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首页> 外文会议>International Conference on Offshore Mechanics and Arctic Engineering, Jun 23-28, 2002, Oslo, Norway >MAXIMUM LIKELIHOOD METHOD AS A MEANS TO ESTIMATE THE DIRECTIONAL WAVE SPECTRUM AND THE MEAN WAVE DRIFT FORCE ON A DYNAMICALLY POSITIONED VESSEL
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MAXIMUM LIKELIHOOD METHOD AS A MEANS TO ESTIMATE THE DIRECTIONAL WAVE SPECTRUM AND THE MEAN WAVE DRIFT FORCE ON A DYNAMICALLY POSITIONED VESSEL

机译：最大似然法估算动态定位船舶上的方向波谱和平均波力

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摘要

Feed forward in control theory is a method in which real time information about system disturbance is fed into the controller to improve its performance. As such, feed forward of the wave drift forces would improve DP behavior of a ship in terms of fuel consumption as well as position keeping. In the present study the wave drift forces have been divided in a constant part and a low frequent oscillating part. The constant part directly depends on the directional wave energy spectrum. In this paper the directional spectrum and mean drift force will be estimated from six relative wave height measurements on a dynamically positioned vessel. The Extended Maximum Likelihood Method (EMLM) is known to make a reliable estimate of the directional wave spectrum from wave measurements at fixed locations in the wave field. For a wave feed forward application the EMLM had to be implemented on a moving ship. Six relative wave height probes have been installed on board of a shuttle tanker. The EMLM has been applied to these relative motions and the low frequent yawing motion has been taken into account to calculate an earth bound spectral estimate. The estimate for the spectrum is based on a 30min average and is updated every minute in a moving average algorithm. Finally, the mean wave drift force is calculated for the actual heading of the ship.
机译：控制理论中的前馈是一种将有关系统扰动的实时信息馈入控制器以提高其性能的方法。这样，波浪漂移力的前馈将在燃料消耗以及位置保持方面改善船舶的DP性能。在本研究中，波浪漂移力被分为恒定部分和低频振荡部分。常数部分直接取决于定向波能谱。在本文中，将从动态定位的船舶上的六个相对波高测量值中估算出方向谱和平均漂移力。已知扩展最大似然法（EMLM）可根据波场中固定位置处的波测量结果对方向波谱进行可靠的估计。对于波浪前馈应用，必须在移动的船舶上实施EMLM。航天飞机上安装了六个相对波高探头。 EMLM已应用于这些相对运动，并且考虑了低频偏航运动以计算地球边界频谱估计。频谱的估算基于30分钟的平均值，并在移动平均值算法中每分钟更新一次。最后，计算出船舶实际航向的平均波漂移力。

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