Abstract
Hydraulic power-take-off (PTO) systems which utilize high-pressure oil circuits to transmit energy are widely applied in wave energy generation. The properties of hydraulic oil are significantly influenced by environmental conditions, and its dynamic viscosity is sensitive to temperature, especially in relatively low-temperature cases. This paper studies the characteristics of the hydraulic PTO when started in different temperature conditions via numerical analysis and experimental verification. An improved numerical model of the hydraulic PTO system is proposed, in which the effects of temperature on the hydraulic oil viscosity and hydraulic motor efficiency are quantitatively investigated, and consequently, the thermal-hydraulic characteristics can be sufficiently considered. The performances of the hydraulic PTO in start-up processes with different initial temperatures and in long term operation are assessed. The results show that the presented model can reasonably describe the hydraulic PTO characteristics. The efficiency of hydraulic PTO degrades when it starts at low temperatures. The efficiency increases in relatively high temperature, while larger fluctuations of the flow rate and output power are observed. This study can provide guidance for enhancing the efficiency and consistency of hydraulic PTO operating in actual sea conditions.
Highlights
As a widespread renewable energy source, ocean wave energy has gradually received extensive attention from scientists since the oil crisis broke out in the 1870s [1,2]
From the perspective of hydraulic oil characteristics, this paper studies the influence of temperature on the performance of the hydraulic power take-off (PTO) system during operation
The experiments were conducted in a hydraulic PTO test platform and the ECD movements were simplified as prescribed piston motions
Summary
As a widespread renewable energy source, ocean wave energy has gradually received extensive attention from scientists since the oil crisis broke out in the 1870s [1,2]. PTO systems are frequently employed in oscillating body WECs, and they use hydraulic oil circuits to transmit energy, which can cope with low frequency-large torque inputs of waves and overload protection. Their advantages of stabilizing power output are attractive for engineering applications. The focus of the research on the consistency and efficiency of the hydraulic PTO system is focused on how to select pivotal components and optimize parameters and control strategies, which ignored the influence of the characteristics of the working medium on the consistency of the output power and efficiency when the wave energy converters are running.
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