General Guidance and Introduction to Ice Model Testing
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ITTC – Recommended 7.5-02 -04-01 Procedures and Guidelines Page 1 of 10 General Guidance and Introduction to Effective Date Revision Ice Model Testing 2017 02 ITTC Quality System Manual Recommended Procedures and Guidelines Guideline General Guidance and Introduction to Ice Model Testing 7.5 Process Control 7.5-02 Testing and Extrapolation Methods 7.5-02-04 Ice Testing 7.5-02-04-01 General Guidance and Introduction to Ice Model Testing Updated / Edited by Approved Specialist Committee on Ice of the 28th ITTC 28th ITTC 2017 Date: 03/2017 Date: 09/2017 ITTC – Recommended 7.5-02 -04-01 Procedures and Guidelines Page 1 of 10 General Guidance and Introduction to Effective Date Revision Ice Model Testing 2017 02 Table of Contents 2.4 Modellig of different ice conditions.. 5 1. PURPOSE OF THE PROCEDURE .... 2 2.4.1 Level Ice ....................................... 5 2. GENERAL GUIDELINES ................... 2 2.4.2 Presawn Ice .................................. 5 2.1 Facilities, Ice Conditions and Ship 2.4.3 Modelling of ice floes .................. 5 Model .................................................. 2 2.4.4 Modeling of managed ice ............. 6 2.2 Model Ice Production ........................ 2 2.4.5 Brash ice channel ......................... 6 2.2.1 Model Ice Production Methods .... 3 2.4.6 First year ridges ............................ 6 2.2.1.1 Seeding Method ............................ 4 2.4.7 Rubble ice fields ........................... 6 2.2.1.2 Spraying Method .......................... 4 2.5 The ship model parameters ............... 7 2.3 Scaling ................................................. 4 3. BENCHMARK TESTS ......................... 7 4. REFERENCES ...................................... 7 7.5-02 ITTC – Recommended -04-01 Procedures and Guidelines Page 2 of 10 General Guidance and Introduction to Effective Date Revision Ice Model Testing 2017 02 General Guidance and Introduction to Ice Model Testing the ship should proceed in ice at least two ship lengths (see 15th ITTC). The other factor, which 1. PURPOSE OF THE GUIDELINE may restrict the test program, is the vicinity of the basin walls. The level ice sheet may be The purpose of this guideline is to assist in considered to have infinite extent if the shortest making the test results from different test series distance from the point of application of any and different laboratories more consistent. The loads to the nearest tank wall is more than three ice committee has reviewed the earlier ITTC characteristic lengths. The characteristic length ice committee reports; this section represents a is defined as: collection of methods developed during the past years. The following test types are discussed: 3 2 ¼ lc = [E HI / 12 (1-ν ) / ρw g ] (1) • Ship resistance in level ice where E is Young’s modulus of ice, HI is the • Ship propulsion in level ice ice thickness, ν is Poisson’s ratio of ice (ν = • Manoeuvring of ships in level ice 0.3 - 0.33), ρ is the density of water and g is • Ship tests in deformed ice w the acceleration of gravity (see also Test • Tests with offshore structures Methods for Model Ice Properties, 7.5-02 -04- • Modeling and testing in complex ice 02). In resistance tests with the basin width, D, environments and the breadth of the vessel, B, the requirement is (subscript “M” refers to model scale): Some important information is common to all of the above test types. lc (M) < (D – B (M) ) / 6 (2) 2. GENERAL GUIDELINES It is useful to present a layout of the test facility in the model test report. This layout should be used to report how the ice sheet was 2.1 Facilities, Ice Conditions and Ship used in the tests and where ice properties Model measurements were carried out. It has to be noted that model ice might behave elastic- Differences in the dimensions and layout of plastic (e.g. von Bock und Polach, 2015) the facility may have some influence on the tests. which limits the accuracy of Equation 1 and 2. An important factor is the effect of the basin Additional specific information is found in the size on the number of tests that can be run in particular guidelines of 7.5-02-04 Ice Testing. one ice sheet. The test length, in linear tests, limits this number. This test length should be such that the transients due to entering the 2.2 Model Ice Production testing ice have disappeared. Different methods and procedures are used Thus, if the model comes to level ice from in the various ice tank facilities to produce open water, the stem must be in the level ice part model ice and to adjust its properties (see Test before the actual test run can start. In this case, Methods for Model Ice Properties, 7.5-02 -04- 7.5-02 ITTC – Recommended -04-01 Procedures and Guidelines Page 3 of 10 General Guidelines for Ice Model Effective Date Revision Testing 2017 02 02). Table 1 provides an overview of grain 2.2.1 Model Ice Production Methods structure and chemical composition of the model ice in operating facilities. In the model ice production generally two methods are distinguished: spraying and seeding. Today’s modelling practice favours the use Spraying means that several layers of ice of laboratory ice with weakening additives crystals are sprayed onto the cold tank surface a (dopants). Doped ice was developed originally fine grained ice structure is build upwards layer for modelling ice forces on structures and by layer. Seeding means that only one layer of icebreaker vessels. In difference to testing in ice crystal seeds in sprayed onto the surface, open water, in ice model testing also scaling from which columnar structures ice grows into similarities for the ice properties have to be met the tank. Each facility has its own customized (e.g. Schwarz, 1977). chemical composition of spraying or seeding water and tank water (Table 1). Note: In some facilities fresh water is used for seeding and spraying and in others tank water. Table 1: Ice sheet production methods in various refrigerated ice tank facilities Ice tank facility Grain structure Chemical composition Aalto University, Finland fine grained ethanol Aker Arctic, Finland fine grained sodium chloride Japan Marine United (former Universal Shipbuilding Corporation) (former NKK), fine grained urea Japan columnar and fine Krylov State Research Center (KSRC), grained sodium chloride Russia National Research Council Canada, Ocean, Coastal and River Engineering (NRC-OCRE, columnar EG/AD/S *) formerly the Institute for Ocean Technology and Canadian Hydraulic Laboratory), Canada Maritime Ocean Engineering Research columnar EG/AD *) Institute (KRISO), Korea National Maritime Research Institute of Japan columnar polypropylene glycol (NMRI), Japan The Hamburg Ship Model Basin (HSVA), columnar sodium chloride Germany Tianjin University, China columnar urea *) EG = ethylene glycol, AD = aliphatic detergent, S = sugar 7.5-02 ITTC – Recommended -04-01 Procedures and Guidelines Page 4 of 10 General Guidance and Introduction to Effective Date Revision Ice Model Testing 2017 02 ice) instead of columnar (Nortala-Hoikkanen, 2.2.1.1 Seeding Method 1990). The preparation of the ice sheet is started by Basin water is sprayed into the cold air and a seeding procedure (Figure 1). For this purpose the water droplets will somewhat freeze before water is sprayed into the cold air of the ice tank. reaching the water surface. In some cases the The droplets freeze in the air forming small ice basin water is mixed with or replaced by fresh crystals which settle on the water surface. By water. This might vary from layer to layer. Each this method the growth of a fine-grained ice of spraying pass produces a layer of soft granular primarily columnar crystal structure is initiated. white ice slush. The process is repeated until the required thickness is obtained. Thereafter the By using a sufficiently cold temperature, strength properties are adjusted by the cooling both water and dopant are frozen in solution process. Figure 2 illustrates the spraying process. together forming an ice sheet. This impure ice sheet is inherently softer than pure-water ice but may be harder than the scaled target strength. Once a desired thickness is achieved, the air temperature is raised to a tempering temperature. Figure 2: The spraying process Figure 1: Water is sprayed under high pressure into the air of the pre-cooled ice tank forming crystal nuclides Furthermore, it must be acknowledged that which settle down on the water surface non-standard tests may require different procedures. Lau et al (2007) have reviewed and Prior to model testing the relevant ice summarized the ice modeling techniques used in properties (e.g. ice strength, ice density and ice different ice modeling facilities worldwide. thickness) are measured along the ice tank at locations in accordance with the test run 2.3 Scaling sections see Test Methods for Model Ice Properties, 7.5-02 -04-02). This section presents only the traditional scaling approach which found its origin in the 2.2.1.2 Spraying Method scaling of ships breaking ice. In ice model testing geometrical scaling is applied with the In the spraying method a dense water fog is scaling factor, λ. In order to satisfy dynamic sprayed onto the ice. Unlike natural ice the similarities both Froude and Cauchy similarity model ice produced is growing upwards and not are maintained. The Froude similarity postulates downwards. Compared to the seeding method to maintain the ratio of gravity and inertia forces the ice texture is fine granular (FG-ice and FGX- in both scales. Cauchy similitude reflects the ratio of inertia and elastic forces. The elastic 7.5-02 ITTC – Recommended -04-01 Procedures and Guidelines Page 5 of 10 General Guidelines for Ice Model Effective Date Revision Testing 2017 02 reaction forces refer to the elasticity of ice.