Armfield Ltd. S8 MkII ÜLEDÉKSZÁLLÍTÁST BEMUTATÓ CSATORNA

Termékleírás:

RENDELÉSI SPECIFIKÁCIÓK

Átlátszó nyitott csatorna melyben a víz szivattyú segítségével keringtethetõ egy mobil mederben, üledékszállítással kapcsolatos bemutatók és kísérletek elvégzéséhez.
Három különbözõ áramlási sebesség választható (és mérhetõ) 0,2-0,6 l/sec között.
A csatorna dõlése állítható 0-10% között.
A mérési szakasz 1,55 m hosszú, 78 mm széles és 110 mm mély.
Az egység önálló és hordozható.
Alulcsapott gát és hídpillér modellek az eróziós kísérletekhez.
Vízszintmérõ is tartozék az alulcsapott gát kalibrálásához.

KÍSÉRLETI LEHETÕSÉGEK

Áramlás rögzített sima mederben.
Áramlás mobil homok-mederben.
Az üledékszállítás mechanikája.
Alámosódások.
Áramlási struktúrák.
Áramlás rögzített kavicsos mederben, stb.

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DESCRIPTION

The unit consists of an inclinable channel mounted on a frame, together with a discharge tank and recirculating pump. To commence a demonstration, sand is placed evenly along the channel bed, between the inlet tank and the overfall discharge weir. Water is circulated around the system at one of the three selectable flow rates. The channel slope is adjusted by means of a fine screw jack to which is attached an accurate slope indicator. The channel sides are transparent in order that bed profile changes can be readily observed, and a section of one side is provided with graphical grid markings to permit quantitative assessments to be made of bedform dynamics.

DEMONSTRATION CAPABILITIES

FIXED, SMOOTH BED FLOW

The flume may be used without sediment on the bed to demonstrate the following flow phenomena and governing equations:

> Tranquil, sub-critical flow - movement of surface waves upstream against flow

> Rapid, super-critical flow - dominance of intertial over gravity forces, "shock waves" from flow obstructions

> Hydraulic jump - transition from super to sub critical flow, air entrainment, mixing

> Turbulence - flow visualisation for example by dye injection from a hypodermic syringe (not supplied)

> Flow measurement - using sharp crested weirs

> Governing equations of open channel flow -

Reynolds number, Froude number, continuity, Bernoullis equation, weir equations

FLOW OVER A MOBILE SAND-BED

Sequence of bedforms associated with increasing flow intensity and sediment transport rate. The following bedforms are exhibited (as discharge and/or slope are increased):-

> Lower Regime

- plane-bed (no motion)

- ripples

- ripples and dunes

- dunes

- washed-out dunes

> Upper Regime

- plane-bed (with motion)

- standing waves

- anti-dunes

- breaking anti-dunes

- chutes and pools

MECHANICS OF SEDIMENT TRANSPORT

Starting from a plane-bed with no motion, the movement of grains can be observed with emphasis on the following:-

- initiation of motion

- trajectory of initial motion

- movement by rolling and sliding (contact load)

- movement by hopping (saltation load)

- movement by suspension (suspended load)

A water level gauge is supplied to measure the head over the channel discharge weir to deduce flow rates from a calibration chart. Solid models of a bridge pier and an undershot weir are provided to demonstrate the scour effects on river beds of man-made structures:

DEPOSITIONARY FEATURES AND FACIES

The deposition of sediment load can be observed and the resulting patterns of grains within the sand body (such as cross-bedding, foreset beds etc.) may be identified. The significance of such features when found in geological records can be discussed.

LOCAL SCOUR

Scour under boils and vortices in the flow is observed under both the lower and upper regime bedforms. Artificial obstructions may be introduced to represent bridge piers, revetments, sills or other man-made structures, and the resulting pattern of scour examined. Two such models are included.

FLOW STRUCTURES

The structure of turbulence in the flow may be examined using dye injection (dye injector not included). This is particularly interesting for the dune bedform configuration and clearly demonstrates separation on the lee face.

BEDFORM HYSTERESIS

If the discharge in the flume changes quickly, there is insufficient time for bedforms to adjust to the new flow regime. Hence, if a flood hydrograph is simulated by increasing and then decreasing the discharge, different depths (stages) will occur for the same discharge on the rising and falling limbs. This effect is of major importance to gauging stations on sand-bed rivers. It is easily and clearly demonstrated in the flume.

COMPUTATIONAL WORK

In addition to illustrating flow and sediment phenomena, the flume can be used for basic data collection and numerical evaluation of the following:

�Flow resistance:

- Manning, Chezy and Darcy

- Weisbach friction factors for various bedform configurations

�Bedform prediction:

- Hjulstrom Diagram (velocity)

- Bogardi Diagram (Shields parameter)

- Simons and Richardson Charts (Stream power)

- Leeder Chart (Boundary shear stress)

�Initiation of Motion:

- Hjulstroms Curve

- Shields Diagram

FLOW OVER A FIXED, GRAVEL-BED

The flume cannot transport gravel, but can be used to investigate flow resistance in gravel and polder-bed rivers. The flow resistance coefficients may be calculated using equations (such as those of Bray, Limerinos, Hey, Lacey, Thompson & Campbell and Bathurst) and the results compared to the actual values obtained by observation. It is recommended that users obtain actual gravel material from local sources, (Armfield cannot supply gravel).

BEDFORMS IN SAND

As water flows over sand in a river or on a beach it exerts a shear force on the bed. If the flow is strong enough, sand grains are lifted to roll and bounce along the bed. The shape of the bed responds to this motion by transforming into ripples. As the energy of the flow and transport rate of sand increase, the bedforms change. Ripples are replaced by larger dunes.

At higher energy still, the dunes are washed out to produced a flat bed and in extremely energetic flows anti-dunes appear.

Bedforms are important in affecting the flow of water and movement of sediment in rivers and on beaches. They also occur in deserts due to the movement of sand by the wind.

Bedforms are preserved when sand deposits are turned into sandstone by geological processes. They are used to reconstruct environments under which the sand was deposited.