A new general contact model is proposed for preventing inter‐leaflet penetration of bio‐prosthetic heart valves (BHV) at the end of the systole, which has the advantage of applying kinematic constraints directly and creating smooth free edges. At the end of each time step, the impenetrability constraints and momentum exchange between the impacting bodies are applied separately based on the coefficient of restitution. The contact method is implemented in a rotation‐free, large deformation, and thin shell finite‐element (FE) framework based on loop's subdivision surfaces. A nonlinear, anisotropic material model for a BHV is employed which uses Fung‐elastic constitutive laws for in‐plane and bending responses, respectively. The contact model is verified and validated against several benchmark problems. For a BHV‐specific validation, the computed strains on different regions of a BHV under constant pressure are compared with experimentally measured data. Finally, dynamic simulations of BHV under physiological pressure waveform are performed for symmetrical and asymmetrical fiber orientations incorporating the new contact model and compared with the penalty contact method. The proposed contact model provides the coaptation area of a functioning BHV during the closing phase for both of the fiber orientations. Our results show that fiber orientation affects the dynamic of leaflets during the opening and closing phases. A swirling motion for the BHV with asymmetrical fiber orientation is observed, similar to experimental data. To include the fluid effects, fluid–structure interaction (FSI) simulation of the BHV is performed and compared to the dynamic results.
In this paper, we present an open-source software (Simulator of Asteroid Malformation Under Stress,
- NSF-PAR ID:
- 10411013
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 4
- Issue:
- 5
- ISSN:
- 2632-3338
- Format(s):
- Medium: X Size: Article No. 79
- Size(s):
- ["Article No. 79"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract We present an approach for the inclusion of nonspherical constituents in high-resolution
N -body discrete element method (DEM) simulations. We use aggregates composed of bonded spheres to model nonspherical components. Though the method may be applied more generally, we detail our implementation in the existingN -body codepkdgrav . It has long been acknowledged that nonspherical grains confer additional shear strength and resistance to flow when compared with spheres. As a result, we expect that rubble-pile asteroids will also exhibit these properties and may behave differently than comparable rubble piles composed of idealized spheres. Since spherical particles avoid some significant technical challenges, most DEM gravity codes have used only spherical particles or have been confined to relatively low resolutions. We also discuss the work that has gone into improving performance with nonspherical grains, building onpkdgrav 's existing leading-edge computational efficiency among DEM gravity codes. This allows for the addition of nonspherical shapes while maintaining the efficiencies afforded bypkdgrav 's tree implementation and parallelization. As a test, we simulated the gravitational collapse of 25,000 nonspherical bodies in parallel. In this case, the efficiency improvements allowed for an increase in speed by nearly a factor of 3 when compared with the naive implementation. Without these enhancements, large runs with nonspherical components would remain prohibitively expensive. Finally, we present the results of several small-scale tests: spin-up due to the YORP effect, tidal encounters, and the Brazil nut effect. In all cases, we find that the inclusion of nonspherical constituents has a measurable impact on simulation outcomes. -
more » « less
Temporal variations of surface masses, such as the hydrosphere and atmosphere of the Earth, load the surfaces of planetary bodies causing temporal variations in deformation. Surface shear forces and gravitational fields also drive ongoing planetary deformation. Characterizing the spatiotemporal patterns of planetary deformation can constrain allowable models for the interior structure of a planetary body as well as for the distribution of surface and body forces. Pertinent applications include hydrology, glaciology, geodynamics, atmospheric science, and climatology. To address the diversity of emerging applications, we introduce a software suite called
LoadDef that provides a collection of modular functions for modeling planetary deformation within a self‐consistent,Python ‐based computational framework. Key features ofLoadDef include computation of real‐valued potential, load, and shear Love numbers for self‐gravitating and spherically symmetric planetary models; computation of Love‐number partial derivatives with respect to planetary density and elastic structure; computation of displacement, gravity, tilt, and strain load Green's functions; and computation of three‐component surface displacements induced by surface mass loading. At a most basic level, only a planetary‐structure model and a mass‐load model must be supplied as input toLoadDef to utilize all the main features of the software. The end‐to‐end forward‐modeling capabilities for mass‐loading applications lay the foundation for sensitivity studies and geodetic tomography.LoadDef results have been validated with Global Navigation Satellite System observations and verified against independent software and published results. As a case study, we useLoadDef to predict the solid Earth's elastic response to ocean tidal loading across the western United States. -
more » « less
Abstract About ten percent of Sun-like (1–2
M ⊙) stars will engulf a 1–10M Jplanet as they expand during the red giant branch (RGB) or asymptotic giant branch (AGB) phase of their evolution. Once engulfed, these planets experience a strong drag force in the star’s convective envelope and spiral inward, depositing energy and angular momentum. For these mass ratios, the inspiral takes ∼10–102yr (∼102–103orbits); the planet undergoes tidal disruption at a radius of ∼1R ⊙. We use the Modules for Experiments in Stellar Astrophysics (MESA ) software instrument to track the stellar response to the energy deposition while simultaneously evolving the planetary orbit. For RGB stars, as well as AGB stars withM p≲ 5M Jplanets, the star responds quasi-statically but still brightens measurably on a timescale of years. In addition, asteroseismic indicators, such as the frequency spacing or rotational splitting, differ before and after engulfment. For AGB stars, engulfment of anM p≳ 5M Jplanet drives supersonic expansion of the envelope, causing a bright, red, dusty eruption similar to a “luminous red nova.” Based on the peak luminosity, color, duration, and expected rate of these events, we suggest that engulfment events on the AGB could be a significant fraction of low-luminosity red novae in the Galaxy. We do not find conditions where the envelope is ejected prior to the planet’s tidal disruption, complicating the interpretation of short-period giant planets orbiting white dwarfs as survivors of common envelope evolution. -
Aims. The modelling of spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly formed accretion disks are mostly quasi-circular. In this work we study the transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow. Methods. We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations and spectral line content and evolution. We identify transient, double-peaked Bowen (N III ), He I , He II, and H α emission lines. We model medium-resolution optical spectroscopy of the He II (after careful de-blending of the N III contribution) and H α lines during the rise, peak, and early decline of the light curve using relativistic, elliptical accretion disk models. Results. We find that the spectral evolution before the peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around the peak, the envelope reaches its maximum extent (approximately 10 15 cm, or ∼3000–6000 gravitational radii for an inferred black hole mass of 5−10 × 10 5 M ⊙ ) and becomes optically thin. The H α and He II emission lines at and after the peak can be reproduced with a highly inclined ( i = 85 ± 5 degrees), highly elliptical ( e = 0.97 ± 0.01), and relatively compact ( R in = several 100 R g and R out = several 1000 R g ) accretion disk. Conclusions. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs, where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary supermassive black hole hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination). We constrain the disk alignment timescale to > 15 days in AT2020zso, which rules out high black hole spin values ( a < 0.8) for M BH ∼ 10 6 M ⊙ and disk viscosity α ≳ 0.1.more » « less
