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661.
A new simple and accurate shell FE-based structural Hot Spot Stress (HSS) determination method for web-stiffened cruciform joints has been proposed. Local stress of welded joints in full-scale bulk carrier (BC)’s lower stool models subject to bending and pressure loadings are examined. HSSs determined by the proposed method are compared with those derived by Lotsberg’s method and the conventional 0.5t-1.5t extrapolation. As results, following are found:
- (1)
- The local stress of full-scale BC lower stool models with various stool angle and plate thickness can be calculated accurately solely from shell FE results by means of the proposed method.
- (2)
- HSSs of welded joints in full-scale BC lower stool models subject to bending and pressure loadings derived by the proposed method show good agreement with the target HSSs determined from fine solid models. This demonstrates the validity of the proposed method for actual ship structures under the real load.
- (3)
- The excessive safety allowance of HSS determined by the conventional 0.5t-1.5t extrapolation can be reduced substantially by adopting Lotsberg’s method or our proposal. The proposed HSS determination method gives more accurate estimates compared to Lotsberg’s method under the conditions chosen, and the application range of the proposed method is equal to or wider than Lotsberg’s method.
662.
It is hypothesized that steady anguilliform swimming motion of aquatic animals is purely reactive such that no net vortex wake is left downstream. This is versus carangiform and tunniform swimming of fish, where vortex streams are shed from tail, fins, and body. But there the animal movements are such to produce partial vortex cancellation downstream in maximizing propulsive efficiency. In anguilliform swimming characteristic of the eel family, it is argued that the swimming motions are configured by the animal such that vortex shedding does not occur at all. However, the propulsive thrust in this case is higher order in the motion amplitude, so that relatively large coils are needed to produce relatively small thrust; the speeds of anguilliform swimmers are less than the carangiform and tunniform, which develop first order thrusts via lifting processes. Results of experimentation on live lamprey are compared to theoretical prediction which assumes the no-wake hypothesis. Two-dimensional analysis is first performed to set the concept. This is followed by three-dimensional analysis using slender-body theory. Slender-body theory has been applied by others in studying anguilliform swimming, as it is ideally suited to the geometry of the lamprey and other eel-like animals. The agreement between this new approach based on the hypothesis of wakeless swimming and the experiments is remarkably good in spite of the physical complexities. 相似文献
663.
B. C. Choi S. K. Choi S. H. Chung J. S. Kim J. H. Choi 《International Journal of Automotive Technology》2011,12(2):183-191
Experimental and numerical analyses of laminar diffusion flames were performed to identify the effect of fuel mixing on soot
formation in a counterflow burner. In this experiment, the volume fraction, number density, and particle size of soot were
investigated using light extinction/scattering systems. The experimental results showed that the synergistic effect of an
ethylene-propane flame is appreciable. Numerical simulations showed that the benzene (C6H6) concentration in mixture flames was higher than in ethylene-base flames because of the increase in the concentration of
propargyl radicals. Methyl radicals were found to play an important role in the formation of propargyl, and the recombination
of propargyl with benzene was found to lead to an increase in the number density for cases exhibiting synergistic effects.
These results imply that methyl radicals play an important role in soot formation, particularly with regard to the number
density. 相似文献
664.
We analyzed the lubrication characteristics of a design-selected spiral groove liquid seal for the critical component, the
carrier, of a rotary vane-type fuel pump developed for external installation on fuel tanks for liquid phase LPG (liquefied
petroleum gas) injection (LPLi) vehicles, with the aim of fundamentally improving lubrication performance and so protecting
the carrier from early frictional wear damage at its suction face. The main reason for selecting a spiral groove pattern was
because the viscosity of liquid LPG is very low, comparable to that of air, and current commercial dry gas seals adopting
spiral grooves have been successfully employed in completely noncontacting applications. Utilizing the Galerkin finite element
lubrication analysis method, a detailed lubrication characteristic analysis of the seal was performed, and lubrication performance
optimization was performed by systematic parameter analyses of the design variables. Compared to the initial reference design,
the final optimized spiral groove seal design had a groove depth increased by 66.7% and an equilibrium seal clearance increased
by 65.3%. Our model also predicted that under a condition of equilibrium between the closing force of the pumping pressure
and the seal opening force, the optimally designed carrier spiral groove liquid seal was capable of maintaining a stable lubricating
film with sufficient axial stiffness and thereby demonstrated successful noncontact operation; in addition, leakage through
the seal was minimal. 相似文献
665.
S. B. Choi 《International Journal of Automotive Technology》2011,12(2):207-212
An adaptive control algorithm was developed for the sensorless speed control of a permanent-magnet DC motor directly connected
to the hydraulic pump of an antilock brake system. Due to the severe cost and reliability constraints of the application,
the motor speed was controlled by a very simple on-off switching method, in which the only measurement required is the voltage
across the control switch. The motor speed was calculated solely from the back-EMF voltage during the period of the control
cycle when the switching controller is in the switch-off mode. The stability of the developed adaptiveswitching control algorithm
was proven mathematically and confirmed experimentally in several vehicle tests over a wide range of target speeds and pump-load
conditions. The accuracy and the response time of the controller can easily be tuned by adjusting a single tuning parameter.
The switching frequency of the controller can also easily be tuned by adjusting the over-and undershoot thresholds independently
from the accuracy of the speed-tracking control. 相似文献
666.
This paper presents the design optimization process of a short fiber-reinforced plastic armrest frame to minimize its weight
by replacing the steel frame with a plastic frame. The analysis was carried out with the equivalent mechanical model and design
of experiment (DOE) method. Instead of considering the whole structure, it is divided into three simpler regions to reduce
the complexity of the problem through examining its structural characteristics and load conditions. The maximum stress and
deflection of the regions that carry the normal load are calculated by the analytical mathematical form derived from an equivalent
model. The other regions loaded by contact stress are handled by FEM (finite element method), the DOE method, and the RSM
(response surface model). To optimize the design variables in both cases, the object functions derived from these calculations
are solved with a CAE (computer aided engineering) tool. This method clearly shows the mechanical and mathematical representation
of structural optimization and reduces the computing costs. After design optimization, the weight of the optimum plastic-based
armrest frame is reduced by about 18% compared to the initial design of a plastic frame and is decreased by 50% in comparison
with the steel frame. Some prototypical armrest frames were also made by injection molding and tested. The research results
fulfilled all of the design requirements. 相似文献
667.
S. J. Kang M. F. Kader Y. D. Jun K. B. Lee 《International Journal of Automotive Technology》2011,12(1):39-44
Adequate visibility through the automobile windshield is of paramount practical significance, most often at very low temperatures
when ice tends to form on the windshield screen. But the numerical simulation of the defrost process is a challenging task
because phase change is involved. In this study numerical solution was computed by a finite volume computational fluid dynamics
(CFD) program and experimental investigations were performed to validate the numerical results. It was found that the airflow
produced by the defrost nozzle is highly nonuniform in nature and does not cover the whole windshield area. The nonuniformity
also severely affected the heating temperature pattern on the windshield. The windshield temperature reached a maximum in
the vicinity of the defroster nozzle in the lower part of the windshield and ranged from 9∼31°C over a period of 30 min, which
caused the frost to melt on the windshield. The melting time was under 10 minutes, which satisfied the NHTSA standard. The
numerical predictions were in close agreement with the experimental results. Thus, CFD can be a very useful design tool for
an automobile HVAC system. 相似文献
668.
W. M. Choi J. S. Kim H. S. Jung T. S. Kwon 《International Journal of Automotive Technology》2011,12(3):383-389
As a crash energy absorber, a tube-type crash element (expansion tube) dissipates kinetic energy through the internal deformation
energy of the tube and through frictional energy. In this paper, the effects of the variation of punch angles on the energy-absorbing
characteristics of expansion tubes were studied by quasi-static tests using three punch angles (15°, 30°, and 45°). A finite
element analysis of the tube expanding process (m = τ
max
/K) was performed using a shear friction model to confirm the variation of the shear friction factor with respect to punch angles
using the inverse method. Additional analyses were performed using angles of 20°, 25°, 35°, and 40° to study the effect of
the punch angles on the internal deformation energy, frictional energy, and expansion ratio of the tubes. The results of the
experiment and finite element analysis showed that the shear friction factor was inversely proportional to the punch angles,
and a specific punch angle existed at which the absorbed energy and expansion ratio remained constant. 相似文献
669.
M. H. Lee H. M. Lee K. S. Lee S. K. Ha J. I. Bae J. H. Park H. G. Park H. J. Choi H. H. Chun 《International Journal of Automotive Technology》2011,12(5):733-744
In this paper, a hardware-in-the-loop simulation (HILS) system was developed before the development of an electric power steering
(EPS) system in a vehicle. This study was focused on the establishment of the HILS system. Driving conditions are simulated
with the HILS system. The actual steering input parameters are confirmed on the monitor while driving the HILS system. The
steering forces observed in the simulation with the developed HILS system are similar to those in real vehicle tests. The
developed HILS system can be applied in the development of various types of EPS systems. 相似文献
670.
An experiment was conducted to characterize the effects of SOF on EGR cooler fouling. A removable singletube test rig combined with a soot generator was developed to represent an EGR cooler and diesel exhaust gas. The use of a soot generator, which controlled the size and concentration of soot particles, enabled independent variables to be completely controlled. Either n-dodecane or diesel lube oil as substitute SOFs were vaporized and injected into the test rig to evaluate their effects on the growth of PM deposits and the degradation performance of the EGR cooler. Coolant temperature, which seemed to be associated with SOF content, was chosen as an independent variable, and PM deposit mass per unit area and the effectiveness drop versus time increased as the coolant temperature decreased. The PM deposit mass per unit area and effectiveness drop had maximum values at a coolant temperature of 40°C for every n-dodecane injection rate. For substitute SOFs tested in this experiment, the deposit mass increased when either n-dodecane or diesel lube oil was injected, but the effect of lube oil was more significant. Diesel lube oil seemed to have a stronger effect on the reduction of thermal conductivity by filling pores in the deposits. When diesel lube oil was injected, the deposit mass per unit area increased 127% compared to dry soot without injection. The effectiveness drop after 10 hours increased only 12.5%. 相似文献