Acoustic Non-Reciprocal Band Structure in a Passive, Nonlinear, 1D Material

2019 ◽  
Author(s):  
Lezheng Fang ◽  
Amir Darabi ◽  
Alexander F. Vakakis ◽  
Michael J. Leamy
Keyword(s):  
Numerical Study ◽  
The Other ◽  
Signal Frequency ◽  
Strong Nonlinearity ◽  
Frequency Content ◽  
Minimal Distortion ◽  
Shape Structure ◽  
Band Pass ◽  
Path Dependent ◽  
Mechanical Devices

Abstract Acoustic non-reciprocity, referring to the phenomenon of path-dependent propagation, has diverse applications in mechanical devices. This paper presents a numerical study on a periodic triangle-shape structure that breaks reciprocity in a passive manner over a broad range of frequency and energy. The proposed structure contains strong nonlinearity and geometric asymmetry, which contributes to a direction-dependent dispersion relationship. When the signal frequency falls in the band pass in one direction, and band gap in the other, a unidirectional wave propagation results. The system achieves giant non-reciprocity with minimal distortion in the frequency content of the signal.

Tunnel performance during the Puebla-Mexico 19 September 2017 earthquake

2020 ◽  
Vol 36 (2_suppl) ◽  
pp. 288-313
Author(s):  
Juan M Mayoral ◽  
Gilberto Mosqueda ◽  
Daniel De La Rosa ◽  
Mauricio Alcaraz
Keyword(s):  
Mexico City ◽  
Seismic Performance ◽  
Urban Areas ◽  
Numerical Study ◽  
Three Dimensional ◽  
Frequency Content ◽  
Seismic Performance Evaluation ◽  
Ground Deformations ◽  
Under Construction ◽  
Observed Damage

Seismic performance of tunnels during earthquakes in densely populated areas requires assessing complex interactions with existing infrastructure such as bridges, urban overpasses, and metro stations, including low- to medium-rise buildings. This article presents the numerical study of an instrumented tunnel, currently under construction on stiff soils, located in the western part of Mexico City, during the Puebla-Mexico 19 September 2017 earthquake. Three-dimensional finite difference models were developed using the software FLAC3D. Initially, the static response of the tunnel was evaluated accounting for the excavation technique. Then, the seismic performance evaluation of the tunnel was carried out, computing ground deformations and factors of safety, considering soil nonlinearities. Good agreement was observed between predicted and observed damage during post-event site observations. Once the soundness of the numerical model was established, a numerical study was undertaken to investigate the effect of frequency content in tunnel-induced ground motion incoherence for tunnels built in cemented stiff soils. A series of strong ground motions recorded during normal and subduction events were used in the simulations, considering a return period of 250 years, as recommended in the Mexico City building code. From the results, it was concluded that the tunnel presence leads to important frequency content modification in the tunnel surroundings which can affect low- to mid-rise stiff structures located nearby. This important finding must be taken into account when assessing the seismic risk in highly populated urban areas, such as Mexico City.

Experimental and numerical study of an overlay composite absorber plate material for a solar air heater

2021 ◽  
Vol 63 (7) ◽  
pp. 681-686
Author(s):  
Duraisamy Jagadeesh ◽  
Ramasamy Venkatachalam ◽  
Gurusamy Nallakumarasamy
Keyword(s):  
Numerical Study ◽  
The Other ◽  
Solar Air Heater ◽  
Outlet Temperature ◽  
Cfd Analysis ◽  
Plate Material ◽  
Absorber Plate ◽  
Air Heater ◽  
Margin Of Error ◽  
Computational Processes

Abstract The research in this paper is a sequel of an earlier work by the author in which experimental and CFD results were compared for an absorber plate made of iron with and without fins for two flow rates. The research yielded a good comparative result between the experimental and computational process for an optimized flow rate and the effect of the fins. The objective of this paper is to verify the effect of the overlay composite absorber plate material on a solar air heater through experimental and computational fluid dynamics. The experimental setup consists of an absorber plate as an overlay composite of aluminum and copper for enhanced heat transfer. Experiments and CFD analysis were done in three configurations. In configuration one, only the aluminum absorber plate with fins was considered. In configuration two, the overlay composite was considered with copper on the top and aluminum at the bottom as fins, and in configuration three, the overlay composite was considered with aluminum at the top and copper at the bottom as fins. A transient 8 hours CFD analysis was carried out using these configurations. While validating the results it was found that the overlay absorber plate Cu-Al was capable of generating a high outlet temperature Max of 88 °C and capable of generating 83 °C air for 5 hours and had good thermal efficiency when compared to the other materials in the other two configuration. It was found that experimental and computational analysis were in very close agreement, and the margin of error between the experimental and computational processes was less than 8 %.

Numerical Study on Flow and Heat Transfer of a Cooled First Stage Vane of a Gas Turbine

2016 ◽  
Author(s):  
Lv Ye ◽  
Zhao Liu ◽  
Xiangyu Wang ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Numerical Study ◽  
Coolant Flow ◽  
The Other ◽  
Edge Region ◽  
Flow Rates ◽  
Flow And Heat Transfer ◽  
Film Cooling Holes

This paper presents a numerical simulation of composite cooling on a first stage vane of a gas turbine, in which gas by fixed composition mixture is adopted. To investigate the flow and heat transfer characteristics, two internal chambers which contain multiple arrays of impingement holes are arranged in the vane, several arrays of pin-fins are arranged in the trailing edge region, and a few arrays of film cooling holes are arranged on the vane surfaces to form the cooling film. The coolant enters through the shroud inlet, and then divided into two parts. One part is transferred into the chamber in the leading edge region, and then after impinging on the target surfaces, it proceeds further to go through the film cooling holes distributed on the vane surface, while the other part enters into the second chamber immediately and then exits to the mainstream in two ways to effectively cool the other sections of the vane. In this study, five different coolant flow rates and six different inlet pressure ratios were investigated. All the cases were performed with the same domain grids and same boundary conditions. It can be concluded that for the internal surfaces, the heat transfer coefficient changes gradually with the coolant flow rate and the inlet total pressure ratio, while for the external surfaces, the average cooling effectiveness increases with the increase of coolant mass flow rates while decreases with the increase of the inlet stagnation pressure ratios within the study range.

SELF-TUNING BIQUAD BAND-PASS FILTER

2013 ◽  
Vol 22 (03) ◽  
pp. 1350008 ◽  
Author(s):  
GORAN JOVANOVIĆ ◽  
DARKO MITIĆ ◽  
MILE STOJČEV ◽  
DRAGAN ANTIĆ
Keyword(s):  
Dynamic Range ◽  
Signal Frequency ◽  
Band Pass Filter ◽  
Central Frequency ◽  
Pass Filter ◽  
Input Signal Frequency ◽  
Bicmos Technology ◽  
Self Tuning ◽  
Band Pass ◽  
Constant Bandwidth

One approach to design self-tuning gm-C biquad band-pass filter is considered in this paper. The phase control loop is introduced to force filter central frequency to be equal to input signal frequency what is achieved by adjusting the amplifier transconductance gm. Thanks to that, the filter is robust to parameter perturbations and it can be used as a selective amplifier. In the full tuning range, it has a constant maximum gain at central frequency as well as a constant bandwidth. The 0.25 μm SiGe BiCMOS technology was used during design and verification of the band-pass filter. The filter has 26 dB gain, quality factor Q = 20 and central frequency up to 150 MHz. Simulation results indicate that the total in-band noise is 59 μV rms , the output third intercept point OIP3 = 4.36 dB and the dynamic range is 35 dB. Maximal power consumption at 3 V power supply is 1.115 mW.

scholarly journals A numerical study of the response of tropical Pacific SST to atmospheric forcing

MAUSAM ◽  
2021 ◽  
Vol 48 (4) ◽  
pp. 657-668
Author(s):  
XIAOMING LIU ◽  
JOHN M. MORRISON ◽  
LIAN XIE
Keyword(s):  
Ocean Circulation ◽  
Numerical Study ◽  
Ocean Model ◽  
Tropical Pacific ◽  
The Other ◽  
Atmospheric Forcing ◽  
Transfer Coefficients ◽  
Low Wind Speed ◽  
Sensitivity Tests ◽  
The Tropical Pacific

Two sets of atmospheric forcing from NCEP/NCAR 40-year reanalysis project, one based on monthly averaged climatological data and the other on 1982-83 monthly averaged data, are used to derive the global Miami Isopycnic Coordinate Ocean Model (MICOM). These two runs are referred to as the climatological experiments and 1982-83 El Nino experiments. Sensitivity tests of tropical Pacific SST to different bulk parameterizations of air-sea heat and momentum fluxes are carried out in the two experiments. Primary results show that constant transfer coefficients                          (1.2 × 10-3) for heat flux greatly overestimate the tropical Pacific SST, whereas the Liu-Katsaros-Businger (Liu et al. 1979) method can significantly improve the SST simulation especially under very low-wind speed conditions. On the other hand, Large and Pond (1982) formulation of the drag coefficient made little difference on the tropical Pacific SST simulation although it might modify the surface ocean circulation. The SST seasonal cycle and interannual variability of tropical Pacific SST are also examined in this study. Since SST is the most important oceanic parameter that provides the link between the atmosphere and the ocean, this evaluation of different parameterization schemes may facilitate future studies on coupling ocean-atmospheric numeric models.    

Numerical Study on Mixing of Two Fluids With Modified Tesla Structure

2009 ◽  
Author(s):  
Shakhawat Hossain ◽  
Mubashshir Ahmad Ansari ◽  
Afzal Husain ◽  
Kwang-Yong Kim
Keyword(s):  
Vortical Structure ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
The Other ◽  
Channel Width ◽  
Geometrical Parameters ◽  
Fluid Stream ◽  
Mixing Performance ◽  
Two Fluids ◽  
Wide Range

In this study, a parametric investigation on mixing of two fluids in a modified Tesla microchannel, has been preformed. Modified Tesla micromixer applies both flow separation and vortices string principles to enhance the mixing. The fluid stream splits into two sub-streams and one of them mixes with the other again at the exit of the Tesla unit. Analyses of mixing and flow field have been carried out for a wide range of Reynolds number from 0.05 to 40. Mixing performance and pressure drop characteristics with two geometrical parameters, i.e, ratio of the diffuser gap to channel width (h/w) and ratio of the curved gap to the channel width (s/w), have been analyzed at six different Reynolds numbers. The vortical structure of the flow has been analyzed to explain mixing performance. The sensitivity analysis reveals that mixing is more sensitive s/w, than the h/w.

scholarly journals Energy distribution in globular star clusters

1964 ◽  
Vol 20 ◽  
pp. 358-370
Author(s):  
L. H. Aller ◽  
D. J. Faulkner
Keyword(s):  
Energy Distribution ◽  
Spectral Range ◽  
Globular Clusters ◽  
Broad Band ◽  
Star Clusters ◽  
The Other ◽  
Energy Distributions ◽  
Single Observation ◽  
Band Pass ◽  
Time Required

The present investigation is concerned with the energy distributions in globular clusters. In a sense, energy-distribution measurements are comparable with multi-colour photometry. The chief advantage is that narrower band-passes may be used and the entire spectrum traced, whereas in multi-colour photometry one is limited to effective wavelengths determined by the filter and a rather broad band-pass. On the other hand, broad band-pass photometry often permits one to cover a broader spectral range, and to work much faster. Since the time required for a single observation is much shorter, the observer is less at the mercy of the sky transparency. Hence a greater accuracy can be obtained.

Fast Locking Time Biquadratic Band-Pass Filter Utilizing Nonlinear Sliding-Mode Controller

2020 ◽  
pp. 2150154
Author(s):  
Darko Mitić ◽  
Goran Jovanović ◽  
Mile Stojčev ◽  
Dragan Antić
Keyword(s):  
Input Signal ◽  
Sliding Mode ◽  
Design Procedure ◽  
Signal Frequency ◽  
Sliding Mode Controller ◽  
Band Pass Filter ◽  
Central Frequency ◽  
Pass Filter ◽  
Bicmos Technology ◽  
Band Pass

This paper considers design procedure of fast locking time self-tuning [Formula: see text] biquadratic band-pass filter with nonlinear sliding mode control. A sliding mode controller is building block of the phase control loop (PCL) involved to push central frequency to reach input signal frequency very fast, approximately 100–200[Formula: see text]ns. The sliding mode controller is realized by using a tunable delay line, enabling optimal filter locking time for different input signal frequencies. The filter possesses low sensitivity to component discrepancy and is applied as a selective amplifier. The 0.13[Formula: see text][Formula: see text]m SiGe BiCMOS technology has been utilized for design and verification of the presented filter. This filter has central frequency up to 220[Formula: see text]MHz, quality factor [Formula: see text] and 25[Formula: see text]dB gain.

Comparing high-sensitivity geophones to fiber-optic DAS technologies in a hard-rock VSP survey

2020 ◽  
Author(s):  
Björn Lund ◽  
Anna Stork ◽  
Michael Roth ◽  
Ari David ◽  
Andy Clarke ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Transfer Functions ◽  
Incidence Angle ◽  
High Sensitivity ◽  
Gauge Length ◽  
Signal Frequency ◽  
Nuclear Waste Repository ◽  
High Signal ◽  
Frequency Content ◽  
Velocity Signal

<p>As part of the preparations for a microseismic network on the planned nuclear waste repository in Forsmark, Sweden, we carried out a suite of measurements for site characterisation and instrument testing using geophones and DAS fiber-optic technology. Three high-sensitivity 240 V/m/s geophones were grouted into a 200 m deep borehole together with a linear, a helical and a helical engineered fiber-optical cable. Two different interrogators were used for DAS acquisition. We performed a walk-away vertical seismic profile (VSP) survey with 10 m source spacing out to 1.1 km offset and compare the responses of the four different measurement systems. The complete transfer functions of the fiber-optic systems have not yet been determined, and depend on factors such as incidence angle, signal frequency content and the fiber gauge length. Preliminary results show that all systems record signals with high signal-to-noise ratio and that which system has highest performance depends on source-receiver distance, signal frequency content and wave incidence angle. Due to incomplete knowledge of the fiber transfer functions we cannot match the DAS velocity signal with the geophone signal. Investigation of the detection capabilities of the fiber and geophone systems is underway and will be presented together with a discussion of the relative merits of the various systems for microseismic monitoring.</p>

Towards a self-consistent thermodynamic magmatic model for conduit transport processes

2020 ◽  
Author(s):  
Jost von der Lieth ◽  
Matthias Hort
Keyword(s):  
Numerical Study ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Dynamic Modelling ◽  
Explosive Volcanism ◽  
Transport Processes ◽  
The Other ◽  
Full Potential ◽  
Holistic View ◽  
Self Consistent

<p>The geodynamical side of explosive volcanic eruption modelling on the one hand, as well as the petrological one on the other, have reached a high degree of sophistication and maturity independently from each other over the years. Unfortunately, adherents of one discipline often only utilize the other’s tools in a simplified and makeshift way, obscuring the full potential of their synergies. Over the past decade efforts have been made to re-integrate both approaches to the issue into a more holistic view on the sub-surface processes leading to and concurrent with explosive volcanism.<br>One of the difficulties encountered in that effort are conceptual and technical incompatibilities between thermo- and fluid-dynamic modelling toolboxes. While the tools perform well individually, they are often not suitable to work in combination in highly complex numerical models, due to interface problems impeding performance.<br>For an ongoing numerical study on transport processes within a volcanic conduit, it has been deemed necessary to re-implement an established thermodynamic model based on Holland and Powell (2011, and follow-ups) in order to a) attain the required computing performance and b) to gain sufficient petrological insight (starting from a geophysical point of view) to be able to make apt use of the tool then at hand.<br>The path to the intermediate goal of deriving the thermodynamic and transport properties (e.g. density, viscosity, heat capacity and conductivity) in a <em>self-consistent and stable</em> manner suitable for further use in a numerical fluid-dynamics model is illustrated here. The focus is on problems encountered with the petrological modelling, and on the subsequent derivation of the above properties, that are not directly available from the former results. The methods presented are general and applicable to various settings regarding volcanic chemistry and transport processes, however, they will be demonstrated on low-viscosity open-conduit systems typical for strombolian activity.</p>

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