Collision Coefficient Research Articles

Nonlinear Ball and Beam Control System Identification

The Ball and Beam system is a common didactical experiment in control laboratories that can be used to illustrate many different closed-loop control techniques. The plant itself is subjected to many nonlinear effects, which the most common comes from the relative motion between the ball and the beam. The modeling process normally uses the lagrangean formulation. However, many other nonlinear effects, such as non-viscous friction, beam flexibility, ball slip, actuator elasticity, collisions at the end of the beam, to name a few, are present. Besides that, the system is naturally unstable. In this work, we analyze a subset of these characteristics, in which the ball rolls with slipping and the friction force between the ball and the beam is non-viscous (Coulomb friction). Also, we consider collisions at the ends of the beam, the actuator consists of a (rubber made) belt attached at the free ends of the beam and connected to a DC motor. The model becomes, with those nonlinearities, a differential inclusion system. The elastic coefficients of the belt are experimentally identified, as well as the collision coefficients. The nonlinear behavior of the system is studied and a control strategy is proposed.

Simulation of the heterogeneous semi-dry flue gas desulfurization in a pilot CFB riser using the two-fluid model

Simi-dry flue gas desulfurization (FGD) in a pilot circulating fluidized bed (CFB) reactor was studied by the CFD method. Heterogeneous hydrodynamics and desulfurization reaction were simulated in a three-dimensional domain of the CFB riser. Euler–Euler approach was adopted and the O–S drag model was utilized for the unsteady gas–solid two-phase flow, which achieved the typical core-annulus structure of both the particle concentration and the particle velocity. The collision coefficient (e) was selected by comparing with the experimental data of the solid volume fraction. The desulfurization was described by the continuous conversion model and the liquid film thickness equation for interphase mass transport was modified to avoid “divided by zero”. Detailed analysis figured out that the water mass fraction in the particle phase played a significant role in the desulfurization. The sorbent dissolving might be a controlling step when the water mass fraction was very small, and should be taken into consideration rather than neglected. Operating parameters were discussed for their impact on the desulfurization efficiency. Computational results showed that the jet water flow rate was the most significant parameter as the circulating solid mass flow rate followed closely behind, suggesting that uniform water jetting will be the most improving method.

Azimuthal anisotropy of charged particles from multiparticle correlations in pPb and PbPb collisions with CMS

Abstract Motivated by two- and four-particle azimuthal correlation measurements that suggest possible collective flow for charged particles emitted in pPb collisions at s NN = 5.02 TeV , we extend the correlation results for these collisions using the six- and eight-particle cumulant methods, and the Lee–Yang Zeros method. CMS has an extensive program studying azimuthal harmonic coefficients for both PbPb and pPb collisions using various methods. The current pPb results will be presented in this context. The data were collected by the CMS experiment at the LHC using both minimum bias and high-multiplicity collision triggers over a wide range in pseudorapidity. The results are compared to 2.76 TeV semi-peripheral PbPb collision data collected in 2011 covering a similar range of particle multiplicities. The second-order azimuthal anisotropy Fourier harmonic ( v 2 ) is shown for the different methods. A comparison of the six- and greater particle correlations to the previously published two- and four-particle correlation results sheds light on the multiparticle nature of the azimuthal anisotropy. The results are also discussed in terms of recent calculations that explore the role of participant fluctuations on measurements of higher-order particle correlations in pPb collisions.

Study on natural contamination performance of typical types of insulators

As natural contamination of insulators may lead to flashover, its determining factors should be studied to prevent the occurrence of pollution flashover. In this paper, the fluid mechanics models of insulators with typical shed types were established to simulate their flow field distribution and particle collision coefficient (F). At the same time, a natural contamination test lasting for 8 months was carried out in order to contrast the experimental data and simulation results. The research results have shown that: wind velocity and shed type affect the flow field near the insulators; F is affected by particle diameter and wind velocity; under certain particle diameter and wind velocity, F reaches the maximum value; rainfall has different effects on contamination of insulators with different shed types; wind causes non-uniformly distribution of pollution on the surfaces; the simulation test and the experimental test are comparable. The research method and results can provide not only reference to establishing natural contaminating model but also significant meaning for the external insulation design and selection.

Rotational excitation of HCN by para- and ortho-H₂.

Rotational excitation of the hydrogen cyanide (HCN) molecule by collisions with para-H2(j = 0, 2) and ortho-H2(j = 1) is investigated at low temperatures using a quantum time independent approach. Both molecules are treated as rigid rotors. The scattering calculations are based on a highly correlated ab initio 4-dimensional (4D) potential energy surface recently published. Rotationally inelastic cross sections among the 13 first rotational levels of HCN were obtained using a pure quantum close coupling approach for total energies up to 1200 cm(-1). The corresponding thermal rate coefficients were computed for temperatures ranging from 5 to 100 K. The HCN rate coefficients are strongly dependent on the rotational level of the H2 molecule. In particular, the rate coefficients for collisions with para-H2(j = 0) are significantly lower than those for collisions with ortho-H2(j = 1) and para-H2(j = 2). Propensity rules in favor of even Δj transitions were found for HCN in collisions with para-H2(j = 0) whereas propensity rules in favor of odd Δj transitions were found for HCN in collisions with H2(j ⩾ 1). The new rate coefficients were compared with previously published HCN-para-H2(j = 0) rate coefficients. Significant differences were found due the inclusion of the H2 rotational structure in the scattering calculations. These new rate coefficients will be crucial to improve the estimation of the HCN abundance in the interstellar medium.

Non-radiative inelastic processes in lithium-helium ion-atom collisions

Aims. The aims are to estimate efficiencies of non-radiative inelastic processes in lithium-helium ion-atom collisions and to compare them to those for radiative processes. Methods. Non-radiative inelastic cross-sections and rate coefficients for different lithium-helium ion-atom collisions are estimated by means of the recently proposed branching probability current method, which is based on the accurate ab initio adiabatic Born-Oppenheimer potentials that have been recently calculated for the low-lying 1,3 Σ+ and 1,3 Π states of the LiHe+ ion.Results. It is shown that at low temperatures the radiative depopulation in Li+ + He and Li + He+ collisions dominates over the non-radiative processes, while in Li+ + He(2s 3 S) collisions the non-radiative processes dominate over the radiative association at temperatures above 3000 K, which can be expected to have some influence on depopulations of metastable He in high temperature astrophysical environments.

Influence of cycles of high and low turbulent shear on the growth rate and equilibrium size of mud flocs

Abstract Effects of repeated exposure to multiple cycles of high and low turbulent shear on mud floc growth pattern and equilibrium size were investigated through a laboratory study. The specific research questions examined were: (1) do repeated cycles of floc growth and breakup change the equilibrium floc size from one cycle to the next?; and (2) do these repeated cycles impact the floc growth rate and path to equilibrium? For the experiments, a 50 mg/l mixture of kaolinite and montmorillonite clay was sonicated and introduced to a mixing chamber to allow for flocculation under a mean turbulent shear rate of G = 35 s− 1. Floc size time series, floc circularity index, and time series of the number of flocs were measured using a camera system and image processing routines. After the flocs reached an equilibrium size, the floc suspension was broken down with vigorous turbulent mixing (G = 400 s− 1) for 15 h. Flocs were then allowed to regrow at a shear rate of G = 35 s− 1. This procedure was repeated seven consecutive times. The data show that the different initial particle size distributions after sonication and after intense shearing had almost no effect on the equilibrium floc size, but that difference in initial size did significantly impact the floc growth pattern before the equilibrium was reached. With each repeated floc breakup and growth cycle, the rate of floc growth decreased. Each of the seven regrowth cycles was modeled with the Winterwerp (1998) equation for the mean floc size by calibrating the collision and breakup efficiency coefficients for each cycle. To obtain a good fit to the data, both the collision and breakup efficiency coefficients had to be reduced with each successive cycle. The observations and modeling results suggest that flocs become slightly stronger and less reactive with each repeated cycle of growth and breakup. The consistency of the equilibrium floc size in the experiment suggest that given enough time, floc settling velocity maybe reasonably modeled as a function of local conditions. However, if the time it takes to reach equilibrium is larger than the time scale of the flow of interest, then the floc settling velocity may be difficult to define without knowledge of the turbulent shear conditions encountered prior to the point of analysis; even when using a size evolving floc modeling approach.

Analysis of the stability of intermittent cut with energy lost

This paper studies the chatter stability of the intermittent cutting in view of the energy loss that caused by the collision which happens in the tooth enters the workpiece. As one of the important factors, the energy loss is integrated into the analysis process. As the cutting system behaves differently under the circumstances of being cutting or uncut, the temporal finite element method is chosen to solve this problem. It derived functions of the displacement and the velocity at the beginning and end of each element. The complete solution is obtained by combining these functions with the collision coefficient which is the mathematical expression of the energy loss. Then, the global transition matrix is formed and used to determine stability. The influences of other four parameters are considered. Comparison of the results from the theoretical analysis and the simulations are made to validate the accuracy of the proposed method.

Numerical Simulation for Hydrodynamic Analysis and Pressure Drop Prediction in Horizontal Gas-Solid Flows

Two fluid or Eulerian modeling incorporating the kinetic theory for granular particles and accounting for four-way coupling was performed to investigate the hydrodynamics and pressure drop characteristics of gas-solid flows in horizontal pipes. The model was validated by comparison with the experimental data found in literature and the predictions agreed reasonably well with experimental results. It was found that lift force along with particle-wall collision and specularity coefficient play significant role in the simulation of horizontal gas-solid flows. Granular temperature model by Ding and Gidaspow (1990) predicts the velocity profiles of both phases accurately. The gas-solid two-phase flow in the horizontal pipe generally has an asymmetric structure in the vertical direction, which is due to the effect of gravity. An extensive investigation was also done to study the effect of various flow parameters like particle properties, gas velocity, and solid concentration on pressure drop prediction. Finally a simplified correlation was proposed for fully developed pressure drop in horizontal gas-solid flows. Unlike the existing correlations, this correlation is valid for a wide range of particle size, pipe diameter, and mass loading.

Research on Driving Risk Model of Freeway Interchange Entrance Area for Accident Prevention

Based on analysis of traffic characteristics of freeway interchange entrance area, Collision Risk Index (CRI) is put forward to evaluate driving risk. Possibility of collision coefficient, speed difference between two colliding vehicles, colliding speed and acceleration of the following car on the target lane are took into consideration in the risk assessment model of CRI. Traffic collisions that may occur in the entrance area are divided into five kinds. The occurrence conditions and risk assessment models of 5 cases are studied correspondingly. Finally, against running speed of main line, distance headway, running speed of vehicle on entrance ramp (front vehicle), three-dimensional numerical simulation has been carried out and driving risk variation laws have been obtained.

Dual – Temperature Electron distribution in a Laboratory Plasma

The dual-temperature distribution function is used to investigate theoretically the effect of a perturbation of Maxwell distribution function on density ratios in a laboratory plasma produced solely by collision. By assuming a foreknowledge of collision coefficients and cross-sections and an atomic model which sets at two statistical weights for all states including continuum, calculations show that a collision transition between close neighbouring levels is of more significance than that between widely separated or non-neighbouring levels; also population and electron densities in plasma do not only depend on the energy distribution of free electrons but on both the excitation and binding energies of the atomic levels.KEYWORDS: Dual – temperature distribution function, Maxwell distribution function, Perturbation, Density ratios, Laboratory plasma, Collision transition.

Biotin- and Glycoprotein-Coated Microspheres: Potential Surrogates for Studying Filtration of Cryptosporidium parvum in Porous Media

Cryptosporidium parvum is a waterborne pathogen, yet no suitable surrogate has been established for quantifying its filtration removal in porous media. Carboxyl polystyrene microspheres with size, density, and shape similar to C. parvum were coated with biotin (free and containing amine, NH(2)) and glycoprotein. These biomolecules have isoelectric points similar to C. parvum (pH ≈ 2), and glycoprotein is a major type of surface protein that oocysts possess. Zeta potential (ζ) and filtration removal of particles in sand of two different grain sizes were examined. Compared to unmodified microspheres, modified microspheres achieved a superior match to the oocysts in ζ, concentration, mass recovery, and collision coefficient. They showed the same log reduction in concentration as oocysts, whereas results from unmodified microspheres deviated by 1 order of magnitude. Of the three types of modified microspheres, glycoprotein-coated microspheres best resembled oocyst concentration, despite having ζ similar to NH(2)-biotin-coated microspheres, suggesting that surface protein also played an important role in particle attachment on solid surfaces. With further validation in environmental conditions, the surrogates developed here could be a cost-effective new tool for assessing oocyst filtration in porous media, for example, to evaluate the performance of sand filters in water and wastewater treatment, water recycling through riverbank filtration, and aquifer recharge.

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2 and NO molecules

Electron-impact vibrational-excitation cross sections, involving rovibrationally excited N2 and NO molecules, are calculated for collisions occurring through the nitrogen resonant electronic state , and the three resonant states of nitric oxide NO−(3Σ−, 1Δ, 1Σ+). Complete sets of cross sections have been obtained for all possible transitions involving 68 vibrational levels of and 55 levels of NO(X 2Π), for incident electron energy between 0.1 and 10 eV. In order to study the rotational motion in the resonant processes, cross sections have also been computed for rotationally elastic transitions characterized by the rotational quantum number J running from 0 to 150. The calculations are performed within the framework of the local complex potential model, using potential energies and widths optimized to reproduce the experimental cross sections available in the literature. Rate coefficients are calculated for transitions between all vibrational levels by assuming a Maxwellian electron energy distribution function in the temperature range from 0.1 to 100 eV.All numerical data are available at http://users.ba.cnr.it/imip/cscpal38/phys4entry/database.html

Vibrational relaxation and vibration-rotation energy transfer between highly vibrationally excited KH(X1Σ+, v=14–21) and CO2

The vibrational levels of KH(X1Σ+, v″=0–3) were generated in the reaction of K (5P) and H2. Vibrational state total relaxation rate coefficientskv″(CO2) for KH (v″=14–21) are measured in an overtone pump-probe configuration. The rate coefficient kv″(CO2) is strongly dependent on vibrational quantum number. Scattered CO2 (0000, 32≤J≤48) molecules were excited to CO2 (1005, J+1) states. The rotational temperatures of CO2 (0000, J=32–48) states populated by collisions with highly vibrationally excited KH (v″=14–21) are obtained. The average rotational energy of the scattered CO2 molecules is increased by a factor of 2.33 when KH level v″=14 increases to v″=21. The average translational energy of the scattered CO2 molecules is increased roughly linearly as a function of CO2J state. Under single collision conditions, state-specific energy transfer rate coefficients for collisions of highly excited KH with CO2 are obtained. For v″=19, the integrated rate coefficients kint increases by a factor of 4.5 to v″=14.

Analyzing observations of molecules in the ISM: Theoretical and experimental studies of energy transfer

Our laboratories have recently calculated a set of collision coefficients characterizing the efficiency of energy transfer between helium and/or hydrogen and a large variety of interstellar molecules. We have considered with molecules ranging from light hydrides, observed by the Herschel Space Observatory, to medium size molecules, observed by mm antennas, to heavy complex organic molecules, observed also in the cm range. We present a review of recent theoretical results obtained in our laboratories, for various kinds of commonly observed molecules.

Outer-Sphere Investigation of MRI Relaxation Contrast Agents. Example of a Cyclodecapeptide Gadolinium Complex with Second-Sphere Water

We show how the purely outer-sphere (OS) relaxivity of a probe solute due to a Gd(3+) complex can help characterize the outer (O), inner (I), and second (2) sphere (S) contributions to the water proton relaxivity. Because of the difficulties of accurate theoretical predictions, we propose an experimental determination of the OS dipolar time correlation function (OS-DTCF) of the relative position of Gd(3+) with respect to any of the equivalent protons of the purely OS probe p-dioxane, which moves around the complex without binding to it. The method is illustrated by the GdPA complex with PA = c(AspArgGluProGlyGluTrpAspProGly). The experimental DTCF for dioxane is obtained by a model-free analysis of the high-field relaxivity of its protons. The time-modulation of the dioxane DTCF by the Gd(3+) electronic spin relaxation yields a measurable quenching of the longitudinal relaxivity at low-to-medium field, which serves us to deduce the fluctuating zero-field splitting (ZFS) Hamiltonian causing this electronic relaxation. The DTCF for water is derived from that for dioxane by appropriate scaling of the geometry of collision and relative diffusion coefficients of these molecules with respect to GdPA. The information obtained on the OS motion for water and the ZFS Hamiltonian together with an independent characterization of the IS contribution allows us to disentangle the OS, IS, and 2S mechanisms and interpret the relaxivity profile of the water protons from 2.35 mT to 18.8 T. The presence of a large 2S contribution is confirmed.

Temperature dependence of the fine-structure resolved rate coefficients for collisions of O2(XΣ3g−) with He

Rotational excitation of the O(2)(X(3)Sigma(g) (-)) with He is investigated. The calculations are based on the potential energy surface of Groenenboom and Struniewicz [J. Chem. Phys. 113, 9562 (2000)]. Close coupling calculations of the collisional excitation cross sections of the fine-structure levels of O(2) by He are calculated for energies up to 2500 cm(-1) which yield, after thermal average, rate coefficients up to 350 K. The exact level splitting is taken into account. The propensity rules between fine-structure levels are studied and it is shown that F-conserving cross sections are much larger, especially for high-N rotational levels, than F-changing cross sections, as expected from theoretical considerations. The rate coefficients are almost independent of the rotational quantum number of the O(2) molecule for F-conserving transitions. The new rate coefficients can induce important consequences on astrophysical modeling.

Modelling line emission of deuterated H3+from prestellar cores

Context: The depletion of heavy elements in cold cores of interstellar molecular clouds can lead to a situation where deuterated forms of H_3^+ are the most useful spectroscopic probes of the physical conditions. Aims: The aim is to predict the observability of the rotational lines of H_2D^+ and D_2H^+ from prestellar cores. Methods: Recently derived rate coefficients for the H_3^+ + H_2 isotopic system were applied to the "complete depletion" reaction scheme to calculate abundance profiles in hydrostatic core models. The ground-state lines of H_2D^+(o) (372 GHz) and D_2H^+(p) (692 GHz) arising from these cores were simulated. The excitation of the rotational levels of these molecules was approximated by using the state-to-state coefficients for collisions with H_2. We also predicted line profiles from cores with a power-law density distribution advocated in some previous studies. Results: The new rate coefficients introduce some changes to the complete depletion model, but do not alter the general tendencies. One of the modifications with respect to the previous results is the increase of the D_3^+ abundance at the cost of other isotopologues. Furthermore, the present model predicts a lower H_2D^+ (o/p) ratio, and a slightly higher D_2H^+ (p/o) ratio in very cold, dense cores, as compared with previous modelling results. These nuclear spin ratios affect the detectability of the submm lines of H_2D^+(o) and D_2H^+(p). The previously detected H_2D^+ and D_2H^+ lines towards the core I16293E, and the H_2D^+ line observed towards Oph D can be reproduced using the present excitation model and the physical models suggested in the original papers.

A CFD approach for modeling the rime-ice accretion process on a horizontal-axis wind turbine

The main objective of this paper is to model the rime-ice accretion process on a horizontal-axis wind turbine (HAWT) operating under icing conditions. The model calculation procedure was divided into two stages. The first stage consists of computing the two-phase flow that is composed of air and water phases. The two-phase flow was solved using the Eulerian–Eulerian approach with the help of Fluent, a commercial CFD code. At the end of the calculations, it is possible to obtain the local volume fraction and local water incidence velocity, which can be used to estimate the local collision coefficient. In the second stage, the thickness of the newly accreted ice layer was calculated and the geometry so obtained was processed with an in-house smoothing algorithm. From the model simulation, it is possible to obtain the 3-D ice shape, as well as the ice load on the HAWT blade, which can then be used to analyze the performance of the HAWT under icing conditions, or to help develop a feasible de-icing solution. The important model input parameters include: air speed, median volume diameter (MVD) of water droplets, liquid water content (LWC) and air temperature. The turbine under consideration is a NREL VI turbine that rotates along its axis at a constant angular speed. In the flow domain, a rotating reference frame was defined to account for the angular movement of the wind turbine. The results reveal, among other things, ice geometry information that can otherwise hardly be obtained by on-site observations.

Spin-dependent inelastic collisions in spin-2 Bose-Einstein condensates

We studied spin-dependent two-body inelastic collisions in $F=2$ $^{87}\text{R}\text{b}$ Bose-Einstein condensates both experimentally and theoretically. The $^{87}\text{R}\text{b}$ condensates were confined in an optical trap and selectively prepared in various spin states in the $F=2$ manifold at a magnetic field of 3.0 G. The measured atom loss rates depend on the spin states of colliding atoms. We measured two fundamental loss coefficients for two-body inelastic collisions with total spins of 0 and 2. The loss coefficients determine the loss rates of all the spin pairs. The experimental results for mixtures of all spin combinations are in good agreement with numerical solutions of the Gross-Pitaevskii equations that include the effect of a magnetic field gradient.