Numerical Simulation of Free-end Effects on Local Scour Around a Full-scale Subsea Hydrogen Storage Accumulator

Abstract

Green hydrogen production is an emerging pathway aimed at substituting the exploitation of offshore renewable energies and ultimately resulting in the decarbonization of global economies. Large-scale hydrogen storage is a critical link in achieving this. Subsea hydrogen storage provides several advantages over conventional storage, such as near-isothermal and isobaric conditions. However, local scour around the subsea hydrogen storage accumulator may degrade the stability of anchoring. In this study, the local scour characteristics around low-aspect-ratio subsea hydrogen storage accumulators with different free ends, namely flat tip (FT), tip with filleted edges (FET), and approximate hemispherical tip (AHT), are investigated. The numerical simulation of the interaction between accumulators, ocean currents, and the seabed is conducted using the large eddy simulation (LES) model and the sediment scour model. The shapes of scour pits around the three accumulators, the scour time history in different directions, and the spatial distribution of the scour depth are compared and analyzed. The equilibrium scour depth and characteristic time scale are quantified. The results indicate that the shapes of the scour pits around the three accumulators exhibit a horseshoe distribution. The scour processes and spatial distributions of sediment in different directions revealed certain differences between the sediment scour and accumulation processes, but the scour change trends are relatively consistent. The flow diagram of the transient scour shows that the horseshoe vortex has the smallest influence range upstream of the AHT accumulator, but the downstream downwash flow is highly significant. The equilibrium scour depths of the three accumulators are −0.49 (FT), −0.41 (FET) and −0.35 (AHT), respectively, and the scour characteristic time scale gradually increases. These results illustrate that the design of the AHT accumulator has an inhibitory effect on local scour. The scour depth corresponding to the characteristic time scales of the three accumulators can reach 60%–65% of the equilibrium scour depth.

Keywords

Local scour / Free end / Subsea hydrogen storage / Sediment transport / Numerical simulation / Renewable energy

References

[1] Chen B, Li S. Experimental study of local scour around a vertical cylinder under wave-only and combined wave-current conditions in a large-scale flume. Journal of Hydraulic Engineering, 2018, 144(9): 04018058.

[2] Dey S, Raikar RV, Roy A. Scour at submerged cylindrical obstacles under steady flow. Journal of Hydraulic Engineering, 2008, 134(1): 105-109.

[3] Dey S, Sumer BM, Fredsge J. Control of scour at vertical circular piles under waves and current. Journal of Hydraulic Engineering, 2006, 132(3): 270-279.

[4] Hu K, Bai X, Vaz MA. Numerical simulation on the local scour processing and influencing factors of submarine pipeline. Journal of Marine Science and Engineering, 2023, 11(1): 234.

[5] Imberger J, Alach D, Schepis J. Scour behind circular cylinders in deep water. 18th International Conference on Coastal Engineering, Cape Town, South Africa, 19821522-1554

[6] Kim YJ, Lee DY, Kim DH. Risk assessment of offshore wind turbine support structures considering scouring. Journal of Korean Society of Coastal and Ocean Engineers, 2020, 32(6): 524-530.

[7] Li D, Zheng Z, Hu Z, Ma H. Microscopic investigation of shape effect on local scour around the monopile using CFD-DEM. Computers and Geotechnics, 2025, 177: 106872.

[8] Liu Q, Wang Z, Zhang N, Zhao H, Liu L, Huang K, Chen X. Local scour mechanism of offshore wind power pile foundation based on CFD-DEM. Journal of Marine Science and Engineering, 2022, 10(11): 1724.

[9] Lyu X, Cheng Y, Wang W, An H, Li Y. Experimental study on local scour around submerged monopile under combined waves and current. Ocean Engineering, 2021, 240: 109929.

[10] Ma H, Zhang S, Li B, Huang W. Local scour around the monopile based on the CFD-DEM method: Experimental and numerical study. Computers and Geotechnics, 2024, 168: 106117.

[11] Mastbergen DR, Berg JHVD. Breaching in fine sands and the generation of sustained turbidity currents in submarine canyons. Sedimentology, 2003, 50(4): 625-637.

[12] Melville BW, Chiew YM. Time scale for local scour at bridge piers. Journal of Hydraulic Engineering, 1999, 125: 59-65.

[13] Meyer-Peter E, Müller R. Formulas for bed-load transport. Proceedings of the 2nd Meeting of the International Association for Hydraulic Structures Research, Delft, Netherland, 194839-64

[14] Petersen TU, Sumer BM, Fredsøe J. Time scale of scour around a pile in combined waves and current. International Conference on Coastal Engineering, 2012, 30(8): 981-988

[15] Qu L, An H, Draper S, Watson P, Zhao M, Harris J, Whitehouse R, Zhang D. A review of scour impacting monopiles for offshore wind. Ocean Engineering, 2024, 301: 117385.

[16] Ramakrishnan S, Delpisheh M, Convery C, Niblett D, Vinothkannan M, Mamlouk M. Offshore green hydrogen production from wind energy: Critical review and perspective. Renewable and Sustainable Energy Reviews, 2024, 195: 114320.

[17] Sarkar A. Scour and flow around submerged structures. Water Management, 2014, 167(2): 65-78

[18] Sheppard DM, Odeh M, Glasser T. Large scale clear-water local pier scour experiments. Journal of Hydraulic Engineering, 2004, 130(10): 957-963.

[19] Soulsby R. Dynamics of marine sands: A manual for practical applications, 1997, London. Thomas Telford Ltd.

[20] Su X, Chen J, Yuan L, Xu W, Xiong C, Wang X. Current status of development and application of ocean renewable energy technology. Sustainability, 2025, 17(12): 5648.

[21] Sumner D. Flow above the free end of a surface-mounted finite-height circular cylinder: A review. Journal of Fluids and Structures, 2013, 43: 41-63.

[22] Tsutsui T, Kawahara M. Heat transfer around a cylindrical protuberance mounted in a plane turbulent boundary layer. Journal of Heat and Mass Transfer, 2006, 161: 153-161

[23] Tu W, Shu D, Gu X, Cheng X, He Y, Ren S. Effect of scour-hole dimensions on the failure mechanism of suction caisson for offshore wind turbine in clay. Ocean Engineering, 2025, 320: 120320.

[24] van Rijn, Leo C. Sediment transport, part I: Bed load transport. Journal of Hydraulic Engineering, 1984, 110(10): 14311456.

[25] Wang H, Wang Z, Liang C, Carriveau R, Ting DSK, Li P, Cen H, Xiong W. Underwater compressed gas energy storage (UWCGES): current status, challenges, and future perspectives. Applied Sciences, 2022, 12(18): 9361.

[26] Wang H, Wang Z, Ting DSK, Carriveau R, Sant T, Xiong W. Structural strength and fatigue analyses of large-scale underwater compressed hydrogen energy storage accumulator. Marine Structures, 2024, 98: 103684.

[27] Wang Q, Pan L. Study on floating offshore wind power hydrogen production and hydrogen production ship. 2022 IEEE International Conference on Artificial Intelligence and Computer Applications (ICAICA), Dalian, China, 2022899-905

[28] Wang Z, Wang H, Sant T, Zhao Z, Carriveau R, Ting DSK, Li P, Xiong W. Subsea energy storage as an enabler for floating offshore wind hydrogen production: Review and perspective. International Journal of Hydrogen Energy, 2024, 71: 1266-1282.

[29] Yagmur S, Dogan S, Aksoy MH, Goktepeli I. Turbulence modeling approaches on unsteady flow structures around a semicircular cylinder. Ocean Engineering, 2020, 200: 107051.

[30] Yao W, An H, Draper S, Cheng L, Harris JM. Experimental investigation of local scour around submerged piles in steady current. Coastal Engineering, 2018, 142: 27-41.

[31] Yao W, Draper S, An H, Cheng L, Harris JM, Whitehouse RJ. Experimental study of local scour around submerged compound piles in steady current. Coastal Engineering, 2021, 165: 103831.

[32] Zhang Q, Draper S, Cheng L, An H. Time scale of local scour around pipelines in current, waves, and combined waves and current. Journal of Hydraulic Engineering, 2017, 143(4): 04016093.

[33] Zhang S, Li B, Ma H. Numerical investigation of scour around the monopile using CFD-DEM coupling method. Coastal Engineering, 2023, 183: 104334.

[34] Zhang W, Zapata MU, Bai X, Pham-Van-Bang D, Nguyen KD. Three-dimensional simulation of horseshoe vortex and local scour around a vertical cylinder using an unstructured finite-volume technique. International Journal of Sediment Research, 2020, 35(3): 295-306.

[35] Zhao M. A comprehensive review of the research on local scour below subsea pipelines under steady currents and waves. Ocean Engineering, 2025, 318: 120114.

[36] Zhao M, Cheng L, Zang Z. Experimental and numerical investigation of local scour around a submerged vertical circular cylinder in steady currents. Coastal Engineering, 2010, 57(8): 709-721.

[37] Zhao X, Chen X, Sui S, Deng W, Shen K. Experimental study of local scour around bucket foundation in sand. Ocean Engineering, 2023, 286: 115482.

[38] Zhi Y. Large-eddy simulation: Past, present and the future. Chinese Journal of Aeronautics, 2015, 28(1): 11-24.

[39] Zhu C, Wu W, Liu X, Liu H, Hu R, Yu P. Experimental study of structure dimensions effects on local scour of submerged compound suction anchor foundation. Ocean Engineering, 2024, 294: 116742.

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