Structural Assessment of Unmanned Aircraft with Collision Risks: Uncertainty Quantification and Propagation in Composite Materials and Stochastic Loads = 충돌 위험을 고려한 무인 항공기 구조 평가: 복합재 및 확률론적 하중에 대한 불확실성 정량화 및 전파

다국어 초록 (Multilingual Abstract)

This dissertation presents an integrated framework that systematically captures and propagates uncertainties in advanced composite materials and aerodynamic loads to assess the structural reliability of unmanned aircraft. The research introduces a novel combination of R-vine copula modeling, Sparse Polynomial Chaos Expansion (SPCE), and Bayesian inference to quantify composite material variability from the microstructural level to full-scale laminate properties.
For loads with inherent uncertainties, the proposed finite element analysis (FEA) strategy models element-level aerodynamic loads using Gaussian Random Fields (GRFs) that reflect probability distributions and spatial correlations. This approach enables the integration of deterministic safety factors with stochastic load modeling, ultimately deriving failure probabilities and failure rates for critical maneuvers, which form the basis for structural reliability assessments aligned with airworthiness standards.
Furthermore, the framework includes a dynamic impact analysis for bird strike scenarios using Smoothed Particle Hydrodynamics (SPH), enabling a precise representation of localized, high-intensity pressure effects on overall structural integrity. In addition, a design strategy is proposed that selectively reduces safety factors for primary and secondary structures under combined dynamic impact and maneuvering conditions, thereby achieving structural weight reduction while still satisfying airworthiness requirements.
The proposed framework was validated using a full-scale unmanned aircraft model, where it defined and quantified the uncertainties and variabilities in both composite materials and loads, thus demonstrating high performance, computational efficiency, and strong potential for industrial application. Ultimately, this dissertation presents an integrated methodology for unmanned aircraft assessment that is structurally reliable, efficient, and compatible with airworthiness certification frameworks.

국문 초록 (Abstract)

본 학위논문은 복합재료 및 공력 하중에 내재된 불확실성을 체계적으로 정의하고 전달하여 무인항공기의 구조 신뢰성을 평가할 수 있는 통합 프레임워크를 제시한다. 본 연구는 R-vine 코퓰라(copula) 모델링, 희소 다항 혼돈 전개 (Sparse Polynomial Chaos Expansion, SPCE), 그리고 베이지안 추론을 결합한 새로운 방법론을 도입하여, 복합재의 변동성을 미세 구조 스케일부터 항공기 전기체 수준까지 정량화한다. 불확실성을 갖는 하중에 대해 제안된 유한요소해석 전략에서는, 요소 수준의 공기역학적 하중이 사전 정의된 확률 분포와 공간 상관성을 반영하는 가우시안 랜덤 필드(Gaussian Random Field, GRF)를 사용하여 모델링된다. 이러한 접근은 결정론적 안전 계수와 확률론적 하중 모델링을 통합할 수 있게 하며, 이를 통해 주요 기동 조건에 대한 파손 확률과 고장률을 도출하고, 이는 감항 기준에 부합하는 구조 신뢰성 평가의 근거로 활용된다.
또한, 본 프레임워크는 조류 충돌 시나리오에 대한 동적 충격 해석을 평활입자동역학법(Smoothed Particle Hydrodynamics, SPH)을 이용하여 포함하고 있으며, 이를 통해 국소적인 고강도 압력 하중이 전체 항공기 구조 건전성에 미치는 영향을 정밀하게 반영한다. 더불어, 동적 충격과 기동 조건이 복합적으로 작용하는 상황을 고려하여, 주구조 및 부구조에 대한 안전 계수를 선택적으로 저감함으로써 감항 요건을 만족하면서도 구조 중량의 절감을 달성할 수 있는 설계 전략을 제안한다.
제안된 프레임워크는 전기체 규모의 무인항공기 모델을 통해 검증되었으며, 복합재와 하중의 불확실성 및 변동성을 정의하고 이들을 정량화하는데에 있어 높은 성능과 계산 효율성, 그리고 산업적 적용 가능성을 입증하였다. 궁극적으로 본 논문은 구조적으로 신뢰할 수 있고 효율적이며, 감항 인증 체계와 연계 가능한 무인항공기 평가를 위한 통합적 방법론을 제시한다.

목차 (Table of Contents)

• Abstract iv
• List of Contents vi
• List of Figures x
• List of Tables xv
• Chapter 1. Introduction 1
• 1.1. Background 1
• 1.2. Literature review 4
• 1.3. Aims and scope 13
• 1.4. Outline of dissertation 16
• Chapter 2. Multiscale Probabilistic Framework for Uncertainty Quantification in Composite Material 20
• 2.1. Multiscale Dependency Characterization via R-vine Copula 20
• 2.1.1. Fundamentals of Copula 20
• 2.1.2. R-vine Copula Structure and Conditional Dependency Modeling 30
• 2.1.3. High-dimensional Conditional Copula Modeling via Gaussian Mixture Model 40
• 2.2 Uncertainty Propagation via SPCE and Bayesian approaches 46
• 2.2.1 Sparse Polynomial Chaos Expansion (SPCE) for Uncertainty Propagation 46
• 2.2.2. Bayesian Approaches for Probabilistic Model Definition 53
• 2.3. Application of Multiscale Uncertainty Propagation Framework to Composite Material 55
• 2.3.1 Uncertainty Propagation of Composite Material Properties for Unmanned Aircraft 55
• 2.3.2 Comparative Performance Analysis: SPCE-based vs. Traditional Methods 70
• Chapter 3. Probabilistic Modeling and Uncertainty Quantification of Loads for Unmanned aircraft 77
• 3.1. Key Maneuvers and Aerodynamic Load Profiles 78
• 3.1.1. Critical Flight Maneuvers and Aerodynamic Loads 78
• 3.2. Hybrid Deterministic-Probabilistic Framework for Uncertainty Quantification of Loads 82
• 3.2.1. Load Uncertainty Quantification using Finite Element Model 82
• 3.2.2. Gaussian Random Field-Based Spatial Correlation Modeling of Loads 84
• 3.2.3. Hybrid Deterministic–Probabilistic Modeling of Load Uncertainty via FEM and GRFs 87
• Chapter 4. Probabilistic Structural Reliability Assessment under Flight Maneuvers 90
• 4.1. Structural Analysis Model and Airworthiness Evaluation Criteria Construction 91
• 4.1.1. Structural Analysis Model of Unmanned Aircraft for Finite Element Method 91
• 4.1.2. Airworthiness Requirements and Structural Evaluation Framework 100
• 4.2. Structural Analysis with Hybrid Deterministic–Probabilistic method under Key Flight Maneuvers 117
• 4.2.1. Structural Response in Critical Flight Envelopes 117
• 4.2.2. Key Maneuver with Integrated Method and Safety Factor 1.5 123
• Chapter 5. Impact Assessment and Structural Response Under Bird Strike Events 132
• 5.1. Bird Strike Modeling and Simulation Framework 133
• 5.1.1. Overview of Bird Strike Phenomena for Aircraft 133
• 5.1.2. Bird Model and Equation of State for SPH 135
• 5.2. Structural Analysis Results Under Bird Strike Scenarios 147
• 5.2.1. Bird Strikes under Take-off and landing Phases of Flight 147
• 5.2.2. Bird-strike applying Integrated method with Safety factor 1.5 152
• Chapter 6. Weight Reduction for Unmanned Aircraft 158
• 6.1. Adjusted Safety Factors in Non-Primary Structures of Unmanned Aircraft 158
• 6.1.1. Adjusted safety factor and Primary/Secondary Structures 158
• 6.1.2. Structural Analysis of Weight-Reduced Aircraft 164
• 6.1.3. Weight Reduction Measures for Unmanned Aircraft Structures 168
• Chapter 7. Conclusion 172
• 7.1. Summary 172
• 7.2. Contributions 175
• 7.3. Limitations and Future Works 178
• References 182
• 국문초록 191