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961.
The optical rays that form the image of an object and propagate a supersonic flow over a vehicle are refracted by the density
variations. A numerical analysis of the aero-optical characteristics of supersonic flow over blunt wedge with a cavity window
is carried out. A hybrid method of Reynold averaged Navier-Stokes and direct simulation Monte Carlo (RANS/DSMC) is employed
to simulate the flowfield. Refraction factor is introduced to evaluate the flowfield’s aero-optical characteristic. The results
show that mean flow’s aero-optical effects are mainly caused by the shock wave, the expansion wave and the turbulent boundary
layer. Fluctuation flow’s aero-optical effects are mainly caused by the turbulent boundary layer and the shock wave induced
by the cavity window. The aero-optical effects at the leading side of window are caused by the mean density variations, while
the effects at the trailing side are caused by the density fluctuations. Different draft angles of the cavity window are investigated.
The airborne optical devices of supersonic vehicle should be mounted in the middle of the cavity window with a large draft
angle. 相似文献
962.
运用界壳论,分析高速公路系统周界的界壳特征及界壳结构,构建高速公路界壳理论的研究框架,提出高速公路界壳论的基础理论研究主要包括:高速公路系统界壳结构分析及结构要素定义,高速公路界壳要素功能分析及功能参数描述方法,高速公路界壳行为剖析等内容。高速公路界壳理论应用研究主要包括:基于界壳论的入口匝道控制参量分析及控制模型,高速公路系统优化控制中界壳参数变化关系,高速公路系统总调控优化模型,高速公路界壁抵抗力与事件属性之间的关系,高速公路事件管理界壁抵抗力调控模型。最后,阐明研究中拟解决的关键问题及其技术路线。 相似文献
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Giorgio Contento Guido Lupieri Marco Venturi Tiziana Ciuffardi 《Journal of Marine Science and Technology》2011,16(2):181-201
The present study is aimed at determining the confidence limits of design wave parameters derived from numerical modeling—for
both extremes and operational conditions—over the Central and Western Mediterranean Sea. The paper presents the methodology
and results of an extensive validation activity conducted on a chain of medium-resolution third-generation wave models used
for hindcast purposes. The stringent requirements of state-of-the-art coastal and offshore engineering applications over this
area make the adoption of medium- or high-resolution hindcast wave and wind models almost mandatory because of the complex
coastal geometry, bathymetry, and orography that in turn lead to large variations of the design wave parameters even within
small regions. The chains of nested meteorological and wave models used in this hindcast study belong to the ETA and WaveWatch III
families, respectively. In this study the wind and wave numerical models have been run over the past 20 years, with increasing
resolutions of the wave models from 0.2° up to 0.04°. The results presented herein have 0.1° resolution for both wind and
wave models. The wave data obtained are compared with available measurements from 14 wave buoys in coastal zones in the Central
and Western Mediterranean Sea. 相似文献
966.
Levent Kirkayak Vinicius Aguiar de Souza Katsuyuki Suzuki Hideyuki Ando Hidetoshi Sueoka 《Journal of Marine Science and Technology》2011,16(3):354-365
It is estimated that around 10,000 containers are lost during maritime transportation every year, representing an economic
loss to the liner industry. Regulations and norms used to calculate values to secure them to the ship’s deck account for static
loads only, neglecting more realistic conditions. This paper describes an approach to simulate a two-tier scaled model of
a 20-ft ISO freight container and its linking connectors, denominated twist locks, subject to a dynamical load induced by
its base. To analyze this problem two methods were employed: a shaking table test and finite-element analysis. Results of
this study indicate that the numerical model built to simulate two-tier container stack dynamics is a promising tool for further
studies. Moreover, the model is able to predict conditions close to real situations faced by container stacks while stored
on deck. 相似文献
967.
The experimental procedure to predict the full-scale performance of the CRP-POD propulsion system is studied. In the CRP-POD
system, the RPM ratio of the two propellers is not mechanically fixed, in contrast with conventional CRP systems. Therefore
the existing procedure for conventional CRP systems is not appropriate for evaluating the performance of each propeller. In
this paper, the characteristics of the CRP-POD system, designed for a 9,600 TEU class container carrier, are studied experimentally.
Based on this study, a procedure for propulsive performance prediction for CRP-POD propulsion ships is suggested. 相似文献
968.
Tomohiro Takai Manivannan Kandasamy Frederick Stern 《Journal of Marine Science and Technology》2011,16(4):434-447
The accurate prediction of waterjet propulsion using computational fluid dynamics (CFD) is of interest for performance analyses
of existing waterjet designs as well as for improvement and design optimization of new waterjet propulsion systems for high-speed
marine vehicles. The present work is performed for three main purposes: (1) to investigate the capability of a URANS flow
solver, CFDSHIP-IOWA, for the accurate simulation of waterjet propelled ships, including waterjet–hull interactions; (2) to
carry out detailed verification and validation (V&V) analysis; and (3) to identify optimization opportunities for intake duct
shape design. A concentrated effort is applied to V&V work and performance analysis of waterjet propelled simulations which
form the focus of this paper. The joint high speed sealift design (JHSS), which is a design concept for very large high-speed
ships operating at transit speeds of at least 36 knots using four axial flow waterjets, is selected as the initial geometry
for the current work and subsequent optimization study. For self-propelled simulations, the ship accelerates until the resistance
equals the prescribed thrust and added tow force, and converges to the self propulsion point (SPP). Quantitative V&V studies
are performed on both barehull and waterjet appended designs, with corresponding experimental fluid dynamics (EFD) data from
1/34 scale model testing. Uncertainty assessments are performed on iterative convergence and grid size. As a result, the total
resistance coefficient for the barehull case and SPP for the waterjet propelled case are validated at the average uncertainty
intervals of 7.0 and 1.1%D, respectively. Predictions of CFD computations capture the general trend of resistance over the speed range of 18–42 knots,
and show reasonable agreement with EFD with average errors of 1.8 and 8.0%D for the barehull and waterjet cases, respectively. Furthermore, results show that URANS is able to accurately predict the
major propulsion related features such as volume flow rate, inlet wake fraction, and net jet thrust with an accuracy of ~9%D. The flow feature details inside the duct and interference of the exit jets are qualitatively well-predicted as well. It
is found that there are significant losses in inlet efficiency over the speed range; hence, one objective for subsequent optimization
studies could be maximizing the inlet efficiency. Overall, the V&V work indicates that the present approach is an efficient
tool for predicting the performance of waterjet propelled JHSS ships and paves the way for future optimization work. The main
objective of the optimization will be reduction of powering requirements by increasing the inlet efficiency through modification
of intake duct shape. 相似文献
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