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Статті в журналах з теми "TBL Pressure Spectrum Model"
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Biplab Ranjan Adhikary, Ananya Majumdar, Atanu Sahu, and Partha Bhattacharya. "Sensitivity of TBL Wall-Pressure over the Flat Plate on Numerical Turbulence Model Parameter Variations." CFD Letters 15, no. 7 (May 29, 2023): 148–74. http://dx.doi.org/10.37934/cfdl.15.7.148174.
Повний текст джерелаАнотація:
A two-fold sensitivity of the zero-pressure gradient (ZPG) turbulent boundary layer (TBL) wall-pressure spectrum to different RANS model parameters is investigated for a flat plate case, which is a close approximation to the aircraft fuselage or wing. The alteration in the mean square pressure fluctuations due choice of semi-empirical pressure model and the choice of computational model parameters like solver, near wall grid clustering, measuring location, and flow velocity are separately studied. The underlying effect of different TBL parameters in the said sensitivity has been studied while numerically replicating wind tunnel experiments and in-flight tests considering different RANS configurations. Initially, the best-predicting pressure spectrum models are selected by comparing them with available in-flight and wind tunnel test data. Subsequently, the accuracy of all the individual model parameters in predicting mean TBL flow quantities like wall shear stress, boundary layer thickness, displacement thickness, momentum thickness, etc., and eventually mean square pressure (MSP) is estimated. The sensitivity of the mean square pressure fluctuations value to the TBL flow quantities and the near-wall grid clustering is observed to be significant. In general, family of models is found to be best in terms of numerical convergence and closeness when compared to the experimental MSP values. family of models is suggested to be avoided while estimating MSP in flat plate TBL case
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Shao, Jianwang, Jinmeng Yang, Xian Wu, Cheng Wang, and Guoming Deng. "Study on Radiated Noise of a Panel under Fluctuating Surface Pressure Due to an Idealized Side Mirror." Applied Sciences 10, no. 3 (February 3, 2020): 994. http://dx.doi.org/10.3390/app10030994.
Повний текст джерелаАнотація:
As traditional automobiles develop towards new energy vehicles, the noise, vibration and harshness (NVH) performance of automobiles is facing new challenges. Without the cover of the traditional engine noise and inlet and exhaust noise, the high-speed wind noise becomes more prominent. Thus, research on the calculation method of vehicle interior noise in high-speed driving condition is needed. However, vehicle body structure is complex, and the external excitation components are complicated. In order to analyze the method of predicting the vehicle interior noise at high speed, an idealized side mirror model is taken as the research object in this paper and the radiated noise of a panel under the fluctuating surface pressure (FSP) due to the idealized side mirror is studied. The FSP of the panel is first studied by the numerical simulations of incompressible and compressible flow field. For the incompressible flow field, the Corcos turbulent boundary layer (TBL) model is established to simulate the convective component and the boundary element method (BEM) is used to extract the acoustic component. Subsequently, the Corcos model coupling BEM method, the random modal force coupling BEM method and the deterministic modal force coupling BEM method are used separately to calculate the noise of the panel under the FSP. For the compressible flow field, the convective and acoustic component in the fluctuating pressure are separated by the wavenumber-frequency spectrum (WFS) method. The radiated noise of the panel under the FSP is calculated again by using the WFS, the method of random modal force and the method of deterministic modal force, respectively. Then, the computational time of the six methods of incompressible and compressible calculation is compared. Finally, a fast and accurate method of calculating the panel radiated noise under FSP is obtained by comparing the computational accuracy with the experimental results and combining the computational time: the method of incompressible random modal force. This method can be used to quickly and accurately analyze the vehicle interior noise at high speed, and to optimize the exterior protrusions and the vehicle sound package for improving the vehicle NVH performance at high speed.
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Leehey, P. "Structural Excitation by a Turbulent Boundary Layer: An Overview." Journal of Vibration and Acoustics 110, no. 2 (April 1, 1988): 220–25. http://dx.doi.org/10.1115/1.3269502.
Повний текст джерелаАнотація:
Thirty years of theoretical and experimental research have yet to resolve a number of questions regarding the vibratory response of, and acoustic radiation from, a structure excited by a turbulent boundary layer (TBL). The most important questions are: (a) Can the TBL be characterized as a Thevenin source—particularly when vibratory power flow into the structure is maximized at hydrodynamic coincidence? Alternatively, at what level does structural vibration fundamentally change the character of the TBL? (b) Is the low wave number portion of the wall pressure spectrum of dominant importance in structural excitation away from hydrodynamic coincidence? Or do structural discontinuities cause the convective ridge of wall pressure to be of greater practical interest? (c) Can one quantify the radiation from a turbulent boundary layer about a rigid finite body? Is it dipole or quadrupole? What is the role of fluctuating wall shear stress? Current research on dense fluid loading and on modeling the behavior of the TBL is yielding new, and sometimes surprising, answers to some of these questions. Free resonant structural vibration in the dense fluid limit and the use of a bounded, non-causal, Green function representing the TBL are two of the surprises discussed.
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Rao, V. Bhujanga, P. V. S. Ganesh Kumar, and P. K. Gupta. "Viscous Effects on Turbulent Boundary-Layer Noise of Ship's Sonar Dome in a Water Tunnel." Journal of Ship Research 35, no. 04 (December 1, 1991): 331–38. http://dx.doi.org/10.5957/jsr.1991.35.4.331.
Повний текст джерелаАнотація:
Turbulent boundary-layer (TBL) wall pressure fluctuations of a body measured in a water tunnel need correction to obtain unbounded free-field values. Besides blockage effects in a tunnel which are easily accounted for, viscous effects on TBL noise are to be evaluated to quantify this correction. An analytical method using suitable wave vector spectrum modeling to estimate the correction needed due to viscous effects is presented. A sonar dome body is considered as a typical example.
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Huang, Chunlong, Hui Li, and Nansong Li. "Flow Noise Spectrum Analysis for Vertical Line Array During Descent in Deep Water." Journal of Theoretical and Computational Acoustics 28, no. 04 (October 19, 2020): 2050022. http://dx.doi.org/10.1142/s259172852050022x.
Повний текст джерелаАнотація:
Reliable acoustic path (RAP) is a direct path used for sound propagation between a shallow source and a deep receiver in deep water. The RAP environment can provide a high signal-to-noise ratio (SNR) environment for source localization, so it has been widely studied for underwater passive detection. Active detection can be used for source localization during the descent of a vertical line array (VLA). However, the flow noise originating from the pressure fluctuations in the turbulent boundary layer (TBL) during the descent degrades the detection performance of the VLA. This paper presents a calculation of the response of the cylindrical hydrophones to axisymmetric turbulent wall pressure and the physical properties of flow noise. The flow noise was calculated using the wavenumber-frequency spectrum analysis method, which is based on Carpenter’s TBL pressure spectrum. The results show that the energy of the flow noise is concentrated mainly in low frequencies and it increases and spreads toward high frequencies with increasing stream velocity. The conclusions have been verified with experimental data. In addition, the noise correlation between two hydrophones will undergo oscillatory decay as the hydrophone spacing increases. The above findings will be beneficial for signal processing of an active sonar array.
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Shi, Beiji, Zhaoyue Xu, and Shizhao Wang. "A non-equilibrium slip wall model for large-eddy simulation with an immersed boundary method." AIP Advances 12, no. 9 (September 1, 2022): 095014. http://dx.doi.org/10.1063/5.0101010.
Повний текст джерелаАнотація:
A non-equilibrium wall model for large-eddy simulation with the immersed boundary (IB) method is proposed to reduce the required number of grid points in simulating wall-bounded turbulence. The proposed wall model is presented as an appropriate slip velocity on the wall. The slip velocity is constructed by integrating the simplified turbulent boundary layer (TBL) equation along the wall-normal direction, which enhances the integral momentum balance near the wall on a coarse grid. The effect of pressure gradient on the near wall flow is taken into account by retaining the pressure gradient term in the simplified TBL equation. The proposed model is implemented in the form of a direct-forcing IB method with moving-least-square reconstruction near the wall. The benchmarks of plane channel turbulence and the flows over a backward-facing step are used for validation. The proposed model improves the wall stresses and velocity profiles in the region where the pressure gradient dominates the near wall flows.
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Guillon, Corentin, Emmanuel Redon, and Laurent Maxit. "Vibroacoustic simulations with non-homogeneous TBL excitations: Synthesis of wall pressure fields with the Continuously-varying Uncorrelated Wall Plane Waves approach." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, no. 7 (February 1, 2023): 544–51. http://dx.doi.org/10.3397/in_2022_0075.
Повний текст джерелаАнотація:
A numerical method is presented to predict the vibro-acoustic response of a vibrating structure excited by a spatially inhomogeneous turbulent boundary layer(TBL). It is based on the synthesis of different realizations of the random pressure fluctuations that can be introduced as loadings of a vibro-acoustic model (such as a finite element model). To generate the pressures of the non-homogeneous turbulent boundary layer, the Uncorrelated Wall Plane Wave(UWPW) approach used so far for homogeneous TBL is extended. On a first step, this extension is based on a decomposition of the excited surface into sub-areas and on the averaged TBL parameters for each sub-area. In a second step, it consists in taking into account the interaction between the sub-areas and a refinement of the sub-area decomposition. This leads to the Continuously-varying Uncorrelated Wall Plane Waves (C-UWPW) approach. The accuracy of the proposed approach is investigated on a panel with a varying thickness and excited by a growing TBL triggered at one edge of the plate. The interests of the proposed approach in terms of accuracy and computation time are discussed. Finally, an illustration of the proposed approach to predict the radiated noise from a blade immersed in a water flow is proposed.
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Shepherd, Micah. "Excitation of structures by partially correlated pressures: A review of diffuse acoustic field and turbulent boundary layer models." Journal of the Acoustical Society of America 153, no. 3_supplement (March 1, 2023): A75. http://dx.doi.org/10.1121/10.0018211.
Повний текст джерелаАнотація:
Structures are sometimes excited by pressure distributions which exhibit complex spatial correlation. This differs from common acoustic excitations since the pressure at one location is only partially correlated with the pressure at another location due to inherent spatial randomness within the forcing function. Two forcing functions which exhibit partially-correlated pressures are the diffuse acoustic field (DAF) and turbulent boundary layer (TBL) flow. A basic model for representing the spatial correlation for these two forcing functions will be reviewed in both the spatial and wavenumber domains. Recent approaches for computing the vibration of structures excited by DAF or TBL flow will then be summarized. Interesting physical effects, such as intermodal coupling, will be highlighted to illustrate the importance of properly modeling partial correlations when they exist.
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OWEIS, GHANEM F., ERIC S. WINKEL, JAMES M. CUTBRITH, STEVEN L. CECCIO, MARC PERLIN, and DAVID R. DOWLING. "The mean velocity profile of a smooth-flat-plate turbulent boundary layer at high Reynolds number." Journal of Fluid Mechanics 665 (December 6, 2010): 357–81. http://dx.doi.org/10.1017/s0022112010003952.
Повний текст джерелаАнотація:
Smooth flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century. However, there is a relative dearth of measurements at Reynolds numbers typical of full-scale marine and aerospace transportation systems (Reθ = Ueθ/ν > 105, where Ue = free-stream speed, θ = TBL momentum thickness and ν = kinematic viscosity). This paper presents new experimental results for the TBL that forms on a smooth flat plate at nominal Reθ values of 0.5 × 105, 1.0 × 105 and 1.5 × 105. Nominal boundary layer thicknesses (δ) were 80–90mm, and Karman numbers (δ+) were 17000, 32000 and 47000, respectively. The experiments were conducted in the William B. Morgan Large Cavitation Channel on a polished (k+ < 0.2) flat-plate test model 12.9m long and 3.05m wide at water flow speeds up to 20ms−1. Direct measurements of static pressure and mean wall shear stress were obtained with pressure taps and floating-plate skin friction force balances. The TBL developed a mild favourable pressure gradient that led to a streamwise flow speed increase of ~2.5% over the 11m long test surface, and was consistent with test section sidewall and model surface boundary-layer growth. At each Reθ, mean streamwise velocity profile pairs, separated by 24cm, were measured more than 10m from the model's leading edge using conventional laser Doppler velocimetry. Between these profile pairs, a unique near-wall implementation of particle tracking velocimetry was used to measure the near-wall velocity profile. The composite profile measurements span the wall-normal coordinate range from y+ < 1 to y > 2δ. To within experimental uncertainty, the measured mean velocity profiles can be fit using traditional zero-pressure-gradient (ZPG) TBL asymptotics with some modifications for the mild favourable pressure gradient. The fitted profile pairs satisfy the von-Kármán momentum integral equation to within 1%. However, the profiles reported here show distinct differences from equivalent ZPG profiles. The near-wall indicator function has more prominent extrema, the log-law constants differ slightly, and the profiles' wake component is less pronounced.
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Goody, Michael. "An empirical model for the frequency spectrum of surface pressure fluctuations." Journal of the Acoustical Society of America 111, no. 5 (2002): 2379. http://dx.doi.org/10.1121/1.4778064.
Повний текст джерелаДисертації з теми "TBL Pressure Spectrum Model"
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Sen, Shoham. "Simulation and Study of Noise Generated due to Turbulent Boundary Layer in Towed Hydrophone Array." Thesis, 2016. https://etd.iisc.ac.in/handle/2005/4331.
Повний текст джерелаАнотація:
In this thesis, a wave propagation based analytical model is developed for an underwater towed array. The towed array is modeled as an in finite tube filled with a certain liquid and submerged in an in finite volume of water. This tube is excited by turbulent boundary layer (TBL) excitation which is modeled using both the Corcos and the Chase models. The acoustic response (self-noise) of the towed array is found using the transfer function of the tube and the PSD of the turbulent excitation.
The acoustic response spectrum is compared with the results from the literature. This happens to be the main contribution of the work. This is so because very little literature is available on towed arrays. There is only one analytical work available and our results match exactly with theirs. With respect to experimental results, although there are several articles, numerical values of the tube material properties, the fluid properties and the tube dimensions have not been reported in full. This makes the comparison very difficult. Hence, by doing several parametric studies and investigating properties of materials that were applicable like rubber or Nylon, we have managed to narrow down the parameter ranges and made comparisons with the experimental results.
We have matched single hydrophone TBL response with experimental results from two separate groups. We have had to vary several parameter values in order to do this. The parameters include the Young's Modulus, density, Poisson's ratio and the thickness and diameter of the tube. Also included are the density and the speed of sound of the internal fluid. Sometimes a material from a handbook was chosen that gave a set of parameters. After having matched with the experimental values, the idea was to conduct a parametric study to decide the most influential parameters. We have done this using both the dimensional physical variables as well as non-dimensional variables. We nondimensionalized the equations to help reduce the number of variables in the system and then studied the effect that each parameter has on the noise generated due to Turbulent Boundary Layer developed as a result of the tow. The dominant parameter that influences the TBL response at the hydrophone location is the tube radius a, followed by the Young Modulus E, the density of internal fluid pfi and the thickness h of the tube. An increment in a, E and h reduces the TBL response, while an pfi increment in increases the TBL response.
In addition, several analytical studies were conducted to understand the dispersion characteristics of fluid-_filled submerged tubes. This study is presented in the appendix in order to avoid cluttering the main document. The main idea that emerges from this study is that there is a single real wavenumber in this coupled fluid-structure system which responds at its resonance when the TBL spectrum wavenumber matches the wavenumber value. All other free waves are complex and hence under forced excitation, they do not respond.
Книги з теми "TBL Pressure Spectrum Model"
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Delgado Martín, Jordi, Andrea Muñoz-Ibáñez, and Ismael Himar Falcón-Suárez. 6th International Workshop on Rock Physics: A Coruña, Spain 13 -17 June 2022: Book of Abstracts. 2022nd ed. Servizo de Publicacións da UDC, 2022. http://dx.doi.org/10.17979/spudc.000005.
Повний текст джерелаАнотація:
[Abstract] The 6th International Workshop on Rock Physics (6IWRP) was held A Coruña, Spain, between 13th and 17th of June, 2022. This meeting follows the track of the five successful encounters held in Golden (USA, 2011), Southampton (UK, 2013), Perth (Australia, 2015), Trondheim (Norway, 2017) and Hong Kong (China, 2019). The aim of the workshop was to bring together experiences allowing to illustrate, discuss and exchange recent advances in the wide realm of rock physics, including theoretical developments, in situ and laboratory scale experiments as well as digital analysis. While rock physics is at the core of the oil & gas industry applications, it is also essential to enable the energy transition challenge (e.g. CO2 and H2 storage, geothermal), ensure a safe and adequate use of natural resources and develop efficient waste management strategies. The topics of 6IWRP covered a broad spectrum of rock physics-related research activities, including: • Experimental rock physics. New techniques, approaches and applications; Characterization of the static and dynamic properties of rocks and fluids; Multiphysics measurements (NMR, electrical resistivity…); Deep/crustal scale rock physics. • Modelling and multiscale applications: from the lab to the field. Numerical analysis and model development; Data science applications; Upscaling; Microseismicity and earthquakes; Subsurface stresses and tectonic deformations. • Coupled phenomena and rock properties: exploring interactions. Anisotropy; Flow and fractures; Temperature effects; Rock-fluid interaction; Fluid and pressure effects on geophysical signatures. • The energy transition challenge. Applications to energy storage (hydrogen storage in porous media), geothermal resources, energy production (gas hydrates), geological utilization and storage of CO2, nuclear waste disposal. • Rock physics templates: advances and applications. Quantitative assessment; Applications to reser voir characterization (role of seismic wave anisotropy and fracture networks). • Advanced rock physics tools. Machine learning; application of imaging (X-ray CT, X-ray μCT, FIB-SEM…) to obtain rock proper ties. This book compiles more than 50 abstracts, summarizing the works presented in the 6IWRP by rock physicists from all over the world, belonging to both academia and industry. This book means an updated overview of the rock physics research worldwide.
Частини книг з теми "TBL Pressure Spectrum Model"
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Madeira, Fabiana Ferreira Braga, and Gerlinde Agate Platais Brasil Teixeira. "Project-based learning – A significant learning at Júlia Kubitschek state college." In DEVELOPMENT AND ITS APPLICATIONS IN SCIENTIFIC KNOWLEDGE. Seven Editora, 2023. http://dx.doi.org/10.56238/devopinterscie-200.
Повний текст джерелаАнотація:
The project entitled Project-based learning was developed at Colégio Estadual Júlia Kubitscheck and was inspired by the period of the COVID-19 pandemic in a hybrid teaching format. The classes taught had a remote profile, sometimes they were carried out by video call communication service, sometimes by recorded classes, and made available on the SEEDUC/RJ platform. Faced with this reality, active methodologies enable the construction of collaborative classes based on more lively and meaningful learning experiences for students. The objective of the project was to highlight the themes of inclusive education - deafness, physical disability, autism spectrum disorder, intellectual disability, blindness, high abilities, and giftedness through an active methodology that awakens youth protagonism related to the programmatic contents of Portuguese Language, when possible and that the contents of the Portuguese Language curricular component were discussed in the projects. As a theoretical basis for the development of the project, it was based on Bacich (2017) who designs models of active methodologies for innovative practices in the classroom. The work methodology used was TBL Team-based learning – learning in teams that offer a participatory teaching model, as students can do it together, share ideas, and collaborate (AMARAL, 2017). The results indicate that it is possible in a public education system to offer innovative educational models to students, according to the national curriculum base, and that integrate them into the new literacies resulting from a contemporary society that consumes new technologies. The students resignified their knowledge, and their learning, they felt part of the teaching process.
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Walser, Hannah. "Epistemic Reality." In Writing the Mind, 69–105. Stanford University Press, 2022. http://dx.doi.org/10.11126/stanford/9781503630079.003.0003.
Повний текст джерелаАнотація:
Through readings of Poe's Dupin trilogy and Melville's “Bartleby,” this chapter develops the concept of a pragmatics of behavior, highlighting the way that formal and narratological choices steer a reader’s ad hoc epistemic stance in real time. By focalizing these texts through narrators who shift from one psychological model to another under pressure from a seemingly inexplicable series of actions (whether human or, in the case of Poe’s “The Murders in the Rue Morgue,” of ambiguous origin), Poe and Melville not only define a spectrum of epistemic stances toward the propositional contents of other minds, but also indicate the utilitarian goals of enforcing laws, managing subordinates, and maintaining a good-enough social harmony that inform even the most abstract theories of will and psychological interiority. As tightly controlled as philosophical thought experiments, these fictions delineate the conditions under which behaviorist explanations and predictions are more successful than intentionalist ones.
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Yung, Yuk L., and William B. DeMore. "Mars." In Photochemistry of Planetary Atmospheres. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195105018.003.0010.
Повний текст джерелаАнотація:
Mars has been extensively studied by a series of spacecraft since the dawn of the space age: by Mariners 4, 6, 7, and 9 (1965-1972), Mars 2 through 6 (1971-1974), and the two Viking Landers and Orbiters in 1976. The knowledge from spacecraft is supplemented by ground-based observations. The essential aspects of Mars are summarized in table 7.1. It is a smaller planet than Earth; the radius and mass are, respectively, 53% and 11% of Earth. The surface gravity is 3.71 m s~2, compared with the terrestrial value of 9.82 m s~2. The physical properties and composition of the Martian atmosphere are summarized in tables 7.1 and 7.2; isotopic composition is given in table 7.3. An example of how this knowledge is obtained is illustrated in figure 7.1, showing the mass spectrum obtained by the mass spectrometer experiment on Viking. The bulk atmosphere is composed of CO2, with small amounts of N2 and Ar and a trace amount of water vapor. Located at 1.52 AU from the sun, the mean insolation at Mars is about half that of Earth. As a result, it is a colder planet, with mean surface temperature of 220 K, too cold for water to flow on the surface in the current epoch. The lack of an ocean results in an arid and dusty climate. The obliquity of Mars is 25.2°, close to the terrestrial value of 23.5°; however, Mars has an eccentric orbit, with eccentricity of 0.093. The ratio of incident solar radiation at perihelion to aphelion is 1.45. The large seasonal variation in heating is believed to be responsible for the spectacular global dust storms that can be observed from Earth and have inspired imaginative but erroneous theories about their origin. The polar regions of Mars can be as cold as 125 K, so CO2 will condense as frost on the surface. In fact, according to the Leighton-Murray model, this is what determines the pressure of the atmosphere. Figure 7.2 shows the seasonal pressure variations at the Viking lander sites for 3.3 Mars years from 1976. Note that the magnitude of the pressure changes is of the order of 20%, compared to the maximum change of 1% on the surface of Earth.
Тези доповідей конференцій з теми "TBL Pressure Spectrum Model"
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Hambric, Stephen A., Yun Fan Hwang, and William K. Bonness. "Vibrations of Plates With Clamped and Free Edges Excited by Highly Subsonic Turbulent Boundary Layer Flow." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32224.
Повний текст джерелаАнотація:
Plate vibrations due to turbulent boundary layer (TBL) excitation can depend strongly on the plate boundary conditions, especially when the flow convects over the plate at speeds much slower than those of the bending waves in the plate. The vibration response of a TBL excited flat rectangular plate is analyzed with two sets of boundary conditions: (A) all four edges clamped, and (B) three edges clamped and one edge free, with the flow direction perpendicular to the free edge. A finite element model with discretization sufficient to resolve the convective wavenumbers in the flow excitation field is used for the study. Three TBL wall pressure excitation models are applied to the plates to represent the cross-spectra of the wall pressures: (1) a modified Corcos model, which includes all wavenumber components of excitation; (2) a low-wavenumber excitation model previously derived by one of the authors, which only models the wavenumber-white region of the modified Corcos model; and (3) an equivalent edge force model which only models the convective component in the modified Corcos model. The TBL wall pressure autospectrum is approximated using the model derived by Smolyakov and Tkachenko. The results obtained from applying models (2) and (3) to the clamped and free edge plates are compared to those generated using model (1). For the completely clamped boundary conditions, the low-wavenumber and Modified Corcos models yield nearly identical vibration spectra, indicating that surface interactions dominate the response of fully clamped plates excited by TBL pressures. For the free edge boundary condition, the vibrations predicted using the equivalent edge force and modified Corcos models match very well, showing that edge interactions between TBL pressures and structural modes dominate the vibrations of plates with free edges excited by TBL flow.
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Hwang, Y. F. "A Discrete Model of Turbulence Loading Function for Computation of Flow-Induced Vibration and Noise." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0534.
Повний текст джерелаАнотація:
Abstract This paper discusses a discrete representation of the spatially homogeneous and temporally stationary turbulence loading on a structure induced by low speed incompressible flow. In the classical random vibration theory involved with continuous structural systems, this forcing function is expressed as the space-time cross correlation function or its Fourier conjugate, the wavevector-frequency spectrum of the turbulent boundary layer (TBL) wall pressure. These functions cannot be applied directly to finite discrete systems, such as most finite-element structural models, because they contain a fine-scale oscillating component which represents the predominant pressure fluctuations convected with the flow. For example, at mid- and moderate high frequencies, this fluctuating length scale may become smaller than the mesh size of a discrete structure model. An approximated discrete forcing function model to ease this numerical difficulty is presented in this paper. The approximate forcing function model is verified by comparing the numerically calculated modal input force spectra to that obtained from exact analytical solutions. The numerical calculated values approach the exact solutions as the finite-element mesh size becomes smaller.
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Winkel, E. S., B. R. Elbing, D. R. Dowling, S. L. Ceccio, and M. Perlin. "High-Reynolds-Number Turbulent-Boundary-Layer Surface Pressure Fluctuations With Bubble or Polymer Additives." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79740.
Повний текст джерелаАнотація:
This paper reports multi-point dynamic pressure fluctuation measurements made beneath a high-Reynolds-number turbulent boundary layer (TBL) with wall-injection of air or polymer additives for the purpose of skin-friction drag reduction. Two independent experiments were conducted in the U.S. Navy’s Large Cavitation Channel (LCC) on a 12.9 m long, 3.05 m wide hydro-dynamically smooth (k+ < 1) flat plate at free-stream speeds from 6.5 to 20.0 m/s. The first, a bubble drag reduction experiment (BDR), involved injecting gas at flow rates ranging from 100 to 800 CFM (17.8 to 142.5 liter/s per meter of injector span) from one of two injectors located 1.32 and 9.78 m from the model leading edge. The second, a polymer drag reduction experiment (PDR), involved injecting polymer from a single slot injector, 1.32 m from the leading edge, at flow-rates ranging from 6 to 30 GPM (0.14 to 0.71 liter/s per meter of injector span). Dynamic pressure measurements were made with 16 flush-mounted transducers in “L”-shaped arrays located 10.7 and 9.8 m (70 × 106 < ReX < 210 × 106) from the leading edge for the BDR and PDR experiments, respectively. Measurements show modifications in the spectra, stream-wise coherence, and convection velocity of the pressure fluctuations due to the presence of gas or polymer in the near-wall region of the TBL. At the dynamic pressure measurement locations the maximum skin-friction drag reduction approached 100% for the BDR experiment and 63% for the PDR experiment.
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Haridas, Akash, and Nagabhushana Rao Vadlamani. "Modelling Wall-Pressure Spectra in Turbulent Boundary Layers Using Neural Networks." In ASME 2021 Gas Turbine India Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gtindia2021-76301.
Повний текст джерелаАнотація:
Abstract In this work, we model the spectra of wall-pressure fluctuations beneath subsonic, supersonic and hypersonic turbulent boundary layers (TBLs) at zero pressure gradient using neural networks (NNs). We collect and compile data pertaining to wall-pressure fluctuation spectra from several experimental and computational studies on TBLs. In contrast to conventional methods of hand-tuning the parameters of a model to fit the available data, the use of modern powerful statistical learning techniques such as neural networks provide an automatic and quick way to fit a model. We explore four different scenarios of making use of the compiled data. In comparison with COMPRA-G, an empirical model recently proposed to account for compressibility effects in TBLs, we achieve a better fit to observed data using the NN model, particularly at low frequencies of the spectra.
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Oh, Jinho, Jinbok Choi, and Jeong-Soo Ryu. "A Response Spectrum Approach Using Model Order Reduction for Seismic Analysis." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97225.
Повний текст джерелаАнотація:
A response spectrum analysis (RSA) has been widely known as one of the methods used for the purpose of an earthquake-resistant design of a structure in the nuclear industry through evaluating the structural integrity during and after seismic events. Recently, as the structures, systems, and components for the design are massive, complex, and complicate, a considerable amount of computational resources and time is required for applying the RSA. Reduced methods have been considered as important technique to resolve computational resources and time problem. For a few decades, various approximate techniques have been developed to obtain the dynamic characteristic in a reduced manner. This paper adopts the model order reduction (MOR) technique known as the one of various reduction methods. The MOR for solving the large linear system in mathematics has been studied by a number of researchers. The MOR is achieved by applying a projection from a higher-order to a lower-order space using Krylov subspaces generated by the Arnoldi algorithm. It has been extended to engineering applications such as circuit analysis, structural analysis, and multi-scale analysis. However, it has not yet been applied in RSA. The aim of this study is to evaluate applicability of the MOR into RSA. Numerical examples demonstrate that the proposed method saves computational costs effectively with maintaining accuracy. Thus, it is confirmed that the proposed method is valid and applicable in predicting seismic responses.
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Somogyine Molnar, J., A. Abordan, T. E. Dobroka, T. Ormos, and M. Dobroka. "Characteristic Pressure Spectrum Produced with a New Multi-Exponential Model Describing Quality Factor-Pressure Relationship." In NSG2020 26th European Meeting of Environmental and Engineering Geophysics. European Association of Geoscientists & Engineers, 2020. http://dx.doi.org/10.3997/2214-4609.202020074.
Повний текст джерела
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Franco, F., S. De Rosa, E. Ciappi, and F. Magionesi. "Sensitivity of the Predictive Structural Models Under Stochastic and Convective Excitation." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30022.
Повний текст джерелаАнотація:
The quality of the predictive response of a structural domain, under a random and convective load, is here analyzed by discussing each step of the numerical procedure. The structural response, due to a wall pressure distribution, is derived in modal coordinates according to a finite element scheme. The modal basis can include the dry or wet (aeroelastic) structural mode shapes: in the present analysis only the in vacuum eigenvectors are used. For such a problem one of the most critical points is the transformation of the pressure distribution into discrete locations. In fact, this step depends on (i) the assumed TBL model, (ii) the integration scheme and (iii) the frequency range. These three points are the goals of the present work where the specific sensitivity to each of them is investigated. The transformation of the pressure distribution into discrete locations can be computationally expensive for the desired level of the required numerical approximation. The use of consistent formulation in the finite element scheme can be unfeasible. Moreover the approximations, in expressing the pressure field, can have a different influence on the structural responses according to the chosen TBL models. This is another key aspect of the present work.
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Tan, X. Gary, and Amit Bagchi. "Computational Analysis for Validation of Blast Induced Traumatic Brain Injury and Protection of Combat Helmet." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87689.
Повний текст джерелаАнотація:
Current understanding of blast wave transmission and mechanism of primary traumatic brain injury (TBI) and the role of helmet is incomplete thus limiting the development of protection and therapeutic measures. Combat helmets are usually designed based on costly and time consuming laboratory tests, firing range, and forensic data. Until now advanced medical imaging and computational modeling tools have not been adequately utilized in the design and optimization of combat helmets. The goal of this work is to develop high fidelity computational tools, representative virtual human head and combat helmet models that could help in the design of next generation helmets with improved blast and ballistic protection. We explore different helmet configurations to investigate blast induced brain biomechanics and understand the protection role of helmet by utilizing an integrated experimental and computational method. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we solved the dynamic problem of helmet and head under the blast exposure. Experimental shock tube tests of the head surrogate provide benchmark quality data and were used for the validation of computational models. The full-scale computational NRL head-neck model with a combat helmet provides physical quantities such as acceleration, pressure, strain, and energy to blast loads thus provides a more complete understanding of the conditions that may contribute to TBI. This paper discusses possible pathways of blast energy transmission to the brain and the effectiveness of helmet systems at blast loads. The existing high-fidelity image-based finite element (FE) head model was applied to investigate the influence of helmet configuration, suspension pads, and shell material stiffness. The two-phase flow model was developed to simulate the helium-air shock wave interaction with the helmeted head in the shock tube. The main contribution was the elucidation of blast wave brain injury pathways, including wave focusing in ocular cavities and the back of head under the helmet, the effect of neck, and the frequency spectrum entering the brain through the helmet and head. The suspension material was seen to significantly affect the ICP results and energy transmission. These findings can be used to design next generation helmets including helmet shape, suspension system, and eye protection.
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Onitsuka, Shohei, Tadashi Iijima, Yuichi Ushio, Yukihiko Okuda, Takamasa Hirai, and Katsuhisa Inagaki. "Seismic Margin Evaluation Methods Using Equivalent SDOF Model and Elasto-Plastic Response Spectrum." In ASME 2015 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/pvp2015-45469.
Повний текст джерелаАнотація:
Two simplified methods for evaluating seismic margin due to elasto-plastic response were proposed. Generally, elasto-plastic response is evaluated by nonlinear time-history response analysis using three-dimensional FEM model (3D FEM model). It, however, takes an immense amount of time with commonly used computers. In order to evaluate it in a shorter time, this study developed seismic margin evaluation methods using Equivalent Single Degree Of Freedom (ESDOF) model and elasto-plastic response spectrum. Additionally, the accuracy of the two methods was verified by static loading tests and vibration tests. Simple cantilever test specimens with several natural frequencies were used in the vibration tests, and input waves with several frequency characteristics were applied to each vibration test. Response displacement, response acceleration of the test specimens and input acceleration were measured in each vibration test. Maximum displacement given by ESDOF model of the test specimens was compared with the corresponding measured values of each vibration test in order to verify the accuracy of ESDOF model. Difference between the maximum displacement given by the ESDOF model and the vibration tests was around 5%, and computation time of the ESDOF model was one-tenth of 3D FEM model of the test specimens. In addition, elasto-plastic response spectrum of input waves in the vibration tests were compared with measured yield accelerations of the specimens in order to verify the accuracy of elasto-plastic response spectrum. Difference between the calculated elasto-plastic response spectrum and the measured yield acceleration of the test specimens was around 10%, and computation time of elasto-plastic response spectrum was one-tenth of the 3D FEM model. As a result, it is concluded that ESDOF model and elasto-plastic response spectrum are powerful tool to evaluate seismic margin.
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Lucchini, Andrea, Paolo Franchin, and Fabrizio Mollaioli. "A Spectrum-to-Spectrum Method for Calculating Uniform Hazard Floor Response Spectra." In ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65293.
Повний текст джерелаАнотація:
In codes’ provisions and design procedures for acceleration-sensitive nonstructural components, seismic demand is commonly defined by means of floor response spectra expressed in terms of pseudo-acceleration. Depending on the considered analysis method, floor response spectra may be derived from floors’ acceleration histories, based on structural response-history analysis, or calculated using a predictive equation from a given input ground motion spectrum. Methods for estimating floor response spectra that are based on the second alternative are commonly called spectrum-to-spectrum methods. The objective of this paper is to briefly review these methods, and to discuss the main assumptions they are based on. Both predictive equations from selected seismic codes and proposals from the literature are included in the review. A new probability-based method, recently developed by the Authors for generating uniform hazard floor response spectra, namely, floor response spectra whose ordinates are characterized by a given target value of the mean annual frequency of being exceeded, is also described. By using this method floor spectra are determined through closed-form equations, given the mean annual frequency of interest, the damping ratio of the spectra, the modal properties of the structure, and three uniform hazard ground spectra. The method is built on a proposal for a probabilistic seismic demand model that relates the ground spectral acceleration with the floor spectral acceleration, and is able to explicitly account for the ground motion variability of the nonstructural response. Results for a case study consisting of a service frame of a visbreaking unit in an oil refinery are presented to show the good predictive accuracy of the method with respect to exact uniform hazard floor response spectra obtained through a standard probabilistic analysis.
Звіти організацій з теми "TBL Pressure Spectrum Model"
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Alchanatis, Victor, Stephen W. Searcy, Moshe Meron, W. Lee, G. Y. Li, and A. Ben Porath. Prediction of Nitrogen Stress Using Reflectance Techniques. United States Department of Agriculture, November 2001. http://dx.doi.org/10.32747/2001.7580664.bard.
Повний текст джерелаАнотація:
Commercial agriculture has come under increasing pressure to reduce nitrogen fertilizer inputs in order to minimize potential nonpoint source pollution of ground and surface waters. This has resulted in increased interest in site specific fertilizer management. One way to solve pollution problems would be to determine crop nutrient needs in real time, using remote detection, and regulating fertilizer dispensed by an applicator. By detecting actual plant needs, only the additional nitrogen necessary to optimize production would be supplied. This research aimed to develop techniques for real time assessment of nitrogen status of corn using a mobile sensor with the potential to regulate nitrogen application based on data from that sensor. Specifically, the research first attempted to determine the system parameters necessary to optimize reflectance spectra of corn plants as a function of growth stage, chlorophyll and nitrogen status. In addition to that, an adaptable, multispectral sensor and the signal processing algorithm to provide real time, in-field assessment of corn nitrogen status was developed. Spectral characteristics of corn leaves reflectance were investigated in order to estimate the nitrogen status of the plants, using a commercial laboratory spectrometer. Statistical models relating leaf N and reflectance spectra were developed for both greenhouse and field plots. A basis was established for assessing nitrogen status using spectral reflectance from plant canopies. The combined effect of variety and N treatment was studied by measuring the reflectance of three varieties of different leaf characteristic color and five different N treatments. The variety effect on the reflectance at 552 nm was not significant (a = 0.01), while canonical discriminant analysis showed promising results for distinguishing different variety and N treatment, using spectral reflectance. Ambient illumination was found inappropriate for reliable, one-beam spectral reflectance measurement of the plants canopy due to the strong spectral lines of sunlight. Therefore, artificial light was consequently used. For in-field N status measurement, a dark chamber was constructed, to include the sensor, along with artificial illumination. Two different approaches were tested (i) use of spatially scattered artificial light, and (ii) use of collimated artificial light beam. It was found that the collimated beam along with a proper design of the sensor-beam geometry yielded the best results in terms of reducing the noise due to variable background, and maintaining the same distance from the sensor to the sample point of the canopy. A multispectral sensor assembly, based on a linear variable filter was designed, constructed and tested. The sensor assembly combined two sensors to cover the range of 400 to 1100 nm, a mounting frame, and a field data acquisition system. Using the mobile dark chamber and the developed sensor, as well as an off-the-shelf sensor, in- field nitrogen status of the plants canopy was measured. Statistical analysis of the acquired in-field data showed that the nitrogen status of the com leaves can be predicted with a SEP (Standard Error of Prediction) of 0.27%. The stage of maturity of the crop affected the relationship between the reflectance spectrum and the nitrogen status of the leaves. Specifically, the best prediction results were obtained when a separate model was used for each maturity stage. In-field assessment of the nitrogen status of corn leaves was successfully carried out by non contact measurement of the reflectance spectrum. This technology is now mature to be incorporated in field implements for on-line control of fertilizer application.