The design of structures for ice conditions requires knowledge of local ice pressures to allow for appropriate levels of structural strengthening. Full-scale field data are keys to enhancing our understanding and modeling of ice behavior. Data collected during icebreaker ramming events represent an important source of information for use in design load estimation, and the evaluation of design methodologies. This paper examines several ship-ice interaction data sets using the ‘event-maximum’ method of local pressure analysis developed by Jordaan and et al. (1993, “Probabilistic Analysis of Local Ice Pressures,” ASME J. Offshore Mech. Arct. Eng., 115, pp. 83–89). In this method, the local pressure is obtained from a normalized curve, which contains two parameters α and x0. The parameter α is a function of the area, well represented by the curve α=CaD, where a is the local area of interest, and C and D are constants. The parameter x0 is assumed a constant for a given design scenario. An alternative approach, the up-crossing rate method, is presented in a companion paper (2009, “Estimation of Local Ice Pressure Using Up-Crossing Rate,” Proceedings of the OMAE 2009, Honolulu, HI). Local pressure analysis results for data from the USCGS Polar Sea, CCGS Terry Fox, CCGS Louis St. Laurent, and Swedish Icebreaker Oden are presented. A discussion of panel exposure, event duration, and the effects of these factors on x0 is given. New design curves are included. For all data considered, the calculated values of α fall below the design curve. For the design, it is recommended that α is calculated using a C value based on the impact data collected under ice conditions similar to those for the design scenario; D may be treated as a constant having a value of −0.7. A design value of x0 may be determined based on the analysis of appropriate data sets. The treatment of exposure is described for data analysis and design. The effects of exposure must be removed during data analysis to provide a design curve based on single panel exposure. For the design, estimates from the design curves must be adjusted to properly reflect the design exposure.
In order to improve the estimation of the ice load during ice-structure interaction, this study aims to investigate the behaviour of high pressure zones at different scales. Small scale indentation tests of ice with four different sizes of indentors (10 mm, 20 mm, 40 mm and 100 mm in diameter) were conducted at Ocean Engineering Research Centre of Memorial University. The tests were conducted at −10 °C. The grain sizes were scaled up with the indentor sizes. The tests consist of three series with different orders of displacement rates. In this paper, Part of the field test data will be retrieved for the investigation. Microstructural changes of the ice after deformation in laboratory will be studied. A relationship between stress and nominal contact area is derived based on the data. Numerical simulations are conducted for the series with low displacement rates of laboratory tests. The simulation shows a good agreement with the tests.
Ice load estimation is required for offshore structures designed for arctic and sub-arctic conditions. This paper focuses on the estimation of local ice pressures. The ‘event-maximum’ method for local ice pressure analysis is based on the maximum pressure of a given event; other local peaks in the data are not included. To study how this may affect local ice pressure estimates, a method based on the up-crossing rate was developed. Field data from 1982 Polar Sea arctic trials in the Beaufort Sea are processed as a time series. Up-crossing rates at different local pressure levels are obtained for local areas of interest. A relationship between up-crossing rate and local pressure-area results is established. Results from the analysis of full-scale data using the event-maximum method are presented in a companion paper. For a sample case, local ice pressure estimates obtained using the up-crossing rate method are compared with those presented in the companion paper, based on analysis using the event-maximum method. The local pressure-area relationship is found to be similar for both the up-crossing rate method and the event-maximum method. Both methods and corresponding analysis results are compared.
Electron-positron pair (EPP) creation under the Gaussian and super-Gaussian potential wells are studied by the computational quantum field theory (CQFT). We find that the EPP creation rate decreases, while the positron spectra have better monochromaticity when the potential well is wider and gentler. The phenomenon is explained from the Feshbach resonance by the complex scaling method (CSM). The width of the Feshbach resonance is narrower in the wider and gentler potential well, and the narrower Feshbach resonance can lead to lower creation rate and better energy monochromaticity. This study indicates that the width of the Feshbach resonance plays an important role in the EPP creation, and the Gaussian-type potential well has an advantage in tuning the Feshbach resonance width.
To relieve the drop of groundwater and seawater intrusion in Weizhou Island caused by overexploitation, the analysis model of precipitation-runoff and variable-density groundwater flow in Weizhou Island was established and the model’s parameter identification results were used to investigate groundwater level and seawater/freshwater interface changes under different groundwater exploitation plans. Thereafter, a rational groundwater exploitation plan could be made to prevent the lowering of groundwater levels caused by ground water overexploitation and ecological deterioration caused by seawater intrusion. This could help accelerating the recovery of ground water and maintaining ecological system.
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