KorEArtH NET

  - Fluid : gas, liquid

  - Shear force : stress(pressure) parallel to the surface

  - Body force : gravity, inertia

  - Dynamic viscosity (μ)mju : coefficient of the shear to its rate of shear

                                            (=molecular viscosity) : 분자간 작용하는 힘

                                            (두 판사이의 얇은 film layer가 가지는 tangential force)

  - Kinematic viscosity (ν)nu =

           =

      Laminar flow   : Re <    0.1 ┐ normally  Re 〈 2000

      Turbulent flow : Re ～ 1000 ┘     Re 〉 2000

  - Fr : Fr 〈   1 : tranquil flow . wave can not pass upstream (subcritical flow)

       Fr      〉 1 : rapid flow   . wave can not pass upstream (supercritical flow)

  - Hjulstrom's diagram

  - Hydraulic sortion - sliding, rolling, saltation, intermittent suspension or continuous suspension

  - Hydraulic equivalence : depending on intensity of the flow

  - Competence

  - Capacity

1.Biological Processes

  1) degradation : 미생물에 의한 다른 생물체의 crushing, scraping, site reduction

                         caused by consumption, burrowing, boring (해삼, gastropod, sea urchins, 소화)

  2) pelletization : 배설에 의한 pellet - filter feeder, deposit feeder

  3) organism - enhanced sedimentation

      sediment baffles → energy 감쇠 (marine grass)

      sediment trapper → blue green algae → stromatolites

2.Physical Processes

  1) Fluid flow ┌ Turbulent, laminar

                               └ Rapid, tranquil

                 force per unit area (pressure) : normal to surface : gravity

                 stress(shear) : parallel to surface

        Shear Stress : maximum at base

        (τ)      zero at free surface

     Renold number :

             (1883, 1884 : 영국수학자)

             ν(nu) : Kinematic viscosity

             η(eta) : morecular viscosity

             ρ : density

             μ : viscosity

             U : velocity

             L : unit length (pipe diameter) (mean flow depth)

       * Open channel에서

         ┌ Re  〉 2000 : tubulent flow (turbulent eddies)

         └ Re 〈  2000 : laminar

       * Flow 내에 towing sphere가 있을 때

             Re = 24 → eddies in the wake

             Re 〈 1 : under laminar flow

     Froude number : 영국조선설계사

            Fr =

            U=관성 (유속), D=depth of water, g=gravity acceleration

           ┌ Fr 〈 1.0 : tranquil or subcritical

           └ Fr 〉 1.0 : supercritical, rapid flow

     * boundary layer : zone of shear stress

         → downstream (velocity increase)

                                                                                      thicker - turbulent

     * flow separation : Figure 2-6

         change in diameter

     * flow (natural current)의 구분

        ┌ Steady : 일정한 지점에서만 flow velosity (방향 속도) 가 일정 (하류 방향은 속도 감소)

        └ unsteady : 일정만 지점에서만 flow velocity 가 일정하지 않음 (river →계절)

        ┌ uniform : 흐르는 방향을 따라 속도가 항상 같음 (streamline 이 평행)

        └ non - uniform : 흐르는 방향을 따라 속도가 항상 다름 (강굽이에서 처럼)

         streamline : flow 의 세기 방향의 변화를 묘사 ( 밀집 → velocity 증가)

  2) Settling of particles

       Stoke's law : for single particle

       W_S : settling velocity

       d   : diameter

       ρs-ρ : density difference

       μ : viscosity

       * effect of shape ⇒ equivalent diamater (ex : shell)

  3) Sediment entertainment

   : threshold velocity - 임계속도 for moving

      Hjulstrom diagram : clay, silt size grain의 침식 이동이 fine sand 에 비해 어려움

      Cc : 임계조건

      d : 입도

      g(σ-ρ) : 잠수중력

      τ_o : shear stress    

      ν  : kinematic viscosity

      f   : Reynold 수

     * grain movement

         - two mechanism : ① fluid drag on grains in contact with fluid

                                    ② hydrodynamic lift force

         - 방해 요소: 입자의 무게, 입자간 점착력

         - motion type: ① traction - slide, roll     ┐ bed load

                             ② saltation - hop, boune ┘

                             ③ suspended or wash load

                              Mississippi          전세계

             뜬짐                65%                300억t

             녹은짐             29%                 36억t

             밑짐                 6%                  30억t

  4) Hydraulics and sediment texture

      hydraulic sorting, abrasion

       - Competence - 일정한 유속의 유체가 운반할 수 있는 최대 입자 크기

       - Capacity: 일정 유체가 운반 가능한 퇴적물 총량

      Saltation population : 90～95% 의 총 bedload (figure 2-9)

      *입자모양 : flow에 가장 적은 저항을 갖는 자세로 퇴적

3.Bedforms

  * Flow regime : fluid flow, bed configuration, dissipation of energy, phase(bed and water surface)

                           의 관계들의 총체로서 표현

     Upper flow regime Fr   〉1.0

     Lower flow regime Fr 〈 1.0

  * ripple → sand wave → megaripple(dune) → plane(flat) bed → antidune → chutes and pools

    ----------------Lower F. R..------------╂------------ Upper F. R..---------------------

  * bedform은 turbulence of flow와 grain 의 interaction에 의해 형성

    (flow power :: product of velocity(V) × boundary shear stress(τ_o))

   Figure 2-9, 2-10, 2-11 참조

4.Sediment gravity processes (mass flow)

 ⓐ turbidity current : density currents - turbidite

 ⓑ liquified sediment flow : upward flowing 에 의해 supporting

 ⓒ grain flow : grain to grain collision: dry grain flow

 ⓓ debris flow : mixtune of fine coarse -matrix strength & buoyancy

 ⓔ slump/slide

  Figure 2-14 참조

5.Tides and tidal currents)

 ┌ spring tide : 사리

 └ neep tide : 조금

  micro tidal range : 〈 2m

  meso tidal range : 2-4m

  macro tidal range : 〉4m

  * unequal high and low tidal velocity - currents

                                 └→ time - velocity asymmetry

    ┌ flood slack : 만조

    └ ebb slack : 저조

  * maximum flood tidal current : after mid tide

     maximum ebb tidal current : near low tide

     flood-dominated or ebb-dominated

6. Waves

     Surface wave = gravity wave → height period

 ┌ sea wave

 └ swell wave

                          f(W.F.D)

                          W : wind velocity

                          D : duration of wind

                          F : fetch, distance of water surface

   surf : mean coast

  * water motion in waves

                      ordital motion : effective depth = 1/2 of wavelength

  * longshore current : parallel to shore

  * rip current : after breaking surf : back-flowing currents