scholarly journals Atmospheric tides and their consequences on the rotational dynamics of terrestrial planets

2019 ◽  
Vol 82 ◽  
pp. 81-90
Author(s):  
P. Auclair-Desrotour ◽  
J. Laskar ◽  
S. Mathis
Keyword(s):  
The Body ◽  
Rotational Dynamics ◽  
Atmospheric Tides ◽  
Terrestrial Planets ◽  
Physical Parameters ◽  
Strong Impact ◽  
Tidal Torque ◽  
Analytic Expressions ◽  
Dynamical Coupling ◽  
Neutral Stratification

Atmospheric tides can have a strong impact on the rotational dynamics of planets. They are of most importance for terrestrial planets located in the habitable zone of their host star, where their competition with solid tides is likely to drive the body towards non-synchronized rotation states of equilibrium, as observed in the case of Venus. Contrary to other planetary layers, the atmosphere is sensitive to both gravitational and thermal forcings, through a complex dynamical coupling involving the effects of Coriolis acceleration and characteristics of the atmospheric structure. These key physics are usually not taken into account in modelings used to compute the evolution of planetary systems, where tides are described with parametrised prescriptions. In this work, we present a new ab initio modeling of atmospheric tides adapting the theory of the Earth’s atmospheric tides (Chapman & Lindzen 1970) to other terrestrial planets. We derive analytic expressions of the tidal torque, as a function of the tidal frequency and parameters characterizing the internal structure (e.g. the Brunt-Väisälä frequency, the radiative frequency, the pressure heigh scale). We show that stratification plays a key role, the tidal torque being strong in the case of convective atmospheres (i.e. with a neutral stratification) and weak in case of atmosphere convectively stable. In a second step, the model is used to determine the non-synchronized rotation states of equilibrium of Venus-like planets as functions of the physical parameters of the system. These results are detailed in Auclair-Desrotour et al. (2016a) and Auclair-Desrotour et al. (2016b).

scholarly journals The rotation of planets hosting atmospheric tides: from Venus to habitable super-Earths

2017 ◽  
Vol 603 ◽  
pp. A108 ◽  
Author(s):  
P. Auclair-Desrotour ◽  
J. Laskar ◽  
S. Mathis ◽  
A. C. M. Correia
Keyword(s):  
Equilibrium States ◽  
The Body ◽  
Rotational Dynamics ◽  
Atmospheric Tides ◽  
Strong Impact ◽  
Habitable Zone ◽  
Low Mass Stars ◽  
Equilibrium Configurations ◽  
Low Mass ◽  
The Stability

The competition between the torques induced by solid and thermal tides drives the rotational dynamics of Venus-like planets and super-Earths orbiting in the habitable zone of low-mass stars. The resulting torque determines the possible equilibrium states of the planet’s spin. Here we have computed an analytic expression for the total tidal torque exerted on a Venus-like planet. This expression is used to characterize the equilibrium rotation of the body. Close to the star, the solid tide dominates. Far from it, the thermal tide drives the rotational dynamics of the planet. The transition regime corresponds to the habitable zone, where prograde and retrograde equilibrium states appear. We demonstrate the strong impact of the atmospheric properties and of the rheology of the solid part on the rotational dynamics of Venus-like planets, highlighting the key role played by dissipative mechanisms in the stability of equilibrium configurations.

scholarly journals Generic frequency dependence for the atmospheric tidal torque of terrestrial planets

2019 ◽  
Vol 624 ◽  
pp. A17 ◽  
Author(s):  
P. Auclair-Desrotour ◽  
J. Leconte ◽  
C. Mergny
Keyword(s):  
Surface Pressure ◽  
General Circulation ◽  
Scaling Laws ◽  
Circulation Model ◽  
Resonant Peak ◽  
Atmospheric Tides ◽  
Terrestrial Planets ◽  
Strong Impact ◽  
Tidal Torque ◽  
Orbital Radius

Context. Thermal atmospheric tides have a strong impact on the rotation of terrestrial planets. They can lock these planets into an asynchronous rotation state of equilibrium. Aims. We aim to characterize the dependence of the tidal torque resulting from the semidiurnal thermal tide on the tidal frequency, the planet orbital radius, and the atmospheric surface pressure. Methods. The tidal torque was computed from full 3D simulations of the atmospheric climate and mean flows using a generic version of the LMDZ general circulation model in the case of a nitrogen-dominated atmosphere. Numerical results are discussed with the help of an updated linear analytical framework. Power scaling laws governing the evolution of the torque with the planet orbital radius and surface pressure are derived. Results. The tidal torque exhibits (i) a thermal peak in the vicinity of synchronization, (ii) a resonant peak associated with the excitation of the Lamb mode in the high frequency range, and (iii) well defined frequency slopes outside these resonances. These features are well explained by our linear theory. Whatever the star–planet distance and surface pressure, the torque frequency spectrum – when rescaled with the relevant power laws – always presents the same behaviour. This allows us to provide a single and easily usable empirical formula describing the atmospheric tidal torque over the whole parameter space. With such a formula, the effect of the atmospheric tidal torque can be implemented in evolutionary models of the rotational dynamics of a planet in a computationally efficient, and yet relatively accurate way.

scholarly journals A Computational Study on the Role of Parameters for Identification of Thyroid Nodules by Infrared Images (and Comparison with Real Data)

Sensors ◽  
2021 ◽  
Vol 21 (13) ◽  
pp. 4459
Author(s):  
José R. González ◽  
Charbel Damião ◽  
Maira Moran ◽  
Cristina A. Pantaleão ◽  
Rubens A. Cruz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thyroid Nodules ◽  
Numerical Study ◽  
Computational Study ◽  
Internal Heat ◽  
Heat Transfer Process ◽  
The Body ◽  
Physical Parameters ◽  
Infrared Sensors ◽  
Wide Range

According to experts and medical literature, healthy thyroids and thyroids containing benign nodules tend to be less inflamed and less active than those with malignant nodules. It seems to be a consensus that malignant nodules have more blood veins and more blood circulation. This may be related to the maintenance of the nodule’s heat at a higher level compared with neighboring tissues. If the internal heat modifies the skin radiation, then it could be detected by infrared sensors. The goal of this work is the investigation of the factors that allow this detection, and the possible relation with any pattern referent to nodule malignancy. We aim to consider a wide range of factors, so a great number of numerical simulations of the heat transfer in the region under analysis, based on the Finite Element method, are performed to study the influence of each nodule and patient characteristics on the infrared sensor acquisition. To do so, the protocol for infrared thyroid examination used in our university’s hospital is simulated in the numerical study. This protocol presents two phases. In the first one, the body under observation is in steady state. In the second one, it is submitted to thermal stress (transient state). Both are simulated in order to verify if it is possible (by infrared sensors) to identify different behavior referent to malignant nodules. Moreover, when the simulation indicates possible important aspects, patients with and without similar characteristics are examined to confirm such influences. The results show that the tissues between skin and thyroid, as well as the nodule size, have an influence on superficial temperatures. Other thermal parameters of thyroid nodules show little influence on surface infrared emissions, for instance, those related to the vascularization of the nodule. All details of the physical parameters used in the simulations, characteristics of the real nodules and thermal examinations are publicly available, allowing these simulations to be compared with other types of heat transfer solutions and infrared examination protocols. Among the main contributions of this work, we highlight the simulation of the possible range of parameters, and definition of the simulation approach for mapping the used infrared protocol, promoting the investigation of a possible relation between the heat transfer process and the data obtained by infrared acquisitions.

THE EFFECT OF 10-WEEK BODYWEIGHT TRAINING ON BODY COMPOSITION AND PHYSICAL FITNESS IN YOUNG MALES

2018 ◽  
Vol 28 (82) ◽  
pp. 35-43
Author(s):  
Krzysztof Lipecki
Keyword(s):  
Body Composition ◽  
Physical Fitness ◽  
Body Height ◽  
Dynamic Strength ◽  
Shoulder Girdle ◽  
The Body ◽  
Trunk Muscles ◽  
Physical Parameters ◽  
Young Males ◽  
Balanced Diet

Aim. The aim of the study was to evaluate changes on body compositions and physical fitness in young males performing 10-week bodyweight training. Material and Methods. The study examined body height and composition (body mass, fat percent and body water) in 15 healthy male adults (23.4 ± 3.3 years, 180.3 ± 6.8 cm, 75.7 ± 7.6 kg). The physical parameters included: running speed, agility, explosive power and strength endurance, flexibility and cardiorespiratory capacity. The examinations were conducted before and after 10-week bodyweight training. Results. Results indicated no significant changes in body composition in the men examined. Improvements were observed in measured parameters of physical fitness, agility (4.1%, p<0.01), dynamic strength of the shoulder girdle muscles, the back and the abdomen (by 12.1%, p<0.01), static strength of the right hand (6.7%, p<0.05), strength endurance of the upper limbs (by 30.1%, p<0.01), strength endurance of the body trunk muscles (7.0%, p<0.01), flexibility (20.1%, p<0.05) and cardiorespiratory capacity (6.1%, p<0.05). Conclusion. Bodyweight training without a properly balanced diet has an insignificant effect on changes in body composition of young men. The training concept based on performing bodyweight exercises leads to the significant improvements in muscle strength and endurance, flexibility, agility and cardiovascular endurance. The bodyweight training by Lauren and Clark, due to the high frequency and intensity, is recommended for young people with a high physical fitness level and perseverance.

Physical parameters of neutrality in the work of an osteopathic physician

2021 ◽  
pp. 105-120
Author(s):  
A. A. Gurichev
Keyword(s):  
Mechanical Energy ◽  
The Body ◽  
Spatial Position ◽  
Physical Parameters ◽  
Labor Organization ◽  
Physical Fatigue ◽  
Support Points

An osteopathic practitioner often meets the problem of physical fatigue, which is caused by a forced posture, excessive tension of the muscles of the trunk and arms, irrational biomechanical patterns of posture and movements, lack of support points, or switching points of mechanical energy of movement (fulcrum). These factors lead together to fatigue, which is felt as weariness and prevents the development of a pathophysiological state of overwork. Prevention of overwork by an osteopathic doctor can consist of a number of measures of labor organization and ergonomics, one of which is building a state of physical neutrality — a spatial position of the body that allows working with the patient as efficiently as possible and minimizing fatigue.

scholarly journals The Dynamical Behavior of a Rigid Body Relative Equilibrium Position

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
T. S. Amer
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Numerical Solutions ◽  
Equations Of Motion ◽  
Relative Equilibrium ◽  
Dynamical Behavior ◽  
Vertical Plane ◽  
The Body ◽  
Physical Parameters ◽  
Pendulum Model

In this paper, we will focus on the dynamical behavior of a rigid body suspended on an elastic spring as a pendulum model with three degrees of freedom. It is assumed that the body moves in a rotating vertical plane uniformly with an arbitrary angular velocity. The relative periodic motions of this model are considered. The governing equations of motion are obtained using Lagrange’s equations and represent a nonlinear system of second-order differential equations that can be solved in terms of generalized coordinates. The numerical solutions are investigated using the fourth-order Runge-Kutta algorithms through Matlab packages. These solutions are represented graphically in order to describe and discuss the behavior of the body at any instant for different values of the physical parameters of the body. The obtained results have been discussed and compared with some previous published works. Some concluding remarks have been presented at the end of this work. The importance of this work is due to its numerous applications in life such as the vibrations that occur in buildings and structures.

scholarly journals Body-force modeling for aerodynamic analysis of air intake – fan interactions

2016 ◽  
Vol 26 (7) ◽  
pp. 2048-2065 ◽  
Author(s):  
William Thollet ◽  
Guillaume Dufour ◽  
Xavier Carbonneau ◽  
Florian Blanc
Keyword(s):  
Body Force ◽  
Stokes Equations ◽  
The Body ◽  
Test Case ◽  
Force Model ◽  
Strong Impact ◽  
Analytic Model ◽  
Source Terms ◽  
Content Type ◽  
Air Intake

Purpose The purpose of this paper is to explore a methodology that allows to represent turbomachinery rotating parts by replacing the blades with a body force field. The objective is to capture interactions between a fan and an air intake at reduced cost, as compared to full annulus unsteady computations. Design/methodology/approach The blade effects on the flow are taken into account by adding source terms to the Navier-Stokes equations. These source terms give the proper amount of flow turning, entropy, and blockage to the flow. Two different approaches are compared: the source terms can be computed using an analytic model, or they can directly be extracted from RANS computations with the blade’s geometry. Findings The methodology is first applied to an isolated rotor test case, which allows to show that blockage effects have a strong impact on the performance of the rotor. It is also found that the analytic body force model underestimates the mass flow in the blade row for choked conditions. Finally, the body force approach is used to capture the coupling between a fan and an air intake at high angle of attacks. A comparison with full annulus unsteady computations shows that the model adequately captures the potential effects of the fan on the air intake. Originality/value To the authors’ knowledge, it is the first time that the analytic model used in this paper is combined with the blockage source terms. Furthermore, the capability of the model to deal with flows in choked conditions was never assessed.

Discussions on the Convergence of the Seakeeping Simulations Based on the Panel Methods

2018 ◽  
Author(s):  
Ivana Martić ◽  
Nastia Degiuli ◽  
Šime Malenica ◽  
Andrea Farkas
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Surface Condition ◽  
Wave Length ◽  
Boundary Integral ◽  
The Body ◽  
Numerical Code ◽  
Physical Parameters ◽  
Diffraction Radiation ◽  
Panel Methods

Numerical problems related to the convergence of the classical panel methods which are employed for the diffraction-radiation simulations are discussed. It is well known that, for the panel methods, the convergence issues are not exclusively related to the physical parameters (wave length, body shape, draught ...) but also to the one purely numerical phenomenon which occurs when the Boundary Integral Equation Method (BIEM) based on the use of Kelvin (wave) type Green’s function is used. Indeed, due to the fact that the Green’s function satisfies the free surface condition in the whole fluid domain below z = 0, the numerical solution is polluted, at some particular frequencies, by the solution of the unphysical problem inside the body. This phenomenon which is purely numerical, is known as the problem of irregular frequencies. From practical point of view, it is not always easy to distinguish if the irregularities in the final solution are coming, from the body mesh which is not fine enough, from the physical resonance of the system, from the problem of irregular frequencies or from something else!? In this paper the authors discuss these issues in the context of the evaluation of the seakeeping behavior of one typical FPSO (Floating Production Storage and Offloading). Both the linear (first order) as well as the second order quantities are of concern and the different methods for the elimination of the irregular frequencies are discussed. Special attention is given to the calculations of the different physical quantities at very high frequencies. The numerical tool used within this research is the Bureau Veritas numerical code HYDROSTAR which is based on the panel method with singularities of constant strength.

scholarly journals Theory of Motion of Jupiter’s Galilean Satellites

1978 ◽  
Vol 41 ◽  
pp. 207-207
Author(s):  
J.H. Lieske
Keyword(s):  
Analytic Functions ◽  
Digital Computer ◽  
Algebraic Manipulation ◽  
Physical Parameters ◽  
Galilean Satellites ◽  
Partial Derivatives ◽  
Theory Of Motion ◽  
Analytic Expressions ◽  
Free Libration ◽  
Future Revision

AbstractThe final results for the theory enabling one to calculate the positions of the Galilean satellites and their partial derivatives are presented, following the techniques outlined in earlier papers. Extensive use of algebraic manipulation software on a digital computer is employed to generate the final expressions. The new theory is, in effect, a revitalization of Sampson’s theory in which we (a) remove algebraic and mathematical errors existing in Sampson’s work, (b) introduce some neglected effects due to solar interactions and the 3-7 commensurability, (c) allow for non-zero amplitude and phase of the free libration, (d) express the final results as analytic functions of variations in 49 arbitrary constants of integration and physical parameters, (e) construct the theory in a manner which readily allows for future revision, and (f) provide analytic expressions for the partial derivatives with respect to the 49 parameters.

Orientation Control Using Oscillating Momentum Wheels

2015 ◽  
Author(s):  
Shaoqian Wang ◽  
Amir H. Ghasemi ◽  
Joshua L. Evans ◽  
T. Michael Seigler
Keyword(s):  
Closed Loop ◽  
Inverse Dynamics ◽  
The Body ◽  
Rotational Dynamics ◽  
Fixed Frequency ◽  
Internal Momentum ◽  
Control Techniques ◽  
Sinusoidal Oscillations ◽  
Fixed Axis ◽  
Inverse Dynamics Problem

This paper addresses the problem of controlling a rigid body’s orientation by actuating sinusoidal oscillations of internal momentum wheels. We consider the rotational dynamics of a rigid body having three momentum wheels (one for each body-fixed axis) that are attached to the body by springs. Each wheel is actuated by an internal sinusoidal torque of fixed frequency. The frequency of all sinusoidal torques is equal, but the amplitudes and phases can be varied independently. We analyze the inverse-dynamics problem of determining the amplitudes and phases for each sinusoidal torque such that a desired orientation is achieved. We then present two closed-loop orientation controllers based on this analysis. Numerical simulations demonstrate the effectiveness of the control techniques.

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