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On the distribution of crest to trough wave heights 总被引：1，自引：0，他引：1
Arvid Naess 《Ocean Engineering》1985,12(3):221-234
In the present paper we derive the probability distribution function of crest to trough wave heights in a narrow-band, Gaussian stochastic process. It is shown that the distribution function is a one-parameter Rayleigh distribution where the parameter is expressed in terms of the correlation function of the given process. Comparison based on correlation values obtained via sea wave spectra indicate that the derived distribution function agrees well with observed data. 相似文献
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The existence of detachment surfaces or décollement zones beneath folded rocks of the Valley and Ridge and Plateau provinces of the Appalachians has been recognized as an important condition of folding. Large folds at the border between the two provinces resulted primarily from repetition of strata by thrusting of blocks over ramp faults that connect detachement surfaces at different horizons. Some investigators have suggested that folds in the Plateau province of Pennsylvania were produced by splay faults arising from detachment surfaces, but field observations and theoretical analyses by Sherwin and by Wiltschko & Chapple suggest that the folds are a result of buckling of multilayered rocks above a décollement. An exception may be the Burning Springs anticline in West Virginia, which appears to have formed at the termination of a detachment surface.Investigation of the translation of an homogenous, viscous material above a flat detachment surface that terminates laterally indicates that the termination produces a broad, low-amplitude anticline in passive layering as a result of thickening induced by a gradient of shear stresses in the vertical direction. This thickening above the termination of a detachment is a mechanism of folding. If the viscous fluid contained mechanical layering, the fold would become amplified by buckling. Computations of stresses in the material indicate that minor faults should be generated first near the termination of the flat detachment surface. The Burning Springs anticline probably was initiated by termination of a detachment surface and subsequently amplified by buckling. 相似文献
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The shapes of sills and laccolithic intrusions and associated host rock deformation were studied at several locations on the flanks of the Henry Mountains. Diorite sills range from 0.5 to 10 m in thickness, are less than 1 km2 in areal extent, and have blunt terminations. The laccolithic intrusions range from 10 to 200 m in thickness, and from 1 to 3 km2 in areal extent. The host rock, principally sandstone and shale, is deformed along closely spaced cataclastic shear planes. This deformation is concentrated at contacts, especially near sill terminations and over laccolith peripheries. The diorite contains plagioclase phenocrysts which are usually sheared in a thin zone adjacent to each contact. Field observations suggest that sills are the forerunners of laccolithic intrusions which form only after magma has spread far enough laterally (greater than about 1 km2 in the Henry Mountains) to gain leverage to bend the overburden upward. Further injection of magma results in laccolithic peripheries or terminations with one of three distinct cross-sectional forms: (1) blunt termination of the diorite accompanied by bending and minor faulting of the host rock; (2) termination at a peripheral diorite dike cutting upward across the host rock; or (3) abrupt termination of the diorite against a nearly vertical fault zone.In order to study some of the processes of sill and laccolith intrusion, mechanical models for the driving pressure, physical properties, and flow behavior of the diorite magma are derived and discussed. A static driving pressure (equal to the difference between total magma pressure and lithostatic pressure) of up to 700 bar is estimated. The rheological behavior of the magma in the Henry Mountains is unknown. However, flow behavior is calculated assuming three of the more common models for fluids: Newtonian viscous, pseudoplastic, and Bingham. Suspended crystals probably contributed to the finite strength of the magma (estimated to be at least 103 dyn/cm2 for the Henry Mountains magma) which enables it to support dense zenoliths and also fixes maximum limits on the lengths of sills or dikes. Pressure in magma flowing along tabular intrusions of uniform thickness drops linearly in the flow direction for all three rheological materials. Thickening of tabular intrusions tends to make the pressure drop less rapidly, but pressure drops more rapidly in the tapered region near a termination. Pressure distributions under these and other conditions are derived in order to use them in the models of host rock deformation presented in Part II. 相似文献
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John L. Rich introduced the revolutionary concept that many folds in the Appalachian Mountains can be explained as superficial structures formed by passive translation of thrust blocks over ramps in detachment surfaces. The amount of layer-parallel shortening can be negligible in the formation of these folds. Rich primarily was concerned with an explanation for the Powell Valley anticline, in the southern Appalachians, but the essential kinematic features of his model of folding have been verified in other folds in the Appalachians, in the Canadian Rockies, in the Idaho-Wyoming thrust belt, and in the Pyrenees. In this paper we solve the boundary-value problem for an idealized thrust block moving over a detachment surface and ramp with zero drag, and produce theoretical fold forms in the thrust block that closely resemble those in Rich's idealized model. The anticline is narrow and rounded if the translation is small, and broad and flat-topped if the translation is large. The limbs of the anticline are symmetric. We also incorporate drag along the ramp part of the detachment surface in order to derive a possible explanation for the asymmetry of dips of the two limbs of the Powell Valley anticline. We show that drag can explain the asymmetry, particularly if drag between relatively competent rocks in opposition at the ramp caused an initial anticline to form as the thrust block began to move, and then drag reduced markedly as relatively soft shales at the base of the block were thrust over competent rocks in the ramp. The existence of the initial anticline should be reflected in asymmetry of the two limbs and in a bulge at the distal edge of the broad anticline. 相似文献
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All stages in the development of a duplex structure—from isolated, stepped fault segments, to segments joined by a single ramp, to segments joined by tens of ramps—are preserved along strike-slip and normal faults in Entrada Sandstone in Arches National Park, Utah. Bedding is either absent or at a high angle to the duplex-like structures in Entrada Sandstone, thus it had no significant role in constraining their geometry.We can reproduce the essential features of a duplex structure along a normal fault with mechanical and kinematic models previously used to simulate duplex structures along thrust faults. However the models do not account for the amount of observed thickening at the step where the structure forms. This suggests that the geometry of duplex-like structures along these strike-slip faults may be a result of interaction between the fault segments. 相似文献
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The paper describes a method for the prediction of extreme response statistics of floating offshore structures subjected to random seas by Monte Carlo simulation. The particular case of the horizontal surge motions of a tension leg platform is considered, taking into account both the first order, wave frequency and the second order, slow-drift motions. The advantage of the Monte Carlo method is its simplicity and versatility, which allows us to account for the effect of time-variant wave-drift damping, as well as nonlinear mooring characteristics without noticeable increase in the computational complexity. It is demonstrated in this paper that the commonly assumed obstacle against using the Monte Carlo method for estimating extreme responses, i.e. excessive CPU time, can be circumvented, bringing the computation time down to quite acceptable levels. 相似文献
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The paper describes a novel approach to the problem of estimating the extreme response statistics of a drag-dominated offshore structure exhibiting a pronounced dynamic behaviour when subjected to harsh weather conditions. It is shown that the key quantity for extreme response prediction is the mean upcrossing rate function, which can be simply extracted from simulated response time histories. A commonly adopted practice for obtaining adequate extremes for design purposes requires the execution of 20 or more 3-h time domain analyses for several extreme sea states. For early phase considerations, it would be convenient if extremes of a reasonable accuracy could be obtained based on shorter and fewer simulations. The aim of the work reported in the present paper has therefore been to develop specific methods which make it possible to extract the necessary information about the extreme response from relatively short time histories.The method proposed in this paper opens up the possibility to predict simply and efficiently both short-term and long-term extreme response statistics. The results presented are based on extensive simulation results for the Kvitebjørn jacket structure, in operation on the Norwegian Continental Shelf. Specifically, deck response time histories for different sea states simulated from an MDOF model were used as the basis for our analyses. 相似文献
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Arvid Naess 《Ocean Engineering》1983,10(5):313-324
A general method for investigating the extreme values of certain types of stochastic processes is described through the study of Morison-type wave loading on piles. By using this method, previously published results concerning the level upcrossing frequency of the Morison-type loading function are rederived. Further, the expected largest value of the loading function during a given time interval has been calculated. 相似文献