Masafumi Sakai

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.

The Coefficient of Friction Between Sea Ice and Various Materials Used in Offshore Structure

When structures having inclined surfaces, such as cone type and inclined pile structures, are constructed in coastal and offshore cold regions, sea ice pressure must be considered in their design. In order to estimate this ice pressure, the relationship of the coefficients of static and kinetic friction between sea ice in various conditions and construction materials must be clarified. The authors have been conducting, for four years, coefficient of friction experiments between sea ice and various commonly used offshore construction materials such as concrete and steel. These coefficients have been found to be affected by the following: i) relative velocity ii) sea ice temperature iii) surface roughness of construction material They have been found to be relatively unaffected by the following: i) contact area ii) vertical stress iii) growth direction of sea ice iv) water in the sea ice interface

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.

A CONTROL METHOD OF SURGING IN DISCHARGE CHANNEL WITH VERTICAL SHAFTS

A discharge channel of a power station is composed of open channel, tunnel and vertical shafts. Surging phenomenon occurs in the discharge channel when pumps stop all at once. The surging propagates with highly pressurized flow forward the lower narrow channel to make the water spouting from the vertical shafts.We simulated physically the phenomena in the discharge channel through the laboratory tests and simulated mathmatically the water motion by means of the slot model. The laboratory tests, the calculation and the field investigation showed that the phenomenon of surging and spouting water could be depressed by a sophisticated stopping-operation of the pumps.

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.

Impact Of Ice Loads On Pile Structures AndDeformation Of Ice Floes

The Okhotsk Sea coast of Hokkaido, Japan is covered with ice floes during winter. Aota et al. showed that the temperature in this region has been rising every winter, and in the last ten years the amount of sea ice has been decreasing. Therefore the period of coexistence of waves and ice floes has become more longer and it is very important problem to make clear the impact ice load acting on offshore, harbor and coastal structures which are constructed on Okhotsk Sea coast of Hokkaido. Judging from the mechanical properties of ice sheet, ice sheet is an elastic-plastic substance, and in high strain region, it is seemed as elastic material. Generally ice load acting on structures and mechanisms of its fracture mode depend on the strain and stress rate. In the case of large moving ice sheet colliding with structure, the decision of deformation area of ice sheet was very difficult. Saeki et al. and Takahashi et al. reported that the velocity of ice floes due to wind wave, overtopping over breakwater and tsunami was about 4-8 m/s. In this paper, the authors clarified the impact ice load when ice sheets collide vertically with a circular cross-sectional structure, and the deformation area of ice sheet which collide with pile structures at high speed. 1 Experimental methods The velocity of ice sheets (V) was 4-8 m/s, calculated from abnormal waves in the Okhotsk Sea coast during winter, as well as the average depth of the breakwater foot below the sea surface and the average crown Transactions on the Built Environment vol 32,