Hydraulic and structural evaluation of concrete connecting joints within the seawater exchange flow paths of precast block breakwater

국문 초록 (Abstract)

본 연구는 복수의 프리캐스트 콘크리트 블록으로 연결되는 블록식 해수소통형 방파제의 수리 성능, 구조 안전성 및 안정성을 평가하고, 해수소통구가 없는 일반 케이슨 방파제와 성능을 비교하였으며, 해수소통구 형성을 위해 개발된 연결부 기둥의 단면력을 평가하였다. STAR-CCM+ 기반 2차원 수치파동수조를 구축하고 VOF 기법을 적용하여 파랑 전파와 파–구조물 상호작용을 해석하였다. 연결부 주변의 복잡한 내부 유동 특성을 계산 효율적으로 반영하기 위해, Forchheimer형 압력 손실 관계에 기반한 다공성 배플을 이용하여 연결부 저항을 등가화하는 차원축소 기법을 적용하였다. 유체해석 모델은 2차원 수리모형실험의 규칙파 3케이스, 불규칙파 3케이스 조건에서 수위 시간이력과 입사파 재현성을 비교하여 검증하였다. 검증된 유체해석 결과를 이용해 전달율·반사율을 산정하였으며, 입·반사파 분리는 Mansard and Funke 기법을 데이터 처리 단계로 적용하였다.
구조 성능 평가는 Abaqus/Explicit 기반 3차원 유한요소모델을 이용하여 연결부 기둥의 직경, 해수소통공간 깊이, 기울기 각도를 주요 변수로 한 변수 해석을 수행하여 적정 연결부 형상을 도출하였다. 또한 유체해석에서 산정된 파압을 구조모델에 단방향 결합(one-way coupling) 방식으로 적용하여 실규모 안전성·안정성 평가를 수행하였다. 안정성은 지반–구조물 마찰 모델을 포함하여 활동 및 전도 거동을 검토하였고, 안전성은 원형 기둥 연결부를 보 요소(beam element)로 모델링하여 축력·전단력·휨모멘트 단면력을 산정하였다. 연결부에 해수가 소통하며 연결부 기둥에 전달되는 추가 외력은 유체해석 유속을 이용한 Morison 식으로 평가하였다. 최종적으로 KDS 14 20 64(구조용 무근콘크리트 설계기준) 기준에 따라 단면력 요구와 설계강도를 비교하여 구조 안전성을 검토하였다.
해석 결과, 블록식 해수소통형 방파제는 동일 파조건에서 해수소통구가 없는 일반적인 케이슨 대비 파랑에 의한 요구가 감소하는 경향을 보였으며, 보수적 하중 조건에서도 제시한 연결부 기둥은 설계기준 대비 충분한 안전 여유를 확보하였으며, 기둥 지름 선정에 대한 합리적인 개선 방향을 제시하였다. 또한 해수소통 성능과 연결부 구조 성능, 그리고 연결부 제원 및 해수소통공간 깊이 선정 간의 상충 관계를 정량적으로 확인하였으며, 복잡한 외력 조건하에서 해수소통구 내부 프리캐스트 연결부 기둥의 외력 산정 및 구조해석을 위한 효과적인 방법론을 제시하였다.

다국어 초록 (Multilingual Abstract)

This study evaluates the hydraulic performance, structural safety, and stability of a block-type seawater exchange breakwater assembled with multiple precast concrete blocks, and compares its performance with a conventional caisson-type breakwater without seawater exchange openings. Particular attention is given to the column connecting joint developed to form the seawater exchange opening, where concentrated loads may occur due to wave pressure and flow velocity in the structurally open configuration.
A two-dimensional numerical wave tank was developed using STAR-CCM+, and the Volume of Fluid (VOF) method was applied to simulate wave propagation and wave–structure interaction. To efficiently represent the complex internal flow behavior around the column connecting joint, a dimensional reduction technique was adopted by equivalently modeling the joint resistance using a porous baffle based on a Forchheimer-type pressure-loss relationship. The CFD model was validated against the 2D flume test by comparing free-surface elevation time histories and incident-wave reproducibility under six wave conditions (three regular and three irregular cases). Using the validated CFD results, the transmission and reflection coefficients were evaluated, and incident–reflected wave separation was applied as a data-processing step based on the method of Mansard and Funke.
Structural performance was assessed using a three-dimensional finite element model developed in Abaqus/Explicit, where a parametric study was conducted to determine an appropriate column connecting joint configuration by varying the column diameter, seawater flow-path depth, and inclination angle. In addition, a full-scale safety and stability evaluation was performed by applying CFD-derived wave pressures to the structural model through a one-way coupling approach. Stability was examined in terms of sliding and overturning behavior by incorporating a seabed–structure friction model, while structural safety was evaluated by modeling the column connecting joints using beam elements and extracting the maximum axial force, shear force, and bending moment. The additional hydrodynamic forces acting on the column connecting joints due to seawater flow through the opening were evaluated using the Morison equation with CFD velocity data. Finally, structural safety was reviewed by comparing required sectional forces under the evaluated wave conditions with the corresponding design strengths calculated in accordance with KDS 14 20 64 (Design Standard for Plain Concrete Structures).
The results indicate that the block-type seawater exchange breakwater tends to reduce wave-induced load effects compared with the conventional caisson-type breakwater under the same wave conditions. Even under conservative loading scenarios, the proposed column connecting joints provided sufficient safety margins relative to the design criteria, and a rational direction for improving diameter selection was identified. The study also quantified the trade-off between seawater exchange performance and the structural performance of the column connecting joint, particularly with respect to selecting the flow-path depth and joint geometry. Overall, this work presents an effective methodology for estimating hydrodynamic loads and conducting structural analysis of column connecting joints located inside seawater exchange openings under complex wave-loading conditions.

목차 (Table of Contents)

• Contents
• List of Tables ⅲ
• List of Figures ⅳ
• Abstract ⅵ
• 1. Introduction 1
• 1.1 Background and Motivation 1
• 1.2 Objectives and Scope 3
• 1.3 Thesis Organization 4
• 2. Literature Review 5
• 2.1 Numerical Methodologies 5
• 2.1.1 Governing Equations and Time Integration 5
• 2.1.2 Free-Surface and Multiphase Formulation 6
• 2.1.3 Wave Generation 6
• 2.1.4 Turbulence Modeling 7
• 2.1.5 Dimensional Reduction Method 9
• 2.2 Reflection and Transmission Analysis Method 9
• 2.2.1 Incident-Reflected Wave Separation Method 9
• 2.2.2 Reflection and Transmission Coefficients 10
• 2.3 Material Modeling for Structural Analysis 11
• 2.3.1 Concrete Damaged Plasticity Model 11
• 2.3.2 Contact and Friction Modeling 15
• 3. CFD Model Development and Validation 16
• 3.1 CFD Modeling Frameworks 16
• 3.2 Validation with 2D Wave Flume Test 21
• 3.2.1 2D Flume Test Setup 25
• 3.2.2 Reflection and Transmission Coefficients 28
• 3.3 CFD for Structural Loading 33
• 4. 3D FEM of the Connecting Joint 35
• 4.1 3D FEM Model and Joint Geometry 35
• 4.2 Concrete Material Model and Fracture Energy 36
• 4.3 Parametric Study for Connecting Joint 36
• 4.4 Selection of Baseline Configuration for Connecting Joint 42
• 5. FEM–CFD Coupled Safety and Stability 43
• 5.1 Coupled Evaluation Frameworks 43
• 5.2 One-Way Coupling and Load Application 44
• 5.3 Stability under Wave Loading 45
• 5.4 Safety of the Connecting Joint 47
• 5.5 Comparison of 2D Beam Model Results with 3D Damage Analysis Results 50
• 6. Evaluation of Structural Loads and Sectional force 52
• 6.1 Structural Loads and Morison Forces 52
• 6.2 Sectional Force Response of the connecting joint 52
• 6.3 Additional Diameter Evaluation and P–M Interaction Analysis 54
• 6.4 Safety of the Water Blocking Wall 57
• 7. Conclusions and Further Study 59
• 7.1 Conclusion 59
• 7.2 Further Study 62
• Reference 63
• 초록 69