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Chintu Lai

Publications and source records attributed to Chintu Lai.

7 recordsLinked to original sources
USGS1994

Multicomponent-flow analyses by multimode method of characteristics

For unsteady open-channel flows having N interacting unknown variables, a system of N mutually independent, partial differential equations can be used to describe the flow-field. The system generally belongs to marching-type problems and permits transformation into characteristic equations that are associated with N distinct characteristics directions. Because characteristics can be considered 'wave' or 'disturbance' propagation, a fluvial system so described can be viewed as adequately definable using these N component waves. A numerical algorithm to solve the N families of characteristics can then be introduced for formulation of an N-component flow-simulation model. The multimode method of characteristics (MMOC), a new numerical scheme that has a combined capacity of several specified-time-interval (STI) schemes of the method of characteristics, makes numerical modeling of such N-component riverine flows feasible and attainable. Merging different STI schemes yields different kinds of MMOC schemes, for which two kinds are displayed herein. With the MMOC, each characteristics is dynamically treated by an appropriate numerical mode, which should lead to an effective and suitable global simulation, covering various types of unsteady flow. The scheme is always linearly stable and its numerical accuracy can be systematically analyzed. By increasing the N value, one can develop a progressively sophisticated model that addresses increasingly complex river-mechanics problems.

Journal of Hydraulic Engineering↗
USGS1990

Computational open-channel hydraulics for movable-bed problems

As a major branch of computational hydraulics, notable advances have been made in numerical modeling of unsteady open-channel flow since the beginning of the computer age. According to the broader definition and scope of 'computational hydraulics,' the basic concepts and technology of modeling unsteady open-channel flow have been systematically studied previously. As a natural extension, computational open-channel hydraulics for movable-bed problems are addressed in this paper. The introduction of the multimode method of characteristics (MMOC) has made the modeling of this class of unsteady flows both practical and effective. New modeling techniques are developed, thereby shedding light on several aspects of computational hydraulics. Some special features of movable-bed channel-flow simulation are discussed here in the same order as given by the author in the fixed-bed case.

Conference Paper↗
USGS1988

Comprehensive method of characteristics models for flow simulation

The use of the specified time interval (STI) numerical schemes has been popular in applying the method of characteristics (MOC) to unsteady open‐channel flow problems. Studies and analyses of several variants of the STI schemes have led to the derivation of a new scheme, referred to herein as the multimode scheme, which combines implicit, temporal reachback, spatial reachback, and classical schemes into one. Three numerical models have been developed to implement the implicit and multimode schemes. The IMOCDS model uses an implicit scheme, with which the time step is no longer subject to the Courant constraint. The remaining two models, NEWMOC and SPRMOC, are two versions of the multimode scheme. The NEWMOC and SPRMOC models demonstrate all the advantages previously provided by individual STI schemes, cover the combined flow range of the various schemes involved, and, in addition, display newly acquired benefits such as robustness. Numerical analyses, numerical experiments, and field applications that verify, support, and demonstrate the enhanced model capabilities are presented.

Journal of Hydraulic Engineering↗
USGS1987

NONHOMOGENEOUS TERMS IN THE UNSTEADY FLOW EQUATIONS: MODELING ASPECTS.

A study is in progress to identify the relative significance, effects, and benefits attributable to the use of one-dimensional, unsteady, open-channel, flow-simulation models employing a variety of nonhomogeneous terms in their equation formulations. Nonhomogeneous terms being analyzed include those representing bed slope, frictional resistance, nonprismatic channel geometry, lateral flow, and (surface) wind stress. After an initial theoretical discussion, the results of a set of numerical experiments are presented that demonstrate cause-and-effect relationships and intercomparisons achieved by neglect or improper treatment of important nonhomogeneous terms. Preliminary results of this study are discussed and presented in this paper, both in the form of qualitative considerations and quantitative tabular findings. These results are expected to yield a definitive set of guidelines and suggestions useful to model engineers.

Conference Paper↗
USGS1976

Computation of unsteady flows in rivers and estuaries by the method of characteristics

This report is a program documentation to the latest revision (1975) of the unsteady open-channel flow simulation model by the method of characteristics, Version 13 in the program series, which employs a multiple-reach scheme treating each subreach as a prismatic shape. A long waterway of variable cross section, properties and coefficients may be divided into a number of subreaches, each being considered uniform in geometry and in other factors. The basic method of characteristics using specified time intervals is applied to each subreach, and additional boundary conditions are imposed at the junctions between subreaches. For the user's convenience, the program incorporates several types of options covering input, accuracy, boundary conditions, data formats, output, and continuation. The program accepts input data in three forms. data cards only, cards and user-supplied subroutines, and cards and disk stage data. Boundary values are either stage or velocity and are given either in numerical data or equation form. The user may employ or bypass the extrapolation procedures by weighing the trade-off between accuracy and computer time. By eight output options provided in the program he can also tailor the outputs to suit his need and convenience.

Report↗