either clockwise or counterclockwise, and at S 5  an additional pair of radially-segmented half rings is positioned along the rotating member to form an additional mass ring. S 4  and S 5  may be iteratively looped until the desired number of mass rings is installed on the rotating member. As noted above, if S 4  and S 5  are iteratively looped, the rotation at S 4  is alternately clockwise and counterclockwise. Finally, once all desired mass rings are in place, they may be secured together at S 6 , as, for example, shown in  FIGS. 8 and 9 . 
         [0034]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0035]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any related or incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.