19 research outputs found
Passivity-Preserving, Balancing-Based Model Reduction for Interconnected Systems
This paper proposes a balancing-based model reduction approach for an
interconnection of passive dynamic subsystems. This approach preserves the
passivity and stability of both the subsystems and the interconnected system.
Hereto, one Linear Matrix Inequality (LMI) per subsystem and a single Lyapunov
equation for the entire interconnected system needs to be solved, the latter of
which warrants the relevance of the reduction of the subsystems for the
accurate reduction of the interconnected system, while preserving the
modularity of the reduction approach. In a numerical example from structural
dynamics, the presented approach displays superior accuracy with respect to an
approach in which the individual subsystems are reduced independently.Comment: 6 pages, 4 figures, to appear in Proceedings of IFAC World Congress
202
Translating Assembly Accuracy Requirements to Cut-Off Frequencies for Component Mode Synthesis
One of the most popular methods for reducing the complexity of assemblies of
finite element models in the field of structural dynamics is component mode
synthesis. A main challenge of component mode synthesis is balancing model
complexity and model accuracy, because it is difficult to predict how component
reduction influences assembly model accuracy. This work introduces an approach
that allows for the translation of assembly model accuracy requirements in the
frequency domain to the automatic selection of the cut-off frequencies for the
model-order reduction (MOR) of components. The approach is based on a
mathematical approach for MOR for coupled linear systems in the field of
systems and control. We show how this approach is also applicable to structural
dynamics models. We demonstrate the use of this approach in the scope of
component mode synthesis (CMS) methods with the aim to reduce the complexity of
component models while guaranteeing accuracy requirements of the assembly
model. The proposed approach is illustrated on a mechanical, three-component
structural dynamics system for which reduced-order models are computed that are
reduced further compared to reduction using standard methods. This results in
lower simulation cost, while maintaining the required accuracy
Modular Redesign of Mechatronic Systems: Formulation of Module Specifications Guaranteeing System Dynamics Specifications
Complex mechatronic systems are typically composed of interconnected modules,
often developed by independent teams. This development process challenges the
verification of system specifications before all modules are integrated. To
address this challenge, a modular redesign framework is proposed in this paper.
Herein, first, allowed changes in the dynamics (represented by frequency
response functions (FRFs)) of the redesigned system are defined with respect to
the original system model, which already satisfies system specifications.
Second, these allowed changes in the overall system dynamics (or system
redesign specifications) are automatically translated to dynamics (FRF)
specifications on module level that, when satisfied, guarantee overall system
dynamics (FRF) specifications. This modularity in specification management
supports local analysis and verification of module design changes, enabling
design teams to work in parallel without the need to iteratively rebuild the
system model to check fulfilment of system FRF specifications. A modular
redesign process results that shortens time-to-market and decreases redesign
costs. The framework's effectiveness is demonstrated through three examples of
increasing complexity, highlighting its potential to enable modular mechatronic
system (re)design
Mode Selection for Component Mode Synthesis with Guaranteed Assembly Accuracy
In this work, a modular approach is introduced to select the most important
eigenmodes for each component of a composed structural dynamics system to
obtain the required accuracy of the reduced-order assembly model. To enable the
use of models of complex (structural) dynamical systems in engineering
practice, e.g., in a design, optimization and/or control context, the
complexity of the models needs to be reduced. When the model consist of an
assembly of multiple interconnected structural components, component mode
synthesis is often the preferred model reduction method. The standard approach
to component mode synthesis for such system is to select the eigenmodes of a
component that are most important to accurately model the dynamic behavior of
this component in a certain frequency range of interest. However, often, a more
relevant goal is to obtain, in this frequency range, an accurate model of the
assembly. In the proposed approach, accuracy requirements on the level of the
assembly are translated to accuracy requirements on component level, by
employing techniques from the field of systems and control. With these
component-level requirements, the eigenmodes that are most important to
accurately model the dynamic behavior of the assembly can be selected in a
modular fashion. We demonstrate with two structural dynamics benchmark systems
that this method based on assembly accuracy allows for a computationally
efficient selection of eigenmodes that 1) guarantees satisfaction of the
assembly accuracy requirements and 2) results in most cases in reduced-order
models of significantly lower order with respect to the industrial standard
approach in which component eigenmodes are selected using a frequency
criterion
Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
Precision astrometry at microarcsecond accuracy has application to a wide
range of astrophysical problems. This paper is a study of the science questions
that can be addressed using an instrument that delivers parallaxes at about 4
microarcsec on targets as faint as V = 20, differential accuracy of 0.6
microarcsec on bright targets, and with flexible scheduling. The science topics
are drawn primarily from the Team Key Projects, selected in 2000, for the Space
Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities
of this mission to illustrate the importance of the next level of astrometric
precision in modern astrophysics. SIM PlanetQuest is currently in the detailed
design phase, having completed all of the enabling technologies needed for the
flight instrument in 2005. It will be the first space-based long baseline
Michelson interferometer designed for precision astrometry. SIM will contribute
strongly to many astronomical fields including stellar and galactic
astrophysics, planetary systems around nearby stars, and the study of quasar
and AGN nuclei. SIM will search for planets with masses as small as an Earth
orbiting in the `habitable zone' around the nearest stars using differential
astrometry, and could discover many dozen if Earth-like planets are common. It
will be the most capable instrument for detecting planets around young stars,
thereby providing insights into how planetary systems are born and how they
evolve with time. SIM will observe significant numbers of very high- and
low-mass stars, providing stellar masses to 1%, the accuracy needed to
challenge physical models. Using precision proper motion measurements, SIM will
probe the galactic mass distribution and the formation and evolution of the
Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS
The 2010 very high energy gamma-ray flare & 10 years of multi-wavelength observations of M 87
Abridged: The giant radio galaxy M 87 with its proximity, famous jet, and
very massive black hole provides a unique opportunity to investigate the origin
of very high energy (VHE; E>100 GeV) gamma-ray emission generated in
relativistic outflows and the surroundings of super-massive black holes. M 87
has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray
emission displays strong variability on timescales as short as a day. In this
paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and
VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE
was detected triggering further observations at VHE (H.E.S.S.), X-rays
(Chandra), and radio (43 GHz VLBA). The excellent sampling of the VHE gamma-ray
light curve enables one to derive a precise temporal characterization of the
flare: the single, isolated flare is well described by a two-sided exponential
function with significantly different flux rise and decay times. While the
overall variability pattern of the 2010 flare appears somewhat different from
that of previous VHE flares in 2005 and 2008, they share very similar
timescales (~day), peak fluxes (Phi(>0.35 TeV) ~= (1-3) x 10^-11 ph cm^-2
s^-1), and VHE spectra. 43 GHz VLBA radio observations of the inner jet regions
indicate no enhanced flux in 2010 in contrast to observations in 2008, where an
increase of the radio flux of the innermost core regions coincided with a VHE
flare. On the other hand, Chandra X-ray observations taken ~3 days after the
peak of the VHE gamma-ray emission reveal an enhanced flux from the core. The
long-term (2001-2010) multi-wavelength light curve of M 87, spanning from radio
to VHE and including data from HST, LT, VLA and EVN, is used to further
investigate the origin of the VHE gamma-ray emission. No unique, common MWL
signature of the three VHE flares has been identified.Comment: 19 pages, 5 figures; Corresponding authors: M. Raue, L. Stawarz, D.
Mazin, P. Colin, C. M. Hui, M. Beilicke; Fig. 1 lightcurve data available
online: http://www.desy.de/~mraue/m87
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead