scholarly journals An elastic model of Phobos’ libration

2020 ◽  
Vol 636 ◽  
pp. A27
Author(s):  
Yongzhang Yang ◽  
Jianguo Yan ◽  
Xi Guo ◽  
Qingbao He ◽  
Jean-Pierre Barriot
Keyword(s):  
Numerical Model ◽  
Gravity Field ◽  
Numerical Integration ◽  
Elastic Properties ◽  
Rotational Motion ◽  
Space Mission ◽  
Elastic Model ◽  
Shape Model ◽  
Future Space ◽  
Least Squares Fit

Context. Study the rotation of a celestial body is an efficient way to infer its interior structure, and then may give information of its origin and evolution. In this study, based on the latest shape model of Phobos from Mars Express (MEX) mission, the polyhedron approximation approach was used to simulate the gravity field of Phobos. Then, the gravity information was combined with the newest geophysical parameters such as GM and k2 to construct the numerical model of Phobos’ rotation. And with an appropriate angles transformation, we got the librational series respect to Martian mean equator of date. Aims. The purpose of this paper is to develop a numerical model of Phobos’ rotational motion that includes the elastic properties of Phobos. The frequencies analysis of the librational angles calculated from the numerical integration results emphasize the relationship between geophysical properties and dynamics of Phobos. This work will also be useful for a future space mission dedicated to Phobos. Methods. Based on the latest shape model of Phobos from MEX mission, we firstly modeled the gravity field of Phobos, then the gravity coefficients were combined with some of the newest geophysical parameters to simulate the rotational motion of Phobos. To investigate how the elastic properties of Phobos affect its librational motion, we adopted various k2 into our numerical integration. Then the analysis was performed by iterating a frequency analysis and linear least-squares fit of Phobos’ physical librations. From this analysis, we identified the influence of k2 on the largest librational amplitude and its phase. Results. We showed the first ten periods of the librational angles and found that they agree well with the previous numerical results which Phobos was treated as a perfectly rigid body. We also found that the maximum amplitudes of the three parameters of libration are also close to the results from a rigid model, which is mainly due to the inclination of Phobos and moments of inertia. The other amplitudes are slightly different, since the physics contained in our model is different to that of a previous study, specifically, the different low-degree gravity coefficients and ephemeris. The libration in longitude τ has the same quadratic term with previous numerical study, which is consistent with the secular acceleration of Phobos falling onto Mars. We investigated the influence of the tidal Love number k2 on Phobos’ rotation and found a detectable amplitude changes (0.0005°) expected in the future space mission on τ, which provided a potential possibility to constrain the k2 of Phobos by observing its rotation. We also studied the influence of Phobos’ orbit accuracy on its libration and suggested a simultaneous integration of orbit and rotation in future work.

scholarly journals Geometric correction for thermographic images of asteroid 162173 Ryugu by TIR (thermal infrared imager) onboard Hayabusa2

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Takehiko Arai ◽  
Tatsuaki Okada ◽  
Satoshi Tanaka ◽  
Tetsuya Fukuhara ◽  
Hirohide Demura ◽  
...  
Keyword(s):  
Surface Roughness ◽  
High Surface ◽  
Thermal Inertia ◽  
Thermal Infrared ◽  
Shape Model ◽  
Infrared Imager ◽  
Least Squares Fit ◽  
Temperature Maps ◽  
Pixel Scale ◽  
Thermal Infrared Imager

AbstractThe thermal infrared imager (TIR) onboard the Hayabusa2 spacecraft performed thermographic observations of the asteroid 162173 Ryugu (1999 JU$$_3$$ 3 ) from June 2018 to November 2019. Our previous reports revealed that the surface of Ryugu was globally filled with porous materials and had high surface roughness. These results were derived from making the observed temperature maps of TIR using a projection method onto the shape model of Ryugu as geometric corrections. The pointing directions of TIR were calculated using an interpolation of data from the SPICE kernels (NASA/NAIF) during the periods when the optical navigation camera (ONC) and the light detection and ranging (LIDAR) observations were performed. However, the mapping accuracy of the observed TIR images was degraded when the ONC and LIDAR were not performed with TIR. Also, the orbital and attitudinal fluctuations of Hayabusa2 increased the error of the temperature maps. In this paper, to solve the temperature image mapping problems, we improved the correction method by fitting all of the observed TIR images with the surface coordinate addressed on the high-definition shape model of Ryugu (SFM 800k v20180804). This correction adjusted the pointing direction of TIR by rotating the TIR frame relative to the Hayabusa2 frame using a least squares fit. As a result, the temperature maps spatially spreading areas were converged within high-resolved $$0.5^\circ$$ 0 . 5 ∘ by $$0.5^\circ$$ 0 . 5 ∘ maps. The estimated thermal inertia, for instance, was approximately 300$$\sim$$ ∼ 350 Jm$$^{-2}$$ - 2 s$$^{-0.5}$$ - 0.5 K$$^{-1}$$ - 1 at the hot area of the Ejima Saxum. This estimation was succeeded in case that the surface topographic features were larger than the pixel scale of TIR. However, the thermal inertia estimation of smooth terrains, such as the Urashima crater, was difficult because of surface roughness effects, where roughness was probably much smaller than the pixel scale of TIR.

A numerical model of anisotropic elastic properties of osteons

1988 ◽  
Vol 21 (10) ◽  
pp. 879 ◽  
Author(s):  
J.M. Crolet ◽  
B. Aoubiza ◽  
A. Meunier
Keyword(s):  
Numerical Model ◽  
Elastic Properties ◽  
Anisotropic Elastic

scholarly journals Numerical Simulations of GFRP-Reinforced Columns Having Polypropylene and Polyvinyl Alcohol Fibers

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Liaqat Ali ◽  
Ahsan Nawaz ◽  
Yong Bai ◽  
Ali Raza ◽  
Muhammad Kashif Anwar ◽  
...  
Keyword(s):  
Reinforced Concrete ◽  
Numerical Model ◽  
Polyvinyl Alcohol ◽  
Circular Cross Section ◽  
Fiber Reinforced Concrete ◽  
Elastic Model ◽  
Fiber Reinforced ◽  
Hybrid Fibers ◽  
Element Analysis ◽  
Gfrp Bars

The present investigation aims to propose a numerical model for assessing the complex damaging response of glass fiber-reinforced polymer- (GFRP-) reinforced concrete columns having hybrid fibers and confined with GFRP spirals (GFHF columns) under concentric and eccentric compression. Fiber-reinforced concrete (FRC) consists of polyvinyl alcohol fibers (PVA) and polypropylene fibers (PF). A total of six GFHF circular columns were constructed having a circular cross section of 250 mm and a height of 1200 mm. A commercial package ABAQUS was used for the finite element analysis (FEA) of the GFHF columns by using a modified concrete damage plastic (CDP) model for hybrid fiber-reinforced concrete (HFRC). The damaging response of GFRP bars was defined using a linear elastic model. The results depicted that the failure of GFHF columns occurred either in the upper or in the lower half portion with the rupture of GFRP longitudinal bars and GFRP spirals. The decrease in the pitch of GFRP spirals led to an improvement in the axial strength (AS) of GFHF columns. The eccentric loading caused a significant reduction in the AS of columns. The comparative study solidly substantiates the validity and applicability of the newly developed FEA models for capturing the AS of GFHF columns by considering the axial involvement of longitudinal GFRP bars and the confinement effect of transverse GFRP spirals. So, the suggested numerical model having a complex system of equations for HFRC can be used for the accurate analysis of HFRC members.

scholarly journals Acoustic in-ice positioning in the Enceladus Explorer project

2014 ◽  
Vol 55 (68) ◽  
pp. 253-259 ◽  
Author(s):  
Dmitry Eliseev ◽  
Dirk Heinen ◽  
Klaus Helbing ◽  
Ruth Hoffmann ◽  
Uwe Naumann ◽  
...  
Keyword(s):  
Space Mission ◽  
Positioning System ◽  
Test Scenario ◽  
Full System ◽  
Ice Surface ◽  
Curved Trajectories ◽  
Future Space ◽  
Glacier Ice ◽  
Taylor Glacier ◽  
Acoustic Positioning

AbstractThe Enceladus Explorer project is a preparatory study for a future space mission to Saturn’s moon, Enceladus. Its ultimate goal is to probe liquid-water pockets below the ice surface of Enceladus for signatures of life. A probe could be based on the IceMole concept, which melts curved trajectories through the ice. In the Enceladus Explorer project, a specialized IceMole probe for a terrestrial test scenario is in development. The goal of this exploratory study is to probe water from a liquid crevasse close to Blood Falls at Taylor Glacier, Antarctica. To navigate such a probe it is essential to be able to determine its position and monitor its trajectory. Part of the navigation system is the in-ice acoustic positioning system. For this, the head of the IceMole is equipped with acoustic sensors, which receive signals from synchronized acoustic emitters situated at the ice surface. Based on the measured propagation times, the speed of sound in ice and the positions of the emitters at the surface, the position of the IceMole can be determined by trilateration techniques. Here we present the developed acoustic positioning system, which is designed to track the in-ice melting probe up to distances of 100 m in glacier ice. Results from full-system tests in water and a first field test on Morteratschgletscher, Switzerland, are discussed.

scholarly journals NUMERICAL MODEL FOR AIR POLLUTION SIMULATION FROM ROAD TRANSPORT

2021 ◽  
Vol 1 (5(69)) ◽  
pp. 58-63
Author(s):  
M. Biliaiev ◽  
V. Biliaieva ◽  
O. Berlov ◽  
V. Kozachyna
Keyword(s):  
Air Pollution ◽  
Numerical Model ◽  
Finite Difference ◽  
Numerical Integration ◽  
Complex Terrain ◽  
Computer Code ◽  
Road Transport ◽  
Finite Difference Schemes ◽  
Air Pollution Modelling ◽  
Pollutant Transfer

The problem of air pollution modelling near road which is situated in complex terrain is under consideration. To simulate wind flow pattern in case of complex terrain Navier-Stokes’s equations were used. NavierStokes’s equations were written using Helmholtz variables. Numerical finite difference schemes of splitting were used for numerical integration of Navier-Stokes’s equations. Equation of connective-diffusive pollutant transfer was used to simulate air pollution. Finite difference scheme of splitting was used for numerical integration of convectivediffusive equation of pollutant transfer. Computer code was developed on the basis of created numerical model. The results of a numerical experiment are presented.

scholarly journals Heterogeneous mass distribution of the rubble-pile asteroid (101955) Bennu

2020 ◽  
Vol 6 (41) ◽  
pp. eabc3350 ◽  
Author(s):  
D. J. Scheeres ◽  
A. S. French ◽  
P. Tricarico ◽  
S. R. Chesley ◽  
Y. Takahashi ◽  
...  
Keyword(s):  
Gravity Field ◽  
Mass Distribution ◽  
Small Body ◽  
Parent Body ◽  
Constant Density ◽  
Internal Mass ◽  
Shape Model ◽  
Rapid Rotation ◽  
Insight Into ◽  
Rubble Pile

The gravity field of a small body provides insight into its internal mass distribution. We used two approaches to measure the gravity field of the rubble-pile asteroid (101955) Bennu: (i) tracking and modeling the spacecraft in orbit about the asteroid and (ii) tracking and modeling pebble-sized particles naturally ejected from Bennu’s surface into sustained orbits. These approaches yield statistically consistent results up to degree and order 3, with the particle-based field being statistically significant up to degree and order 9. Comparisons with a constant-density shape model show that Bennu has a heterogeneous mass distribution. These deviations can be modeled with lower densities at Bennu’s equatorial bulge and center. The lower-density equator is consistent with recent migration and redistribution of material. The lower-density center is consistent with a past period of rapid rotation, either from a previous Yarkovsky-O’Keefe-Radzievskii-Paddack cycle or arising during Bennu’s accretion following the disruption of its parent body.

Numerical experiment applicable to planet formation

1984 ◽  
Vol 75 ◽  
pp. 675-676
Author(s):  
Anny Cazenave
Keyword(s):  
Numerical Model ◽  
Numerical Experiment ◽  
Numerical Integration ◽  
Body Problem ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
The Sun ◽  
Gravitational Perturbations ◽  
N Body Problem ◽  
Fragmentation Processes

A three-dimensional numerical model has been developed with the goal of studying limited dynamical problems relevant to the latest stage of planet growth in the accretion theory. A small number of large protoplanets (~ moon-size) of different masses, moving around the Sun, are considered. The dynamical evolution and growth of the population is studied under mutual gravitational perturbations, accretion and collisional fragmentation processes. Gravitational encounters are treated exactly by numerical integration of the N-body problem. Outcomes of collisional fragmentation are modeled according to the results of Greenberg et al. (1978).

The NASA Goddard CO2 Sounder Lidar: 2017 Airborne Campaign as a Demonstration toward a Future Space Mission

2021 ◽  
Author(s):  
Jianping Mao ◽  
James B. Abshire ◽  
S. Randy Kawa ◽  
Haris Riris ◽  
Xiaoli Sun ◽  
...  
Keyword(s):  
Space Mission ◽  
Future Space

Dynamic Response of Hammer Impacting Pile under Gravity Field

2014 ◽  
Vol 610 ◽  
pp. 65-69
Author(s):  
Dong Hua Chen ◽  
Li Quan Wang
Keyword(s):  
Numerical Model ◽  
Dynamic Response ◽  
Gravity Field ◽  
Impact Energy ◽  
Model Simulation ◽  
Gravitational Potential Energy ◽  
Impact System ◽  
Pile Cap ◽  
Hammer Impact ◽  
The Impact

Pile hammer impact system is composed of hammer, pile cap and pile. Gravity field will produce uneven stress in the pile which is placed on a fixed rigid plane, and gravitational potential energy will increase the impact energy which is inputted to the pile during the impact process. These will influence dynamic response of collision process between pile hammer and pile. In this paper, a gravity field factor was added in the Simth difference equations which are based on One-dimensional Wave Equation. The numerical model of pile hammer impact system was established. A program was written to implement the numerical model. Simulation results indicated that the duration of collision, the peak and stable value of impact force and the effective impact energy would be affected by the gravity field.

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