120 research outputs found
Mitigation of Flow-Induced Cylinder Noise Through the Control of Sound Diffraction
The sound emitted by the flow past a circular cylinder can be described by a quadrupole placed at the outbreak location of the shedding instability and diffracted surface into the far field by the body with a dipolar directivity. This mechanism is greatly stabilized for a cylinder coated with a porous material, which features a substantial downstream shift of the onset location of the shed vortices that leads, in turn, to a reduction in the efficiency of the sound scattering and consequent noise mitigation. In this research, a novel design for a porous treatment of the cylinder based on the enhancement of this effect is proposed. Far-field acoustics tests were performed at the Delft University of Technology for Reynolds numbers based on the cylinder diameter ranging in the subcritical regime. The outcomes of the analysis demonstrate that, when the aft part of the flow-permeable coating is modified to make the internal flow more streamlined, an additional sound attenuation of up to 10 dB is achieved in comparison with a uniform porous cover. Moreover, a significant noise decrease of up to 10 dB and potential drag reduction are obtained if these components are connected to the bare cylinder without the use of a porous coating. This result can open up interesting opportunities to design disruptive and more optimized sound-mitigation solution
In-situ poling and structurization of piezoelectric particulate composites
Composites of lead zirconate titanate particles in an epoxy matrix are prepared in the form of 0β3 and quasi 1β3 with different ceramic volume contents from 10% to 50%. Two different processing routes are tested. Firstly a conventional dielectrophoretic structuring is used to induce a chain-like particle configuration, followed by curing the matrix and poling at a high temperature and under a high voltage. Secondly a simultaneous combination of dielectrophoresis and poling is applied at room temperature while the polymer is in the liquid state followed by subsequent curing. This new processing route is practiced in an uncured thermoset system while the polymer matrix still possess a relatively high electrical conductivity. Composites with different degrees of alignment are produced by altering the magnitude of the applied electric field. A significant improvement in piezoelectric properties of quasi 1β3 composites can be achieved by a combination of dielectrophoretic alignment of the ceramic particles and poling process. It has been observed that the degree of structuring as well as the functional properties of the in-situ structured and poled composites enhance significantly compared to those of the conventionally manufactured structured composites. Improving the alignment quality enhances the piezoelectric properties of the particulate composites.Novel Aerospace Material
Response to Comment on βTurning Vulcanized Natural Rubber into a Self-Healing Polymer: Effect of the Disulfide/Polysulfide Ratioβ
Π‘ΠΎΡΠΈΠ°Π»ΡΠ½ΠΎΠ΅ Π±Π»Π°Π³ΠΎΠΏΠΎΠ»ΡΡΠΈΠ΅ ΠΊΠ°ΠΊ ΠΊΡΠΈΡΠ΅ΡΠΈΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ Π½Π΅ΠΎΠΈΠ½Π΄ΡΡΡΡΠΈΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΈ
ΠΠ΅ΠΎΠΈΠ½Π΄ΡΡΡΡΠΈΠ°Π»ΠΈΠ·Π°ΡΠΈΡ ΠΏΡΠ΅Π΄ΠΏΠΎΠ»Π°Π³Π°Π΅Ρ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΡ, ΠΎΡΠ½ΠΎΠ²Π°Π½Π½ΡΡ Π½Π° Π·Π½Π°Π½ΠΈΡΡ
ΠΈ ΡΠ΅ΡΡΡ
. Π ΠΎΡΠ»ΠΈΡΠΈΠ΅ ΠΎΡ ΠΈΠ½Π΄ΡΡΡΡΠΈΠ°Π»ΡΠ½ΠΎΠΉ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΈ, Π³Π΄Π΅ ΠΊΠ»ΡΡΠ΅Π²ΡΠΌΠΈ ΡΠ°ΠΊΡΠΎΡΠ°ΠΌΠΈ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΠ²Π»ΡΡΡΡΡ Π΄ΠΎΠ±ΡΡΠ° ΠΈ ΠΏΠ΅ΡΠ΅ΡΠ°Π±ΠΎΡΠΊΠ° ΡΡΡΡΡ, Π² Π½ΠΎΠ²ΠΎΠΉ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠ΅ Π±ΡΠ΄Π΅Ρ Π΄ΠΎΠΌΠΈΠ½ΠΈΡΠΎΠ²Π°ΡΡ ΠΈΠ½ΠΆΠ΅Π½Π΅ΡΠ½ΠΎΠ΅ ΡΠ²ΠΎΡΡΠ΅ΡΡΠ²ΠΎ, Π΄ΠΈΠ·Π°ΠΉΠ½ ΠΈ ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅. ΠΡΠΎ ΠΊΠΎΡΠ΅Π½Π½ΡΠΌ ΠΎΠ±ΡΠ°Π·ΠΎΠΌ ΠΌΠ΅Π½ΡΠ΅Ρ ΠΊΠ°ΡΡΠΈΠ½Ρ ΡΠΎΡΠΈΠ°Π»ΡΠ½ΠΎΠ³ΠΎ Π±Π»Π°Π³ΠΎΠΏΠΎΠ»ΡΡΠΈΡ, ΠΊΠΎΡΠΎΡΠΎΠ΅ Π²ΡΡΡΡΠΏΠ°Π΅Ρ, Ρ ΠΎΠ΄Π½ΠΎΠΉ ΡΡΠΎΡΠΎΠ½Ρ, ΠΊΡΠΈΡΠ΅ΡΠΈΠ΅ΠΌ, Ρ Π΄ΡΡΠ³ΠΎΠΉ - ΠΊΠΎΠ½Π΅ΡΠ½ΡΠΌ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠΌ Π½Π΅ΠΎΠΈΠ½Π΄ΡΡΡΡΠΈΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΈ
Modelling of thermal-physical properties of composite material
Article represents theoretical determination of effective heat conductivity of composite materials. Authors describe PC program written with Visual Basic for calculation of heat conductivity of composite materials. There is particular focus on various methods for calculation of heat conductivity of composite materials in accordance with offered models and on comparison between calculated and experimental data
Detection of delamination healing of a thermoplastic ionomer interlayer in a model CFRP composite by advanced ultrasonic techniques
Trapping of Nitrogen at the Fe-AlN Precipitate Interface Studied by the Positron Doppler Broadening Technique
High-resolution X-ray diffraction investigation on the evolution of the substructure of individual austenite grains in TRIP steels during tensile deformation
ΠΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΠΊΠΎΡΠΌΠΈΡΠ΅ΡΠΊΠΈΡ ΡΠ½ΠΈΠΌΠΊΠΎΠ² ΠΏΡΠΈ ΠΈΠ·ΡΡΠ΅Π½ΠΈΠΈ Π½Π΅ΡΡΠ΅Π½ΠΎΡΠ½ΡΡ ΡΠ°ΠΉΠΎΠ½ΠΎΠ²
- β¦