Detailed Hydrodynamic Simulations Research Articles

Constraints on thermal conductivity in the merging cluster Abell 2146

ABSTRACT The cluster of galaxies Abell 2146 is undergoing a major merger and is an ideal cluster to study intracluster medium (ICM) physics, as it has a simple geometry with the merger axis in the plane of the sky, its distance allows us to resolve features across the relevant scales and its temperature lies within Chandra’s sensitivity. Gas from the cool core of the subcluster has been partially stripped into a tail of gas, which gives a unique opportunity to look at the survival of such gas and determine the rate of conduction in the ICM. We use deep 2.4-Ms Chandra observations of Abell 2146 to produce a high spatial resolution map of the temperature structure along a plume in the ram-pressure stripped tail, described by a partial cone, which is distinguishable from the hot ambient gas. Previous studies of conduction in the ICM typically rely on estimates of the survival time for key structures, such as cold fronts. Here we use detailed hydrodynamical simulations of Abell 2146 to determine the flow velocities along the stripped plume and measure the time-scale of the temperature increase along its length. We find that conduction must be highly suppressed by multiple orders of magnitude compared to the Spitzer rate, as the energy used is about 1 per cent of the energy available. We discuss magnetic draping around the core as a possible mechanism for suppressing conduction.

Efficient Tropical Cyclone Scenario Selection Based on Cumulative Likelihood of Potential Impacts

AbstractThe incidence of climate‐related disasters is on the rise, which makes it imperative to intensify anticipatory action. Tropical cyclones (TC) bring extreme precipitation and storm surge to coastal areas. This poses a compound flood risk to coastal communities due to the coincidence/concurrence of multiple flood drivers. In the absence of sufficient spatiotemporal coverage of historic TC data, appropriate characterization of compound flood risk mainly relies on running a large number of synthetic scenarios with the hope that it covers the wide range of potential threats posed to a coastal community. Such an approach requires huge computational resources that make it infeasible in many cases. Here, we propose a dependence‐informed sampling scheme that helps reduce the dimensionality of the problem and systematically select a handful of scenarios with the largest Cumulative Likelihood of Potential Impact (CLPI). The CLPI is a compound flood index that ranks the candidate storms with the potential to cause compound flooding based on the regional dependencies between forcing (wind and rainfall) and coastal flooding drivers (storm surge and runoff). The analysis of historic TC records near the coast of Texas, USA shows the usefulness of CLPI in improving the efficiency of hazard risk assessment and providing reliable information at a lower cost. The proposed CLPI successfully ranks candidate hurricane scenarios based on their potential impact and filters out the less relevant scenarios without the need for detailed hydrodynamic simulation.

Laboratory Investigation of Hydrodynamic and Sand Dune Morphology Changes Under Wave Overwash

AbstractSince the field measurement of wave overwash is difficult to obtain during severe storms, a laboratory experiment is conducted to measure the time and space evolution of the overwash and beach profile over the sand dune continuously using high‐speed video image analysis for different wave conditions of irregular waves and solitary waves. Characteristics of the cross‐shore sediment transport and morphology change are discussed from the laboratory experiment data. The inflection point, which marks the shifting turn in dune crest movement during overwash, is determined by analyzing feature points in the variation of dune geometry. It is confirmed that the overwash water volume rate reaches a maximum value when the inflection point occurs. Additionally, the overwash water volume is found to be linearly related to the deposited sediment volume, and the dune erosion volume is proportional to wave energy flux during the overwash process. The presence of secondary dunes is found to significantly alleviate coast erosion during overwash and reduce shoreline retreat by more than 40%, regardless of the height of the secondary dune crest. Furthermore, the advances and limitations in overwash hydrodynamics are discussed. It is recommended that this continuous morphological change monitoring data be combined with a wave resolution model for detailed hydrodynamic simulations to further understand the overwash process.

Impact of systematic nuclear uncertainties on composition and decay heat of dynamical and disc ejecta in compact binary mergers

ABSTRACT Theoretically predicted yields of elements created by the rapid neutron capture (r-)process carry potentially large uncertainties associated with incomplete knowledge of nuclear properties and approximative hydrodynamical modelling of the matter ejection processes. We present an in-depth study of the nuclear uncertainties by varying theoretical nuclear input models that describe the experimentally unknown neutron-rich nuclei. This includes two frameworks for calculating the radiative neutron capture rates and 14 different models for nuclear masses, β-decay rates, and fission properties. Our r-process nuclear network calculations are based on detailed hydrodynamical simulations of dynamically ejected material from NS–NS or NS–BH binary mergers plus the secular ejecta from BH–torus systems. The impact of nuclear uncertainties on the r-process abundance distribution and the early radioactive heating rate is found to be modest (within a factor of ∼20 for individual A > 90 abundances and a factor of 2 for the heating rate). However, the impact on the late-time heating rate is more significant and depends strongly on the contribution from fission. We witness significantly higher sensitivity to the nuclear physics input if only a single trajectory is used compared to considering ensembles with a much larger number of trajectories (ranging between 150 and 300), and the quantitative effects of the nuclear uncertainties strongly depend on the adopted conditions for the individual trajectory. We use the predicted Th/U ratio to estimate the cosmochronometric age of six metal-poor stars and find the impact of the nuclear uncertainties to be up to 2 Gyr.

On characterization of shock propagation and radiative preheating in x-ray driven high-density carbon foils

Recently, much effort has been dedicated to the high-density carbon ablator coated fuel capsule in indirect drive inertial confinement fusion experiments due to its higher density compared to other ablators. By using detailed radiation hydrodynamic simulations over a broad range of drive and target parameters, a thorough analysis is performed on shock speed, shock breakout, and maximum preheating temperature in pure and tungsten doped high density carbon foils. The ablators are irradiated by a non-equilibrium x-ray temperature drive consisting of the usual Planckian plus an additionally imposed Gaussian distribution lying in the high frequency M-band region of the incident spectrum. All variables have shown a complex interdependence on strength of the drive, its spectral distribution, and the thickness of the target. Maximum preheating temperature, an important parameter in designing experiments, reduces up to 34% for thicker high-density carbon (HDC) foils, whereas a mere 0.44% doping of tungsten in pure HDC is able to reduce preheating up to 17% for extreme drive conditions. The results are explained on the basis of variation of average albedo/wall loss behavior in foils, an outcome of the interplay between total extinction coefficient and spectral intensity variation with photon energy. For a better understanding and comparison among different types of ablators, multi-parameter scaling relations are proposed for above-mentioned variables, which govern the dynamics of shock propagation and preheating phenomena in HDC based foils.

The large magellanic cloud revealed in gravitational waves with LISA

ABSTRACTThe Laser Interferometer Space Antenna (LISA) will unveil the non-transient gravitational wave sky full of inspiralling stellar-mass compact binaries within the local universe. The Large Magellanic Cloud (LMC) is expected to be prominent on the LISA sky due to its proximity and its large population of double white dwarfs (DWD). Here, we present the first dedicated study of the LMC with gravitational wave sources. We assemble three LMC models based on: (1) the density distribution and star formation history from optical wavelength observations, (2) a detailed hydrodynamic simulation, and (3) combining the two. Our models yield a hundred to several hundred detectable DWDs: indeed, the LMC will be a resolved galaxy in the LISA sky. Importantly, amongst these we forecast a few tens to a hundred double degenerate supernovae type Ia progenitors, a class of binaries which have never been unambiguously observed. The range in the number of detections is primarily due to differences in the LMC total stellar mass and recent star formation in our models. Our results suggest that the total number, periods, and chirp masses of LISA sources may provide independent constraints on both LMC stellar mass and recent star formation by comparing LISA observations with the models, although such constraints will be highly model-dependent. Our publicly available model populations may be used in future studies of the LMC, including its structure and contribution to LISA confusion noise.

Detailed investigation on x-ray emission from laser-driven high-Z foils in a wide intensity range: Role of conversion layer and re-emission zone

Detailed radiation hydrodynamic simulations are carried out to investigate the x-ray emission process in four high-Z planar targets, namely, tungsten (W), gold (Au), lead (Pb), and uranium (U) irradiated by 1 ns, 351 nm flat top laser pulses. A thorough zoning analysis is performed for all laser-driven high-Z foils over a wide intensity range of 1012–1015 W/cm2 with appropriately chosen photon energy range and recombination parameter. The resulting variation of conversion efficiency over the full intensity range exhibits an optimum for all materials, which is explained by considering the characteristic emission contributions from two different regions of laser irradiated plasma, namely, conversion layer and re-emission zone. A new generalized single scaling relation based upon smooth broken power law is proposed for conversion efficiency variation along with the separate determination (ηS, ηM) in soft and hard/M-band x-ray regions. It has been observed that ηS for Pb and W always lies in between that for Au and U for intensities smaller than ∼3×1013 W/cm2. On further increase in intensity, ηS is observed to be maximum for Au and U, whereas it is minimum for W. Significant contribution to M-band conversion efficiencies is observed in all elements for intensities higher than ∼2×1013 W/cm2 with maximum and minimum values attained by W and U, respectively. The results are explained by considering the contributions from the emission coefficients of all materials in both conversion layer and re-emission zone up to corresponding photon cutoff energies at different laser intensities.

Building level flood exposure analysis using a hydrodynamic model

The advent of detailed hydrodynamic model simulations of urban flooding has not been matched by improved capabilities in flood exposure analysis which rely on validation against observed data. This work introduces a generic, building-level flood exposure analysis tool applying high resolution flood data and building geometries derived from hydrodynamic simulations performed with the 2D hydrodynamic flood modelling software CityCAT. Validation data were obtained from a survey of affected residents following a large pluvial flood event in Newcastle upon Tyne, UK. Sensitivity testing was carried out for different hydrodynamic model and exposure tool settings and between 68% and 75% of the surveyed buildings were correctly modelled as either flooded or not flooded. The tool tends to underrepresent flooding with a better performance in identifying true negatives (i.e. no flooding observed with no flooding modelled) compared to true positives. As higher true positive rates were accompanied by higher false positive rates, no single scenario could be identified as the optimal solution. However, the results suggest a greater sensitivity of the results to the classification scheme than to the buffer distance applied. Overall, if applied to high resolution flood depth maps, the method is efficient and suitable for application to large urban areas for flood risk management and insurance analysis purposes.

Efficient Hazard Assessment for Pluvial Floods in Urban Environments: A Benchmarking Case Study for the City of Berlin, Germany

The presence of impermeable surfaces in urban areas hinders natural drainage and directs the surface runoff to storm drainage systems with finite capacity, which makes these areas prone to pluvial flooding. The occurrence of pluvial flooding depends on the existence of minimal areas for surface runoff generation and concentration. Detailed hydrologic and hydrodynamic simulations are computationally expensive and require intensive resources. This study compared and evaluated the performance of two simplified methods to identify urban pluvial flood-prone areas, namely the fill–spill–merge (FSM) method and the topographic wetness index (TWI) method and used the TELEMAC-2D hydrodynamic numerical model for benchmarking and validation. The FSM method uses common GIS operations to identify flood-prone depressions from a high-resolution digital elevation model (DEM). The TWI method employs the maximum likelihood method (MLE) to probabilistically calibrate a TWI threshold (τ) based on the inundation maps from a 2D hydrodynamic model for a given spatial window (W) within the urban area. We found that the FSM method clearly outperforms the TWI method both conceptually and effectively in terms of model performance.

The effects of multispecies Hohlraum walls on stimulated Brillouin scattering, Hohlraum dynamics, and beam propagation

Experiments and simulations have been conducted to investigate the efficacy of Ta2O5-lined Hohlraum walls at reducing stimulated Brillouin backscattering (SBS) as well as any subsequent effects on the Hohlraum dynamics and capsule implosions in indirect drive experiments at the National Ignition Facility. Using a 1.1 MJ 400 TW, 351 nm, shaped laser pulse, we measure a 5× reduction in SBS power in the peak of the pulse from the wall on the outer 50° cone beams. The SBS spectrum indicates a reduction in the high-Z spectral signature when using multispecies wall materials. Detailed hydrodynamic simulations were performed using different heat conduction models with flux limiters. Additional simulations were performed on the plasma maps using the 3D parallel paraxial code pF3D to compare backscatter powers between the pure Au and Ta2O5-lined Hohlraums. Further analysis, using hydrodynamically equivalent plasmas, shows that the SBS reduction is clearly a result of the added ion Landau damping caused by the oxygen ions and not from differences in plasma conditions. The experimental and simulation results also show an increase in the wall plasma expansion when using the Ta2O5 liner leading to a 70% more oblate implosion.

Structure-based framework for the design and risk assessment of hydraulic structures, with application to offline flood detention basins

The design of hydraulic structures for water control is based on the principle of accepting that structures might fail to fulfill their intended purpose as consequence of extreme, yet rare events producing damages. Traditionally, structures are sized to resist to a “design event”, i.e. a hyetograph or hydrograph associated to a fixed probability of occurrence. This implicitly assumes that the probability of structure failure equals that of the hydrological load, although unjustified under general conditions. Indeed, structure failure also depends on the failure mechanism – which is a characteristic of the specific structure and problem at hand – ruling the interaction between the hydrological load and the structure itself. To overcome the limitations of the hydrological design event approach, we provide here a general, consistent, “structure-based” risk framework, for design or risk assessment. The framework combines the multivariate statistical distribution of the hydrological process and the hydraulic response of the structure. Remarkably, it reduces the potential complexity of the problem to the statistical analysis of the univariate probability distribution of the damage, i.e. the consequence of structure failure. The approach is exemplified for an offline reservoir for flood mitigation, by adopting both a simplified routing model and a Monte Carlo procedure based on a detailed hydrodynamic simulation. Results demonstrate the potential of the framework, regardless of the accuracy of the modeling approach adopted for its implementation. Specifically, the framework allows disentangling the roles of the different design parameters involved, by providing clear indications for practitioners.

Galaxy Look-back Evolution Models: A Comparison with Magneticum Cosmological Simulations and Observations

Abstract We construct empirical models of star-forming galaxy evolution assuming that individual galaxies evolve along well-known scaling relations between stellar mass, gas mass, and star formation rate following a simple description of chemical evolution. We test these models by a comparison with observations and detailed Magneticum high-resolution hydrodynamic cosmological simulations. Galaxy star formation rates, stellar masses, gas masses, ages, interstellar medium, and stellar metallicities are compared. It is found that these simple look-back models capture many of the crucial aspects of galaxy evolution reasonably well. Their key assumption of a redshift-dependent power-law relationship between galaxy interstellar medium gas mass and stellar mass is in agreement with the outcome of the complex Magneticum simulations. Star formation rates decline toward lower redshift not because galaxies are running out of gas, but because the fraction of the cold interstellar medium gas, which is capable of producing stars, becomes significantly smaller. Gas accretion rates in both model approaches are of the same order of magnitude. Metallicity in the Magneticum simulations increases with the ratio of stellar mass to gas mass as predicted by the look-back models. The mass–metallicity relationships agree, and the star formation rate dependence of these relationships is also reproduced. We conclude that these simple models provide a powerful tool for constraining and interpreting more complex models based on cosmological simulations and for population synthesis studies analyzing the integrated spectra of stellar populations.

Equity concerns in transportation infrastructure protection against sea level rise

Waterfront communities are facing unprecedented challenges with global Sea Level Rise (SLR) becoming a reality. The households in these communities are likely to be inundated, and inundation of links in the urban transportation system will bring more interruptions to the communities. Some residents will not be able to access their workplaces or education if the transportation system is interrupted. Among these waterfront communities, many are considered disadvantaged communities that have concentrations of minority and low-income families. Residents in these communities are more vulnerable because they tend to be less able to relocate to other neighborhoods with lower risks of SLR.Many of the proposed protection strategies against SLR are at regional levels, and their goals are usually to achieve the greater good for the whole region. However, the distribution of the benefits or burdens may be unequal across different communities. The present paper utilizes detailed hydrodynamic simulation and activity-based transportation simulation to quantify the impact of potential protection strategies on different communities. The San Francisco Bay Area is the geographical region analyzed. Important insights from the analysis are obtained: the improvements of accessibility and mobility, resulting from protecting access to the Bay-crossing bridges, are often greater in disadvantaged communities than others. However, many of the disadvantaged communities located next to the entrances to the bridges are negatively impacted. Additional measures should be taken on relieving these communities to reduce transportation inequality.

On Passing of Interstellar Clouds Through a Galactic Spiral Arm

It is believed that the taxonomy of interstellar clouds in their vicinity can serve as an indicator of the features of the geometry and intensity of galactic shock waves. In this paper, the authors present the results of a detailed two-dimensional hydrodynamic simulation of the passage of a cloud through the spiral arm of a galaxy and provide a brief analysis of the effects arising from this motion. The model of interstellar gas used assumes adiabatic flow in the spiral arm. The external gravitational field of the galactic disk and spiral arm is taken into account. The transverse dimensions of the arm in the calculations are taken as follows: the half-width of the arm is 1 kpc along the plane of the disk and 0.6 kpc in the vertical direction. A fragment of the flow is considered near and inside the spiral arm, the effects of the curvature of the arm and the influence of the Coriolis forces are neglected. It is shown that clouds passing through the arm are strongly deformed and lose a significant part of the mass or are completely destroyed in the case of low-mass clouds. The boundary value of the cloud mass at which complete destruction occurs lies in the interval between 3 000 and 6 000 M.

Modeling Assessment of Tidal Energy Extraction in the Western Passage

Numerical models have been widely used for the resource characterization and assessment of tidal instream energy. The accurate assessment of tidal stream energy resources at a feasibility or project-design scale requires detailed hydrodynamic model simulations or high-quality field measurements. This study applied a three-dimensional finite-volume community ocean model (FVCOM) to simulate the tidal hydrodynamics in the Passamaquoddy–Cobscook Bay archipelago, with a focus on the Western Passage, to assist tidal energy resource assessment. IEC Technical specifications were considered in the model configurations and simulations. The model was calibrated and validated with field measurements. Energy fluxes and power densities along selected cross sections were calculated to evaluate the feasibility of the tidal energy development at several hotspots that feature strong currents. When taking both the high current speed and water depth into account, the model results showed that the Western Passage has great potential for the deployment of tidal energy farms. The maximum extractable power in the Western Passage was estimated using the Garrett and Cummins method. Different criteria and methods recommended by the IEC for resource characterization were evaluated and discussed using a sensitivity analysis of energy extraction for a hypothetical tidal turbine farm in the Western Passage.

Wind-reprocessed Transients

Abstract We consider the situation where the luminosity from a transient event is reprocessed by an optically thick wind. Potential applications are the tidal disruption of stars by black holes (BHs), engine-powered supernovae, and unique fast transients found by current and future wide-field surveys. We derive relations between the injected and observed luminosity for steady and time-dependent winds, and discuss how the temperature is set for scattering-dominated radiative transport. We apply this framework to specific examples of tidal disruption events and the formation of a BH by a massive star, as well as discuss other applications such as deriving observables from detailed hydrodynamic simulations. We conclude by exploring what is inferred about the mass-loss rate and underlying engine powering AT 2018cow if it is explained as a wind-reprocessed transient, demonstrating that its optical emission is consistent with reprocessing of the observed soft X-rays.

Fast quasi-periodic oscillations in the eclipsing polar VV Puppis from VLT and XMM-Newton observations

We present high time resolution optical photometric data of the polar VV Puppis obtained simultaneously in three filters (u′, HeII λ4686, r′) with the ULTRACAM camera mounted at the ESO-VLT telescope. An analysis of a long 50 ks XMM-Newton observation of the source, retrieved from the database, is also provided. Quasi-periodic oscillations (QPOs) are clearly detected in the optical during the source bright phase intervals when the accreting pole is visible, confirming the association of the QPOs with the basis of the accretion column. QPOs are detected in the three filters at a mean frequency of ∼0.7 Hz with a similar amplitude ∼1%. Mean orbitally-averaged power spectra during the bright phase show a rather broad excess with a quality factor Q = ν/Δν = 5−7 but smaller data segments commonly show a much higher coherency with Q up to 30. The X-ray Multi-mirror Mission XMM (0.5–10 keV) observation provides the first accurate estimation of the hard X-ray component with a high kT ∼ 40 keV temperature and confirms the high extreme ultraviolet (EUV)-soft/hard ratio in the range of 4−15 for VV Pup. The detailed X-ray orbital light curve displays a short Δϕ ≃ 0.05 ingress into self-eclipse of the active pole, indicative of an accretion shock height of ∼75 km. No significant X-ray QPOs are detected with an amplitude upper limit of ∼30% in the range 0.1–5 Hz. Detailed hydrodynamical numerical simulations of the post-shock accretion region with parameters consistent with VV Pup demonstrate that the expected frequencies from radiative instability are identical for X-rays and optical regime at values ν ∼ 40–70 Hz, more than one order magnitude higher than observed. This confirms previous statements suggesting that present instability models are unable to explain the full QPO characteristics within the parameters commonly known for polars.

Spatial distribution of extreme wind speeds over Sakhalin Island based on observations and high-resolution modelling data

An analysis of extreme wind speeds over Sakhalin region shows that a set of wind speed extremes obtained from observations is a mixture of two different subsets, each of them neatly described by a Weibull distribution. The empirical tail of the pdf diverges from a linearized Weibull model, indicating that another model could fit the most extreme wind speed data better. Each of these subsets is characterized by parameters k and A, regarded as coefficient and free terms of the linear Weibull model, these samples are labelled BSs and Ds. The Ds are responsible for the strongest extremes. Mesoscale modelling is used to investigate a possibility of the models to reproduce these statistical features. A detailed hydrodynamic simulation of major meteorological parameters (1985 – 2014) has been performed for the Sea of Okhotsk and Sakhalin Island with horizontal resolutions of ~13.2, ~6.6, and ~2.2 km by using a regional climate model, COSMO-CLM. This dataset is utilized for an investigation of the statistical structure of extreme wind speeds. First, it is shown that a model with a detailed spatial resolution is able to reproduce the statistical structure in general, and a special mechanism is responsible for the generation of the largest of wind extremes. However, a model with a resolution of ~13,2 km could not reproduce some essential parts of the wind speed maximum’ statistical properties, underestimating the parameters k and A of Ds Weibull distribution significantly. This gap could be covered by using a higher resolution, as well as by areal estimation techniques and many others.

Ejecta velocities in twice-shocked liquid metals under extreme conditions: A hydrodynamic approach

We apply a hydrodynamic approach to analyze ejecta emanating from doubly shocked liquid metals. In particular, we are interested in characterizing ejecta velocities in such situations by treating the problem as a limiting case of the Richtmyer–Meshkov instability. We find existing models for ejecta velocities do not adequately capture all the relevant physics, including compressibility, nonlinearities, and nonstandard shapes. We propose an empirical model that is capable of describing ejecta behavior across the entire parameter range of interest. We then suggest a protocol to apply this model when the donor material is shocked twice in rapid succession. Finally, the model and the suggested approach are validated using detailed continuum hydrodynamic simulations. The results provide a baseline understanding of the hydrodynamic aspects of ejecta, which can then be used to interpret experimental data from target experiments.

Application of intense ion beams to planetary physics research at the Facility for Antiprotons and Ion Research facility

This paper presents detailed 2D hydrodynamic simulations of implosion of a multi‐layered cylindrical target that is driven by an intense uranium beam. The target is comprised of a thick, high‐Z, high‐ρ cylindrical shell that encloses a sample material (Fe in the present case). Two options have been used for the focal spot geometry: an annular form and a circular form. The purpose of this work is to show that an intense heavy‐ion beam can induce the extreme physical conditions in the sample material similar to those that exist in the planetary cores. In this study, we use parameters of the beam that will be generated at the Facility for Antiprotons and Ion Research (FAIR), Darmstadt, in a few years' time. Production of these high‐energy‐density (HED) samples will allow us to study planetary physics in the laboratory. It is to be noted that planetary physics research is an important part of the FAIR HED physics program. A dedicated experiment named LAboratory PLAnetary Sciences (LAPLAS) has been proposed for this purpose. These simulations show that in such experiments an Fe sample can be imploded to the Earth's core conditions and to those in more massive rocky planets called Super‐Earths. Similarly, implosion of hydrogen and water samples will generate the core conditions of solar and extrasolar hydrogen‐rich gas giants and water‐rich icy planets, respectively. The LAPLAS experiments will thus provide very valuable information on the equation of state and transport properties of matter under extreme physical conditions, which will help scientists understand the structure and evolution of the planets in our solar system as well as of the extrasolar planets.