modeling and optimization

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부(멀티스케일 기계설계전공),2020. 2. 최해천.The aerodynamic characteristics of a hovering rhinoceros beetle are numerically and theoretically investigated. Its wing kinematics is measured using high speed cameras and used for numerical simulation of flow around a flapping rhinoceros beetle in hovering flight. The numerical results show that the aerodynamic forces generated (especially for lift) and power required by the hind wing during a quasi-periodic state are quite different from those during the first stroke. This indicates that the wing-wake interaction significantly affects the aerodynamic performance of the hind wing during the quasi-periodic state. Also, twisting of the hind wing along the wing span direction does not much contribute to total force generation as compared to that of the flat wing, and the role of elytron and body on the aerodynamic performance is quite small at least for the present hovering flight. Based on a previous model (Wang et al., J. Fluid Mech., vol. 800, 2016, pp. 688-719), we suggest an improved predictive aerodynamic model without any ad hoc model constants for a rigid and flat hind wing by considering the effect of the wing-wake interaction in hovering flight. In this model, we treat the wake as a steady or unsteady non-uniform downwash motion and obtain its magnitude by combining a quasi-steady blade element theory with an inviscid momentum theory. The lift and drag forces and aerodynamic power consumption predicted by this model are in excellent agreements with those obtained from numerical simulations. Based on the developed quasi-steady aerodynamic model, the optimal planform shapes and motions of the hind wing of the hovering beetle for minimum power consumption are investigated. First, we optimize wing motions with the measured wing planform shape for minimum aerodynamic and positive mechanical power consumptions, respectively. We also optimize wing planform shapes with the measured wing motion, as done for the optimization of the wing motion. We find that the measured wing shape is not optimal in terms of aerodynamic power consumption and the optimal wing shape and motion minimizing positive mechanical power consumption are close to the measured ones. For minimum aerodynamic power consumption, the pitching axis of the wing should be located between the 1/4-chord and the mid-chord points, together with the radius of the first moment of wing area of around 0.5. For minimum positive mechanical power consumption, the wing area should be concentrated near the wing root rather than the aerodynamically optimal wing shape, and the pitching axis is between the leading edge and the 1/4-chord point.정지 비행하는 장수풍뎅이의 공기 역학적 특성을 수치적-이론적으로 조사하였다. 날갯짓은 고속 카메라를 통해 측정되었으며, 정지 비행하는 장수풍뎅이 주변의 유동을 수치해석하는 데 사용되었다. 수치해석 결과는 준주기적 상태일 때 속날개로부터 발생되는 힘(특히 양력)과 공기 역학적 요구전력이 첫 번째 날갯짓 동안의 힘 및 공기 역학적 요구전력과 상당히 다르다는 것을 보여준다. 이는 날개-후류 간 상호작용이 준주기적 상태동안 속날개의 공력 특성에 크게 영향을 미친다는 것을 나타낸다. 또한 속날개의 날개 길이 방향에 따른 비틀림은 편평한 속날개와 비교할 때 전체 힘 생성에 크게 기여하지 않으며 공기 역학적 성능에 대한 겉날개와 몸통의 역할은 적어도 현재의 정지 비행에 대해 매우 작음을 확인하였다. 기존의 공력 모델을 바탕으로 날개-후류 간 상호작용의 효과를 고려하여 정지 비행하는 편평한 속날개에 대해 어떠한 모델 상수도 없는 개선된 예측적 공력 모델을 제안하였다. 이 공력 모델에서 후류를 비균일의 정상 또는 비정상 하강기류로 간주하고, 준정상 블레이드 요소 이론과 비점성 운동량 이론을 결합하여 후류의 세기를 구하였다. 현재의 공력 모델로 예측된 양, 항력 및 공기 역학적 요구전력은 수치해석으로부터 얻어진 결과와 매우 잘 일치하였다. 개발된 준정상 공력 모델을 기반으로, 최소 전력 소비를 위한 정지 비행하는 장수풍뎅이 속날개의 최적 평면 형상 및 움직임을 조사하였다. 먼저, 최소 공기 역학적 및 양의 기계적 전력 소비를 위해 측정된 날개 평면 형상으로 날개 움직임을 최적화하였다. 또한 날개 움직임의 최적화를 위해 수행된 것 처럼 측정된 날개 움직임으로 날개 평면 형상을 최적화하였다. 최적화 결과로부터 측정된 날개 형상은 공기 역학적 요구전력 측면에서 최적이 아니며, 양의 기계적 전력 소비를 최소화하는 날개 모양과 움직임이 측정된 것들에 가깝다는 것을 확인하였다. 최소 공기 역학적 전력 소비를 위해서는 날개 면적의 첫 번째 모멘트의 반경은 약 0.5이며, 날개의 피칭 축이 시위 길이의 1/4 지점과 1/2 지점 사이에 있어야함을 확인하였다. 최소 양의 기계적 전력 소비를 위해서는 최소 공기 역학적 전력 소비를 위한 날개보다 날개 면적이 날개 뿌리 근처에 모여있어야하며, 피칭 축은 선단과 시위 길이의 1/4 지점 사이에 있어야함을 확인하였다.Part I A numerical and theoretical study of the aerodynamic performance of a hovering rhinoceros beetle (Trypoxylus dichotomus) 1 1 Introduction: Why rhinoceros beetle? 2 2 Wing kinematics and morphological parameters 7 2.1. Measurement of the wing kinematics 7 2.2. Measured wing kinematic and morphological parameters 8 3 Numerical details 17 4 Simulation results 23 5 Quasi-steady aerodynamic model of a flapping wing in hover 35 5.1. Quasi-steady blade element theory 36 5.2. Estimation of induced downwash motion 43 6 Model validation and discussions 50 7 Further consideration on the induced downwash motion 62 8 Conclusions 68 Part II Optimal wing geometry and kinematics of a hovering rhinoceros beetle for minimum power consumption 71 1 Introduction 72 2 Models for a hovering flight of a rhinoceros beetle 75 2.1. Wing motion and shape 76 2.2. Aerodynamic force and power expenditure 79 3 Optimization 84 4 Results and discussion 88 4.1. Optimal wing motions for the measured wing shape 88 4.2. Optimal wing shapes for the measured wing motion 90 4.3. Numerical simulation on the optimal wing motions and shapes 92 5 Conclusion 104 References 106 Appendix 114 A A predictive model of the drag coefficient for a revolving wing at low Reynolds number 114 A.1. Introduction 114 A.2. An improved model of the drag coefficient 117 A.3. Results and discussion 122 A.4. Conclusion 123 Abstract (in Korean) 128Docto

Quantitative analysis of take-off forces in birds

The increasing interest on Unmanned Air Vehicles (UAV’s) and their several utilities blended with the need of easy carrying and also the stealth, lead to the need to create the concept of Micro Air Vehicles (MAV’s) and the Nano Air Vehicles (NAV’s). Due to the current interest and the present lack of knowledge on the insect’s and bird’s flight, this study was intended to interpret the forces involved on the moment of the take-off of a bird, recurring to an experiment involving a fast data acquisition force sensor and high speed camera, in addition known facts from earlier studies. In order to do that a bibliographic revision was done, to know what was already studied and to find what could yet be studied. That way could be formed a link on the factors involved on the propulsion of a bird at the moment of take-off. The main conclusions obtained by this work is that the bird can produce movements that will enhance the total moment when the bird stretches its neck forward and moving head down followed by stretching even more its neck and moving head up impelling himself into the air, resulting in a main role on the mechanical forces (against perch) for the bird first moments momentum. Columba livia can generate about 4 times its weight worth mechanic force (against perch) and above 8 times its weight during the 2nd downstroke.O interesse crescente nos Veículos Aéreos não Tripulados “Unmanned Air Vehicles (UAV’s)” e suas diversas utilidades em conjunto com a necessidade de seu fácil transporte e furtividade, levaram à necessidade de criar o conceito dos Micro Veículos Aéreos “Micro Air Vehicles (MAV’s)” e os Nano Veículos Aéreos “Nano Air Vehicles (NAV’s)”. Este tipo de veículos tem como fonte inspiradora os insetos e aves devido à necessária produção simultânea de sustentação e propulsão. Tal como no voo convencional, também no voo animal podem ser identificadas as fases de levantamento (descolagem) e aterragem como diferenciadas do voo longe de uma superfície de apoio. Este trabalho é dedicado ao estudo da fase de levantamento de voo de uma ave columba livia. Foram realizadas experiências para medir a força inicial produzida pela ave para iniciar o voo e a respetiva trajetória na zona próxima do ponto de apoio inicial. Estas medidas foram efetuadas com um sensor de força dotado de elevada velocidade de aquisição de dados e uma camara de alta velocidade. As principais conclusões obtidas com a realização deste trabalho é o facto de que a ave consegue produzir movimentos, que aumentar o momento total quando a ave estica o pescoço para a frente e movendo a cabeça para baixo seguido por continuação de esticamento do pescoço e movimento da cabeça para cima impelindo-se para o ar, resultando num papel principal relativamente às forças mecânicas (contra o poleiro) para o momento linear actuante nos primeiros momentos. Columba livia consegue gerar cerca de 4 vezes o seu peso em força mecânica e acima de 8 vezes o seu peso durante o 2º downstroke

Aerodynamic ground effect in fruitfly sized insect takeoff

Aerodynamic ground effect in flapping-wing insect flight is of importance to comparative morphologies and of interest to the micro-air-vehicle (MAV) community. Recent studies, however, show apparently contradictory results of either some significant extra lift or power savings, or zero ground effect. Here we present a numerical study of fruitfly sized insect takeoff with a specific focus on the significance of leg thrust and wing kinematics. Flapping-wing takeoff is studied using numerical modelling and high performance computing. The aerodynamic forces are calculated using a three-dimensional Navier--Stokes solver based on a pseudo-spectral method with volume penalization. It is coupled with a flight dynamics solver that accounts for the body weight, inertia and the leg thrust, while only having two degrees of freedom: the vertical and the longitudinal horizontal displacement. The natural voluntary takeoff of a fruitfly is considered as reference. The parameters of the model are then varied to explore possible effects of interaction between the flapping-wing model and the ground plane. These modified takeoffs include cases with decreased leg thrust parameter, and/or with periodic wing kinematics, constant body pitch angle. The results show that the ground effect during natural voluntary takeoff is negligible. In the modified takeoffs, when the rate of climb is slow, the difference in the aerodynamic forces due to the interaction with the ground is up to 6%. Surprisingly, depending on the kinematics, the difference is either positive or negative, in contrast to the intuition based on the helicopter theory, which suggests positive excess lift. This effect is attributed to unsteady wing-wake interactions. A similar effect is found during hovering

In-plane elasticity of beetle elytra inspired sandwich cores

The Beetle Elytron Plate (BEP) is a new class of biomimetic sandwich core that features excellent compressive strength, energy absorption capacity and flexural properties. These characteristics make BEPs suitable as potential replacements of classical honeycomb cores in sandwich panels. This work describes the behaviour of the in-plane engineering elastic constants of parametric BEP topologies for the first time. The beetle elytron cores configurations are simulated using Finite Element models, including full-scale models and representative unit cells with periodic boundary conditions for asymptotic homogenization. The models are also benchmarked against experimental results obtained from ASTM tensile tests related to the in-plane Young’s modulus, Poisson’s ratio and shear modulus. The benchmarked models are then used to perform a parametric analysis against the geometry characteristics of the cellular configurations. Results obtained from this work will provide a solid foundation for further research on BEP structures and expand their applications into wider engineering fields

Numerical cognition in bees and other insects

The ability to perceive the number of objects has been known to exist in vertebrates for a few decades, but recent behavioral investigations have demonstrated that several invertebrate species can also be placed on the continuum of numerical abilities shared with birds, mammals, and reptiles. In this review article, we present the main experimental studies that have examined the ability of insects to use numerical information. These studies have made use of a wide range of methodologies, and for this reason it is striking that a common finding is the inability of the tested animals to discriminate numerical quantities greater than four. Furthermore, the finding that bees can not only transfer learnt numerical discrimination to novel objects, but also to novel numerosities, is strongly suggestive of a true, albeit limited, ability to count. Later in the review, we evaluate the available evidence to narrow down the possible mechanisms that the animals might be using to solve the number-based experimental tasks presented to them. We conclude by suggesting avenues of further research that take into account variables such as the animals' age and experience, as well as complementary cognitive systems such as attention and the time sense.This publication was funded by the German Research Foundation (DFG) and the University of Wuerzburg in the funding program Open Access Publishing. Shaowu Zhang was supported by the ARC-CoE in Vision Science

Evaluation of Skylab (EREP) data for forest and rangeland surveys

The author has identified the following significant results. Four widely separated sites (near Augusta, Georgia; Lead, South Dakota; Manitou, Colorado; and Redding, California) were selected as typical sites for forest inventory, forest stress, rangeland inventory, and atmospheric and solar measurements, respectively. Results indicated that Skylab S190B color photography is good for classification of Level 1 forest and nonforest land (90 to 95 percent correct) and could be used as a data base for sampling by small and medium scale photography using regression techniques. The accuracy of Level 2 forest and nonforest classes, however, varied from fair to poor. Results of plant community classification tests indicate that both visual and microdensitometric techniques can separate deciduous, conifirous, and grassland classes to the region level in the Ecoclass hierarchical classification system. There was no consistency in classifying tree categories at the series level by visual photointerpretation. The relationship between ground measurements and large scale photo measurements of foliar cover had a correlation coefficient of greater than 0.75. Some of the relationships, however, were site dependent

A History of the Eastern Larch Beetle, \u3ci\u3eDendroctonus Simplex\u3c/i\u3e (Coleoptera: Scolytidae), in North America

The eastern larch beetle, Dendroctonus simplex, is reputedly a secondary pest but may attack and kill tamarack and ornamental larches throughout Canada, the northeastern United Stales, and Alaska. Isolated infestations of this pest have been reported for over 100 years. The first recorded widespread outbreaks of D. simplex started in eastern Canada and the northeastern United States as well as in Alaska in the mid-1970s. During the outbreak in the Atlantic provinces, in excess of 1.4 million m3 of tamarack was killed. No damage estimates are available for Quebec and the United States. Insect defoliators were the most common factors predisposing tamarack to beetle attack

Complex photonic structures in nature: from order to disorder

Structural colours arise from the interaction of visible light with nano-structured materials. The occurrence of such structures in nature has been known for over a century, but it is only in the last few decades that the study of natural photonic structures has fully matured due to the advances in imagining techniques and computational modelling. Even though a plethora of different colour-producing architectures in a variety of species has been investigated, a few significant questions are still open: how do these structures develop in living organisms? Does disorder play a functional role in biological photonics? If so, is it possible to say that the optical response of natural disordered photonics has been optimised under evolutionary pressure? And, finally, can we exploit the well-adapted photonic design principles that we observe in Nature to fabricate functional materials with optimised scattering response? In my thesis I try to answer the questions above: I microscopically investigate $\textit{in vivo}$ the growth of a cuticular multilayer, one of the most common colour-producing strategies in nature, in the green beetles $\textit{Gastrophysa viridula}$ showing how the interplay between different materials varies during the various life stages of the beetles; I further investigate two types of disordered photonic structures and their biological role, the random array of spherical air inclusions in the eggshells of the honeyguide $\textit{Prodotiscus regulus}$, a species under unique evolutionary pressure to produce blue eggs, and the anisotropic chitinous network of fibres in the white beetle $\textit{Cyphochilus}$, the whitest low-refractive index material; finally, inspired by these natural designs, I fabricate and study light transport in biocompatible highly-scattering materials.European Research Council grant awarded to Dr Silvia Vignolin