Variable Mass Distribution Research Articles

A Comprehensive Method for Liquid-to-Solid Interactions.

Realistic real-time water-solid interaction has been an open problem in Computer Graphics since its beginnings, mainly due to the complex interactions that happen at the interface between solid objects and liquids, both when objects are completely or partially wet, or when they are fully submerged.In this paper we present a method that tackles the two main aspects of this problem, namely the buoyancy of objects submerged into fluids, and the superficial liquid propagation and appearance changes that arises at the interface between the surface of solid objects in contact with a liquids.For the first problem (buoyancy) a method is proposed to realistically compute the fluid-to-solid coupling problem. Our proposal is suitable for a wide spectrum of cases, such as rigid or deformable objects, hollow or filled, permeable or impermeable, and with variable mass distribution. In the case of permeable materials, which allow liquid to pass through the object, the presented method incorporates the dynamics of the fluid in which the object is submerged, and decouples the computation of the physical quantities involved in the buoyancy force of the empty object with respect to to the liquid contained within it. On the other hand, the visual appearance of certain materials depends on their intrinsic light transfer properties, the lighting present and other environmental contributions. Thus, complementing the first approach in this paper, a new technique is introduced to model and render the appearance changes of absorbent materials when there is liquid on their surface. Also, a new method was developed to solve the problem of the interaction between the object surface and liquids, taking advantage of texture coordinates. An algorithm was proposed to model the main physical processes that occur on the surface of a wet or wet solid object. Finally, we model the change in appearance that typically arise in most materials in contact with fluids, and an algorithm is implemented achieving real-time performance. The complete solution is designed taking advantage of superscalar architectures and GPU acceleration, allowing a flexible integration with the pipelines of current graphic engines.

No-slip billiards with particles of variable mass distribution.

Astute variations in the geometry of mathematical billiard tables have been and continue to be a source of understanding their wide range of dynamical behaviors, from regular to chaotic. Viewing standard specular billiards in the broader setting of no-slip (or rough) collisions, we show that an equally rich spectrum of dynamics can be called forth by varying the mass distribution of the colliding particle. We look at three two-parameter families of billiards varying both the geometry of the table and the particle, including as special cases examples of standard billiards demonstrating dynamics from integrable to chaotic, and show that markedly divergent dynamics may arise by changing only the mass distribution. Furthermore, for certain parameters, billiards emerge, which display unusual dynamics, including examples of full measure periodic billiards, conjectured to be nonexistent for the standard billiards in Euclidean domains.

Satellite with periodical mass redistribution: relative equilibria and their stability

The dynamics of a spacecraft with variable mass distribution is considered, assuming a central Newtonian gravitational field. The equations of spatial attitude motion are derived within the framework of the so-called satellite approximation and examined via a Hamiltonian approach. The centre of mass of the satellite multibody system moves along an elliptic orbit of arbitrary eccentricity. For a prescribed attitude motion, control via the mass redistribution is determined. Various classes of relative equilibria are detected, and the respective control is obtained. The stability of the spacecraft spatial attitude motions is examined in detail.

Движение спутника с переменным распределением масс в центральном поле сил гравитации

Движение спутника с переменным распределением масс в центральном поле сил гравитации

Digit Position and Forces Covary during Anticipatory Control of Whole-Hand Manipulation.

Theoretical perspectives on anticipatory planning of object manipulation have traditionally been informed by studies that have investigated kinematics (hand shaping and digit position) and kinetics (forces) in isolation. This poses limitations on our understanding of the integration of such domains, which have recently been shown to be strongly interdependent. Specifically, recent studies revealed strong covariation of digit position and load force during the loading phase of two-digit grasping. Here, we determined whether such digit force-position covariation is a general feature of grasping. We investigated the coordination of digit position and forces during five-digit whole-hand manipulation of an object with a variable mass distribution. Subjects were instructed to prevent object roll during the lift. As found in precision grasping, there was strong trial-to-trial covariation of digit position and force. This suggests that the natural variation of digit position that is compensated for by trial-to-trial variation in digit forces is a fundamental feature of grasp control, and not only specific to precision grasp. However, a main difference with precision grasping was that modulation of digit position to the object’s mass distribution was driven predominantly by the thumb, with little to no modulation of finger position. Modulation of thumb position rather than fingers is likely due to its greater range of motion and therefore adaptability to object properties. Our results underscore the flexibility of the central nervous system in implementing a range of solutions along the digit force-to-position continuum for dexterous manipulation.

Exergy analysis of discharging multi-tank thermal energy storage systems with constant heat extraction

Abstract In this work, an exergy analysis of discharging multi-tank thermal energy storage systems with constant heat extraction is studied. Theoretical models are developed to analyze the effect of the induced stratification through storage division into several tanks for different system configurations: multi-tank systems with even mass distribution, and two-tank systems with uneven and variable mass distribution. The instantaneous and the process efficiencies are defined to assess the performance of the system as function of operation parameters. For two- and four-tank systems with mass evenly distributed, efficiency increments around 4% and 7%, respectively, are possible. For two-tank systems, higher efficiencies are accomplished for short times when the mass is unevenly distributed and larger amount of the mass is in the hotter tank. For longer times, the even distributed mass situation provides the highest performance. To achieve superior efficiency of two-tank systems during the entire timespan, a time varying mass distribution χ = 0.5 ( 1 + e - 2 t ∗ ) is proposed. Finally, the energy losses as well as the pumping effects on the performance of one- and two-tank systems are analyzed. It is found that, both, the pumping effects and the energy losses are generally negligible and the efficiency can be improved dividing the storage system, rather than increasing the mass flow rate.

Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons

AbstractWe discuss several classes of improvements to gravity solutions from the Gravity Recovery and Climate Experiment (GRACE) mission. These include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution JPL RL05, and an alternate JPL RL05M mass concentration (mascon) solution benefitting from those same improvements but derived in surface spherical cap mascons. The mascon basis functions allow for convenient application of a priori information derived from near‐global geophysical models to prevent striping in the solutions. The resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions, and do not necessitate empirical filters to remove north‐south stripes, lowering the dependence on using scale factors (the global mean scale factor decreases by 0.17) to gain accurate mass estimates. Ocean bottom pressure (OBP) time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions (increase in correlation coefficient of 0.08 globally), particularly in low‐latitude regions with small signal power (increase in correlation coefficient of 0.35 regionally), in addition to reducing the error RMS with respect to the in situ data (reduction of 0.37 cm globally, and as much as 1 cm regionally). Greenland and Antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results. Computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins; however, mascon solutions typically have greater resolution for smaller spatial regions, in particular when studying secular signals.

SPH for 3D floating bodies using variable mass particle distribution

SUMMARYA floating body with substantial heave motion is a challenging fluid–structure interaction problem for numerical simulation. In this paper we develop SPH in three dimensions to include variable particle mass distribution using an arbitrary Lagrange–Eulerian formulation with an embedded Riemann solver. A wedge or cone in initially still water is forced to move with a displacement equal to the surface elevation of a focused wave group. A two‐dimensional wedge case is used to evaluate two forms of repulsive‐force boundary condition on the body; the force depending on the normal distance from the object surface produced closer agreement with the experiment. For a three‐dimensional heaving cone the comparison between SPH and experiment shows excellent agreement for the force and free surface for motion with low peak spectral frequencies while for a higher peak frequency the agreement is reasonable in terms of phase and magnitude, but a small discrepancy appears at the troughs in the motion. Capturing the entire three‐dimensional flow field using an initially uniform particle distribution with sufficiently fine resolution requires an extremely large number of particles and consequently large computing resource. To mitigate this issue, we employ a variable mass distribution with fine resolution around the body. Using a refined mass distribution in a preselected area avoids the need for a dynamic particle refinement scheme and leads to a computational speedup of more than 600% or much improved results for a given number of particles. SPH with variable mass distribution is then applied to a single heaving‐float wave energy converter, the ‘Manchester Bobber’, in extreme waves and compared with experiments in a wave tank. The SPH simulations are presented for two cases: a single degree‐of‐freedom system with motion restricted to the vertical direction and with general motion allowing six degrees‐of‐freedom. The motion predicted for the float with general motion is in much closer agreement with experimental data than the vertically constrained system. Using variable particle mass distribution is shown to produce close agreement with a computation time 20% of that required with a uniformly fine resolution. Copyright © 2012 John Wiley & Sons, Ltd.

Planar vibrations of a solid with variable mass distribution in an elliptic orbit

Planar vibrations of a solid with variable mass distribution in an elliptic orbit

On planar oscillations of a body with a variable mass distribution in an elliptic orbit

Planar motion of an orbiting body having a variable mass distribution in a central field of gravity is under analysis. Within the so-called ‘satellite approximation’ planar attitude dynamics is reduced to the 3/2-degrees of freedom description by one ODE of second order. The law of the mass distribution variations implying an existence of the special relative equilibria, such that the body is oriented pointing to the attracting centre by the same axis for any value of the orbit eccentricity is indicated. For particular example of an orbiting dumb-bell equipped by a massive cabin, wandering between the ends of the dumb-bell. For this example stability of the equilibria such that the dumb-bell ‘points to’ the attracting centre by one of its ends is studied. The chaoticity of global dynamics is investigated. Two important examples of a vibrating dumb-bell and of a dumb-bell equipped by a cabin wandering between its endpoints are considered. The dynamics of space objects, including moving elements, has been investigated by many authors. These studies usually have been connected with the necessity to estimate the influence of relative motions of moving parts, for example, crew motions [ 1 , 2 ], circulation of liquids [ 3 ], etc. on the attitude dynamics of a spacecraft. The development of projects of large-scale space systems with mobile elements, in particular, of satellite systems with tethered elements and space elevators, has posed problems related to their dynamics. Various aspects of the role of mass distribution even for the simplest orbiting systems, like dumb-bell systems are known since the publications [ 4 – 7 ], etc. The possibility of the sudden loss of stability because of the mass redistribution has been pointed out in reference [ 8 ] (see also references [ 9 – 13 ]). The considered system belongs to the mentioned class of systems and represents by itself one of the simplest systems allowing both analytical and numerical treatment, without supplementary simplifying assumptions such as smallness of the orbital eccentricity. Another set of applied problems is related to orientation keeping of the system for deployment and retrieval of tethered subsatellites as well as for relative cabin motions of space elevators. In particular, the problem of the stabilization/destabilization possibility for the given state of motion due to rapid oscillations of the cabin exists. This could be the subject of another additional investigation.

Wave body interaction in 2D using smoothed particle hydrodynamics (SPH) with variable particle mass

AbstractWave interaction with bodies is an important practical application for smoothed particle hydrodynamics (SPH) which in principle applies to steep and breaking waves without special treatment. However, few detailed tests have been undertaken even with small amplitude waves. In order to reduce computer time a variable particle mass distribution is tested here with fine resolution near the body and coarse resolution further away, while maintaining a uniform kernel size. We consider two well‐defined test cases, in two dimensions, of waves generated by a heaving semi‐immersed cylinder and progressive waves interacting with a fixed cylinder. But first, still water with hydrostatic pressure is tested. The open‐source code SPHysics (http://www.sphysics.org)§Update made here after initial online publication. is used with a Riemann solver in an Arbitrary Lagrangian–Eulerian formulation. For the heaving cylinder, SPH results for far field wave amplitude and cylinder force show good agreement with the data of Yu and Ursell (J. Fluid Mech. 1961; 11:529–551). For wave loading on a half‐submerged cylinder the agreement with the experimental data of Dixon et al. (J. Waterway Port Coastal Ocean Div. 1979; 105:421–438) for the root mean square force is within 2%. For more submerged cases, the results show some discrepancy, but this was also found with other modelling approaches. The sensitivity of results to the value of the slope limiter used in the MUSCL‐based Riemann solver is demonstrated. The variable mass distribution leads to a computer run speedup of nearly 200% in these cases. Copyright © 2011 John Wiley & Sons, Ltd.

Extracting low frequency climate signal from GRACE data

For more than four years, the GRACE pair of satellites have been orbiting the Earth, monitoring the time variable mass distribution for scales ranging from regional to global. The GRACE data have been released for a broad scientific community and sets of gravity fields are available. This paper shows that there are evidences at interrannual time scales for the presence of ENSO signal in the data, strongly correlated with the hydrological mass distribution, and also similar to the expected hydrological signature asso- ciated with the ENSO cycle. This signal dominates, at global scale, the one associated with geodynamic sources.

Nonlinear response of a nonhomogeneous clamped-free beam to pulse loads

The response of a cantilever beam, represented as a non-linear nonhomogeneous system is determined for pulse loads of the form of a stepfunction and a triangular pulse of finite duration. The non-linearity of the beam arises from a non-linear stress-strain relation and the not linearized curvature. The system exhibits a softening characteristic and is approximately solved by a one-term solution. The response amplitude as well as the period are increased due to the non-linearities of the system. Various cases of variable mass distribution and stiffness have been evaluated.

Bending of Rotor Blade in the Plane of Rotation

A theoretical analysis of the bending of the rotor blade in the plane of rotation is given with consideration of the elasticity of the blade. The analysis also includes the bending of a blade with variable mass distribution along the span. The results lead to matrix equations tha t are convenient for arithmetic calculation. The application of this theoretical analysis is illustrated by numerical calculations. The results found in the case of a typical rotor blade show tha t the maximum deflection in the plane of rotation is about one-tenth of that in the flapping plane and tha t the maximum bending moment in the plane of rotation is about one-fourth of that in the flapping plane. When a blade with variable section is compared with one with an equivalent constant blade section, the bending moment for the variable section is found to be appreciably greater than that for the equivalent constant section in the region of the inner half span.