Berker Yalin IMAMOGLU %5bCompatibility Mode%5d

8/3/2019 Berker Yalin IMAMOGLU %5bCompatibility Mode%5d

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Energy dissipators for spillways:

1) Hydraulic jump stilling basins,

2) Free jets and flip buckets,

,

4) Impact type energy dissipators,

eppe sp ways.


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Flip Buckets


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,


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Guri Hydroelectric Project, Venezuela


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Karakaya Dam and HEPP


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A short review about hydraulics of flip buckets


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Keban Dam and HEPP


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Minimum radius,

Minimum height,

ra ec ory ang e,


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Trajectory distance,

Impact angle,

Trajectory lenghts, based on these equations have simulated well inhydraulic models.


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Scour at Downstream of Flip

Buckets

The designer is concerned with the following aspects:

Computation or prediction of scour under various,

Analysis to assess the likely effect of scour on the

, Scour control and remedial measures.


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e eren approac es or es ma on o ep o scour

can be classified under four general groups:


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to approach towards the structure, a

likely in the original concept.


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Relationships developed vary from those extensive

parame ers suc as:

- discharge

-

- bucket geometry- bed material mean particle size

- downstream water de th

- rock mechanic characteristics ( joint pattern, compressive stregth, block size )

Simple relationship:

- discharge

- ea- downstream depth


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The use of com lex relationshi s offer almost the same results

as could be obtained by using very simple relationships.

the maximum depth of scour likely to occur during the operation

of the spillway over the years.


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Approach - 1

Based on the experience, Damles relationship

ds

= A ( q ho

)0,5 (1966)


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Damles equation obtained by the limited data from six prototype

structures ives reliable information on de th scour.

Khatsuria re-evaluated the constant A, when more information

. ,

0.90 instead of 0.65 corresponding to ultimate state of scour.


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Approach 2

Mason (1989) demonstrated that the head drop may not

directly affect the scour depth, other than by varying the

.

affects the force on particles of bed material.


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Approach 3

For free jets spillways such as those on the crests of arch

dams Modified Veronese formula (1976) :

Yldz (1994-b) suggest that for applying this formula to

Im act An le


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Solid and Slotted Roller Buckets When the tail water depth is too great for formation of good hydraulic

jump, submerged roller buckets are suitable for energy dissipation

The ground roller has a tendency to move bed material towards the bucket

li where it could be icked u and carried inside the bucket. The slotted

bucket aims at minimizing this tendency with the help of a bucket design

combined with teeth and apron.


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First solid bucket application on the 85 m high

Grand Coulee Dam,USA


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Scour at Downstream of Roller Buckets


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atsur a con ucte stu es or t e ept o max mumscour and distance of maximum scour from the bucket lip for a

t ical solid roller bucket with 450 li an le for 6 < F


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Scour at Downstream of Slotted Buckets

The performance of both buckets was studied on a two

dimensional model of a typical medium height spillway with

the same invert elevation and tail water conditions.


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Bargi Dam, India ( slotted bucket )

Tooth for Slotted Bucket


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With the solid bucket, diving does not occur. In general, however,

,for lower ranges of tail water depth.


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With the slotted bucket, sweepout occurs at a slightly higher tail

water elevation than with the solid bucket, and if the tail water is

,

channel bed, as shown:


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Analysis

Since scour depth estimation by emprical relationships has

examine the potential scour and perhaps more importantly,any interaction of scour with structure geometry and

y rau c con ons.

However, a physical model has its limitations too in

simulatin the entire rocess of rock scourin fracturin -pulling out-transport)

E i t t A t D S ill


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Erosion test on Angostra Dam Spillway


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Control and Protection Against Scour

The reasons for the scour to occur very near the structure

are often the low flows flowing down the bucket lip or

discharges passed down the spillway with unsymmetrical

gate openings causing spread of the jet or return flows.

Complete elimination of scour is hardly practical since itrequ res pr or rea men o e roc w c may nvo ve

filling of fissures and joints with concrete, laying of

concrete raft, creation of water pool by a check dam in

the downstream.


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The extend and location of scour hole can be controlled

either by the creation of a pre-excavated plunge pool

ormo ca ons n e uc e s ape an geome ry.

concre e apron a ou m

width, just downstream of the

bucket would provide adequate

protection.


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. , .

2. USBR Design of Small Dams, 2006.3 BR H r li i n f illin in

and energy dissipators, Engg Monograph No

25, 1978.4. R.M.Khatsuria, Hydraulics of Spillways

and Energy Dissipators, 2005.

5. Larry W.Mays, Hydraulic DesignHandbook, 2004.

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Berker Yalin IMAMOGLU %5bCompatibility Mode%5d