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1.
One of the most important aspects, in the ACS and multi stepped hull design, is the choice of the geometrical shape of the cavity and the steps. In this article a complete experimental and numerical campaign on a multi stepped ACS has been carried out, varying the velocity and the air flow rate under the hull. The experimental tests have been conducted in an ITTC Towing Tank allowing to validate the numerical simulations obtained by means of a CFD U-RANSe (Unesteady Reynolds Averaged Navier-Stokes equations) code. The CFD setup is described in detail. From this campaign a critical analysis of the Froude number influence on the air cushion shape has been argued. The authors identified four different behaviours, from low to very high Froude numbers. The use of CFD has allowed to observe quantities of difficult evaluation by means of traditional experimental test, as e.g. the frictional component of the resistance, the airflow path lines and the volume of fraction in transversal and longitudinal sections. The results have been discussed. 相似文献
2.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(2):83-101
Protected area management in Norway is undergoing institutional changes with the implementation of management models aimed at increased public participation. At the same time tourism enterprises are increasing in number within the protected areas. Greater levels of interaction with stakeholders place new demands on lead institutions in terms of communication, transparency, involvement, and power sharing. A governance perspective was used to examine some facets of the interaction between a local council managing a national park in Norway and tourism companies using the park for their operations. The main objective was to assess how the tourism sector perceives the cooperation and interface with the management institution. Semi-structured interviews were used, together with a framework of United Nations Development Programme principles of good governance: legitimacy and voice, direction, performance, accountability, and fairness. The results showed rather negative evaluations by the tourism sector, and operators expressed views, implying that the current management model fails to achieve most of the principles of good governance. Although based on a one-sided view by one group of stakeholders, the study suggests that lack of access to important processes and decisions, perceived bias towards traditional conservation, neglect of cultural heritage, and undue restrictions on access could have serious implications for developing an effective management model. 相似文献
3.
山区阶梯式河道是自然界来水来沙和山区大比降河床相互作用所形成的,其水力特性、河道阻力较为复杂。为了深入研究其阻力机理,从河床结构阻水的角度提出阶梯式结构糙率尺度的概念,得到了适用于阶梯式河道跌落水流的形体阻力系数表达式,并由不同来源的阻力分量构成了新的山区阶梯式河道水流总阻力系数公式。新公式结果表明,通过不同类型河段的野外试验数据,表面泥沙、阶梯形状以及漂石产生的阻力系数分量之和与试验测量总阻力系数数据的误差较小。随着雷诺数和阶梯单元尺寸的增加,河床表面的泥沙肤面阻力系数基本不变,阶梯式结构形成的跌落水流过渡到滑行水流,阶梯形体阻力系数逐渐变小,而较大粒径松散漂石产生的水流阻力系数只随着雷诺数的增大而减小。 相似文献
4.
青藏高原东南部的地貌结构是高原隆升深部动力过程与高原扩展的重要指标之一,存在受下地壳流驱动的渐变模型和受宽约50～200km的雅砻-玉龙断裂系控制的陡变模型2种不同认识。文中基于30m分辨率的SRTM数据进行数字高程分析,利用高程和水系参数对研究区地貌加以提取和分析,结合野外地貌和构造调研的结果以及前人的相关研究,对高原东南缘川滇地块中部构造地貌细结构进行了详细的解析。研究认为,青藏高原东南边界具有明显的台阶式构造地貌结构,不同台阶梯度带受不同时期发育的NE-SW向断裂控制。其中一级边界位于木里-玉龙断裂,控制了平均海拔4 200m的高原面的东南边界,是渐新世—中新世早期构造抬升的结果;二级边界受中新世中期逆冲活动的金河-箐河断裂控制,其构成丽江—盐源一带海拔中等(约3 000m)、相对低起伏区域的东南边界。高原东南边界的台阶式构造地貌结构反映了高原向SE的前展式逆冲扩展。这种扩展模式并不支持下地壳管道流连续变形模型。 相似文献
5.
河流的沉积特征是多样的。实际上，多数河流沉积序列与经典曲流河沉积模式存在一定差别。在松辽盆地茂兴地区泉三段地层中阶梯状曲流砂坝河流较为发育，其特征为：发育２层曲流砂坝沉积，下曲流砂坝厚度较大，一般厚２－５ｍ，发育较完好的正韵律，与经典曲流砂坝沉积模式特征相似；上曲流砂坝亦为正韵律，但泥质含量偏高，层理发育较差。上、下曲流砂坝间多为突变接触，或被紫色或杂色泥质层隔开。 相似文献
6.
通过对北阳庄井田综合勘探所获得的构造成果的归纳总结，探讨和分析了井田内褶皱及断层的发育规律、分布特征及其成因机制。对今后的矿井设计、建设和生产均有一定的指导意义。 相似文献
7.
Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband
lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different
types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes
to ground and activities during and following return strokes. It is shown that the structure and development of lightning
discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location
system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated
with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally
at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches
extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude
of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the
stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually
from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative
charge that assisted the leader’s development. The progression speed of fast negative streamers was about ten times faster
than the average speed of lightning channel. 相似文献
8.
Stuart R. Boyd Ian P. Wright Conel M.O'D. Alexander C.T. Pillinger 《Geostandards and Geoanalytical Research》1998,22(1):71-83
An analytical system and operating protocol are described for high resolution, stepped-combustion mass spectrometry, designed for the extraction, purification, quantification and isotopic analysis of light elements (e.g. C and N) in fine-grained reduced components (e.g. diamond) which have been chemically extracted from natural samples (e.g. meteorites). Specifically, a simple model has been developed for the extraction of diamond from meteorite and its analysis by high resolution stepped heating under an atmosphere of oxygen. Changes in the pressure of oxygen within the range 1.3 to 12kPa (10 to 90 torr) were not found to have any detectable effect on the combustion. Results obtained by this procedure were compared with those predicted by a model and excellent agreement was found, taking into account the limitations of this approach. Results of a preliminary attempt to find fine-grained diamond in a lamproite are outlined. 相似文献
9.
2D磁异常分步反演方法是利用二维(剖面)磁测数据确定场源几何参数以及物性参数的一种反演方法,该方法的优点是构造的形态函数S不受场源磁化特征的影响,因此可以在未知场源物性参数的前提下,通过拟合依次反演得到磁性源形体横截面几何参数、磁化强度以及磁化方向.本文阐述了2D磁异常分步反演方法的原理及步骤,对形态函数S的特征及求取方法进行了讨论,分析了区域背景干扰(正常场)对反演结果的影响并提出了初步解决方案.在方法研究的基础上,进行了单一理论模型及组合理论模型的试算,得到了较好的反演结果.为了验证该方法的效果,对实测剖面进行了试算,得到了场源的边界及场源埋深信息,为进一步反演提供了有用的参考. 相似文献
10.
为了明确桩板结构桩-板-土体相互作用机制,基于推导的相似理论,制作了桩板结构在2种跨度、有无板下土体支承等不同条件下的竖向分级加载试验和水平加载试验,系统研究了桩板结构桩-板-土相互作用力学特性。初步得出以下结论：（1）板-土相互作用对桩板结构的受力影响明显。当不考虑板下土体支承作用时,板的位移、应力、桩的受力、板-土接触压力等都会明显增大,且跨度越大,影响越明显。表明目前在工程设计时不考虑板下土体的支承作用进行设计,偏于保守。因此,建议桩板结构在设计时应考虑板下路基土体的支承作用。（2）在横向荷载作用下,桩-土相互作用明显,其主要作用区域在桩的上部1/2范围内。同时试验表明,板的跨度对桩-土相互作用影响较小,但对板的横向位移影响较大,且桩板结构的跨度越大,在横向力作用下,板的弯拉应力也越大。因此,建议在进行桩板结构跨度设计时,应检算横向荷载作用下板的拉应力指标。 相似文献