Cylinder Bore Wear Damage Analysis of a Heaving-Buoy Wave Energy Converter With Hydraulic Power Take-Off

2010 ◽  
Author(s):  
Limin Yang ◽  
Torgeir Moan
Keyword(s):  
Dynamic Response ◽  
Film Thickness ◽  
Wave Energy ◽  
Stribeck Curve ◽  
Cylinder Wall ◽  
Hydraulic Power ◽  
Composite Surface ◽  
Lubrication Regime ◽  
Wear Damage ◽  
Cylinder Bore

Wave energy is a non-polluting and renewable source of energy. Among several wave energy converters (WEC), an oscillating body with a hydraulic power take-off (PTO) is commonly used for energy conversion. For such a hydraulic system, the piston ring and cylinder play very important roles in achieving desired energy converting performance and durability. Among the failure modes of the ring-bore components, wear is a prevailing one. Compared with the ring wear, cylinder wear is more important to the manufacturer and user, because cylinders are more expensive to replace than the rings. Since the floating body is exposed to irregular incident waves, the dynamic response of the PTO is also random. The position of maximum accumulated wear damage along the cylinder bore cannot be as easily determined as the engine bores where the maximum wear occurs near the Top Dead Centre (TDC). It is controlled by the characteristic dynamics of the system together with the lubrication of the interface which can be modelled by the well-known Stribeck curve. The purpose of this paper is to establish and apply a method for estimating the wear damage along the cylinder bore. The dynamic response of the WEC system is based on the nonlinear mathematical model established by Yang et al [1]. A particular issue in this research is to calculate the dimensionless film thickness λ (the ratio between the oil film thickness h and the composite surface roughness σ) in the lubricated contacts and then determine the lubrication regime according to the Stribeck curve. Combining the wear coefficient which is related to the lubrication regime and the contact pressure, the bore wear damage along the cylinder wall is predicted. In this paper, the bore wear damage is estimated on the basis of time domain simulations. The results show that the bore wear distribution is affected by two main factors: sea state condition and the nonlinearity of the PTO system. The position of the bore where the maximum accumulated wear occurs is predicted. Finally, the relative contribution of wear damage from different sea states is obtained.

Stribeck Curve for Starved Line Contacts

2006 ◽  
Vol 129 (1) ◽  
pp. 181-187 ◽  
Author(s):  
I. C. Faraon ◽  
D. J. Schipper
Keyword(s):  
Film Thickness ◽  
Layer Thickness ◽  
Boundary Lubrication ◽  
Numerical Data ◽  
Contact Model ◽  
Stribeck Curve ◽  
Lubrication Regime ◽  
Straight Line ◽  
Line Contacts ◽  
Good Agreement

This paper discusses a mixed lubrication model in order to predict the Stribeck curve for starved lubricated line contacts. This model is based on a combination of the contact model of Greenwood and Williamson and the elastohydrodynamic (EHL) film thickness for starved line contacts. The starved solution to be implemented in the EHL component is obtained by using numerical data of Wolveridge, who computed the starved film thickness for smooth line contacts. Calculations are presented for different oil supply layer thickness over roughness values (hoil∕σs). For values of the oil layer thickness over roughness ratio larger than approximately 6, the Stribeck curve and separation between the rough surfaces do not change compared to the fully flooded situation. If the oil layer thickness over roughness ratio is in the range of 6 down to 0.7, friction starts to increase and the film thickness decreases. When the oil layer thickness over roughness ratio is less than approximately 0.7, the Stribeck curve tends to transform into a straight line and separation stays at the same value as in the boundary lubrication regime. Comparison between measurements and calculations is made and a good agreement is found.

Experimental Investigation of Transition in Lubrication Regime for Thin-Film Coated Surfaces

2012 ◽  
Author(s):  
C. Lorenzo Martin ◽  
O. O. Ajayi ◽  
S. Torrel ◽  
G. R. Fenske ◽  
R. A. Erck
Keyword(s):  
Thin Film ◽  
Experimental Investigation ◽  
Wear Behavior ◽  
Sliding Contact ◽  
Fluid Film ◽  
Stribeck Curve ◽  
Composite Surface ◽  
Mechanical And Tribological Properties ◽  
Lubrication Regime ◽  
The Impact

Friction and wear behavior of lubricated sliding contact is determined by the operating lubrication regime. A useful approach to determining the operating lubrication regime is the calculation of the λ ratio, which is defined as the ratio of lubricant fluid film thickness (h), and the composite surface roughness (ơ) of contacting surfaces (λ = h/ơ). Thin-film tribological coatings are increasingly being used for application in lubricated machine elements such as gears and bearings. It is usually assumed by design engineers that application of thin-film coatings has no effect on fluid-film lubrication. This paper presents our experimental investigation of the impact of several (5) commercially available coatings on lubrication regime during a unidirectional sliding contact. Using a ball-on-flat contact configuration and lubricated with PAO basestock oil, tests were conducted in which the λ ratio was varied as a function of time, for both uncoated and coated flat specimen. In test with uncoated flat, the various distinctive lubrication regime of hydrodynamic, mixed and boundary were observed as indicated by the measured friction coefficient (Stribeck Curve). In tests with some of the coatings, especially the carbon based DLCs, there was no obvious distinctive transition in lubrication regime. In other coatings (ex. TiCN), various lubrication regime were also observed; although the rate of transition from one regime to the other was different. The effects of coatings are attributed to their inherent mechanical and tribological properties as well as their impact on the run-in process.

Research on the hydraulic power take-off unit of a hybrid wave energy converter

2016 ◽  
Author(s):  
Ke Sun ◽  
Wenke Ge ◽  
Liang Luo ◽  
Hui Liang ◽  
Chicheng Xu ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Hybrid Wave ◽  
Energy Converter ◽  
Hydraulic Power

Control strategies for a wave energy converter connected to a hydraulic power take-off

2011 ◽  
Vol 5 (3) ◽  
pp. 234 ◽  
Author(s):  
P. Ricci ◽  
J. Lopez ◽  
M. Santos ◽  
P. Ruiz-Minguela ◽  
J.L. Villate ◽  
...  
Keyword(s):  
Wave Energy ◽  
Control Strategies ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Hydraulic Power

Analysis of Tribological Performance of Piston Ring Lubrication

2011 ◽  
Author(s):  
Yibin Guo ◽  
Wanyou Li ◽  
Dequan Zou ◽  
Xiqun Lu ◽  
Tao He
Keyword(s):  
Film Thickness ◽  
Friction Force ◽  
Power Loss ◽  
Piston Ring ◽  
Design Parameters ◽  
Oil Film ◽  
Starved Lubrication ◽  
Piston Ring Lubrication ◽  
Cylinder Bore ◽  
Lubrication Conditions

In this paper a mixed lubrication model considering lubricant supply conditions on cylinder bore has been developed for the piston ring lubrication. The numerical procedures of both fully flooded and starved lubrication were included in the model. The lubrication equations and boundary conditions at the end of strokes were discussed in detail. The effects of piston ring design parameters, such as ring face profile and ring tension, on oil film thickness, friction force and power loss under fully flooded and starved lubrication conditions due to available lubricant supply on cylinder bore were studied. The simulation results show that the oil available in the inlet region of the oil film is important to the piston ring friction power loss. With different ring face crown heights and tensions, the changes of oil film thickness and friction force were apparent under fully flooded lubrication, but almost no changes were found under starved lubrication except at the end of a stroke. In addition, the oil film thickness and friction force were affected evidently by the ring face profile offsets under both fully flooded and starved lubrication conditions, and the offset towards the combustion chamber made a large contribution to forming thicker oil film during the expansion stroke. So under different lubricant supply conditions on the cylinder bore, the ring profile and tension need to be adjusted to reduce the friction and power loss. Moreover, the effects of lubricant viscosity, surface composite roughness, and engine operating speed on friction force and power loss were also discussed.

Effects of Misaligned Wave and Wind Action on the Response of the Combined Concept WindWEC

2018 ◽  
Author(s):  
Madjid Karimirad ◽  
Constantine Michailides
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Wave Energy ◽  
Power Production ◽  
Energy System ◽  
Mooring Line ◽  
Offshore Platforms ◽  
Dynamic Simulations ◽  
Line System ◽  
Wind Action

In the present paper, the effects of misaligned wave and wind action on the dynamic response of the WindWEC combined concept are evaluated and presented. WindWEC is a recently proposed combined wind and wave energy system; a hybrid offshore energy system that consists of: (a) a 5MW floating wind turbine supported by a spar-type substructure (e.g. Hywind), a Wave Energy Converter (WEC) that is of heaving buoy type (e.g. Wavestar), (c) a structural arm that connects the spar with the WEC and (d) a common mooring system. Hybrid offshore platforms are combining wave and wind energy systems and are designed in order to gain the possible synergy effects and reduce the cost of generated electrical power while increasing the quality of delivered power to grids. During the lifetime of a combined concept, wave and wind can be misaligned which may affect the dynamic response and as a result the functionality of it. In particular, for asymmetric configurations, the misalignment of the wave and wind may result in unexpected behaviour and significant effects that may reduce the produced power. For the case of the WindWEC concept, the relative motion of the spar platform and WEC buoy results to the produced power. In this paper, the dynamic response and power production of the buoy type WEC and wind turbine are examined for different loading conditions where the wave and wind are misaligned. Integrated/coupled aero-hydro-servo-elastic time-domain dynamic simulations considering multi-body analyses are applied. The motion, structural and tension responses as well as power production are examined. The misalignment of wave and wind results to higher loads that affect the mooring line system and motion responses of the spar. It is found that the produced power of wind turbine is not significantly affected.

A high-precise model for the hydraulic power take-off of a raft-type wave energy converter

Energy ◽  
2021 ◽  
Vol 215 ◽  
pp. 119107
Author(s):  
Changhai Liu ◽  
Min Hu ◽  
Wenzhi Gao ◽  
Jian Chen ◽  
Yishan Zeng ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Hydraulic Power ◽  
Type Wave
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