Stability of Rayleigh-Benard convection rolls and bimodal flow at moderate Prandtl number     

John A. Whitehead Jr.  Gerald L. Chan   《Dynamics of Atmospheres and Oceans》1976,1(1):33-49

Experimental observations of cellular convection between two rigid, horizontal, conducting boundaries are reported for two different cases. First, the stability of two-dimensional roll convection of various wavenumbers and Rayleigh numbers is investigated in fluids of Prandtl numbers 16 and 2.7. The results qualitatively agree with earlier observations by Busse and Whitehead of fluid with Prandtl number 126 but they differ somewhat quantitatively. Second, the stability of the bimodal flow, consisting of two rolls of differing and perpendicular wavenumber, is observed to be stable for given bandwidths and ranges of Rayleigh numbers when the configuration of the bimodal flow, consisting of two sets of rolls at right angles, is flawless — without any disruptions in the periodic matrix. The stability range differs from earlier experiments and from our own experiments in which the bimodal planform is uncontrolled.  相似文献   

Approach to complete limit equilibrium analysis for rock wedges — the method of “artificial supports”     

H. C. Chan  H. H. Einstein 《Rock Mechanics and Rock Engineering》1981,14(2):59-86

SummaryApproach to Complete Limit Equilibrium Analysis for Rock Wedges — The Method of Artificial Supports Since the movement of rock wedges or blocks is the primary phenomenon in rock mass failure, it is convenient to use limit equilibrium approaches for stability analysis. In spite of their wide use, limit equilibrium analysis is often restricted due to: 1) the usual procedural simplifications (regarding geometry, force application, failure modes), and 2) basic deficiencies of the limit equilibrium approach (the fundamentally indeterminate rigid body problem requires assumptions regarding the force reactions). The method of artificial supports intends to circumvent or reduce many of these restrictions. In particular, the problem of unknown force distribution on the supporting plane is reduced by specifically considering and optimizing a variety of reactions on these planes. All sliding modes of failure — i. e., translational, free and restrained rotational sliding — can be correctly modelled. Particularly significant is the result that the usual assumption oftranslational sliding can be incorrect andunsafe, if forces other than the weight are significant. The methodologies employed in the artificial support model can be extended to all modes of failure, i. e., lifting off and toppling in addition to the previously mentioned sliding modes; this is demonstrated with a procedure for a complete stability analysis for a 2-joint wedge.

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ZusammenfassungEin Weg zur vollständigen Gleichgewichtsberechnung für Felskörper — Die Methode der Künstlichen Auflager Da die Bewegung von Einzelblöcken das primäre Phänomen bei Felsstürzen ist, eignen sich Grenzgleichgewichtsbetrachtungen besonders gut für Stabilitätsuntersuchungen. Vor allem wegen der üblichen Vereinfachungen (Geometrie, Kräfteansätze, Versagensmechanismen) und grundlegender Unzulänglichkeiten (das grundsätzlich statisch unbestimmte Starrkörperproblem erfordert Annahmen bezüglich der Auflagerkräfte) sind solche Grenzgleichgewichtsbetrachtungen oft nur beschränkt anwendbar, obwohl sie häufig angewendet werden. Es wird versucht, mit der Methode der künstlichen Auflager viele dieser Einschränkungen zu umgehen. Vor allem wird das Problem der unbekannten Spannungsverteilung in den Auflageflächen dadurch reduziert, daß mögliche Kombinationen solcher Reaktionen in die Rechnung einbezogen und optimiert werden. Alle Gleitbewegungen, seien es Translationen oder freie bzw. beschränkte Rotationen auf den Auflageflächen, können korrekt behandelt werden. Besondere Bedeutung kommt aber der Tatsache zu, daß die übliche Annahme einer translatorischen Gleitung falsch ist bzw. daß man damit auf der unsicheren Seite liegt, wenn außer dem Eigengewicht noch andere Kräfte einwirken.Die Überlegungen, die der Modellvorstellung der künstlichen Auflager zugrunde gelegt wurden, können auf alle Instabilitätsfälle ausgedehnt werden, also auch auf Abheben und Kippen zusätzlich zu den vorhin genannten Gleitbewegungen; dies wird am Beispiel einer Rechenprozedur für eine vollständige Stabilitätsuntersuchung eines Gleitkeils gezeigt.

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RésuméTentative visant à compléter l'analyse par équilibre limite — la méthode des supports artificiels Le fait que le déplacement de blocs est le principal phénomène d'instabilité en massif rocheux suggère l'utilisation de méthodes d'équilibre limite à l'étude de sa stabilité. Bien qu'elles soient fréquemment utilisées, les analyses par équilibre limite sont souvent restreintes par suite 1) de simplifications opérationnelles (concernant la géométrie, les forces et les modes d'instabilité), et 2) des insuffisances fondamentales de cette approche (le problème des corps indéformables est en essence statiquement indéterminé et réclame en conséquence l'adoption d'hypothèses sur la teneur des réactions).L'intention de la méthode des supports artificiels est de réduire ou éviter plusieures de ces restrictions. En particulier le problème de la distribution inconnue des forces sur le plan d'assise est résolu en considérant et optimisant un certain nombre de réactions entre corps rigide et le plan de base. Tous les modes d'instabilité au glissement — à savoir translation, rotation restreinte et rotation libre — peuvent être correctement représentés. Spécialement digne d'intérêt est à cet égard le résultat concernant l'habituelle hypothèse de glissement en translation, puisque celui-ci peut s'avérer incorrect et exhiber des facteurs de sécurité supérieurs, par rapport à un glissement en rotation, lorsque des forces autres que le poids sont à considérer.La méthodologie servant de base à la méthode des supports artificiels peut être étendue à tous modes d'instabilité, à savoir: le soulèvement et le renversement venant compléter ceux précités; ceci est illustré par le développement d'une procédure d'analyse complète d'un bloc monolithique découpé par deux fissures.

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With 13 Figures  相似文献   

Non-conservative behavior of barium during mixing of Mississippi River and Gulf of Mexico waters     

Jeffrey S. Hanor  Lui-Heung Chan 《Earth and Planetary Science Letters》1977,37(2):242-250

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Desorption of Ba and²²⁶Ra from river-borne sediments in the Hudson estuary     

Yuan-Hui Li  Lui-Heung Chan 《Earth and Planetary Science Letters》1979,43(3):343-350

The pronounced desorption of Ba and²²⁶Ra from river-borne sediments in the Hudson estuary can be explained quantitatively by the drastic decrease in the distribution coefficients of both elements from a fresh to a salty water medium. The desorption in estuaries can augment, at least, the total global river fluxes of dissolved Ba and²²⁶Ra by one and nine times, respectively. The desorptive flux of²²⁶Ra from estuaries accounts for 17–43% of the total²²⁶Ra flux from coastal sediments. Two mass balance models depicting mixing and adsorption-desorption processes in estuaries are discussed.  相似文献   

Metal contents of the two marine algae found on iron ore tailings     

M.H. Wong  K.Y. Chan  S.H. Kwan  C.F. Mo 《Marine pollution bulletin》1979,10(2):56-59

The two marine algae, Chaetomorpha brychagona and Enteromorpha crinita are found abundantly on the iron ore tailings of Tolo Harbour, Hong Kong, with a rather high level of various metals. Tissue analysis of the algae revealed that the contents of heavy metals (Fe, Mn, Pb and Zn) were higher than in the population collected from the two uncontaminated sites far away from the tailings. It was suggested that the algae were able to adapt to such a harsh environment with a comparatively high level of trace elements and the lack of basic nutrients. However, further studies are needed before any conclusion can be drawn. The delicate situation of the land-locked sea, Tolo Harbour, where the tailings and future heavy industrial site are situated, should not be overlooked.  相似文献   

Trace metals in Hong Kong waters     

J.P. Chan  M.T. Cheung  F.P. Li 《Marine pollution bulletin》1974,5(11):171-174

Hong Kong has a population of between four and five million and is becoming increasingly industrialized. Already there are some 19,000 factories concentrated in a few densely populated areas and most of the effluent and sewage is discharged untreated into the sea. Elevated heavy metal concentrations have been recorded in the receiving waters. Lead has 160 times and cadmium 180 times the concentration found in the open ocean.  相似文献   

Geological and morphological study of the Jiufengershan landslide triggered by the Chi-Chi Taiwan earthquake   总被引：2，自引：4，他引：2  

Kuo-Jen Chang  Alfredo Taboada  Yu-Chang Chan 《Geomorphology》2005,71(3-4):293-309

The Jiufengershan rock and soil avalanche is one of the largest landslides triggered by the Chi-Chi earthquake Taiwan 1999. The landslide destabilized the western limb of the Taanshan syncline along a weak stratigraphic layer. It involved a flatiron remnant, which was almost entirely mobilized during the earthquake. The avalanche was slowed down by NS trending ridges located downstream along the Jiutsaihu creek. The landslide affected a 60 m thick and 1.5 km long sedimentary pile composed of shales and sandstones, which dip 22°SE toward a transverse valley. The triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field. A high-resolution airborne Light Detection and Ranging (LiDAR) image taken 2.5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation. The sliding surface shows several deformation structures such as fault scarps and folds. These structures are interpreted in terms of basal shear stresses created during the avalanche. Three major joint sets were identified at the sliding surface. The isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake. The coseismic volume of mobilized material and landslide deposit data are 42 × 10⁶ m³ and 50 × 10⁶ m³, respectively. The geometry of the landslide accumulation in the field has an irregular star shape. The morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges.  相似文献   

CONCENTRATIONS OF Cd, Cu AND Zn IN SEDIMENTS COLLECTED FROM URBAN LAKES AT KELANA JAYA, PENINSULAR MALAYSIA     

Ahmad Ismail　Chee Kong YAP　Fong Fei Chan 《湿地科学》2004,2(4):248-258