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Synthesis and Characterization of Polyurethane Rigid Foams from Soybean Oil-Based Polyol and Glycerol
Get PDFMixtures of biomass-derived polyols were used to synthesize rigid polyurethane (PU) foams. A commercial polymerized methylene diphenyl diisocyanate (pMDI) was used as crosslinker, and distilled water served as foaming agent. The morphology and mechanical properties of foams with different glycerol and water contents were compared in order to evaluate the most suitable formulations. The rigid foams with higher water contents had larger and more anisotropic cells, explaining their lower density. Compressive moduli ranged from about 2.5 MPa to above 20 MPa and collapse stresses from 55 kPa to more than 1 MPa for densities between 54 and 143 kg/m3. Densification strain did not depend on the density or on the composition of the polymeric matrix. Moreover, results shown herein demonstrate that an increase in the glycerol content leads to an increase in the required pMDI for the synthesis of the PU, but with a negligible change in the mechanical properties of the prepared foams
Low Thrust Minimum Time Orbit Transfer Nonlinear Optimization Using Impulse Discretization via the Modified Picard–Chebyshev Method
Get PDFThe Modified Picard-Chebyshev Method (MPCM) is implemented as an orbit propagation solver for a numerical optimization method that determines minimum time orbit transfer trajectory of a satellite using a series of multiple impulses at intermediate waypoints. The waypoints correspond to instantaneous impulses that are determined using a nonlinear constrained optimization routine, SNOPT with numerical force models for both Two-Body and J2 perturbations. It is found that using the MPCM increases run-time performance of the discretized lowthrust optimization method when compared to other sequential numerical solvers, such as Adams-Bashforth-Moulton and Gauss-Jackson 8th order methods
Permissible Wind Conditions for Optimal Dynamic Soaring with a Small Unmanned Aerial Vehicle
Get PDFDynamic soaring is a flight maneuver to exploit gradient wind field to extend endurance and traveling distance. Optimal trajectories for permissible wind conditions are generated for loitering dynamic soaring as well as for traveling patterns with a small unmanned aerial vehicle. The efficient direct collection approach based on the Runge-Kutta integrator is used to solve the optimization problem. The fast convergence of the optimization process leads to the potential for real-time applications. Based on the results of trajectory optimizations, the general permissible wind conditions which involve the allowable power law exponents and feasible reference wind strengths supporting dynamic soaring are proposed. Increasing the smallest allowable wingtip clearance to trade for robustness and safety of the vehicle system and improving the maximum traveling speed results in shrunken permissible domain of wind conditions for loitering and traveling dynamic soaring respectively. Sensitivity analyses of vehicle model parameters show that properly reducing the wingspan and increasing the maximum lift-to-drag ratio and the wing loading can enlarge the permissible domain. Permissible domains for different traveling directions show that the downwind dynamic soaring benefitting from the drift is more efficient than the upwind traveling pattern in terms of permissible domain size and net traveling speed
High Security Identity Tags Using Spiral Resonators
Get PDFA highly compact chipless tag based on Frequency coding technique using Spiral Resonators is proposed in this paper. Spirals are well known metamaterial structures and thus capable of sharp resonance, and hence Spiral Resonators can serve as a good candidate for RF Identity Tags. The bit capacity of the proposed tag is 10 bits per sqcm. The prototype of the tag is fabricated on a low-cost substrate of dielectric constant 4.4 and loss tangent 0.02. The overall dimension of tag is 15.4 x 3 x 1.6 mm3. Two methods for reading the tags are also discussed in this paper. Scope for bit enhancement is also provided
Higher-Order Line Element Analysis of Potential Field with Slender Heterogeneities
Get PDFPotential field due to line sources residing on slender heterogeneities is involved in various areas, such as heat conduction, potential flow, and electrostatics. Often dipolar line sources are either prescribed or induced due to close interaction with other objects. Its calculation requires a higher-order scheme to take into account the dipolar effect as well as net source effect. In the present work, we apply such a higher-order line element method to analyze the potential field with cylindrical slender heterogeneities. In a benchmark example of two parallel rods, we compare the line element solution with the boundary element solution to show the accuracy as a function in terms of rods distance. Furthermore, we use more complicated examples to demonstrate the capability of the line element technique
Natural Fiber-Polypropylene Composites Made from Caranday Palm
Get PDFComposites made from polypropylene (PP) and local South American fibers traditionally used in yarnderived craftsmanships, Caranday Palm, were studied regarding the effect of fiber addition, concentration and characteristics of the coupling agent (molecular weight and percentage of grafted maleic anhydride), as well as type of processing. A laboratory-scale intensive mixing followed by compression, and pilot plant twin extrusion followed by injection, were the two processes investigated. The use of the first one allowed the selection of processable formulations with high fiber concentration and a percentage of coupling agent below the surface fiber saturation. In fact, it was found that there is a concentration of maleic anhydride moieties that saturates the surface of the fiber irrespective of the agent molecular weight. Increasing the concentration of the coupling agent above that value does not produce further improvement of the mechanical properties. The formulations selected from the results of the laboratory process were considered for the pilot plant (extrusioninjection) process. The use of the second process consisting of extrusion-injection molding showed that the high shear developed in this process leads to defibrillation of the fiber bundles. In the case of the Caranday Palm fibers, this defibrillation resulted in elemental fibers (micron size) being the effective reinforcement of the composite instead of the technical fibers (millimeter size) that were present in the composites prepared by compression. Better mechanical properties were achieved by using the latter method
Opportunities for Cellulose Nanomaterials in Packaging Films: A Review and Future Trends
Get PDFPerformance requirements for packaging films may include barrier properties, transparency, flexibility, and tensile strength. Conventional packaging materials, such as plastic films and laminates, are typically made from petroleum-based polymers. Currently, there is a drive to develop sustainable packaging materials. These alternative materials must be able to be manufactured economically and on a commercial scale, exhibit barrier properties and transparency, and provide adequate mechanical performance. As a biobased, renewable material, cellulose nanomaterials (CNs) are ideally suited to be used in sustainable packaging applications. CNs include cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) and each can provide benefit to packaging films. Manufactured CNF films can be used as packaging films or laminates and have been shown to have good strength properties and good barrier properties, particularly at low humidity. Both CNCs and CNFs can be added to other polymers to improve strength and barrier properties. The flexibility of CNs to be used in a variety of ways in packaging applications has resulted in considerable attention and research activity. This article summarizes the current applicability for CNs in packaging films and discusses the future trends and opportunities for these materials
Cellulose Nanocrystals versus Polyethylene Glycol as Toughening Agents for Poly(Lactic Acid)-Poly(Acrylic Acid) Graft Copolymer
Get PDFPolylactic acid (PLA) is one of the most widely used biodegradable polymers due to the ability to synthesize it economically at industrial scale and its favorable properties for many consumer products. However, the rigid nature of PLA is not desirable for specific applications, requiring the incorporation of effective bioderived additives in order to enhance the PLA toughness and broaden applications. In this work, PLA was modified by graft polymerization of polyacrylic acid (PLA-g-PAA) to increase the hydrophilicity to promote compatibilization of cellulose nanocrystals (CNCs) or high molecular polyethylene glycol (PEG). CNCs were found to act as a nucleating agent for the PLA-g-PAA copolymer due to an enhanced compatibility with these rigid nanocrystals, thus increasing the tensile modulus and reducing toughness. This was not the case for pure PLA, for which the toughness was increased up to 125% for a 1% CNC loading. PEG successfully increased toughness of the PLA-g-PAA by more than 34 times that of neat PLA and PLA-g-PAA with a substantial yet not critical reduction in strength and modulus for a wide range of applications
New Insights on Energy Conserved Planar Motion
Get PDFThe planar motion of a particle within an arbitrary potential field is considered. The particle is additionally subject to an external force wherein the applied thrust-acceleration is constrained to remain normal to the velocity vector. The system is thus non-conservative but since the thrust force is non-working, the total energy is a conserved quantity. Under this setting, a major result of fundamental importance is established in this paper: that the flight direction angle (more precisely, the sine of the angle between the position and velocity vectors) is shown to always satisfy a linear first-order differential equation with variable coefficients that depend upon the underlying potential function. As a consequence, an analytical solution for the flight direction angle can be obtained directly in terms of the particle's distance from the center of the field for a significant number of special cases for the potential function. In the case of J2 perturbed spacecraft motion within equatorial orbits, the problem is reduced to that of solving an incomplete elliptic integral. Another important implication of the main result established here is that motion problems subject to velocity-normal thrusting can always be reduced to the study of equivalent single degree-of-freedom conservative systems with an effective potential function. The paper concludes with various examples of both academic and practical interest including the study of bounded two-body Keplerian orbits and hodograph interpretetions
Continued Fraction Cartesian to Geodetic Coordinate Transformation
Get PDFA singularity-free perturbation solution is presented for inverting the Cartesian to Geodetic transformation. Conventional approaches for inverting the transformation use the natural ellipsoidal coordinates, this work explores the use of the satellite ground-track vector as the differential correction variable. The geodetic latitude is recovered by well-known elementary means. A high-accuracy highperformance 3D vector-valued continued fraction iteration is constructed. Rapid convergence is achieved because the starting guess for the ground-track vector provides a maximum error of 30 m for the satellite height above the Earth's surface, throughout the LEO-GEO range of applications. As a result, a single iteration of the continued fraction iteration yields a maximum error for the satellite height of 1