9. Physical Modeling
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laboratory by applying a suitable model scale, the results of which could be
extended in the field. The extent of sédimentation in a harbour approach
channel, influences by wave and tides, behaviour of estuaries, bottom stability of breakwaters and other gravity structures, behaviour of shoreline
can be investigated through physical model studies.
9.4 Principles of Similitude
9.4.1 General
The behaviour of a model when subjected to external forces holds a definitive relation with that of a prototype. The model should be designed and
tested in accordance with certain principles called the principles of similarity (or) principles of similitude. The principles not only govern the design,
construction and testing; these principle are applicable to the extrapolate
model results in order to predict prototype response.
9.4.2 Similitude in hydrodynamic problems
The principle of similitude adopted for hydrodynamic problems need to be
treated separately from the conventional similitude. The three major types
of similitude viz. géométrie similitude, kinematic similitude and dynamic
similitude and they are explained in detail as follows. A convention of
using “p” as a subscript for prototype and “m” as a subscript for model is
followed.
9.4.3 Types of similitude
Géométrie similitude
Géométrie similarity signifies that the dimensional similarity from the prototype to the model i.e. similarity of the physical form. When the horizontal and vertical scales are same, the model is said to be undistorted
and when the horizontal and vertical scales not equal the model is said to
be a distorted model. Definitive objectives can be achieved by departing
from géométrie similarity. The major problem areas are confining boundaries of laboratory testing facilities, surface roughness of model, scaling
thickness, depth of water, etc. For example, in case of modeling a stretch
offshore structure deployed at higher depths, a distorted model is preferred
for the study because the horizontal scaling dimension becomes extremeh
insignificant.
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laboratory by applying a suitable model scale, the results of which could be
extended in the field. The extent of sédimentation in a harbour approach
channel, influences by wave and tides, behaviour of estuaries, bottom stability of breakwaters and other gravity structures, behaviour of shoreline
can be investigated through physical model studies.
9.4 Principles of Similitude
9.4.1 General
The behaviour of a model when subjected to external forces holds a definitive relation with that of a prototype. The model should be designed and
tested in accordance with certain principles called the principles of similarity (or) principles of similitude. The principles not only govern the design,
construction and testing; these principle are applicable to the extrapolate
model results in order to predict prototype response.
9.4.2 Similitude in hydrodynamic problems
The principle of similitude adopted for hydrodynamic problems need to be
treated separately from the conventional similitude. The three major types
of similitude viz. géométrie similitude, kinematic similitude and dynamic
similitude and they are explained in detail as follows. A convention of
using “p” as a subscript for prototype and “m” as a subscript for model is
followed.
9.4.3 Types of similitude
Géométrie similitude
Géométrie similarity signifies that the dimensional similarity from the prototype to the model i.e. similarity of the physical form. When the horizontal and vertical scales are same, the model is said to be undistorted
and when the horizontal and vertical scales not equal the model is said to
be a distorted model. Definitive objectives can be achieved by departing
from géométrie similarity. The major problem areas are confining boundaries of laboratory testing facilities, surface roughness of model, scaling
thickness, depth of water, etc. For example, in case of modeling a stretch
offshore structure deployed at higher depths, a distorted model is preferred
for the study because the horizontal scaling dimension becomes extremeh
insignificant.