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401.
Both sea battles and testing of ship in underwater explosions reveal unacceptably poor anti-shock performance of important shipboard equipment. Anti-shock performance of shipboard equipment is a significant factor determining fighting strength and survivability. The anti-shock performance of a shipboard gear case based on BV043/85 was investigated using numerical simulation. A geometric model of the gear case was built using MDT software and meshed in HyperMesh software, and then the finite element model of the gear case was formed. Using ABAQUS software, the anti-shock performance of the gear case was simulated. First, shock response of typical regions of gear case was determined. Next, some generalizations were made about the anti-shock performance of the gear case by analyzing the Mises stress of typical regions varied with shock inputs. Third, weak regions were determined from simulation results. The threshold values of shock resistance of the gear case at different impulse widths were obtained through interpolating the numerical simulation results selected from the most dangerous spot. This research provides a basis for further optimization of the design of gear cases. 相似文献
402.
Traffic forecasting provides the estimation of future traffic state to help traffic control,travel guide,etc. This paper compared several widely used traffic forecasting methods,and analyzed each one's performance in detail to make conclusions,which could redound to researchers choosing an appropriate traffic forecasting method in their own works. Compared with conventional works,this paper creatively assessed the performance of traffic forecasting methods based on travel time index (TTI) data prediction,wh... 相似文献
403.
A reconfigurable flexible poles die was developed. The die can be used to implement the process of “the multi-point pressing
and forming sheet”. Sheet metal is restricted by the elastic pressing forces putting on the upper and lower surfaces of sheet
in stamping process. The method is an effective way to enhance the buckling critical stresses and reduce wrinkling of sheet.
The results of tests indicate that the die can achieve “one die brings multi-purpose” and suppress the wrinkle of sheet. The
process of the multi-point pressing and forming sheet provides a practical and effective way for the curved sheet metal forming. 相似文献
404.
This study focuses on the user-interface of the route guidance system with an electronic map display. The ultimate goal of
the study is to aid in designing electronic map displays that can deliver information to the user most efficiently and expeditiously
with minimum confusion. To evaluate the efficiency and understandability of a map display, laboratory experiments were designed
and conducted in this study. In the experiments the subjects were presented with electronic map displays of different attributes
and performed a set of tasks. Their understanding of the information contents was measured based on the outcomes of the tasks,
and subjective ratings of the ease of using the maps were obtained. Using the experimental data obtained, a structural equations
model system is developed to explain the understandability of a map display in terms of the subject’s attributes and the characteristics
of the map display. The experimental procedure and the modeling results are presented in this paper. 相似文献
405.
Naoya Umeda Hirotada Hashimoto Shohei Minegaki Akihiko Matsuda 《Journal of Marine Science and Technology》2008,13(1):16-23
The parametric rolling of modern containerships is emerging as a serious problem, to the extent that its effects warrant a
study into its prevention. In light of this, two methods for reduction of parametric rolling are proposed and examined by
physical model experiments. The first is a sponson attached to the side of a ship, the purpose being to decrease the rate
of change of the rollrestoring moment. The second is an antirolling tank to increase roll damping. By conducting free-running
model experiments for a 6600-TEU post-Panamax container ship with sponsons under typical parametric rolling conditions, it
was found that the sponsons could decrease the magnitude of parametric rolling. The antirolling tank could prevent parametric
rolling completely in certain conditions, even in severe head seas. Using the damping coefficients from experimentally derived
data of a model ship with an antiroll tank, a numerical simulation was established. The numerical model was then compared
with the free-running model experiments. The results indicated that the numerical model could qualitatively verify the experimental
results. Finally, an attempt to optimise the size of an antirolling tank for preventing parametric rolling for the subject
post-Panamax container ship in the North Pacific Ocean is presented. 相似文献
406.
Yusuke Tahara Daniele Peri Emilio Fortunato Campana Frederick Stern 《Journal of Marine Science and Technology》2008,13(2):95-116
The main objective of this article is to describe the development of two advanced multiobjective optimization methods based
on derivative-free techniques and complex computational fluid dynamics (CFD) analysis. Alternatives for the geometry and mesh
manipulation techniques are also described. Emphasis is on advanced strategies for the use of computer resource-intensive
CFD solvers in the optimization process: indeed, two up-to-date free surface-fitting Reynolds-averaged Navier-Stokes equation
solvers are used as analysis tools for the evaluation of the objective function and functional constraints. The two optimization
methods are realized and demonstrated on a real design problem: the optimization of the entire hull form of a surface combatant,
the David Taylor Model Basin—Model 5415. Realistic functional and geometrical constraints for preventing unfeasible results
and to get a final meaningful design are enforced and discussed. Finally, a recently proposed verification and validation
methodology is applied to assess uncertainties and errors in simulation-based optimization, based on the differences between
the numerically predicted improvement of the objective function and the actual improvement measured in a dedicated experimental
campaign. The optimized model demonstrates improved characteristics beyond the numerical and experimental uncertainty, confirming
the validity of the simulation-based design frameworks. 相似文献
407.
This paper presents the numerical analysis of rudder cavitation in propeller slipstream and the development of a new rudder
system aimed for lift augmentation and cavitation suppression. The new rudder system is equipped with cam devices which effectively
close the gap between the horn/pintle and movable wing parts. A computational fluid dynamics code that solves the Reynolds-averaged
Navier–Stokes equations is used to analyze the flow field of various rudder systems in propeller slipstream. The body force
momentum source terms that mimic flow field behind a rotating propeller are added in the momentum equations to represent the
influence of the propeller and its slipstream. For detailed explication of the new rudder system’s lift augmentation and cavitation
suppression mechanism, three-dimensional flow analysis is carried out. Simulations clearly display the mechanism of the lift
augmentation and cavitation suppression. The computational results suggest that the Reynolds-averaged Navier–Stokes-based
computational fluid dynamics reproduces the flow field around a rudder in propeller slipstream and that the present concept
for a cavitation suppressing rudder system is highly feasible and warrant further study for inclusion of the interaction with
hull and mechanical design for manufacturing and operations. 相似文献
408.
Appropriate modeling of roll damping is one of the key issues in accurately predicting ship roll motion. The difficulties
in modeling roll damping arise from the nonlinear nature of the phenomena. In this study, we report a new effort in modeling
the bilge keel roll damping effect based on the blocking mechanisms of an object in the potential flow. This effect can be
implemented as a component of appropriate ship motion models. We used our digital, self-consistent, ship experimental laboratory
(DiSSEL) ship motion model to test its effectiveness in predicting ship roll motion. Our numerical experiment demonstrated
clearly that the implementation of this roll damping component improves significantly the accuracy of numerical model results
(the results were compared with ship experiment data from the Naval Surface Warfare Center, Carderock Division, Maneuvering
and Seakeeping Facility). 相似文献
409.
This article concerns thermal radiation hazards associated with unconfined liquefied natural gas (LNG) spills on water. Consequence
assessment methods were compared to clarify their model characteristics in large-scale LNG spills from an LNG carrier (LNGC).
The consequences of LNG release, pool spread, and pool fire hazards were estimated using the following practical methods:
the Federal Energy Regulatory Commission’s (FERC) method, the Sandia National Laboratories’ method, and the Fay method. The
sensitivity of consequence analysis results to the breach size of a tank was examined under the assumption that LNG is released
from a common type LNGC of 125000 m3 cargo capacity. Consequently, it was found that the FERC method is useful from the practical viewpoint of being applicable
to any breach size. Finally, thermal radiation hazards from pool fires involving spills from one of the latest and largest
LNGCs (250 000 m3 cargo capacity), which are currently considered for construction, were investigated using the recommended FERC method, and
the results are discussed in comparison with those for common type LNGCs. As a result, it was found that the maximum thermal
hazard distance is longer by only about 24% compared with the common type LNGC, whereas the spill volume is twice as much. 相似文献
410.
A directed signature is a type of signature with restricted verification ability. Directed signatures allow only a designated
verifier to check the validity of the signature issued to him, and at the time of trouble or if necessary, any third party
can verify the signature with the help of the signer or the designated verifier. Directed signature schemes are widely used
in situations where the receiver’s privacy should be protected. Proxy signatures allow an entity to delegate its signing capability
to another entity in such a way that the latter can sign message on behalf of the former when the former is not available.
Proxy signature schemes have found numerous practical applications such as distributed systems and mobile agent applications.
In this paper, we firstly define the notion of the directed proxy signature by combining the proxy signature and directed
signature. Then, we formalize its security model and present a concrete scheme in the standard model. Finally, we use the
techniques from provable security to show that the proposed scheme is unforgeable under the gap Diffie-Hellman assumption,
and invisible under the decisional Diffie-Hellman assumption. 相似文献