The temporal and spatial variability of the Yellow Sea Cold Water Mass in the southeastern Yellow Sea, 2009–2011

The Yellow Sea Cold Water Mass （YSCWM） is one of the important water mass in the Yellow Sea （YS）. It is distributed in the lower layer in the Yellow Sea central trough with the temperature less than 10℃ and the salinity lower than 33.0. To understand the variability of the YSCWM, the hydrographic data obtained in April and August during 2009-2011 are analyzed in the southeastern Yellow Sea. In August 2011, relatively warm and saline water compared with that in 2009 and 2010 was detected in the lower layer in the Yellow Sea central area. Although the typhoon passed before the cruise, the salinity in the Yellow Sea central trough is much higher than the previous season. It means that the saline event cannot be explained by the typhoon but only by the intrusion of saline water during the previous winter. In April 2011, actually, warm and saline water （T 〉 10~C, S 〉34） was observed in the deepest water depth of the southeastern area of the Yellow Sea. The wind data show that the northerly wind in 2011 winter is stronger than in 2009 and 2010 winter season. The strong northerly wind can trigger the intrusion of warm and saline Yellow Sea Warm Current. Therefore, it is proposed that the strong northerly wind in winter season leads to the intrusion of the Yellow Sea Warm Current into the Yellow Sea central trough and influenced a variability of the YSCWM in summer.

OWC air chamber performance prediction under impulse turbine damping effects

Oscillating water columns(OWCs)are most widely used in coastal wave energy conversion.The air duct opens into the atmosphere through the air turbine,which is the power take-off device,and this results in a pressure drop across the air chamber.However,because of the complex configure of the impulse turbine and its high rotation speed,it is difficult to install it in the experimental simulator and numerical model.Therefore,the turbine damping effects on the operation of the OWC air chamber are induced to predict its performance more accurately.Orifice plates are used as a substitute for the impulse turbine as it generates a similar pressure drop and power output;the experimental and numerical pressure drops and output powers are compared.A 3D numerical wave tank based on the two-phase VOF model is established using the commercial CFD code Fluent,which can predict air flow and pressure variations in the chamber and duct.Water surface elevations,air flow velocity and pressure variation inside the chamber with the orifice plate are studied numerically,and validated by the corresponding experimental data.The air chamber of the Yongsoo OWC pilot plant is used as the engineering project case.The operating performance of the air chamber installed with a 0.428D orifice plate as the substitute for the designed impulse turbine is computed and analyzed.It is found that the turbine damping effects will cause around 30%reduction in the peak values of the pneumatic energy output of the OWC air chamber in the resonant wave domain.

Development of temperature-robust damage factor based on sensor fusion for a wind turbine structure

Wind power systems have gained much attention due to the relatively high reliability, maturity in technology and cost competitiveness compared to other renewable alternatives. Advances have been made to increase the power efficiency of the wind turbines while less attention has been focused on structural integrity assessment of the structural systems. Vibration-based damage detection has widely been researched to identify damages on a structure based on change in d^mmic characteristics. Widely spread methods are natural frequency-based, mode shape-based, and curvature mode shape-based methods. The natural frequency-based methods are convenient but vulnerable to environmental temperature variation which degrades damage detection capability; mode shapes are less influenced by temperature variation and able to locate damage but requires extensive sensor instrumentation which is costly and vulnerable to signal noises. This study proposes novelty of damage factor based on sensor fusion to exclude effect of temperature variation. The combined use of an accelerometer and an inclinometer was considered and damage factor was defined as a change in relationship between those two measurements. The advantages of the proposed method are： 1） requirement of small number of sensor, 2） robusmess to change in temperature and signal noise and 3） ability to roughly locate damage. Validation of the proposed method is carried out through numerical simulation on a simplified 5 MW wind turbine model.