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1.
Keisuke Watanabe Hideyuki Suzuki Koichiro Yoshida 《Journal of Marine Science and Technology》1998,3(3):151-160
The trend towards deepwater development requires a new approach to underwater installation of offshore structures. The present
method using crane vessels has some drawbacks in operations at more than 2000 m depth. The natural period of the coupled system
of the rigged structure and the crane vessel becomes longer, so that it is no longer possible to manipulate the cranes to
achieve the desired positioning accuracy. This paper examines the application of an active control technique for underwater
installations as one of the solutions to the present problems. An active control technique also has the advantage that it
can deal with the structural flexibility which allows the structure to be large and light-weight. This structural flexibility
imposes problems of suppressing the elastic responses and securing the stability of the control system. In this paper, anH
∞ controller combined with a low authority control/high authority control (LAC/HAC) feedback controller is designed for cases
where structural flexibility cannot be ignored. A robust model-following controller is examined for cases where the structure
can be treated as rigid. In order to confirm the control algorithm and verify the possibility of the active control installation
method, basin tests are executed using two types of neutrally buoyant flexible models with ultrasound ranging systems and
thrusters. 相似文献
2.
Yoshinori Watanabe 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1984,13(3):113-128
The finite element model previously formulated to represent a bias-ply motorcycle tire is improved for more accurate orthotropic stiffness values. Efforts are centered on accurate mapping of the cord angle from an actual tire to the finite element model. Using this improved finite element model, the deformations of the bias-ply motorcycle tire subject to inflation pressure are analyzed. 相似文献
3.
Yoshinori Watanabe 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1984,13(4):173-186
A finite element model suitable for camber thrust analysis is formed. By inclining and pressing this finite element model onto the road plane, the forces prevailing in the contact patch of an inclined standing tire are calculated and the asymmetry-dependent mechanism of camber thrust generation is analyzed. By rotating the inclined standing tire at a constant vertical deflection, the roll-distance-dependent mechanism of camber thrust generation is analyzed. 相似文献
4.
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
-
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]
-
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
-
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]
-
L
rate of liquid energy dissipation [m2/s3]
-
m
coefficient defined by Eq. 30
-
law of wall constant in the turbulent region in absence of bubbles
-
1
law of wall constant in the turbulent region in presence of bubbles 相似文献
5.
During automated driving in urban areas, decisions must be made while recognizing the surrounding environment using sensors such as camera, Light Detection and Ranging (LiDAR), millimeter-wave radar (MWR), and the global navigation satellite system (GNSS). The ability to drive under various environmental conditions is an important issue for automated driving on any road. In order to introduce the automated vehicles into the markets, the ability to evaluate various traffic conditions and navigate safely presents serious challenges. Another important challenge is the development of a robust recognition system can account for adverse weather conditions. Sun glare, rain, fog, and snow are adverse weather conditions that can occur in the driving environment. This paper summarizes research focused on automated driving technologies and discuss challenges to identifying adverse weather and other situations that make driving difficult, thus complicating the introduction of automated vehicles to the market. 相似文献
6.
MVNakhodka collapsed and broke in two on January 2, 1997 in the Sea of Japan, giving rise to a serious and disastrous oil spill on the
coastline of Japan. During the inquiry into the cause of the accident, one of the main tasks of the inquiry committee was
to identify the external loads which made the ship structure collapse. Among the several possible scenarios for the accident,
after careful examination, the wave loads in the heavy weather at the time of the accident were taken to be the most plausible
cause. The results of that research are described in two papers, and the present paper deals with the way in which wave loads
on theNakhodka at the moment of the accident were estimated. We first describe the details of the accident such as the location, the sea
condition, the loading condition, and the ship's heading speed. Then the static loads resulting from the distribution of the
cargo weight and the buoyancy are given to show that the static bending moment at the time of the accident caused extreme
sagging. Next the wave loads in the irregular waves, calculated by the nonlinear time domain simulation program SRSLAM, are
presented. It is shown that the bending moment in the waves reaches 1 087 800 KN*m at maximum SS 6.9, which is where the hull girder collapse took place. It was concluded that the ship broke in two because
the bending moment exceeded the hull girder strength which had been reduced due to corrosion, taking into account conclusions
derived from the research dealing with the structural strength aspect. We also discuss the stochastic significance of the
estimated value and nonlinear nature of the peak distribution, in addition to the effects of the ship speed and wave heading
on the wave load estimation.
This article is based on an article that appeared in Japanese in the Journal of the Society of Naval Architects of Japan,
vol. 183 (1998). 相似文献
7.
8.
Atsuo Maki Jun Arai Tatsuhiro Tsutsumoto Keisuke Suzuki Yoshiki Miyauchi 《Journal of Marine Science and Technology》2016,21(2):344-358
It is well known that a decrease in ship resistance may be achieved due to the installation of a stern flap. Therefore, so far, a considerable amount of research on stern flaps has been conducted. Previous research has demonstrated that the primary mechanism by which a stern appendage reduces resistance is a change in the pressure distribution over the aft body of the hull, and secondly through effects on the running attitude, near and far field wave generation, and local transom flow among other phenomena. However, the change in pressure distribution is influenced by the other components. Hence, there is still room for argument about the relative contribution of each component to the pressure distribution. Therefore, as the first step of the research, by conducting the model experiment in towing tank and CFD (Computational Fluid Dynamics) analysis, we examined the effect of running attitudes and wave making at the after portion of the hull on resistance reduction. As a result, it is concluded that a flap affects a change in the wave generated at the transom part and it could lead to a decrease in wave-making resistance. 相似文献
9.
During the installation operations of underwater structures, offshore structures such as semisubmersibles, the steady nonlinear
hydrodynamic force due to the ocean current, the tidal current, and the hydrodynamic interaction between structures are regarded
as major disturbances. Generally, it is difficult and very expensive to collect information about these disturbances in advance,
although such knowledge would be important and necessary for precise installation. Because of this situation, we have proposed
a learning tracking controller (LTC) for automated tracking/docking operations of offshore structures. The LTC can be operated
without any information about current, and can be applied to the installation problem of flexible structures whose flexibility
cannot be ignored. In order to confirm the effectiveness of the LTC, basin tests were carried out using experimental models
with an unknown current. Two types of basin experiment were executed using an ultrasound ranging system and thrusters. One
was trajectory tracking of a semisubmersible, and the other was the precise mating of flexible underwater structures. In both
cases the LTC showed good performance, and in the latter case in particular, two flexible models were successfully made to
track the given trajectory and dock to the docking targets with an accuracy of ±5 mm, after the trajectory had been tracked
six to seven times for learning purposes. No elastic responses were excited in the flexible model.
Received for publication on Dec. 1, 1999; accepted on March 13, 2000 相似文献
10.
A Sliding Mode Controller for Wheel Slip Ratio Control System 总被引:1,自引:0,他引:1
Taketoshi Kawabe Masao Nakazawa Ikuro Notsu Yoshito Watanabe 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1997,27(5):393-408
A sliding mode controller has been developed for a wheel slip ratio control system for commercial vehicles with sluggish braking actuators to replace conventional if-then rule-like ABS control laws. New techniques overcome the tendency of sliding mode controllers to chatter. Computer simulation (hardware-in-the-loop simulation) and actual vehicle tests verified the effectiveness of this method to suppress chattering and keep the wheel slip ratio in a desirable range during braking on low-friction road surfaces. 相似文献