• Structural Engineering and Mechanics
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• v.70 no.6
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• pp.737-750
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• 2019

This paper investigates the static and dynamic behaviors of imperfect single walled carbon nanotube (SWCNT) modeled as a beam structure by using energy-equivalent model (EEM), for the first time. Based on EEM Young's modulus and Poisson's ratio for zigzag (n, 0), and armchair (n, n) carbon nanotubes (CNTs) are presented as functions of orientation and force constants. Nonlinear Euler-Bernoulli assumptions are proposed considering mid-plane stretching to exhibit a large deformation and a small strain. To simulate the interaction of CNTs with the surrounding elastic medium, nonlinear elastic foundation with cubic nonlinearity and shearing layer are employed. The equation governed the motion of curved CNTs is a nonlinear integropartial-differential equation. It is derived in terms of only the lateral displacement. The nonlinear integro-differential equation that governs the buckling of CNT is numerically solved using the differential integral quadrature method (DIQM) and Newton's method. The linear vibration problem around the static configurations is discretized using DIQM and then is solved as a linear eigenvalue problem. Numerical results are depicted to illustrate the influence of chirality angle and imperfection amplitude on static response, buckling load and dynamic behaviors of armchair and zigzag CNTs. Both, clamped-clamped (C-C) and simply supported (SS-SS) boundary conditions are examined. This model is helpful especially in mechanical design of NEMS manufactured from CNTs.

• International Journal of Highway Engineering
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• v.17 no.5
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• pp.19-24
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• 2015

PURPOSES : The noise, which is typically generated by fast moving vehicles, can be intercepted by installing a noise barrier with a soundproof panel. However, reflections from the panels cause secondary noise, and hence lower the effectiveness of the panels. In this study, the reduction of reflection noise by considering the shape, especially zigzag one, of the soundproof panel have been evaluated. METHODS : The simulation model used in this study was Nord2000, which simulates real-road situations effectively. Based on the simulation results, the joining angle of $133^{\circ}$ with the pattern width (a) equal to 2 m and the projection height (b) equal to 0.5 m was adapted in the zigzag shape as the best profit designing factors. RESULTS: The measuring results at middle height, 15 m showed reduction at all points except the point with average -1.6 dB. At a greater height of 30 m, 2 points showed reduction. A real-sized facility was constructed to investigate the reflected sound from a zigzag shaped panel up to the height of 5 m. CONCLUSIONS: The reduction effects were detected in all the receive points in the range of 2-6 m distances and 1-5 m heights comparing the plane panel. Compared to plane panel, the noises are reduced at an average of 2.4 dBA.

• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.10-16
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• 2016

A trigonometric Layerwise higher order shear deformation theory (TLHSDT) is developed and implemented for free vibration and buckling analysis of laminated composite and sandwich plates by analytical and finite element formulation. The present model assumes parabolic variation of out-plane stresses through the depth of the plate and also accomplish the zero transverse shear stresses over the surface of the plate. Thus a need of shear correction factor is obviated. The present zigzag model able to meet the transverse shear stress continuity and zigzag form of in-plane displacement continuity at the plate interfaces. Hence, botheration of shear correction coefficient is neglected. In the case of analytical method, the governing differential equation and boundary conditions are obtained from the principle of virtual work. For the finite element formulation, an efficient eight noded $C^0$ continuous isoparametric serendipity element is established and employed to examine the dynamic analysis. Like FSDT, the considered mathematical model possesses similar number of variables and which decides the present models computationally more effective. Several numerical predictions are carried out and results are compared with those of other existing numerical approaches.

• Structural Engineering and Mechanics
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• v.71 no.2
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• pp.197-210
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• 2019

Probabilistic buckling behavior of sandwich panel considering random system parameters using a radial basis function (RBF) approach is presented in this paper. The random system properties result in an uncertain response of the sandwich structure. The buckling load of laminated sandwich panel is obtained by employing higher-order-zigzag theory (HOZT) coupled with RBF and probabilistic finite element (FE) model. The in-plane displacement variation of core as well as facesheet is considered to be cubic while transverse displacement is considered to be quadratic within the core and constant in the facesheets. Individual and combined stochasticity in all elemental input parameters (like facesheets thickness, ply-orientation angle, core thickness and properties of material) are considered to know the effect of different degree of stochasticity, ply- orientation angle, boundary conditions, core thickness, number of laminates, and material properties on global response of the structure. In order to achieve the computational efficiency, RBF model is employed as a surrogate to the original finite element model. The stiffness matrix of global response is stored in a single array using skyline technique and simultaneous iteration technique is used to solve the stochastic buckling equations.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.269-277
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• 2019

Using the non-local elasticity theory, Timoshenko beam model is developed to study the non- local buckling of Triple-walled carbon nanotubes (TWCNTs) embedded in an elastic medium under axial compression. The chirality and small scale effects are considered. The effects of the surrounding elastic medium based on a Winkler model and van der Waals' (vdW) forces between the inner and middle, also between the middle and outer nanotubes are taken into account. Considering the small-scale effects, the governing equilibrium equations are derived and the critical buckling loads under axial compression are obtained. The results show that the critical buckling load can be overestimated by the local beam model if the small-scale effect is overlooked for long nanotubes. In addition, significant dependence of the critical buckling loads on the chirality of zigzag carbon nanotube is confirmed. Furthermore, in order to estimate the impact of elastic medium on the non-local critical buckling load of TWCNTs under axial compression, the use of these findings are important in mechanical design considerations, improve and reinforcement of devices that use carbon nanotubes.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.161-169
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• 2017

Recently, ship owners have been requiring the assessment of the maneuverability of twin-screw ships under mechanical failures. Because this kind of assessment has not yet been conducted, it is necessary to study the types of machinery failures that can significantly affect the maneuverability of a ship, and to construct a procedure to simulate the maneuvering behavior under such failures. In this paper, the sole focus is the steering system failure from among the variety of failure types, and the maneuvering behavior of the ship under the single rudder failure is simulated for an investigation of the unique characteristics. First, the mathematical model for the twin-screw container ship is verified by comparing the simulated results for the $35^{\circ}$ turning test, $10^{\circ}/10^{\circ}$ zigzag test, and $20^{\circ}/20^{\circ}$ zigzag test under the normal operating condition with those obtained from free running model tests. After the IMO maneuvering tests are additionally simulated under the single rudder failure, the results are reviewed to investigate the maneuvering characteristics that are due to the failure. Further, the $35^{\circ}/35^{\circ}$ zigzag test and the $35^{\circ}$ turning test are simulated to additionally investigate the effects of the single rudder failure on the steering and turning abilities.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.121-127
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• 2014

An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a single-layer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are $0.86MPa{\sqrt{m}}$ and $0.93MPa{\sqrt{m}}$, respectively.

• Journal of Power Electronics
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• v.7 no.3
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• pp.191-202
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• 2007

This paper deals with pulse multiplication in zigzag connected autotransformer based 12-pulse AC-DC converters feeding vector controlled induction motor drives (VCIMD) for improving the power quality at the point of common coupling (PCC) without using a Zero-Sequence-Blocking-Transformer (ZSBT). The proposed 24-pulse AC-DC converter is based on the principle of DC ripple re-injection technique for pulse multiplication and harmonic mitigation. The design of the autotransformer is carried out for the proposed AC-DC converter and the effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC-DC converter. Test results from a laboratory developed prototype, along with simulated results, are presented to validate the design and model of the proposed 24-pulse AC-DC converter.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.3
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• pp.204-214
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• 2017

Recently, ship owners have been requiring the assessment of the maneuverability of a twin-screw ship under machinery failures. In this paper, we are only focused on the propulsion failure among propulsion failure, power supply failure, steering system failure etc. First of all, the mathematical model for the twin-screw 174K LNGC is verified by comparing the simulated results for $35^{\circ}$ turning test, $10^{\circ}/10^{\circ}$ zigzag test and $20^{\circ}/20^{\circ}$ zigzag test under normal operating condition and those obtained from free running model tests. And, sea trial results of 216K LNGC under single propeller failure are compared with those of 174K LNGC under identical condition to verify the proposed method to predict maneuverability under single propeller failure. After the straight line maneuver is simulated under the single propeller failure, the speed and equilibrated heading and rudder deflection angles at steady state are predicted. After the IMO maneuvering tests are simulated under the single propeller failure, the results are reviewed to investigate the maneuvering characteristics due to the failure.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.494-500
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• 2015

It has been reported that a ship sailing in shallow water possesses better straight-line stability due to the change of fluid flow around the ship. This tendency affects manoeuvring characteristics of the ship. To investigate this phenomenon, indoor free running model test(FRMT) on KVLCC2 was carried out in three water depth conditions(H/T = 1.2, 1.5 & 2.0). Turning circle tests(± 35° ) and zigzag tests(± 20° /5° and ± 20° /10° ) were conducted with newly developed indoor FRMT system, and the manoeuvring results were compared with test results from other institutes. As the water depth decreased, the yaw rate of the ship decreased, and the distances of circular trajectories at the same heading angle increased in the turning circle tests. The first overshoot angles of the zigzag tests decreased. From both tests, the time for course change increased as the water depth decreased. These manoeuvring characteristics show that KVLCC2 in shallow water becomes more stable in terms of straight-line stability.