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Beom-Seon Jang Hisashi Ito Kyung-Su Kim Yong-Suk Suh Hyun-Tae Jeon Young-Soo Ha 《Journal of Marine Science and Technology》2010,15(2):176-189
Predicting fatigue crack growth after its detection during in-service inspection is necessary to prevent a loss of serviceability,
such as the oil and/or water tightness of critical compartments. This paper focuses on the most typical fatigue cracks that
start at the weld joint between a flat bar stiffener on a transverse web frame and the flange of a longitudinal stiffener
on a bottom plate or inner bottom plate. An experiment is carried out to observe the fatigue crack propagation for two kinds
of flat bars at the abovementioned connection. The experimental results, especially the surface crack growth on the flange
(which dominates during the total fatigue life of the longitudinal stiffener), are compared with crack growth curves predicted
using a few existing formulas. Based on the comparative study, a formula that shows the best agreement with the experiment
results is selected. Weld toe magnification factors for the web stiffener are computed from the crack propagation rates measured
in the experiment, and two equations for the magnification factors versus crack depth are developed for two types of web stiffeners.
The selected existing formula and the proposed equations are applied to two connections at the inner bottom and side longitudinal
bulkhead of an LNG carrier. The equivalent stress approach based on a long-term distribution is employed to avoid the complexity
involved in dealing with the actual stress history. Using this prediction, the remaining service life until an oil or water
leakage occurs at a tank boundary can be estimated when a fatigue crack at the connection is detected. 相似文献
33.
介绍GPS高程拟合方法进行铁路高程控制测量的原理、作业方法及精度评定。结合某项目的生产实践,论证了该方法应用于铁路高程控制测量的可行性和优越性。 相似文献
34.
Tran Hong Ha Osami Nishida Hirotsugu Fujita Harano Wataru 《Journal of Marine Science and Technology》2010,15(3):271-279
Marine diesel engines are major sources of air pollution. They emit a large amount of pollutants, including diesel particulate
matter (DPM), carbon oxide (CO
x
), unburned hydrocarbons (HC), nitrogen oxide (NO
x
), sulfur oxide (SO
x
), and other products of combustion. Among these, DPM may cause respiratory and mutagenic diseases in humans, including lung
and bladder cancer (see Donaldson et al. J Aerosol Sci 29:553–560, 1998). In this study, experiments were performed with an
electrostatic water-spraying scrubber (EWSS) to evaluate its effectiveness for the collection of mass- and number-based DPM
emissions from a marine diesel engine. The results show that the collection efficiency of the scrubber increases as the engine
load increases due to an increase in the large DPM concentration and an increase in the amount of DPM collected by the charged
droplets. The effect of water spraying performance on DPM collection at constant engine load was investigated experimentally.
The strength of the electrical attraction between the charged water droplets and the charged DPM within the scrubber led to
a significant increase in total DPM collection efficiency (up to 4–7 times). In addition, the total DPM collection efficiency
was found to be directly related to the corona power, the electrical properties of water, water spraying performance and engine
load. The EWSS appears to be a promising alternative method for controlling mass-based as well as number-based DPM emissions. 相似文献
35.
Idle stability directly affects a vehicle’s NVH (Noise, Vibration and Harshness) and is closely related to driver satisfaction.
The present study proposes a method of measuring an engine’s idle roughness, which is useful in quantifying the idle stability.
Engine brake torque was measured directly using a torque sensor, which can be installed without modification of the engine’s
mounting structure. In addition, angular acceleration was measured at the same position as the torque measurement, to compare
dynamic characteristics of the angular acceleration with the torque variation. Both torque and angular acceleration oscillate
between positive and negative values. In this study, torque data were divided into several regions, and each region starts
from the point where the torque data changes its sign from negative to positive. The root mean square values of both torque
and angular acceleration were calculated for each region. This calculation showed a very good correlation between the torques
and the angular accelerations. The idle stability was evaluated with the standard deviation of the measured torque, and the
cycle-to-cycle variation is a more dominant factor in the idle stability than is the cylinder-to-cylinder variation. Because
it is easier to measure the angular acceleration than to measure the torque, the variations of angular accelerations are usually
compared between engines. However, the present study showed that the moment of inertia of an engine and the angular acceleration
should be considered together when comparing the idle stability between engines. 相似文献
36.
The drag reduction of a pickup truck by a rear flap add-on was examined through CFD simulations and wind tunnel experiments.
When installed at the rear edge of the roof, the flap increased the cabin back surface pressure coefficient, causing the downwash
of the bed flow to be inclined on the tailgate. Thus, the attachment of the bed flow to the tailgate was eliminated; consequently,
the drag coefficient was reduced with increasing flap length and downward angle despite the enlarged reverse flow in the wake.
However, the drag coefficient did not decrease any further after a specific downward angle was reached because the bed flow
increased the drag force at the tailgate and the flap lowered the pressure field above the flap. To maximize the drag reduction
effect, the rear downward flap should be designed to have an optimum downward angle. 相似文献
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通过试验研究了由路面废弃水泥混凝土加工成的再生粗集料的物理特性(级配、吸水率、表观密度)和强度特性(强度指标、硬度指标及坚固性指标等),其性能满足路用要求,具有广阔的应用前景. 相似文献
39.