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  • AIP Publishing  (7)
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  • AIP Publishing  (7)
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  • 1
    Online Resource
    Online Resource
    Quantitative stress measurement of elastic deformation using mechanoluminescent sensor: An intensity ratio model
    AIP Publishing ; 2018
    In:  Review of Scientific Instruments Vol. 89, No. 4 ( 2018-04-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 89, No. 4 ( 2018-04-01)
    Abstract: The mechanoluminescent (ML) sensor is a newly developed non-invasive technique for stress/strain measurement. However, its application has been mostly restricted to qualitative measurement due to the lack of a well-defined relationship between ML intensity and stress. To achieve accurate stress measurement, an intensity ratio model was proposed in this study to establish a quantitative relationship between the stress condition and its ML intensity in elastic deformation. To verify the proposed model, experiments were carried out on a ML measurement system using resin samples mixed with the sensor material SrAl2O4:Eu2+, Dy3+. The ML intensity ratio was found to be dependent on the applied stress and strain rate, and the relationship acquired from the experimental results agreed well with the proposed model. The current study provided a physical explanation for the relationship between ML intensity and its stress condition. The proposed model was applicable in various SrAl2O4:Eu2+, Dy3+-based ML measurement in elastic deformation, and could provide a useful reference for quantitative stress measurement using the ML sensor in general.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.5024417
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Integration of pressure-sensitive paint with persistent phosphor: A light-charged pressure-sensing system
    AIP Publishing ; 2018
    In:  Review of Scientific Instruments Vol. 89, No. 8 ( 2018-08-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 89, No. 8 ( 2018-08-01)
    Abstract: A novel pressure-sensitive paint has been developed by mixing phosphor Sr4Al14O25:Eu,Dy with pressure-sensitive luminophore PtTFPP in a polyethylene binder. The phosphor particles served as hosts for PtTFPP molecules while providing excitation light via their bright blue/green luminescence. The unique long afterglow of Sr4Al14O25:Eu,Dy allows the coating to be charged by a light source (UV-LED or even sunlight) in advance, and then the luminescent signals can be collected by using a color camera for pressure measurement (without an external light source). The persistent luminescence and the pressure-sensitive signal correspond to the green and red channels, respectively. The errors due to time-varying persistent luminescence can be removed by taking an intensity ratio between the two channels. The current formulation of this light-charged pressure-sensitive paint (LC-PSP) has been optimized for the maximum signal level. It showed similar pressure sensitivity to typical pressure-sensitive paints (PSPs), and its capability was demonstrated through a nitrogen jet impingement experiment. This light-charged PSP can be truly free of light source during measurement, which greatly simplifies the optical system and avoids errors due to the inconsistent illumination field, and thus provides a solution for PSP applications in facilities with limited optical access.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.5041359
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Simultaneous measurements of time-resolved velocity and concentration fields behind a sand dune-inspired jet in crossflow
    AIP Publishing ; 2021
    In:  Physics of Fluids Vol. 33, No. 11 ( 2021-11-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 33, No. 11 ( 2021-11-01)
    Abstract: The flow field and scalar concentration behind a sand dune-inspired jet-in-crossflow were measured to quantify the characteristics of flow and scalar mixing. The velocity was resolved from particle image velocimetry measurements, and the time-resolved concentration was simultaneously captured by planar laser-induced fluorescence. During the experiments, the velocity ratio was set to 0.4, 0.6, 0.8, 1.0, and 1.2. The corresponding jet flow statistics, concentration statistics, and flow-concentration dynamics were comparatively analyzed. Aided by the dune, all jets were found to discharge tangentially into the mainstream, forming an energetic shear layer in the dune upper region that not only affects the jet attachment but also influences the flow mixing dynamics. The measured turbulent flow statistics (vorticity, turbulent kinetic energy, and Reynolds stress), concentration statistics (scalar standard deviation and turbulent scalar flux), and dynamics of the flow-concentration fields (instantaneous evolutions, scalar dissipation, and strain rate) revealed not only the complex nature of the generated shear layer but also the significant correlations between the shear flow and scalar mixing. Proper orthogonal decomposition (POD) analysis successfully decomposed the instantaneous velocity and concentration fields into a series of energetic POD modes, vividly demonstrating the modulating effect of the energetic shear layer on the flow and scalar mixing.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0070411
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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    Online Resource
  • 4
    Online Resource
    Online Resource
    Drag reduction by a rotationally oscillating cylinder with a flexible filament
    AIP Publishing ; 2022
    In:  Physics of Fluids Vol. 34, No. 4 ( 2022-04-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 34, No. 4 ( 2022-04-01)
    Abstract: The hydrodynamic mechanism of drag reduction by a rotationally oscillating cylinder with a flexible filament was explored using the penalty immersed boundary method. A simulation of a stationary cylinder without a filament was also performed for comparison. The effects of the filament length, bending rigidity, oscillatory frequency, and oscillatory amplitude on drag reduction were systematically examined. The underlying mechanism of drag reduction was characterized in terms of the shape deformation of the filament, wake pattern, pressure distribution, and flapping dynamics. Two dominant flapping modes were observed: an oscillation mode with less than half a wave on the filament and an undulation mode with more than one wave on the filament. In the oscillation mode, drag reduction is mainly achieved by the thrust generated by the filament, accompanied by an increase in lift fluctuations. The pressure difference caused by the flapping motion between the upper and lower sides of the filament is the main cause of the thrust. In the undulation mode, drag reduction is realized by both the thrust generated by the filament and the decreased form drag of the cylinder. A filament flapping in the oscillation mode can generate greater thrust than a filament flapping in the undulation mode. A long undulatory filament with relatively low oscillatory amplitude effectively stabilizes the wake, resulting in a decrease in the lift fluctuations.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0090086
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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    Online Resource
  • 5
    Online Resource
    Online Resource
    Drag reduction by a flexible afterbody
    AIP Publishing ; 2021
    In:  Physics of Fluids Vol. 33, No. 12 ( 2021-12-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 33, No. 12 ( 2021-12-01)
    Abstract: The hydrodynamic mechanism of drag reduction by a flexible afterbody was explored by using the penalty immersed-boundary method. The flexible afterbody is constituted by a trailing closed flexible filament. A volume penalty method was adopted to conserve the volume of a flexible afterbody during deformation. Simulations of a rigid plate without a flexible afterbody and with a rigid afterbody were also performed for comparison. The results of the present simulation show the same tendency as the experimental data, in which the maximum drag reduction was obtained at a particular length of the flexible filament irrespective of the bending rigidity. We analyzed the underlying mechanism of drag reduction in detail by examining wake patterns, pressure distributions, flapping modes, and the average kinetic energy (E¯k) of the flexible afterbody. The contributions of form drag and skin friction drag to the total drag were determined as functions of the length of a flexible afterbody. An appropriately shaped flexible afterbody delays vortex formation and weakens the vorticity and negative pressure, resulting in drag reduction. Active flapping of the afterbody adversely affects drag reduction. Drag is reduced by increasing the Reynolds number (Re). Drag is insensitive to E¯k but sensitive to the flapping amplitude of the flexible afterbody as Re increases.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0073568
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 6
    Online Resource
    Online Resource
    Hydrodynamic benefits of pectoral fins in a self-propelled flexible plate
    AIP Publishing ; 2022
    In:  Physics of Fluids Vol. 34, No. 2 ( 2022-02-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 34, No. 2 ( 2022-02-01)
    Abstract: The hydrodynamic benefits of fixed and flapping pectoral fins were explored using the penalty immersed boundary method. A self-propelled flexible plate was realized in the present study, where a clamped leading edge of the flexible plate was forced into a prescribed harmonic oscillation in the spanwise direction but was free to move in the horizontal direction. The body and pectoral fins of a fish were modeled using a flexible plate and two rigid/flexible plates. Simulations without the pectoral fins were also performed for comparison. The pressure distributions and vortical structures around the plate were visualized to characterize the hydrodynamic roles of the pectoral fins. The vortices generated by the pectoral fins increase the pressure difference between the upper and lower sides of the plate, resulting in an enhancement of both the cruising speed (10.5%) and thrust. The horizontally flapping pectoral fins with low flapping frequency enhance the propulsive efficiency rather than the fixed pectoral fins. The flexible flapping fins enhance the cruising speed rather than the rigid flapping fins. In addition, the presence of one flapping fin on one side of the flexible plate induces asymmetrical heaving of the flexible plate and increases the lateral forces, which might help fish achieve turning and maintain balance in perturbed flows.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0081698
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 7
    Online Resource
    Online Resource
    Hydrodynamic benefits of protruding eyes and mouth in a self-propelled flexible stingray
    AIP Publishing ; 2021
    In:  Physics of Fluids Vol. 33, No. 8 ( 2021-08-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 33, No. 8 ( 2021-08-01)
    Abstract: The hydrodynamic benefits of the protruding eyes and mouth (e & m) of a stingray's smooth body are explored using the penalty immersed boundary method. A self-propelled flexible plate was realized in the present study; a clamped leading edge of the flexible plate was forced into a prescribed harmonic oscillation in the vertical direction but was free to move in the horizontal direction. The e & m was formulated by the superposition of several rigid plates. Simulations without the e & m were also performed for comparison. The pressure distributions and vortical structures around the flexible plate were visualized to characterize the hydrodynamic roles of the e & m. The streamwise and spanwise vortices generated by the e & m function together enhance the average cruising speed and thrust, where the streamwise vortices enhance the negative pressure at the leading edge of the flexible plate and the spanwise vortices increase the pressure difference between the upper and lower sides of the plate. A parametric study was performed to find an optimal shape of the e & m that maximizes the average cruising speed (U¯c) and propulsion efficiency (η) as a function of the spanwise width. The presence of the e & m increased the U¯c and η by more than 20.5% and 10.6%, respectively.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0061287
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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