BED, BANK & SHORE BED, BANK & SHORE PROTECTION - CHAPTER 8 pdf

BED, BANK & SHORE BED, BANK & SHORE PROTECTION PROTECTION Lecturer: Pham Thu Huong Lecturer: Pham Thu Huong Email: Email: Huong.p.t@wru.edu.vn Huong.p.t@wru.edu.vn Faculty of Coastal Engineering Faculty of Coastal Engineering Chapter 8 Chapter 8 Ships Ships – – Loads, Stability and erosion Loads, Stability and erosion (3 class hours) Content Content 8.1 Introduction 8.2 Loads 8.3 Stability 8.4 Erosion 8.5 Summary Introduction Introduction In inland waterways, ships may cause wave: • Primary wave: starts with the front wave, followed by the depression and ending with the stern wave → severe attack on the banks (narrow navigation channels) • Secondary wave: The much shorter waves that originate from the hull (plays an important role in larger navigation channels) • Propeller wash: The currents caused by the ship's propeller (it is particularly important when ships manoeuvre near a berthing place or a jetty) Introduction (cont) Introduction (cont) Most damage on revetment cause by: • large ships ~ sailing slowly Æ erosion due to return current • small service crafts, tugs… ~ sailing fast Æ bank erosion due to secondary waves Introduction (cont) Introduction (cont) Flow around fixed object & moving object in stagnant water: Introduction (cont) Introduction (cont) Phenomena around a Phenomena around a moving ship in a waterway moving ship in a waterway [...]... 10 m from bank (y= 5 m) canal 40 m wide, 5 m deep Calculate: Maximum Wave height Limit speed: As/Ac = (10*3) / (40*5) = 0.15 Vl/√gh = 0.55 → Vl= 3 .8 m/s Use fig 8. 6 fig 8. 4 design speed 0.9*3 .8= 3.4 m/s z/h=0. 083 → z=0.42 m Ship sails 10 m from bank (y= 5 m), so zmax=1.5((1+2*5/40)*0.42 = 0. 78 m ur = 0.15 *√gh = 1.04 m incl excentricity: (1+5/40)*1.04 = 1.17 m/s eq 8. 6 and 8. 7 H = 1.2 h(s/h )-0 .33*v4/(gh)2...Loads (cont) Definition in 1-d approach As = B.D : cross-section area of the ship Ac = b.h : cross-section of the waterway vs : water flows ur : return flow z : water-level depression Loads (cont) limit speed: ( vs + ur ) vs h+ = h−z+ 2g 2g 2 Bernoulli : continuity: 2 b h vs = ( b h − B D − b z )(... waves Loads (cont) Secondary wave pattern Loads (cont) Secondary wave pattern vs Fr = gh Fr < 0.75, - the cusp locus line is at an angle of about 20o with the sailing line - and the direction of propagation of the cusps is at an angle of about 35o with the sailing line hence the angle of approach for a bank parallel to the sailing line is 55o Fr = 1, transverse and diverging waves coincide Fr > 1 transverse... function of blockage Loads (cont) deviation from the 1-d case (Eccentric position ship): 2y ⎞ ⎛ z ecc = ⎜ 1 + ⎟z b ⎠ ⎝ y⎞ ⎛ u r − ecc = ⎜ 1 + ⎟ u r b⎠ ⎝ Multiple ships (when two ships encounter or when a ship overtakes another one): zmax = 1.5 zecc Loads (cont) Secondary waves - Secondary waves are formed by a number of periodic waves, a wave train - Secondary waves are caused by the pressure pattern... “Breuksteen in de praktijk” The Suez Canal The Suez Canal, damage Bank erosion along the Suez Canal A normal ferry and a fast ferry Loads (cont) Propeller action Loads (cont) turbulence in propeller wash and in free circular jet Loads (cont) equations for propeller jets 2.8u0 um = x/d b = 0.21x u = um e ⎛r⎞ −0.69⎜ ⎟ ⎝b⎠ 2 ⎫ ⎪ 2 ⎛r⎞ ⎪ 2.8u0 −15.7⎜ x ⎟ u= e ⎝ ⎠ ⎬ x/d ⎪ ⎪ ⎭ Loads (cont) velocity distribution... m from bank (y= 5 m), so zmax=1.5((1+2*5/40)*0.42 = 0. 78 m ur = 0.15 *√gh = 1.04 m incl excentricity: (1+5/40)*1.04 = 1.17 m/s eq 8. 6 and 8. 7 H = 1.2 h(s/h )-0 .33*v4/(gh)2 = 1.2*5*(10/5 )-0 .33*3.44/(10*5)2 = 0.27 m eq 9 .8 standard values in the Netherlands Lakes Canals Rivers Small waters Wave heights (m) Wind waves Ship waves 0.25 – 1.00 0.10 – 0.50 0.10 – 0.25 0.25 – 0.75 0.25 – 1.00 0.25 – 0.75 0.10... function of blockage As/Ac As Vl 2 3 Vl 2 / 3 + − =1 1/ 3 Ac 2 gh 2 ( gh ) Loads (cont) limit speed as a function of waterdepth and blockage For the purpose of bank design, a speed of 90% of Vl is recommended Loads (cont) primary waves The water-level depression (z) and the return current (ur) can be calculated in A dimensionless form: vs 2 gh ur gh = = 2 z/h (1 − As / Ac − z / h ) −2 −1 ⎡ ⎤ vs 1 − 1⎥ . BED, BANK & SHORE BED, BANK & SHORE PROTECTION PROTECTION Lecturer: Pham Thu Huong Lecturer: Pham Thu Huong Email:. Engineering Chapter 8 Chapter 8 Ships Ships – – Loads, Stability and erosion Loads, Stability and erosion (3 class hours) Content Content 8. 1 Introduction 8. 2 Loads 8. 3 Stability 8. 4 Erosion 8. 5 Summary Introduction Introduction In. h Vc L L LcT π π π π ⎫ = ⎪ == ⎬ ⎪ = ⎭ Definition in 1-d approach Loads (cont) Loads (cont) A s = B.D : cross-section area of the ship A c = b.h : cross-section of the waterway v s : water flows u r : return flow z : water-level depression