86,826 research outputs found
INVESTIGATION ON SMART SENSORS TO PREDICT FLUTTER AND AEROLASTIC RESPONSE
No full textThis research is devoted to the identification of non-linear aeroelastic systems in real time. The proposed studies will be related to develop new sensory techniques to identify aeroelastic modes and unsteady aerodynamics in fixed and rotary wings. These studies are important because the interaction of the vibration natural modes of the aircraft structure with the unsteady aerodynamic loading may become unstable under certain flight conditions, leading to the flutter phenomenon. Moreover, in a less severe scenario, these loads generate high levels of aircraft forced vibration that cause passenger discomfort and lead to structural fatigue and even failure. All these studies, although ultimately directed to helicopter blades, will be initially conducted with fixed-wing configurations, and will include both numerical simulations and experimental work conducted in still air and wind tunnel. From the project originality point-of-view, it is well known that the main line of research on aeroelasticity today is associated with non-linear phenomena. In the low speed range, the non-linearity is often associated with the structure alone (free play of control surfaces in most cases). However, in the high-speed transonic regime, non-linearities are also generated from the aerodynamics unsteadiness, and these are normally associated with localized shocks on supercritical airfoil configurations. There is no efficient method that can be used in the industry today to deal analytically with non-linear phenomena. The development of reliable and computationally efficient analytical methods is of fundamental importance for the industry. However, this development can only be done with the existence of carefully controlled wind tunnel tests to serve as a source of comparison data. As wind tunnel tests are very expensive, reliable experimental data must be acquired in the shortest period of time. The objective of this research is, therefore, to develop new sensory techniques based on smart materials to maximize the efficiency of wind tunnel tests to produce accurate data pertinent to aeroelasticity. In fact, Carleton University is engaged to pursue with several international partners a collaborative project on an experimental investigation to determine the aeroelastic flutter and forced vibration characteristics of a model of a typical commuter aircraft configuration using the National Research Council Canada (NRCC) Institute for Aerospace Research 5-foot square test section of their blow-down wind tunnel facility. The main investigation will be performed in the high-speed transonic regime where non-linear aerodynamic behavior occurs. Notwithstanding the panned NRCC tests, this research will be complemented with low-speed wind tunnel tests on a full-aircraft configuration to be carried out by partners at CTA (Centro Tecnico Aeroespacial) in Brazil to investigate the effect of structural non-linearities on flutter characteristics. This collaborative project is seen of strategic interest in terms of advancing the general knowledge as well as the partners' expertise in a research area that is of great and timely interest for the aerospace industry. It is further proposed that "La Sapienza" becomes a partner in this international research effort. One of the proposed wind tunnel models is a reflection plane wing-body model where a fairing allows a smooth transition between the wing and the fuselage. The model includes a swept-tapered wing, which supports a nacelle and a jet engine modeled as a hollow cylinder. Under terms of this collaboration, the wind tunnel model will be designed and fabricated at Carleton University. The model will be tested for flutter in the NRCC blow-down wind tunnel in the transonic regime for different pitch angles, Reynolds and Mach numbers. A mass damper ("flutter stopper") will be incorporated inside the wing structure to prevent flutter bifurcation and model accidental destruction. This is usually achieved using a mechanical device that is traditionally a small weight that is suddenly moved inside the structure by the release of a spring. The change in the wing mass distribution provided by the device stabilizes the onset of flutter. The wing structure deformation is traditionally measured using two mini-accelerometers mounted near the wing tip in the chord-wise direction. The accelerometers pick up the bending and torsion deformations of the wing, as the sum and difference of the individual signals. However, accelerometers are localized sensors that do not bring enough information to a generalized structural phenomenon such as flutter and aeroelastic response. Hence, piezoelectric fiber (Active Fiber Composite - AFC) sensors will be suitably embedded in the wing to measure its generalized modal deformations as well. This will be one of the main and novel aspects of this research project. These embedded geometric sensors are expected to allow for the first time a better determination of the flutter characteristics, as (distributed) modal sensors can identify the aeroelastic phenomena much more precisely in terms of the "modal participation". This work will be an extension of the studies on AFC-related geometric modal sensors developed in a present collaboration involving EMPA, ETH in Switzerland and Carleton University. It is suggested that Prof. Nitzsche and Prof. Coppotelli will join research efforts during Prof. Nitzsche's proposed tenure at "La Sapienza" to perform feasibility studies aiming to develop advanced smart sensors using AFC-related techniques for aeroelastic modal identification in the transonic regime for immediate application in the programmed wind tunnel tests, including the feasibility of measuring unsteady aerodynamic loads at certain wing cross-sections. In summary, the objective of the planned research is the development of analytical techniques to identify fundamental aspects of aeroelastic phenomena from AFC-generated signals. In this context, advanced studies, performed at "La Sapienza", on the identification of dynamic systems vibrating in the actual operating conditions represent an excellent starting point for the proposed project. This research is seen of great value for the organizations involved, not only for its novelty that will surely allow the publication of a number of joint papers, but also for its special and timely relevance in face of the planned wind tunnel tests, the potential industrial applications, and the basis of a established long-term collaboration
Identification of a Root ``Smart Spring'' System for Augmentation of Aeroelastic Stability of a Helicopter Rotor in Hover
No full text
Seiner Hochehrwürden, dem Herrn M. Friedrich Heinrich Starken hochverordneten Superintendenten und Pastori Primario zu Bitterfeld bey dem erfreulichen Antritte dieses Amtes am 1. Januar 1800.
No full textehrfurchtsvoll gewidmet von den sämmtlichen Predigern der Inspection [C. G. Blüthner, Pastor in Alt-Jessnitz. M. A. W. Hofmann, Pastor in Sandersdorf. M. J. G. Köpping, Diaconus in Brena. M. C. G. Martius, Pastor in Niemeck. M. J. A. Mulert, Pastor in Crina. M. F. Ch. Nitzsche, Past. sen. in Roitzsch. J. A. Nitzsche, Past. subst. [in Roitzsch.] G. L. Richter, Pastor in Mühlbeck. W. G. Richter, Pastor in Pouch. M. J. G. Rieck, Pastor in Brena. M. J. Ch. Schmidt, Pastor in Priorau. F. G. Schulz, Diaconus in Bitterfeld. C. A. Schulze, Past. sen. in Rösa. M. C. G. Schulze, Pastor subst. [in Rösa.] C. F. Schulze, Pastor in Sausedlitz. M. J. G. Seyfert, Pastor in Beyersdorf. S. T. Siebold, Pastor in Petersroda. C. A. Wachsmuth, Pastor in Pösigck. J. S. Walther, Pastor in Reuden. M. S. G. Wegner, Pastor in Burgkemnitz. M. C. F. G. Werner, Pastor in Capella]Autopsie nach Exemplar der ULB Sachsen-AnhaltVorlageform des Erscheinungsvermerks: Leipzig, gedruckt in der Sommerschen Buchdruckerey
Identification of the smart spring properties from FRFs measurements
No full textThe objective of this paper is the dynamic identification of a reduced-scale helicopter
blade system that incorporates an active pitch link or smart spring for vibration control.
The identification of the Smart Spring parameters, in terms of the masses and stiffnesses
associated to its components, is carried out in the frequency domain using a developed
sensitivity-based updating method. This method, called Predictor-Corrector, iteratively
minimizes a residual vector of correlation functions, defined on the Frequency Response
Functions (FRFs), in order to obtain the unknown values of the parameters that well rep-
resent the dynamic behavior of the smart spring. In the paper the accuracy of the solution
provided by the developed technique is assessed through several numerical analyses. For
this purpose, a lumped parameter numerical model of the Smart Spring was developed
and the effects of various mass and stiffness distribution scenarios on the modal properties
of the system are presented. Due to the nonlinear dynamic behavior of the smart spring
system, a linear approximation of the system around a prescribed operative working con-
dition is considered. Finally, the developed approach is applied for the identification of the
dynamic parameters of a real smart spring system. It is shown that acceptable values of
the equivalent lumped parameters were achieved also considering experimental data such
as those recorded during a test campaign carried out at the Smart Rotor Laboratory of
the Carleton University, thus validating the identification approach
Closed-loop control of the smart spring. An analytical solution for the actuator model
No full textThe analytical modeling of the Smart Spring actuator for vibration reduction of periodically excited systems is performed. The mathematical model is developed in the frequency domain using the harmonic balance method, assuming that the solution is harmonic on the exciting frequency. Both the fixed-base and base-excited configurations are studied. It is shown that the Smart Spring transmissibility at the target frequency depends on only three dimensionless parameters associated with the stiffness modulation characteristics of the device for the fixed-base configuration and five dimensionless parameters for the base-excited configuration. The fundamental values for the Smart Spring closed-loop control are discussed
Identification of the Dynamic Properties of Active Twist Rotor Model Blade Using Output-Only Data
No full textn this paper, an approach to estimate the dynamic characteristics of a rotating
blade using response data is proposed. A test campaign devoted to demonstrate the capability
of the Smart Spring device to alter the dynamic properties of the rotating blade is carried out in
the framework of the Smart Hybrid Active Rotor Control System, SHARCS, project. Within this
project, the key factor is an active vibration control concept that uses piezoceramic actuators to
preferentially vary dry friction and stiffness of a structure. This device, if located at the blade
root, could adaptively vary the dynamic stiffness of the blade to change its flexural characteristics,
thus allowing control of the aeroelastic response of the entire blade. In this paper it is shown how
the modal parameters will be estimated from the time histories recorded, by a distributed array
of sensors, at different rotational speed of the blade and for different values of the stiffness of the
Smart Spring device. Both time domain and frequency domain methods were applied in order
to quantify the effects on the modal properties of different operating conditions of a prototype
version of the Smart Spring device. This device was attached to the push rod of an Active Twist
Rotor blade developed at the German Aerospace Center (DLR). From the performed experimental
investigation, carried out at the DLR’s whirl tower test facility, it was possible first to draw the
typical fan plots of the rotating blade, from which useful information about the dynamic behavior
of the system could be achieved. Then, a validation of the numerical model of the smart spring
device was obtained
Whirl Tower Demonstrations of the SHARCS Hybrid Control Concept
No full textElements of the SHARCS (Smart Hybrid Active Rotor Control System) Hybrid Control concept are demonstrated via two sets of whirl tower tests. Hybrid Control stands for combining a flow control (such as an Actively Controlled Flap or Active Twist Rotor) and of a structural (or stiffness) control device on a helicopter blade. A Hybrid Control system promises to reduce vibration and noise on helicopters simultaneously as well as to improve the efficiency of the flow control device. For the structural control system, a unique and entirely original Active Pitch Link has been developed at Carleton University, which is capable of dynamically controlling the torsional stiffness of a blade. Design, prototyping, static and whirl tower testing of this device is presented in the paper. A second set of whirl tower tests of an Active Twist Rotor equipped with a range of springs instead of the conventional pitch link, demonstrates that the Active Pitch Link shall indeed be capable of lowering the torsional stiffness of the blade. For these tests, the modal parameters of the blade were evalu-ated via a novel “Output-Only” method, which represents the first application of such methodology for rotary-wing applications
Experimental Investigation on the Modal Signature of the Smart Spring/Helicopter Blade System of SHARCS Project
No full textTo achieve efficient attenuation of noise and vibration characteristics within the helicopter environment, solid state actuators are seen as one of the most promising smart technologies. The Smart Hybrid Active Rotor Control System project is expected to demonstrate the ability of smart structure systems, employing multiple active material actuators, sensors, and closed-loop controllers, to reduce simultaneously rotorcraft vibration and noise. Within this project, piezoceramic elements were used as actuators to vary the dry friction and the stiffness of the whole helicopter blade system. This active control concept, named Smart Spring, originated a prototype used to demonstrate the ability to attenuate vibrations. Before testing the Smart Hybrid Active Rotor Control System in operative conditions, the dynamic properties of the Smart Spring installed on a nonrotating helicopter blade are investigated. The effects of the Smart Spring actuator on the modal properties are studied through experimental activities carried out at Carleton University. Furthermore, the capability of the Smart Spring to change the dynamic behavior of the helicopter blade is demonstrated by analyzing the shifts in the modal parameters. Finally, a beam finite element model of the blade, with stiffness and mass properties tuned to the experimental structure, is presented
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