為提升拖航水槽的實驗範圍，成功大學於民國 113 年新建了一段水深5公尺的深水槽段，並以長4公尺的過渡段連接至原有水深3.5公尺的淺水槽。然而，水深驟變及過渡斜坡的幾何特性有可能對實驗船隻的流場分佈與阻力特性產生影響，需進一步研究其對拖航實驗結果準確性與可靠性的潛在影響。故本研究以 SUBOFF潛艇模型為對象，結合計算流體力學（CFD）技術，模擬其從深水槽運動至淺水槽的過程分析水槽深度變化對潛艇模型阻力及流場結構的影響。本研究亦對5個不同深度(H1~H5)的潛艇模型進行模擬，其深度範圍介於0.75 m~2.75 m之間，同時也從深水槽到淺水槽的運動過程中，取出4個時刻的潛艇模型位置進行討論。
研究中採用了ANSYS的動網格技術，使潛艇模型能直接運動，取代傳統給予周圍流體速度的靜網格模擬方式，更真實地捕捉了模型運動過程中的流場變化。結合滑移網格技術，將計算域劃分為運動區域與靜止區域，有效降低了網格變形的影響，並提升了模擬效率與穩定性。經由驗證與確認，無限水域模擬結果的阻力值與實驗數據誤差極小，證實了模擬條件與方法的可靠性。
模擬結果表明，潛艇模型從深水槽運動至淺水槽的過程中，其阻力會逐漸減小，顯示過渡斜坡的幾何特性對潛艇模型阻力的影響。同時，當潛艇模型接近自由液面時，波浪效應的干擾增強，流場中的高壓區與低壓區分佈顯著；而當模型接近槽底時，邊界層的發展抑制了部分動量損失，進一步影響阻力特性。
未來可考慮延長水槽模擬區域並提高潛艇模型的運動速度，或調整過渡段槽底的幾何設計，以進一步探討幾何形狀對流場特性及阻力的影響，為拖航水槽的設計優化提供依據。

To expand the experimental range of towing tanks, National Cheng Kung University constructed a new deep tank segment with a depth of 5 meters in 2024, connected to the existing shallow tank segment with a depth of 3.5 meters via a 4-meter-long transition section. However, the sudden depth change and the geometric characteristics of the transition slope may affect the flow distribution and drag characteristics of ship models. This study uses the SUBOFF submarine model and Computational Fluid Dynamics (CFD) techniques to simulate its movement from the deep tank to the shallow tank, analyzing the effects of depth variations on the model's drag and flow structures. The simulation examines five depths and four time-step positions of the submarine.
The study employs ANSYS dynamic meshing to allow direct motion of the model, replacing traditional static mesh methods, enabling realistic capture of flow variations during motion. The integration of sliding mesh techniques effectively reduces mesh deformation, enhancing simulation stability and efficiency. Validation results show minimal deviation between the simulated drag values and experimental data, confirming the reliability of the simulation conditions and methodology.
The results indicate that the submarine model's drag decreases progressively as it moves from the deep tank to the shallow tank. The geometric characteristics of the transition slope significantly influence drag and flow structures, with free surface proximity and tank bottom position also playing critical roles. Future studies could explore different velocities and geometric conditions to optimize towing tank design.

[1] O. Reynolds, "On the dynamical theory of incompressible viscous fluids and the determination of the criterion," Philosophical Transactions of the Royal Society of London, vol. 186, pp. 123–164, 1895.
[2] B. E. Launder and D. B. Spalding, "The numerical computation of turbulent flows," Computer Methods in Applied Mechanics and Engineering, vol. 3, no. 2, pp. 269–289, 1974.
[3] T.-H. Shih, W. W. Liou, A. Shabbir, Z. Yang, and J. Zhu, "A new k-ε eddy-viscosity model for high Reynolds number turbulent flows: Model development and validation," Computers & Fluids, vol. 24, no. 3, pp. 227–238, 1995.
[4] C. W. Hirt and B. D. Nichols, "Volume of fluid (VOF) method for the dynamics of free boundaries," Journal of Computational Physics, vol. 39, no. 1, pp. 201–225, 1981.
[5] Y. Zhang, H. Wu, and X. Zhang, "Validation of free-surface effects on submarine drag using CFD and experiments," Physics of Fluids, vol. 27, no. 9, p. 095106, 2015.
[6] N. C. Groves, T. T. Huang, and M. S. Chang, Geometric Characteristics of DARPA (Defense Advanced Research Projects Agency) SUBOFF Models (DTRC Model Numbers 5470 and 5471), Bethesda, MD: David Taylor Research Center, Ship Hydromechanics Dept., 1989.
[7] F. Stern, R. V. Wilson, H. W. Coleman, and E. G. Paterson, "Comprehensive approach to verification and validation of CFD simulations," Journal of Fluids Engineering, vol. 122, no. 4, pp. 803–810, 2000.
[8] J. Zhou, Y. Ren, and Q. Wei, "Unsteady turbulence behavior of the wake region of a submarine," Ocean Engineering, vol. 172, pp. 563–574, 2019.
[9] Z. Yang, C. Wen, and G. Xu, "Wall-modeled large-eddy simulation of turbulent flows past axisymmetric hulls," Physics of Fluids, vol. 29, no. 3, p. 035107, 2017.
[10] J. Krátik, “CFD Simulation of Air Flow Over an Object with Gable Roof, Revised with Y+ Approach,” Transactions of the VŠB - Technical University of Ostrava, Civil Engineering Series, vol. 16, no. 2, Dec. 2016
[11] International Towing Tank Conference (ITTC), Uncertainty Analysis in CFD Verification and Validation, Methodology and Procedures, ITTC Quality System Manual, 7.5-03-01-01, Revision 04, 2021.
[12] H.-L. Liu and T. T. Huang, Summary of DARPA Suboff Experimental Program Data, CRDKNSWC/HD-1298-11, Naval Surface Warfare Center, Carderock Division, Jun. 1998.