Quantcast Hydrodynamic added mass.

 
  
 
ETL 1110-2-563
30 Sep 04
(d) The distribution for the mass of a barge train can be determined using existing traffic information
from OMNI or WBC. From data collected at various lock projects, the distribution for barge train mass is
generally dominated by single- or double-humped (camel-backed) distributions. The reason for this is that
at least one or two typical barge train configurations (e.g., 6 or 15 barges) exist in several navigation
systems. This distribution should also account for any anticipated future traffic changes. Generally, the
distribution for mass is the easiest one to determine.
(3) Hydrodynamic added mass.
(a) Forces due to the momentum of the water associated with the moving barge train are typically
included when developing impact forces. This phenomenon is known as hydrodynamic added mass and
would normally be considered in the transverse, longitudinal, and rotational directions. Equations to cal-
culate the added mass are based on traditional ship design techniques. Generally, the added mass for
barge trains has been assigned 40 percent in the longitudinal, 5 percent in the transverse, and 40 percent in
the rotational directions.
(b) It is important to recognize that the effect of hydrodynamic added mass is included in the mea-
sured force data used to develop the empirical relationship discussed in paragraph B-2. Therefore, the
mass term in the empirical correlation used in this ETL should include only the mass of the barge train.
(4) Drag and cushioning effects on barge trains. The drag force is the resisting force of water to the
momentum of the barge train, and it can be applied as a damping coefficient or percent damping in an
MDOF analysis. The drag force on a barge train is not significant in comparison to the magnitude of the
impact force. Cushioning forces between the barges and walls are usually not included, but may be
significant for broadside impacts. The effects of drag and cushioning forces were included in the
measured force data used to develop the empirical relationship discussed in paragraph B-2. Further
consideration of these forces is not necessary in the empirical model.
(5) Velocity components normal and parallel to the wall.
(a) Velocities for barge trains can be estimated using field and/or laboratory methods. Two com-
ponents of barge velocity (forward V0x and lateral V0y) should be determined for barge impact analysis.
These components are shown in Figure B-5. These components of the barge motion are combined to form
components normal and parallel to the rigid wall. Typically, the normal component is important since it
usually contributes to the primary force used for the wall design. The parallel component will be
important to structures that use end support piers to handle the shear load and for operating conditions
that cause a broadside impact of the barges against the lock wall.
(b) For flood events, the upper limit for velocities of barge trains approaching a lock can be based on
the velocities of the currents, the local flow regimes, or results from navigation models. During a major
flood event, navigation ceases for safety, which should be considered when selecting appropriate veloci-
ties for design. Outdraft or currents near open or ported approach walls should also be considered in
selecting velocities that are used for the impact analysis. For usual events, the maximum barge train
velocities can be estimated using average daily flow velocities of the currents adjusted for the ability of
the operator to control the barge train. For unusual events, the maximum velocity may be estimated using
daily flow velocities of the currents adjusted for local conditions, such as an outdraft, that challenge the
ability of the operator to control the barge train. For extreme events, the maximum velocity may be
estimated using flow velocities for river conditions approaching major flood stages that challenge the
ability of the operator to control the barge train.
B-9


 


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