{"id":378,"date":"2020-01-26T13:50:52","date_gmt":"2020-01-26T13:50:52","guid":{"rendered":"https:\/\/seismicconsolidation.com\/?p=378"},"modified":"2020-01-26T13:50:52","modified_gmt":"2020-01-26T13:50:52","slug":"to-measure-energy-dissipation-downstream-of-spillway-by-various-energy-dissipation-arrangements","status":"publish","type":"post","link":"https:\/\/seismicconsolidation.com\/to-measure-energy-dissipation-downstream-of-spillway-by-various-energy-dissipation-arrangements\/","title":{"rendered":"To measure energy dissipation downstream of spillway by various energy dissipation arrangements"},"content":{"rendered":"

<\/h3>\n

<\/a>3.\u00a0\u00a0\u00a0\u00a0 To measure energy dissipation downstream of spillway by various energy dissipation arrangements<\/h2>\n

<\/a>3.1.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Objectives:<\/h3>\n
    \n
  1. To observe formation of hydraulic jump in channel<\/li>\n
  2. To note the sequent depths & to compare value of y2<\/sub> by using formula<\/li>\n
  3. To find the type of hydraulic jump formed in channel<\/li>\n
  4. To find energy dissipation by using hydraulic jump<\/li>\n
  5. To find energy dissipation by ski jump<\/li>\n
  6. To find energy dissipation by chute blocks<\/li>\n
  7. To find energy dissipation by gravel bed<\/li>\n
  8. To compare the energy dissipation by various dissipators<\/li>\n<\/ol>\n

    <\/a>3.2.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Apparatus:<\/h3>\n
      \n
    1. S6 Tilting flume assembly<\/li>\n
    2. Point gauge<\/li>\n
    3. Ogee weir<\/li>\n
    4. Downstream channel gate<\/li>\n
    5. Ski jump<\/li>\n
    6. Baffle\/Chute blocks<\/li>\n
    7. Gravel bed<\/li>\n<\/ol>\n

      <\/a>3.3.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Related theory:<\/h3>\n

      3.3.1.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Energy dissipation below overflow spillways<\/h4>\n

      The water flowing over the spillway acquires a lot of kinetic energy by the time it reaches near tow of the spillway (because of conversion of potential energy into kinetic energy). If arrangements are not made to dissipate this huge kinetic energy of water, and if the velocity of water is not reduced, large scale scour can take place on the downstream side near the toe of the dam and away for it. Energy dissipators need to be designed for proper dissipation of high energy.<\/p>\n

      In general, the K.E. of this super critical flow can be dissipated in following ways:<\/p>\n

        \n
      1. By converting the super critical flow into sub critical flow by hydraulic jump.<\/li>\n
      2. By directing the flow of water into air and then making it fall away from the toe of the structure. The energy is dissipated by the aeration of jet and impact of water on the river bed. Though some scour will take place but it is too small or too far away from the dam to endanger it. Bucket type dissipators work on this principle.<\/li>\n
      3. By providing auxiliary devices such as chute blocks, sills, baffle walls etc. in stilling basins.<\/li>\n<\/ol>\n

        3.3.2.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Various cases of energy dissipators<\/h4>\n

        3.3.2.1.\u00a0\u00a0\u00a0\u00a0\u00a0 Simple horizontal apron<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.1: Simple horizontal apron<\/p>\n

        3.3.2.2.\u00a0\u00a0\u00a0\u00a0\u00a0 Sloping apron above the bed<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.2: Sloping apron above the bed<\/p>\n

        3.3.2.3.\u00a0\u00a0\u00a0\u00a0\u00a0 Roller bucket<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.3: Roller bucket<\/p>\n

        3.3.2.4.\u00a0\u00a0\u00a0\u00a0\u00a0 Ski jump bucket<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.4: Ski jump bucket<\/p>\n

        3.3.2.5.\u00a0\u00a0\u00a0\u00a0\u00a0 Sloping apron below the bed<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.5: Sloping apron below the bed<\/p>\n

        3.3.2.6.\u00a0\u00a0\u00a0\u00a0\u00a0 Subsidiary dam construction<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.6: Subsidiary dam construction<\/p>\n

        3.3.2.7.\u00a0\u00a0\u00a0\u00a0\u00a0 Sloping apron partly above and partly below ground level<\/h5>\n

        \"\"<\/p>\n

        <\/a>Figure 3.7: Sloping apron partly above and partly below ground level<\/p>\n

        3.3.3.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Hydraulic jump<\/h4>\n

        A hydraulic jump occurs when a supercritical stream meets a subcritical stream of sufficient depth. The supercritical stream jumps up to meet its alternate depth. While doing so it generates considerable disturbances in the form of large-scale eddies and a reverse flow roller with the result that the jump falls short of its alternate depth.<\/p>\n

        Figure 3.8. is a schematic sketch of a typical hydraulic jump in a horizontal channel. Section 1, where the incoming supercritical stream undergoes an abrupt rise in the depth forming the commencement of the jump, is called the toe of the jump<\/em><\/strong>. The jump proper consists of a steep change in the water-surface elevation with a reverse flow roller on the major part. The roller entrains considerable quantity of air and the surface has white, frothy and choppy appearance. The jump, while essentially steady, will normally oscillate about a mean position in the longitudinal direction and the surface will be uneven.<\/p>\n

        Section 2, which lies beyond the roller and with an essentially level water surface is called the end of the jump<\/em><\/strong> and the distance between Sections 1 and 2 is the length of the jump, L<\/em>j<\/em>. The initial depth of the supercritical stream is y<\/em>1 and y<\/em>2 is the final depth, after the jump, of the subcritical stream. The two depths y<\/em>1. And y<\/em>2 at the ends of the jump are called sequent depths<\/em><\/strong>.<\/em><\/p>\n

        Due to high turbulence and shear action of the roller, there is considerable loss of energy in the jump between Sections 1 and 2. In view of the high energy loss, the nature of which is difficult to estimate, the energy equation cannot be applied to Sections 1 and 2 to relate the various flow parameters. In such situations, the use of the momentum equation with suitable assumptions is advocated. In fact, the hydraulic jump is a typical example where a judicious use of the momentum equation yields meaningful results.<\/p>\n

        \"\"<\/p>\n

        Figure 3.8. Sketch of hydraulic jump<\/p>\n

        3.3.3.1.\u00a0\u00a0\u00a0\u00a0\u00a0 Uses of hydraulic jump:<\/h5>\n

        A hydraulic jump primarily serves as an energy dissipator to dissipate the excess energy of flowing water downstream of hydraulic structures, such as spillways and sluice gates. Some of the other uses are:<\/p>\n

          \n
        1. Efficient operation of flow-measurement flumes<\/li>\n
        2. Mixing of chemicals.<\/li>\n
        3. To aid intense mixing and gas transfer in chemical processes<\/li>\n
        4. In the desalination of sea water<\/li>\n
        5. In the aeration of streams which are polluted by bio-degradable wastes<\/li>\n<\/ol>\n
          3.3.3.2.\u00a0\u00a0\u00a0\u00a0\u00a0 Hydraulic jump in a horizontal rectangular channel<\/h5>\n
            \n
          1. \"\"<\/li>\n<\/ol>\n
            3.3.3.3.\u00a0\u00a0\u00a0\u00a0\u00a0 Classification of hydraulic jumps<\/h5>\n

            The hydraulic jumps in horizontal rectangular channels are classified into five categories based on the Froude number F<\/em>1 of the supercritical flow, as follows:<\/p>\n