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901.
The deep understanding on sand and sand dunes scale can be useful to reveal the formation mechanism of the sandstorm for early sandstorm forecast. The current sandstorm observation methods are mainly based on conventional meteorological station and satellites remote sensing, which are difficult to acquire sand scale information. A wireless sensing network is implemented in the hinterland of desert, which includes ad hoc network, sensor, global positioning system (GPS) and system integration technology. The wireless network is a three-layer architecture and daisy chain topology network, which consists of control station, master robots and slave robots. Every three robots including one master robot and its two slave robots forms an ad hoc network. Master robots directly communicate with radio base station. Information will be sent to remote information center. Data sensing system including different kinds of sensors and desert robots is developed. A desert robot is designed and implemented as unmanned probing movable nodes and sensors’ carrier. A new optical fiber sensor is exploited to measure vibration of sand in particular. The whole system, which is delivered to the testing field in hinterland of desert (25 km far from base station), has been proved efficient for data acquisition. 相似文献
902.
903.
高速铁路简支箱梁架设工期研究 总被引:4,自引:2,他引:2
薛国华 《铁路工程造价管理》2006,21(4):13-16
0引言高速铁路安全、舒适、快速的运行,对路基的稳定、桥梁的刚度、轨道的平顺提出了更高的要求,因此路基、桥梁、轨道结构与一般铁路干线存在很大不同,集中体现在:路基的地基处理、基床表层级配碎石、压实密度、路桥过渡段、工后沉降要求;桥梁采用体积大、梁体重的双线箱梁;轨 相似文献
904.
Longitudinal stresses due to combined horizontal and vertical bending moments in ships, corresponding to a return period
of 20 years, are estimated by linear response analysis. In principle, the stress should be obtained by combining the stress
in all sea states that can occur over a long-term period. A method to determine the desired long-term extreme stress by considering
only a few short-term sea states is presented. The sea states have a certain probability of occurrence, and are each identified
by a contour line in the (H
s, T
p)-plane. This approach makes it possible to estimate the extreme loads on the vessel in a practical and accurate manner. Moreover,
it is shown that the long-term stress can be estimated by combining the individual long-term extreme stresses due to vertical
and horizontal bending moments by using the sum-of-squares approach and accounting for the correlation between stresses. It
was found that the correlation coefficient can be taken as the largest of the ones calculated along the contour line. It is
shown that this correlation coefficient can even be approximated by the normalized phase angle at the wave length where the
dominant response has its peak value. A comparison with the results obtained using well-known combination rules is presented.
While linear analysis has been used here, it is believed that the approach can be generalized to stresses with nonlinear behavior,
and hence represent a significant improvement in calculation efficiency.
Received: September 18, 2001 / Accepted: December 18, 2001 相似文献
905.
The mathematical modeling group (MMG) model is well known and is widely used in the field of ship maneuverability. However,
the MMG model can be applied only after determination of the hydrodynamic coefficients either from comprehensive captive model
tests or from general empirical data. Around the cruising speed, when a ship's drift angle is relatively small, several methods
have been developed to predict hydrodynamic coefficients from the ship's principal particulars, e.g., Kijima's method. Kijima's
method is efficient in predicting the ship's maneuverability at the initial design stage and is even able to assess the effect
of changes in stern design. Similarly, for the low speed range when a ship's drift angle is relatively large, several methods
for predicting the ship's hydrodynamic coefficients have been proposed, based on captive model tests, such as those by Kose,
Kobayashi, and Yumuro. However, most of the methods developed for low speeds cannot be applied to general ship types without
additional experiments being performed. In contrast, Karasuno's method uses theoretical and empirical approaches to predict
the hydrodynamic forces, even for large drift motions. Although Karasuno's model utilizes the ship's principal particulars
and is applicable to a general vessel, it has not been widely used. This is because the form of Karasuno's model is relatively
complicated and its accuracy around the cruising speed is less than that for other methods that have been specifically developed
for the cruising speed range. A practical method for predicting hydrodynamic forces for the entire operating speed range of
blunt-body ships is proposed in this article. It is based on the MMG model and predicts hydrodynamic coefficients based on
a ship's principal particulars. A regression model for the proposed method has also been proposed by analyzing 21 different
blunt-body ships. Finally, simulations of a very large 4-m crude carrier (VLCC) model using the proposed method were carried
out and the results compared with free-running experiments (both at the cruising speed and at low speeds) to validate the
efficacy of the model. 相似文献
906.
Many experimental investigations have previously been performed and recently done on different shipbuilding structural steels
where the specimens size and crack depth/specimen width (a/W) were varied. A series of interesting results have been gained. It is worthwhile to have a review on the effect of a/W ratio on fracture toughness, and further theoretical analysis is necessary. In this paper, experimental work in elasticplastic
fracture mechanics (EPFM) was discussed. Tests had been carried out on 10 kinds of strength steels. Results showed that J
i
and δ1 values increased with decreasing a/W when a/W<0.3 for three-point bend specimens and that shallow crack specimens which have less constrained flow field give markedly
higher values of toughness than deeply notched specimens. However, for a/W>0.3, the toughness was found to be independent of a/W. Slip line field analysis shows that for shallow cracks, the hydrostatic stress is lower than that from standard deeply cracked
bend specimen which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will
ensure an unduly conservative approach when applied to structure defects especially if initiation values of COD/J-integral are used. 相似文献
907.
Francisco Pérez José A. Suárez Juan A. Clemente Antonio Souto 《Journal of Marine Science and Technology》2007,12(2):83-94
Nowadays, bulbous bow forms have become a common design feature in most conventional ship designs. The design of a bulbous
bow is usually attempted with the use of certain form parameters that are imposed using the designer's experience or regression
values that provide the optimum parameters based on experimental tests or computational fluid dynamics (CFD) calculations.
In this article, the geometric modelling of a bulbous bow form that complies with a series of parameters is presented. First,
a wire model was constructed with cubic B-spline curves that hold certain form parameters that the designer wants to impose.
Second, a B-spline surface that fits these splines was mathematically constructed. A review of the influence of the design
parameters used on the bulbous bow properties was made. This method could be used prior to numerical optimization of a bulbous
bow because different variations of the design can be easily generated. These variations can be tested numerically using CFD
software. A practical application example of the method is shown. 相似文献
908.
铅对儿童血液多种金属元素代谢的影响 总被引:1,自引:1,他引:0
动物实验和铅暴露儿童调查发现,铅可干扰体内钙、锌、铁、铜、镁等金属元素的代谢,进一步诱导铅毒性的产生。提示膳食或强化补充因铅暴露而引起缺乏的元素能抑制肠道对铅的吸收,降低铅毒性。 相似文献
909.
文章讲述了将船舶操纵模拟器作为航海英语听说训练平台的可行性,阐明了训练的内容和方式,分析了训练所能达到的效果,最后提出了几点改进建议。 相似文献
910.