Dynamic response analysis of multi-module floating concrete platforms under wave loading

다국어 초록 (Multilingual Abstract)

This study investigates the dynamic response characteristics of multi-module floating concrete platforms under wave loading and clarifies how connection conditions and structural geometry influence motions and internal loads. Both a single-module (N1) configuration and hinge -connected modular assemblies were considered. Key parameters included the number of subdivisions, structural height and wall thickness, incident wavelength, and connection conditions. Hydrodynamic responses were computed using linear potential-flow analysis in ANSYS AQWA. System-level behavior was assessed by jointly examining connector reactions (axial force, shear force, and moment) and global motions, with particular attention to the global pitch response to identify dominant behaviors and sensitive period bands. Where necessary, response indicators were organized with reference to a structural analysis model, and the observed trends were also compared under irregular-wave conditions. The results show that structural subdivision with hinge connections alters the global bending-type behavior and local response concentrations relative to the monolithic case, and that the global pitch response is closely associated with variations in connector loads. As the number of modules increased, the period at which the global pitch response reached its maximum tended to shift toward shorter periods.For highly subdivided cases, modal density and coupling led to multiple local response peaks rather than a single dominant peak. To compare the efficiency of structural subdivision, an efficiency index was defined as the product of the maximum stress and the structural volume and then normalized with respect to the single-module (N1) case. Using this metric, the efficiency index was evaluated as 0.5775 for the 4-module (N4) assembly and 0.9 for the 16-module (N16) assembly. The relatively high value in the 16-module (N16) configuration is mainly due to stress concentration at the connections, which increases as the module size decreases when a single hinge is used. Using multiple hinges or a linear hinge connection can reduce stress concentration and improve the efficiency index. The findings provide useful guidance for understanding response mechanisms and for developing subdivision and connector-design strategies for hinge-connected modular floating concrete platforms.

국문 초록 (Abstract)

본 연구는 파랑하중을 받는 다중 모듈 부유식 콘크리트 플랫폼의 동적 응답 특성을 수치해석 기법을 이용하여 평가하고, 모듈을 연결해 주는 연결부 조건 및 모듈 구조 형상이 운동 응답과 내부 하중에 미치는 영향을 검토하는 것을 목적으로 한다. 대상 구조는 단일 모듈과 다중 모듈 연결로 구성하였으며, 모듈 분할 수, 구조 높이 및 벽체 두께, 입사 파장길이 그리고 연결 조건을 주요 변수로 설정하였다. 수리응답은 ANSYS AQWA 기반 선형 포텐셜 이론을 이용해 산정하였고, 연결부 반력(축력, 전단력, 모멘트)과 전역 운동을 함께 검토하여 시스템 수준의 지배 거동과 민감 주기대를 식별하였다. 또한 필요 시 구조 해석 모델과의 연계를 통해 확인 지표를 정리하고, 불규칙파 조건에서도 결과를 비교하였다. 해석 결과, 힌지 연결을 포함한 분할 구조는 일체형 대비 연결부 응력 집중과 글로벌 굽힘 거동이 변화하며, 운동 성분 중 전역 피치가 연결부 하중 변화와 밀접하게 연계됨을 확인하였다. 특히 모듈 분할 수가 증가할수록 전역 피치 응답의 최대가 나타나는 주기가 단주기 방향으로 이동하는 경향이 관찰되었으며, 다 분할에서는 모드 밀집 및 결합에 의해 응답 피크가 다중화되는 특성이 나타났다. 구조 분할의 효율성을 비교하기 위해 최대 응력과 구조 체적의 곱으로 효율 지수(efficiency index)를 정의하고, 이를 단일 모듈 조건을 기준으로 정규화하였다. 해당 지표에 따르면 4모듈 조립체의 효율 지수는 0.5775, 16모듈 조립체는 0.9로 평가되었다. 16모듈 구성에서 효율 지수가 상대적으로 크게 나타난 주요 원인은 연결부에서의 응력 집중이며, 단일 힌지를 적용할 경우 모듈 크기가 감소할수록 이 응력 집중이 증가하는 경향을 보였다. 향후 다중 힌지 또는 선형(연속) 힌지 연결을 적용하면 응력 집중을 완화하여 효율 지수를 개선할 수 있을 것으로 판단된다.

목차 (Table of Contents)

• List of Tables ⅳ
• List of Figures ⅴ
• ABSTRACT· ⅶ
• 1. Introduction 1
• 1.1 Background and motivation 1
• 1.2 Objectives 3
• 1.3 Methodology and thesis organization 4
• 2. Literature Review 6
• 2.1 Overview of literature review 6
• 2.2 The evolution of VLFS research 6
• 2.3 Recent studies on modular multi-body floating systems 7
• 2.4 Connector loads and performance characteristics 8
• 2.5 The gap-flow and gap-resonance 9
• 2.6 Application of modular floating structures 10
• 3. Research Methodology and Theoretical Background 11
• 3.1 Research methodology 11
• 3.2 Theoretical background 12
• 3.2.1 Hydrodynamic model (ANSYS AQWA, BEM) 12
• 3.2.2 Structural model (ANSYS Mechanical, shell‐element representation) · 15
• 3.2.3 Hydrodynamic pressure Add-on (ANSYS Workbench) 18
• 3.2.3.1 Evaluation of hydrodynamic pressure on wetted surfaces 18
• 3.2.3.2 Hydrostatic pressure contribution 19
• 3.2.3.3 Morison loads on submerged line bodies 19
• 3.2.3.4 Mapping of pressures and line forces to the structural model 20
• 3.2.3.5 Mass and inertia consistency and application of accelerations 21
• 3.2.3.6 Governing structural equation with hydrodynamic Add-on loads ·· 21
• 3.3 Analytical model 22
• 3.3.1 Determination of grid size 22
• 3.2.2 Mooring line setting 24
• 3.4 Verification of developed analytical model 28
• 3.4.1 Experimental motion behavior of a floating structure 28
• 3.4.2 Experimental connection loads of a floating structure 31
• 4. Evaluate the Dynamic Response Characteristics of Floating Concrete Platforms under Various Conditions 34
• 4.1 Analysis model setup 34
• 4.1.1 Modular subdivision of the platform and inter-module connections · 34
• 4.1.2 Model shape condition 35
• 4.1.3 Wave conditions 37
• 4.2 Obtained results from AQWA 41
• 4.2.1 Hydrostatic suitability results 41
• 4.2.2 Effect of water depth on structural response 43
• 4.2.3 Frequency-domain response evaluation 45
• 4.2.4 Global motion assessment of a hinge-connected multi-module system 54
• 4.2.5 Maximum heave along the length of the structures 56
• 4.2.6 Effect of wavelength on structural response 64
• 4.2.7 Effect of number of module divisions on structural response 71
• 4.3 Obtained results from structural analysis 73
• 4.3.1 Obtained maximum moment 76
• 4.3.2 Obtained maximum stress 80
• 4.3.4 Obtained axial force on hinge joints 84
• 5. Effect of Connection Stiffness and Damping on Dynamic Response 87
• 5.1 Determination of connection stiffness and damping for parametric study 87
• 5.2 Results of parametric study on connection 88
• 5.2.1 Hydrodynamic result 88
• 5.2.2 Results of structrual analysis 95
• 5.2.3 Effect of module subdivision considering connection stiffness and damping 99
• 5.2.4 Obtained results under irregular wave conditions 100
• 6. Conclusion and Future Work 102
• 6.1 Conclusion 102
• 6.2 Future work 105
• References 106
• Abstract 113