Abstract:
A method of positioning a bearing of a turbomachine in a squeeze film annulus is disclosed. The method includes providing a bearing in which a rotor shaft is disposed and a bearing support mounted about and radially supporting the bearing, with the bearing support at least in part defining the squeeze film annulus. A further step typically includes providing a plurality of centering elements associated with the bearing and bearing support and acting to center the bearing within the squeeze film annulus, with the centering elements provided at radially spaced locations around the bearing. An additional step in the method may include individually machining or shimming the centering elements to adjust the positioning of the bearing in the squeeze film annulus or to impart pre-load to improve the resiliency of the centering elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of and claims priority to U.S. patent application Ser. No. 11/237,332, filed on Sep. 28, 2005, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to bearings, such as roller bearings, journal bearings, sleeve bearings and the like, used to support rotating shafts in turbomachinery such as compressors and turbines and, more particularly, a bearing assembly including a squeeze film damper with a support structure for centering support of a bearing within the squeeze film damper annulus. 
     2. Description of Related Art 
     Large axial and radial forces act on high-speed rotors, such as the shafts of compressors or turbines, and these forces are compensated for by appropriately configured and arranged thrust bearings and journal bearings. In addition, it is also necessary to provide compensation for the radial rotor vibrations if trouble-free operation of such turbomachinery is to be ensured. For this purpose, squeeze film dampers are often employed in turbomachines to reduce the amplitude of the rotor vibrations. Typically, a squeeze film damper consists essentially of an annular gap configured between a bearing and a bearing support that is connected to an oil supply. The bearing may be a roller bearing, or may be of the hydrodynamic bearing type with hydrodynamic lubricating film on the shaft side, or may be any other bearing that supports a rotating shaft. The bearing may or may not be assembled into a sleeve. The bearing or bearing and sleeve may be referred to as a floating sleeve. In the case of a floating sleeve located within the annular gap of a squeeze film damper, the problem arises, particularly in the case of heavy rotors, that the floating sleeve is not centered in the annular gap during operation. Rather, the floating sleeve is positioned in the lower region of the bore in which it is situated. This arrangement can lead to poor damping properties and, further, to wear of the corresponding components. 
     Numerous possibilities for centering a floating sleeve within a squeeze film damper are known to avoid these disadvantages. One arrangement uses centering O-rings in the annular region of the squeeze film damper. Another arrangement uses centering provided by means of a lateral spring rod cage and by means of leaf springs arranged radially and locally at the periphery. A further squeeze film damper centering arrangement uses bending rods arranged radially at the outside periphery. A disadvantageous feature of O-ring centering, however, is that this arrangement has a nonlinear spring characteristic and unsatisfactory long-term behavior whereas, in the case of the spring rod cage, a very large amount of axial installation space is necessary. Moreover, bending rods require a large amount of radial space and, because of the large number of individual parts, are high cost and often deliver unsatisfactory concentricity accuracy. The leaf spring solution, which likewise requires a large amount of radial space, can only be manufactured by an electrical discharge machining method. In this case, furthermore, there is danger of shaft-side deformation of the bearing sleeve. 
     Based on the foregoing, there is considerable room for improvement in the field of bearing design and in the design of squeeze film dampers, particularly spring-backed or aided squeeze film dampers. The invention disclosed herein provides an improved and flexible structural support for centering a floating sleeve in a squeeze film annulus and overcomes many of the foregoing disadvantages found in current bearing and squeeze film damper design. 
     SUMMARY OF THE INVENTION 
     The bearing assembly for a rotating shaft according to one embodiment comprises a bearing in which the shaft is disposed, a bearing support mounted about and radially supporting the bearing, the bearing support at least in part defining a squeeze film annulus of the bearing assembly, and at least one centering element associated with the bearing and bearing support and acting to center the bearing within the squeeze film annulus. 
     In one embodiment, the at least one centering element may comprise at least one wave spring. The at least one wave spring may substantially encircle the bearing support. 
     In another embodiment, the at least one centering element may comprise a plurality of beam springs provided at radially spaced locations around the bearing. The bearing assembly may further comprise a housing enclosing the bearing support, and each beam spring may comprise a raised support pad at each end to seat against the housing and a raised support pad at an approximate center of the beam spring to seat against the bearing support. The beam springs are typically uniformly distributed around the bearing. 
     In a further embodiment, the at least one centering element may comprise a plurality of cylinder springs provided at radially spaced locations around the bearing. The cylinder springs are typically uniformly spaced around the bearing. The cylinder springs may be tapered on at least one axial end. 
     In a still further embodiment, the at least one centering element may comprise a plurality of load cell springs positioned at radially spaced locations around the bearing. Each load cell spring typically comprises at least one beam member. The beam member may define at least one internal space therein. Each load cell spring may further comprise a plurality of overlapping beam members. At least one of the overlapping beam members may define an internal space therein. The overlapping beam members may define intervening spaces between the beam members. Each load cell spring may comprise a body defining at least one internal space therein. 
     The bearing assembly, in another embodiment, comprises a bearing in which a shaft is disposed, a bearing support mounted about and radially supporting the bearing, the bearing support at least in part defining a squeeze film annulus of the bearing assembly, and a plurality of centering elements associated with the bearing and bearing support and acting to center the bearing within the squeeze film annulus, the centering elements provided at radially spaced locations around the bearing. 
     In one embodiment, the centering elements comprise cylinder springs provided at the radially spaced locations around the bearing. In another embodiment, the centering elements comprise a plurality of load cell springs provided at the radially spaced locations around the bearing. Each load cell spring typically comprises at least one beam member. The beam member may define at least one internal space therein. Each load cell spring may further comprise a plurality of overlapping beam members. At least one of the overlapping beam members may define an internal space therein. The overlapping beam members may define intervening spaces between the beam members. Each load cell spring may comprise a body defining at least one internal space therein. 
     In a further aspect, the present invention is a method of positioning a bearing of a turbomachine in a squeeze film annulus. The method may include the steps of providing a bearing in which a rotor shaft is disposed and a bearing support mounted about and radially supporting the bearing, with the bearing support at least in part defining the squeeze film annulus. A further step typically comprises providing a plurality of centering elements associated with the bearing and bearing support and acting to center the bearing within the squeeze film annulus, with the centering elements provided at radially spaced locations around the bearing. An additional step in the method may comprise individually machining or shimming the centering elements to adjust the positioning of the bearing in the squeeze film annulus or to impart pre-load to improve the resiliency of the centering elements. 
     In one embodiment, the centering elements comprise cylinder springs provided at the radially spaced locations around the bearing. In another embodiment, the centering elements comprise a plurality of load cell springs provided at the radially spaced locations around the bearing. The step of providing the plurality of centering elements may comprise providing the load cell springs at uniformly spaced locations around the bearing. Each load cell spring typically comprises at least one beam member. The beam member may define at least one internal space therein. Each load cell spring may further comprise a plurality of overlapping beam members. At least one of the overlapping beam members may define an internal space therein. The overlapping beam members may define intervening spaces between the beam members. Each load cell spring may comprise a body defining at least one internal space therein. As in the prior art, O-rings may be used to seal fluid into a squeeze film annulus, but unlike some of the prior art, the O-rings do not act as a support device for the floating sleeve. 
     Further details and advantages of the present invention will become clear upon reading the following detailed description in conjunction with the accompanying drawings, wherein like elements are identified with like reference numerals throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a bearing assembly with an embodiment of a centering support structure comprising centering beam springs; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a bearing assembly with another embodiment of a centering support structure comprising a centering wave spring; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of a bearing assembly with a further embodiment of a centering support structure support incorporating cylindrical centering elements; 
         FIG. 6  is a cross-sectional view taken along line  6 - 6  in  FIG. 5 ; 
         FIG. 7A  is a detail view of detail  7 A in  FIG. 5 ; 
         FIG. 7B  is a detail view of an alternative configuration of the cylindrical centering element shown in  FIG. 7A ; 
         FIG. 8A  is a cross-sectional view of the bearing assembly of  FIG. 5  comprising load cell springs according to a first embodiment provided in place of the cylindrical centering elements in the centering support structure; 
         FIG. 8B  is a cross-sectional view of one of the load cell spring shown in  FIG. 8A ; 
         FIG. 8C  is a cross-sectional view of a first exemplary alternative design for the load cell spring of  FIG. 8B ; 
         FIG. 8D  is a cross-sectional view of a second exemplary alternative design for the load cell spring of  FIG. 8B ; 
         FIG. 8E  is a cross-sectional view of a third exemplary alternative design for the load cell spring of  FIG. 8B ; 
         FIG. 9A  is a cross-sectional view of the bearing assembly of  FIG. 5  comprising load cell springs according to a second embodiment; 
         FIG. 9B  is a cross-sectional view of one of the load cell springs shown in  FIG. 9A ; 
         FIG. 10A  is a cross-sectional view of the bearing assembly of  FIG. 5  comprising load cell springs according to a third embodiment; 
         FIG. 10B  is a cross-sectional view of one of the load cell springs shown in  FIG. 10A ; 
         FIG. 10C  is a cross-sectional view of a first exemplary alternative design for the load cell spring of  FIG. 10B ; 
         FIG. 10D  is a cross-sectional view of a second exemplary alternative design for the load cell spring of  FIG. 10B ; 
         FIG. 10E  is a cross-sectional view of a third exemplary alternative design for the load cell spring of  FIG. 10B ; 
         FIG. 10F  is a cross-sectional view of a fourth exemplary alternative design for the load cell spring of  FIG. 10B ; 
         FIG. 11A  is a cross-sectional view of the bearing assembly of  FIG. 5  comprising load cell springs according to a fourth embodiment; and 
         FIG. 11B  is a cross-sectional view of one of the load cell springs shown in  FIG. 11A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of the description hereinafter, spatial orientation terms, if used, shall relate to the embodiment of the invention as it is oriented in the accompanying drawing figures. However, it is to be understood that the present invention may assume many alternative variations and embodiments except where expressly specified to the contrary. It is also to be understood that the specific devices and embodiments illustrated in the accompanying drawing figures and described herein are simply exemplary embodiments of the invention, and wherein like elements are designated with like reference numerals throughout. 
     As illustrated in  FIGS. 1 and 2 , a bearing assembly  10  is generally shown supporting a rotor shaft of a rotary machine, such as a turbine or a compressor. Such rotor shafts are adapted to carry the turbomachine components and are thus subjected to deflections and vibrations at resonant conditions. Typically, bearing reaction to a rotor shaft at resonant conditions will produce rotor instability if not attenuated. Attenuation is herein achieved by appropriate centering of a bearing of the bearing assembly  10  by the use of various embodiments of a support structure comprising one or more centering elements, typically centering spring elements, and fluid squeeze film damping. 
     With continued reference to  FIGS. 1 and 2  of the drawings, a first embodiment of bearing assembly  10  is illustrated. Bearing assembly  10  generally comprises a bearing  12  and a bearing support structure  14  disposed about and radially supporting bearing  12 . Bearing  12  is, in turn, disposed about a rotor shaft  15  aligned on a longitudinal central shaft axis L. As illustrated, the major components of bearing assembly  10 , namely bearing  12  and support structure  14 , are also symmetrical about axis L and rotor shaft  15 . Rotor shaft  15  may be a solid element, as illustrated, or be provided as a cylindrical-shaped structure aligned on and rotatable about axis L. Rotor shaft  15  has an outer surface S that is engaged in bearing  12 . Bearing  12  is illustrated as a tilt pad bearing as one possible embodiment of bearing  12 . However, bearing  12  may also take the form of a roller bearing, comprising an inner race rigidly attached to rotor shaft  15 , an outer race having an outer cylindrical surface and an annular side face, and a plurality of rollers disposed between the inner and outer races as is typical for roller bearings, or as a sleeve bearing as illustrated in  FIGS. 5 and 6  discussed herein. 
     Bearing  12  generally comprises a plurality of tilt pads  16  and a typically circumferentially-extending tilt pad retainer  18 . Tilt pads  16  and tilt pad retainer  18  are typically assembled into an outer sleeve-shaped bearing support  19 , and tilt pads  16 , tilt pad retainer  18 , and sleeve-shaped bearing support  19  may be referred to either as a “damper journal” or as a “floating sleeve” structure; terms that are well-known in the turbomachinery field. Reference character “F” is used herein to identify such a floating sleeve structure. Accordingly, the term “floating sleeve structure” F is intended to comprise tilt pads  16 , tilt pad retainer  18 , and outer bearing support  19 . Bearing  12  typically extends around the circumference or perimeter of rotor shaft  15 , with tilt pads  16  generally individually engaged with rotor shaft  15 , tilt pad retainer  18 , and bearing support  19  forming a generally annular or ring-shaped structure about tilt pads  16  and shaft  15 . 
     Support structure  14  forms a resilient damping structure about bearing  12  and further comprises an outer housing  20  typically enclosing the components of bearing  12  and the individual damping components of the support structure  14 . Damping support structure  14  further comprises a plurality of resilient (i.e., flexible) centering elements  80  as described further herein. Centering elements  80  are disposed within housing  20  and generally act between housing  20  and bearing support  19  to resiliently support the floating sleeve structure F. 
     As indicated previously, bearing  12  depicted in  FIGS. 1 and 2  is a multi-component structure comprising tilt pads  16  and tilt pad retainer  18  with bearing support  19  enclosing tilt pads  16  and tilt pad retainer  18 . Support structure  14  is disposed about bearing  12  and bearing support  19  on rotor shaft  15 . Bearing support  19 , as indicated previously, is generally a circumferentially-extending structure disposed about and supporting tilt pads  16 . Bearing support  19  further assembles tilts pads  16  and tilt pad retainer  18  into a singular unit or the floating sleeve structure F described previously. Tilt pad retainer  18  and bearing support  19  together cooperatively define a plurality of radial bores  40  (as shown in  FIG. 2 ), to provide lubricating hydraulic fluid to the tilt pads  16 . O-ring type axial seals  50  are disposed in respective grooves  52  defined in the axial ends of bearing support  19 , and which sealingly abut opposed inner sides  54  of housing  20  to seal a squeeze film annulus H from the external environment. Housing  20  further defines a radial inner side or surface  56 . 
     Bearing support  19  comprises a cylindrical or radial outer side or surface  60  that is enclosed by housing  20 . Radial outer side  60  of bearing support  19  is disposed radially inward from radial inner side  56  of housing  20 . Housing  20  defines a plurality of discrete recesses  70  that are substantially enclosed by the radial outer side  60  of bearing support  19 , and wherein centering elements  80  are individually disposed and retained. Recesses (i.e., chambers)  70  are provided in the radial inner side  56  of housing  20 . A hydraulic fluid squeeze film damper is associated with the radial outer side  60  of bearing support  19  and is disposed between the radial outer side  60  and the radial inner side  56  of housing  20 . The squeeze film damper is essentially an annulus H filled at least in part with hydraulic fluid between the radial outer side  60  of bearing support  19  and the radial inner side  56  of housing  20  for damping the amplitude of vibration of rotor shaft  15  and floating sleeve structure F. Squeeze film annulus H is in fluid communication with an outside source of hydraulic fluid via a plurality of radial supply openings  72  in housing  20  to supply hydraulic fluid under system pressure to squeeze film annulus H. Supply openings  72  are further in fluid communication with radial bores  40  and are typically continuous with radial bores  40  as illustrated to supply lubricating hydraulic fluid to bearing  12  for lubrication of tilt pads  16 . 
     Centering elements  80  are typically centering spring elements, such as beam springs, and are disposed in the respective recesses  70 . Multiple centering elements  80  are disposed about floating sleeve structure F and interrupt the squeeze film annulus H. Typically, centering elements  80  are symmetrically or uniformly distributed or spaced about the circumference of floating sleeve structure F and interrupt squeeze film annulus H at regular intervals, such as 90° or 72° apart. Centering elements  80  are positioned radially outward from bearing  12  and uniformly distributed or spaced about bearing  12 . Centering elements  80  act radially on floating sleeve structure F for centering floating sleeve structure F and, hence, bearing  12  in squeeze film annulus H. Centering elements  80  generally provide a centering force that will resist motion of floating sleeve structure F and, therefore, bearing  12 , and thereby center floating sleeve structure F in squeeze film annulus H to enhance the effectiveness of squeeze film annulus H in dampening vibration of rotor shaft  15 . Centering elements  80  in conjunction with the squeeze film annulus H are used to dampen or control synchronous or non-synchronous vibration in a rotating turbomachine incorporating a rotating shaft such as rotor shaft  15 . Such turbomachinery, with which bearing assembly  10  is intended to be applied, typically include high speed rotating turbomachinery, including high speed compressors, turbines, and high pressure-high gas density applications where potential for high subsynchronous vibration is present. 
     Centering elements  80  are generally disposed to act between housing  20  in each recess  70  and the radial outer side  60  of bearing support  19 . Centering elements  80  are generally slightly shorter in axial length than the axial length of the discrete recesses  70 . In other embodiments described in this disclosure, a singular or unitary “centering” structure that extends circumferentially about floating sleeve structure F is provided. Such a unitary structure may also be provided as a segmented or multi-component structure comprised of several distinct centering structures or elements that cooperatively form an annular structure to encompass floating sleeve structure F. For example, such a singular or unitary centering structure may comprise a singular, circumferential wave spring, as depicted in  FIGS. 3 and 4  discussed herein. 
     As indicated, centering elements  80  are generally adapted to act on floating sleeve structure F within squeeze film annulus H and, in particular, act between housing  20  and bearing support  19  to provide the centering force to floating sleeve structure F. Centering elements  80  may take any suitable form to accomplish the centering of floating sleeve structure F. However, a desirable form for centering elements  80  is illustrated in  FIG. 1 . As shown in  FIG. 1 , centering elements  80  each comprise two axial ends formed with raised support pads  82 ,  84  which contact the radial inner side  56  of housing  20  in each recess  70 . The radial inner side of each centering element  80  is formed with a centrally located reaction pad  86  adapted to contact the outer periphery or radial outer side  60  of bearing support  19 . In practice, each centering element  80  is positioned within a respective recesses  70  which is formed continuous with squeeze film annulus H so that central reaction pad  86  of each centering element  80  acts radially on floating sleeve structure F. 
     Referring to  FIGS. 3 and 4 , another embodiment of bearing assembly  10   a  is shown and is generally similar to bearing assembly  10  described hereinabove, with certain modifications to centering support structure  14 . In bearing assembly  10   a , respective wave springs  100 ,  102  are associated with floating sleeve structure F a  to provide the centering force to floating sleeve structure F a . As illustrated in  FIG. 3 , bearing support  19   a  is formed for cooperating engagement with housing  20   a . Squeeze film annulus H a  is defined or formed between bearing support  19   a  and housing  20   a.  Accordingly, housing  20   a  is formed to engage bearing support  19   a  and define squeeze film annulus H a  with the bearing support  19   a . Hydraulic fluid is supplied through supply openings  72   a  in housing  20   a  directly to squeeze film annulus H a  and to tilt pads  16   a  via continuous radial openings or bores  40   a  in bearing support  19   a  and tilt pad retainer  18   a . It will generally be understood that tilt pads  16   a , tilt pad retainer  18   a , and bearing support  19   a  continue to form a floating sleeve structure F a  in a similar manner to that described in connection with  FIGS. 1 and 2 . 
     Housing  20   a  further defines respective axially-separated radial receiving openings or recesses  104 ,  106  wherein wave springs  100 ,  102  are disposed. The radial outer side  60   a  of bearing support  19   a  substantially encloses wave springs  100 ,  102  in recesses  104 ,  106 . Generally, wave springs  100 ,  102  act between housing  20   a  and bearing support  19   a  to provide the centering force to centering floating sleeve structure F a  in squeeze film annulus H a . Radial receiving recesses  104 ,  106  are typically defined at respective axial ends  108 ,  110  of housing  20   a . Waves spring  100 ,  102  are disposed in radial receiving recesses  104 ,  106 , respectively, and are adapted to act between housing  20   a  in receiving recesses  104 ,  106  and the radial outer side  60   a  of bearing support  19   a . Wave springs  100 ,  102  act in radial receiving recesses  104 ,  106  to provide the centering force to floating sleeve structure F a . Wave springs  102 ,  104  exert radially inwardly directed forces on floating sleeve structure F a  and radially outwardly directed forces on housing  20   a . These applied forces are equal and opposite and function to center floating sleeve structure F a  in squeeze film annulus H a  to inhibit floating sleeve structure F a  from “bottoming” or “topping” out in annulus H a . 
     As shown in  FIG. 3 , housing  20   a  and bearing support  19   a  are formed for a cooperating or mating engagement such that squeeze film annulus H a  is formed between these structures. In one possible embodiment, housing  20   a  comprises a radial depending portion  112  that engages a recessed receiving portion  114  defined in radial outer side  60   a  of bearing support  19   a  in a complimentary fashion. Radial depending portion  112  and recessed receiving portion  114  define squeeze film annulus H a  therebetween. In contrast to bearing assembly  10  discussed previously in connection with  FIGS. 1 and 2 , O-ring type seals  50   a  are disposed in a pair of grooves  52   a  now defined substantially in the axial ends of radial depending portion  112  of housing  20   a . As indicated previously, a continuous passage is defined by supply openings  72   a  in housing  20   a  and radial openings  40   a  in bearing support  19   a  and tilt pad retainer  18   a  to supply hydraulic fluid under system pressure directly to squeeze film annulus H a  and tilt pads  16   a . O-ring seals  50   a , or equivalent sealing structures, provide a sealing engagement with recessed receiving portion  114  of bearing support  19   a  to seal squeeze film annulus H a  from the exterior environment. 
     The various configurations and specified arrangements of bearing assembly  10 ,  10   a  described hereinabove in connection with  FIGS. 1-4 , are adapted to support both static and dynamic loads as transmitted by bearings  12 ,  12   a  to respective support structures  14 ,  14   a . More particularly, with rotor shafts  15 ,  15   a  at rest, the static load or weight of the rotor shafts  15 ,  15   a  is transmitted from bearings  14 ,  14   a  to floating sleeve structures F, F a . The weight of rotor shafts  15 ,  15   a  on the lower portion of floating sleeve structures F, F a  underneath shafts  15 ,  15   a  will compress the respective squeeze film annulus H, H a . However, the centering elements  80 , in the case of bearing assembly  10  of  FIGS. 1 and 2 , and wave springs  100 ,  102 , in the case of bearing assembly  10   a  of  FIGS. 3 and 4  will resist such distortion of the squeeze film annulus H, H a  and carry the static weight of rotor shafts  15 ,  15   a  without significant deflection. When dynamic loading is experience with rotor shafts  15 ,  15   a  rotating at high speed, as in a gas turbine engine application, unbalances in rotor shafts  15 ,  15   a  resolve themselves into a resultant radially outwardly directed force which rotates with rotor shafts  15 ,  15   a . The magnitude of the resultant force is proportional to speed and, at high shaft speed, significantly exceeds the static weight of rotor shafts  15 ,  15   a . Since the resultant force exceeds the weight of rotor shafts  15 ,  15   a  and tends to deflect rotor shafts  15 ,  15   a  radially, centering elements  80  and wave springs  100 ,  102  act in concert with the hydraulic fluid in the respective squeeze film annulus H, H a  to resist radial movement of rotor shafts  15 ,  15   a  and dampen both synchronous and non-synchronous vibration that may occur in rotating shafts  15 ,  15   a . 
     A further embodiment of a bearing assembly  10   b  is shown in  FIGS. 5-7 . Bearing assembly  10   b  is generally similar to bearing assembly  10  discussed previously in connection with  FIGS. 1 and 2 , in that bearing assembly  10   b  returns to the concept of using multiple, discrete centering elements  80   b  rather than circumferential or annular wave springs as discussed immediately above in connection with  FIGS. 3 and 4 . As indicated previously, any suitable bearing structure used in the field of turbomachinery, such as tilt pad bearings, roller bearings, and sleeve bearings, may be used in any of the embodiments of bearing assembly  10 ,  10   a ,  10   b  described in this disclosure with appropriate modification to the support structure of the bearings  12 ,  12   a ,  12   b . In  FIGS. 5-7 , bearing  12   b  is shown as a sleeve bearing rather than the tilt bearings shown and described previously in connection with  FIGS. 1-4 . Bearing  12   b  may also take the form of these multi-piece bearing constructions if desired. The chief difference between bearing assembly  10   b  shown in  FIGS. 5-7  and bearing assemblies  10 ,  10   a  discussed previously lies in the configuration of support structure  14   b . Certain modifications are made to support structure  14   b  when compared to support structure  14  shown in  FIGS. 1 and 2  and support structure  14   a  shown in  FIGS. 3 and 4  to accommodate sleeve bearing  12   b . 
     In bearing assembly  10   b , a bearing support, such as bearing supports  19 ,  19   a  used previously in bearing assemblies  10 ,  10   a , is omitted from bearing assembly  10   b , with their functions incorporated or integrated into sleeve bearing  12   b . In bearing assembly  10   b , a singular “bearing retainer”  18   b  performs the function of housings  20 ,  20   a  in bearing assemblies  10 ,  10   a , and the term “bearing retainer  18   b ” is intended to be synonymous in this disclosure with housings  20 ,  20   a  discussed previously. Sleeve bearing  12   b  alone forms a “floating sleeve structure” F b  similar to floating sleeve structures F, F a  described previously. Bearing retainer or “support”  18   b  now cooperates or engages directly with sleeve bearing  12   b  and supports sleeve bearing  12   b . Multiple centering elements  80   b  are provided to act between bearing retainer  18   b  and sleeve bearing  12   b  to provide the centering force directly to bearing  12   b  and assist the squeeze film damping provided by squeeze film annulus H b . 
     Bearing retainer  18   b  is disposed radially outward from sleeve bearing  12   b  and defines squeeze film annulus H b  with sleeve bearing  12   b . Bearing retainer  18   b  and bearing  12   b  are formed in an analogous manner to housing  20   a  and bearing support  19   a  discussed previously in connection with  FIGS. 3 and 4  and cooperate in a similar complimentary fashion. In particular, in one possible embodiment, bearing retainer  18   b  comprises a radial depending portion  120  that engages a recessed receiving portion  122  defined in a radial outer surface  124  of sleeve bearing  12   b . Radial depending portion  120  and recessed receiving portion  122  define squeeze film annulus H b  therebetween. In a similar manner to bearing assembly  10   a , O-ring type seals  50   b  are disposed in a pair of grooves  52   b  now defined substantially in axial ends  126 ,  128  of radial depending portion  120  of bearing retainer  18   b . A continuous passage is defined by radial openings or bores  72   b  in bearing retainer  18   b  to supply hydraulic fluid under system pressure to an annular distribution groove  129  that feeds directly to squeeze film annulus H b  and to sleeve bearing  12   b  through radial bores  40   a , now provided in sleeve bearing  12   b . O-ring seals  50   b , or equivalent sealing structures, provide a sealing engagement with recessed receiving portion  122  of bearing retainer  19   b  to seal squeeze film annulus H b  from the exterior environment. 
     Bearing retainer  18   b  and sleeve bearing  12   b , when associated, cooperatively define a plurality of individual receiving recesses  70   b  that are generally similar to recesses  70  discussed previously in connection with bearing assembly  10 . More particularly, bearing retainer  18   b  defines the discrete recesses  70   b  with sleeve bearing  12   b  axially outside of the cooperative engagement between radial depending portion  120  and recessed receiving portion  122  (i.e., in the axial ends of bearing retainer  18   b ). Recesses  70   b  are discretely defined between a radial inner surface or side  130  of bearing retainer  18   b  and the radial outer side  124  of sleeve bearing  12   b . Centering elements  80   b  are typically centering spring elements and are disposed in the respective recesses  70   b . Multiple centering elements  80   b  are typically disposed about sleeve bearing  12   b , but unlike the embodiment shown in  FIGS. 1 and 2  do not physically interrupt the squeeze film annulus H b . Typically, centering elements  80   b  are symmetrically or uniformly distributed or spaced about the circumference of sleeve bearing  12   b  such as 90° apart as illustrated in  FIG. 6  or 72° apart as illustrated in  FIG. 2 . Centering elements  80   b  are positioned radially outward from bearing  12   b  in discrete recesses  70   b  and act on sleeve bearing  12   b  for centering sleeve bearing  12   b  in squeeze film annulus H b  and act to enhance the effectiveness of the squeeze film annulus H b  to dampen vibration of rotor shaft  15   b . 
     Centering elements  80   b  are generally disposed to act between the radial inner surface  130  of bearing retainer  18   b  and radial outer surface  124  of sleeve bearing  12   b  axially outside of the cooperative engagement between depending portion  120  of bearing retainer  18   b and recessed receiving portion  122  of sleeve bearing  12   b . Centering elements  80   b  are typically in the form of cylindrical spring elements having an open, cylindrical cross-sectional shape, but may also be oval or elliptical. Centering elements  80   b  resiliently deform when radial force is applied to the centering elements  80   b  such as during resonance vibration of shaft  15  that is transmitted through bearing  12   b . As a result, centering elements  80   b  act as stiff springs with an associated stiffness to accommodate the vibration of shaft  15   b  and resultant motion of bearing  12   b  while supporting bearing  12   b  within squeeze film annulus H b . Accordingly, cylindrical centering elements  80   b  are typically in direct contact with bearing retainer  18   b  and sleeve bearing  12   b  and provide a stiff spring force acting between these two structures to accommodate vibration of shaft  15   b . Centering elements  80   b  are generally slightly shorter in axial length than the axial length of the discrete recesses  70   b  to allow for a slight vertical compression and accompanying horizontal expansion. While recesses  70   b  are depicted as open space for accommodating the respective centering elements  80   b , a cage ring such as that used to the rolling elements of a rolling element bearing may be provided in place of the respective recesses  70   b  as an alternative configuration to the structure shown in  FIGS. 5-7 . 
     Recesses  70   b  are defined by the cooperative engagement of bearing retainer  18   b  and sleeve bearing  12   b , and are adapted to capture cylindrical centering elements  80   b  therein. As shown in  FIG. 5 , recesses  70   b  are not necessarily required to be enclosed recesses (i.e., “chambers”) as was substantially the case in  FIGS. 1 and 2 . Bearing retainer  18   b  and sleeve bearing  12   b  may comprise respective opposed radial tabs  140 ,  142  for securing the respective cylindrical centering elements  80   b  within recesses  70   b . Thus, cylindrical centering elements  80   b  are typically captured in recesses  70   b  in both the axial and radial directions.  FIG. 7B  illustrates a modification to recesses  70   b  and cylindrical centering elements  80   b , wherein outward facing axial ends  144  of cylindrical centering elements  80   b  are slightly coned or tapered to assist with pre-loading sleeve bearing  12   b  within squeeze film annulus H b . During operation, cylindrical centering elements  80   b  substantially do not “roll” within recesses  70   b  or may roll a minimal amount when following the precessional motion of bearing  12   b . As indicated, the multiple centering elements  80   b  act between bearing retainer  18   b  and bearing  12   b  to center sleeve bearing  12   b  within squeeze film annulus H b  to enhance performance of squeeze film annulus H b  and prevent the “bottoming-out” or “topping-out” of sleeve bearing  12   b  within squeeze film annulus H b . Centering elements  80   b  exert radially inwardly directed forces on sleeve bearing  12   b  and radially outwardly directed forces on bearing retainer  18   b  to accomplish the centering of sleeve bearing  12   b . These applied forces are equal and opposite and function to center sleeve bearing  12   b  radially within squeeze film annulus H b . 
       FIGS. 8-11  show several additional embodiments of centering elements  150  that may be used in bearing assembly  10   b  described hereinabove. Centering elements  150  shown in  FIGS. 8-11  are disposed in respective recesses  152  which are generally similar to recesses  70   b  discussed previously, only now shaped or formed to the configuration of the centering elements  150 . Centering elements  150  may be secured in the recesses  152  by similar structure discussed previously in connection with  FIGS. 5-7  or by other suitable methods including a friction fit insertion or by being welded in place in recesses  152 . 
     With the foregoing in mind,  FIGS. 8A and 8B  show bearing assembly  10   b  with centering elements  150   a  according to a first embodiment. As indicated, centering elements  150   a  are disposed at uniformly spaced locations around sleeve bearing  12   b  in recesses  152   a  provided at these locations. More particularly, centering elements  150   a  are symmetrically or uniformly distributed or spaced about the circumference of sleeve bearing  12   b  such as 90° apart as illustrated in  FIG. 8A  or 72° apart as illustrated in  FIG. 2 . Centering elements  150   a  are positioned radially outward from bearing  12   b  and act on sleeve bearing  12   b  for centering sleeve bearing  12   b  in squeeze film annulus H b  and act to enhance the effectiveness of the squeeze film annulus H b  to dampen vibration of rotor shaft  15   b . Centering elements  150   a  are representative of the various embodiments of this structure shown in  FIG. 8-11 , and are generally pad-like structures disposed, as indicated, at four (4), 90° radial locations around sleeve bearing  12   b . Spring elements  150   a  each generally comprise a body  160   a  comprising a base beam member or element  162   a , a distal beam member  164   a , and an intermediate beam member or element  166   a  connecting base beam member  162   a  and distal beam member  164   a . Distal beam member  164   a  and intermediate beam member  166   a  generally form or define a plurality of overlapping cantilevered beam spring elements radially outward from base member  162   a . Overlapping distal beam member  164   a  and intermediate beam member  166   a  form a resilient beam spring network for each centering element  150   a  and, as can be appreciated from  FIGS. 8 and 8A , are cantilevered outward from a central area or portion  168   a  of body  160   a  of each centering element  150   a . Additionally, intervening spaces  172   a  are defined between distal beam member  164   a  and intermediate beam member  166   a  and between intermediate beam member  166   a  and base beam member  162   a , which allows the distal and intermediate beam members  164   a ,  166   a  to function as beam spring elements under radial load conditions applied to centering elements  150   a . Intermediate beam member  166   a , as shown in  FIGS. 8A and 8B , may define an internal space  174   a  therein, thus making the wall of intermediate beam member  166   a  thin to allow compression thereof when radial force is applied to body  160   a . Such an internal space  174   a  (as shown in dashed lines) may also be provided in distal beam member  164   a . In particular, as radial force is applied to body  160   a , distal beam member  164   a  will deflect about central portion  168   a  to typically contact intermediate beam member  166   a , which will also typically compress towards base beam member  162   a . However, the spring force in each of these beam “springs” will act to resist such deflection or compression thereof, and provide a resilient force resisting the radial load or force applied to centering elements  150   a . 
     As will also be appreciated from  FIGS. 8A and 8B , intermediate beam member  166   a  and distal beam member  164   a  are relatively short beams which will limit their flexibility and thereby increase their stiffness. Thus, each centering element  150   a , taken as a whole, will be a relative stiff “resilient” structure of only moderate flexibility, and will operate in a manner analogous to a load cell, and may alternatively be referred to as “load cell springs”. It will be recognized that such “load cell springs” are used primarily as springs and not as conventional load cells, but could further be used or instrumented to operate as load cells, if desired. A plurality of load cell springs are arranged in discrete, stationary positions along the radial inner surface  130  of bearing retainer  18   b . They center the rotating shaft by making discrete points of contact with the radial outer surface  124  of sleeve bearing  12   b . Accordingly, the load cell springs, as shown in  FIGS. 8A-8E ,  9 A- 9 B,  10 A- 10 F, and  11 A- 11 B are different than the centering wave spring shown in  FIGS. 3 and 4 . Additionally, as further shown in  FIG. 8A , the generally flat or planar underside of base beam member  162   a  is in contact with sleeve bearing  12   b  and the width (i.e., radial height) of base member  162   a  may be machined or shimmed to adjust the centering clearance of sleeve bearing  12   b  in squeeze film annulus H b . Each individual centering element  150   a  may be individual machined or shimmed as necessary to adjust the centering clearance of sleeve bearing  12   b  in squeeze film annulus H b  thereby improving maintenance and operation of the turbomachine incorporating bearing assembly  10   b . In addition, grinding or shimming can also be used to assist with pre-loading sleeve bearing  12   b  within squeeze film annulus H b . This process may be repeated with any of the embodiments of centering elements  150  discussed herein. 
     As indicated previously, an internal space  174   a  may optionally be provided in distal beam member  164   a , as shown in dashed lines in  FIG. 8B . Internal spaces  174   a  make distal beam member  164   a  and/or intermediate beam member  166   a  relatively thin-walled to allow for the deflection and compression of distal beam member  164   a  toward intermediate beam member  164   a  and intermediate beam member  166   a  toward base beam member  162   a . One or both of internal spaces  174   a  may be omitted, if desired, in centering element  150   a . Additionally, internal spaces  174   a  may each be provided as a plurality of individual internal spaces  174   a , for example in the manner shown in  FIG. 10E  described herein, rather than the singular space or void illustrated in  FIG. 8A . 
       FIGS. 9A and 9B  illustrate bearing assembly  10   b  with a second embodiment of centering elements  150   b . In centering elements  150   b , intermediate beam member  166   a  is omitted and distal beam member  164   b  and base beam member  162   b  are connected by a central connecting “post” portion or member  168   b  of body  160   b . Post member  168   b  will permit distal beam member  164   b  to deflect about post portion  168   b  and compress towards base beam member  162   b  when radial force is applied to centering element  150   b . Base beam member  162   b  and distal beam member  164   b  may each define an elongated internal space  174   b  making these members relatively thin-walled in the vicinity of post portion  168   b  to allow for the deflection and compression of distal beam member  164   b  about post member  162   b . One or both of internal spaces  174   b  may be omitted, if desired, in centering element  150   b . Additionally, internal spaces  174   b  may each be alternatively provided as a plurality of individual internal spaces  174   b , for example, in the manner shown in  FIG. 10E  described herein, rather than the singular space or void illustrated in  FIGS. 9A-9B . 
       FIGS. 10A and 10B  illustrate bearing assembly  10   b  with a third embodiment of centering elements  150   c . In centering elements  150   c , base beam member  162   c , intermediate beam member  166   c , and distal beam member  164   c  define an overall S-shape for centering elements  150   c . Intervening spaces  172   c  are defined between intermediate beam member  166   c  and base beam member  162   c  and distal beam member  164   c  and intermediate beam member  166   c  to allow deflection of distal beam member  164   c  and intermediate beam member  166   c . Deflection characteristics of distal beam member  164   c  and intermediate beam member  166   c  may be controlled by the sizing of cut-out areas  180  in the areas of body  160   c  connecting intermediate beam member  166   c  to base beam member  162   c  and connecting distal beam member  164   c  to intermediate beam member  166   c . Cut-out areas  180  may be provided in shapes other than the circular shape illustrated in  FIGS. 10A and 10B , such as oval, elliptical or be simply elongated, generally polygonal shaped cut-out areas  180 , as shown in  FIG. 10D . Cut-out areas  180  may also be omitted altogether if desired as shown in  FIG. 10C . As will be appreciated from  FIGS. 10A and 10B , intermediate beam member  166   c  and distal beam member  164   c  comprise two oppositely facing cantilevered beam springs which will deflect toward base beam member  162   c  when external radial force is applied to the body  160   c  of centering element  150   c , and provide a resilient counter-acting force to such a compressive radial force. 
     Finally, and as shown in  FIGS. 10E and 10F  with respect to centering elements  150   c , intermediate beam member  166   c  and distal beam member  164   c  may each define one or more internal spaces  174   c  to make these structures thinner-walled and aid in the deflection and compression of distal beam member  164   c  toward intermediate beam member  166   c  and intermediate beam member  166   c  toward base beam member  162   c . Generally, internal spaces  174   c  in this embodiment, and in the previous embodiments shown in  FIGS. 8A and 8B ,  9 A and  9 B, and in  FIGS. 11A-11E  to be discussed herein, may be used to adjust the overall “stiffness” of the respective centering elements  150 . The internal space(s)  174   c  in one or both of the distal beam member  164   c  and intermediate beam member  166   c  may be omitted, if desired, in centering elements  150   c . Additionally, the internal spaces  174   c  may be provided as a plurality of internal spaces  174   c  in the distal beam member  164   c  and/or the intermediate beam member  166   c  as shown in  FIGS. 10E-10F . The internal spaces  174   c  may also be elongated in the manner shown, for example, in  FIG. 9B  to span the length of the body  160   c  of the centering elements  150   c . 
       FIGS. 11A and 11B , illustrate bearing assembly  10   b  with a fourth embodiment of centering elements  150   d . Centering elements  150   d  are substantially similarly to centering elements  150   b  discussed previously, with the exception that base beam member  162   d  does not define an internal space as was the case in centering element  150   b . Accordingly, centering elements  150   d  will generally provide a stiffer reaction force to a radial force applied to centering elements  150   d  than will centering elements  150   b  of  FIGS. 9A and 9B . Centering elements  150   a - 150   d  described hereinabove are each essentially formed as a single or unitary component. Additionally, the thickness and length of the respective beam segments or members forming the respective centering elements  150   a - 150   d  may be altered to change the stiffness values of the respective centering elements  150   a - 150   d  as desired. 
     Alternative variations of centering elements  150   a  are shown in  FIGS. 8C-8E , wherein the body  160   a  of centering elements  150   a  is formed without an intermediate beam member  166   a  and defines one or more internal spaces  174   a  which take the place of intermediate beam member  166   1 . As shown in  FIGS. 8C-8D , a singular, elongated internal space  174   a  may be sufficient, or multiple internal spaces  174   a  may be provided as shown in  FIG. 8E . Each internal space  174   a  may be provided as a plurality of internal spaces  174   a  as illustrated in  FIGS. 10E and 10F  discussed previously. Additionally, as shown in  FIG. 8D , a singular, elongated internal space  174   a  may be defined with cut-out areas  180   a  similar to that illustrated in  FIG. 10B  or, further, as shown in  FIG. 10D  if desired. 
     While the present invention was described with reference to several distinct embodiments of a bearing assembly and support structure therefor, those skilled in the art may make modifications and alterations to the present invention without departing from the scope and spirit of the invention. Accordingly, the above-detailed description is intended to be illustrative rather than restrictive. The invention is defined by the appended claims, and all changes to the invention that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.