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Pedro J. Gutiérrez - One of the best experts on this subject based on the ideXlab platform.
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non Gravitational Force modeling of comet 81p wild 2 ii rotational evolution
Icarus, 2007Co-Authors: Pedro J. Gutiérrez, Björn DavidssonAbstract:In this paper, we have studied both the dynamical and the rotational evolution of an 81P/Wild 2-like comet under the effects of the outgassing-induced Force and torque. The main aim is to study if it is possible to reproduce the non-Gravitational orbital changes observed in this comet, and to establish the likely evolution of both orbital and rotational parameters. To perform this study, a simple thermophysical model has been used to estimate the torque acting on the nucleus. Once the torque is calculated, Euler equations are solved numerically considering a nucleus mass directly estimated from the changes in the orbital elements (as determined from astrometry). According to these simulations, when the water production rate and changes in orbital parameters for 1997, as well as observational rotational parameters for 2004 are imposed as constraints, the change in the orbital period of 81P/Wild 2, ΔP=P˙, will decrease so that P¨=‑5 to ‑1minorbit, which is similar to the actual tendency observed from 1988 up to 1997. This nearly constant decreasing can be explained as due to a slight drift of the spin axis orientation towards larger ecliptic longitudes. After studying the possible spin axis orientations proposed for 1997, simulations suggest that the spin obliquity and argument (I,Φ)=(56°,167°) is the most likely. As for rotational evolution, changes per orbit smaller than 10% of the actual spin velocity are probable, while the most likely value corresponds to a change between 2 and 7% of the spin velocity. Equally, net changes in the spin axis orientation of 4° 8° per orbit are highly expected.
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nucleus properties of comet 9p tempel 1 estimated from non Gravitational Force modeling
Icarus, 2007Co-Authors: B Davidsson, Pedro J. Gutiérrez, H RickmanAbstract:Abstract The nucleus mass and bulk density of Comet 9P/Tempel 1 have been estimated by utilizing the non-Gravitational Force modeling technique. Here, the water production rates and non-Gravitational perturbations of the orbit are calculated for a large number of model nuclei with different surface ice distribution patterns. By requiring that the empirical water production rate curve is reproduced, a subset of model nuclei are selected, for which masses are calculated by demanding that empirical non-Gravitational changes of the orbital period and in the longitude of perihelion (per revolution) are reproduced. We obtain a mass M = 5.8 ( ± 1.6 ) × 10 13 kg , and a bulk density ρ bulk = 450 ± 250 kg m −3 , which compares very well with measurements made by the Deep Impact Science Team. The main goal of the current work is therefore to demonstrate functionality of an indirect method, i.e., mass estimation through non-Gravitational Force modeling, by comparing such results to ground truth data. Furthermore, the thermal inertia of active areas is estimated as 30–100 MKS, using a comparatively realistic thermophysical model (although a value in the range 100–350 MKS is obtained with a more simple model). An active area fraction of ∼ 3 % is predicted, and these areas are probably confined to the northern hemisphere, being located close to the cometary equator.
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non Gravitational Force modeling of comet 81p wild 2 i a nucleus bulk density estimate
Icarus, 2006Co-Authors: Björn Davidsson, Pedro J. GutiérrezAbstract:Abstract The nucleus of Comet 81P/Wild 2 is modeled by assuming various smooth triaxial ellipsoidal or irregular body shapes, having different rotational periods, spin axis orientations, and thermophysical properties. For these model nuclei, a large number of surface activity patterns (e.g., maps of active and inactive areas) are studied, and in each case the resulting water production rate and non-Gravitational Force vector versus time are calculated. By requiring that the model nuclei simultaneously reproduce certain properties of the empirical water production curve and non-Gravitational changes of the orbit (focusing on changes of the orbital period and in the longitude of perihelion), constraints are placed on several properties of the nucleus. The simulations suggest that the mass of Comet 81P/Wild 2 is M ≲ 2.3 × 10 13 kg , resulting in a rather low bulk density, ρ bulk ≲ 600 – 800 kg m −3 (depending on the assumed nucleus volume), and that the nucleus rotation is prograde rather than retrograde. The active area fraction is difficult to constrain, but at most 60% of the nucleus is likely to have near-surface ice.
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nucleus properties of comet 67p churyumov gerasimenko estimated from non Gravitational Force modeling
cosp, 2004Co-Authors: Björn Davidsson, Pedro J. GutiérrezAbstract:Nucleus properties of Comet 67P/Churyumov-Gerasimenko estimated from non-Gravitational Force modeling
Björn Davidsson - One of the best experts on this subject based on the ideXlab platform.
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non Gravitational Force modeling of comet 81p wild 2 ii rotational evolution
Icarus, 2007Co-Authors: Pedro J. Gutiérrez, Björn DavidssonAbstract:In this paper, we have studied both the dynamical and the rotational evolution of an 81P/Wild 2-like comet under the effects of the outgassing-induced Force and torque. The main aim is to study if it is possible to reproduce the non-Gravitational orbital changes observed in this comet, and to establish the likely evolution of both orbital and rotational parameters. To perform this study, a simple thermophysical model has been used to estimate the torque acting on the nucleus. Once the torque is calculated, Euler equations are solved numerically considering a nucleus mass directly estimated from the changes in the orbital elements (as determined from astrometry). According to these simulations, when the water production rate and changes in orbital parameters for 1997, as well as observational rotational parameters for 2004 are imposed as constraints, the change in the orbital period of 81P/Wild 2, ΔP=P˙, will decrease so that P¨=‑5 to ‑1minorbit, which is similar to the actual tendency observed from 1988 up to 1997. This nearly constant decreasing can be explained as due to a slight drift of the spin axis orientation towards larger ecliptic longitudes. After studying the possible spin axis orientations proposed for 1997, simulations suggest that the spin obliquity and argument (I,Φ)=(56°,167°) is the most likely. As for rotational evolution, changes per orbit smaller than 10% of the actual spin velocity are probable, while the most likely value corresponds to a change between 2 and 7% of the spin velocity. Equally, net changes in the spin axis orientation of 4° 8° per orbit are highly expected.
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non Gravitational Force modeling of comet 81p wild 2 i a nucleus bulk density estimate
Icarus, 2006Co-Authors: Björn Davidsson, Pedro J. GutiérrezAbstract:Abstract The nucleus of Comet 81P/Wild 2 is modeled by assuming various smooth triaxial ellipsoidal or irregular body shapes, having different rotational periods, spin axis orientations, and thermophysical properties. For these model nuclei, a large number of surface activity patterns (e.g., maps of active and inactive areas) are studied, and in each case the resulting water production rate and non-Gravitational Force vector versus time are calculated. By requiring that the model nuclei simultaneously reproduce certain properties of the empirical water production curve and non-Gravitational changes of the orbit (focusing on changes of the orbital period and in the longitude of perihelion), constraints are placed on several properties of the nucleus. The simulations suggest that the mass of Comet 81P/Wild 2 is M ≲ 2.3 × 10 13 kg , resulting in a rather low bulk density, ρ bulk ≲ 600 – 800 kg m −3 (depending on the assumed nucleus volume), and that the nucleus rotation is prograde rather than retrograde. The active area fraction is difficult to constrain, but at most 60% of the nucleus is likely to have near-surface ice.
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nucleus properties of comet 67p churyumov gerasimenko estimated from non Gravitational Force modeling
cosp, 2004Co-Authors: Björn Davidsson, Pedro J. GutiérrezAbstract:Nucleus properties of Comet 67P/Churyumov-Gerasimenko estimated from non-Gravitational Force modeling
David C. C. Yen - One of the best experts on this subject based on the ideXlab platform.
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Self-Gravitational Force Calculation of Infinitesimally Thin Gaseous Disks on Nested Grids
The Astrophysical Journal Supplement Series, 2016Co-Authors: Hsiang-hsu Wang, Ronald E. Taam, David C. C. YenAbstract:We extend the work of Yen et al. (2012) and develop 2nd order formulae to accommodate a nested grid discretization for the direct self-Gravitational Force calculation for infinitesimally thin gaseous disks. This approach uses a two-dimensional kernel derived for infinitesimally thin disks and is free of artificial boundary conditions. The self-Gravitational Force calculation is presented in generalized convolution forms for a nested grid configuration. A numerical technique derived from a fast Fourier transform is employed to reduce the computational complexity to be nearly linear. By comparing with analytic potential-density pairs associated with the generalized Maclaurin disks, the extended approach is verified to be of second order accuracy using numerical simulations. The proposed method is accurate, computationally fast and has the potential to be applied to the studies of planetary migration and the gaseous morphology of disk galaxies.
J J Monaghan - One of the best experts on this subject based on the ideXlab platform.
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an energy conserving formalism for adaptive Gravitational Force softening in smoothed particle hydrodynamics and n body codes
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Daniel J Price, J J MonaghanAbstract:In this paper, we describe an adaptive softening length formalism for collisionless N-body and self-gravitating smoothed particle hydrodynamics (SPH) calculations which conserves momentum and energy exactly. This means that spatially variable softening lengths can be used in N-body calculations without secular increases in energy. The formalism requires the calculation of a small additional term to the Gravitational Force related to the gradient of the softening length. The extra term is similar in form to the usual SPH pressure Force (although opposite in direction) and is therefore straightforward to implement in any SPH code at almost no extra cost. For N-body codes, some additional cost is involved as the formalism requires the computation of the density through a summation over neighbouring particles using the smoothing kernel. The results of numerical tests demonstrate that, for homogeneous mass distributions, the use of adaptive softening lengths gives a softening which is always close to the ‘optimal’ choice of fixed softening parameter, removing the need for fine-tuning. For a heterogeneous mass distribution (as may be found in any large-scale N-body simulation), we find that the errors on the least-dense component are lowered by an order of magnitude compared to the use of a fixed softening length tuned to the densest component. For SPH codes, our method presents a natural and an elegant choice of softening formalism which makes a small improvement to both the Force resolution and the total energy conservation at almost zero additional cost.
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an energy conserving formalism for adaptive Gravitational Force softening in sph and n body codes
arXiv: Astrophysics, 2006Co-Authors: Daniel J Price, J J MonaghanAbstract:In this paper we describe an adaptive softening length formalism for collisionless N-body and self-gravitating Smoothed Particle Hydrodynamics (SPH) calculations which conserves momentum and energy exactly. This means that spatially variable softening lengths can be used in N-body calculations without secular increases in energy. The formalism requires the calculation of a small additional term to the Gravitational Force related to the gradient of the softening length. The extra term is similar in form to the usual SPH pressure Force (although opposite in direction) and is therefore straightforward to implement in any SPH code at almost no extra cost. For N-body codes some additional cost is involved as the formalism requires the computation of the density via a summation over neighbouring particles using the smoothing kernel. The results of numerical tests demonstrate that, for homogeneous mass distributions, the use of adaptive softening lengths gives a softening which is always close to the `optimal' choice of fixed softening parameter, removing the need for fine-tuning. For a heterogeneous mass distribution (as may be found in any large scale N-body simulation) we find that the errors on the least-dense component are lowered by an order of magnitude compared to the use of a fixed softening length tuned to the densest component. For SPH codes our method presents a natural and elegant choice of softening formalism which makes a small improvement to both the Force resolution and the total energy conservation at almost zero additional cost.
Ronald E. Taam - One of the best experts on this subject based on the ideXlab platform.
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Self-Gravitational Force Calculation of Infinitesimally Thin Gaseous Disks on Nested Grids
The Astrophysical Journal Supplement Series, 2016Co-Authors: Hsiang-hsu Wang, Ronald E. Taam, David C. C. YenAbstract:We extend the work of Yen et al. (2012) and develop 2nd order formulae to accommodate a nested grid discretization for the direct self-Gravitational Force calculation for infinitesimally thin gaseous disks. This approach uses a two-dimensional kernel derived for infinitesimally thin disks and is free of artificial boundary conditions. The self-Gravitational Force calculation is presented in generalized convolution forms for a nested grid configuration. A numerical technique derived from a fast Fourier transform is employed to reduce the computational complexity to be nearly linear. By comparing with analytic potential-density pairs associated with the generalized Maclaurin disks, the extended approach is verified to be of second order accuracy using numerical simulations. The proposed method is accurate, computationally fast and has the potential to be applied to the studies of planetary migration and the gaseous morphology of disk galaxies.
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self Gravitational Force calculation of infinitesimally thin gaseous disks
Journal of Computational Physics, 2012Co-Authors: Chienchang Yen, Ronald E. Taam, Ken Huaiche Yeh, Kang C JeaAbstract:A thin gaseous disk has often been investigated in the context of various phenomena in galaxies, which point to the existence of starburst rings and dense circumnuclear molecular disks. The effect of self-gravity of the gas in the 2D disk can be important in confronting observations and numerical simulations in detail. For use in such applications, a new method for the calculation of the Gravitational Force of a 2D disk is presented. Instead of solving the complete potential function problem, we calculate the Force in infinite planes in Cartesian and polar coordinates by a reproducing kernel method. Under the limitation of a 2D disk, we specifically represent the Force as a double summation of a convolution of the surface density and a fundamental kernel and employ a fast Fourier transform technique. In this method, the entire computational complexity can be reduced from O(N^2xN^2) to O(N^2(log"2N)^2), where N is the number of zones in one dimension. This approach does not require softening. The proposed method is similar to a spectral method, but without the necessity of imposing a periodic boundary condition. We further show this approach is of near second order accuracy for a smooth surface density in a Cartesian coordinate system.
