The taking tidal energy devices present similarities to the air current energy turbines. In fact the bulk of the engineerings in tidal devices utilize two to three blades to bring forth electricity. Tidal Energy Limited ( Fig.39 ) show the most advanced engineering, as they incorporate to their fixed turbine a swerve mechanism leting them to flip to be able to capture the maximal speed of the tides [ 62 ] .
Figure 1: Tidal Energy Limited device
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The penetration on bearing applications in Ocean Energy devices has brought out several interesting points. The first of import point to pull out is that the initial claim of SKF being able to supply a bearing solution for ocean energy devices can non be met, as the battalion of devices and engineerings runing otherwise necessitate different types of bearings to accommodate the demands of each class.
Conditionss and burdens, Ocean Energy Bearing Requirements
As to understand farther, a questionnaire has been sent to application applied scientists seeking to understand and acquire more penetration on the conditions and burdens subject on bearings. The questionnaire ( attached in Appendix ) was setup to measure the potency of apparent bearings in moving ridge and tidal energy. Unfortunately during the five months period merely few replies were given back to SKF. The makers that answered the questionnaire have been put in Table 16. The deficiency of replies was as already mentioned, due to the fright of unwraping excessively much information about their devices, the deficiency of cognition of burdens and conditions as their design is still in construct or design phase, or understanding of non-disclosure with other providers of bearings have hindered the assemblage of more information.
Bearing map and expected bearing life
Frequency of rotary motion
SKF or FAG
accommodate shaft burden and axial burden from propeller/ 20 old ages ( 175200hrs )
radial burden: 1- propeler weight 108kN. 2- shaft weight 58.8kN. 3-Coupling weight 19.6kN Axial burden ( thrust burden ) +/- 1160kN
0.5Hz ( 0.625Hz soap )
30 revolutions per minute ( 37.5rpm soap )
shaft tantrum: SRB 440p6/650F7 SRTB 420j6/730
Stern tubing seal ( non a radial shaft seal )
11 months for prototype trial ( oil lubrication, KEMEL TH-100 or Hydrox BIO 100 )
chief shaft bearing/ 25years
front bearing ( 241/630 ECA/W33 ) Fr: 80.6kN, Fa:1390kN / Rear bearing ( 23096 CA/W33 )
ocean current power generator bearing for chief shaft and swerving for blades/ 10 old ages
Radial burden: chief shaft front/back bearing: 2.93MN/104kN Axial burden: front bearing 2.71MN/ inactive burden for swerving bearing radial 1600kN and axial tilting minute 10100kNm
Andritz Hydro Hammerfest
actively looking for provider
swerve bearing depth 30m / 25years with 4 rhythms per twenty-four hours ( 36500 )
runing environment prohibitionist, but extremly humide ( 95-100 % ) , filled with pressurised Nitrogen ( 5bar ) / Maximum torsion for design 460kNm, max radial 250kN
0.5 – 1 deg/s
5 old ages
Aquamrine Power Oyster
Hinge between flap and anchored construction
Radial tonss =7.4MN, sway load= 2.5MN.
outside diameter of bearing 1200mm
20 yearsTable 1: Questionnaire Consequences
The advantages of apparent bearings have been shown to be more cost effectual and necessitate less care whilst transporting much higher tonss. The aim of the old subdivisions was to look into the type of bearing applications that need to be supplied for each industry, as a individual bearing engineering will non be able to run into all the demands of all makers of ocean energy devices.
The replies provided to the questionnaire were chiefly from Tidal Energy devices, and the purpose of the field bearing section was to measure the possibilities of replacing the already provided Ball bearings with Plain bearings or bushing, as the advantages of apparent bearings have been drawn out to be more cost effectual and be able to defy much higher tonss so conventional ball bearings. However a cardinal success factor was to measure the speeds that those makers claim. As apparent bearing or bushings can non run at high speeds.
For tidal devices, the close comparing with air current energy explains the prevailing usage of ball bearing for the rotary motion of the turbines, nevertheless to this twenty-four hours ball bearings are sing lading failures due to the high tonss that they are subjected to. This tax write-off can be carried out for tidal turbines, as from the tabular array the burdens are even greater partially due to the denseness of the H2O being much greater than air.
The plausible usage of a bushing would be to relieve the high tonss subjected on ball bearings nevertheless the keeping factor for the prominence of such application is the frequence of rotary motion that they will be subjected to. As bushing can non defy high speeds, treatments within SKF plain bearing section have lead to demo the possible option to ball bearings whilst still utilizing bushings. In fact treatment of new province of the art engineering enabling to bring on a hydrostatic movie as the first running of the turbines are created so go forthing the submersed construction to run hydro-dynamically minimising all types of wear and frictional losingss.
As a concluding designation procedure in the proficient section illustrated in the SKF direction theoretical account, the probe of all makers of apparent bearings that are providing or claim to be able to provide ocean energy engineering were identified.
Ocean Energy Bearing Suppliers
The probe was really difficult to set about, as providers of bearings every bit good as ocean energy makers did non desire to unwrap any information sing this affair. That is refering all the devices expect the 1s that are in commercial stage such as Pelamis, Aquamarine and some other taking Tidal Energy devices.
Figure 2: Schaeffler Bearings and Sliding stuff layout
In fact the merely published information sing bearings providers was found to be for both Pelamis and Aquamarine Oyster. Where Pelamis is trusting on the engineering of Schaeffler who is supplying them with bearings to accommodate their application ( Fig.50 ) [ 52 ] . No farther inside informations on the type of bearing stuffs they have used have been published.
However after analyzing the imperativeness releases on the company web site, Schaeffler claim that they have provided a bearing that eliminated all “ stick-slip ” with the usage of an advanced line drive stuff PTFE ( Teflon ) [ 63 ] . The latter will be discussed in the undermentioned chapter. After a meeting held with the Plain bearing section the decision brought out was that Schaeffler were supplying a bearing from their Elgoglide household, non listed in their catalogue [ 64 ] , nevertheless they still do non offer any H2O lubricated solution as all their bearings are tightly sealed. Figure 50 above shows the composing of the Elgoglide stuff that is used in their spherical field bearings ( bearing on the right, the line drive stuff is shown with a ruddy line ) . The exhibited bearings claim to hold coefficient of clash of 0.02 to 0.20, that is dependent on the tonss and skiding speed that are subjected on the bearing.
The other known provider to Aquamarine Power Oyster is Drie-D, the claims were brought out in a imperativeness release on HydroWorld [ 65 ] . It is understood that Drie-D is providing a spherical field bearing of 1.2m in diameter utilizing their D-Glide engineering stuff. The builder claims that these bearing provide low clash and low erosion and offer high burden transporting capacity ( Fig.41 ) [ 66 ] .
Figure 3: Drie-D D-glide bearing
The D-glide composite field bearing is composed of man-made fibres and rosins with PTFE. Drie-D claim that their bearing show clash degrees lower than fictile bearing stuffs, every bit good as to greased apparent bearings. Furthermore the “ stick faux pas ” issue is wholly vanished with the usage of the D-glide bearings, and their H2O soaking up is about negligible [ 66 ] . The survey of the D-glide catalogue revealed that the bearing supplied to Oyster is a derivative of the D-glide FC bearing, where Dire-D claims that the FC bearing is suited for the rough environments and fortunes i.e. in instance of linear applications where the counter face conditions are non every bit good cognize or controlled as the usual simple revolving gesture [ 66 ] .
Research has revealed that the figure of apparent bearing providers is someway limited. The list of provider is neither thorough nor complete as no information is available on the emerging new companies specifically for the engineering in inquiry. Thus the list comprises chiefly providers that have a huge experience in apparent bearings and/or offshore industry ( Table 17 ) .
Table 2: List of Ocean Energy Plain Bearing Rivals
PTFE tape line drive, endorsing uninterrupted woven glass fibre cloth laminate impregnated and cured with epoxy rosin
Continuous lesion PTFE, high strength fibres encapsulated in ego lubricating high temperature epoxy rosin, backup: lesion glass fibre epoxy rosin
Phenolic rosin matrix transporting man-made fibre with PTFE low wear
Orkot ( trelleborg )
Reinforced polymer ( man-made polymer metal )
PTFE layer several millimeters thick backed by Orkot polymer TXMM low wear
Homogeneous polymer signifier, elastomeric stuff low clash
Polymer filled with PTFE
Homogeneous polymer, 20 % PTFE fibres low wear/high PV
Fabric reinforced double bed laminate, glass fiber reinforced epoxy rosin base low friction/shock tonss
Homogeneous polymer signifier, thermoplastic stuffs, low wear
Lubron ( RBC )
Reinforcing polyester fibres thermosetting rosins and PTFE
High tonss low velocities, exellent dry wear belongingss in slow traffic circle or reciprocating bearings low clash, high impact
Designed to manage higher rotational and lenear velocities. ( submersed and semi-submerged )
Homogeneous polymer, PTFE based rosin Low wear/corrosion/velocity
Laminated plastic with infusing cloth with thermosetting rosin low wear/shock tonss
Homogeneous polymer signifier, stuff: Ultra High molecular weight polythene
The sum-up of all the possible providers to the Ocean Energy industry has been based on their catalogue claims. Equally good as on a judgement of their possible public presentation based on their stuff belongingss claimed on their web site deemed suited for the Ocean Energy industry. Table 17 shows a brief material description and high spots their key-performing feature. A rival catalogue was designed to obtain all the relevant information sing each bearing every bit good as their proficient catalogue ( appendix ) [ 67-77 ] .
From the proficient catalogue, a drumhead tabular array was created to enable a clear comparing of all the rivals. The tabular array included the chief of import standards deemed of import by SKF plain bearing section to compare it with their ain merchandises. Table 18 below shows an norm of these rivals and will be used as an appraisal to value the SKF offering.
Table 3: SKF catalogue VS. Competitor Average
Average bearing for Hydro
Max PV factor ( Mpa x m/s )
Compressive Strength Mpa
& gt ; than norm
& lt ; than norm
Tensile Strength ( Mpa )
& gt ; than norm
& lt ; than norm
Coefficient of clash
Max skiding velocity ( m/s )
Max inactive burden ( Mpa )
Max dynamic burden ( Mpa )
Surface coating ( um )
Volumetric Swell ( % )
The values presented for SKF bearings are drawn from the PV diagrams as SKF do non supply one alone value for their proficient specifications. In fact, the maximal allowable inactive tonss are dependent on the conditions the bearing is subjected to, therefore doing for a more accurate value, if force per unit area and speed standards ‘s are identified. However for the intent of comparing the maximal allowable values have been drawn for the comparing. The maximal inactive and dynamic tonss are the result of the compressive and tensile strength, as to maintain the mechanical stableness of the stuff, i.e. plastic/elastic distortion. On that standard the TX exhibits higher tensile and compressive strength since it is able to defy comparatively higher inactive and dynamic tonss. The instance continues with the SKF FRP ( fiber reinforced polymer ) bearing since they exhibit comparatively lower inactive and dynamic tonss hence their tensile and compressive strength are comparatively lower. This in no instance brings out the better public presentation of TX stuff, although it presents better tribological features. In fact the SKF offering of these two bearing types is due to its apprehension that each applications ( or client demands ) are different. The figure below depicts the wear rate of each of the FRP and TX stuffs over clip [ 78 ] .
Figure 4: Wear Behavior of SKF FRP and SKF TX stuffs over clip
The cloth line drive ( TX ) used in bearings is normally of 100th micrometer thickness whereas for the fibre reinforced polymers, the thickness is about a twosome centimetres. The “ terminal of life ” for the bearing is marked by the thickness of the cloth line drive for the TX bearing and the fibre reinforced polymer for the FRP bearing. The wear rate for the FRP stuffs shows a more additive signifier than the fabric line drive stuff. However the point to pull out of this graph is that dependant on the application and tolerances of the client a bearing can be selected, the FRP can farther make a spread of 3mm between the bearing and the shaft as its polymer matrix is have oning off, whereas 0.4 millimeters will demo the terminal of life of the cloth line drive bearing. Thus dependant on the conditions and velocities the FRP stuff may show a longer service life so the TX stuff, based on the premises described.
The benchmarking of the rivals will enable SKF to place high profile campaigners with bearings suited for the applications in ocean energy, every bit good as measure the stuffs used for a simple comparing with SKFs ‘ ain FRP and TX bearing.
Benchmarking of SKF chief rivals
As some success factors are more of import than others from the point of position of SKF, the burdening factor was established consequently, where it was viewed that rivals already involved in the engineering will transport the most weighting as they are a measure in front in informations aggregation and excavation. The public presentation of the bearing carried the 2nd highest burdening as from the proficient information ; the rivals possessing the highest tribological belongingss would able to defy the tough conditions of the seas. The invention and the ability to industry and work outside the available catalogue are of importance every bit good, as rivals who are able to treat and analyse the demands of the clients and industry a bearing consequently.
Table 4: Benchmarking Criteria ‘s and Weighting
Deduction in the market
Composition & A ; construction public presentation
Innovation ( dvlpmt competencies )
Work outside catalogue ( in-house production/engineering research
Apparent bearings: chief concern ( 9 ) , one of chief concerns ( 5 ) , one concern ( 3 ) , no concern ( 0 )
Market visual aspect
In add-on, it was of import to look into on the company ‘s profile. In fact the probe on whether the company has a chief focal point on apparent bearings or it is portion of their chief concern, or whether the company works on multiple platforms eventually demoing their market visual aspect. Table 19 above illustrates the weighting factors attributed for each standard ; the benchmarking was attached to the rival catalogue in the appendix.
The consequences of this benchmarking were so oriented at demoing the primary rivals of SKF in this field based on the classs they obtained. The tabular array below shows the primary and secondary rivals where SKF has to be able to set up itself within.
Table 5: Consequences of Benchmarking
Federal Mogul Deva
Michell Bearings ( R.R )
Primary SKF rival
Third category ( provider of marine stuffs )
Ball bearings ( short term deduction )
Ball bearings ( short term deduction )
Supporting SeaGen gear box
DYM field bearings
merely Asiatic company in the list
Influential in east Asia
Table 20 shows that Drie-D, Schaeffler, TrisTar, Orkot and Thordon should be considered as primary rivals. This led to looking into what type of bearing these rivals are providing, and categorise them in three chief groups that can be easy assessed by SKF with its bearing offerings. As SKF offers a Fabric Reinforced Polymer bearing every bit good as a Fabric liner/Filament lesion bearing, the two classs will be added to the tabular array along with Polymer Matrix Composites. Table 21 below illustrates the categorization of each bearing harmonizing to the standards proposed.
Table 6: Skiding stuff categorization harmonizing to SKF catalogue
Polymer Matrix Composites
Fiber Reinforced Polymers
Fabric Liner/Filament lesion
Thordon SXL & A ; Compac
Thordon HPSXL & A ; GM2401
Tristar UC300 -UC 400
The bulk of the rivals are utilizing the same engineering as SKF TX. The fabric line drive engineering enables the bearing to keep its structural rigidness and enables to cut down the clash and wear for optimized efficiency and public presentation.
From the primary rivals, it is known that Drie-D and Schaeffler are already provding bearing solutions to Oyster and Pelamis severally. The probe on the two old bearing providers set some uncertainties sing their potency in accomplishing the demands of ocean energy engineering. As both makers claim that they provide the best suited field bearings for the hardest of conditions for moving ridge and tidal energy. The bulk of the primary rivals offer a broad scope of field bearing from bushings to spherical field bearings. However Thordon a top rival provides the industry with bushings and hydrodynamic or inactive bushings from its experience in the Marine and Offshore industry.
As portion of the designation processes from the SKF direction theoretical account, the primary rivals to SKF were established and classified in conformity to SKF catalogue. The identify standard has enabled to cast the visible radiation on the different possible field bearing deduction in each engineering, brushing up on the possible tonss and forces that the bearings will be subjected to. The potency of providing one bearing to accommodate all application is out of focal point, the apprehension of environmental restraints it subjected to is critical, as the proficient scheme has been elaborated upon the concluding scheme in the methodological analysis is the analysis of the scientific and proving that have been done in the field of ocean renewable energy.