Steady-state Source Research Articles

Coupling of an Unsteady Aerodynamics Model with a Computational Fluid Dynamics Solver

Momentum source methods are an efficient means of representing airfoils in Navier–Stokes computational fluid dynamics (CFD) simulations. Momentum source terms are added to the Navier–Stokes equations instead of resolving the solid boundary of the airfoil with a mesh. These source terms are calculated using an aerodynamics model. This approach is useful where the overall performance and mid- to far-field influence of a wing or rotor are desired and details of the flowfield near the blade are not the objective of the simulation. One example is simulation of rotorcraft operations where the objective may be to assess an operation’s feasibility in terms of control margins, rather than to inform rotor design decisions. Coupling an aerodynamics model to a CFD solver is straightforward in cases where the airflow relative to the blade is steady. Unsteady conditions require an unsteady aerodynamics model, complicating the coupling with the CFD solver. A coupling method is proposed whereby the incident velocity is extracted from the CFD solution and corrected using a theory-based approximation for the unsteady induced velocity. The steady-state momentum source method is demonstrated for two- and three-dimensional simulations, and the unsteady coupling method is validated against experiments on a pitching airfoil and verified for blade–vortex interactions. The unsteady coupling method enables meaningful incident velocities to be extracted from unsteady flowfields, as shown by agreement with experiments and simulations using analytical expressions for the incident velocity in place of the CFD solver.

How the NEUWAVE workshop series has pushed neutron imaging developments

ABSTRACTIn 2008, a series of international workshops—named NEUtron WAVElength-dependent Imaging (NEUWAVE)—was initiated after several decisions were taken to build new neutron spallation sources in the world, namely target station two of ISIS in the UK, J-PARC in Japan, SNS in the US, and the future ESS, now being built in Sweden. The aim was to collect existing knowledge about energy-dependent effects in neutron imaging, but also to develop new energy-selective imaging methods for the upcoming spallation sources, and also for steady-state sources using energy selecting devices for neutrons. The special format was a workshop with plenty of discussions but without explicit publications, where participants discussed not their past work, but their ideas and future plans. This paper gives a résumé after nine such meetings and highlights the most important progress features. The series will continue in 2019 with NEUWAVE-10 to be organized by Paul Scherrer Institut.

High resolution Thomson scattering system for steady-state linear plasma sources.

The high resolution Thomson scattering system with 63 points along a 25 mm line measures the radial electron temperature (Te) and its density (ne) in an argon plasma. By using a DC arc source with lanthanum hexaboride (LaB6) electrode, plasmas with electron temperature of over 5 eV and densities of 1.5 × 1019 m-3 have been measured. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer via optical-fibers, where images are recorded by an intensified charge coupled device (ICCD) camera. Although excellent in stray-light reduction, a disadvantage comes with its relatively low optical transmission and in sampling a tiny scattering volume. Thus requires accumulating multitude of images. In order to improve photon statistics, pixel binning in the ICCD camera as well as enlarging the intermediate slit-width inside the triple-grating spectrometer has been exploited. In addition, the ICCD camera capture images at 40 Hz while the laser is at 20 Hz. This operation mode allows us to alternate between background and scattering shot images. By image subtraction, influences from the plasma background are effectively taken out. Maximum likelihood estimation that uses a parameter sweep finds best fitting parameters Te and ne with the incoherent scattering spectrum.

Ignition in tokamaks with modulated source of auxiliary heating

It is shown that the ignition may be achieved in tokamaks with the modulated power source. The time-averaged source power may be smaller than the steady-state source power, which is sufficient for the ignition. Nevertheless, the maximal power must be large enough, because the ignition must be achieved within a finite time interval.

On concentrated solute sources in faulted aquifers

Finite aperture faults and fractures within aquifers (collectively called ‘faults’ hereafter) theoretically enable flowing water to move through them but with refractive displacement, both on entry and exit. When a 2D or 3D point source of solute concentration is located upstream of the fault, the plume emanating from the source relative to one in a fault-free aquifer is affected by the fault, both before it and after it. Previous attempts to analyze this situation using numerical methods faced challenges in overcoming computational constraints that accompany requisite fine mesh resolutions. To address these, an analytical solution of this problem is developed and interrogated using statistical evaluation of solute distributions. The method of solution is based on novel spatial integral representations of the source with axes rotated from the direction of uniform water flow and aligning with fault faces and normals. Numerical exemplification is given to the case of a 2D steady state source, using various parameter combinations. Statistical attributes of solute plumes show the relative impact of parameters, the most important being, fault rotation, aperture and conductivity ratio. New general observations of fault-affected solution plumes are offered, including: (a) the plume's mode (i.e. peak concentration) on the downstream face of the fault is less displaced than the refracted groundwater flowline, but at some distance downstream of the fault, these realign; (b) porosities have no influence in steady state calculations; (c) previous numerical modeling results of barrier faults show significant boundary effects. The current solution adds to available benchmark problems involving fractures, faults and layered aquifers, in which grid resolution effects are often barriers to accurate simulation.

The concentration of energy from Edge Lasers by Diffractive Optical Component

The aim of this paper is to design a diffractive optical element based on the laser junction numerical model. We assumed a ?long? laser junction emitting quasi-monochromatic, spatially incoherent light that corresponds to the high power laser. Diffractive optics approach can be used due to the narrowband illumination. The especially designed numerical junction model was experimentally verified. Then a numerically designed diffractive focusing element was manufactured and tested in the experimental setup. This paper includes theoretical investigations, numerical modeling as well as experimental data. Full Text: PDF ReferencesE. Wolf, "New theory of partial coherence in the space?frequency domain. Part I: spectra and cross spectra of steady-state sources", J. Opt. Soc. Am. 72, 343 (1982). CrossRef E. Wolf, "Coherence theory of laser resonator modes", J. Opt. Soc. Am. A 1, 541 (1984). CrossRef A. Naqwi and F. Durst, "Focusing of diode laser beams: a simple mathematical model", Appl. Opt. 29, 1780 (1990) CrossRef J. Yang, T. Chen, G. Ding and X. Yuan, "Focusing of diode laser beams: a partially coherent Lorentz model", Proc. SPIE 6824, 68240A (2007); CrossRef X. Zeng and A. Naqwi, "Far-field distribution of double-heterostructure diode laser beams", Appl. Opt. 32, 4491 (1993). CrossRef Y. Li and J. Katz, "Nonparaxial analysis of the far-field radiation patterns of double-heterostructure lasers", Appl. Opt. 35, 1442 (1996). CrossRef X. Zeng, Z. Feng, and Y. An, "Far-field expression of a high-power laser diode", Appl. Opt. 43, 5168 (2004) CrossRef J. Tervo, J. Turunen, P. Vahimaa, and F. Wyrowski, "Shifted-elementary-mode representation for partially coherent vectorial fields", J. Opt. Soc. Am. A 27, 2004 (2010). CrossRef J. Turunen, "Elementary-field representations in partially coherent optics", J. Mod. Opt. 58, 509 (2011). CrossRef H. Partanen, J. Tervo, and J. Turunen, "Spatial coherence of broad-area laser diodes", Appl. Opt. 52, 3221 (2013) CrossRef M. Sypek, "Light propagation in the Fresnel region. New numerical approach", Opt. Commun., 116, 43 (1995) CrossRef Z. Jaroszewicz, A. Kolodziejczyk, M. Sypek, C. Gomez-Reino, "Non-paraxial analytical solution for the generation of focal curves", J. Mod. Opt., 43, 617 (1996) CrossRef M. Sypek, C. Prokopowicz, M. Gorecki, "Image multiplying and high-frequency oscillations effects in the Fresnel region light propagation simulation", Opt. Eng., 42, 3158 (2003) CrossRef C. Prokopowicz, "Numerical calculation of light propagation in off-axis region", Proc. SPIE, 5484, 482 (2004). CrossRef A. Sobczyk, Z. Jaroszewicz, A. Kolodziejczyk, A. Kowalik, Cz. Prokopowicz, M. Sypek, "Nonparaxial anamorphic diffractive lenses", J. Opt., 15, 025702 (1-5) (2013) CrossRef

Spectral analysis of hearing protector impulsive insertion loss

Objective: To characterise the performance of hearing protection devices (HPDs) in impulsive-noise conditions and to compare various protection metrics between impulsive and steady-state noise sources with different characteristics. Design: HPDs were measured per the impulsive test methods of ANSI/ASA S12.42-2010. Protectors were measured with impulses generated by both an acoustic shock tube and an AR-15 rifle. The measured data were analysed for impulse peak insertion loss (IPIL) and impulsive spectral insertion loss (ISIL). These impulsive measurements were compared to insertion loss measured with steady-state noise and with real-ear attenuation at threshold (REAT). Study sample: Tested HPDs included a foam earplug, a level-dependent earplug and an electronic sound-restoration earmuff. Results: IPIL for a given protector varied between measurements with the two impulse noise sources, but ISIL agreed between the two sources. The level-dependent earplug demonstrated level-dependent effects both in IPIL and ISIL. Steady-state insertion loss and REAT measurements tended to provide a conservative estimate of the impulsively-measured attenuation. Conclusions: Measurements of IPIL depend strongly on the source used to measure them, especially for HPDs with less attenuation at low frequencies. ISIL provides an alternative measurement of impulse protection and appears to be a more complete description of an HPD’s performance.

Macromolecular structure phasing by neutron anomalous diffraction.

In this report we show for the first time that neutron anomalous dispersion can be used in a practical manner to determine experimental phases of a protein crystal structure, providing a new tool for structural biologists. The approach is demonstrated through the use of a state-of-the-art monochromatic neutron diffractometer at the Institut Laue-Langevin (ILL) in combination with crystals of perdeuterated protein that minimise the level of hydrogen incoherent scattering and enhance the visibility of the anomalous signal. The protein used was rubredoxin in which cadmium replaced the iron at the iron-sulphur site. While this study was carried out using a steady-state neutron beam source, the results will be of major interest for capabilities at existing and emerging spallation neutron sources where time-of-flight instruments provide inherent energy discrimination. In particular this capability may be expected to offer unique opportunities to a rapidly developing structural biology community where there is increasing interest in the identification of protonation states, protein/water interactions and protein-ligand interactions – all of which are of central importance to a wide range of fundamental and applied areas in the biosciences.

Analytical solution of the simplified spherical harmonics equations in spherical turbid media

We present for the first time an analytical solution for the simplified spherical harmonics equations (so-called SPN equations) in the case of a steady-state isotropic point source inside a spherical homogeneous absorbing and scattering medium. The SPN equations provide a reliable approximation to the radiative transfer equation for describing light transport inside turbid media. The SPN equations consist of a set of coupled partial differential equations and the eigen method is used to obtain a set of decoupled equations, each resembling the heat equation in the Laplace domain. The equations are solved for the realistic partial reflection boundary conditions accounting for the difference in refractive indices between the turbid medium and its environment (air) as occurs in practical cases of interest in biomedical optics. Specifically, we provide the complete solution methodology for the SP3, which is readily applicable to higher orders as well, and also give results for the SP5. This computationally easy to obtain solution is investigated for different optical properties of the turbid medium. For validation, the solution is also compared to the analytical solution of the diffusion equation and to gold standard Monte Carlo simulation results. The SP3 and SP5 analytical solutions prove to be in good agreement with the Monte Carlo results. This work provides an additional tool for validating numerical solutions of the SPN equations for curved geometries.

Variation of ocean sediment thickness with crustal age

AbstractGlobal ocean sediment thickness and present‐day ocean sediment accumulation rates are analyzed with respect to the age of the underlying ocean crust. Trends in average sediment thickness and present‐day accumulation rate are well fit by cubic polynomials in crustal age for the global ocean and for individual ocean basins. Sediment thickness and accumulation rates are larger in the North and South Atlantic and Indian Oceans compared to the Pacific Ocean, primarily because the anomalous sediment accumulations that followed continental rifting and collision in the Atlantic and Indian Ocean basins are missing in the Pacific Ocean. Modern ocean sediment accumulation rates, extrapolated into the past assuming steady state conditions, account within uncertainties for the global average sediment thickness on 0–65 Ma (Cenozoic age) ocean crust, while the profile of anomalously thick sediments on older (Mesozoic age) ocean crust is well fit by adding localized, diffusive sediment transport from a steady state source referenced to the adjacent continental margin. Apart from a distinct 0–5 Ma (Quaternary age) sediment pulse, deviations in average sediment thickness from this simple model are generally small and are uncorrelated across ocean basins.

Experimental test of the system of vertical and longitudinal lithium limiters on T-11M tokamak as a prototype of plasma facing components of a steady-state fusion neutron source

A new functional model of the prototype of closed Li circuit for protection of the chamber wall was tested in T-11M tokamak by simultaneous use of the vertical Li limiter as an emitter of Li and a new longitudinal Li limiter as its collector. Such technological scheme can be suggested for the steady-state fusion neutron source on the tokamak basis. During plasma shots the cryogenic target of T-11M collected Li flow emitted by the vertical capillary Li limiter almost completely (up to 80%). These Li and hydrogen isotopes were captured and extracted outside the tokamak vacuum chamber without venting of the vessel which is a key requirement for the use of Li in the steady-state tokamak reactor.

New opportunities for quasielastic and inelastic neutron scattering at steady-state sources using mechanical selection of the incident and final neutron energy

We propose a modification of the neutron wide-angle velocity selector (WAVES) device that enables inelastic (in particular, quasielastic) scattering measurements not relying on the neutron time-of-flight. The proposed device is highly suitable for a steady-state neutron source, somewhat similar to a triple-axis spectrometer, but with simultaneous selection of the incident and final neutron energy over a broad range of scattering momentum transfer. Both the incident and final neutron velocities are defined by the WAVES geometry and rotation frequency. The variable energy transfer is achieved through the natural variation of the velocity of the transmitted neutrons as a function of the scattering angle component out of the equatorial plane.

Shot noise characteristics of Majorana fermions in transport through double quantum dots

Majorana fermions are their own antiparticles, which play an important role in fault-tolerant topological quantum computation. Recently, the search for Majorana fermions in condensed matter physics, is attracting a great deal of attention as quasiparticles emerge. In this paper we consider a specific model consisting of double quantum dots and a tunnel-coupled semiconductor nanowire on an s-wave superconductor, since the nanowire may support Majorana fermions under appropriate conditions. We study the electron transport through the double quantum dots by using the particle-number resolved master equation. We pay particular attention to the effects of Majorana's dynamics on the current fluctuation (shot noise). It is shown that the current and the shot noise measurement can be used to distinguish Majorana fermions from the usual resonant-tunneling levels. When there exist Majorana fermions coupling to the double quantum dots, a difference between the steady-state source and drain currents depends on the asymmetry of electron tunneling rates. The asymmetric behaviors of the currents can reveal the essential features of the Majorana fermion. Moreover, the dynamics of Majorana coherent oscillations between the semiconductor nanowire and the double quantum dots is revealed in the shot noise, via spectral dips together with a pronounced zero-frequency noise enhancement effect. We find, on the one hand, that the peak of the zero-frequency noise becomes a dip in the case of weak coupling between double quantum dots and the nanowire; on the other hand, for the strong coupling the dip of the zero-frequency noise becomes even further deep with side dips towards high frequency regimes. Furthermore, the dip of the zero-frequency noise disappears and a zero-frequency noise peak gradually develops when the dot-electrode coupling is tuned by gate voltage. As a result, the combination of the current and the shot noise through double quantum dots allows one to probe the presence of Majorana fermions.

Protection of tokamak plasma facing components by a capillary porous system with lithium

Development of plasma facing material (PFM) based on the Capillary-Porous System (CPS) with lithium and activity on realization of lithium application strategy are addressed to meet the challenges under the creation of steady-state tokamak fusion reactor and fusion neutron source. Presented overview of experimental study of lithium CPS in plasma devices demonstrates the progress in protection of tokamak plasma facing components (PFC) from damage, stabilization and self-renewal of liquid lithium surface, elimination of plasma pollution and lithium accumulation in tokamak chamber. The possibility of PFC protection from the high power load related to cooling of the tokamak boundary plasma by radiation of non-fully stripped lithium ions supported by experimental results. This approach demonstrated in scheme of closed loops of Li circulation in the tokamak vacuum chamber and realized in a series of design of tokamak in-vessel elements.

Three-dimensional Green’s functions for a fluid and pyroelectric two-phase material

The three-dimensional Green’s functions for a steady-state point heat source in the interior of a fluid and pyroelectric two-phase material are presented in this paper. By virtue of the three-dimensional general solutions which are expressed in harmonic functions, six newly introduced harmonic functions with undetermined constants are constructed. Then, all the pyroelectric components in the fluid and pyroelectric two-phase material can be derived by substituting these harmonic functions into the corresponding general solutions. And the undetermined constants can be obtained by the interface compatibility conditions and the mechanical, electric and thermal equilibrium conditions. Numerical results are given graphically by contours.

Tolerable Limits of Construction Vibrations

Construction impact and steady-state vibration sources such as pile driving, dynamic compaction, and other machinery generate ground and structural vibrations that may detrimentally affect diverse adjacent and remote structures, people, and sensitive devices. Vibration effects on structures depend on numerous factors. Vibration limits developed in the blasting industry are often used for evaluation of the construction vibration effects on structures. However, these vibration limits were derived only for specific combinations of blasting, soil conditions, and structures. Soil deformations and soil-structure interaction determine soil and structure responses to vibration excitation. Soil and structure vibration responses should be the basis for applied tolerable limits. Diverse tolerable limits are proposed for various soil and structure vibrations. In addition to vibration measurements, condition surveys should be performed for analysis of the causes of the existing damage to structures.

Arc plasma generator of atomic driver for steady-state negative ion source

The paper reviews the results of development of steady-state arc-discharge plasma generator with directly heated LaB6 cathode. This arc-discharge plasma generator produces a plasma jet which is to be converted into an atomic one after recombination on a metallic plate. The plate is electrically biased relative to the plasma in order to control the atom energies. Such an intensive jet of hydrogen atoms can be used in negative ion sources for effective production of negative ions on a cesiated surface of plasma grid. All elements of the plasma generator have an augmented water cooling to operate in long pulse mode or in steady state. The thermo-mechanical stresses and deformations of the most critical elements of the plasma generator were determined by simulations. Magnetic field inside the discharge chamber was optimized to reduce the local power loads. The first tests of the steady-state arc plasma generator prototype have performed in long-pulse mode.

Mass–Mobility Measurements Using a Centrifugal Particle Mass Analyzer and Differential Mobility Spectrometer

Mass–mobility measurements using a centrifugal particle mass analyzer (CPMA) and differential mobility spectrometer (DMS) are demonstrated. The CPMA, which classifies an aerosol by mass-to-charge ratio, is used upstream of a DMS, which measures the mobility size distribution of the mass-classified particles in real-time. This system allows for mass–mobility measurements to be made on transient sources at one particle mass or an entire effective density distribution for steady state sources in minutes. Since the CPMA classifies particles by mass-to-charge ratio and multiply charged particles are present, particles of several different masses will be measured by the DMS. Therefore, a correction scheme is required to make accurate measurements. To validate this measurement scheme, two different CPMA-DMS systems were used to measure the known density of di(2ethylhexyl) sebacate (DEHS). The first system consisted of a CPMA and standard DMS500 (Cambustion). This system measured an average effective density of 1...

Characteristic and Model Analysizes of Steady-State Harmonic Source for DC Charger

The objective of this paper is to present the system construction and operational principle for a DC charger of electric vehicle. By means of analyzing AC and DC sides for the chargers, a reason was derived theoretically for producing specified harmonic current while absorbing fundamental wave of electric power system. The modeling and measuring procedures of multi-harmonic source for single and multiple chargers were proposed. The summation effect of harmonics for charge/exchange station which was regard as a public coupling circuit (PCC) of the electric power system. The simulation and measuring results indicate that as a new type of nonlinear load, the charger represented a characteristic of steady-state harmonic source.

Comparison on Thermal Conductivity and Permeability of Granular and Consolidated Activated Carbon for Refrigeration

This paper focuses on the development of three types of activated carbon (AC) adsorbents, i.e. granular AC, consolidated AC with chemical binder, and consolidated AC with expanded natural graphite (ENG). Their thermal conductivity was investigated with the steady-state heat source method and the permeability was tested with nitrogen as the gas source. Results show that the thermal conductivity of granular AC with different sizes almost maintains a constant at 0.36 W·(m·K)−1, while the value modestly increases to 0.40 W·(m·K)−1 for the consolidated AC with chemical binder. The consolidated AC with ENG at the density of 600 kg·m−3 shows the best heat transfer performance and their thermal conductivity vary from 2.08 W·(m·K)−1 to 2.61 W·(m·K)−1 according to its fraction of AC. However, the granular AC and consolidated AC with chemical binder show the better permeability performance than consolidated AC with ENG binder whose permeability changes from 6.98×10−13 m2 to 5.16×10−11 m2 and the maximum occurs when the content of AC reaches 71.4% (by mass). According to the different thermal properties, the refrigeration application of three types of adsorbents is analyzed.