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统计能量法计算声呐自噪声的水动力噪声分量 总被引:11,自引:2,他引:11
本文针对水下航行器舷侧的声呐基阵,采用统计能量法建立自噪声中水动力噪声分量的计算模型,并计算分析不同罩壁材料、吸声处理对声呐自噪声的影响. 相似文献
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集成统计能量法计算声呐自噪声水动力噪声分量 总被引:3,自引:1,他引:3
针对舰船艏部非规则形状声呐罩的自噪声预报,借鉴集成模态法思路[1,2],采用虚拟弹性膜技术,建立集成统计能量法(Integro-SEA),并以矩形腔声呐罩为例验证计算精度.在此基础上,采用集成统计能量法计算舰船艏部声呐自噪声的水动力噪声分量,并修正计算艏部边界层转捩区湍流猝发声源对声呐自噪声的作用.研究表明:用经典SEA和集成SEA方法计算矩形腔声呐罩自噪声,偏差小于1dB,集成SEA方法加边界层转捩区声源修正,计算的舰船艏部声呐自噪声与实艇测试结果比较,在200Hz~6kHz的中频范围内相差2~3dB. 相似文献
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利用以统计能量分析原理为基础的声仿真软件AutoSEA2建立典型动力源激励的某船分段3D模型,分析了动力源激励力的等效计算及此激励产生的辐射噪声.首先根据舱段的特点,划分子系统并建立耦合关系,得到了统计能量分析模型.然后利用动力设备基座的面导纳概念,将基座面板分别简化为有限简支矩形薄板和无限大薄板,计算并对比了在中高频段这两种简化方案下的激励力.根据确定的激励方案计算得到r该舱段的舱室噪声和水下辐射噪声,并与试验结果进行了比较.对比表明,依此激励计算得到的声振环境预示结果与试验结果吻合较好,证明了统计能量分析在高频区预示船舶声振环境的可靠性. 相似文献
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高速船是在船舶航速上出现突破、慨念新颖的新一代船型。船舶高速化的同时却带来了严重的振动噪声问题。在船舶设计初期预估舱室噪声水平,及时采取预防措施显得至关重要。应用统计能量分析软件AutoSEA对高速船客舱区进行设计初期的噪声预报,并分析噪声传播路径,提出噪声控制的初步方案,模拟计算经采取控制措施后的客舱区噪声值。 相似文献
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水下结构物自噪声统计能量分析 总被引:7,自引:0,他引:7
用统计能量分析方法,对湍流边界层脉动压力激励下水下结构物自噪声进行了分析,得到相应的自噪声工程估算关系。根据工程条件进行简化,得到忽略壳体内损耗和边界层伪声直接透射的高频情况下的工程估算公式。 相似文献
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Yuki Yoshida Yoshiaki Takahashi Hiroharu Kato Akira Masuko Osamu Watanabe 《Journal of Marine Science and Technology》1997,2(1):1-11
For the theoretical consideration of a system for reducing skin friction, a mathematical model was derived to represent, in a two-phase field, the effect on skin friction of the injection of micro air bubbles into the turbulent boundary layer of a liquid stream. Based on the Lagrangian method, the equation of motion governing a single bubble was derived. The random motion of bubbles in a field initially devoid of bubbles was then traced in three dimensions to estimate void fraction distributions across sections of the flow channel, and to determine local bubble behavior. The liquid phase was modeled on the principle of mixing length. Assuming that the force exerted on the liquid phase was equal to the fluid drag generated by bubble slip, an equation was derived to express the reduction in turbulent shear stress. Corroborating experimental data were obtained from tests using a cavitation tunnel equipped with a slit in the ceiling from which bubbly water was injected. The measurement data provided qualitative substantiation of the trend shown by the calculated results with regard to the skin friction ratio between cases with and without bubble injection as function of the distance downstream from the point of bubble injection.List of symbols
B
law of wall constant
-
C
f
local coefficient of skin friction
-
C
f0
local coefficient of skin friction in the absence of bubbles
-
d
b
bubble diameter [m]
-
g
acceleration of gravity [m/s2]
-
k
1 k4
proportional coefficient
-
k
L
turbulent energy of the liquid phase [m2/s2]
-
L
representative length [m]
-
l
b
mean free path of a bubble [m]
-
m
A
added mass of a single bubble [kg]
-
m
b
mass of a single bubble [kg]
-
N
x
,N
y
,N
z
force perpendicular to the wall or ceiling exerted on a bubble adhering to that wall or ceiling [N]
-
P
absolute pressure [Pa]
-
Q
G
rate of air supply [/min]
-
q
L
(i)
turbulent velocity at the ith time increment [m/s]
-
R>
ex
Reynolds number defined by Eq. 32
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T
*L
integral time scale of the liquid phase [s]
-
U
velocity of the main stream [m/s]
-
,¯v,¯w
time-averaged velocity components [m/s]
-
u,v,w
turbulent velocity components [m/s]
-
û
L
,vL
root mean square values of liquid phase turbulence components in thex- and y-directions [m/s]
-
V
volume of a single bubble [m3]
-
X,Y,Z
components of bubble displacement [m]
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x
s
,y
s
,z
s
coordinate of a random point on a sphere of unit diameter centered at the coordinate origin
-
root mean square of bubble displacement in they-direction in reference to the turbulent liquid phase velocity [m]
-
local void fraction
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m
mean void fraction in a turbulent region
-
regular random number
- R
v
increment of the horizontal component of the force acting on a single bubble, defined by Eq. 22 [N]
- t
time increment [s]
- 1
reduction of turbulent stress [N/m2]
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L
rate of liquid energy dissipation [m2/s3]
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m
coefficient defined by Eq. 30
-
law of wall constant in the turbulent region in absence of bubbles
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1
law of wall constant in the turbulent region in presence of bubbles 相似文献
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湍流边界层流动精细涡结构的分析对于水下航行体表面减阻乃至降噪机理的深入研究都具有重要意义.文章应用粒子图像测速技术(PIV),对Reθ=1 743和5 400时的平板湍流边界层的流向—法向平面流场进行了测试研究.一方面,直接对瞬时速度场精细涡结构进行提取分析,通过Galilean分解和λci准则识别出流向—法向平面中的发卡涡及发卡涡包.研究表明,发卡涡和雷诺应力的分布特征具有高度相关性;发卡涡包产生了流向动量的法向不规则分层分布特征.另一方面,文中通过对500个瞬时速度场子样进行时间平均分析,获得了不同雷诺数下平均速度以及湍流度分量的法向分布规律.此外,文中还对发卡涡的几何尺寸和漩涡强度λci进行了统计分析.研究表明,在y+<50范围内无量纲化的漩涡强度λciδ/uт沿法向迅速衰减,且在不同雷诺数下变化曲线基本一致;在y+ >50后λciδ/uт衰减平缓,且低雷诺数下的值较大. 相似文献
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Hiroharu Kato Tomoaki Iwashina Masaru Miyanaga Hajime Yamaguchi 《Journal of Marine Science and Technology》1999,4(4):155-162
The time-averaged velocity and turbulence intensity distributions were measured by a laser Doppler velocimeter in a turbulent
boundary layer filled with microbubbles. The void fraction distribution was also measured using a fiber-optic probe. The velocity
decreased in the region below 100 wall units with an increase in bubble density. This led to a decrease in the velocity gradient
at the wall, which was consistent with a decrease in shearing stress on the wall. The turbulence intensity in the buffer layer
increased at a low microbubble density, and then began to decrease with an increasing microbubble density. Based on the present
measurements, the mechanism of turbulence reduction by microbubbles is discussed and a model is proposed.
Received for publication on Dec. 3, 1999; accepted on April 18, 2000 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
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B
law-of-the-wall constant
-
C
f
local skin-friction coefficient in the presence of bubbles
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C
f0
local skin-friction coefficient in the absence of bubbles
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d
b
bubble diameter (m)
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g
acceleration of gravity (m/s2)
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j
g
flow flux of gas phase accountable to buoyancy (m/s)
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j
t
flow flux of gas phase accountable to turbulence (m/s)
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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
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l
b
mixing length of gas phase (m)
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l
m
mixing length of liquid phase (m)
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l
mb
diminution of liquid phase mixing length by bubble presence (m)
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Q
G
rate of air supply to liquid stream (l/min)
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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)
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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)
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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)
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v
kinematic viscosity (m2/s)
-
density (kg/m3)
Suffixes
G
gas
-
L
liquid
- 0
absence of bubbles 相似文献