Advances in Mechanics Engineering

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Authors: Yun Long Yao, Guang Ying Ma, Shi Lin Dong
Abstract: The large-span space beam string-structure system is a kind of economic and larger spanning spatial structure system. A new type of space beam-string-structure with outer truss torus is introduced. Sunflower-patterned space beam-string-structure was taken as an example and its dynamic characteristics under full-span load and half-span load were analyzed by block Lanczos method. The efect of prestress level and load level on dynamic behavior of the structure was studied. The results are valuable for the dynamic response research on the earthquakes and wind vibration and will provide a reference for a further design and project application of such structure.
1960
Authors: Li Dan Wu, Chun Bao Miao
Abstract: Internal tides generated by the interaction of the barotropic tide with bottom topography are studied by using an analytical solution. Tide-topography resonance takes place when the wavenumber of the truncated sinusoidal topography is equal to that of one baroclinic mode. The minimum amplitude of the resonant mode increases from the center of the domain to both sides of the topography; while the maximum keeps the same. Amplitudes of the internal tides and mode conversion rate are analyzed as a function of the length and wavenumber of the topography. For non-resonant modes, the amplitudes are weak and vary periodically with the extending of the topography, and are exactly zero when the length of topography is integral times of the mode-1 wavelength. For resonant modes, the amplitudes increase with the length of the topography. For each internal tide mode, there is a response zone, where the amplitude for one mode is obviously larger than other baroclinic modes. The response zones for high modes are wider than those for low modes. Mode conversion rate is obviously high when the wavenumber of the topography is equal to that of the baroclinic modes; otherwise it is almost zero. Furthermore, mode conversion rate for small topography wavenumber is more than that for large topography wavenumber with the same number of the sinusoidal topography, and is less with the same topography length.
1964
Authors: Li Dan Wu, Chun Bao Miao
Abstract: Here the process of internal tide generation over idealized (sinusoidal) topography was investigated using numerical techniques, in which the barotropic-to-baroclinic energy conversion was discussed. The result shows that when the wavenumber of the sinusoidal topography, ktopo, is equal to the horizontal wavenumber of the m-th baroclinic mode km, the conversion from the barotropic tide to the m-th baroclinic mode is enhanced with the increase of topography length; When the wavenumber of the sinusoidal topography is not equal to horizontal wavenumbers of any baroclinic modes, ktopo≠km (m=1,2,...), conversion from the barotropic energy to baroclinic modes is decreased with the increase of topography length. Furthermore, it shows that in resonance case, the phase of the perturbation pressure gradually agrees with the phase of the truncated sinusoidal topography, and the conversion rate is always positive over the topography, thus the baroclinic mode which matches with the wavenumber of the sinusoidal topography persists in absorbing energy from the barotropic tide, and the conversion rate is increased.
1972
Authors: Wen Hua Chen, Qi Song, Meng Li
Abstract: Nanjing’s metro is studied as a example to introduce resist liquefaction method in this paper. Dynamic diffuse theory of structure is supposed to evaluate the width and depth of foundation treatment to resist the seismic liquefaction to think of metro structure, liquefied soil layers and different liquefaction-index. High pressure jet grouting method is researched as shield machine construction through foundations of buildings or ancient wall. An improved segments of shield tunneling method is suggest to ensure the resist liquefaction method to success.
1979
Authors: Meng Qiao Chen, Jian Kun Liu, Jun Hua Xiao
Abstract: Based on the under river tunneling project of Nanjing Metro Puzhulu-Binjianglu interval, a numerical model was built to simulate the process of losing stability, variation of soil stress and the soil arching effect caused by soil stress redistribution under high hydraulic pressure were studied. The results show that, compared to no hydraulic pressure, the limit supporting pressure is reached when smaller soil deformation has occurred and it is much greater under high hydraulic pressure. Along the depth from the bottom, soil vertical stress first decreases and then remains unchanged with increasing face displacement; Soil horizontal stress first decreases and then increases slightly. Soil lateral pressure coefficient first increases and then decreases along the depth from the bottom. Soil vertical and horizontal stress decrease in front of the tunnel face, where the failure region forms. Soil vertical stress decreases and horizontal stress increases above the failure region, where the vault region forms. Soil vertical stress increases and horizontal stress decreases around the failure region, where the skewback region forms. The results are conductive to better reveal the failure mechanism and determine the limit supporting pressure under high hydraulic pressure.
1983
Authors: Ba Teer Wu, Er Gen Gao
Abstract: Based on the primary theory of location, it is found that the data recorded at nearby stations are applicable in double difference relocation algorithm, but not in other relative location algorithms. Equation derivation and simulated calculation demonstrate that double difference algorithm allows to get the absolute locations of earthquakes with certain accuracy by using the nearby stations records. The errors of relative location become larger when using the nearby station records alone than that using the distant station records. Combining the nearby and distant station records, the best locations are obtained. In the case that hypocenter depth is far less than the epicenter distance without depth phases available, only the relative epicenter distribution could be obtained accurately by double difference method, the depth determined would be not stable. The relocation test of a part of aftershocks in Jiashi earthquake sequence verify the effect of nearby station records on the double difference algorithm mentioned above.
1988
Authors: Jun Xia Yan, Jian Feng Zhang
Abstract: Land use changes and land intensification has played a more and more important role in food production. The environment has been influenced by it greatly. Land use data were derived from several sources: aerial photographs, current land use maps, Second National Soil Survey (SNSS) map, and fieldwork. The aerial photographs, 1:50,000 for both 1980 and 2006 were obtained from the Department of Surveys and Mapping (DSM). Bulk soil samples were collected at 79 sites across Quzhou district. Samples were collected again at the same locations in 2000 and 2006. To compare the soil data of 2006, 2000 and 1980, latitude and longitude of the sampling locations were recorded using the Global Position System at the time of soil collection. The samples site selection was done on behalf of the Second National Soil Survey. A great change had taken place in land use and land use intensification. The changes, which have converted natural landscapes into the use for human, have made a large proportion of the Quhzou’s landscape change greatly.
1999
Authors: Cui Xiang Zhong, Ming He Huang
Abstract: A scientific analysis on the geographical environments and regional geological tectonic features of some notable earthquakes over the world revealed the root cause of tectonic earthquakes—that is, a tectonic earthquake is generally caused by underground water erosion instead of inter-continental plate collision. According to this new law, it’s easy to explain many past great earthquakes around the world, and also easy to predict some future possible earthquake foci by observing landforms, that is, great earthquakes occur easily in coastal areas, or areas retaining large amounts of water, but not in areas lacking water. So these research results are important to economically protecting against earthquakes and reducing disasters. Especially, according to this new explanation, many digital seismograph networks in the world can be improved. Through on-the-spot investigation or observing topographic maps, one can find that Xi’an urban area and some of its surrounding areas lack underground water, and the possibility of devastating earthquakes occurring in these areas is vey low. Hence the observation on these areas can be lessened. But some areas such as Weihe down-faulted basin near Huaxian and Huayin is seismic risk area, the observation on these areas should be enhanced.
2003
Authors: Si Cheng, Yun Sheng Wang, Ming Liang
Abstract: Geohazards occur in south west mountain area of China each year frequently. Therefore, selecting a typical region to establish a geohazard early warning system and to research the mechanisms of geohazard can greatly improve the ability of geohazard prevention in that mountain area, and then a geohazard early warning system is established at Huaying Mountain region. This article not only presents the construction of that system, but also elaborately analyses mechanism of some geohazards in that mountain region.
2009
Authors: Dong Tao Li, Jing Long Yan, Le Zhang
Abstract: Introduced the theory of S-transform, designed simulation experiment and the frequency components distribution versus time was, verified that the S-transformation method is suitable for blasting vibration signal time-frequency analyzed. Applied it to the time-frequency analysis of measured blasting vibration signals at situ, the results show that S-transform has excellent time-frequency representation ability and higher resolution, reveals the detail information of blasting vibration wave changing with time and frequency, and provides a new way for blasting vibration research. Determined the desired delay intervals through comparing the energy of signal and the time duration of the waveform at characteristic frequency between two-hole blasting vibration signals with different delay intervals.
2013

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