• Steel and Composite Structures
• /
• v.18 no.4
• /
• pp.1063-1081
• /
• 2015

In this paper, a new nonlocal hyperbolic refined plate model is presented for free vibration properties of functionally graded (FG) plates. This nonlocal nano-plate model incorporates the length scale parameter which can capture the small scale effect. The displacement field of the present theory is chosen based on a hyperbolic variation in the in-plane displacements through the thickness of the nano-plate. By dividing the transverse displacement into the bending and shear parts, the number of unknowns and equations of motion of the present theory is reduced, significantly facilitating structural analysis. The material properties are assumed to vary only in the thickness direction and the effective properties for the FG nano-plate are computed using Mori-Tanaka homogenization scheme. The governing equations of motion are derived based on the nonlocal differential constitutive relations of Eringen in conjunction with the refined four variable plate theory via Hamilton's principle. Analytical solution for the simply supported FG nano-plates is obtained to verify the theory by comparing its results with other available solutions in the open literature. The effects of nonlocal parameter, the plate thickness, the plate aspect ratio, and various material compositions on the dynamic response of the FG nano-plate are discussed.

• Smart Structures and Systems
• /
• v.16 no.4
• /
• pp.579-591
• /
• 2015

This paper investigates a magnetoelectric (ME) vibration energy harvester that can scavenge energy in arbitrary directions in a plane as well as wide working bandwidth. In this harvester, a circular cross-section cantilever rod is adopted to extract the external vibration energy due to the capability of it's free end oscillating in arbitrary in-plane directions. And permanent magnets are fixed to the free end of the cantilever rod, causing it to experience a non-linear force as it moves with respect to stationary ME transducers and magnets. The magnetically coupled cantilever rod exhibits a nonlinear and two-mode motion, and responds to vibration over a much broader frequency range than a standard cantilever. The effects of the magnetic field distribution and the magnetic force on the harvester's voltage response are investigated with the aim to obtain the optimal vibration energy harvesting performances. A prototype harvester was fabricated and experimentally tested, and the experimental results verified that the harvester can extract energy from arbitrary in-plane directions, and had maximum bandwidth of 5.5 Hz, and output power of 0.13 mW at an acceleration of 0.6 g (with $g=9.8ms^{-2}$).

• Smart Structures and Systems
• /
• v.16 no.5
• /
• pp.891-918
• /
• 2015

In many of microdevices a part of a microbeam is covered by a piezoelectric layer. Depend on the application a DC or AC voltage is applied between upper and lower side of the piezoelectric layer. A common method in many of previous works for evaluating the response of these structures is discretizing by Galerkin method. In these works often single mode shape of a uniform microbeam i.e. the microbeam without piezoelectric layer has been used as comparison function, and so the convergence of the solution has not been verified. In this paper the Galerkin method is used for discretization, and a comprehensive analysis on the convergence of solution of equation that is discretized using this comparison function is studied for both clamped-clamped and clamped-free microbeams. The static and dynamic solution resulted from Galerkin method is compared to the modal expansion solution. In addition the static solution is compared to an exact solution. It is denoted that the required numbers of uniform microbeam mode shapes for convergence of static solution due to DC voltage depends on the position and thickness of deposited piezoelectric layer. It is shown that when the clamped-clamped microbeam is coated symmetrically by piezoelectric layer, then the convergence for static solution may be obtained using only first mode. This result is valid for clamped-free case when it is covered by piezoelectric layer from left clamped side to the right. It is shown that when voltage is AC then the number of required uniform microbeam shape mode for convergence is much more than the number of required mode in modal expansion due to the dynamic effect of piezoelectric layer. This difference increases by increasing the piezoelectric thickness, the closeness of the excitation frequency to natural frequency and decreasing the damping coefficient. This condition is often indefeasible in microresonator system. It is concluded that discreitizing the equation of motion using one mode shape of uniform microbeam as comparison function in many of previous works causes considerable errors.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.26 no.2
• /
• pp.25-31
• /
• 1989

Two-dimensional large-amplitude motions in regular harmonic wave are treated in time domain, by satisfying the exact body boundary condition and the linear free surface condition. For the present numerical calculation, the method of free-surface spectral representation with simple source distribution on the instantaneous body surface has been extended to include the effect of the incident wave. Calculations of the wave exciting force are performed for a submerged circular cylinder fixed or oscillating with large amplitude. Especially, nonlinear effects on the time-mean forces are studied in detail. It is shown that relative motion between the body and the fluid particle gives a significant effect on the lift and drift forces. Also, large-amplitude motion of a submerged circular cylinder and that of a floating Lewis-form cylinder are directly simulated in time domain. In the calculation results, some nonlinear effects are shown.

• Ocean Systems Engineering
• /
• v.3 no.3
• /
• pp.219-236
• /
• 2013

The accurate prediction of motion in waves of a marine vehicle is essential to assess the maximum sea state vs. operational requirements. This is particularly true for small crafts, such as Autonomous Surface Vessels (ASV). Two different numerical methods to predict motions of a SWATH-ASV are considered: an inviscid strip theory initially developed at MIT for catamarans and then adapted for SWATHs and new a hybrid strip theory, based on the numerical solution of the radiation forces by an unsteady viscous, non-linear free surface flow solver. Motion predictions obtained by the viscous flow method are critically discussed against those obtained by potential flow strip theory. Effects of viscosity are analyzed by comparison of sectional added mass and damping calculated at different frequencies and for different sections, RAOs and motions response in irregular waves at zero speed. Some relevant conclusions can be drawn from this study: influence of viscosity is definitely non negligible for SWATH vessels like the one presented: amplitude of the pitch and heave motions predicted at the resonance frequency differ of 20% respectively and 50%; in this respect, the hybrid method with fully non-linear, viscous free surface calculation of the radiation forces turns out to be a very valuable tool to improve the accuracy of traditional strip theories, without the burden of long computational times requested by fully viscous time domain three dimensional simulations.

• Archives of Reconstructive Microsurgery
• /
• v.4 no.1
• /
• pp.16-22
• /
• 1995

We analyzed 11 children who underwent epiphyseal transplantation to the forearm for manage growing deformity ranged from 2 years 6 months to years(average 5 years 10 months) follow-up period. Etiologies of the functional impairment of the eleven were five traumatic, three congenital and three tumorous conditions. Lesions of epiphysis were distal radius in eight patients and distal ulna in three patients. Operation was performed with removal of non-functioning or deformed epiphysis followed by transplantation of free vascularized proximal fibular epiphysis with microvascular anastomesis. Evaluation was performed radiologically and functionally. The 9(81.8%) patients showed growth of transplanted epiphysis by radiological examination during follow up. At the last follow up, average growth rate was 0.86cm per year excepts 2 cases of no growth. Active wrist motion near normal to contralateral joint was achieved in 7 patients. In other 2 patients, active joint motion was improved but weaker than contralateral joint. Complications on donor site were two transient peroneal nerve palsy which have been resolved after 2 and 5 months post operation and one valgus ankle deformity. The ankle deformity was corrected with $Langenski\"{o}ld$ operation of the dital tibiofibular fusion. At recipient site, there was one superficial infection and it was easily controlled by systemic antibiotics. Many subsequent reports have described successful nonvascularized epiphyseal transplante, but overall results have been inconsistent and unsatisfactory. Other experimental and clinical studies in the transfer of vascularized epiphyses has encourage its clinical application. We also could gel successful growth in several cases with free vascularized epiphyseal transplantation.

• Archives of Reconstructive Microsurgery
• /
• v.12 no.1
• /
• pp.38-43
• /
• 2003

Purpose : Various free flaps and pedicled island flaps are effective for reconstruction of soft tissue defect developed after tumor excision. We want to know the advantage of dorsalis pedis island flap for reconstruction of soft tissue defect caused by soft tissue tumor excision. Materials and Methods : Between 1992 and 2002, we performed 4 dorsalis pedis island flap procedure for reconstruction of soft tissue defect of lower limb developed after soft tissue tumor excision. Average age was 54.7 years old $(40{\sim}68)$, and male 2 cases, female 2 cases. The kinds and number of soft tissue tumors were 2 squamous cell carcinoma and 2 malignant melanoma. The procedures that we performed were all dorsalis pedis island flap. The analysis for the result of treatment was retrospectively accessed by physical examination and questionnaire for whether the change of symptom after operation, range of adjacent joint motion. Also we reviewed associated complication after operative treatment. Results : All dorsalis pedis island flaps were alive. There is no problem for activity of daily living, no skin necrosis and no limitation of motion of adjacent joint. In 1 case of them, the patients died of distant metastasis. Conclusion: Dorsalis pedis island flap procedure as a pedicled island flap procedure is very effective and easy operative procedure for reconstruction of soft tissue defect of lower limb developed after tumor excision compared to free flap procedure because there is no need for microvascular surgery, we can obtain relatively large flap and the lesion and flap donor site locate in the same limb.

• International Journal of Fluid Machinery and Systems
• /
• v.2 no.4
• /
• pp.363-374
• /
• 2009

The 2D flow around 13 similar stay-vane profiles with different trailing edge geometries is investigated to determinate the main characteristics of the excitation forces for each one of them and their respective dynamic behaviors when modeled as a free-oscillating system. The main goal is avoid problems with cracks of hydraulic turbines components. A stay vane profile with a history of cracks was selected as the basis for this work. The commercial finite-volume code $FLUENT^{(R)}$ was employed in the simulations of the stationary profiles and, then, modified to take into account the transversal motion of elastically mounted profiles with equivalent structural stiffness and damping. The k-$\omega$ SST turbulence model is employed in all simulations and a deforming mesh technique used for models with profile motion. The static-model simulations were carried out for each one of the 13 geometries using a constant far field flow velocity value in order to determine the lift force oscillating frequency and amplitude as a function of the geometry. The free-oscillating stay-vane simulations were run with a low mass-damping parameter ($m^*{\xi}=0.0072$) and a single mean flow velocity value (5m/s). The structural bending stiffness of the stay-vane is defined by the Reduced Velocity parameter (Vr). The dynamic analyses were divided into two sets. The first set of simulations was carried out only for one profile with $2{\leq}Vr{\leq}12$. The second set of simulations focused on determining the behavior of each one of the 13 profiles in resonance.

• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.3
• /
• pp.131-139
• /
• 1992

By introducing a body potential, the high-oder spectal method of Dommermuth and Yue(1987) is extended to treat the nonlinear interactions between the free surface and the submerged cylinder. A 2-dimensional numerical wave tank is developed based on this numerical scheme, and applied to the wave resistance problem and the wave maker problem. In the simulations, it is shown that the transient waves due to the impulsive start of the body motion make a practical obstacle to the acquisition of useful data from the numerical experiments. Gradual starting procedures are devised, and successful result of the quasi-steady state or the uniform regular wave group was obtained. Within the author's present knowledge, the present numerical scheme is one of the most efficient numerical schemes which can treat the nonlinear interactions between the free surface and the body motion in time-domain.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.6
• /
• pp.550-558
• /
• 2019

The roll motion of a general vessel, which is more influenced by resonance as compared to other motions, adversely affects the passenger and hull. Therefore, reducing the roll motion through an anti-rolling system is critical, and most ships use various devices such as anti-rolling tanks, bilge keels, and fin stabilizers to accomplish this. In this study, a simplified model is developed for the application of an anti-rolling device for unmanned semi-submersible vessels. The applied anti-rolling device is installed on the stern and stem of a ship using a pair of servo motors with added weight, and the motor is controlled through the Arduino. The moment of the motor is designed and implemented based on a mathematical model such that it is calculated through the restoring force according to the heel angle of the ship. The performance of the proposed system was verified by utilizing the roll damping coefficient calculated by the free-roll decay test and logarithmic decrement method and was validated by a towing tank test. The system is expected to be used for unmanned vessels to perform sustainable missions.