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- Esfandiari, A., et al.
(författare)
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Comparison between the dynamic behavior of the non-stepped and double-stepped planing hulls in rough water : A numerical study
- 2020
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Ingår i: Journal of Ship Production and Design. - : The Society of Naval Architects and Marine Engineers. - 2158-2866 .- 2158-2874. ; 36:1, s. 52-66
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Tidskriftsartikel (refereegranskat)abstract
- Reducing vertical motions of high-speed planing hulls in rough water is one of the most important factors that help a boat to becomemore operable, andwill benefit the structure of the boat and the crew on board. In the recent decade, stepped planing hulls have been investigated with emphasis on their better performance in calm water than that of nonstepped planing hulls. However, there are still doubts about their performance in rough water. In this study, we investigate this problem by providing numerical simulations for motions of a double-stepped and a non-stepped planing hull in a vertical plane when they encounter head waves. The problem will be solved using the finite volume method and volume of fluidmethod. To this end, anumerical computational fluid dynamics code (STARCCM1) has been used. Accuracy of the numerical simulations is evaluated by comparing their outcome with available experimental data. The dynamic response of the investigated hulls has been numerically modeled for two different wave lengths, one of which is smaller than the boat length and the other which is larger than the boat length. Using the numerical simulations, heave and pitch motions as well as vertical acceleration are found. It has been found that at wave lengths larger than the boat length, heave amplitude decreases by 10-40%when twosteps are added to the bottom of a vessel. It has also been observed that pitch of a planing hull is reduced by 18-32% in the presence of the two steps on its bottom. Finally, it has been observed that forwave lengths larger than the boat length, the maximum vertical acceleration decreases by a gravitational acceleration of about .2-.7.
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- Fadel, Shaimaa M, et al.
(författare)
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Improving tensile strength and moisture barrier properties of gelatin using microfibrillated cellulose
- 2013
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Ingår i: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 47:16, s. 1977-1985
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Tidskriftsartikel (refereegranskat)abstract
- Microfibrillated cellulose isolated from bagasse was used to prepare novel nanocomposites using cross-linked gelatin as a biodegradable polymer matrix. Microfibrillated cellulose loadings up to 25% (weight percent) were used. The prepared nanocomposites were characterized regarding their wet and dry tensile strength, water sorption, and water vapor permeability. Nanocomposites’ surfaces were examined by scanning electron microscopy; the scanning electron microscopy images indicated homogeneous distribution of microfibrillated cellulose in the gelatin matrix. Microfibrillated cellulose improved wet and dry maximum tensile stress and modulus of cross-linked gelatin but resulted in a decrease of its strain at break. Microfibrillated cellulose did not affect the water absorption of cross-linked gelatin but significantly improved its moisture barrier property.
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- Fader, Marianela, et al.
(författare)
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Past and present biophysical redundancy of countries as a buffer to changes in food supply
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Spatially diverse trends in population growth, climate change, industrialization, urbanization and economic development are expected to change future food supply and demand. These changes may affect the suitability of land for food production, implying elevated risks especially for resource-constrained, food-importing countries. We present the evolution of biophysical redundancy for agricultural production at country level, from 1992 to 2012. Biophysical redundancy, defined as unused biotic and abiotic environmental resources, is represented by the potential food production of 'spare land', available water resources (i.e., not already used for human activities), as well as production increases through yield gap closure on cultivated areas and potential agricultural areas. In 2012, the biophysical redundancy of 75 (48) countries, mainly in North Africa, Western Europe, the Middle East and Asia, was insufficient to produce the caloric nutritional needs for at least 50% (25%) of their population during a year. Biophysical redundancy has decreased in the last two decades in 102 out of 155 countries, 11 of these went from high to limited redundancy, and nine of these from limited to very low redundancy. Although the variability of the drivers of change across different countries is high, improvements in yield and population growth have a clear impact on the decreases of redundancy towards the very low redundancy category. We took a more detailed look at countries classified as 'Low Income Economies (LIEs)' since they are particularly vulnerable to domestic or external food supply changes, due to their limited capacity to offset for food supply decreases with higher purchasing power on the international market. Currently, nine LIEs have limited or very low biophysical redundancy. Many of these showed a decrease in redundancy over the last two decades, which is not always linked with improvements in per capita food availability.
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Faderskap
- 1985
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)
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