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Biplab Ranjan Adhikary, Ananya Majumdar, Atanu Sahu i Partha Bhattacharya. "Sensitivity of TBL Wall-Pressure over the Flat Plate on Numerical Turbulence Model Parameter Variations". CFD Letters 15, nr 7 (29.05.2023): 148–74. http://dx.doi.org/10.37934/cfdl.15.7.148174.
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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 i Guoming Deng. "Study on Radiated Noise of a Panel under Fluctuating Surface Pressure Due to an Idealized Side Mirror". Applied Sciences 10, nr 3 (3.02.2020): 994. http://dx.doi.org/10.3390/app10030994.
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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, nr 2 (1.04.1988): 220–25. http://dx.doi.org/10.1115/1.3269502.
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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 i P. K. Gupta. "Viscous Effects on Turbulent Boundary-Layer Noise of Ship's Sonar Dome in a Water Tunnel". Journal of Ship Research 35, nr 04 (1.12.1991): 331–38. http://dx.doi.org/10.5957/jsr.1991.35.4.331.
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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 i Nansong Li. "Flow Noise Spectrum Analysis for Vertical Line Array During Descent in Deep Water". Journal of Theoretical and Computational Acoustics 28, nr 04 (19.10.2020): 2050022. http://dx.doi.org/10.1142/s259172852050022x.
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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 i Shizhao Wang. "A non-equilibrium slip wall model for large-eddy simulation with an immersed boundary method". AIP Advances 12, nr 9 (1.09.2022): 095014. http://dx.doi.org/10.1063/5.0101010.
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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 i 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, nr 7 (1.02.2023): 544–51. http://dx.doi.org/10.3397/in_2022_0075.
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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, nr 3_supplement (1.03.2023): A75. http://dx.doi.org/10.1121/10.0018211.
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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 i DAVID R. DOWLING. "The mean velocity profile of a smooth-flat-plate turbulent boundary layer at high Reynolds number". Journal of Fluid Mechanics 665 (6.12.2010): 357–81. http://dx.doi.org/10.1017/s0022112010003952.
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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, nr 5 (2002): 2379. http://dx.doi.org/10.1121/1.4778064.
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Lysak, Peter D. "Modeling the Wall Pressure Spectrum in Turbulent Pipe Flows". Journal of Fluids Engineering 128, nr 2 (19.08.2005): 216–22. http://dx.doi.org/10.1115/1.2170125.
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An important source of vibration and noise in piping systems is the fluctuating wall pressure produced by the turbulent boundary layer. One approach to calculating the wall pressure fluctuations is to use a stochastic model based on the Poisson pressure equation. If the model is developed in the wave-number domain, the solution to the wave-number-frequency spectrum can be expressed as an integral of the turbulent sources over the boundary layer thickness. Models based on this formulation have been reported in the literature which show good agreement with measured pressure spectra, but they have relied on adjustable “tuning” constants to account for the unknown properties of the turbulent velocity fluctuations. A variation on this approach is presented in this paper, in which only well-known “universal” constants are used to model the turbulent velocity spectrum. The resulting pressure spectrum predictions are shown to be in good agreement with canonical data sets over a wide range of Reynolds numbers.
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Lam, N. T. K., Priyan Mendis i Tuan Ngo. "Response Spectrum Solutions for Blast Loading". Electronic Journal of Structural Engineering 4 (1.01.2004): 28–44. http://dx.doi.org/10.56748/ejse.439.
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Existing knowledge on the modelling of blast pressure have been further developed in this paper for engineering applications. Parametric studies involving time-history analyses of simple cantilevered wall models have been undertaken based on pre-defined pressure functions to study basic trends. The "corner period" of the velocity response spectrum was found to be the key controlling parameter in response behaviour modelling of the walls. An important contribution from this study is the identification of the directrelationship between the corner period and the "clearing time" for the blast. A simple and yet realistic capacity spectrum model has been developed for the design and assessment of cantilevered walls for its performance under blast loads. The practicality of the proposed model has been demonstrated herein by a worked example.
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Brown, Michael G. "A directional spectrum evolution model for ship noise". Journal of the Acoustical Society of America 153, nr 6 (1.06.2023): 3469. http://dx.doi.org/10.1121/10.0019851.
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A radiation transport equation that describes the spatiotemporal evolution of the directional spectrum of underwater acoustic noise is presented and applied to ship noise. A ray-based algorithm is used to solve the transport equation and numerically simulate the evolution of the directional noise spectrum produced by a passing ship. The model described accounts for the transient and highly episodic nature of shipping noise, the strong anisotropy of the radiated shipping noise, the directional dependence of the resulting acoustic field, and the critical angle dependence of bottom-reflected energy. The model predicts time histories of sound pressure level and directional spectral energy density at distant locations if the ship track and the ship's radiated noise power are known. Simulations are shown to be in qualitatively good agreement with observations.
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Beqiri, Erta, Marek Czosnyka, Afroditi D. Lalou, Frederick A. Zeiler, Marta Fedriga, Luzius A. Steiner, Arturo Chieregato i Peter Smielewski. "Influence of mild-moderate hypocapnia on intracranial pressure slow waves activity in TBI". Acta Neurochirurgica 162, nr 2 (16.12.2019): 345–56. http://dx.doi.org/10.1007/s00701-019-04118-6.
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Abstract Background In traumatic brain injury (TBI) the patterns of intracranial pressure (ICP) waveforms may reflect pathological processes that ultimately lead to unfavorable outcome. In particular, ICP slow waves (sw) (0.005–0.05 Hz) magnitude and complexity have been shown to have positive association with favorable outcome. Mild-moderate hypocapnia is currently used for short periods to treat critical elevations in ICP. Our goals were to assess changes in the ICP sw activity occurring following sudden onset of mild-moderate hypocapnia and to examine the relationship between changes in ICP sw activity and other physiological variables during the hypocapnic challenge. Methods ICP, arterial blood pressure (ABP), and bilateral middle cerebral artery blood flow velocity (FV), were prospectively collected in 29 adult severe TBI patients requiring ICP monitoring and mechanical ventilation in whom a minute volume ventilation increase (15–20% increase in respiratory minute volume) was performed as part of a clinical CO2-reactivity test. The time series were first treated using FFT filter (pass-band set to 0.005–0.05 Hz). Power spectral density analysis was performed. We calculated the following: mean value, standard deviation, variance and coefficient of variation in the time domain; total power and frequency centroid in the frequency domain; cerebrospinal compliance (Ci) and compensatory reserve index (RAP). Results Hypocapnia led to a decrease in power and increase in frequency centroid and entropy of slow waves in ICP and FV (not ABP). In a multiple linear regression model, RAP at the baseline was the strongest predictor for the decrease in the power of ICP slow waves (p < 0.001). Conclusion In severe TBI patients, a sudden mild-moderate hypocapnia induces a decrease in mean ICP and FV, but also in slow waves power of both signals. At the same time, it increases their higher frequency content and their morphological complexity. The difference in power of the ICP slow waves between the baseline and the hypocapnia period depends on the baseline cerebrospinal compensatory reserve as measured by RAP.
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Xu, Qian, i Zhong-Qi Wang. "Model for Calculating Seismic Wave Spectrum Excited by Explosive Source". Shock and Vibration 2021 (3.06.2021): 1–15. http://dx.doi.org/10.1155/2021/6544453.
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To reveal the characteristics and laws of the seismic wavefield amplitude-frequency excited by explosive source, the method for computing the seismic wave spectrum excited by explosive was studied in this paper. The model for calculating the seismic wave spectrum excited by explosive source was acquired by taking the seismic source model of spherical cavity as the basis. The results of using this model show that the main frequency and the bandwidth of the seismic waves caused by the explosion are influenced by the initial detonation pressure, the adiabatic expansion of the explosive, and the geotechnical parameters, which increase with the reduction of initial detonation pressure and the increase of the adiabatic expansion. The main frequency and the bandwidth of the seismic waves formed by the detonation of the explosives in the silt clay increase by 23.2% and 13.6% compared to those exploded in the silt. The research shows that the theoretical model built up in this study can describe the characteristics of the seismic wave spectrum excited by explosive in a comparatively accurate way.
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Kato, Hiroharu, Akihisa Konno, Masatsugu Maeda i Hajime Yamaguchi. "Possibility of Quantitative Prediction of Cavitation Erosion Without Model Test". Journal of Fluids Engineering 118, nr 3 (1.09.1996): 582–88. http://dx.doi.org/10.1115/1.2817798.
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A scenario for quantitative prediction of cavitation erosion was proposed. The key value is the impact force/pressure spectrum on a solid surface caused by cavitation bubble collapse. As the first step of prediction, the authors constructed the scenario from an estimation of the cavity generation rate to the prediction of impact force spectrum, including the estimations of collapsing cavity number and impact pressure. The prediction was compared with measurements of impact force spectra on a partially cavitating hydrofoil. A good quantitative agreement was obtained between the prediction and the experiment. However, the present method predicted a larger effect of main flow velocity than that observed. The present scenario is promising as a method of predicting erosion without using a model test.
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Rocha, Joana, Afzal Suleman i Fernando Lau. "Prediction of Turbulent Boundary Layer Induced Noise in the Cabin of a BWB Aircraft". Shock and Vibration 19, nr 4 (2012): 693–705. http://dx.doi.org/10.1155/2012/153204.
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This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). While, in previous works, the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is analyzed. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabin of a Blended Wing Body (BWB) aircraft, for the frequency range 0–1000 Hz. The results show that the number of vibrating panels significantly affects the interior noise levels. It is shown that the average SPL, over the cabin volume, increases with the number of vibrating panels. Additionally, the model is able to predict local SPL values, at specific locations in the cabin, which are also affected with by number of vibrating panels, and are different from the average values.
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Kamruzzaman, M., D. Bekiropoulos, Th Lutz, W. Würz i E. Krämer. "A Semi-Empirical Surface Pressure Spectrum Model for Airfoil Trailing-Edge Noise Prediction". International Journal of Aeroacoustics 14, nr 5-6 (październik 2015): 833–82. http://dx.doi.org/10.1260/1475-472x.14.5-6.833.
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Liodakis, I. "Toy model for the acceleration of blazar jets". Astronomy & Astrophysics 616 (sierpień 2018): A93. http://dx.doi.org/10.1051/0004-6361/201832766.
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Context. Understanding the acceleration mechanism of astrophysical jets has been a cumbersome endeavor from both the theoretical and observational perspective. Although several breakthroughs have been achieved in recent years, on all sides, we are still missing a comprehensive model for the acceleration of astrophysical jets. Aims. In this work we attempt to construct a simple toy model that can account for several observational and theoretical results and allow us to probe different aspects of blazar jets usually inaccessible to observations. Methods. We used the toy model and Lorentz factor estimates from the literature to constrain the black hole spin and external pressure gradient distributions of blazars. Results. Our results show that (1) the model can reproduce the velocity, spin and external pressure gradient of the jet in M 87 inferred independently by observations; (2) blazars host highly spinning black holes with 99% of BL Lac objects and 80% of flat spectrum radio quasars having spins a > 0.6; (3) the dichotomy between BL Lac objects and flat spectrum radio quasars could be attributed to their respective accretion rates. Using the results of the proposed model, we estimated the spin and external pressure gradient for 75 blazars.
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Lee, Yu-Tai, William K. Blake i Theodore M. Farabee. "Modeling of Wall Pressure Fluctuations Based on Time Mean Flow Field". Journal of Fluids Engineering 127, nr 2 (20.09.2004): 233–40. http://dx.doi.org/10.1115/1.1881698.
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Time-mean flow fields and turbulent flow characteristics obtained from solving the Reynolds averaged Navier-Stokes equations with a k‐ε turbulence model are used to predict the frequency spectrum of wall pressure fluctuations. The vertical turbulent velocity is represented by the turbulent kinetic energy contained in the local flow. An anisotropic distribution of the turbulent kinetic energy is implemented based on an equilibrium turbulent shear flow, which assumes flow with a zero streamwise pressure gradient. The spectral correlation model for predicting the wall pressure fluctuation is obtained through a Green’s function formulation and modeling of the streamwise and spanwise wave number spectra. Predictions for equilibrium flow agree well with measurements and demonstrate that when outer-flow and inner-flow activity contribute significantly, an overlap region exists in which the pressure spectrum scales as the inverse of frequency. Predictions of the surface pressure spectrum for flow over a backward-facing step are used to validate the current approach for a nonequilibrium flow.
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Luesutthiviboon, Salil, Daniele Ragni, Francesco Avallone i Mirjam Snellen. "An alternative permeable topology design space for trailing-edge noise attenuation". International Journal of Aeroacoustics 20, nr 3-4 (28.03.2021): 221–53. http://dx.doi.org/10.1177/1475472x211003295.
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This study focuses upon a new permeable topology design concept as an alternative to porous metal foams, for turbulent boundary layer trailing-edge (TBL-TE) noise attenuation. The present permeable topology has unconventional characteristics with respect to the metal foams: a combination of low flow resistivity r and high form drag coefficient C. The unconventional characteristics are realized by a Kevlar-covered 3D-printed perforated structure. An experimental study featuring a NACA 0018 airfoil model with a Kevlar-covered 3D-printed TE insert at chord-based Reynolds numbers up to [Formula: see text] is carried out. The airfoil with this TE insert gives a broadband TBL-TE noise reduction up to approximately 5 dB, compared to a solid TE. This reduction varies only slightly with airfoil loading (lower than 1 dB variation), in contrast to the porous metal foams (up to 3 dB variation). When comparing the variation of noise attenuation given by all the permeable materials considered, the variation is found to decrease with the increasing C. This is because C specifies the permeable material's ability to withstand the increasing pressure difference, which causes cross flow that might interfere with the noise attenuation mechanism. Additionally, the drag coefficients as well as the roughness noise of the airfoil equipped with the present TE insert are also significantly lower than those of the metal-foam TE, and are mostly negligible compared to the fully solid airfoil. Based on the findings, design guidelines for permeable TE are proposed: the permeable material shall have a combination of a low flow resistivity and a high form drag coefficient as well as a negligible surface roughness.
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Slama, Myriam, Cédric Leblond i Pierre Sagaut. "A Kriging-based elliptic extended anisotropic model for the turbulent boundary layer wall pressure spectrum". Journal of Fluid Mechanics 840 (6.02.2018): 25–55. http://dx.doi.org/10.1017/jfm.2017.810.
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The present study addresses the computation of the wall pressure spectrum for a turbulent boundary layer flow without pressure gradient, at high Reynolds numbers, using a new model, the Kriging-based elliptic extended anisotropic model (KEEAM). A space–time solution to the Poisson equation for the wall pressure fluctuations is used. Both the turbulence–turbulence and turbulence–mean shear interactions are taken into account. It involves the mean velocity field and space–time velocity correlations which are modelled using Reynolds stresses and velocity correlation coefficients. We propose a new model, referred to as the extended anisotropic model, to evaluate the latter in all regions of the boundary layer. This model is an extension of the simplified anisotropic model of Gavin (PhD thesis, 2002, The Pennsylvania State University, University Park, PA) which was developed for the outer part of the boundary layer. It relies on a new expression for the spatial velocity correlation function and new parameters calibrated using the direct numerical simulation results of Sillero et al. (Phys. Fluids, vol. 26, 2014, 105109). Spatial correlation coefficients are related to space–time coefficients with the elliptic model of He & Zhang (Phys. Rev. E, vol. 73, 2006, 055303). The turbulent quantities necessary for the pressure computation are obtained by Reynolds-averaged Navier–Stokes solutions with a Reynolds stress turbulence model. Then, the pressure correlations are evaluated with a self-adaptive sampling strategy based on Kriging in order to reduce the computation time. The frequency and wavenumber–frequency wall pressure spectra obtained with the KEEAM agree well with empirical models developed for turbulent boundary layer flows without pressure gradient.
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Smol’yakov, A. V. "A new model for the cross spectrum and wavenumber-frequency spectrum of turbulent pressure fluctuations in a boundary layer". Acoustical Physics 52, nr 3 (maj 2006): 331–37. http://dx.doi.org/10.1134/s1063771006030146.
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Mead, A. J., T. Tröster, C. Heymans, L. Van Waerbeke i I. G. McCarthy. "A hydrodynamical halo model for weak-lensing cross correlations". Astronomy & Astrophysics 641 (wrzesień 2020): A130. http://dx.doi.org/10.1051/0004-6361/202038308.
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On the scale of galactic haloes, the distribution of matter in the cosmos is affected by energetic, non-gravitational processes, the so-called baryonic feedback. A lack of knowledge about the details of how feedback processes redistribute matter is a source of uncertainty for weak-lensing surveys, which accurately probe the clustering of matter in the Universe over a wide range of scales. We developed a cosmology-dependent model for the matter distribution that simultaneously accounts for the clustering of dark matter, gas, and stars. We informed our model by comparing it to power spectra measured from the BAHAMAS suite of hydrodynamical simulations. In addition to considering matter power spectra, we also considered spectra involving the electron-pressure field, which directly relates to the thermal Sunyaev-Zel’dovich (tSZ) effect. We fitted parameters in our model so that it can simultaneously model both matter and pressure data and such that the distribution of gas as inferred from tSZ has an influence on the matter spectrum predicted by our model. We present two variants, one that matches the feedback-induced suppression seen in the matter–matter power spectrum at the percent level and a second that matches the matter–matter data to a slightly lesser degree (≃2%). However, the latter is able to simultaneously model the matter–electron pressure spectrum at the ≃15% level. We envisage our models being used to simultaneously learn about cosmological parameters and the strength of baryonic feedback using a combination of tSZ and lensing auto- and cross-correlation data.
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Dadhich, Yogesh, Nazek Alessa, Reema Jain, Abdul Razak Kaladgi, Karuppusamy Loganathan i V. Radhika Devi. "Thermal Onsets of Viscous Dissipation for Radiative Mixed Convective Flow of Jeffery Nanofluid across a Wedge". Symmetry 15, nr 2 (1.02.2023): 385. http://dx.doi.org/10.3390/sym15020385.
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The current analysis discusses Jeffery nanofluid’s thermally radiative flow with convection over a stretching wedge. It takes into account the Brownian movement and thermophoresis of the Buongiorno nanofluid model. The guiding partial differential equations (PDEs) are modified by introducing the symmetry variables, leading to non-dimensional ordinary differential equations (ODEs). To solve the generated ODEs, the MATLAB function bvp4c is implemented. Examined are the impacts of different flow variables on the rate of transmission of heat transfer (HT), temperature, mass, velocity, and nanoparticle concentration (NC). It has been noted that the velocity and mass transfer were increased by the pressure gradient factor. Additionally, the thermal boundary layer (TBL) and nanoparticle concentration are reduced by the mixed convection (MC) factor. In order to validate the present research, the derived numerical results were compared to previous findings from the literature while taking into account the specific circumstances. It was found that there was good agreement in both sets of data.
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Batrakov, Andrei. "Experimental and numerical simulation of the wall-pressure fluctuation on the isolated helicopter fuselage". EPJ Web of Conferences 269 (2022): 01002. http://dx.doi.org/10.1051/epjconf/202226901002.
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This work is devoted to wall-pressure fluctuation analysis. The object of investigation was an isolated helicopter fuselage. Investigation was carried out by experimental and numerical methods. Numerical simulation was based on RANS and DES approaches. The experiment was carried out in a lowspeed wind tunnel with an open test section. Wall-pressure fluctuation was measurement by high-frequency pressure probes ENDEVCO 8510B-2. The experimental results were compared with both DES data and results by the semi-empirical model based on the RANS simulation. It was shown that DES modelling provides a wall-pressure spectrum for low and middle-frequency parts. For simulation high-frequency part of the spectrum, the semi-empirical model is preferable.
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Ou, Li Jian, Feng Hong Wang i Wei Zhang. "Marine Ducted Propeller Blade Fracture Fault Diagnosis Technology Based on CFD". Applied Mechanics and Materials 488-489 (styczeń 2014): 1219–23. http://dx.doi.org/10.4028/www.scientific.net/amm.488-489.1219.
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The numerical model of the unsteady flow field of ducted propellers is based on CFD (computational fluid dynamics). By applying the numerical model, the unsteady flow field of the ducted propeller with the fracture in different positions of a certain blade is simulated and its unsteady hydrodynamic performance is numerically analyzed. By extracting the fluctuating pressure data of the duct inner wall monitoring points,the fluctuating pressure-time oscillogram of ducted propellers is obtained, and then the spectrum is obtained by FFT transformation of the oscillogram. A blade fracture fault diagnosis technology of ducted propellers, which combines oscillogram analysis method with spectrum analysis method, is put forward by analyzing and studying the oscillogram and the spectrum.
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Rao, V. Bhujanga. "Selection of a Suitable Wall Pressure Spectrum Model for Estimating Flow-Induced Noise in Sonar Applications". Shock and Vibration 2, nr 5 (1995): 403–12. http://dx.doi.org/10.1155/1995/720535.
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Flow-induced structural noise of a sonar dome in which the sonar transducer is housed, constitutes a major source of self-noise above a certain speed of the vessel. Excitation of the sonar dome structure by random pressure fluctuations in turbulent boundary layer flow leads to acoustic radiation into the interior of the dome. This acoustic radiation is termed flow-induced structural noise. Such noise contributes significantly to sonar self-noise of submerged vessels cruising at high speed and plays an important role in surface ships, torpedos, and towed sonars as well. Various turbulent boundary layer wall pressure models published were analyzed and the most suitable analytical model for the sonar dome application selected while taking into account high frequency, fluid loading, low wave number contribution, and pressure gradient effects. These investigations included type of coupling that exists between turbulent boundary layer pressure fluctuations and dome wall structure of a typical sonar dome. Comparison of theoretical data with measured data onboard a ship are also reported.
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Fu, Liufang, Peng Li, Xinhua Zhang, Shuqing Ma i Chengzhi Gao. "Vector Ocean Ambient Noise Spectrum Simulation Based on Parabolic Equation Model in Shallow Water". Journal of Computational Acoustics 25, nr 02 (31.03.2017): 1750034. http://dx.doi.org/10.1142/s0218396x17500345.
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Ocean ambient noise spectrum is one of the most important characteristics of ambient noise. An ocean vector ambient noise field model was built up based on parabolic equation in this paper. Then the spectra of sound pressure, horizontal particle velocity and vertical particle velocity were calculated applying the model considering noise sources well distributed on the surface with typical summer sound speed profile in South China Sea. The simulation results showed that spectra of sound pressure, horizontal particle velocity and vertical particle velocity were obviously not varied with depth. Then, the simulated results were compared with the experiment results at the receiving depth of a trail in South China Sea in July 2012. Compared with the experimental results, the simulation results are consistent well with the experimental one of sound pressure and horizontal particle velocity in the trend. But the simulation values at low frequency band below 500[Formula: see text]Hz, are not consistent with the experimental one very well, in the band the simulation results are lower than the experimental by about 3–5[Formula: see text]dB. But the simulation result of vertical particle velocity was not consistent with the experimental one, illustrating that the precision of the model might not be enough in the vertical direction.
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Tamisier, R., J. L. Pepin, B. Wuyam, R. Smith, J. Argod i P. Levy. "Characterization of pharyngeal resistance during sleep in a spectrum of sleep-disordered breathing". Journal of Applied Physiology 89, nr 1 (1.07.2000): 120–30. http://dx.doi.org/10.1152/jappl.2000.89.1.120.
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Aims of the study were 1) to compare Hudgel's hyperbolic with Rohrer's polynomial model in describing the pressure-flow relationship, 2) to use this pressure-flow relationship to describe these resistances and to evaluate the effects of sleep stages on pharyngeal resistances, and 3) to compare these resistances to the pressure-to-flow ratio (ΔP/V˙). We studied 12 patients: three with upper airway resistance syndrome (UARS), four with obstructive sleep hypopnea syndrome (OSHS), three with obstructive sleep apnea syndrome (OSAS), and two with simple snoring (SS). Transpharyngeal pressures were calculated between choanae and epiglottis. Flow was measured by use of a pneumotachometer. The pressure-flow relationship was established by using nonlinear regression and was appreciated by the Pearson's square ( r 2). Mean resistance at peak pressure (Rmax) was calculated according to the hyperbolic model during stable respiration. In 78% of the cases, the value of r 2 was greater when the hyperbolic model was used. We demonstrated that Rmax was in excellent agreement with P/V˙. UARS patients exhibited higher awake mean Rmax than normal subjects and other subgroups and a larger increase from wakefulness to slow-wave sleep than subjects with OSAS, OSHS, and SS. Analysis of breath-by-breath changes in Rmax was also a sensitive method to detect episodes of high resistance during sleep.
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Grasso, G., P. Jaiswal, H. Wu, S. Moreau i M. Roger. "Analytical models of the wall-pressure spectrum under a turbulent boundary layer with adverse pressure gradient". Journal of Fluid Mechanics 877 (2.09.2019): 1007–62. http://dx.doi.org/10.1017/jfm.2019.616.
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This paper presents a comprehensive analytical approach to the modelling of wall-pressure fluctuations under a turbulent boundary layer, unifying and expanding the analytical models that have been proposed over many decades. The Poisson equation governing pressure fluctuations is Fourier transformed in the wavenumber domain to obtain a modified Helmholtz equation, which is solved with a Green’s function technique. The source term of the differential equations is composed of turbulence–mean shear and turbulence–turbulence interaction terms, which are modelled separately within the hypothesis of a joint normal probability distribution of the turbulent field. The functional expression of the turbulence statistics is shown to be the most critical point for a correct representation of the wall-pressure spectrum. The effect of various assumptions on the shape of the longitudinal correlation function of turbulence is assessed in the first place with purely analytical considerations using an idealised flow model. Then, the effect of the hypothesis on the spectral distribution of boundary-layer turbulence on the resulting wall-pressure spectrum is compared with the results of direct numerical simulation computations and pressure measurements on a controlled-diffusion aerofoil. The boundary layer developing over the suction side of this aerofoil in test conditions is characterised by an adverse pressure gradient. The final part of the paper discusses the numerical aspect of wall-pressure spectrum computation. A Monte Carlo technique is used for a fast evaluation of the multi-dimensional integral formulation developed in the theoretical part.
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Stosiak, Michał, Mykola Karpenko, Adam Deptuła, Kamil Urbanowicz, Paulius Skačkauskas, Anna Małgorzata Deptuła, Algimantas Danilevičius, Šarūnas Šukevičius i Mariusz Łapka. "Research of Vibration Effects on a Hydraulic Valve in the Pressure Pulsation Spectrum Analysis". Journal of Marine Science and Engineering 11, nr 2 (1.02.2023): 301. http://dx.doi.org/10.3390/jmse11020301.
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This paper identifies mechanical vibrations occurring in the operating environment of hydraulic systems used in marine engineering. Particular attention was paid to the influence of periodic vibrations on changes in the amplitude-frequency spectrum in a marine hydraulic system. For the case of analysing the effect of vibration on changes in the pressure pulsation spectrum with a proportional directional valve, a modified mathematical model was used. Experimental results were presented and compared with the results obtained from the mathematical model. A way of limiting the transmission of vibrations to the directional control valve body was proposed.
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Burkhoff, D., J. Alexander i J. Schipke. "Assessment of Windkessel as a model of aortic input impedance". American Journal of Physiology-Heart and Circulatory Physiology 255, nr 4 (1.10.1988): H742—H753. http://dx.doi.org/10.1152/ajpheart.1988.255.4.h742.
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To facilitate the analysis of aortic-ventricular coupling, simplified models of aortic input properties have been developed, such as the three-element Windkessel. Even though the impedance spectrum of the Windkessel reproduces the gross features of the real aortic input impedance, it fails to reproduce many of its details. In the present study we assessed the physiological significance of the differences between real and Windkessel impedance. We measured aortic input impedance spectra from five anesthetized open-chest dogs under a wide range of conditions. For each experimentally determined spectrum we estimated the corresponding values of the best-fit Windkessel parameters. By computer simulation we imposed both the real and best-fit Windkessel impedances on a model left ventricle and assessed the differences in seven different coupling variables. The analysis indicated that the Windkessel model provides a reasonable representation of afterload for purposes of predicting stroke volume, stroke work, oxygen consumption, and systolic and diastolic aortic pressures. However, the Windkessel model significantly underestimates peak aortic flow, slightly underestimates mean arterial pressure, and, of course, does not provide realistic aortic pressure and flow waveforms.
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Grenner, J. "Significance of a notch in the otoacoustic emission stimulus spectrum". Journal of Laryngology & Otology 126, nr 9 (17.07.2012): 897–901. http://dx.doi.org/10.1017/s0022215112001533.
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AbstractObjective:To explain a clinical observation: a notch in the stimulus spectrum during transient evoked otoacoustic emission measurement in ears with secretory otitis media.Methods:The effects of tympanic under-pressure were investigated using a pressure chamber. A model of the ear canal was also studied.Results:Tympanic membrane reflectance increased as a consequence of increased stiffness, causing a notch in the stimulus spectrum. In an adult, the notch could be clearly distinguished at an under-pressure of approximately −185 daPa. The sound frequency of the notch corresponded to a wavelength four times the ear canal length. The ear canal of infants was too short to cause a notch within the displayed frequency range. The notch was demonstrated using both Otodynamics and Madsen equipment.Conclusion:A notch in the otoacoustic emission stimulus spectrum can be caused by increased stiffness of the tympanic membrane, raising suspicion of low middle-ear pressure or secretory otitis media. This finding is not applicable to infants.
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Josserand, M. A., i G. C. Lauchle. "Modeling the Wavevector-Frequency Spectrum of Boundary-Layer Wall Pressure During Transition on a Flat Plate". Journal of Vibration and Acoustics 112, nr 4 (1.10.1990): 523–34. http://dx.doi.org/10.1115/1.2930138.
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A spectral model for the wall-pressure fluctuations induced on a zero pressure gradient, flat, rigid surface by a transitioning boundary layer at low Mach number is developed in this paper. The central assumption used in this modeling is that the space-time statistics associated with the formation, convection, and interaction of turbulent spots in a naturally occurring boundary-layer transition are independent of the space-time statistics of the wall-pressure fluctuations that are induced by the turbulence in the individual spots. Space-time correlations for the spots were determined experimentally and semi-empirical formulae are developed to predict these correlations. Previously published statistical descriptions of turbulence-induced wall-pressure fluctuations are coupled with the spot statistics to arrive at the model for the wavevector-frequency spectrum of the transition region. The basic result suggests that the wall-pressure wavevector-frequency spectrum of a transitioning boundary layer is approximately that produced by a fully-turbulent layer weighted by the intermittency factor.
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Layton, Anita T., Leon C. Moore i Harold E. Layton. "Multistability in tubuloglomerular feedback and spectral complexity in spontaneously hypertensive rats". American Journal of Physiology-Renal Physiology 291, nr 1 (lipiec 2006): F79—F97. http://dx.doi.org/10.1152/ajprenal.00048.2005.
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Single-nephron proximal tubule pressure in spontaneously hypertensive rats (SHR) can exhibit highly irregular oscillations similar to deterministic chaos. We used a mathematical model of tubuloglomerular feedback (TGF) to investigate potential sources of the irregular oscillations and the corresponding complex power spectra in SHR. A bifurcation analysis of the TGF model equations, for nonzero thick ascending limb (TAL) NaCl permeability, was performed by finding roots of the characteristic equation, and numerical simulations of model solutions were conducted to assist in the interpretation of the analysis. These techniques revealed four parameter regions, consistent with TGF gain and delays in SHR, where multiple stable model solutions are possible: 1) a region having one stable, time-independent steady-state solution; 2) a region having one stable oscillatory solution only, of frequency f1; 3) a region having one stable oscillatory solution only, of frequency f2, which is approximately equal to 2 f1; and 4) a region having two possible stable oscillatory solutions, of frequencies f1 and f2. In addition, we conducted simulations in which TAL volume was assumed to vary as a function of time and simulations in which two or three nephrons were assumed to have coupled TGF systems. Four potential sources of spectral complexity in SHR were identified: 1) bifurcations that permit switching between different stable oscillatory modes, leading to multiple spectral peaks and their respective harmonic peaks; 2) sustained lability in delay parameters, leading to broadening of peaks and of their harmonics; 3) episodic, but abrupt, lability in delay parameters, leading to multiple peaks and their harmonics; and 4) coupling of small numbers of nephrons, leading to multiple peaks and their harmonics. We conclude that the TGF system in SHR may exhibit multistability and that the complex power spectra of the irregular TGF fluctuations in this strain may be explained by switching between multiple dynamic modes, temporal variation in TGF parameters, and nephron coupling.
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Wang, Yue, Wanlong Ren, Gang Liu, Jin Liu, Juan Xu i Zongrui Hao. "The Pressure Pulsation and Spectrum Analysis of Ducted Propeller Based on SST k-ω model". Journal of Physics: Conference Series 1300 (sierpień 2019): 012080. http://dx.doi.org/10.1088/1742-6596/1300/1/012080.
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Yan, Fuyong, De-Hua Han i Xue-Lian Chen. "Pore Aspect Ratio Spectrum Inversion from Ultrasonic Measurements and Its Application". Journal of Computational Acoustics 23, nr 04 (grudzień 2015): 1540009. http://dx.doi.org/10.1142/s0218396x15400093.
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We have conducted simultaneous ultrasonic velocity and pore volume change measurements on a carbonate rock sample. By including of pressure dependent porosity data, we have improved Cheng’s pore aspect ratio spectrum inversion methodology and made the inverted pore aspect ratio spectrum more realistic. Tang’s unified velocity dispersion and attenuation model is modified and extended to poroelastic media with complex pore structure under undrained condition. Using improved pore aspect ratio spectra inversion methodology and modified Tang’s model, we have explored the potential application of pore aspect ratio spectrum in prediction of seismic wave dispersion and attenuation.
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Thomson, Nicholas, i Joana Rocha. "Comparison of Semi-Empirical Single Point Wall Pressure Spectrum Models with Experimental Data". Fluids 6, nr 8 (31.07.2021): 270. http://dx.doi.org/10.3390/fluids6080270.
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This study presents an evaluation of semi-empirical single-point wall pressure spectrum models by comparing model predictions with wind tunnel and flight test data. The mean squared error was used to compare the power spectral density of the wall pressure fluctuations predicted by semi-empirical models with a large amount of experimental data. Results show that the models proposed by Goody and Smol’yakov have the lowest mean squared error when predicting the power spectral density for wind tunnel experiments and the Rackl and Weston model has the lowest mean squared error when predicting the power spectral density for flight test data. In addition, although current studies of the power spectra obtained in the wind tunnel are similar, they are not generally an accurate representation of flight test experiments.
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Xie, Yingchun, Yucheng Xiao, Xuyan Liu, Guijie Liu, Weixiong Jiang i Jin Qin. "Time-Frequency Distribution Map-Based Convolutional Neural Network (CNN) Model for Underwater Pipeline Leakage Detection Using Acoustic Signals". Sensors 20, nr 18 (4.09.2020): 5040. http://dx.doi.org/10.3390/s20185040.
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Detection technology of underwater pipeline leakage plays an important role in the subsea production system. In this paper, a new method based on the acoustic leak signal collected by a hydrophone is proposed to detect pipeline leakage in the subsea production system. Through the pipeline leakage test, it is found that the radiation noise is a continuous spectrum of the medium and high-frequency noise. Both the increase in pipe pressure and the diameter of the leak hole will narrow the spectral structure and shift the spectrum center towards the low frequencies. Under the same condition, the pipe pressure has a greater impact on the noise; every 0.05 MPa increase in the pressure, the radiation sound pressure level increases by 6-7 dB. The time-frequency images were obtained by processing the acoustic signals using the Ensemble Empirical Mode Decomposition (EEMD) and Hilbert–Huang transform (HHT), and fed into a two-layer Convolutional Neural Network (CNN) for leakage detection. The results show that CNN can correctly identify the degree of pipeline leakage. Hence, the proposed method provides a new approach for the detection of pipeline leakage in underwater engineering applications.
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Lee, Shouyan, i Geert W. Schmid-Scho¨nbein. "Biomechanical Model for the Myogenic Response in the Microcirculation: Part I—Formulation and Initial Testing". Journal of Biomechanical Engineering 118, nr 2 (1.05.1996): 145–51. http://dx.doi.org/10.1115/1.2795952.
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The pressure dependent or myogenic contraction of arterioles is one of the most fundamental control mechanisms of microvascular perfusion. While many experimental observations have been obtained on the myogenic response, no generally accepted biomechanical model has been formulated. A novel biomechanical theory is proposed based on two fundamental assumptions: the arteriolar wall exhibits viscoelastic properties before and during myogenic contractions, and the contraction is achieved by a pressure dependent change of reference length. The formulation of the model and its application to different experimental procedures on microvascular smooth muscle in the literature is presented. The model describes closely a broad spectrum of steady and unsteady pressure dependent diameter variations of arterioles under a pressure dependent stimulus.
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Zuckerman, B. D., H. F. Weisman i F. C. Yin. "Arterial hemodynamics in a rabbit model of atherosclerosis". American Journal of Physiology-Heart and Circulatory Physiology 257, nr 3 (1.09.1989): H891—H897. http://dx.doi.org/10.1152/ajpheart.1989.257.3.h891.
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Although atherosclerosis significantly alters the structural characteristics of the arterial tree, its effect on arterial impedance, which is a means of quantifying the functional characteristics of the arterial system, has not been characterized. To assess how one type of atherosclerosis affects impedance, we studied arterial impedance in New Zealand White rabbits after 11 wk on a 2% cholesterol diet. From open-chest aortic pressures and flows, impedance data were obtained from spectral analysis of randomly paced and Fourier analysis of nonpaced beats. Compliance was calculated from the low-frequency impedance moduli by assuming a windkessel model for the arterial system. Under base-line conditions, the atherosclerotic impedance phase spectrum in the low-frequency range remained negative for higher values of frequency than in controls. There was no difference between the groups in mean arterial blood pressure, impedance modulus spectrum, characteristic impedance, compliance, or total peripheral resistance. Wave reflections were, however, increased in the atherosclerotic animals. The differences between the two groups in phase and wave reflection were completely abolished after phenylephrine (3 micrograms.kg-1.min-1). Thus this study demonstrates that under base-line conditions atherosclerosis increases wave reflection at the input to the arterial system in the absence of an alteration in global arterial compliance, total peripheral resistance, or mean blood pressure. This increase is presumably secondary to atherosclerotic changes at arterial sites, which produce local impedance mismatching.
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Zhang, Jian Guo, i Hui Min Zhuang. "Wind Tunnel Test of Symmetrical Twin-Tower Tall Building Model". Advanced Materials Research 919-921 (kwiecień 2014): 518–22. http://dx.doi.org/10.4028/www.scientific.net/amr.919-921.518.
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In this paper, taking symmetrical twin-tower tall building model as an example, a wind tunnel test with simultaneous surface pressure measurement, in 7 wind directions, was carried out. Integration of the surface pressures leads to base moment coefficient, of which the amplitude and frequency-domain characteristics were analyzed and compared with those of single tall building model. The result shows that mean value and root mean square of the interfering tower, in all wind directions, are basically the same as those of single tower, while in 0o wind direction, they differ greatly; mean value and root mean square of the interfered tower differ significantly, in every wind directions, from those of single tower. In 0o wind direction, the reduced spectrum of along-wind and across-wind base moment coefficient is greatly different from that of the single tower; in 90o wind direction, the along-wind base moment coefficient reduced spectrum for interfered tower is different from Davenport spectrum, while the peak value of across-wind base moment coefficient is half the corresponding value of single tower.
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Ethier, L., N. E. Massa, A. Béliveau i C. Carlone. "The Raman spectrum of Cs2SeO4 crystals". Canadian Journal of Physics 67, nr 7 (1.07.1989): 657–63. http://dx.doi.org/10.1139/p89-120.
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The Raman spectrum of Cs2SeO4 crystals has been obtained at T = 20 K. We have observed 23 of the 24 external modes predicted by a model with four formula units per unit cell. A comparison of the internal mode frequencies with those of the solution spectrum shows that the charge on the SeO4 tetrahedron is, in the crystal phase, less than two electrons. We have obtained the temperature dependence of the Raman spectrum from 20 to 650 K. For the internal modes only, we have observed the pressure dependence up to 25 kbars, and we have evaluated the volume dilatation and the interaction contributions to their total temperature dependence. (1 bar = 100 kPa.)
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Galindo, José, Francisco José Arnau, Luis Miguel García-Cuevas i Pablo Soler. "Experimental validation of a quasi-two-dimensional radial turbine model". International Journal of Engine Research 21, nr 6 (20.07.2018): 915–26. http://dx.doi.org/10.1177/1468087418788502.
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This article presents the experimental validation of a quasi-two-dimensional radial turbine model able to be used in turbocharged reciprocating internal combustion engine simulations. A passenger car variable-geometry turbine has been tested under steady and pulsating flow conditions, instrumented with multiple pressure probes, temperature sensors and mass flow sensors. Using the data obtained, a pressure decomposition has been performed. The pressure at the turbine inlet and outlet has been split into forward and backward travelling waves, employing the reflected and transmitted waves to verify the goodness of the model. The experimental results have been used to compare the quasi-two-dimensional radial turbine model as well as a classic one-dimensional model. The quasi-two-dimensional code presents a good degree of correlation with the experimental results, providing better results than the one-dimensional approach, especially when studying the high-frequency spectrum.
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Hao, Jin Feng, Jian Hua Gao, Yang Liu i Gui De Liu. "Spectrum Analysis of Isolated Vertical Seismic Response Storage Tanks". Applied Mechanics and Materials 166-169 (maj 2012): 2270–74. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.2270.
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Aiming at the problem of seismic response of the base isolation tanks, make the tanks simplify the mechanical model of three particles, considering the quality of continuous liquid that is in the tanks equivalent to convection quality, pulse quality and rigid quality and introducing isolation stiffness. According to the stiffness of each particle and quality calculate natural vibration period, making sure the power amplification coefficient, and analysis on the response spectrum of isolation vertical seismic response storage tanks. The results show that the response spectrum method calculating isolation vertical seismic response storage tanks tends to safety；With the site categories and isolation cycle's increasing, basal shear shock absorption rate gradually reduce , the change of shaking height of wave is not obvious, after isolating the earthquake , hydraulic pressure show linear change, hydraulic pressure increase as the increasing of the site categories and ratio of height to radius, along with the increasing of the isolation of the cycle increasing, hydraulic pressure decrease；ratio of height to radius exists certain optimization period, in the period of optimization , basal shear shock absorption rate is bigger, isolating effect is better.
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LI, CHENXI, JINGYING JIANG i KEXIN XU. "THE VARIATIONS OF WATER IN HUMAN TISSUE UNDER CERTAIN COMPRESSION: STUDIED WITH DIFFUSE REFLECTANCE SPECTROSCOPY". Journal of Innovative Optical Health Sciences 06, nr 01 (styczeń 2013): 1350005. http://dx.doi.org/10.1142/s1793545813500053.
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The reflectance spectrum has been widely adopted to extract diagnosis information of human tissue because it possesses the advantages of noninvasive and rapidity. The external pressure brought by fiber optic probe may influence the accuracy of measurement. In this paper, a systematic study is focused on the effects of probe pressure on intrinsic changes of water and scattering particles in tissue. According to the biphasic nonlinear mixture model, the pressure modulated reflectance spectrum of both in vitro and in vivo tissue is measured and processed with second-derivation. The results indicate that the variations of bulk and bonded water in tissue have a nonlinear relationship with the pressure. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Then the finite element (FEM) and Monte Carlo (MC) method is employed to simulate the deformation and reflectance spectrum variations of tissue before and after compression. The simulation results show that as the pressure of fiber optic probe applied to the detected skin increased to 80 kPa, the effective photon proportion form dermis decreases significantly from 86% to 76%. Future designs might benefit from the research of change of water volume inside the tissue to mitigate the pressure applied to skin.
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Chase, D. M. "The character of the turbulent wall pressure spectrum at subconvective wavenumbers and a suggested comprehensive model". Journal of Sound and Vibration 112, nr 1 (styczeń 1987): 125–47. http://dx.doi.org/10.1016/s0022-460x(87)80098-6.
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Gisby, J. A., i S. H. Walmsley. "A model of the effects of pressure on the near ultraviolet absorption spectrum of crystalline naphthalene". Chemical Physics Letters 135, nr 3 (kwiecień 1987): 275–78. http://dx.doi.org/10.1016/0009-2614(87)85155-2.
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Segovia-Chaves, Francis, Herbert Vinck-Posada i Edgar A. Gómez. "Transmittance in a dispersive quasiperiodic photonic crystal". International Journal of Modern Physics B 35, nr 04 (28.01.2021): 2150061. http://dx.doi.org/10.1142/s0217979221500612.
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In this work, transmittance spectrum for a quasiperiodic one-dimensional photonic crystal, composed of high-temperature superconductor and semiconductor layers arranged within the crystal based on a Dodecanacci sequence, has been calculated using the transfer matrix method and the two-fluid model. The critical temperature of the superconductor depends on the hydrostatic pressure, while the semiconductor’s plasma frequency and dielectric constant were considered to be dependent on both the pressure and temperature applied. We have found that the transmittance spectrum shows the band gaps unfolded and increased in number when the Dodecanacci sequence increased. In addition, this work shows that transmission responses can be tuned to higher frequencies as pressure increases. However, a small red shift of the transmittance spectrum can be observed as temperature increases. Finally, the research observed the maximization of the band gaps by increasing the thickness of the superconductor layers. We hope this work may be considered for application in tunable narrowband filters.