• Steel and Composite Structures
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• v.25 no.2
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• pp.141-155
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• 2017

This paper presents an investigation into the magneto-thermo-mechanical vibration and damping of a viscoelastic functionally graded-carbon nanotubes (FG-CNTs)-reinforced curved microbeam based on Timoshenko beam and strain gradient theories. The structure is surrounded by a viscoelastic medium which is simulated with spring, damper and shear elements. The effective temperature-dependent material properties of the CNTs-reinforced composite beam are obtained using the extended rule of mixture. The structure is assumed to be subjected to a longitudinal magnetic field. The governing equations of motion are derived using Hamilton's principle and solved by employing differential quadrature method (DQM). The effect of various parameter like volume percent and distribution type of CNTs, temperature change, magnetic field, boundary conditions, material length scale parameter, central angle, viscoelastic medium and structural damping on the vibration and damping behaviors of the nanocomposite curved microbeam is examined. The results show that with increasing volume percent of CNTs and considering magnetic field, material length scale parameter and viscoelastic medium, the frequency of the system increases and critically damped situation occurs at higher values of damper constant. In addition, the structure with FGX distribution type of CNTs has the highest stiffness. It is also observed that increasing temperature, structural damping and central angle of curved microbeam decreases the frequency of the system.

• Smart Structures and Systems
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• v.20 no.1
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• pp.85-97
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• 2017

The aim of this research is to develop a new method to use magnetorheological (MR) damper for vibration control. It is a new way to achieve the MR damper response without the need to have detailed constant parameters estimations. The methodology adopted in designing the control structure in this work is based on the experimental results. In order to investigate and understand the behaviour of an MR damper, an experiment is first conducted. Force-displacement and force-velocity responses with varying current have been established to model the MR damper. The force for upward and downward motions of the damper piston is found to be increasing with current and velocity. In cyclic motion, which is the combination of upward and downward motions of the piston, the force with hysteresis behaviour is seen to be increasing with current. In addition, the energy dissipated is also found to be linear with current. A proportional-integral-derivative (PID) controller, based on the established characteristics for a quarter car suspension model, has been adapted in this study. A fuzzy rule based PID controller (F-PID) is opted to achieve better response for a varying frequency input. The outcome of this study can be used in the modelling of MR damper and applied to control engineering. Moreover, the identified behaviour can help in further development of the MR damper technology.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.605-613
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• 2007

The purpose of this study is to develop a structural analysis system of LNG pump tower structure. The system affords to build optimized finite element model and procedure of the pump tower structure. The pump tower structure is one of the most important components of LNG (liquefied natural gas) carriers. The pump tower structure is subject to sloshing load of LNG induced by ship motion depending on filling ratio. Three typer of loading components, which are thermal, inertia and self-gravity are considered in the analysis. The finite element analysis is performed with ANSYS commercial code. The failure of each members can be evaluated of API unity and punching shear in ABS rule. The GUI is newly developed using Tcl/tk script language. All these design and analysis procedures are embedded in to the analysis system successfully.

• Steel and Composite Structures
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• v.43 no.5
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• pp.581-601
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• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.5
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• pp.827-834
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• 2022

Recently, marine surveys using unmanned ships are attracting attention, and research on small unmanned ships using sails is on the rise. Sail drones can be used for marine surveys, monitoring, and pollution management. Therefore, in this study, using the method of estimating the ship speed for twin sail drones, the optimal conditions for sailing are checked, and the performance to be considered in the initial design stage, such as the motion performance and resistance of the sail drone. Consequently, the twin sail drone had a speed lower than 2.0 m/s, and the stability satisfied the rule by DNV. In addition, the maximum speed at an angle of attack of 20° at TWA 100° was 1.69 m/s and that at an angle of attack of 25° at TWA 100° was 1.74 m/s.

• Journal of Oral Medicine and Pain
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• v.31 no.3
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• pp.231-236
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• 2006

Rheumatoid arthritis(RA) is an of autoimmune inflammatory systemic disease. It is characterized by uncontrolled proliferation of synovial tissue and a wide array multisystem comorbidities. The disease may involve any joint of the body, but often statrs in the peripheral joints. It was reported that more than 50% of RA patients exhibit clinical involvement of TMJ. This report is a case report of dental management and progression for 16 months in patients who had severe bony change in TMJ involved rheumatoid arthritis Dental management was included palliative treatment such as interocclusal splints, physical therapy, mouth opening exercise. Although it was progressed rapidly osteolytic bone change during follow-up, no more advanced occulsal change and improved symptom and jaw motion. Further investigations about rule of dentistry in TMJ involvement in RA maybe needed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.9-20
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• 2018

Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.5
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• pp.487-495
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• 2016

In the offshore project such as semi-submersible FPU and FPSO, the free fall type life boat called TEMPSC (Totally Enclosed Motor Propelled Survival Craft) has been installed for the use of an emergency evacuation of POB (People on Board) from the topside platform. For the design of life boat arrangement for semi-submersible FPU in the initial design stage, the drop height and launch angle are required fulfill with the limitation of classification society rule and Company requirement, including type of approval as applicable when intact and damage condition of the platform. In this paper, we have been performed the numerical studies to find proper arrangement for the life boats consider drop height in various environmental conditions such as wave, wind and current. In the calculations, the contributions from static and low frequency (LF) motions are considered from the hydrodynamic and mooring analysis as well as damage angle from the intact and damage stability analysis. Also, Air-gap calculation at the life boat positions has been carried out to check the effect on the life boat arrangement. The air-gap assessment is based on the extreme air-gap method includes the effect of 1st order wave frequency (WF) motions, 2nd order low frequency roll/pitch motion, static trim/heel and set down.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.9
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• pp.1759-1771
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• 1994

We proposed the iterative image restoration method based on the method of steepest descent with a regularization constraint for restoring the noisy motion-blurred images. The conventional method proposed by Jan Biemond et al, had drawback to amplify the additive noise and make ringing effects in the restored images by determining the value of regularization parameter experimentally from the degraded image to be restored without considering local information of the restored one. The method we proposed had a merit to suppress the noise amplification and restoration error by using the regularization parameter which estimate the value of it adaptively from each pixels of the image being restored in order to reduce the noise amplification and ringing effects efficiently. Also we proposed the termination rule to stop the iteration automatically when restored results approach into or diverse from the original solution in satisfaction. Through the experiments, proposed method showed better result not only in a MSE of 196 and 453 but also in the suppression of the noise amplification in the flat region compared with those proposed by Jan Biemond et al. of which MSE of 216 and 467 respectively when we used 'Lean' and 'Jaguar' images as original images.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.201-212
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• 2023

The inscription of Cheonsang Yeolcha Bunyajido (天象列次分野之圖) has the sun's locations at the equinoxes, which must have been copied from the astronomical treatises in Chinese historical annals, Songshu (宋書) and Jinshu (晉書). According to the treatises, an astronomer Wang Fan (王蕃, 228-266 CE) referred those values from a calendrical system called Qianxiangli (乾象曆, 223 CE), from which it is confirmed that it adopted the sun's location at the winter solstice of the $(21{\frac{1}{4}})^{th}$ du of the 8th lunar lodge Dou (斗) as the reference direction for equatorial lodge angles. This indicates that the sun's locations at equinoxes and solstices in the calendrical system are the same as those in Jingchuli (景初曆, 237 CE). Hence, we propose that the sun's location at the autumnal equinox in Cheonsang Yeolcha Bunyajido should be corrected from 'wu du shao ruo' (五度少弱), meaning the $(5{\frac{1}{6}})^{th}$ du, to 'wu du ruo' (五度弱), meaning the $(4{\frac{11}{12}})^{th}$ du, of the first lunar lodge Jiao (角), as seen in Jingchuli. We reconstruct the polar coordinate system used in circular star charts, assuming that the mean motion rule was applied and its reference direction was the sun's location at the winter solstice. Considering the precession, we determined the observational epoch of the sun's location at the winter solstice to be t_o = -18.3 ± 43.0 adopting the observational error of the so-called archaic determinatives (古度). It is noteworthy that the sun's locations at equinoxes inscribed in Cheonsang Yeolcha Bunyajido originated from Houhan Sifenli (後漢 四分曆) of the Latter Han dynasty (85 CE), while the coordinate origin in the star chart is related to Taichuli (太初曆) of the Former Han dynasty (104 BCE).