A study on the motion characteristics and their impact on the wind measurement post-processing of the GPS dropwindsonde Part I: effects of the wind-finding equations

Since Global Positioning System dropwindsonde wind measurements are taken in neither a conventional Eulerian framework nor a perfect Lagrangian framework, proper post-processing is necessary to derive conventional Eulerian wind statistics from dropwindsonde measurements. In this study, the equations governing the dropwindsonde motions were first linearized and then analytically solved to explore the effects of the wind-finding equations introduced by Hock and Franklin (Bull Amer Meteor Soc 80:407–420, 1999) when retrieving horizontal winds from dropwindsonde measurements. It is found that the wind-finding equations are essential for calculating turbulence statistics from dropwindsonde measurements. To confirm, numerical simulations of dropwindsonde motions in a pseudo-stochastic wind field were further conducted based on the full nonlinear dropwindsonde motion-governing equations. Based on the simulation results, the present paper showed the effects of the wind-finding equations and the companion paper discussed the impacts of various post-processing/composition schemes on both the mean and turbulent wind statistics composited from pseudo-dropwindsonde measurements.     

The variation of the GPS dropwindsonde drag coefficient and its impact on the wind retrieval from dropwindsonde measurements

The wind finding equations currently used to retrieve horizontal winds from Global Positioning System dropwindsonde wind measurements are derived based on a point object model in which the drag coefficient of the dropwindsonde is assumed to be a constant. The wind tunnel tests performed as part of this study showed, however, that the dropwindsonde aerodynamic coefficients vary appreciably with angles of attack. To investigate the impact of this finding, the dropwindsonde motion in a pseudo-stochastic wind field has been simulated using a motion model more sophisticated than the point object model. The results showed that, although the constant drag coefficient assumption is not supported by the wind tunnel test results, the wind finding equations still correctly calculate both the mean and the turbulence intensity profiles. In addition, a revised method to calculate the vertical wind was proposed based on the derivation of the improved motion model, which enhanced the accuracy of vertical wind estimates by including the real-time dropwindsonde drag coefficient and the dropwindsonde vertical acceleration into calculation.     

深水脐带缆结构阻尼的数值与试验研究

深水动态脐带缆内部结构复杂,其阻尼特性对脐带缆的舞动以及疲劳损伤有着重要的影响。脐带缆在和流体相互作用过程中,脐带缆内部构件可能会产生滑动,进而影响脐带缆的结构阻尼,这也使得真实海况中脐带缆的舞动和疲劳是一项复杂而值得深入研究的课题。为验证有限元模型能够很好地模拟脐带缆的结构阻尼特性,在考虑内部结构单元间摩擦的基础上,利用ANSYS建立了用于中国南海某油田的脐带缆多层滑移接触摩擦模型。同时,采用自由衰减法对该动态脐带缆开展了原型试验,测得了该缆的结构阻尼比与自振周期。通过对比有限元模型计算结果与原型试验结果发现：数值模型获得的该脐带缆的结构阻尼值与试验值非常接近,这为工程中获得脐带缆结构阻尼比的值提供了好的方向。     

A study on the motion characteristics and their impact on the wind measurement post-processing of the GPS dropwindsonde. Part II: impacts of post-processing/composition schemes

When the Global Positioning System dropwindsonde wind measurements are used, post-processing and composition approaches are necessary to calculate the vertical profiles of wind statistics. In order to understand the impacts of post-processing/composition schemes on the wind statistics calculated based on dropwindsonde measurements, various post-processing/composition schemes were utilized to post-process and to composite pseudo-dropsonde measurements resulting from numerical simulation of dropsonde motions in a pseudo-stochastic wind field. Since the wind statistics of the pseudo-stochastic wind field were specified, the comparison between wind statistics calculated based on pseudo-dropsonde measurements and the specified values provided some insights into the impacts of different post-processing/composition schemes. The post-processing/composition schemes investigated include the low-pass filter to reduce high-frequency dropsonde measurement noises, the finite difference scheme to calculate dropsonde accelerations, which is needed to dynamically correct dropsonde measurements and composition data size.