Detection of Communities within the Multibody System Dynamics Network and Analysis of Their Relations

Multibody system dynamics is already a well developed branch of theoretical, computational and applied mechanics. Thousands of documents can be found in any of the well-known scientific databases. In this work it is demonstrated that multibody system dynamics is built of many thematic communities. Using the Elsevier’s abstract and citation database SCOPUS, a massive amount of data is collected and analyzed with the use of the open source visualization tool Gephi. The information is represented as a large set of nodes with connections to study their graphical distribution and explore geometry and symmetries. A randomized radial symmetry is found in the graphical representation of the collected information. Furthermore, the concept of modularity is used to demonstrate that community structures are present in the field of multibody system dynamics. In particular, twenty-four different thematic communities have been identified. The scientific production of each community is analyzed, which allows to predict its growing rate in the next years. The journals and conference proceedings mainly used by the authors belonging to the community as well as the cooperation between them by country are also analyzed

Rotorcraft aeroelastic stability

Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low-frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability in hover and forward flight, and analysis of tilt-rotor dynamic stability are considered. Results of parametric investigations of system behavior are presented, and correlation between theoretical results and experimental data from small and large scale wind tunnel and flight testing are discussed

Survey of Army/NASA rotorcraft aeroelastic stability research

Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability are considered. Results of parametric investigations of system behavior are presented, and correlations between theoretical results and experimental data from small- and large-scale wind tunnel and flight testing are discussed

An analytically linearized helicopter model with improved modeling accuracy

An analytically linearized model for helicopter flight response including rotor blade dynamics and dynamic inflow, that was recently developed, was studied with the objective of increasing the understanding, the ease of use, and the accuracy of the model. The mathematical model is described along with a description of the UH-60A Black Hawk helicopter and flight test used to validate the model. To aid in utilization of the model for sensitivity analysis, a new, faster, and more efficient implementation of the model was developed. It is shown that several errors in the mathematical modeling of the system caused a reduction in accuracy. These errors in rotor force resolution, trim force and moment calculation, and rotor inertia terms were corrected along with improvements to the programming style and documentation. Use of a trim input file to drive the model is examined. Trim file errors in blade twist, control input phase angle, coning and lag angles, main and tail rotor pitch, and uniform induced velocity, were corrected. Finally, through direct comparison of the original and corrected model responses to flight test data, the effect of the corrections on overall model output is shown

유격을 고려한 무미익 초소형 날갯짓 비행체 통합 설계: 기하분석 및 수치 해석을 통한 접근

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 협동과정 우주시스템 전공, 2021. 2. 신상준.Unlike birds, an insect type tailless flapping wing does not possess tail wings. Therefore, insect type flapping wing may be fabricated in small size and of decreased weight. Because of the taillessness, however, stable flight of an insect type flapping wing depends only on main wings. Thus, a number of researches were conducted regarding its control mechanisms. In this thesis, the trailing edge control, one of the methods developed to produce control moments, is adopted. Such method requires additional shafts that connect the root of the main wing and control mechanism, and the shafts are rotated to deform the wing shape. In this manner, asymmetric aerodynamic forces are produced. The control mechanism uses micro actuators for compact design. However, small size of the micro actuator gearbox causes relatively large backlash and the resulting free play of the main wings that generates undesirable aerodynamic forces. Under such circumstance, design improvement of the control mechanism is conducted to minimize the effects of the free play. First, geometry analysis is performed to investigate the factors that cause the free play. Control mechanism design for the minimized free play is obtained. Then, three-dimensional computer aided design (CAD) of modified configuration is drawn, and kinematic simulations are conducted by RecurDyn to determine the prevention of interference. Finally, the feasibility of modified design is examined by the numerical simulation. The main wings are modeled by the displacement-based geometrically exact beam model combined with cross-sectional analysis. To mimic the free play appropriately, the spring elements are attached to the joints. At the same time, two-dimensional unsteady aerodynamic model is used for aerodynamic forces. Consequently, the reasonable control moments are gathered in terms of the maneuverability.곤충 모방형 날갯짓 비행체는 꼬리날개가 없기 때문에 새 모방형 날갯짓 비행체와 비교하여 가볍고 작게 설계될 수 있다. 그러나, 곤충 모방형 날갯짓 비행체는 꼬리날개가 없다는 특징으로 인하여, 오직 두 날개만을 이용하여 조종력을 발생시킨다. 따라서, 이에 대한 많은 연구가 수행되었고 개발된 여러 자세 제어 방법 중 본 학위 논문에선 날개 끝단 비틀림을 이용한 자세 제어 장치를 다룬다. 해당 방법은 주날개의 뿌리 부분을 자세 제어 장치와 연결하고 이를 회전시켜 날개 끝단에 변형을 발생시킨다. 자세 제어 장치에는 경량화를 위하여 가볍고 작은 장비들이 사용된다. 그러나, 자세 제어 장치 제작에 사용되는 초소형 구동기는 작은 크기로 인하여 내부 기어에 백래시를 갖고 있다. 따라서, 이는 주날개의 불필요한 유격을 발생시킬 수 있다. 이러한 유격은 주날개의 진동으로 이어져, 불필요한 비대칭적 공력을 발생시킬 수 있다. 이러한 상황 때문에 유격이 최소화된 자세 제어 장치 설계를 수행하였다. 첫째로, 기하학적 해석을 통하여 유격에 영향을 주는 요인을 파악하였다. 이를 통하여 유격을 최소화한 설계를 도출하였으며, 3차원 computer aided design (CAD) 형상과 RecurDyn을 이용하여 동역학적 해석을 수행하였다. 이를 통하여 자세 제어 장치의 구동 중 발생하는 간섭을 확인하였다. 최종적으로, 수치적 시뮬레이션을 이용하여 개선된 자세 제어 장치의 타당성을 확인하였다. 이때, 주날개는 변위 기반 기하학적 정밀 보로 모델링 되었으며, 2차원 단면 해석 결과를 사용하여 해석을 수행하였고 공력 모델은 2차원 비정상 모델을 사용하였다. 또한, 유격을 모사하기 위하여 스프링 요소를 관절에 삽입하여 해석을 수행하였다. 결과적으로, 본 연구에서 설계한 자세 제어 장치가 유효한 조종력을 발생시키는 것을 확인하였다.Abstract i Contents iii List of Tables vi List of Figures vii List of Symbols x Preface xi Chpater 1 Introduction 1 1.1 Background 1 1.2 Previous Researches 3 1.2.1 Review of Control Mechanism Design Regarding the Insect-Type Flapping Wing 3 1.2.2 Review of Numerical Simulation Studies Regarding the Insect-type Flapping Wing 6 1.3 Research Objectives and Thesis Outline 8 Chpater 2 Control Mechanism Design with Free play 9 2.1 Overview of Control Mechanism Design with Free play 9 2.2 Control Mechanism: Trailing Edge Control 11 2.3 Components of the Control Mechanism 14 2.4 Control Mechanism Design with Minimize free play effect 17 Chpater 3 Numerical Simulations of FWMAV 25 3.1 Overview of Numerical Simulation based on Flexible Multibody Dynamics 25 3.2 Simulation Setup 26 3.2.1 Simulation Methodology 31 3.2.2 Aerodynamics 34 3.3 Numerical Simulation 37 Chpater 4 Conclusions 47 4.1 Contirbutions 47 4.2 Future Works 48 Acknowledgments 50 References 50 국문초록 55Maste

Multi-objective/loading optimization for rotating composite flexbeams

With the evolution of advanced composites, the feasibility of designing bearingless rotor systems for high speed, demanding maneuver envelopes, and high aircraft gross weights has become a reality. These systems eliminate the need for hinges and heavily loaded bearings by incorporating a composite flexbeam structure which accommodates flapping, lead-lag, and feathering motions by bending and twisting while reacting full blade centrifugal force. The flight characteristics of a bearingless rotor system are largely dependent on hub design, and the principal element in this type of system is the composite flexbeam. As in any hub design, trade off studies must be performed in order to optimize performance, dynamics (stability), handling qualities, and stresses. However, since the flexbeam structure is the primary component which will determine the balance of these characteristics, its design and fabrication are not straightforward. It was concluded that: pitchcase and snubber damper representations are required in the flexbeam model for proper sizing resulting from dynamic requirements; optimization is necessary for flexbeam design, since it reduces the design iteration time and results in an improved design; and inclusion of multiple flight conditions and their corresponding fatigue allowables is necessary for the optimization procedure