The mechanical behavior of model-scale ice: experiments, numerical modeling and scalability

Increasing levels of transportation and exploratory activities in the High North increase the significance of ice-capable ship designs, and the demand for them. This demand covers a wide range of ship types; such as tugs, vessels for search and rescue (SAR), patrol boats, military vessels, cruise ships, and merchant ships. Both the economically driven preference for operations in the Arctic over operations in a warmer climate, and the safety of the operations, require adequate performance prediction methods. The capability of model-scale ice and its availability and advantages in handling compared to sea ice spurred to the decision to investigate its material behavior to develop a numerical model. This model serves as a corner-stone towards a numerical ice tank and provides insight into the mechanical behavior of model-scale ice. Therefore, systematic ice property tests were conducted with the model-scale ice of Aalto University to define the material behavior. The model-scale ice is fine grained (FG) and doped with ethanol to artificially weaken the material. The experiments investigate the behavior until failure in tension, compression and bending. Furthermore, the elastic modulus is determined by ice sheet deflection experiments and the grain-size is measured. The stress plane that is investigated is orthogonal to the vertical (thickness) coordinate and is the same as the one in which stresses occur when ships interact with ice. On the basis of the experiments, the mechanics and the constitution of the model-scale ice are investigated to define a suitable material model and its parameters. It was found that a damage based elasto-plastic material model represents the behavior of the Aalto model-scale ice well. The numerical model accounts explicitly for flaws in the model-scale ice, comprised of voids filled with liquid and air, which are randomly distributed. It is found that the random distribution of flaws enables the reproduction of the variation in experimentally observed failure patterns and affects the response forces. Furthermore, the cantilever beam bending experiments and their simulation reveal that the gradual change of ice properties over thickness has to be modeled to represent the experimentally measured axial stiffness and flexural stiffness in the same model. Ultimately, the model-scale ice is demonstrated to be a functionally graded material which is capable of representing tensile, compressive and flexural failure modes.Additionally, the development of the numerical model of the Aalto model-scale ice provides a deeper insight into its mechanical deformation processes. The material behavior that is found reveals that Cauchy similitude in scaling cannot be applied, because the model-scale ice of Aalto University is on micro scale not a purely elastic material. Consequently, model-scale ice consumes more energy prior to bending failure than a material complying Cauchy similitude

Non-instantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for generation and characterization of some of the shortest optical pulses to date, for optical switching applications, and for spectroscopy. In many cases, nonlinear optical effects are used far off resonance, and then an instantaneous temporal response is expected. Here, we show for the first time resonant frequency-resolved optical gating measurements that indicate substantial nonlinear polarization relaxation times up to 6.5\,fs in dielectric media, i.e., significantly beyond the shortest pulses directly available from commercial lasers. These effects are among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schr\"odinger equation are in excellent agreement with experimental observations. The simulations indicate that pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect. Moreover, our approach opens an avenue for application of frequency-resolved optical gating as a highly selective spectroscopic probe in high-field physics

Non-instantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for generation1,2 and characterization 3-5 of some of the shortest optical pulses to date, for optical switching applications6,7, and for spectroscopy8,9. In many cases, nonlinear optical effects are used far off resonance, and then an instantaneous temporal response is expected. Here, we show for the first time resonant frequency-resolved optical gating measurements1012 that indicate substantial nonlinear polarization relaxation times up to 6.5 fs in dielectric media, i.e., significantly beyond the shortest pulses directly available from commercial lasers. These effects are among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrödinger equation13,14 are in excellent agreement with experimental observations. The simulations indicate that pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect. Moreover, our approach opens an avenue for application of frequency-resolved optical gating as a highly selective spectroscopic probe in high-field physics

Sensitivity to Gravitational Waves from Compact Binary Coalescences Achieved during LIGO's Fifth and Virgo's First Science Run

We summarize the sensitivity achieved by the LIGO and Virgo gravitational wave detectors for compact binary coalescence (CBC) searches during LIGO's fifth science run and Virgo's first science run. We present noise spectral density curves for each of the four detectors that operated during these science runs which are representative of the typical performance achieved by the detectors for CBC searches. These spectra are intended for release to the public as a summary of detector performance for CBC searches during these science runs.Comment: 12 pages, 5 figure

Swift follow-up observations of candidate gravitational-wave transient events

We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge". With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.Comment: Submitted for publication 2012 May 25, accepted 2012 October 25, published 2012 November 21, in ApJS, 203, 28 ( http://stacks.iop.org/0067-0049/203/28 ); 14 pages, 3 figures, 6 tables; LIGO-P1100038; Science summary at http://www.ligo.org/science/Publication-S6LVSwift/index.php ; Public access area to figures, tables at https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p110003

Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009 and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25 solar masses; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90%-confidence rate upper limits of the binary coalescence of binary neutron star, neutron star- black hole and binary black hole systems are 1.3 x 10^{-4}, 3.1 x 10^{-5} and 6.4 x 10^{-6} Mpc^{-3}yr^{-1}, respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.Comment: 11 pages, 5 figures. For a repository of data used in the publication, go to: . Also see the announcement for this paper on ligo.org at: <http://www.ligo.org/science/Publication-S6CBCLowMass/index.php

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not included in v1. Accepted for publication in Astronomy & Astrophysic