A moored floating platform has great potential in ocean engineering applications because the mooring system is necessary to keep a floating platform in the station. It relates directly to operational efficiency and safety of a floating platform. This study presents a comprehensive assessment of the dynamics of a moored semi-submersible in waves by performing model test and numerical simulation. First, a three-dimensional panel method was used to estimate the motion of a moored semi-submersible in waves. A semi-submersible is modelled as a rigid body with six degrees-of-freedom (6DOF) motion. Dynamic response analysis of a semi-submersible is performed in regular wave and irregular wave. Second, the model test is performed in various wave directions. An Optical-based system is used to measure 6DOF motion of a semi-submersible. Numerical results are compared with the experimental results in various wave directions. Wavelength and wave direction showed significant effects on the motion response of a semi-submersible in regular wave. Third, to obtain a better understanding of response frequencies, the time histories of motion responses in irregular wave are converted from the time domain to the frequency domain. Effects of the wave frequency component on motion responses and mooring dynamics are analyzed. Motion spectrum in irregular wave has a strong response to the natural frequency of a moored semi-submersible and the peak of wave frequency. Finally, exceedance probability is estimated to predict probable extreme values of motion responses of a moored semi-submersible as well as mooring dynamics.

The maneuvering performance of a ship on the actual sea is very different from that in calm water due to wave-induced motion. It is crucial to account for the ship's maneuverability in waves at the design stage. Numerous prior studies have investigated the maneuverability of ships in waves. According to the International Towing Tank Conference (ITTC) (ITTC, 2011), there are four methods of predicting the movements of a ship maneuvering in waves: experiments, two-time scale, unified theory, and contract for difference (CFD) methods.Yasukawa ( 2006) proposed a method of estimating the hydrodynamic force components, including added mass, wave damping, and wave excitation forces. In his study, the basic motion equations were divided into two groups, high-frequency induced motion problems, and low-frequency maneuvering problems.Yasukawa (2006, 2008) performed a free-running model test in regular waves using the SR108 container ship. The experiment was conducted with various wavelengths in head sea and beam sea conditions. Skejic and Faltinsen (2007, 2008) presented a seakeeping and maneuvering analysis of two ships. They focused on overtaking and replenishment maneuvers between two ships. Seo et al. (2011) applied linear and nonlinear ship motion analysis toanalyze ship-maneuvering performance in high-amplitude waves. The maneuvering performance of the S-175 container ship was discussed with regard to wave slope. Also, the wave drift force was calculated using the direct pressure integration method. Skejic (2013) presented a maneuvering simulation of ships in a seaway and discussed the significant role of unified maneuvering and seakeeping. Zhang et al.

Moored floating platforms have great potential in ocean engineering applications because a mooring system is necessary to keep the platform in station, which is directly related to the operational efficiency and safety of the platform. This paper briefly introduces the technical and operational details of an optical sensor for measuring the tension of mooring lines of a moored platform in waves. In order to check the performance of optical sensors, an experiment with a moored floating platform in waves is carried out in the wave tank at Changwon National University. The experiment is performed in regular waves and irregular waves with a semi-submersible and triangle platform. The performance of the optical sensor is confirmed by comparing the results of the tension of the mooring lines by the optical sensor and tension gauges. The maximum tension of the mooring lines is estimated to investigate the mooring dynamics due to the effect of the wave direction and wavelength in the regular waves. The significant value of the tension of mooring lines in various wave directions is estimated in the case of irregular waves. The results show that the optical sensor is effective in measuring the tension of the mooring lines.

We revisit our earlier paper, with two of the coauthors, in which we proposed an unbiased and consistent estimator μ^n for an unknown mutation rate μ of microorganisms. Previously, we proved that the associated sequence of estimators μ^n converges to μ almost surely pointwise on a nonextinct set Ω0. Here, we show that this sequence converges also in the mean square with respect to conditional probability measure P0·=P·∩Ω0/PΩ0 and that, with respect to P0, the estimator is asymptotically unbiased. We further assume that a microorganism can mutate or turn to a different variant of one of the two types. In particular, it can mean that bacteria under attack by a virus or chemical agent are either perishing or surviving, turning them to stronger variant. We propose estimators for their respective types and show that they are a.s. pointwise and L2-consistent and asymptotically unbiased with respect to measure P0.

Green water impact occurs frequently on offshore platform due to waves with a height greater relative to the freeboard of the structure. This phenomenon exerts a large impact load on the deck. In this paper, offshore platform models with green water protectors of various shapes were fixed to the center of a 3D wave tank to measure the impact pressure acting on the various points on deck and protectors. The impact pressure distribution differed depending on the protector shape, and various patterns of wave creeping up the protector were observed. The protector shape that exerted the lowest pressure impact on the deck will be useful in the deck design of offshore platform, and the model test results will be expected to be used for designers to select the best protector form.