排序方式: 共有11条查询结果,搜索用时 15 毫秒
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Madan Mohan Guin Hiroharu Kato Hajime Yamaguchi Masatsugu Maeda Masaru Miyanaga 《Journal of Marine Science and Technology》1996,1(5):241-254
Determination of the flow structure near the wall is essential for a clear insight into the phenomenon of skin friction reduction
by microbubbles in a turbulent boundary layer. An important parameter, is the bubble concentration or void fraction in the
wall region in drag-reducing conditions. The purpose of this paper is to show drag-reducing effects due to microbubbles in
a water channel and, more importantly, to show the dependence of the drag-reduction values on the near-wall void fraction.
A two-dimensional channel with an aspect ratio of 10 was specially built for this purpose with provisions for air injection
through porous plates. Skin friction was directly measured by a miniature floating element transducer with a 5-mm circular
sensing disk mounted flush on the top wall 67 channel-heights downstream of the injector. The wall friction in the presence
of air bubbles was found to be reduced under the same bulk velocity when compared with the value without air. Detailed void
fraction profiles across the channel were obtained by a sampling probe and a fiber-optic probe. Better collapse of the drag
reduction data, independent of different profile shapes, was found when plotted against the near-wall void fraction than against
a cross-sectional mean void fraction. While this dependence reconfirms that the phenomena are essentially inner-region dependent,
the lack of influence of the bubble distribution patterns away from the wall implies lack of outer region influence. 相似文献
3.
Kaviti Shruthi Venigalla Mohan M. Zhu Shanjiang Lucas Kimberly Brodie Stefanie 《Transportation》2020,47(2):641-662
Transportation - Bikeshare operators routinely explore options to improve ridership and revenue by studying interaction among pricing, service and operations. The objective of this research is to... 相似文献
4.
In this paper, we use estimates of the effectiveness of existing road safety technologies and interventions to estimate the reduction in road safety deaths in six Indian cities over the next decade, in order to achieve the SDG 3.6 goal of a 50% reduction by 2030. Only the existing interventions are considered and technologies that might be available in the future are not accounted for. The results show that similar policies for all cities will not produce the same results, and that achieving the SDG 3.6 goal does not automatically reduce fatality rates in cities with high fatality rates. The introduction of safer cars with currently available safety technologies, although necessary, will have much less effect than the combined effect of motorcycle safety technologies, speed control and traffic calming. This study suggests that while SDG 3.6 targets may be satisfied by 2030 with great effort in India, the presently available safety interventions may not be adequate to bring about death rates below 2.0 per hundred thousand persons. Since the situation differs significantly between cities, it will be important to evolve city-specific policies for safety intervention priorities and changes in travel behavior. The desired reduction in road traffic injuries in India will not be possible without much greater investment in road safety research and road design for safer travel. 相似文献
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Yuki Yoshida Yoshiaki Takahashi Hiroharu Kato Madan Mohan Guin 《Journal of Marine Science and Technology》1998,3(1):30-36
A method of enveloping the hull with a sheet of microbubbles is discussed. It forms part of a study on means of reducing the skin friction acting on a ship's hull. In this report, a bubble traveling through a horizontal channel is regarded as a diffusive particle. Based on this assumption, an equation based on flow flux balance is derived for determining the void fraction in approximation. The equation thus derived is used for calculation, and the calculation results are compared with reported experimental data. The equation is further manipulated to make it compatible with a mixing length model that takes into account the presence of bubbles in the liquid stream. Among the factors contained in the equation thus derived, those affected by the presence of bubbles are the change of mixing length and the difference in the ratio of skin friction between cases with and without bubbles. These factors can be calculated using the mean void fraction in the boundary layer determined by the rate of air supply into the flow field. It is suggested that the ratio between boundary layer thickness and bubble diameter could constitute a significant parameter to replace the scale effect in estimating values applicable to actual ships from corresponding data obtained in model experiments.List of symbols
a
1
proportionality constant indicating directionality of turbulence
-
B
law-of-the-wall constant
-
C
f
local skin-friction coefficient in the presence of bubbles
-
C
f0
local skin-friction coefficient in the absence of bubbles
-
d
b
bubble diameter (m)
-
g
acceleration of gravity (m/s2)
-
j
g
flow flux of gas phase accountable to buoyancy (m/s)
-
j
t
flow flux of gas phase accountable to turbulence (m/s)
-
k
4
constant relating reduction of liquid shear stress by bubble presence to decrease of force imparted to bubble by its displacement due to turbulence
-
l
b
mixing length of gas phase (m)
-
l
m
mixing length of liquid phase (m)
-
l
mb
diminution of liquid phase mixing length by bubble presence (m)
-
Q
G
rate of air supply to liquid stream (l/min)
-
q
/g
velocity of bubble rise (m/s)
- 2R
height of horizontal channel (m)
-
T
*
integral time scale (s)
-
U
m
mean stream velocity in channel (m/s)
-
U
friction velocity in channel (m/s)
-
V
volume of a bubble (m3)
-
u, ¯ v
time-averaged stream velocities inx- andy-directions, respectively (m/s)
-
u, v
turbulent velocity components inx- andy-directions, respectively (m/s)
- v
root mean square of turbulence component in they-direction (m/s)
-
root mean square of bubble displacement iny-direction with reference to turbulent liquid phase velocity (m)
-
y
displacement from ceiling (m)
-
local void fraction
- m
mean void fraction in boundary layer
- m
constant relating local void fraction to law-of-the-wall constant
- t
reduction of turbulent stress (N/m2)
-
law-of-the-wall constant in turbulent liquid region in absence of bubbles
- 1
law-of-the-wall constant in turbulent liquid region in presence of bubbles
- 2
law-of-the-wall constant in gas phase
- m
constant indicating representative turbulence scale (m)
-
viscosity (Pa × s)
-
v
kinematic viscosity (m2/s)
-
density (kg/m3)
Suffixes
G
gas
-
L
liquid
- 0
absence of bubbles 相似文献
8.
PI_3激酶参与AT_1受体介导Ang II调节SHR脑神经元电活动的信号转导 总被引:1,自引:0,他引:1
目的 探索AT1受体介导AngII调节SHR和WKY鼠脑神经元电活动的信号转导机制。 方法 原代培养SHR和WKY新生鼠脑干和下丘脑神经元 ,用全细胞膜片钳以电流箝方式记录神经元的放电活动 ,观察AngII及各种信号分子抑制剂对脑神经元放电频率的影响。结果 AngⅡ (10 0nmol·L-1)可使WKY新生鼠脑神经元的放电频率从 (0 .4 4± 0 .0 8)Hz增加到 (1.39± 0 .16 )Hz。这种效应在SHR鼠更加显著。由AngⅡ引起的这两种鼠脑神经元放电频率的增加均可被AT1受体拮抗剂Losartan完全消除。使用PKC抑制剂calphostinC和钙调蛋白激酶II抑制剂KN 93能完全阻断AngⅡ对WKY鼠脑神经元的作用 ,但对SHR鼠脑神经元的放电频率仅阻抑约 5 0 %。磷脂酰肌醇 3(PI3 )激酶抑制剂LY2 94 0 0 2 (10 μmol·L-1)对SHR鼠脑神经元的放电频率可产生部分阻断作用 ,但对WKY鼠脑神经元无明显影响。结论 AngII增加SHR和WKY鼠脑神经元放电频率的作用均由AT1受体介导。PI3 激酶在AngⅡ调节SHR鼠脑神经元电活动的信号转导机制中发挥重要作用 相似文献
9.
AngiotensinⅡ (AngⅡ ) playsanimportantroleintheregulationofbloodpressure[1 ] .Theac tionofAngⅡismediatedmainlybystimulationoftheangiotensintype 1(AT1 )receptorandinvolvesintheactivityofcatecholaminergicsystem .Im munostainingstudieshaveindicatedthattheAT1 re ceptorexistsonthecatecholaminergicneurons[2 ] .AdministrationofAngⅡintorat’sbrainincreasedtheconcentrationsofdopamine ,epinephrine ,andnorepinephrineinthebrain[3 ] .Althoughanatomicalandfunctionalevidencessupporttheinteractionbe twe… 相似文献
10.
Travel demand model system for the information era 总被引:5,自引:0,他引:5
The emergence of new information technologies and recent advances in existing technologies have provided new dimensions for travel demand decisions. In this paper we propose a comprehensive travel demand modeling framework to identify and model the urban development decisions of firms and developers and the mobility, activity and travel decisions of individuals and households, and to develop a system of models that can be used by decision makers and planners to evaluate the effects of changes in the transportation system and development of information technologies (e.g. various tele-commuting, tele-services and Intelligent Transportation Systems).The implementation of an operational model system based on this framework is envisioned as an incremental process starting with the current best practice of disaggregate travel demand model systems. To this end, we present an activity-based model system as the first stage in the development of an operational model system. 相似文献