Improvement Of Numerical Simulation Research Articles

The Challenges Ahead for Multimessenger Analyses of Gravitational Waves and Kilonova: A Case Study on GW190425

Abstract In recent years, there have been significant advances in multimessenger astronomy due to the discovery of the first, and so far only confirmed, gravitational wave event with a simultaneous electromagnetic (EM) counterpart, as well as improvements in numerical simulations, gravitational wave (GW) detectors, and transient astronomy. This has led to the exciting possibility of performing joint analyses of the GW and EM data, providing additional constraints on fundamental properties of the binary progenitor and merger remnant. Here, we present a new Bayesian framework that allows inference of these properties, while taking into account the systematic modeling uncertainties that arise when mapping from GW binary progenitor properties to photometric light curves. We extend the relative binning method presented in Zackay et al. to include extrinsic GW parameters for fast analysis of the GW signal. The focus of our EM framework is on light curves arising from r-process nucleosynthesis in the ejected material during and after merger, the so-called kilonova, and particularly on black hole−neutron star systems. As a case study, we examine the recent detection of GW190425, where the primary object is consistent with being either a black hole or a neutron star. We show quantitatively how improved mapping between binary progenitor and outflow properties, and/or an increase in EM data quantity and quality are required in order to break degeneracies in the fundamental source parameters.

Improvement of Numerical Simulation Using Applied Statistical Properties of Directional Waves by Typhoons

Kim, D.-H.; Yoo, C.-I.; Jeong, Y.-H.; Lee, S.-Y., and Kim, H.-J., 2021. Improvement of numerical simulation using applied statistical properties of directional waves by typhoons. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 231–235. Coconut Creek (Florida), ISSN 0749-0208. Typhoon-generated wave fields are of importance both scientifically for understanding coastal zone protection and operationally for predicting potentially hazardous conditions for coastal regions. However, the effects of directional wave-to-wave characteristics near bays and estuaries during typhoons are poorly understood due to a strong lack of wave field data. To improve the accuracy of wave height design, this study investigated a highly accurate numerical simulation using the statistical properties of directional waves. Directional wave data were collected using the directional wave recorder MIDAS-DWR, the Geoje and Haeundae floating buoys, and the Gwangan light beacon on typhoons Ma-on and Muifa in July and August, 2011. Moreover, numerical simulation results from STWAVE based on the wave action balance equation were compared with significant wave heights and periods of collected in-situ measurement data. Model input parameters included significant wave height and peak period, as well as wave direction either from wave gauge observations (Case 1) or wave direction statistical properties (Cases 2 and 3). Numerical simulations using the mean and standard deviation of principal wave direction observation data in Mode ± 45° for the largest wave height (Case 3) showed excellent agreement. Results show that wave characteristics can be accurately analyzed using statistical analysis of wave direction rather than actual wave direction inputs, which fluctuates highly in the outer sea. Further, a numerical experiment considering the influence of local wind and flow was performed, showing that the influence of these factors on wave characteristics during typhoons can be studied continuously.

KiDS-450: enhancing cosmic shear with clipping transformations

We present the first "clipped" cosmic shear measurement using data from the Kilo-Degree Survey (KiDS-450). "Clipping" transformations suppress the signal from the highest density, non-linear regions of cosmological fields. We demonstrate that these transformations improve constraints on $S_8=\sigma_8(\Omega_{\rm{m}}/0.3)^{0.5}$ when used in combination with conventional two-point statistics. For the KiDS-450 data, we find that the combined measurements improve the constraints on $S_8$ by 17%, compared to shear correlation functions alone. We determine the expectation value of the clipped shear correlation function using a suite of numerical simulations, and develop methodology to mitigate the impact of masking and shot noise. Future improvements in numerical simulations and mass reconstruction methodology will permit the precise calibration of clipped cosmic shear statistics such that clipping can become a standard tool in weak lensing analyses.

Status of the Electrostatic Levitation Furnace (ELF) in the ISS-KIBO

The electrostatic levitation method is a containerless processing technique that utilizes Coulomb force between a charged sample and the surrounding electrodes. The Japan Aerospace Exploration Agency (JAXA) has been developing this technique for more than 20 years. In 2016, JAXA completed the flight model assembly, and the Electrostatic Levitation Furnace (ELF) for the International Space Station (ISS) was launched to the ISS. The ELF is mainly intended to handle oxide melts that are difficult to levitate on the ground based electrostatic levitator due to gravity and due to insufficient charging. ISS-ELF can measure the thermophysical properties (density, surface tension and viscosity) of high temperature melts above 2000 ∘C. The thermophysical properties data of materials at high temperature is useful for the study of liquid states and improvement of numerical simulation by modeling the manufacturing processes using the liquid state. Moreover, the interfacial energy of immiscible melts will be measured by creating a core-shell droplet configuration which otherwise cannot be obtained on the ground due to sedimentation. This paper briefly describes the ELF facility and presents the results of a functional checkout that includes the density measurement of molten alumina.

Weighted Matrix Completion and Recovery With Prior Subspace Information

An incoherent low-rank matrix can be efficiently reconstructed after observing a few of its entries at random, and then, solving a convex program that minimizes the nuclear norm . In many applications, in addition to these entries, potentially valuable prior knowledge about the column and row spaces of the matrix is also available to the practitioner. In this paper, we incorporate this prior knowledge in matrix completion—by minimizing a weighted nuclear norm—and precisely quantify any improvements. In particular, we find in theory that reliable prior knowledge reduces the sample complexity of matrix completion by a logarithmic factor, and the observed improvement in numerical simulations is considerably more magnified. We also present similar results for the closely related problem of matrix recovery from generic linear measurements.

Experimental investigation of the thermal hydraulics of a spent fuel pool under loss of active heat removal conditions

In case of a temporal undefined failure of the active cooling system of a spent fuel pool (SFP), the water inside the pool heats up depending on the decay heat of the stored spent fuel. In the worst case, this leads to a boil-off scenario with a water level decrease and, after appropriate time, to a progressive uncovery of the fuel assemblies (FA). The cooling of the uncovered structures is limited by the steam production in the lower still wetted part of the FA, radiative heat transfer, radial heat conduction and convection inside the FA and interaction with ambient air depending on the storage conditions. As a result, the removal of decay heat can be endangered and, by reaching certain cladding temperatures, the integrity of the cladding tubes can be compromised. The detailed heat and mass transfer mechanisms of the boil-off scenario are not yet sufficiently investigated – especially experimentally. Therefore, reliable conclusions about the development of the cladding temperatures cannot be made.Against this background, the SINABEL project was launched in 2013 at TU Dresden for an improved understanding of the heat transport processes inside a SFP under accident conditions. Studies are performed both experimentally on the test facility ALADIN and theoretically by using computational fluid dynamics (CFD) calculations and integral codes for severe accidents. The test facility simulates a generic boiling water reactor (BWR) FA on almost original scale with regard to the boundary and ambient conditions within a SFP. Through an appropriate unique net of instrumentation, the distribution and development of radial and axial cladding temperatures and the development of the water level can be investigated in detail.Experiments were carried out for various decay heats respectively rod powers and changing storage distances. The thermal hydraulics of the heat-up and the boil-off phase with the occurrence of subcooled boiling in the beginning followed by geysering-like instabilities are described in the present paper. The higher the heat load, the faster the heat-up and, as boiling temperature is reached, the lowering of the water level. The maximum limit of the water level and the influence by the radial heat conduction, convection and radiative heat transfer is shown and explained.The experimental data and thermohydraulic findings provide the basis for the phenomenological understanding of this accident scenario and are used for the validation and improvement of numerical simulations.

Improvements in numerical simulation of the SPR process using a thermo-mechanical finite element analysis

Self-piercing riveting (SPR) has been widely used over recent years in the automotive industry to join lightweight aluminium structures. However, the extensive experimental trials needed to assess the feasible rivet/die combinations within a body in white assembly facility present a serious constraint for the application of this process on a large manufacturing scale. Therefore, having a virtual tool able to assess or predict the feasibility of a rivet/die combination is of primary importance for the automotive industry. In this study, a 2D axisymmetric model based on thermo-mechanical finite element analysis (FEA) was proposed to simulate the SPR process using material data determined at a strain rate of 1s−1 and temperatures ranging from ambient to 300°C. The increase in temperature due to friction and plastic deformation was numerically investigated using simufact.forming™ software. The effects of thermal softening and strain hardening at different strain rates were characterized for the substrate material (aluminium alloy AA5754) and their influence on the numerical simulation assessed. Accounting for these parameters led to a significantly higher level of correlation between simulation and experimental results for a number of different SPR joint configurations representative of industrial applications.

Nudging of vertical profiles of meteorological parameters in one-dimensional atmospheric model: A step towards improvements in numerical simulations

In this article, we describe a simple yet effective method for insertion of observational datasets in a mesoscale atmospheric model used in one-dimensional configuration through Nudging. To demonstrate the effectiveness of this technique, vertical profiles of meteorological parameters obtained from GLASS Sonde launches from a tiny island of Kaashidhoo in the Republic of Maldives are injected in a mesoscale atmospheric model — Advanced Regional Prediction System (ARPS), and model simulated parameters are compared with the available observational datasets. Analysis of one-time nudging in the model simulations over Kaashidhoo show that incorporation of this technique reasonably improves the model simulations within a time domain of +6 to +12 Hrs, while its impact on +18 Hrs simulations and beyond becomes literally null.

An Observational Case for the Prevalence of Roll Vortices in the Hurricane Boundary Layer*

Abstract Doppler velocity data from Weather Surveillance Radar-1988 Doppler (WSR-88D) radars during four hurricane landfalls are analyzed to investigate the presence of organized vortices in the hurricane boundary layer (HBL). The wavelength, depth, magnitude, and track of velocity anomalies were compiled through analysis of Doppler velocity data. The analysis reveals alternating bands of enhanced and reduced azimuthal winds closely aligned with the mean wind direction. Resulting statistics provide compelling evidence for the presence of organized secondary circulations or boundary layer rolls across significant areas during four hurricane landfalls. The results confirm previous observations of the presence of rolls in the HBL. A potential limitation of the study presented here is the resolution of the WSR-88D data. In particular, analysis of higher-resolution data (e.g., from the Doppler on Wheels) is needed to confirm that data aliasing has not unduly impacted the statistics reported here. Momentum fluxes associated with the secondary circulations are estimated using the covariance between the horizontal and vertical components of the wind fluctuations in rolls, with resulting fluxes 2–3 times greater than estimated by parameterizations in numerical weather prediction models. The observational analysis presented here, showing a prevalence of roll vortices in the HBL, has significant implications for the vertical transport of energy in hurricanes, for the character of wind damage, and for improvements in numerical simulations of hurricanes.

Towards standard benchmarks and reference data for validation and improvement of numerical simulation in sheet metal forming

The last decade has witnessed many advances and a lot of improvement in FE codes for simulation of sheet metal forming processes. Such advances could be followed mainly by benchmarks proposed in Numisheet conferences. It was possible to notice that the scatter of results among numerical codes has decreased so significantly that recently scattering of experimental results among different corporations was evident. However in order to pursue further developments and validate numerical results it is fundamental to have reliable reference experimental data. This is one of the objectives of a current IMS project called 3DS-Digital Die Design System. In this paper such objectives are presented as well as some of the proposed benchmarks. It is intended to show part of the developed work concerning tool design and manufacturing methodology. Also an experimental case study about the use of piercing holes in parts and the use of counter-punch is presented. Finally some simulation results are also shown concerning one of the proposed benchmarks.

‘First light’ in the universe: what ended the ‘dark age’?

The universe would have been completely dark between the epoch of recombination and the development of the first non-linear structure. But at redshifts beyond 5 – perhaps even beyond 20 – stars formed within ‘subgalaxies’ and created the first heavy elements; these same systems (together perhaps with ‘miniquasars’) generated the UV radiation that ionised the IGM, and may be also the first significant magnetic fields. Although we can already probe back to z≃5, these very first objects may be so faint that their detection must await next-generation optical and infrared telescopes. Observations in other wavebands may offer indirect clues to when reionisation occurred. Despite the rapid improvements in numerical simulations, the processes of star formation and feedback are likely to remain a challenge for the next decade.