Status and needs for ice tank testing in a changing climate

The drilling rig Sunkar, owned and operated by Parker Drilling under contract to Agip KCO, was the first drilling rig in the North Caspian Sea. In this area sea ice may occur between November and April. The original ice protection concept of the drilling rig was based on the fact that ice loads were partly taken and/or reduced by two rows of heavy piles. As an alternative concept ice model tests for Sunkar with installed ice barriers (Ice Rubble Generators) around the rig were carried out in the Large Ice Model Basin of HSVA in order to establish the design ice loads and to prove that the design forces can be reduced significantly by using these ice barriers. The test series were carried out in 1.3 m thick level ice with a bending strength of 770 kPa. Ice drift angle, ice drift speed, spacing between the ice barriers, as well as the angle of the ice barriers were varied. The design water level simulated in the model tests was about 4 m. As maximum measured ice load values are a result of coincidental ice failure occurrences these values are much more scattered than the mean values of ice model tests. Even if an individual model test could be repeated exactly, i.e. exactly within measurable limits, the maximum load would be different. Therefore the design load needs to be obtained by using a sophisticated statistical approach. To establish the design load an extreme value distribution, a Gumbel-Probability-Distribution (GPD) for each individual model run has been applied. The ice model tests have shown that a significant ice force reduction can be achieved if the drilling rig Sunkar is protected with ice barriers. The reduction of the maximum horizontal global ice load amounts to approx. 63% when Sunkar is protected by ice barriers. The ice barriers initiate ice rubble and areas of rafted ice as well as ice accumulation between the barriers, which lead to ice bridging with a spacing of 60 to 80 m between the ice barriers. As a final result it was found that the stability of Sunkar will be sufficient under any angle of drifting ice if ice barriers are installed.

Different kinds of offshore structures are designed and built to resist the scenarios of the arctic environment. This paper focuses on different ice load scenarios and the challenges for fixed offshore structures. Model test methods will be presented to assess the suitability of the design for the corresponding environmental scenarios. Measurement possibilities will be explained monitoring the design challenges as ice resistance, vibrations and encroachment of ice. The feasibility of different ice model test setups will be described and the main observations will be presented. The findings of the general phenomena of the resistance and encroachment will be discussed to assist the design process of offshore 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.

The experimental studies in the ice model tank of the Krylov State Research Centre are described in the paper. This study aimed at researching a possibility of close-coupled towing of large-sized vessels by icebreaker. The displacement of considered commercial vessels is several times greater than the icebreaker displacement. Due to the fact that an amount of cargo transported along the Northern Sea Route is growing every year and new terminals are being constructed for the export of raw materials extracted in the Arctic, it has been shown in the paper that new transport vessels with high cargo capacity should be designed and built for the efficient operation of terminal. It has also been shown that the organization of independent year-round operation of such vessels in the Arctic region is extremely difficult, therefore, even at the stage of their design it’s important to consider the possibility of their escorting by existing icebreakers. The feasibility of close-coupled towing in the escorting of large-sized vessels with low ice class by icebreakers in the Arctic waters has been studied in the paper. The models of the greatest existing nuclear-powered icebreaker and conditional bulk carrier are used as an object of the ice model tests. The study of the close-coupled towing features in the continuous flat ice conditions is carried out at straightforward movement and gyration, as well as for the case of an emergency stop of the icebreaker. During ice model tests the ice forces acting on the hull of the model are measured, as well as the load on a towing notch with rubber fenders in the stern of icebreaker and the tension in the wire rope. The comparison of the wire rope tension with its breaking force is taken as a criterion to assess the possibility of the close-coupled towing operation. The results can be used as the basis for choosing the hull concept of the future large-sized vessels, its ice class and main dimensions and in strategic simulations of Arctic marine transport systems.

: This report presents the results of resistance and propulsion tests in level ice of a 1:20-scale model of the R-class icebreaker of the Canadian Coast Guard. On the basis of the model test results, full-scale performance is predicted and compared with available full-scale trials data. Predicted ice resistance and required propeller rpm, thrust and delivered power are lower than full-scale measurements. This disagreement was attributed to the fact that the ship model had a much lower ice friction coefficient than the prototype. On the other hand, predictions of thrust and power for a given ship speed and propeller rpm are in good agreement with corresponding full-scale measurements.

To determine the bank-head’s ice force of the lead-navigating bank at key position that faces the ice directly of certain water conservancy, ice model test in reduced scale is designed and carried out based on the local situation on the spot and data observed. Preliminary conclusions are got through the analysis of the experimental data such as effect of the ice velocity on the ice force, ratio of components of forces when ice sheet acting on the vertical bank-head, ice force ratio of vertical to 45° incline as well as ratio of level ice force to the vertical ice force when acting on 45° incline. Finally, suggestions on determination of the ice force using formula are given after comparison between the result calculated by the present formula of ice force and the experimental results.

The dynamic characteristics of the flow around the pile directly determine the distribution law of the force of the flow on the pile, which is the basis of the calculation of the flow load of the hydraulic structure. At present, the model test and numerical simulation methods are mainly used to study the flow characteristics around the pile. There are problems of model scale effect and test accuracy in the laboratory model test, and inherent problems in the numerical simulation method, such as the determination of medium parameters, mesh division, and boundary conditions. Therefore, the research results cannot reflect the actual situation of the interaction between water flow and pile. This paper developed a field test system for measuring the hydrodynamic pressures on surface of piles which are the vital foundations of wharves under superhigh Reynolds number. And the analysis methods of in-situ data, which can realize the multifunction including calibration and transformation for test data, frequency and time-domain statistical analysis process, were put forward according to the theory of stationary random process and mathematical statistics method. A representative frame wharf located in the upper reaches of the Yangtze River was performed as a case study, and the developed system was utilized to operate the in-situ test on this practice. Application showed that the field test system and the analysis methods can be applied to obtain the more accurate distribution of the pile surface hydrodynamic pressure. And the drag coefficient in wharf field ranged from 0.30 to 0.40. These findings in this paper may provide significant technical support for the in-situ test in similar structures and some reference for drag force calculation of flow around pile in the engineering design.

Physical model tests in ice are performed at two different model scales with a tender design bridge pier for the Great Belt West Bridge in Denmark. The 6.6‐km‐long West Bridge constitutes the western part of the 18‐km‐long Great Belt link connecting Denmark's two main islands, Zealand and Funen. The investigated pier has two vertical cylindrical shafts penetrating the ice level. A comparison of tests at scale 1:14.76 carried out at Hamburgische Schiffbau Versuchsanstalt (HSVA), in Hamburg, Germany, to tests at scale 1:30 at the Hydraulics Laboratory of the National Research Council (NRC), Ottawa, Ontario, Canada, lends support to the use of Froude's model law for ice loads on vertical structures. The removal of loads due to structural oscillations from the recorded force time series is necessary to obtain comparability between data sets, and it has a substantial effect on conclusions regarding scaling. Once proper processing to remove loads from structural oscillations is completed, the test series from the different laboratories compare favorably. This gives confidence in the ability of different ice laboratories to reproduce each other's results.

To obtain the flow characteristics inside the draft tube of the model Kaplan turbine, a model test method was developed and carried out in this paper. The method includes introducing the model test system, test method, and parameters of model Kaplan turbine. Subsequently, experiments are conducted under different operating conditions and the results are analyzed. The result shows that, for the same blade angle and unit speed, operating conditions with larger guide vane openings (GVO) generally have higher axial velocities and lower tangential velocities than those with smaller GVO. In addition, particularly at higher flow velocities, a low velocity or backflow zone can occur in the center of the draft tube. Vortex rope is found to have a significant impact on the turbulence intensity in the mid-section of the draft tube, resulting in an unstable flow state. Also, under higher unit speed operating conditions, the turbulence intensity in the middle of the measurement area is greater and has a larger sphere of influence. Finally, the tangential pulsation intensity at the same measuring point under the same operating conditions is larger than the axial pulsation intensity, showing that vortex ropes have a more significant influence in the tangential direction.

This report discusses the effect which different methods of simulating an irregular seaway has on the ability to predict second order behaviour of moored offshore structures by model tests. A theoretical discussion of the problem is given. This is followed by the experimental results obtained from model tests of an offshore platform subjected to different simulated irregular seaways. These were produced by the two main methods of simulation applied today. One is to superimpose a finite number of regular wave trains. The other consists in filtering white noise so as to obtain a time series with the correct spectral shape, usually in the form of an electric signal, which is then used to guide a wave maker. The conclusion to be drawn from the obtained results is that the second method of simulating an irregular seaway gives us the most reliable estimate of the second order behaviour of moored offshore structures. 1. INTRODUCTION This report is part of a research program which centers on the investigation of the slowly varying second order wave forces induced on a floating structure resulting from non-linear interactions between contiguous parts of the wave spectrum, see for instance references (1), (2), (3) and (4). The practical importance of these second order forces has its origin mainly in the offshore activities. When drilling for oil from a floating platform, it is important to keep the platform in an approximately fixed position over the drilling hole. This is done mostly by mechanical mooring. But to be able to design these mooring systems properly, it is necessary to have a good quantitative prediction of the wave-induced loads that they must be capable of withstanding. When analyzing the recorded response of the moored large-volume structures applied in the offshore sector to an irregular wave field, a distinct characteristic property presents itself. It turns' out that the motion of the structures take place within two different frequency domains. One corresponds directly to the waves, while the other takes place in a frequency domain characterized by much longer periods than those of the wave field itself. That part of the motion corresponding to this latter domain is denoted by "slow-drift oscillations" or "second order oscillations". Although this second order motion, as the name indicates, is a second order effect, it may well contribute the major part of the wave-induced loads that the mooring system must handle, cfr. references (5) and (6). Consequently, it has become increasingly important to be able to give reliable estimates of these second order contributions. At present, however, it seems that there does not exist a manageable theoretical or numerical procedure for handling this problem properly. Therefore, recourse has to be taken to model testing. Accordingly, we are faced with the problem of designing as reliable testing procedures as possible. One of the most important components of a model testing set-up is no doubt the simulated sea-way, and that will be the subject matter of this report.

Development of floating offshore wind turbine technology is in need of more scaled model tests to investigate its dynamical characteristics. This paper presents the model testing investigations of a spar-buoy and semi-submersible floating wind turbines, and conducts a series of comparisons on the experimental results of the two floating wind turbines. It is found that the spar-buoy floating wind turbine is more sensitive to wind loading and has larger amplitudes of platform motion in wind only cases, especially for the yaw motion. By contrast, the semi-submersible floating wind turbine is more sensitive to wave loading, especially for the second order difference-frequency wave loading. In addition, the dynamic responses of the two floating wind turbines are both influenced by the current flow. Compared to the semi-submersible floating wind turbine, the more regular “figure-eight” surge-sway trajectory is observed in the spar-buoy floating wind turbines, showing the influence from vortex-induced-motion. This paper provides more valuable experimental details and results to the scientific community with regard to the spar-buoy and semi-submersible floating wind turbines. Moreover, the comparison of the dynamic behaviours of the two floating wind turbines in various conditions helps to understand the characteristics and mechanism about the floating wind turbine technology.

Although the hull shapes of modern ice breaking vessels seem to be quite similar at a first glance, there are significant differences in their ice breaking performance. A significant amount of research effort was spent on investigations of the icebreaking process and the resulting forces. However, little information is available on the correlations between ice floe characteristics, hull shape parameters, ice properties and the ice resistance. Thus, systematic model tests in level ice and pre-sawn ice with four icebreaking ship models of one ship type have been conducted to gain new insight on these correlations. During the tests in level ice under water video records have been taken from below the ship model. Video frames have been analyzed by application of a dedicated image analysis procedure which is mainly based on a number of semiautomatic scripts applied in Matlab®. Results of the analysis are presented and discussed within this paper.

The forebay of pumping stations is an important hydraulic structure that connects the channel with the inlet channel. Actual test observations and theoretical studies have shown that poor precursors produce backflow, vortex, and water flow disturbances in the forebay water. In this paper, taking a lateral inlet pump station as an example, we study the nonmeasures and five rectification measures—“Y” type diversion pier, “T” shaped diversion pier, narrow bottom hole, high and wide bottom, and diversion wall—through adopting the method of numerical simulation and model test. For the numerical simulation, the corresponding three-dimensional model is established by UG solid modeling software, and then the computational fluid is simulated numerically with CFX. Based on the analysis and comparison of the results during the test of numerical simulation and model test, the stability of the rectification measures is considered after taking into consideration the results of the uniformity test of the velocity distribution of the surface layer, the bottom layer, and the front section of each scheme. The proposed scheme 3 (“T” diversion pier) is regarded as the pumping station flow control measures.

An analysis is presented for the models and test methods used to simulate the electrostatic discharge (ESD) event for a charged semiconductor device. A new constant energy charged device model (CECDM) test method is proposed to provide control of charge and potential for constant energy discharges, and give a better evaluation of device reliability. Experimental results are presented for tests conducted on a basic CMOS structure.

The model tests on the interaction between new constructions and adjacent existing buildings were summarized and analyzed from four aspects: the preparation methods of the model soil, the selection of pile model and tunnel model, the simulation methods of excavation process, and the loading methods of model tests. Several conclusions can be drawn as follows: (I) the influence of the superstructure stiffness and the pile cap is almost not considered in the past; (II) the influence of the sequence between installing the supporting structure and filling the soil still not be completely avoided, and more advanced supporting structure system should be designed; (III) most model tests on tunneling are based on two-dimensional hypothesis, and three-dimensional tests need to be conducted in the future; (IV) adverse influences of segment joints are seldom considered in the present tests on shield tunnels, and better tunnels model reflects the effect of segment joints should be adopted.