Showing papers by "Dumitru I. Caruntu published in 2005"

Fabrication of magnetic hollow silica nanospheres for bioapplications

Abstract: Different kinds of nanospheres are used in magnetic nanosphere fabrication for bioapplications. In this paper, we report a successful synthesis of magnetic hollow silica nanospheres (MHSNS). The MHSNS were fabricated with a one step coating of Fe3O4 magnetic nanoparticles (NPs)(∼10nm) and silica on nanosized (20–100nm) spherical calcium carbonate (CaCO3) surface under alkaline conditions, in which the nanosized CaCO3 were used as nanotemplates and tetraethoxysilane and magnetic NPs were used as precursors. The as-synthesized nanoshperes were immersed in an acidic solution to remove nanosized CaCO3, forming MHSNS. The MHSNS were characterized by SEM, TEM, and SQUID. SEM and TEM results showed that a smooth surface of MHSNS and a thin layer of silica (∼10nm) embedded with the magnetic NPs was successfully formed. No nanosized CaCO3 nanotemplates were observed. SQUID measurement demonstrated that magnetization of MHSNS was dependent on temperature, exhibiting superparamagnetism. The MHSNS have potential appl...

Systems Stability Using Weight Functions Method

Abstract: A new method for systems stability analysis is presented. This method is called weight functions method and it replaces the problem of Liapunov function finding with a problem of finding a number of functions (weight functions) equal to the number of first order differential equations describing the system. It is known that there are not general methods for finding Liapunov functions. The weight functions method is simpler than the classical method since one function at a time has to found. This method’s conditions of solution stability for linear and nonlinear systems are presented. Applications such as Lurie-Postnikov problem and controlled systems stability are presented as well.Copyright © 2005 by ASME

Dynamic Analysis of Composite Plates

Abstract: The paper presents comparatively the measured and estimated natural frequencies and mode shapes of a rectangular orthotropic panel. The experimental tests were performed using a shaker. The plate was fixed in horizontal position directly on the shaker armature using a rigid rod. The experimental modes shapes were visualized using sand particles. The measured natural frequencies and also the modes shapes correspond to the whole system in motion. So, the analytic model of the plate must include the effect of the vibrator connected to the plates. The purpose of this experimental measurements and analytic modeling of such plates is to further developing a methodology to estimate the material properties of the composite panels. At this research stage, an orthotropic plate with unknown material properties was investigated. Using an adequate finite element model, the mechanical properties of the material were estimated. Using these properties it is possible to numerically estimate the dynamic behavior of the plate for additional sets of boundary conditions.Copyright © 2005 by ASME

Improvement of the Dynamic Behavior of a Fan Using Finite Element Method

Abstract: The first part of this article presents a dynamic analysis of the fan of a generator connected by rigid coupling to a diesel engine. The purpose of this analysis is to correlate the main components of the fan’s frequency response spectrum with the ones of the excitation source, i.e., the diesel engine. The second part describes a finite element analysis of the fan in order to find the best design solution.Copyright © 2005 by ASME

On Transverse Vibrations of Rectangular Plates of Unidirectional Parabolic Thickness Variation

Abstract: This paper presents an approach for finding the solution of partial differential equation describing the motion of transverse vibrations of rectangular plates of unidirectional convex parabolic varying thickness. The partial differential equation consists of three operators: fourth-order spatial-dependent, second-order spatial-dependent, and second-order time-dependent. Using the method of multiple scales, the partial differential equation has been reduced to two simpler partial differential equations which can be analytically solved and which represent two levels of approximation. The first partial differential equation was a homogeneous equation and consisted of two operators, the fourth-order spatial-dependent and second-order time-dependent. Using the factorization method, so-called zero-order approximation of the exact solution has been found. The second partial differential equation was an inhomogeneous equation. Its solution, so-called first-order approximation of the exact solution has been found. This way the first-order approximations of the natural frequencies and mode shapes are found. Various boundary conditions can be considered. The influence of Poisson’s ratio on the natural frequencies and mode shapes could be further studied using the approximations reported here. This approach can be extended to nonlinear, and/or forced vibrations.Copyright © 2005 by ASME

Nonlinear Vibrations of Non-Uniform Beams Including Inertia Effects

Abstract: This papers deals with nonlinear vibrations of non-uniform beams with geometrical nonlinearities such as moderately large curvatures, and inertia nonlinearities such as longitudinal and rotary inertia forces. The nonlinear fourth-order partial-differential equation describing the above nonlinear effects is presented. Using the method of multiple scales, each effect is found by reducing the nonlinear partial-differential equation of motion to two simpler linear partial-differential equations, homogeneous and nonhomogeneous. These equations along with given boundary conditions are analytically solved obtaining so-called zero-and first-order approximations of the beam’s nonlinear frequencies. Since the effect of mid-plane stretching is ignored, any boundary conditions could be considered as long as the supports are not fixed a constant distance apart. Analytical expressions showing the influence of these three nonlinearities on beam’s frequencies are presented up to some constant coefficients. These coefficients depend on the geometry of the beam. This paper can be used to study these influences on frequencies of different classes of beams. However, numerical results are presented for uniform beams. These results show that as beam slenderness increases the effect of these nonlinearities decreases. Also, they show that the most important nonlinear effect is due to moderately large curvature for slender beams.Copyright © 2005 by ASME

Overview of Payload Vibration Isolation Systems

Abstract: This paper is an overview of recent spacecraft payload vibration isolation systems for further possible application to reusable launch vehicles sub-orbital missions A summary of vibro-acoustic environment of Orbital Science and Kistler Aerospace’s small launch vehicles indicated a severe level of random vibrations, shock and acoustics that the payload must endure The same level of random vibrations has been found for an entire family of sounding rockets: Black Brant, Orion, Nike-Orion, Taurus-Orion and Terrier-Orion This paper also presents recent flight experiments designed to test either launch isolation or on-orbit isolation systems While the on-orbit vibration isolation systems were active-passive systems, which lately used smart structures and new control algorithms including adaptive neural network-based, launch isolation systems evolved from passive to active-passive systems which were lately tested during the VALPE-2 experiment Launch active-passive systems provided a vibration reduction 10 to 1 versus up to 5 to 1 provided by passive systems Also, on-orbit active-passive systems provided a vibration reduction of about 10 to 1 Suborbital missions became very important due to the growing number of research projects dedicated to remote sensing of high resolution and effects of microgravity The number of orbital and especially suborbital reusable launch missions is estimated to increase considerably in the near future as vehicles develop The actual tendency is to reduce payload weight and mission costs, and to improve the payload environment This requires more efficient vibration isolation systems that will guarantee payload safety and better operational performance for reusable launch vehiclesCopyright © 2005 by ASME