Takahiro Takeuchi

Medium-scale indentation tests on sea ice at various speeds

Abstract As part of a five-year program involving laboratory and field tests in Japan, we conducted medium-scale indentation tests on sea ice in the harbor of Lake Notoro, Hokkaido, by pushing a segmented indentor against the edge of a floating ice sheet. Measurements on each 10-cm-wide segment included forces in three directions and the moment about a horizontal line parallel to the indentor face. During the tests in 1998, we also installed four pressure-sensing panels on the face of the segmented indentor and measured interfacial pressure during indentation tests at three speeds. We present the results from the load cells and the pressure-sensing panels. We obtained data on the actual contact area and the magnitude of interfacial pressures from the pressure-sensing panels. We observed both a `line-like contact during high-speed (3- and 30-mm s −1 ) indentation tests, and a gradually enlarging contact area attributable to creep deformation of the ice during low-speed (0.3-mm s −1 ) indentation tests. Using the results of a brittle flaking model from the literature, we estimate the apparent fracture toughness of the ice from the data on interfacial pressure and the width of the contact area. Taking creep and fracture properties into account, we present a theoretical model to estimate the speed at which the transition from ductile to brittle failure of ice takes place during ice-structure interaction.

On the Factors Influencing the Scaling of Ice Forces

A series of ice indentation tests have been performed since the winter of 1996 at Lake Notoro in Hokkaido, Japan (JOIA reports: 1996, 1997, 1998 and 1999), as part of the JOIA project. The main factors affecting the total ice load (F) on a structure were investigated using data derived under systematic test conditions, using natural sea ice. The width (W) of the model structure, ice thickness (h), indentation speed (V) and uniaxial compressive strength (σc) are the major factors influencing ice load on a stmcture with a vertical face. The paper determines the dependence of (W/h), (V/h) and (h) on indentation pressure (Pt). It also describes the pressure distribution examined by a 2-dimensional panel sensor that could simultaneously measure pressures at 2112 points for various indentation speeds. From field data, the paper investigates factors explaining the scaling effect, by which the ice load decreases with increasing indentation area.

Shoreline Changes Around Artificial Headlands Along the Misawa Coast, Japan

Artificial headlands were constructed along the Misawa coast of Japan to prevent beach erosion caused by the construction of the Misawa fishery port in 1971. In order to assess the protection afforded by the artificial headlands, monitoring of shoreline changes was undertaken by conducting monthly GPS surveys and aerial photographs Based on the average position of the shorelines in 2006, advance of the shoreline has occurred along the coasts to the north and south of headlands B1, B3, and B11 The headlands B1 and B13 are in the south end and in the north end of the headlands group. Those lengths are 200 and 100 meters. The shorelines of the coasts to the north and south of headlands B5, B7 and B9 were stable, and the coast to the north of headland B13 was retreating. While the position of the shoreline along the north coast changes every month, change in the position of the averaged shoreline has decreased since the latter half of 2004. In conclusion, the artificial headlands were effective measures for countering beach erosion along the Misawa coast.

Calculation of Water That Flows in River in North District, Japan

In this study, two models for snow and snowmelt were extended. Using those models, the calculation of water flowing in river was carried out. The results were compared with the observations. The outflow estimated by using the snow model in winter is in good agreement with the observations, and the snowmelt runoff predicted by using the snowmelt model in spring, April, May and June, is also at the good accuracy. The snowmelt runoff starts increasing from the early April, and it reaches the peak in the early May.Copyright

Energy Loss in Snow-Water Mixture Flow

Energy losses in the solid-water mixture flow where the density of solid is nearly equal to that of fluid were observed in horizontal pipelines. The observation was carried out to investigate the influence that the specific gravity of the solid particles exerted on the energy loss. A relative friction factor based on the friction factor of the pure water flow becomes larger as the solid concentration increases in the mixture flow of solid particles with the specific gravity 0.86 and 1.04. The relative friction factor is given with the Froude number, the solid concentration and the specific gravity of solid.Copyright

The Physical Properties of Consolidated Ridge Ice Modeled as Frozen Rubble

In cold regions, given that first year-year ice ridges often govern the design load for offshore structure, it is important to obtain knowledge about ice ridges, especially the consolidated portion, in designing offshore structures. However, the physical properties and strength of sea ice ridge appear to be much more complex than those of undeformed ice or level ice. We performed a preliminary series of tests (uniaxial compression tests) in the laboratory on model ice (refrozen rubble) to investigate the strength and the physical properties of the consolidated portion. In order to construct an ice ridge model, cubical ice blocks of size (a) were randomly arranged in the ice tank filled with saline water that had greater salinity than that of the ice blocks. After they were refrozen, using a core drill with various diameters (d), we collected test core samples with a range of d/a ratios. We then examined their physical properties and mechanical characteristics with regard to size effects. In our test results, the difference in ice strength according to the sample’s original location and orientation was small in an ice ridge model compared with level ice, suggesting that the ice ridge strength may be macroscopically isotropic. As with level ice, the strength of the ice ridge decreased with increase in specimen size, indicating a size effect. We discuss this size effect of ice strength on the basis of weakest link theory. Each of the expectation and the standard deviation of the strength is proportional to volume to the -1/β power, where β is regarded as a shape parameter. Both the calculated value estimated from the theory and the experimental value on the ice strength show that the strength of level ice slightly exceeds that of ice ridge model for small specimens, but that the values approach each other as the size of the specimen increases. Also, the strength of level ice and ridge ice appear to have the same asymptotic strength and they may be essentially of the same order. Finally, we proposed a practical application of ridge strength.

ON THE EFFECTS OF CONCEPTION OF THE EXCAVATED CHANNEL ON FLOW VELOCITYIN THE INNER PART OF MUTSU BAY, ENVIRONMENT, AND GOODS MOVEMENT

The concept of the excavated channel at Shimokita arm is considered to increase the tidal exchange between the innerpart of the Mutsu Bay and the open sea.The change of flow velocity is calculated by FEM under two conditions with and without the excavated channel.In additions, the utilizing the excavated chamel as seaway gives the possibility of the reduction of carbon dioxide emission and energy consumption due to shortcut of seaway route.And, the possibility of reduction of goods movement cost is also investigated in the paper.

ICE PRESSURE DISTRBUTION IN ICE-STRUCTURE NIERFACE AND STRUCTURE STIFFNESS EFFECTS ONICE-STRUCTURE INTERACTTON

Field indentation tests using medium-scale model structures have been conducted since the winter of 1996. In the winter 1998 tests, two-dimensional pressure sensing panels were first installed on the face of the indentor. These panels clearly showed actual contact area, ice pressure distribution and movement of ice force location on the indentor surface during interaction. Ice flaking failure associated with a thin line-like contact area was observed from 3-D plots of pressure data in tests with an indentor velocity of 3.0mm/s. In the winter 1999 tests, a spring system (spring constant 15KN/mm) was first installed in the model structure to simulate a vibrating structure. These tests showed structure stiffness difference causes different manner of ice failure.

On the interaction of structure with ice sheet in medium scale field indentationtests

The consiruction of structure in ice in fested arca requires the proper evaluation ofdesign ice load on structure.For that, it is required to clarify that the scale effect, that indentation ice pressure decreases as an area of structure with ice sheetincreascs, is caused by the nonsimulaneo us failure of ice sheet. Medium scale fieldindenlation test (MSFIT) in JOIA project includes ice in dentation tests, tests onphysical pmperties of ice sheet and image sensing on ice deformaion. In thispaper, the whole plan of MSFIT and the resuhs of ice indemation tests conducted in 1996 winter are reported.