1,721,014 research outputs found
Sonic Boom Minimization Through a Simplified Approach for the Preliminary Design of Civil Supersonic Aircraft
No full textIn this paper a simple approach aimed to the definition of a supersonic configuration optimized in terms of sonic boom signature will be presented. This approach is based on the application of Carlson’s method that is a simplified method for the calculation of sonic-boom characteristics for a wide variety of supersonic airplane configurations and spacecraft. Sonic-boom overpressures and signature duration may be predicted for the entire affected ground area for vehicles in level flight or in moderate climbing or descending flight paths. This prediction technique is based on simplification of the purely theoretical methods, which are able to provide quite acceptable estimates of sonic-boom phenomena for a wide range of flight conditions for conventional airplane configurations. Experimental measurements have shown that this approach describes properly sonic-boom properties for extremely blunt bodies at high supersonic speeds, providing reliable numerical information at distances large relative to body dimensions. The effects of flight-path curvature and aircraft acceleration, however, are not considered, and the method is further restricted to a standard atmosphere without winds. Furthermore, it is assumed that the pressure signal generated by the aircraft is of the far-field type, the classical N-wave. The information required, for the calculations and the pressure-signature predictions provided by the simplified method, are: aircraft shape-factor; aircraft operating conditions; atmospheric data. The signature data provided by the method include: N-wave bow-shock overpressure; the signature duration; the location of the ground impact point relative to the aircraft position at the time the boom was generated. This approach has been adopted to evaluate the sonic boom properties of a supersonic reference configuration comparing the numerical results with a more refined CFD approach. Then an optimization procedure has been applied to minimize the maximum value of overpressure: the geometry of the reference configuration has been modified iteratively following the criteria suggested by the Carlson’s method and keeping in mind several operational constraints: this iterative method has permitted the definition, in a preliminary stage of design, of an optimized supersonic configuration
Introduction to Ship Acoustics
No full textSome basic concepts involved in the ship acoustics are reported in the lesson.
The main noise sources on board are briefly overviewed as
well as the typical transmission paths along which noise can be transmitted to a receiving position. The peculiarities of the ship context with respect to other industrial environments are outlined.
Some problems connected with the characterization of the various sources strength are presented.
The basic concepts of noise reduction (absorption, damping, isolation) are overviewed together with some quantities commonly used to describe the effectiveness of different counter-measures adooted on board
Proceedings of the International Symposium on Scale Modeling (Napoli, 02-04 marzo 2022)
No full textThis volume contains the works presented at the ninth edition of the symposium on scale models, ISSM9. The symposium brought together 53 scientists from 8 different countries and 3 continents, from both Academia and Research Centers; they participated virtually or in person to present the latest developments and trends in scale application and progress in several engineering fields (mostly in continuum mechanics and fluid dynamics). During the symposium there were 4 keynote talks, its related abstracts are here enclosed too. The contents of the talks are about the state-of-the-art of similitude theory and scale modeling and they are useful for any researcher interested in similar topics
Noise and Vibration
No full textThe basic concepts of noise and vibration are herein presented, in their hystorical view, physical analogies, similarities and diversification. Main definítions in the 'noise' area are given, together with the related physics, in order to provide background to the following lessons; simple exercises are also proposed.
A glossary containing the basic terminology in the fields concerned is finally given
Numerical comparison between a simplified method and a full CFD approach for sonic boom evaluation on supersonic innovative configurations
No full textIn this paper the comparison between two different numerical approaches for sonic boom evaluation is presented: one is based on the Carlson method, the other is based on CFD computations and both are aimed to evaluate the ground signature due to a supersonic flight. The Carlson’s method is a simplified method for the calculation of sonic-boom characteristics for a wide variety of supersonic airplane configurations and spacecraft operating at altitudes up to 76 km. Sonic-boom overpressures and signature duration may be predicted for the entire affected ground area for vehicles in level flight or in moderate climbing or descending flight paths and the prediction requires in input the geometry of airplane and the operative conditions. A classical, more general approach for the sonic boom analysis is based on solution of the aerodynamic field in the vicinity of the aircraft, evaluation of the pressure disturbance far field propagation and prediction of the ground acoustic signature from the effective sonic boom perceived annoyance. These two methods have been used for sonic boom evaluation on a conventional reference supersonic geometry: the ground signature has been obtained and the comparison has shown a reasonable numerical agreement under some physical conditions. The paper shows the technical aspects of two before mentioned different approaches with special regard to the computational effort needed, low for the simplified Carlson’s method, high for CFD approach, and the numerical reliability of the solution
Proceedings of MEDYNA2020, 3rd Euro-Mediterranean Conference on Structural Dynamics and Vibroacoustics
Full text linkFULL STOCHASTIC RESPONSE, PSEUDO EXCITATION METHOD AND PSEUDO EQUIVALENT DETERMINISTIC EXCITATION: TWO SIMPLE SYSTEMS
No full textThe computational costs associated to the analysis of a stochastic response of a linear system can become unacceptable high, even using a full modal representation. Here, a new approach is proposed by invoking a pseudo equivalent deterministic excitation (PEDE). This is based on the given spectral load representation. The load used in a deterministic loop is derived from the column of the spectral load matrix. The method allows a good representation without using the eigenvalues and eigenvectors of the spectral load matrix; in fact the pseudo excitation method, (PEM), is just based on these, and the PEM is an exact representation being based on the modal decomposition of the spectral excitation. The two methods, PEM and PEDE, are then compared with a full stochastic response for two simple systems: a chain of five oscillators (mass and stiffness) and a plate. Both the system are considered excited by a spectral load representing the classical form due to Corcos for the wall pressure distribution due to a turbulent boundary layer: a random and convective excitation. A dimensionless representation of the frequency axis is also used; on this scale, the results demonstrated that in the first frequency ranges the PEDE is a very useful approximation
Sensitivity Investigation of Aircraft Engine Noise to Operational Parameters
No full textAircraft noise is associated to two main groups of acoustic sources: those which produce airframe noise and the other ones which produce engine noise. Airframe noise can be numerically simulated once defined aircraft geometry and its intensity depends on aerodynamic configuration of aircraft. Engine noise is due to contribution of several sources according to engine’s type: in several cases these sources are not all well theoretically defined for the difficulty of performing experimental campaigns, and this does not allow a general validation of numerical simulation tools. Sound pressure levels associated to fans, compressors, jets, propellers can be numerically evaluated through commercial codes that require a big amount of input parameters concerning the geometric description of the different engine parts and the engine operational conditions that are well known from a physical standpoint but can be difficult to manage in a preliminary assessment of the noise emission due to a typical civil aircraft engine. The numerical definition of all these parameters requires a deep knowledge of the mechanism of the engine part subject of investigation and, often, also having a clear view of how this part works, the values of operational parameters, during the aircraft engine working, can be not available. For this reason an investigation of the sensitivity of the overall sound pressure levels associated to the different noise sources to the engine operational parameters can be useful to understand how much the noise can change if the working conditions change and to rank the variables from an acoustic standpoint fixing the most influential parameters. The present paper focuses on some of the acoustic sources acting on a typical civil aircraft engine and is based on the use of commercial codes able to simulate numerically the sound pressure levels associated to these sources
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