1,721,051 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
EXPERIMENTS ON NOISE REDUCTION IN AIRCRAFT WITH ACTIVE SIDEWALL PANELS
Full text linkThe present work focuses on the active reduction of aircraft interior noise by means of smart lining (sidewall panel) modules. In general, the interior noise floor of jet-driven aircraft is on an acceptable level. This, however, might change, if energy-efficient engines with open rotors are
used in combination with stiff lightweight fuselage structures. In such a case, unacceptably high noise levels might arise especially at low frequencies (< 500 Hz). In this frequency range, passive sound insulation methods are usually incompatible with the mass and volume restrictions of aircraft. The linings are coupled to the fuselage and radiate sound into the cabin. They have large sound-emitting surfaces and many passengers are sitting directly in front of them. Therefore, it is reasonable to reduce the low-frequency sound emission of linings with active control. Furthermore, smart linings could be used for secondary tasks like passenger announcements or noise masking. Multiple functionalities can be realized in parallel. This contribution describes recent experimental research work on smart linings conducted in the DLR test aircraft Dornier Do728. The Do728 provides a fully equipped cabin with a realistic acoustic environment. The external acoustic excitation is realized with a loudspeaker array placed directly in front of the fuselage. A synthesized counter-rotating open rotor (CROR) noise containing the first five harmonics (< 500 Hz) is used to emulate the acoustic fuselage excitation of a real CROR engine. Two smart lining
modules are driven in parallel, each with two inertial actuators and an independent adaptive feedforward control unit. Microphones are used as error sensors and for capturing the sound Emission and noise reduction capability of the smart linings. Mean sound pressure level reductions up to 10 dB are achieved in the monitored area of the cabin
Active Reduction of Car Interior Noise
No full textActive Structural Acoustic Control (ASAC) is an effective measure to reduce the windshield-vibration-induced interior noise in an automobile passenger compartment.
Different control strategies for the active reduction of windshield-vibration-induced car interior noise are developed, experimentally validated, and now available. The comparison of the vibration levels in open and closed loop show a global reduction of 5dB to 7dB in the acoustically relevant frequency band containing the second and third eigenmode of the windshield system (100 Hz to 150 Hz). The acoustic effects are reflected in a reduction of up to 15dB in SPL at 145Hz
Lärmreduktion in der Flugzeugkabine durch Smart-Lining-Technologie
No full textDie geringe Schalldämmung von Flugzeug-Seitenwandpaneelen (Linings) kann in Kombination mit
neuartigen Rumpfstrukturen aus CFK und/oder energieeffizienten Antrieben wie z.B. Counter Rotating
Open Rotor (CROR) Triebwerken zu einer Beeinträchtigung des Passagierkomforts führen. Die Smart-Lining-Technologie verwendet die aus der Adaptronik bekannte aktive Struktur-Akustik-Regelung (ASAC), um die Strukturschwingungen und damit den Kabinenlärm auf
leichtbaugerechte Weise zu reduzieren. Mit Hilfe von ASAC
können die durch das Massegesetz (Bergersches Gesetz) formulierten physikalischen Grenzen passiver Schalldämmungsmethoden überwunden werden. Das große
Potenzial der Smart-Lining Technologie zeigte sich im
Laborversuch mit über 6 dB(A) Schallleistungsreduktion gemessen in 1/3-Oktaven (Terzen)
Aktive Steuerung des Transmissionsverhaltens stochastischer Störquellen durch flächige Leichtbaustrukturen [Active feedforward control of the transmission of stochastic disturbances through lightweight panel structures]
Full text linkLeichtbaustrukturen weisen eine geringe Schalldämmung bei tiefen Frequenzen auf. Ihr Einsatz bei Gebäuden, Fahr- oder Flugzeugen ist daher mit negativen Auswirkungen auf die Innenraumakustik verbunden. Adaptronische Maßnahmen, wie die aktive Struktur-Akustik-Regelung (ASAC), können passive Maßnahmen der Schalldämmung flankieren oder ersetzen. Gegenstand dieser Arbeit ist die Beeinflussung der Transmission stochastischer Störquellen durch ein- und doppelwandige Leichtbaustruktursysteme mithilfe von aktiven Steuerungen. Die Beeinflussung stochastischer oder breitbandiger Störquellen mit aktiven Steuerungen setzt eine hohe Signalkohärenz sowie die Kausalität des aktiven Systems voraus. Im Zentrum dieser Arbeit stehen daher die Fragen, welchen Restriktionen aktive Einzelschalensysteme unterliegen und ob es möglich ist, die erweiterte Systemgrenze eines Doppelschalensystems zur Verbesserung der Kohärenz und der Kausalität eines aktiven Steuerungssystems zu nutzen. Es werden Begriffe und Methoden zur Analyse der Kohärenz und der Kausalität aktiv gesteuerter Einzel- und Doppelschalensysteme erarbeitet sowie Simulationen von und Messungen an aktiven Einzel- und Doppelschalensystemen in einem Transmissionsprüfstand durchgeführt. [Lightweight structures are characterized by a poor sound insulation at low frequencies. Their application for buildings, cars or aircraft therefore implies negative effects on the interior acoustics. Adaptronic means, like active structural acoustic control (ASAC), are suitable to flank or replace passive measures of soundproofing. In this work, active feedforward control is applied to influence the transmission of stochastic disturbance sources through single and double panel lightweight structures. The ability of the active feedforward control system to influence stochastic or broadband disturbance sources depends on the signal’s coherence and on the causality of the active system. The central issue of this work is to determine the restrictions of active single panel structures and to ascertain whether or not the extended system boundary of a double panel system can be utilized for the improvement of the coherence and the causality of an active feedforward control system. Terms and methods for the analysis of the coherence and the causality of active single and active double panel structures with feedforward control are developed. Simulations of generic active single and double panel structures are performed and realistic aircraft panel structures with active feedforward control are measured in a sound transmission loss facility.
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
New Sound Transmission Loss Test Facility for Acoustic Evaluation of Smart Lightweight Panels
No full textThe activities of the Institute of Composite Structures and Adaptive Systems in the field of ASAC are focused on the development of smart lightweight structures with improved acoustic properties, especially in the challenging low-frequency domain. The new sound transmission loss test facility will provide the experimental conditions necessary for the Investigation and validation of numerically designed and optimized ASAC systems
Full-scale experiments on the reduction of propeller-induced aircraft interior noise with active trim panels
Full text linkResults are presented of full-scale experiments on the active reduction of rotor-induced passenger cabin noise in a Dornier Do728 aircraft. Two active sidewall panels (smart linings) are used to reduce the sound pressure in a control region in front of the linings. The fuselage pressure distribution associated with the first five harmonics of a generic counter-rotating open rotor (CROR) engine is emulated with a loudspeaker array. Each smart lining is equipped with two inertial force actuators. It uses up to eight error microphones and implements an adaptive feedforward controller. The two smart linings are driven in parallel. A maximum SPL reduction of 11.3 dB is achieved in the controlled area. The mean SPL reduction over 18 microphones is 6.8 dB. At the most critical second frequency, a mean SPL reduction of 9.3 dB is
achieved by the two smart linings working in parallel. It is observed that the SPLs near the lining (at the window seat positions) are significantly higher than the SPLs near the aisle. This leads to the conclusion that the major part of the sound energy is transmitted through the linings, which is seen as an argument for the suitability of the smart lining concept
ACTIVE SIDEWALL PANELS WITH REMOTE MICROPHONE TECHNIQUE FOR AIRCRAFT INTERIOR NOISE REDUCTION
Full text linkThe main issue of this contribution is the reduction of aircraft interior noise by means of actively controlled sidewall panels (linings). It was shown in prior work that considerable reductions of interior sound pressure level can be achieved using structural actuators on the lining and microphones distributed in the seat area in front of the linings. The use of microphones is undesirable for several reasons and it contradicts the aim of a fully integrated and autonomous lining module (smart lining).
Therefore, the present contribution aims at the replacement of the error microphones by a number of structural sensors and an acoustic filter. This method is called the remote microphone technique for active control. Several steps are undertaken to define the smart lining with remote microphones. The whole work is based on experimental data of a double panel system mounted in a sound transmission loss facility. A multi-tonal acoustic excitation, typical for a counter rotation open rotor (CROR) engine, is used as the load case for the definition of the actuators and a broadband acoustic excitation, is used as the load case for the definition of structural sensors. 19 accelerometers are mounted on the lining and 20 microphones are placed in front of it. All sensor signals are sampled simultaneously for deterministic and broadband load cases. The lining is equipped with two inertial mass actuators at fixed positions which are used for the active control. The measurement data is used for the derivation of an observer and for the simulation of a smart lining with remote microphones
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