Wave propagation in layered media by time domain BEM     

Y. K. Cheung  L. G. Tham  Z. X. Lei 《地震工程与结构动力学》1993,22(3):225-244

A time domain boundary element in a cylindrical co-ordinate system is developed for the analysis of wave propagation in a layered half-space. The field quantities (displacements and tractions) are expressed as products of Fourier series in the circumferential direction and as linear polynomials in the other spatial directions. An integral equation is written for each layer as an independent domain, and these equations are then assembled into a general equation by virtue of compatibility and equilibrium conditions between the interfaces. Examples of three-dimensional wave propagation in the layered half-spaces due to various forms of surface and inner-domain excitations are reported to demonstrate the accuracy and versatility of the method.  相似文献   

Sodar observations of the stable lower atmospheric boundary layer at Barrow,Alaska     

Tak Kee Cheung 《Boundary-Layer Meteorology》1991,57(3):251-274

Events in the stably stratified lower atmospheric boundary layer within the first several hundreds of meters at Barrow, Alaska were recorded from 27 March to 5 April 1990 using an acoustic sounder (sodar), a tethered balloon, radiosondes, and an instrumented meteorological tower. These events include ground-based and low-level inversion layers, gravity waves, breaking waves, and multiple-layer structures. Even though these events are commonly found in a stable boundary layer, it is perhaps surprising to find them in such a slowly changing environment and over a terrain that is essentially devoid of immediate orographic influence.Visiting Scientist at Wave Propagation Laboratory, NOAA/ERL 325 Broadway, Boulder, CO, 80303, U.S.A.  相似文献   

Transient elastodynamic analysis by time domain bem in cylindrical coordinates     

Z. X. Lei  L. G. Tham  Y. K. Cheung 《地震工程与结构动力学》1992,21(12):1071-1089

A time domain boundary element in a cylindrical coordinate system is developed for the analysis of wave propagation in a half space. The integral formulation is based on Graffi's dynamic reciprocal theorem and Stokes' fundamental solutions. The field quantities (displacements and tractions) are expressed as products of Fourier series in the tangential direction and linear polynomials in the other spatial directions. Gaussian integration is used to integrate the non-singular parts of the integral equations, whereas the integration of the singular components, which are either of order 1/r or 1/r², is handled by special numerical schemes. In the time marching aspect, the field quantities are assumed to vary linearly in the temporal direction as well. Examples for wave propagation due to various forms of surface excitations are reported to demonstrate the accuracy of the method.  相似文献   

A semi-analytical boundary element method for scattering of waves in a half space     

Cao Zhi Yuan  Zhu Jian Xiong  Y. K. Cheung 《地震工程与结构动力学》1990,19(7):1073-1082

A boundary element method using finite strip discretization is proposed to investigate the three-dimensional scattering behaviour of waves in a half space. The scatterers examined are an irregular surface and a cavity in a half space. The numerical examples demonstrate the remarkably good accuracy of the results and validate the application of the present method to solve three-dimensional scattering problems.  相似文献   

Infinite layer for the analysis of a single pile     

D. J. Guo  L. G. Tham  Y. K. Cheung 《Computers and Geotechnics》1987,3(4):229-249

This paper proposes a solution for single pile embedded in layered soil. The soil is divided into a number of infinite layers and the displacement shape functions of the layer are given as a product of piecewise polynomial expansion along the depth and series expansions in radial as well as tangential directions. The pile is divided into a number of solid bar elements along its length and it deforms as a rigid section in the horizontal plane. The interaction between the two components can be treated in the standard manner. Typical examples of a single pile are presented to demonstrate the versatility and accuracy of the method.  相似文献   

Approximate frequency analysis of shear wall frame structures     

Y. K. Cheung  C. Kasemset 《地震工程与结构动力学》1978,6(2):221-229

The finite strip method is used to determine the natural frequencies of shear wall frame buildings. The structure can be modelled in two different ways. In the first approach both the shear walls and the frames are idealized simply as an assemblage of finite strips of varying thicknesses with given or computed properties, while in the second approach the shear walls are still idealized as a series of finite strips, but the frames are regarded as a number of long columns which are interconnected with each other or with finite strips through the horizontal beams. Numerical results obtained from both models indicate good agreement with finite element solutions. The proposed models can be applied to a wide range of shear wall frame assemblies and are therefore more versatile than most existing models.  相似文献   

The gabbroic rocks of the Peninsular ranges batholith, Southern California: cumulate rocks associated with calc-alkalic basalts and andesites     

T.E. Smith  C.H. Huang  M.J. Walawender  P. Cheung  C. Wheeler 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

Gabbroic rocks occur only in the west, and are the oldest intrusions in the Peninsular Ranges Cordilleran batholith. They comprise an olivine-pyroxene gabbronorite series and an amphibole gabbro series both of which contain abundant plagioclase and amphibole. They formed by crystal accumulation and in situ differentiation, in multiple intrusive complexes, and are not considered to be related by fractionation to the granitoid rocks of the batholith.Pure mineral separates of plagioclase, olivine, clinopyroxene, orthopyroxene, and amphibole were obtained by magnetic and heavy-liquid methods from a representative suite of gabbroic rocks. Their major- and trace-element contents were determined by X-ray fluorescence, and the data used to test hypotheses on the genesis and fractionation of the gabbros.The plagioclases range from An₉₈ to An₆₅ in composition, olivines, Fo₇₉ to Fo₇₀, occur in rocks where An>₃₆. All clinopyroxenes are augite with Mg #'s varying from 81.1 to 64.7. Orthopyroxene occurs where An<₉₂, and is generally inverted pigeonite or bronzite, and has Mg #'s ranging from 77.9 to 52.1. The amphiboles include tschermakite, tschermakitic hornblende, pargasite, pargasitic hornblende, ferroan pargasite, magnesio-hornblende, and magnesio-taramite, Mg #'s range from 80.4 to 62.5. Systematic chemical and mineralogical changes confirm that differentiation, controlled by mineral assemblages of plagioclase, olivine, spinel, and clinopyroxene initially, and orthopyroxene, amphibole, and magnetite later, took place between intrusive episodes and in situ.The highly clacic plagioclase coexisting with olivine and amphibole suggests that the gabbros were formed from hydrous mafic magmas. The modal mineralogy of the gabbros, and the chemistry of the minerals is very similar to that of the cumulate blocks of the Lesser Antillean volcanoes. These features confirm that the gabbros were derived from a hydrous mafic magma, with high Al₂O₃ and low TiO₂ contents, typical of orogenic environments.Cumulate minerals from the gabbros show little or no zoning and are considered to have formed in equilibrium with the evolving melts. Selected trace-element contents and distribution coefficients are used to calculate the compositions of the melts. The calculations show that the melts in equilibrium with the olivine-pyroxene gabbronorite series contain approximately 100–200 ppm Ba, 200–400 ppm Sr, 30-10 ppm Ni, 20-10 ppm Co, and 300-100 ppm V. K/Rb ratios of the melts, derived from post-cumulus and prismatic amphiboles, are generally in the range 550-250. These values are typical of calc-alkalic basalts and andesites, and it is suggested that they may have erupted at the surface to form a coeval calc-alkalic volcanic sequence.  相似文献   

Frequency analysis of rectangular plates continuous in one or two directions     

C. I. Wu  Y. K. Cheung 《地震工程与结构动力学》1974,3(1):1-14

The finite strip method is extended to the free vibration of rectangular plates continuous in one or two directions. A subroutine has been written for the computation of beam functions for continuous beams over any number of intermediate rigid supports and with simply supported or clamped end conditions. The standard finite strip method can thus be applied to plates continuous in both directions using the computed beam functions. The frequencies of 2 × 2 and 3 × 3 continuous panels with many different end conditions have been computed. The computations are also checked against published solutions and the accuracy is shown to be excellent.  相似文献   

Burrowing responses of the short-neck clam Ruditapes philippinarum to sediment contaminants     

P. K. S. Shin  A. W. M. Ng  R. Y. H. Cheung 《Marine pollution bulletin》2002,45(1-12)

The burrowing responses of a common tropical bivalve, the short-neck clam Ruditapes philippinarum, to cadmium (Cd)-spiked sediment, variations of sediment grain size and natural sediments collected from 15 locations in Hong Kong's inshore waters were investigated through a series of laboratory tests. Results showed that the burrowing response exhibited a negative relationship with an increase in Cd concentration in the spiked sediments. The level of Cd was also found to be directly proportional to the percent mortality of the clam. However, there was no significant difference (p>0.05) in the time elapsed for the clam to burrow into sediments with different grain size composition. The elapsed time for 50% of the test clams to burrow into the sediment (ET₅₀) over a period of 48 h was calculated for the sediment samples collected from the 15 locations. Results of ANOVA showed significant difference (p<0.05) among the sediment samples. Tukey's multiple comparison test revealed two groups of sediments: group 1 containing 3 sediment samples collected from Victoria Harbour and group 2 containing 12 samples obtained from other coastal areas of Hong Kong. The ET₅₀ value for group 1 sediments was found to be greater than 2880 min whilst the ET₅₀ for group 2 sediments had a mean of 173.9 min. Agglomerative classification of the sediment samples, based on metal content (As, Cd, Cr, Cu, Ni, Pb, Zn), also showed two similar groups, suggesting that the ET₅₀ values were correlated with the metal level of the sediment samples. Group 1 sediments collected from Victoria Harbour had greater concentrations of Cd, Cr, Cu, Ni and Zn as compared to that in group 2. The present study demonstrated that high metal content in the sediment tends to inhibit the burrowing responses of the clam and that there is potential to develop the burrowing responses of R. philippinarum as a sublethal sediment toxicity test.  相似文献   

The problem of the future in postwar Anglo-American political philosophy     

Katrina Forrester 《Climatic change》2018,151(1):55-66

Among the conceptual problems raised by climate change is that of how to think about the future. Theories of intergenerational justice and other accounts of obligations to the future in Anglo-American philosophy tend to argue that the remote future matters morally. Where did these arguments come from? This essay explores the roots of contemporary ideas about the remote future in debates that took place among Anglophone philosophers in the 1970s.  相似文献