Fluttering energy harvesters in the wind: A review

The growing area of harvesting energy by aerodynamically induced flutter in a fluid stream is reviewed. Numerous approaches were found to understand, demonstrate and [sometimes] optimise harvester performance based on Movement-Induced or Extraneously Induced Excitation. Almost all research was conducted in smooth, unidirectional flow domains; either experimental or computational. The power outputs were found to be very low when compared to conventional wind turbines, but potential advantages could be lower noise levels. A consideration of the likely outdoor environment for fluttering harvesters revealed that the flow would be highly turbulent and having a mean flow angle in the horizontal plane that could approach a harvester from any direction. Whilst some multiple harvester systems in smooth, well-aligned flow found enhanced efficiency (due to beneficial wake interaction) this would require an invariant flow approach angle. It was concluded that further work needs to be performed to find a universally accepted metric for efficiency and to understand the effects of the realities of the outdoors, including the highly variable and turbulent flow conditions likely to be experienced

A preliminary study on passive and active flutter suppression concepts for aeronautical components

The scope of this work is to study computationally both passive and active flutter suppression characteristics of a cantilever cork agglomerate core sandwich with CFRP facings and an aluminum plate, the latter through the application of piezoelectric patches, respectively. Recently, cork agglomerates have been gaining an increasing interest from the aerospace industry due to their good thermal and acoustic insulation capabilities. In addition, cork based materials intrinsically have excellent vibration suppression properties, which suggest that the combination of cork with high performance composites (such as CFRPs) may lead to high specific strength materials with improved damping characteristics suitable for flutter prevention. Sandwich specimens were modeled using commercially available software ANSYS® and a demo version of ZAERO® software for the determination of the flutter speed and related frequencies. ANSYS® piezoelectric modeling and transient analysis capabilities were used for the active vibration study. Specimen aspect ratio and thickness were chosen as a function of wind tunnel maximum speed for further experimental tests. Results were compared with conventional CFRP and aluminum plates. It was demonstrated that a cork agglomerate core sandwich with CFRP facings can act as a natural flutter suppresser which allows the reduction of the wing weight for a given flight envelope and that the application of piezoelectric actuators is a valuable aeroelastic control concept. An increase of about 20% in flutter speed was achieved using actuated piezoelectric devices. The main goal remains in investigating higher strain smart materials and control strategies, since these improvements are only possible in small structures.O objectivo deste trabalho é o estudo computacional de soluções de supressão de flutter, passiva e activa, através de uma sandwich com núcleo de aglomerado de cortiça e faces de carbonoepoxy e de uma placa de alumínio, esta última através de actuadores piezoeléctricos, respectivamente. Recentemente, os aglomerados de cortiça têm ganho um interesse crescente por parte da indústria aeronáutica devido às suas propriedades de isolamento térmico e acústico. Além disso, os materiais à base de cortiça têm intrinsecamente excelentes propriedades antivibráticas, o que sugere que a sua combinação com materiais de alto desempenho (como o carbono-epoxy) pode levar a materiais de resistência específica elevada e com características de amortecimento melhoradas, adequados à prevenção do flutter. A sandwich foi modelada usando o software de elementos finitos ANSYS® e uma versão de demonstração do ZAERO® para a determinação da velocidade de flutter e respectiva frequência. Por sua vez, as capacidades de modelação piezoeléctrica e transiente do ANSYS® foram usadas para o estudo do controlo de vibração activa. A razão de aspecto das placas foi escolhida em função da velocidade máxima do túnel de vento, para posteriores testes experimentais. Os resultados foram comparados com placas de alumínio e carbono-epoxy convencionais. Foi demonstrado que a sandwich com núcleo de aglomerado de cortiça pode actuar como um supressor natural de flutter que permite uma redução do peso da estrutura para um dado envelope de voo. No que concerne ao controlo activo, a aplicação de actuadores piezoeléctricos é um conceito de controlo aeroelástico valioso que permitiu, neste estudo, um aumento de 20% na velocidade de flutter. No entanto, o principal objectivo permanece em investigar estratégias de controlo e materiais de características piezoeléctricas com capacidade de induzir maiores extensões a custo de uma menor potência

Passive Aeroelastic Tailoring

The Passive Aeroelastic Tailoring (PAT) project was tasked with investigating novel methods to achieve passive aeroelastic tailoring on high aspect ratio wings. The goal of the project was to identify structural designs or topologies that can improve performance and/or reduce structural weight for high-aspect ratio wings. This project considered two unique approaches, which were pursued in parallel: through-thickness topology optimization and composite tow-steering

Wind Tunnel Investigation of Ground Wind Loads for Ares Launch Vehicle

A three year program was conducted at the NASA Langley Research Center (LaRC) Aeroelasticity Branch (AB) and Transonic Dynamics Tunnel (TDT) with the primary objective to acquire scaled steady and dynamic ground-wind loads (GWL) wind-tunnel data for rollout, on-pad stay, and on-pad launch configurations for the Ares I-X Flight Test Vehicle (FTV). The experimental effort was conducted to obtain an understanding of the coupling of aerodynamic and structural characteristics that can result in large sustained wind-induced oscillations (WIO) on such a tall and slender launch vehicle and to generate a unique database for development and evaluation of analytical methods for predicting steady and dynamic GWL, especially those caused by vortex shedding, and resulting in significant WIO. This paper summarizes the wind-tunnel test program that employed two dynamically-aeroelastically scaled GWL models based on the Ares I-X Flight Test Vehicle. The first model tested, the GWL Checkout Model (CM), was a relatively simple model with a secondary objective of restoration and development of processes and methods for design, fabrication, testing, and data analysis of a representative ground wind loads model. In addition, parametric variations in surface roughness, Reynolds number, and protuberances (on/off) were investigated to determine effects on GWL characteristics. The second windtunnel model, the Ares I-X GWL Model, was significantly more complex and representative of the Ares I-X FTV and included the addition of simplified rigid geometrically-scaled models of the Kennedy Space Center (KSC) Mobile Launch Platform (MLP) and Launch Complex 39B primary structures. Steady and dynamic base bending moment as well as model response and steady and unsteady pressure data was acquired during the testing of both models. During wind-tunnel testing of each model, flow conditions (speed and azimuth) where significant WIO occurred, were identified and thoroughly investigated. Scaled data from the Ares I-X GWL model test was used in the determination of worst-case loads for the analysis of Ares I-X FTV design wind conditions. Finally, this paper includes a brief discussion of the limited full-scale GWL data acquired during the rollout and on-pad stay of the Ares I-X FTV that was launched from KSC on October 28, 2009

Semi-Passive Control Strategy using Piezoceramic Patches in Non Linear Commutation Architecture for Structural-Acoustic Smart Systems

The demands for novel smart damping materials can be summarized in: external power source not required for operation; device not needing to be tuned to a specific frequency; device operation not affected by changes in modal frequency; device suppressing vibration over a number of modes, weight and size minimized; self-contained unit device. This thesis focuses on these points and it shows that the dilemma between active and passive vibration control may be solved with a new approach, implementing a semipassive technique without penalties in terms of robustness and performance. Connecting a shunt circuit to a piezoelectric transducer leads to a simple and low cost vibration controller that is able to efficiently suppress unwanted structural vibrations: this is a way to fulfil the abovementioned demands. The objective of this work is to develop and validate by an experimental campaign a computational tool integrated with finite element Nastran software. An original 4-channel switched shunt control system has been realized using a tachometer device. The control system has been tested first of all on a simple cantilevered beam attaining a max vibrations reduction of 16.2 dB for the first bending mode. Further reference test article consisted of a 10 ply fibreglass laminate plate. A multimodal control has applied within a band range of 700Hz including the first seven modes. A maximum reduction of 16 dB has been found. Further numerical and experimental tests have been planned to extend the ability of the SSC to produce structural-borne sound reduction in acoustic rigid cavities for fluid-structure interaction problems. Numerical sound power radiation of an aluminium plate, controlled by synchronized switch system, compared with the experimental acoustic energy detected in acoustic room, has been planned in the ongoing activities

Control of structures using SMA wires and piezoelectric patches

Smart materials and structures systems are increasingly being developed to handle more complex problems. One of the main research schemes is the augmentation of the control authority of the smart actuators used in such systems. The augmentation can be obtained by constructing hybrid and multi- smart materials actuator systems and/or by the optimization of the location and orientation of those actuators. In the first part of this study, the alteration of the natural frequency of composite structures using Nitinol-based Shape Memory Alloy (SMA) wires will be presented using the analyses of strain energy perturbations on a plate. These governing strain equations were solved analytically and numerically to show the effect of point forces acting in a distributive manner and the subsequent effect it has on the plate's stiffness and hence it's natural frequency. In the second part of the thesis, a more complex loading condition is considered to investigate piezoceramic actuator control authority in relation to wing flutter control. The advancement in the application of active material induced-strain actuation such as piezoelectric materials in suppression of structural vibrations drew wide interest in its use for wing flutter control. Higher flutter speed and hence wider operating envelope was achieved by delaying the coalescence of the eigenvalues for plunge and twist modes. . This delay is obtained by adding more strain energy to the system as a result of the activation of the piezoelectric actuators. Most of the studies done were by controlling the plunge/bending motion, where the piezoelectric actuators are bonded longitudinally to produce bending moments. In this study, the control of the pitch/twisting motion was investigated and it showed better control of flutter by using simultaneous multi-actuations compared to single piezo actuations. It was shown that within the scope of the angular orientations of the piezoelectric patches investigated in this study, piezoelectric patches oriented about +150 from the beam's longitudinal ax is resulted in the most optimal piezo-configuration. This was corroborated by both the numerical flutter speed and actuator moment evaluations. In addition, the orientation of the piezoelectric patches was shown to significantly affect the pitch angle of the beam relative to each other. The damping ratio was also investigated and this showed greater instability for piezoelectric patches oriented at negative angles, thus further supporting the finding of the aforementioned optimal orientation of +150. These findings confirmed the dominance of the base (closest to the fixed portion of the beam) piezo when actuated with other piezos

Finite Element Simulation Of Repair Of Delaminated Composite Structures Using Piezoelectric Layers

Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures

Vibration Analysis And Shape Control Of A Beam With Piezoelectric Patches

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011Günümüzde kullanım alanları oldukça genişleyen piezoelektrik malzemeler, araştırma ve geliştirme için uygun konu olarak algılayıcı, kumanda elemanı ve akıllı yapıların kullanımında sıklıkla karşımıza çıkmaktadırlar. Piezoelektrik malzemeler elektriksel alana maruz kaldıklarında boyutlarında değişiklikler olmakta ve tersi durumda boyutsal şekil değişikliklere zorlandıklarında da elektrik sinyalleri üretmektedirler. Mekanik gerilmeye maruz kaldıklarında elektrik alan oluşturan piezoelektrik malzemeler, yüksek elastisite modülleri sayesinde ana yapının katılık ve kütle matrislerine ihmal edilebilir boyutta bir artış sağladığından ana yapıda çok sayıda kullanılıp titreşim ve şekil kontrolünün sağlanması işlevini görmektedirler. Yan sistemlerin desteğini almaksızın sağladıkları bu özellikleri ile piezoelektrik malzemeler havacılık ve uzay sanayinde aktif titreşim kontrolünde yaygın olarak tercih edilmektedirler. Bu çalışmada, piezoelektrik yamalı bir kirişin farklı sınır koşulları ve farklı yükler altında titreşim analizinin yapılması amaçlanmaktadır. Buna bağlı, piezoelektik yamalı bir kirişin Euler-Bernoulli Kiriş Teorisi ve Timoshenko Kiriş Teorisi göz önünde bulundurularak şekil fonksiyonu ve şekil kontrol analizleri yapılmıştır. Farklı sınır koşulları için kiriş davranışının inceleneceği teorik çalışmada, piezoelektrik yama yer değişimi etkisi ve farklı voltaj uygulamlarının sonuçları araştırılmıştır. Piezoelektrik yama içeren, farklı sınır koşullarına maruz kalmış bir kirişin hareket denklemleri çıkartılmış ve doğal frekans hesapları yapılmıştır. Teorinin literatür çalışmaları ile doğrulanmasının amaçlandığı bu çalışma ile ülkemizde piezoelektrik malzeme teknolojisinin geliştirilmesi; bu sayede bilim ve mühendislik alanlarında kullanımının daha da yaygın hale gelmesi sağlanacaktır.Piezoelectric materials have been affirmative subjects to be investigated and very popular in engineering applications in the latest researches. Piezoelectric structures are commonly less rigid, so they are more sensitive to enormous vibration problems and that is why they are increasingly needed for aerospace applications, likewise they provide new important capabilities in military and civilian aerospace applications. In particular, there are plenteous studies, which are aimed to estimate to control the vibration characteristics of structures with piezoelectrics. In this thesis, first of all, shape analysis and control of a beam with piezoelectric patches are examined with considering both Euler Bernoulli Beam Theory (EBT) and Timoshenko Beam Theory (TBT). In the determination of structural models, all solutions are performed analytically to a beam subjected to different boundary conditions. Moreover, the effects of not only different voltage but also piezoelectric patch position on frequency and on shape functions of beam are interrogated. With a view to control the shape of beam in a good manner and obtaining better results, the errors are minimized. Furthermore, how the piezoelectric patches can impose the shape of a beam is shown by the obtained solutions. In addition to all, equations of motion and natural frequencies of beams with piezoelectric patches are achieved by means of Euler Bernoulli Beam Theory (EBT).Yüksek LisansM.Sc

Aeroelastic Tailoring of Transport Aircraft Wings: State-of-the-Art and Potential Enabling Technologies

This paper provides a brief overview of the state-of-the-art for aeroelastic tailoring of subsonic transport aircraft and offers additional resources on related research efforts. Emphasis is placed on aircraft having straight or aft swept wings. The literature covers computational synthesis tools developed for aeroelastic tailoring and numerous design studies focused on discovering new methods for passive aeroelastic control. Several new structural and material technologies are presented as potential enablers of aeroelastic tailoring, including selectively reinforced materials, functionally graded materials, fiber tow steered composite laminates, and various nonconventional structural designs. In addition, smart materials and structures whose properties or configurations change in response to external stimuli are presented as potential active approaches to aeroelastic tailoring