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This paper presents a potential based boundary element method for solving a nonlinear free surface flow problem for a ship moving with a uniform speed in finite depth of water. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter up to third order. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The second order solution gives better result than the first or third order solution. So the present method with the second order solution can be adopted as a powerful tool for the hydrodynamic analysis of the thin ship in finite depth of water. 相似文献
2.
Evening and morning twilight enhancements of 5577 Å and 5893 Å lines were observed by Dunn-Manring type photometer at Calcutta during the period 1983–1985 and that of 5577 Å have been collected from Allahabad observatory. The following paper presents the correlation between the enhanced intensity of airglow lines (A
G
) and solar flare index (I
f
) which is calculated considering all the flares which occurred 24 hr before the times of occurrence of enhancements. It is observed that the intensity of airglow lines varies with the flare index in an oscillatory manner upto a certain limiting value ofI
f
. Afterwards intensity of both lines increases with the increase ofI
f
. The nature of variation is the same for both sunspot maximum and minimum periods. A possible explanation of such type of variation has also been invoked. 相似文献
3.
A modified Rankine source panel method is presented for solving a linearized free-surface flow problem with respect to the double-body potential. The method of solution is based on the distribution of Rankine sources on the hull as well as its image and on the free surface. An iterative algorithm is used for determining the free surface and wave resistance using upstream finite difference operator. A verification of numerical modeling is made using the Wigley hull and the validity of the computer program is examined by comparing the details of wave profiles and wave making resistance with Series 60 model. 相似文献
4.
A precise, accurate and rapid method for the sequential determination of FeO and Fe2O3 in rocks, soils and some non‐refractory minerals by 1,10‐phenanthroline spectrophotometry is described. Fe(II) and Fe(III) were leached from the sample (?200 mesh) using a mixture of NH4HF2 and H2SO4 at 40–80 °C for 10 min on a hot plate. Both Fe(II) and Fe(III) could be conveniently estimated sequentially from the same reaction mixture at the μg g?1 to percentage level. The method is better than the existing wet chemical methods, including the commonly used Pratt's titrimetric redox method, for Fe(II) and Fe(III) determinations in rock and soil samples in terms of precision, accuracy and rapidity. The throughput of the method was very high; at least forty to fifty samples could be estimated easily in a day. The results obtained compare favourably with those obtained by Pratt's method, as well as for certified/recommended values of a set of eleven certified reference materials having FeO and Fe2O3 contents in the range 0.21–14.63% and 0.58–8.48%, respectively. The optimised 1,10 phenanthroline method was found to be accurate to within 0.21% m/m FeO and 0.30% m/m Fe2O3 compared with the literature values of the certified reference materials studied. 相似文献
5.
The disastrous Mw 9.3(seismic moment 1.0×1030 dyn/cm) earthquake that struck northwest Sumatra on 26 December 2004 and triggered～30 m high tsunami has rejuvenated the quest for identifying the forcing behind subduction related earthquakes around the world.Studies reveal that the strongest part（elastic core） of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper （～7 km thick） crustal layer,and compressive stress of GPa order is required to fail the rock-layers within the core zone.Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part（at the interface of semi-brittle and brittle zone）,and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature,unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state.The increased compressive stress field coupled with upward migration of the neutral surface（of zero stress fields） under noncoaxial deformation triggers shear crack.The growth of the shear crack is initially confined in the near-brittle domain,and propagates later through the more brittle crustal part of the descending oceanic lithosphere in the form of cataclastic failure. 相似文献
6.
Computation of wave-making resistance of a catamaran in deep water using a potential-based panel method 总被引：1，自引：0，他引：1
This paper presents a potential-based boundary element method for solving a nonlinear free-surface flow problem for a Wigley catamaran moving with a uniform speed in deep water. Since the interior flow of each monohull of the catamaran is different from the exterior flow, both monohulls must be considered as lifting bodies. The pressure Kutta condition is imposed at the trailing-edge of the lifting body by determining the dipole distribution, which generates required circulation on the lifting part. The effects of wave interference and hull separation on the hydrodynamic characteristics of the catamaran hull are analyzed and the validity of the computer scheme is examined by comparing the wave resistance with the numerical results of others. The present method could be a useful design tool for screening the suitable combinations of hull parameters and hull spacing at the preliminary design stage of catamaran hull. 相似文献
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