بررسي اثرات سطح آزاد بر روي ضرايب ليفت و درگ يك شناور زير سطحي

چكيده انگليسي :

78 Effects of Free Surface on Lift and Drag Coefficients of an Underwater Vehicle Mohamad Oghbaei M oghbaei89@gmail com Date of Submission 1230332014 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Shahriar Mansoorzade Shahriar@cc iut ac ir Abstract Over the last decades the increased desire to use autonomous underwater vehicles AUVs for commercial andmilitary applications has led to a great deal of research in this field for the purpose of not risking human life indangerous operations Extensive use of autonomous underwater vehicles AUV in oceanographic applicationsnecessitates investigation into the hydrodynamic forces acting over an AUV hull form operating undersubmerge condition When a completely submerged body moves under water a resisting force including africtional and a pressure drag form drag force applies into the body of the vehicle When an AUV moves nearfree surface it creates a wave at the free surface which changes its hydrodynamic coefficient including the dragand lift coefficients of the AUV comparing with those when the AUV moves in an infinite medium Indeed drag and lift coefficients near the surface are influenced by the wave making resistance created near the freesurface which is due to changing the pressure distribution on the body of the vehicle The aim of the currentinvestigation is to study the effect of free surface on the drag and lift coefficients of an autonomousunderwater vehicle The AUV designed and constructed in subsea research and development center of IsfahanUniversity of Technology used for this numerical study The two phase flow Reynolds Averaged Navier Stokessolver ANSYS CFX is used to simulate the motion of the axisymmetric geometry of the AUV The currentnumerical investigations were carried out to calculate the hydrodynamic coefficients for a velocity range of 0 5to 3 m s corresponding to a Reynolds number range of 97000 to 579000 a n d a submergence depth range of0 87D to 4 83D where D refers to AUV hull diameter In addition the drag coefficients are calculated forangle of attacks varied from 12 to 12 degree in steps of 3 degrees Validation of numerical results isperformed by comparing t h e experimental results obtained in subsea R D towing tank of IUT The obtainednumerical results showed that at all AUV speeds investigated as the vehicle approaches the free surface thedrag coefficient increases The results showed that the pressure drag varies sharply near the free surface whilethe friction drag is almost independent of the submergence depth and remains almost constant This can beexplained by the fact that pressure around the body is strongly influenced by waves formed by moving body Also the numerical results showed that the depth at which the free surface effect becomes negligible depends onthe speed of the AUV For example at a velocity of 1 5 m s Re 280000 free surface effects onhydrodynamics coefficients eliminate in submergence depth of 2 6D while in velocity of 3 m s Re 579000 free surface effects eliminate in submergence depth of 4 8D It was also shown that in the absence of freesurface the drag coefficient decreases constantly with velocity while when the AUV moves near the freesurface at some velocity in which the surface wave length becomes equal to the AUV length a sudden increasein the drag coefficient can be seen Key worlds Free surface effect hydrodynamic coefficient underwater vehicle CFD

عقبايي، محمد

بررسي اثرات سطح آزاد بر روي ضرايب ليفت و درگ يك شناور زير سطحي

اثرسطح آزاد , ضرايب هيدروديناميكي