24 research outputs found
Modeling and Simulation in Engineering
This book provides an open platform to establish and share knowledge developed by scholars, scientists, and engineers from all over the world, about various applications of the modeling and simulation in the design process of products, in various engineering fields. The book consists of 12 chapters arranged in two sections (3D Modeling and Virtual Prototyping), reflecting the multidimensionality of applications related to modeling and simulation. Some of the most recent modeling and simulation techniques, as well as some of the most accurate and sophisticated software in treating complex systems, are applied. All the original contributions in this book are jointed by the basic principle of a successful modeling and simulation process: as complex as necessary, and as simple as possible. The idea is to manipulate the simplifying assumptions in a way that reduces the complexity of the model (in order to make a real-time simulation), but without altering the precision of the results
Underwater Vehicles
For the latest twenty to thirty years, a significant number of AUVs has been created for the solving of wide spectrum of scientific and applied tasks of ocean development and research. For the short time period the AUVs have shown the efficiency at performance of complex search and inspection works and opened a number of new important applications. Initially the information about AUVs had mainly review-advertising character but now more attention is paid to practical achievements, problems and systems technologies. AUVs are losing their prototype status and have become a fully operational, reliable and effective tool and modern multi-purpose AUVs represent the new class of underwater robotic objects with inherent tasks and practical applications, particular features of technology, systems structure and functional properties
Submm Observations of Massive Star Formation in the Giant Molecular Cloud NGC 6334 : Gas Kinematics with Radiative Transfer Models
Context. How massive stars (M>8 Ms) form and how they accrete gas is still an open research
field, but it is known that their influence on the interstellar medium (ISM) is immense. Star
formation involves the gravitational collapse of gas from scales of giant molecular clouds
(GMCs) down to dense hot molecular cores (HMCs). Thus, it is important to understand the
mass flows and kinematics in the ISM.
Aims. This dissertation focuses on the detailed study of the region NGC 6334, located in
the Galaxy at a distance of 1.7 kpc. It is aimed to trace the gas velocities in the filamentary,
massive star-forming region NGC 6334 at several scales and to explain its dynamics. For
that purpose, different scales are examined from 0.01–10 pc to collect information about the
density, molecular abundance, temperature and velocity, and consequently to gain insights about
the physio-chemical conditions of molecular clouds. The two embedded massive protostellar
clusters NGC 6334I and I(N), which are at different stages of development, were selected to
determine their infall velocities and mass accretion rates.
Methods. This astronomical source was surveyed by a combination of different observatories,
namely with the Submillimeter Array (SMA), the single-dish telescope Atacama Pathfinder
Experiment (APEX), and the Herschel Space Observatory (HSO). It was mapped with APEX in
carbon monoxide (13CO and C18O, J=2–1) at 220.4 GHz to study the filamentary structure and
turbulent kinematics on the largest scales of 10 pc. The spectral line profiles are decomposed
by Gaussian fitting and a dendrogram algorithm is applied to distinguish velocity-coherent
structures and to derive statistical properties. The velocity gradient method is used to derive
mass flow rates. The main filament was mapped with APEX in hydrogen cyanide (HCN) and
oxomethylium (HCO+, J=3–2) at 267.6 GHz to trace the dense gas. To reproduce the position-
velocity diagram (PVD), a cylindrical model with the radiative transfer code Line Modeling
Engine (LIME) is created with a collapsing velocity field. Both clusters NGC 6334I and I(N)
were observed with the interferometer SMA in HCN (J=4–3) at 354.5 GHz at the smallest
scales of 0.01 pc. The combination of interferometric and multi-frequency single-dish data gives
a wide range of rotational transitions, which probe the gas at different excitation conditions and
optical depths. The molecule HCN and its isotopologues H13CN/HC15N trace radii of a HMC
from 1.0–0.01 pc by a range of level energies (E=4–1067 K) and optical depths (tau=100–0.1).
The HMCs, which have a rich line spectra, are analyzed by using 1D (myXCLASS) and 3D
numerical radiative transfer codes (RADMC-3D and LIME) in and outside of local thermodynamic
equilibrium (LTE). Multiple components and the fragmentation of the clusters are modeled
with these tools. Together with the optimization package MAGIX, the data are compared and
reproduced with synthetic maps and spectra from these models.
Results. 1. The main filament shows a velocity gradient from the end toward its center, where
the most massive clumps accumulate at both ends, in accordance to predictions of a longitudinal
contraction. The 3D structure is determined by taking the inclination and curvature of the
filament into account, and the free-fall time is estimated to approximately 1 Myr; 2. The total gas mass is
2.3E5 Ms and the average temperature 20 K. The majority of the velocity gradients are aligned
with the magnetic field, which runs perpendicular to the filaments. The calculation of the average
Mach numbers yields a turbulence which is super-sonic (M_S=5.7) and sub-Alfvénic (M_A=0.86).
In general, the derived scaling relations are in agreement with Larson's relations. 3. The SMA
observations reveal multiple bipolar molecular outflows, blue asymmetric infall profiles, rotating
cores and an ultra compact (UC) HII region in NGC 6334I which affects the surrounding gas.
The average mass accretion rates are 1E-3 Ms/yr for the envelopes and 3E-4 Ms/yr for the
cores, where the latter are derived from modified Bondi-Hoyle models. The orientation of the
magnetic field is in NGC 6334I(N) consistent over all scales and most outflows are aligned
perpendicular to it; 4. In the line surveys of the HMCs, 20 different molecules are identified
with typical temperatures of 100 K. A cruel separation between the HMCs of the clusters is
determined on the basis of the relative abundances.
Conclusions. The combination of single-dish with interferometric data is helpful to constrain
the parameter space of a model. The envelope hinders the determination of infall velocities in
HMCs via line profiles. Systematic motions as a result of gravitational attraction are diffcult to
find because of the turbulent nature of the ISM. The magnetic field energy in NGC 6334 is as
important as the kinetic energy and regulates partly the direction of the inflowing gas and thus
the geometry and collapse of the molecular clouds. NGC 6334 is heavily affected by the HII
regions (produced by the OB stars), and the free-fall time and mass surface density suggest that
it classifies as a starburst system
Advanced Operation and Maintenance in Solar Plants, Wind Farms and Microgrids
This reprint presents advances in operation and maintenance in solar plants, wind farms and microgrids. This compendium of scientific articles will help clarify the current advances in this subject, so it is expected that it will please the reader