scholarly journals The Impact of Initial Conditions in N-Body Simulations of Debris Discs

2015 ◽  
Vol 32 ◽  
Author(s):  
E. Thilliez ◽  
S. T. Maddison
Keyword(s):  
Numerical Simulations ◽  
Initial Conditions ◽  
Parent Body ◽  
Dust Trapping ◽  
Physical Context ◽  
Disc Width ◽  
Wide Range ◽  
Belt Width ◽  
New Generation ◽  
The Impact

AbstractNumerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

scholarly journals The Status of Multi-Dimensional Core-Collapse Supernova Models

2016 ◽  
Vol 33 ◽  
Author(s):  
B. Müller
Keyword(s):  
Initial Conditions ◽  
Massive Stars ◽  
Core Collapse ◽  
Solar Mass ◽  
Convective Boundary ◽  
3D Simulations ◽  
Core Collapse Supernova ◽  
Wide Range ◽  
Supernova Explosions ◽  
The Impact

AbstractModels of neutrino-driven core-collapse supernova explosions have matured considerably in recent years. Explosions of low-mass progenitors can routinely be simulated in 1D, 2D, and 3D. Nucleosynthesis calculations indicate that these supernovae could be contributors of some lighter neutron-rich elements beyond iron. The explosion mechanism of more massive stars remains under investigation, although first 3D models of neutrino-driven explosions employing multi-group neutrino transport have become available. Together with earlier 2D models and more simplified 3D simulations, these have elucidated the interplay between neutrino heating and hydrodynamic instabilities in the post-shock region that is essential for shock revival. However, some physical ingredients may still need to be added/improved before simulations can robustly explain supernova explosions over a wide range of progenitors. Solutions recently suggested in the literature include uncertainties in the neutrino rates, rotation, and seed perturbations from convective shell burning. We review the implications of 3D simulations of shell burning in supernova progenitors for the ‘perturbations-aided neutrino-driven mechanism,’ whose efficacy is illustrated by the first successful multi-group neutrino hydrodynamics simulation of an 18 solar mass progenitor with 3D initial conditions. We conclude with speculations about the impact of 3D effects on the structure of massive stars through convective boundary mixing.

scholarly journals A Robust Numerical Solution of the Stochastic Collection–Breakup Equation for Warm Rain

2007 ◽  
Vol 46 (9) ◽  
pp. 1480-1497 ◽  
Author(s):  
Olivier P. Prat ◽  
Ana P. Barros
Keyword(s):  
Numerical Solution ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Strong Dependence ◽  
Discrete Equations ◽  
Warm Rain ◽  
Wide Range ◽  
Short Time ◽  
Rain Rates ◽  
The Impact

Abstract The focus of this paper is on the numerical solution of the stochastic collection equation–stochastic breakup equation (SCE–SBE) describing the evolution of raindrop spectra in warm rain. The drop size distribution (DSD) is discretized using the fixed-pivot scheme proposed by Kumar and Ramkrishna, and new discrete equations for solving collision breakup are presented. The model is evaluated using established coalescence and breakup parameterizations (kernels) available in the literature, and in that regard this paper provides a substantial review of the relevant science. The challenges posed by the need to achieve stable and accurate numerical solutions of the SCE–SBE are examined in detail. In particular, this paper focuses on the impact of varying the shape of the initial DSD on the equilibrium solution of the SCE–SBE for a wide range of rain rates and breakup kernels. The results show that, although there is no dependence of the equilibrium DSD on initial conditions for the same rain rate and breakup kernel, there is large variation in the time that it takes to reach steady state. This result suggests that, in coupled simulations of in-cloud motions and microphysics and for short time scales (&lt;30 min) for which transient conditions prevail, the equilibrium DSD may not be attainable except for very heavy rainfall. Furthermore, simulations for the same initial conditions show a strong dependence of the dynamic evolution of the DSD on the breakup parameterization. The implication of this result is that, before the debate on the uniqueness of the shape of the equilibrium DSD can be settled, there is critical need for fundamental research including laboratory experiments to improve understanding of collisional mechanisms in DSD evolution.

scholarly journals Rapid mass segregation in young star clusters without substructure?

2010 ◽  
Vol 6 (S271) ◽  
pp. 389-390
Author(s):  
C. Olczak ◽  
R. Spurzem ◽  
Th. Henning
Keyword(s):  
Initial Conditions ◽  
Star Clusters ◽  
Building Blocks ◽  
Young Star ◽  
Subsequent Formation ◽  
Multiple Systems ◽  
Mass Segregation ◽  
New Generation ◽  
The Impact ◽  
Young Star Clusters

AbstractThe young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the initial conditions under which star clusters form and the impact of these often harsh environments on the formation and evolution of their stellar and substellar members.We present recent results showing that mass segregation in realistic models of young star clusters occurs very quickly for subvirial spherical systems without substructure. This finding is a critical step to resolve the controversial debate on mass segregation in young star clusters and provides strong constraints on their initial conditions. The rapid concentration of massive stars is usually associated with strong gravitational interactions early on during cluster evolution and the subsequent formation of multiple systems and ejection of stars.

scholarly journals Impact of a Random Sequence of Debris Flows on Torrential Fan Formation

Geosciences ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 64 ◽  
Author(s):  
Nejc Bezak ◽  
Jošt Sodnik ◽  
Matjaž Mikoš
Keyword(s):  
Debris Flow ◽  
Numerical Simulations ◽  
Rheological Properties ◽  
Debris Flows ◽  
Random Sequence ◽  
Rheological Parameters ◽  
Model Parameters ◽  
Maximum Height ◽  
Wide Range ◽  
The Impact

Debris flows with different magnitudes can have a large impact on debris fan characteristics such as height or slope. Moreover, knowledge about the impact of random sequences of debris flows of different magnitudes on debris fan properties is sparse in the literature and can be improved using numerical simulations of debris fan formation. Therefore, in this paper we present the results of numerical simulations wherein we investigated the impact of a random sequence of debris flows on torrential fan formation, where the total volume of transported debris was kept constant, but different rheological properties were used. Overall, 62 debris flow events with different magnitudes from 100 m3 to 20,000 m3 were selected, and the total volume was approximately 225,000 m3. The sequence of these debris flows was randomly generated, and selected debris fan characteristics after the 62 events were compared. For modeling purposes, we applied the Rapid Mass Movement Simulations (RAMMS) software and its debris flow module (RAMMS-DF). The modeling was carried out using (a) real fan topography from an alpine environment (i.e., an actual debris fan in north-west (NW) Slovenia formed by the Suhelj torrent) and (b) an artificial surface with a constant slope. Several RAMMS model parameters were tested. The simulation results confirm that the random sequence of debris flow events has only some minor effects on the fan formation (e.g., slope, maximum height), even when changing debris flow rheological properties in a wide range. After the 62 events, independent of the selected sequence of debris flows, the final fan characteristics were not significantly different from each other. Mann–Whitney (MW) tests and t-tests were used for this purpose, and the selected significance level was 0.05. Moreover, this conclusion applies for artificial and real terrain and for a wide range of tested RAMMS model rheological parameters. Further testing of the RAMMS-DF model in real situations is proposed in order to better understand its applicability and limitations under real conditions for debris flow hazard assessment or the planning of mitigation measures.

scholarly journals Early-time jet formation in liquid–liquid impact problems: theory and simulations

2018 ◽  
Vol 856 ◽  
pp. 764-796 ◽  
Author(s):  
R. Cimpeanu ◽  
M. R. Moore
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Early Stage ◽  
Early Time ◽  
Leading Order ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Jet Velocity ◽  
The Impact ◽  
Wagner Theory

We perform a thorough qualitative and quantitative comparison of theoretical predictions and direct numerical simulations for the two-dimensional, vertical impact of two droplets of the same fluid. In particular, we show that the theoretical predictions for the location and velocity of the jet root are excellent in the early stages of the impact, while the predicted jet velocity and thickness profiles are also in good agreement with the computations before the jet begins to bend. By neglecting the role of the surrounding gas both before and after impact, we are able to use Wagner theory to describe the early-time structure of the impact. We derive the model for general droplet velocities and radii, which encompasses a wide range of impact scenarios from the symmetric impact of identical drops to liquid drops impacting a deep pool. The leading-order solution is sufficient to predict the curve along which the root of the high-speed jet travels. After moving into a frame fixed in this curve, we are able to derive the zero-gravity shallow-water equations governing the leading-order thickness and velocity of the jet. Our numerical simulations are performed in the open-source software Gerris, which allows for the level of local grid refinement necessary for a problem with such a wide variety of length scales. The numerical simulations incorporate more of the physics of the problem, in particular the surrounding gas, the fluid viscosities, gravity and surface tension. We compare the computed and predicted solutions for a range of droplet radii and velocities, finding excellent agreement in the early stage. In light of these successful comparisons, we discuss the tangible benefits of using Wagner theory to confidently track properties such as the jet-root location, jet thickness and jet velocity in future studies of splash jet/ejecta evolution.

Nonlinear Airy Wave Pulses on the Sea Surface

2019 ◽  
Author(s):  
Igor Shugan ◽  
Sergei Kuznetsov ◽  
Yana Saprykina ◽  
Yang-Yih Chen
Keyword(s):  
Wave Packet ◽  
Deep Water ◽  
Water Wave ◽  
Initial Conditions ◽  
Nonlinear Effects ◽  
Dispersive Waves ◽  
Spatial And Temporal Scales ◽  
Wide Range ◽  
Steep Waves ◽  
The Impact

Abstract The possibility of self-acceleration of the water-wave pulse with a permanent envelope in the form of the nonlinear Airy function during its long propagation in deep water is experimentally and theoretically analyzed. This wave packet has amazing properties — accelerates without any external force, and preserves shape in a dispersive medium. The inverted Airy envelope wave function can propagate at velocity that is faster than the group velocity. We experimentally study the behavior of Airy water-wave pulses in a super-tank and long scaled propagation, to investigate its main properties, nonlinear effects and stability. Theoretical modeling analysis is based on the nonlinear Schrodinger equation. We investigate the scope of applicability, feasibility and stability conditions of nonlinear Airy wave trains in the deep water conditions; defining regimes of self-acceleration of the main pulse, immutability shape of Airy envelope; assessing the impact of nonlinearity and dissipation on the propagation of Airy waves. We analyzed the influence of the initial pulse characteristics on self-acceleration of wave packet and the stability of the envelope form. The anticipated results allow extending the physical understanding of the evolution of nonlinear dispersive waves in a wide range of initial conditions and at different spatial and temporal scales, from both theoretical and experimental points of view. Steep waves start to become an unstable, we observe spectrum widening and downshifting. Wave propagation is accompained by the intensive wave breaking and the generation of water-wave solitons.

scholarly journals A scattered Uranus and Neptune, and implications for the asteroid belt

2004 ◽  
Vol 202 ◽  
pp. 241-243
Author(s):  
Edward W. Thommes ◽  
Martin J. Duncan ◽  
Harold F. Levison ◽  
John E. Chambers
Keyword(s):  
Solar System ◽  
Numerical Simulations ◽  
Initial Conditions ◽  
Asteroid Belt ◽  
Outer Solar System ◽  
Wide Range ◽  
Gas Giant ◽  
Gas Accretion ◽  
High Degree

It has been proposed that Uranus and Neptune originated interior to ∽ 10 AU, as potential gas giant cores which were scattered outward when Jupiter won the race to reach runaway gas accretion. We present further numerical simulations of this scenario, which show that it reproduces the present configuration of the outer Solar System with a high degree of success for a wide range of initial conditions. Also, we show that this mechanism may have simultaneously ejected planets from the asteroid belt.

The European Summer of 2003: Sensitivity to Soil Water Initial Conditions

2006 ◽  
Vol 19 (15) ◽  
pp. 3659-3680 ◽  
Author(s):  
Laura Ferranti ◽  
Pedro Viterbo
Keyword(s):  
Numerical Simulations ◽  
Soil Water ◽  
Initial Conditions ◽  
Soil Depth ◽  
Atmospheric Model ◽  
Shortwave Radiation ◽  
Initial Soil ◽  
Water Conditions ◽  
Soil Water Conditions ◽  
The Impact

Abstract The European summer of 2003 is used as a case study to analyze the land surface role in augmenting the local temperature anomalies. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and the 40-yr ECMWF Re-Analysis (ERA-40) climate, it is shown that in the months preceding the extreme summer events, positive anomalies in the surface shortwave radiation and a large precipitation deficit indicated an impending dry summer in early June. The use of soil water analysis values as possible predictors for drought is currently limited by the systematic attenuation of its seasonal cycle. Several numerical simulations with the ECMWF atmospheric model have been used to explore the atmospheric model sensitivity to the initial soil water conditions. The atmospheric response to large initial perturbations in the root zone extends up to month 2 and is nonlinear, and larger for drier regimes. Perturbations to the whole soil depth increase the amplitude of the atmospheric anomaly and extend its duration up to 3 months. The response of large initial dry soil anomalies greatly exceeds the impact of the ocean boundary forcing. Results from numerical simulations indicate the possible benefit of using perturbations in the initial soil water conditions, commensurate with soil moisture uncertainties, in the generation of the seasonal forecast ensembles.

Impacts of 4DVAR Assimilation of Airborne Doppler Radar Observations on Numerical Simulations of the Genesis of Typhoon Nuri (2008)

2014 ◽  
Vol 53 (10) ◽  
pp. 2325-2343 ◽  
Author(s):  
Zhan Li ◽  
Zhaoxia Pu ◽  
Juanzhen Sun ◽  
Wen-Chau Lee
Keyword(s):  
Data Assimilation ◽  
Radial Velocity ◽  
Numerical Simulations ◽  
Doppler Radar ◽  
Initial Conditions ◽  
Radar Data ◽  
Radar Observations ◽  
Wind Analysis ◽  
The Impact ◽  
Airborne Doppler Radar

AbstractThe Weather Research and Forecasting Model and its four-dimensional variational data assimilation (4DVAR) system are employed to examine the impact of airborne Doppler radar observations on predicting the genesis of Typhoon Nuri (2008). Electra Doppler Radar (ELDORA) airborne radar data, collected during the Office of Naval Research–sponsored Tropical Cyclone Structure 2008 field experiment, are used for data assimilation experiments. Two assimilation methods are evaluated and compared, namely, the direct assimilation of radar-measured radial velocity and the assimilation of three-dimensional wind analysis derived from the radar radial velocity. Results show that direct assimilation of radar radial velocity leads to better intensity forecasts, as this process enhances the development of convective systems and improves the inner-core structure of Nuri, whereas assimilation of the radar-retrieved wind analysis is more beneficial for tracking forecasts, as it results in improved environmental flows. The assimilation of both the radar-retrieved wind and the radial velocity can lead to better forecasts in both intensity and tracking, if the radial velocity observations are assimilated first and the retrieved winds are then assimilated in the same data assimilation window. In addition, experiments with and without radar data assimilation led to developing and nondeveloping disturbances in numerical simulations of Nuri’s genesis. The improved initial conditions and forecasts from the data assimilation imply that the enhanced midlevel vortex and moisture conditions are favorable for the development of deep convection in the center of the pouch and eventually contribute to Nuri’s genesis. The improved simulations of the convection and associated environmental conditions produce enhanced upper-level warming in the core region and lead to the drop in sea level pressure.

scholarly journals Numerical Simulations of the Genesis of Typhoon Nuri (2008): Sensitivity to Initial Conditions and Implications for the Roles of Intense Convection and Moisture Conditions

2014 ◽  
Vol 29 (6) ◽  
pp. 1402-1424 ◽  
Author(s):  
Zhan Li ◽  
Zhaoxia Pu
Keyword(s):  
Numerical Simulations ◽  
Heat Release ◽  
Latent Heat ◽  
Initial Conditions ◽  
Deep Convection ◽  
Tropical Cyclone Genesis ◽  
Latent Heat Release ◽  
Numerical Predictions ◽  
Upper Level ◽  
The Impact

Abstract The sensitivity of numerical simulations of the genesis of Typhoon Nuri (2008) to initial conditions is examined using the Advanced Research core of the Weather Research and Forecasting (WRF) Model. The initial and boundary conditions are derived from two different global analyses at different lead times. One simulation successfully captures the processes of Nuri’s genesis and early intensification, whereas other simulations fail to predict the genesis of Nuri. Discrepancies between simulations with and without Nuri’s development are diagnosed. Significant differences are found in the development and organization of the intense convection during Nuri’s pregenesis phase. In the developing case, convection evolves and organizes into a “pouch” center of a westward-propagating wavelike disturbance. In the nondeveloping case, the convection fails to develop and organize. Favorable conditions for the development of deep convection include strong closed circulation patterns with high humidity, especially at the middle levels. An additional set of sensitivity experiments is performed to examine the impact of the moisture field on numerical simulations of Nuri’s genesis. Results confirm that the enhancement of mid- to upper-level moisture is favorable for Nuri’s genesis, mainly because moist conditions benefit deep convection, which produces diabatic heating from latent heat release when vertical airmass flux maxima occur in the mid- to upper-level atmosphere. The substantial warming at upper levels induced by latent heat release from persistent deep convection contributes to the drop in Nuri’s minimum central sea level pressure. Overall, results from this study demonstrate that it is essential to accurately represent the initial conditions in numerical predictions of tropical cyclone genesis.

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