The relative-velocity version of the Morison equation for obstacle arrays in combined steady, low and high frequency motion

2018 ◽  
Vol 842 ◽  
pp. 188-214 ◽  
Author(s):  
H. Santo ◽  
P. H. Taylor ◽  
C. H. K. Williamson ◽  
Y. S. Choo
Keyword(s):  
Drag Force ◽  
High Frequency ◽  
Relative Velocity ◽  
Wave Drag ◽  
Mean Flow ◽  
Structural Dynamic ◽  
New Model ◽  
Forced Motion ◽  
Wide Range ◽  
Current Drag

This paper revisits the problem of forces on obstacle arrays in combined waves, an in-line steady current and structural dynamic motions. The intended application is the design and re-assessment of dynamically responding offshore platforms. Planar grids of perforated plates are moved in forced motion on three scales through otherwise stationary water. A new analytical wave–current–structure blockage model is developed by building on the existing wave–current blockage model presented by Santo et al. (J. Fluid Mech., vol. 739, 2014b, pp. 143–178) using a similar set of experiments but with forced motion on two scales. The new model, which is an improved Morison relative-velocity formulation, is tested against the experimental data for a range of structural to wave oscillation frequency ratios, $f_{s}/f_{w}=2$, 2.5 and 3. For relatively small current speed ($u_{c}$) and oscillatory structural velocity ($u_{s}$) compared with the oscillatory wave velocity ($u_{w}$), the drag force time history on grids is well approximated by a summation of the wave drag and the current drag components independently, without a $u_{w}\times u_{c}$ cross-term, consistent with the previous model. The wave drag component contains an additional $u_{s}$ contribution, while the current drag component may or may not contain an additional $u_{s}$ contribution depending on $f_{s}/f_{w}$. The measured drag force is observed to be asymmetric in time due to biasing from the mean flow. This is supported by numerical simulation using a porous block as a numerical model of the grids, although the simulated force asymmetry is weaker. All these effects can be sufficiently accounted for in the analytical model. The new model is shown to fit the variation of the experimental forces and force harmonics in time well for a wide range of cases, requiring only calibration of the Morison type drag and inertia coefficients. In contrast, the industry-standard version of the Morison relative-velocity formulation cannot reproduce the variation of the measured force in time, so present practice should be regarded as inadequate for combined steady, low frequency and high frequency motion acting on obstacle arrays.

Silencer for high-frequency turbocharger compressor noise via an acoustic straightener

2021 ◽  
Vol 263 (5) ◽  
pp. 1744-1755
Author(s):  
Pranav Sriganesh ◽  
Rick Dehner ◽  
Ahmet Selamet
Keyword(s):  
Wave Propagation ◽  
Plane Wave ◽  
High Frequency ◽  
Three Dimensional ◽  
Mean Flow ◽  
Analytical Treatment ◽  
Underlying Assumption ◽  
Wide Range ◽  
Plane Wave Propagation ◽  
Dimensional Wave

Decades of successful research and development on automotive silencers for engine breathing systems have brought about significant reductions in emitted engine noise. A majority of this research has pursued airborne noise at relatively low frequencies, which typically involve plane wave propagation. However, with the increasing demand for downsized turbocharged engines in passenger cars, high-frequency compressor noise has become a challenge in engine induction systems. Elevated frequencies promote multi-dimensional wave propagation rendering at times conventional silencer treatments ineffective due to the underlying assumption of one-dimensional wave propagation in their design. The present work focuses on developing a high-frequency silencer that targets tonal noise at the blade-pass frequency within the compressor inlet duct for a wide range of rotational speeds. The approach features a novel "acoustic straightener" that creates exclusive plane wave propagation near the silencing elements. An analytical treatment is combined with a three-dimensional acoustic finite element method to guide the early design process. The effects of mean flow and nonlinearities on acoustics are then captured by three-dimensional computational fluid dynamics simulations. The configuration developed by the current computational effort will set the stage for further refinement through future experiments.

Current blockage experiments: force time histories on obstacle arrays in combined steady and oscillatory motion

2013 ◽  
Vol 739 ◽  
pp. 143-178 ◽  
Author(s):  
H. Santo ◽  
P. H. Taylor ◽  
C. H. K. Williamson ◽  
Y. S. Choo
Keyword(s):  
Drag Force ◽  
Time History ◽  
Wave Drag ◽  
Oscillatory Motion ◽  
Velocity Amplitude ◽  
Steady Current ◽  
Oscillatory Velocity ◽  
Force Time ◽  
Current Blockage ◽  
Current Drag

AbstractThis paper revisits the problem of forces on obstacle arrays in combined waves and an in-line steady current. The intended application is the design and reassessment of offshore platforms. A series of experiments are performed on planar grids moved in both steady and oscillatory motion through otherwise stationary water. Detailed comparisons are made to a wave-current–structure interaction model recently presented by Taylor, Santo & Choo (Ocean Engng, vol. 57, 2013, pp. 11–24). We present new features of the model and test these against the experimental data. For relatively small current speed (${u}_{c} $) compared with oscillatory velocity amplitude (${u}_{w} $) with phase angle ($\omega t$), the drag force time history on grids with solid area ($A$) and projected frontal area (${A}_{f} $) is well approximated by a summation of the wave drag and the current drag components independently, so there is no ${u}_{w} \times {u}_{c} $ cross-term. The wave drag component is proportional to $\cos \omega t\vert \cos \omega t\vert $, while the current drag component to $\vert \cos \omega t\vert $, i.e. it is phase-locked to the oscillatory wave crests. The form of the predicted time history is new, so much of this paper is occupied in testing the adequacy of this theoretical form both in terms of an improved Morison-type formulation and also in the precise variation of the experimental drag force in time. We show that the measured crest and trough peak values of the drag force are consistent with the force peaks and troughs of the model prediction. The odd frequency harmonics of the measured drag force scale as the square of the oscillatory velocity amplitude $({ u}_{w}^{2} )$ and on the total hydrodynamic area (${C}_{d} A$). The shape of the odd harmonics is very similar to that for a pure oscillatory motion without steady current, but there are also even frequency harmonics associated with the current component. The even harmonics of the force scale as the square of the current speed $({ u}_{c}^{2} )$ and on the ${A}_{f} $, not on the ${C}_{d} A$. All of the above features are identified within the experimental data, and provide considerable support for the new current blockage model.The new model is also shown to fit the entire force time history well for a wide range of individual cases, with different blockage ratio ($A/ {A}_{f} $) and number of grids, requiring only calibration of the Morison-type drag and inertia coefficients. In contrast, the industry-standard form of the Morison equation can only be matched at a single instant of the oscillation cycle, so present practice should be regarded as seriously inadequate for combined steady current and oscillatory flow acting on obstacle arrays.

Drag on flat plates of arbitrary porosity

2018 ◽  
Vol 853 ◽  
Author(s):  
K. Steiros ◽  
M. Hultmark
Keyword(s):  
Flat Plate ◽  
Drag Force ◽  
Free Stream ◽  
Two Dimensional ◽  
Flat Plates ◽  
New Model ◽  
Momentum Theory ◽  
Wide Range ◽  
Model Predictions

A new model for the drag force on a two-dimensional flat plate of arbitrary porosity, oriented normal to the free stream, is introduced. The model is an extension of that introduced by Koo & James (J. Fluid Mech., vol. 60(3), 1973, pp. 513–538), where the performance at low porosities is improved by including a base-suction term. The additional drag due to the base suction is calculated implicitly using momentum theory, which makes the model self-contained. The model predictions exhibit convincing agreement with experimental observations over a wide range of porosities, including the solid case, as long as shedding is absent or suppressed.

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland
Keyword(s):  
Gravity Wave ◽  
Middle Atmosphere ◽  
Wave Train ◽  
Leading Edge ◽  
Wave Theory ◽  
Wave Drag ◽  
Tuning Parameter ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

scholarly journals Assessing evidence for adaptive evolution in two hearing-related genes important for high-frequency hearing in echolocating mammals

2021 ◽  
Author(s):  
Hui Wang ◽  
Hanbo Zhao ◽  
Yujia Chu ◽  
Jiang Feng ◽  
Keping Sun
Keyword(s):  
Adaptive Evolution ◽  
Hair Cells ◽  
High Frequency ◽  
Phylogenetic Trees ◽  
Outer Hair Cells ◽  
Functional Domain ◽  
Coding Region ◽  
Selective Pressures ◽  
Wide Range ◽  
Different Parts

Abstract High-frequency hearing is particularly important for echolocating bats and toothed whales. Previously, studies of the hearing-related genes Prestin, KCNQ4, and TMC1 documented that adaptive evolution of high-frequency hearing has taken place in echolocating bats and toothed whales. In this study, we present two additional candidate hearing-related genes, Shh and SK2, that may also have contributed to the evolution of echolocation in mammals. Shh is a member of the vertebrate Hedgehog gene family and is required in the specification of the mammalian cochlea. SK2 is expressed in both inner and outer hair cells, and it plays an important role in the auditory system. The coding region sequences of Shh and SK2 were obtained from a wide range of mammals with and without echolocating ability. The topologies of phylogenetic trees constructed using Shh and SK2 were different; however, multiple molecular evolutionary analyses showed that those two genes experienced different selective pressures in echolocating bats and toothed whales compared to non-echolocating mammals. In addition, several nominally significant positively selected sites were detected in the non-functional domain of the SK2 gene, indicating that different selective pressures were acting on different parts of the SK2 gene. This study has expanded our knowledge of the adaptive evolution of high-frequency hearing in echolocating mammals.

Parasites in Antarctic krill guts inferred from DNA sequences

2019 ◽  
Vol 31 (1) ◽  
pp. 16-22 ◽  
Author(s):  
Alison C. Cleary ◽  
Maria C. Casas ◽  
Edward G. Durbin ◽  
Jaime Gómez-Gutiérrez
Keyword(s):  
Dna Sequences ◽  
High Frequency ◽  
Dna Analysis ◽  
Antarctic Krill ◽  
Euphausia Superba ◽  
Gut Contents ◽  
The West ◽  
West Antarctic ◽  
Wide Range

AbstractThe keystone role of Antarctic krill,Euphausia superbaDana, in Southern Ocean ecosystems, means it is essential to understand the factors controlling their abundance and secondary production. One such factor that remains poorly known is the role of parasites. A recent study of krill diet using DNA analysis of gut contents provided a snapshot of the parasites present within 170E. superbaguts in a small area along the West Antarctic Peninsula. These parasites includedMetschnikowiaspp. fungi,Haptoglossasp. peronosporomycetes,LankesteriaandParalecudinaspp. apicomplexa,Stegophorussp. nematodes, andPseudocolliniaspp. ciliates. Of these parasites,Metschnikowiaspp. fungi andPseudocolliniaspp. ciliates had previously been observed inE. superba, as had other genera of apicomplexans, though notLankesteriaandParalecudina.In contrast, nematodes had previously only been observed in eggs ofE. superba, and there are no literature reports of peronosporomycetes in euphausiids.Pseudocolliniaspp., parasitoids which obligately kill their host, were the most frequently observed infection, with a prevalence of 12%. The wide range of observed parasites and the relatively high frequency of infections suggest parasites may play a more important role than previously acknowledged inE. superbaecology and population dynamics.

scholarly journals High frequency and wide range of human kidney papillary crystalline plugs

Urolithiasis ◽  
2017 ◽  
Vol 46 (4) ◽  
pp. 333-341 ◽  
Author(s):  
Léa Huguet ◽  
Marine Le Dudal ◽  
Marine Livrozet ◽  
Dominique Bazin ◽  
Vincent Frochot ◽  
...  
Keyword(s):  
High Frequency ◽  
Human Kidney ◽  
Wide Range

A Geometric Parametric Analysis of a Magnetorheological Engine Mount

2010 ◽  
Author(s):  
Walter Anderson ◽  
Constantine Ciocanel ◽  
Mohammad Elahinia
Keyword(s):  
High Frequency ◽  
New Technology ◽  
Low Frequency ◽  
Variable Stiffness ◽  
Small Displacement ◽  
Element Analysis ◽  
Mr Fluid ◽  
Wide Range ◽  
Engine Mount ◽  
Vehicle Technology

Engine vibration has caused a great deal of research for isolation to be performed. Traditionally, isolation was achieved through the use of pure elastomeric (rubber) mounts. However, with advances in vehicle technology, these types of mounts have become inadequate. The inadequacy stems from the vibration profile associated with the engine, i.e. high displacement at low frequency and small displacement at high frequency. Ideal isolation would be achieved through a stiff mount for low frequency and a soft mount for high frequency. This is contradictory to the performance of the elastomeric mounts. Hydraulic mounts were then developed to address this problem. A hydraulic mount has variable stiffness and damping due to the use of a decoupler and an inertia track. However, further advances in vehicle technology have rendered these mounts inadequate as well. Examples of these advances are hybridization (electric and hydraulic) and cylinder on demand (VCM, MDS & ACC). With these technologies, the vibration excitation has a significantly different profile, occurs over a wide range of frequencies, and calls for a new technology that can address this need. Magnetorheological (MR) fluid is a smart material that is able to change viscosity in the presence of a magnetic field. With the use of MR fluid, variable damping and stiffness can be achieved. An MR mount has been developed and tested. The performance of the mount depends on the geometry of the rubber part as well as the behavior of the MR fluid. The rubber top of the mount is the topic of this study due to its major impact on the isolation characteristics of the MR mount. To develop a design methodology to address the isolation needs of different hybrid vehicles, a geometric parametric finite element analysis has been completed and presented in this paper.

CLASSICAL-LIKE RESONANCE INDUCED BY NOISE IN A FITZHUGH–NAGUMO NEURON MODEL

1999 ◽  
Vol 09 (12) ◽  
pp. 2295-2303 ◽  
Author(s):  
S. RIPOLL MASSANÉS ◽  
C. J. PÉREZ VICENTE
Keyword(s):  
High Frequency ◽  
Interspike Interval ◽  
Low Frequency ◽  
Resonance Phenomenon ◽  
Characteristic Time Scale ◽  
Wide Range ◽  
External Stimuli ◽  
Interspike Interval Distribution ◽  
Stochastic Resonance Phenomenon ◽  
Interval Distribution

We have studied the stochastic behavior of Fitzhugh–Nagumo neuron-like model (FN) induced by subthreshold external stimuli. Our analysis based on three standard measures: the power spectrum, interspike interval distribution (ISI) and autocorrelation function shows that it is possible to define a characteristic time scale which can be identified in the response of the system for a wide range of frequencies. In contrast to previous studies we have focused our attention on high frequency signals which could be of interest for real systems such as nervous fibers in the auditory system. We report behaviors which resemble those of classical deterministic oscillators but never the stochastic resonance phenomenon typical of low frequency signals.

Design of high-frequency wide-range all digital phase locked loop in 90 nm CMOS

2013 ◽  
Vol 75 (1) ◽  
pp. 133-145 ◽  
Author(s):  
Prashanth Muppala ◽  
Saiyu Ren ◽  
George Yu-Heng Lee
Keyword(s):  
High Frequency ◽  
Phase Locked Loop ◽  
Digital Phase ◽  
Wide Range
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