Airborne Electromagnetic Sea Ice Thickness Sounding in Shallow, Brackish Water Environments of the Caspian and Baltic Seas

Ice engineering projects often rely on the knowledge of ice thickness in shallow, brackish water like in the Baltic and Caspian Seas. By means of field data and model results, the paper shows that helicopter-borne electromagnetic induction measurements using frequencies of 3.68 and 112 kHz can yield accurate thickness estimates with salinities as low as 3 ppt. The higher frequency yields the strongest EM signals. In addition, in shallow water the higher frequency is less sensitive to the sea floor signal, and can thus be used in water depths as shallow as 4 to 6 m, depending on flying altitude. Because the low frequency signal is very sensitive on shallow water depth, a combination of both signals will allow the retrieval of both ice thickness and water depth.

A Coupled-Mode Technique for the Run-Up of Non-Breaking Dispersive Waves on Plane Beaches

A coupled-mode model is developed and applied to the transformation and run-up of dispersive water waves on plane beaches. The present work is based on the consistent coupled-mode theory for the propagation of water waves in variable bathymetry regions, developed by Athanassoulis & Belibassakis (1999) and extended to 3D by Belibassakis et al (2001), which is suitably modified to apply to a uniform plane beach. The key feature of the coupled-mode theory is a complete modal-type expansion of the wave potential, containing both propagating and evanescent modes, being able to consistently satisfy the Neumann boundary condition on the sloping bottom. Thus, the present approach extends previous works based on the modified mild-slope equation in conjunction with analytical solution of the linearised shallow water equations, see, e.g., Massel & Pelinovsky (2001). Numerical results concerning non-breaking waves on plane beaches are presented and compared with exact analytical solutions; see, e.g., Wehausen & Laitone (1960, Sec. 18). Also, numerical results are presented concerning the run-up of non-breaking solitary waves on plane beaches and compared with the ones obtained by the solution of the shallow-water wave equations, Synolakis (1987), Li & Raichlen (2002), and experimental data, Synolakis (1987).

A Method to Implement the Random Signals for Time Varying Offshore Wave Height During Storm Condition in an Intra-Wave Period Wave Model

In this paper, a method to implement the surface elevation at the offshore boundary during storm conditions is presented in the intra-wave period wave model. At storm condition, the offshore incident significant wave height is time varying. In the case of time varying incident wave height, the JONSWAP energy spectrum can be manipulated as follows: H1/32s(f). s(f) is the energy density function for a unit wave height. During a storm event not only the offshore boundary significant wave heights but also the peak frequency varies. If we choose a mean peak frequency during a storm event, s(f) can be calculated for the mean peak frequency for the storm event. The amplitudes of the component waves for the random signals are calculated from the unit energy density function s(f), and the phase angle of the component wave, So we can numerically generate surface elevation time series for the time varying offshore wave heights. The method was verified in the intra-wave period wave model using field measurements at Sea Palling site Norfolk UK.

Numerical Simulations of Large Deep Water Waves: The Application of a Boundary Element Method

This paper concerns the description of extreme surface water waves in deep water. A fully nonlinear numerical wave model in three dimensions is presented, based on the Boundary Element Method (BEM), and is applied to nonlinear focusing of wave components with varying frequency and direction of propagation to form highly nonlinear groups. By using multiple fluxes at corners and edges of the numerical domain the “corner problem” associated with BEM-based models in physical space is overcome. A two-dimensional version of the method is also employed to model unidirectional cases, and examples presented include the focusing of Top Hat spectra in deep water to form highly nonlinear wave groups at or close to their breaking limit. The ability of the model to accurately simulate these sea states is highlighted by comparison to the fully nonlinear model of Bateman, Swan and Taylor (2001, 2003).

Non-Linear Effects of Roll Damping Tanks on Ship Motions

This article describes the application of two numerical methods of computing the flow in u-tube and free surface roll damping tanks. These methods account for the most important non-linear effects in tank flows. i) The programs based on these methods are integrated in a non-linear time simulation strip program. ii) Response curves of tanks are computed with the mentioned tank programs and the results are incorporated in a linear strip program. iii) With both strip programs (linear and non-linear), sea keeping computations are carried out and the results are compared.

Sea Water Distillatory Using Rising Film on the Fluted Surface of Horizontal Tubes

The purpose of this study is to investigate the mechanism of the seawater distillatory using rising liquid thin film on the fluted surface of a horizontal tube. By analyzing the formation of the rising film, a process of the HRF evaporators was designed to analysis the efficiency of the system. The numerical solution of heat transfer model shows that the temperature difference of HRF in one effect is lower than that of HFF. The behaviors of the flow characteristics were discussed. The results show that the rising liquid thin film could be formed when the rate of roll equaled 15°. The results from theoretical analysis suggest that seawater distillatory using rising liquid thin film on the fluted surface of a horizontal tube was especially suitable for the wobble environment.

First Experience in the Next Generation Ice Laboratory for Testing Ships and Structures

Ice model testing has a history of almost 50 years. The first basin started operation in the middle of 1950ies in Russia by Arctic and Antarctic Research Institute (AARI). Ever since there has been a number of facilities built worldwide. In Finland the first facility was built by Wa¨rtsila¨ in 1969 for testing tankers intended for North-west passage (Manhattan project). In the eighties new facilities were built in Finland, Germany, Canada, Russia and Japan. In the present facility of Kvaerner Masa-Yards Arctic Technology (MARC) in Helsinki the operation started in 1983 under the name of Wa¨rtsila¨ Arctic Research Centre (WARC). The operation of the facility was originally planned to continue till 2011, but as part of the Helsinki City planning activity it was agreed that the facility is to end its successful work during 2005. In spring 2004 decisions were made by the new parent Aker Yards group and Aker Finnyards (that time Kvaerner Masa-Yards) to build a new facility and establish a separate company to handle ICE ISSUES for the whole Aker group. The new company, Aker Arctic Technology “AARC”, started operation in the beginning of 2005 and the new model testing facility was opened in February 2006. Aker Arctic Technology Inc. is owned by Aker Finnyards, Aker Kvaerner, Wa¨rtsila¨ and ABB. The services of the new company, in addition to the traditional model testing and related issues (environment studies, design bases and ship design concepts) will cover also total vessel design packages. This paper describes the novelties of the new ice model testing facility and reveals technical improvements, lessons learned and possibilities for more enhanced operation. Also the first experience in the new facility will be discussed.

Laboratory Simulation and Analysis of Wave Groups

The coastal and offshore structures are some times exposed to group of waves with successive higher wave elevations exceeding the significant wave height, which is considered to be vulnerable for the stability of the structures. Hence, the knowledge on the existence and frequency of occurrence of ocean wave groups at a particular region of interest is important for the design of the ocean structures. In the present study, the wave groups were simulated theoretically and the same was generated in the laboratory wave flume. The measured wave elevations were analysed through statistical, spectral and wavelet approaches to detect the existence of the groupiness.

Instantaneous Spectral Analysis of Non-Stationary Ship Motion Data

The time varying coefficient vector autoregressive (TVVAR) modeling is applied to the cross-spectral analysis of non-stationary ship motion data. Introducing the instantaneous response, a vector autoregressive model can be reduced to simple time varying coefficient autoregressive (TVAR) models for each ship motion and the required CPU time is effectively reduced. The TVVAR model and stochastic perturbed difference equations are transformed into a state space model. The vector-valued unknown coefficients can be evaluated and the instantaneous cross spectra of ship motions can be calculated at every moment. The results showed good agreements with one of the TVAR modeling and also with the stationary autoregressive (SAR) modeling analysis under stationary conditions. Furthermore, the instantaneous relative noise contribution was also estimated using the TVVAR coefficients and illustrated how the structure of a spectrum changed according to the ship manoeuvres for the first time. Optimum order of the model and Akaike’s information criterion were also examined for several changes of parameters. Moreover, it is confirmed that the TVVAR modeling can estimate the instantaneous cross spectra and relative noise contribution of ship motions even under non-stationary conditions.

Satellite Observation of the Mesoscale Features in the Taiwan Strait

In this paper, we discuss the kinematic properties of the mesoscale features in the Taiwan Strait (TS). Two kinds of mesoscale features can be seen in the TS. One is the shear wave; it is a lateral wavelike train with phase speed and wave period. The other one is the eddy-like cold-water wedge; it mainly rotates with a little translation. The shear wave mainly occurs in the boundary of the China cold water along the western TS in winter and spring. The eddy-like cold-water wedge can be seen in the mid-winter when the strong southward China coastal cold water covers up most of the northern TS and creates a very unstable front with the northward warm water. In this study, selected NOAA satellite AVHRR channel 4 infrared images during 2000–2003 are considered to detect the movement of the above mesoscale features through a feature-tracking method. It is found that the development of these features is highly related to the monsoon winds. Meanwhile, the local tidal pattern can also affect their movements.