• Steel and Composite Structures
• /
• v.49 no.3
• /
• pp.325-335
• /
• 2023

The missile is affected by both spinning and axial motion during its movement, which will have a very adverse impact on the stability and reliability of the missile. This paper regards missiles as cylindrical shell structures with spinning and axial motion. In this article, the forced vibration of carbon nanotube-reinforced composites (CNTRCs) cylindrical shells with spinning motion and axial motion is investigated, in which the clamped-clamped and simply-simply supported boundary conditions are considered. The displacement field is described by the first-order shear theory, and the vibration equation is deduced by using the Euler-Lagrange equation, after dimensionless processing, the dimensionless equation of motion is obtained. The correctness of this paper is verified by comparing with the results of the existing literature, in which the simply-simply supported ends are taken into account. In the end, the effects of different parameters such as spinning velocity, axial velocity, carbon nanotube volume fraction, length thickness ratio and load position on the resonance behavior of cylindrical shells are given. It can be found that these parameters can significantly change the resonance of axially moving and rotating moving CNTRCs cylindrical shells.

• Journal of Advanced Marine Engineering and Technology
• /
• v.25 no.4
• /
• pp.857-868
• /
• 2001

The aerodynamic forces and wake structures of the non-rotating downstream cylinder which is located behind the spinning upstream cylinder in tandem and staggered arrangement have been investigated by experimental method at Re= $1.32{\times}10^4$. The measurements of wake flow and pressure distributions of downstream cylinder are carried out in various spin parameters by combination of both longitudinal spacing rations L/d=1.5, 3.0, 4.5 and transverse spacing ratios T/d =0.0, -0.5, 0.5. For the present experiment, it has been found that the spin parameter of spinning upstream cylinder affect more easily the downstream cylinder in tandem arrangement than that in staggered arrangement.

• Steel and Composite Structures
• /
• v.51 no.4
• /
• pp.457-471
• /
• 2024

In this research, for the first time the instability boundaries for a spinning shaft reinforced with graphene nanoplatelets undergone the principle parametric resonance are determined and examined taking into account the gyroscopic effect. In this respect, the extracted equations of motion in our previous research (Ref. Asadi et al. (2023)) are implemented and efficiently upgraded. In the upgraded discretized equations the effect of the Rayleigh's damping and the varying spinning speed is included that leads to a different dynamical discretized governing equations. The previous research was about the free vibration analysis of spinning graphene-based shafts examined by an eigen-value problem analysis; while, in the current research an advanced mechanical analysis is addressed in details for the first time that is the dynamics instability of the aforementioned shaft subjected to the principal parametric resonance. The spinning speed of the shaft is considered to be varied harmonically as a function of time. Rayleigh's damping effect is applied to the governing equations in order to regard the energy loss of the system. Resorting to Bolotin's route, Floquet theory and β-Newmark method, the instability region and its accompanied boundaries are defined. Accordingly, the effects of the graphene nanoplatelet on the instability region are elucidated.

• 한국연소학회:학술대회논문집
• /
• 2006.04a
• /
• pp.205-212
• /
• 2006

Three-dimensional numerical study was carried out for the investigation of the detonation wave structures propagating in tubes. Fluid dynamics equations and conservation equation of reaction progress variable were analyzed by a MUSCL-type TVD scheme and four stage Runge-Kutta time integration. Chemical reaction was modeled by using a simplified one-step irreversible kinetics model. The variable gas properties between unburned and burned states were considered by using variable specific heat ratio formulation. The unsteady computational results in three-dimension show the detailed mechanisms of rectangular and diagonal mode of detonation wave instabilities resulting same cell length but different cell width in smoked-foil record. The results for the small reaction constant shows the spinning mode of three-dimensional detonation wave dynamics, which was rarely observed in the previous numerical simulation of the detonation waves.

• Journal of Advanced Marine Engineering and Technology
• /
• v.16 no.4
• /
• pp.39-49
• /
• 1992

The coherent wake structures behind a spinning cylinder placed in a uniform flow were experimentally investigated by means of phase averaging technique. With a fixed cylinder Reynolds number (Re=6,600), the conditionally sampled velocity vectors were obtained at a section of 3.0 and 10 diameters behind the cylinder for the range of spin parameter S(the ratio of the peripheral velocity to that of the uniform flow) 0 to 2. Spectral analysis and vorticity contours of the velocity data show that up to S=1.2, a Karman vortex street exists within the wake, however, the coherent structures become obscure and their vorticity strength decreases as S increase. Beyond S=1.2, a distinct vortex shedding frequency no longer exists, furthermore coherent structures disappear when S is over 1.6.

• Journal of the Korean Magnetic Resonance Society
• /
• v.16 no.2
• /
• pp.103-110
• /
• 2012

Membrane proteins play a essential role in the biological systems and it is not easy to handle a membrane protein for its structural study. Solid-state NMR (ssNMR) can be a good tool to investigate the structures and dynamics of membrane proteins. In ssNMR, Magic Angle Spinning (MAS) and Cross Polarization (CP) can be utilized to reduce the line-broadening, leading to high resolution and sensitivity in the spectrum. ssNMR, if combined with other spectroscopic methods, can provide us a enough knowledge on structures and dynamics of membrane proteins in biological condition.

• Bulletin of the Korean Chemical Society
• /
• v.17 no.1
• /
• pp.66-68
• /
• 1996

It has been found that mesoporous structures of MCM-41 and MCM-48 disintegrate readily in distilled water around 370 K, while the structures can be stable in 100%-steam of 1 atmospheric pressure at much higher temperatures around 820 K. Thus, the structure disintegration is thermodynamically more favorable in water than under the steaming condition. X-ray powder diffraction and magic angle spinning 29Si NMR spectroscopy indicate that the disintegration of the mesoporous structures in water occurs due to silicate hydrolysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.3 s.96
• /
• pp.251-258
• /
• 2005

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings (HDB) in an HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Reynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigen value problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.572-578
• /
• 2003

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings in a HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Raynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigenvalue problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.128-135
• /
• 2006

This paper presents a finite element method to analyze the free vibration of a flexible HDD composed of the spinning disk-spindle system with fluid dynamic bearings(FDBs), the head-suspension-actuator with pivot bearings, and the base plate with complicated geometry. Experimental modal testing shows that the proposed method well predicts tue vibration characteristics of a HDD. This research also shows that even the vibration motion of the spinning disk corresponding to half-speed whirl and the pure disk mode are transferred to a head-suspension-actuator and base plate through the air bearing and the pivot bearing consecutively. The proposed method can be effectively extended to investigate the forced vibration of a HDD and to design a robust HDD against shock.