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Integration of the Coupled Orbit-Attitude Dynamics Using Modified Chebyshev-Picard Iteration Methods
Get PDFThis paper presents Modified Chebyshev-Picard Iteration (MCPI) methods for long-term integration of the coupled orbit and attitude dynamics. Although most orbit predictions for operational satellites have assumed that the attitude dynamics is decoupled from the orbit dynamics, the fully coupled dynamics is required for the solutions of uncontrolled space debris and space objects with high area-to-mass ratio, for which cross sectional area is constantly changing leading to significant change on the solar radiation pressure and atmospheric drag. MCPI is a set of methods for solution of initial value problems and boundary value problems. The methods refine an orthogonal function approximation of long-time-interval segments of state trajectories iteratively by fusing Chebyshev polynomials with the classical Picard iteration and have been applied to multiple challenging aerospace problems. Through the studies on integrating a torque-free rigid body rotation and a long-term integration of the coupled orbit-attitude dynamics through the effect of solar radiation pressure, MCPI methods are shown to achieve several times speedup over the Runge-Kutta 7(8) methods with several orders of magnitudes of better accuracy. MCPI methods are further optimized by integrating the decoupled dynamics at the beginning of the iteration and coupling the full dynamics when the attitude solutions and orbit solutions are converging during the iteration. The approach of decoupling and then coupling during iterations provides a unique and promising perspective on the way to warm start the solution process for the longterm integration of the coupled orbit-attitude dynamics. Furthermore, an attractive feature of MCPI in maintaining the unity constraint for the integration of quaternions within machine accuracy is illustrated to be very appealing
A Tree-Based Approach for Efficient and Accurate Conjunction Analysis
Get PDFConjunction analysis is the study of possible collisions between objects in space. Conventional conjunction analysis algorithms are geared towards computing the collision probability between any two resident space objects. Currently, there are few heuristic methods available to select which objects should be considered for a detailed collision analysis. A simple all-on-all collision analysis results in an O(N2) procedure, which quickly becomes intractable for large datasets. The main objective of this research work is to preemptively determine which catalogued objects should be considered for a more detailed conjunction analysis, significantly reducing the number of object pairs to be investigated. The heart of the approach lies in the efficient kd-tree algorithm. It has been found that this binary search method significantly reduces computational cost to a tractable complexity of O(N logN). The conventional tree-based search is modified slightly by accounting for probabilistic nearest neighbors via the Hellinger Distance. Finally, the method is extended to account for Non-Gaussian errors via the inclusion of Gaussian Mixture Models. It has been found that the reduced computational complexity of the kd-tree is maintained, while the applicability of the method is extended to uncertain cases
Formation of Highly Oriented Cellulose Nanocrystal Films by Spin Coating Film from Aqueous Suspensions
Get PDFSpin coating was used to cast a uniform film of cellulose nanocrystals with low surface roughness and variable thickness as a function of operational parameters that include rotational speed and dispense suspension concentration. The film thickness was controllable from 40 nm up to 1 μm with surface roughness an order of magnitude less than blade-coating methods. The degree of radial orientation was qualitatively assessed and shown to be variable with processing parameters. Under specific processing conditions, the formation of striation patterns was observed and associated with film drying instability. The striation patterns are periodic in nature where the wavelength and amplitude are controllable to a certain degree with wetting film concentration and rotational speed. The striation patterns possess ordered, oriented nanorods, which exist as both rippled ring-like structures and radial ridges along the shear direction. There is potential to employ these rippled structures as low-cost manufacturing of ordered materials, device platforms, or optical components such as diffraction gratings. Mechanical properties of the films were measured by nanoindentation. The maximum elastic modulus of the films was 8.3 GPa and the maximum hardness was 322 MPa. A post-drying heat treatment (80 °C) was employed and resulted in a 17% increase in modulus and 35% increase in hardness, which is attributed to the formation of an enhanced intermolecular hydrogen bonding network between nanocrystals with removal of bound water
Thermomagnetic Convection-Surface Radiation Interactions in Microgravity Environment
Get PDFThe numerical study of combined thermo-magnetic convection and surface radiation is presented in this paper and computations are performed for a paramagnetic fluid filled square cavity whose four walls have the same emissivity, placed in a micro-gravity environment (g ≈0), and subjected to various strong non-uniform magnetic field gradients. The vertical walls were isothermal, and the horizontal walls were adiabatic. Finite volume method based on the concepts of staggered grid and SIMPLER algorithm has been applied, and the view factors were determined by analytical formula. Representative results, illustrating the effect of magnetic field strength on streamlines, temperature contours and Nusselt numbers, show that temperature differences occur within the cavity giving rise to convectif motion of the paramagnetic fluid which takes place even in a zero-gravity environment
Reflection of PlaneWaves from Electro-magneto-thermoelastic Half-space with a Dual-Phase-Lag Model
Get PDFThe aim of this paper is to study the reflection of plane harmonic waves from a semi-infinite elastic solid under the effect of magnetic field in a vacuum. The expressions for the reflection coefficients, which are the relations of the amplitudes of the reflected waves to the amplitude of the incident waves, are obtained. Similarly, the reflection coefficient ratio variations with the angle of incident under different conditions are shown graphically. Comparisons are made with the results predicted by the dual-phase-lag model and Lord-Shulman theory in the presence and absence of magnetic field
Transient Heat Conduction in Materials with Linear Power-Law Temperature-Dependent Thermal Conductivity: Integral-Balance Approach
Get PDFClosed form approximate solutions to nonlinear transient heat conduction with linear power-law k = k0(1±βTm) temperature-dependent thermal diffusivity have been developed by the integral-balance integral method under transient conditions. The solutions use improved direct approaches of the integral method and avoid the commonly used linearization by the Kirchhoff transformation. The main steps in the new solutions are improvements in the integration technique of the double-integration technique and the optimization of the exponent of the approximate parabolic profile with unspecified exponent. Solutions to Dirichlet boundary condition problem have been developed as examples by the classical Heat-balance Integral method (HBIM) and the Double-integration method (DIM)
Electro-Deposition of Asphaltenes from Abu Dhabi Crude Oil/Synthetic Formation Water Mixtures
Get PDFIn this work, asphaltenes precipitation and deposition induced by applying an electric field to Abu Dhabi crude oil sample were studied. The asphaltic particle electrical charge and asphaltic deposits mass at different operating conditions were determined. Direct current (DC) was applied between two graphite electrodes dipped in crude oil/synthetic formation water mixture of 240K ppm salinity. Three current densities of 10, 20, and 30 A/m2 were applied. Deposits were collected on the electrodes surfaces and their mass was recorded using low capacity load cells (up to 50g). Anodic and cathodic deposits were observed at different operating conditions. The results revealed that asphaltic nature deposits were detected on the anode. The mass of deposits on the electrodes increased with experiment time and current density. With higher current density at experiment times below 10 hrs, the rate of the mass increase was faster. No charge alterations noticed with increasing run time and current density. Experiments showed that the maximum amount of asphaltic material arrested on the anode was 18% of the original asphaltic material in crude oil sample for current density of 30 A/m2 and 24 hours run time. Eventually, an asphaltene preventive/minimizing criterion can be set to combat deposition during production and enhanced oil recovery processes
Modeling Active Contraction and Relaxation of Left Ventricle Using Different Zero-load Diastole and Systole Geometries for Better Material Parameter Estimation and Stress/Strain Calculations
Get PDFModeling ventricle active contraction based on in vivo data is extremely challenging because of complex ventricle geometry, dynamic heart motion and active contraction where the reference geometry (zero-stress geometry) changes constantly. A new modeling approach using different diastole and systole zero-load geometries was introduced to handle the changing zero-load geometries for more accurate stress/strain calculations. Echo image data were acquired from 5 patients with infarction (Infarct Group) and 10 without (Non-Infarcted Group). Echo-based computational two-layer left ventricle models using one zero-load geometry (1G) and two zero-load geometries (2G) were constructed. Material parameter values in Mooney-Rivlin models were adjusted to match volume data. Effective Young’s moduli (YM) were calculated for easy comparison. For diastole phase, begin-filling (BF) mean YM value in the fiber direction (YMf) was 738%higher than its end-diastole (ED) value (645.39 kPa vs. 76.97 kPa, p=3.38E-06). For systole phase, end-systole (ES) YMf was 903% higher than its begin-ejection (BE) value (1025.10 kPa vs. 102.11 kPa, p=6.10E-05). Comparing systolic and diastolic material properties, ES YMf was 59% higher than its BF value (1025.10 kPa vs. 645.39 kPa. p=0.0002). BE mean stress value was 514% higher than its ED value (299.69 kPa vs. 48.81 kPa, p=3.39E-06), while BE mean strain value was 31.5% higher than its ED value (0.9417 vs. 0.7162, p=0.004). Similarly, ES mean stress value was 562% higher than its BF value (19.74 kPa vs. 2.98 kPa, p=6.22E-05), and ES mean strain value was 264% higher than its BF value (0.1985 vs. 0.0546, p=3.42E-06). 2G models improved over 1G model limitations and may provide better material parameter estimation and stress/strain calculations
Influence of Isocyanate Index on Selected Properties of Flexible Polyurethane Foams Modified with Various Bio-Components
Get PDFIn this article, the results of the foaming process analysis of fl exible polyurethane with different isocyanate indexes are presented. Two types of flexible polyurethane foams (FPURF) were obtained: (1) by using petrochemical components and a rapeseed-oil-based polyol (used in the amount of 20 wt%), (2) by using petrochemical components and cellulose as a natural fi ller in the amount of 3 php (per hundred parts of polyol). The characteristic parameters of the foaming process, such as the foam’s growth velocity, the core temperature and dielectric polarization, were measured using a Foamat device. Moreover, the following properties of flexible polyurethane foams were determined: apparent density, resilience, compressive strength, hardness, hysteresis and support factor, in order to determine the infl uence of isocyanate index on selected properties of the foams modified with bio-polyol and bio-filler
Editorial
Get PDFThere is an increasing awareness among the general
public of the importance of the intelligent use
of earth’s biological resources for the production of
chemicals, materials and precursors, resulting in an
economy that is turning towards considering the
valuable contributions offered by these resources.
To face the present challenges of reducing the use of
nonrenewable resources and the negative impact of
polymer pollution on the environment, the world’s
scientists are making their contribution by unraveling
biological structures and studying and developing
new materials and applications from biomass
resources