ISSN:0022-1686    

DOI:10.1080/00221689009499016

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Existing ice jam theories, which consider the static equilibrium of a floating ice mass in a river, can predict ice jam profiles. These theories, however, cannot be used to describe the transport of river ice and the process of ice jam initiation. In this paper, a theoretical model for the dynamic transport of river ice is formulated. The model can be used to describe the initiation and evolution of ice jams. A one-dimensional numerical scheme is developed for solving the governing equations. A set of numerical examples are presented to illustrate the application of the model and factors that affect the ice jam formation. The analysis shows that ice jams usually occur as a result of ice mass convergence.

ISSN:0022-1686    

DOI:10.1080/00221689009499017

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Described herein are results of a laboratory study aimed at investigating the proposition that wall (or bank) resistance may initiate jamming of comparatively small ice pieces conveyed in prismatic channels. Ice-jam literature suggests that jams are initiated only by obstructions, such as channel constrictions, bridge piers or single-layer-thick assemblages of large ice pieces spanning a congested section of channel. The experiments show that wall resistance can initiate jamming, though the lengths of wall, or channel, required to do so are relatively long. In rivers, jams are more readily initiated by channel obstructions such as constricted bridge crossings, sand bars, etc.

ISSN:0022-1686    

DOI:10.1080/00221689009499018

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper reports on the processes governing the transfer of solar radiation energy to river-ice covers, the effects of snow-cover properties on transmittance and reflectance and the nature of shortwave radiation absorption in ice leading to intergranular melt. The influence of this melt on ice strength is illustrated using previously obtained borehole jack indentation data and concomitant determinations of porosity. The indentation data are analyzed using a plastic yield approach to estimate the uniaxial compression strength for ice idealized as a Tresca material. The analysis reveals that the ultimate platen-indentation-pressure to uniaxial-compressive-strength ratio is approximately 5.7; agreeing closely with available borehole jack and uniaxial compression data for columnar grained ice at 0°C. Available data describing the strength reductions associated with intergranular melt are reviewed. They show good correspondence with those resulting from existing theoretical strength-porosity models. The utility of the borehole jack for field-portable mechanical testing of ice strength is illustrated with respect to sampling in highly variable decaying ice covers. Further research should address the mechanisms of intergrannular melt, in particular, the specific geometry and distribution of the melt and its effect on the capacity of the ice cover to resist downstream forcing.

ISSN:0022-1686    

DOI:10.1080/00221689009499019

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The paper shows, on the instance of the river Berounka, the approach to the determination of ice jams and flood events and the way of their elimination. The solution is based on analysis of floods and ice phenomena on rivers and on application of new findings about ice processes, especially freeze-up of rivers during ice run. The result of this study is an optimal design for flood control.

ISSN:0022-1686    

DOI:10.1080/00221689009499020

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ice regime of natural rivers is influenced by climate, water regime and channel morphology. Since channel morphology and water regime are influenced by river dams, changes in ice conditions can be expected. Ice appears commonly on the Hungarian rivers uninfluenced by human activities. Ice observations has a long tradition and data on ice are available from several sources. Important basic data from observations between 1875 and 1986 were derived. Characteristic parameters can be established from the time series for particular gaging sections. The time series of Danube stations indicate the modification of the ice regime. A sharp decline in the number of ice-run days and even more dramatic drop in that of ice cover days is observed in the frequency curves due to the effect of the upstream hydropower stations and thermal effluents. On the basis of the experiences of operating river barrages certain rules have been derived for winter operation of the planned river barrages. The changes of ice conditions due to these dams were characterized. Thickness of the ice in the reservoirs, length of period of ice cover, sensitivity for ice jam formation were predicted.

ISSN:0022-1686    

DOI:10.1080/00221689009499021

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ice stoppages and/or ice jams that occur on the upper Niagara River can cause reductions in hydroelectric power generation at the plants operating on the river. A method for monitoring and predicting the potential occurrence of ice stoppages and/or jams on the river was developed. The method was incorporated into a computerized, on-line early warning information system for use by the operators of the generating facilities. The information is used by the operators in making decisions that may help reduce the impacts of the ice.

ISSN:0022-1686    

DOI:10.1080/00221689009499022

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The rotational stability of floating and submerged rectangular blocks is described. The limit of stability is reached when the underturning moment acting on the block is equal to the maximum hydrostatic righting moment. The hydrostatic righting moment is derived and a convenient expression for its maximum is presented in nondimensional form. A moment coefficient is defined that relates the underturning moment at the limit of stability to the moment produced by the product of the dynamic pressure of the flow and the plan area of the block. An exponential function of the ratio of block thickness to flow depth is postulated as a general expression for the moment coefficient. The parameters of this function are related to the block geometry by analyzing the existing experimental data. The limit of rotational stability for rectangular blocks can then be described in terms of a densimetric Froude number based on block thickness.

ISSN:0022-1686    

DOI:10.1080/00221689009499023

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

An experimental investigation of the flow resulting from the continuous breaking of a dam is presented. Based on these experimental results, a coherent and consistent picture is built about the flow characteristics associated with the finite removal time. Plausible speculations about the flow behaviour for the small and large removal time limits, where no experimental data could be obtained, are offered. This constitutes a solid theoretical basis for future mathematical models. A practical method for calculating discharge and water depth hydrographs at the dam site is presented, which can be used to predict the propagation of the resulting wave.

ISSN:0022-1686    

DOI:10.1080/00221689009499024

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Current State Of Technology In Hydraulic MachineryEdited by Adrian P. Boldy and Duan Chang Guo Gower Technical, (Gower House, Croft Road, Aldershot, Hampshire GU 11 3HR), England, in association with Science Press, Beijing 1989, 320 pages, 282 figures, 72 tables, 320 references. Price: £ 45.

ISSN:0022-1686    

DOI:10.1080/00221689009499025

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor