collection are shown on Figure 1.
equations, which are applicable to
pool lowering. Project personnel
The pressure cells provided tempo-
the conduits within the system; with
want the option of using the lock's
ral variations of the water surface in
the free-surface equations describing
filling and emptying system during
the upper and lower approaches, in
the approach reservoirs, valve wells,
emergencies which require rapid
the lock chamber, and in the valve
and lock chamber. The model com-
pool lowering. Guidelines and opera-
wells. The pressure cells also mea-
putes pressures and flow distribu-
tion procedures are needed to pro-
sured the soffit pressure down-
tions throughout a lock system. Dis-
vide lock operators instruction for
stream of the valves during lock
charge and piezometric head in the
lock valve operation during an emer-
operations.
lock system components are com-
gency. An earlier hydraulic model
puted by numerically solving partial
study (Ables 1979) found that low
differential equations for
pressures exist in the lock culvert
Model Parameters and
one-dimensional unsteady flow. The
during the unsteady flow of lock
relationships between discharge and
operations, which might induce cavi-
Loss Coefficients
piezometric head difference for
tation in the culvert system. The
valves and culvert losses are
objective of the present study is to
described by algebraic energy equa-
compute a head-discharge relation
The contraction coefficient is a
tions. The position of a valve is pre-
for the culvert system and to
parameter used to calculate the
scribed as a function of simulation
develop a safe operation procedure
piezometric head at the culvert soffit
time. Functions are also used for
that avoids excessively low pres-
immediately downstream of the filling
manifold components, which simu-
sures and that swiftly reaches
and emptying valves and the cavita-
late combining and dividing flow, to
steady state. First, a numerical
tion index for the low-pressure
describe the variation of the branch
model of the filling and emptying
region downstream of the valves.
head loss coefficients with the ratios
system was constructed. The numer-
Published data quantifying the con-
of the individual branch discharges
ical model provided information for
traction coefficient for reverse tainter
to the combined discharge. Available
simulations of different head and
valves shows considerable scatter
time-varying numerical results
tailwater conditions. The computed
(Engineer Manual 1110-2-1610). The
include pressure, hydraulic grade
discharge and pressures were vali-
coefficient of contraction for the
line elevation, and discharge at all
dated with prototype data. Informa-
reverse tainter valves was specified
computational points. The stage,
tion needed for numerical model val-
as a fourth-order polynomial function
velocity, depth, top width, and chan-
idation were the temporal variations
in terms of the relative valve open-
nel area are provided at each com-
of the upper and lower pool, the lock
ing. This function is a best fit of the
putational point within the
chamber water surface, the gate
prototype data presented in
free-surface components and the
position, and the lock culvert pres-
EM 1110-2-1610 "Hydraulic Design
velocity, shear stress, and vapor
sures downstream of the filling and
of Lock Culvert Valves" (Schohl
cavity volume are given for each
emptying valves. The validated
1999). The contraction coefficient for
computational point within the
model was then coupled with optimi-
a reverse tainter valve is very sensi-
closed-conduit components. The
zation software to determine the
tive to the shape of the bottom edge
minimum pressures and cavitation
best method of using the lock culvert
of the valve, therefore there is no
indices in the wakes of reverse
system to pass flow in the event that
universal description of contraction
tainter valves are also computed.
pool lowering is required. The study
coefficients for reverse tainter
determines if the lock system can be
valves. However, the values used
This study's principal objective is
used as an outlet structure and the
for this study are believed to be ade-
to construct a model of the Lock 1
optimum operation scheme for pool
quate for estimating the lowest pres-
system and then develop an opera-
lowering. This paper describes the
sures at partial gate openings.
tional scheme that would transition
development of the lock model and
the flow from unsteady to steady
Field data obtained during lock
the determination of the optimum
state for passing discharge through
operations were used to determine
valve operation. The optimization
the system. The numerical model
energy loss coefficients on the
model minimizes the time required
reproduced the entire filling and
components for which no published
to reach steady-state flow while
emptying system including the
data are available. Loss coefficients
maximizing the minimum cavitation
intakes, valves, culverts, lock cham-
for many hydraulic components are
indexes downstream of the operat-
ber, and outlets. Field data
well established and are readily
ing valves during the transient condi-
(Stockstill, Fagerburg, and Waller
available in the literature (e.g., Miller
tions of steady flow establishment.
2000) were used to quantify loss
1990; U.S. Army Corps of Engineers
coefficients of the lock system.
1952). However, lock culvert system
Energy loss coefficients were deter-
components are often unique to a
Lock System Model
mined for primary components of the
particular project and the loss
system for which there is limited
coefficients have not been
published data. Both the filling com-
determined. The unknown
The numerical flow model,
ponents and the emptying compo-
coefficients were determined from
LOCKSIM (Schohl 1999) serves as
nents of the lock system were vali-
field data using the optimization
an evaluation tool for lock filling and
dated with field data. The location of
techniques provided in the
emptying system designs. LOCKSIM
the pressure cells used in the data
commercial-software package
couples the unsteady pressure-flow
38
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