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Publications (71)
“Seong-Yeun Yoo, In-Kook Kang, Namhyun Kim, Sanggyu Kim, Kangil Choe” were not included as authors in the original publication [...]
The volume contents of composite materials directly affect the tensile strength of long-fiber-reinforced thermoplastics (LFTs). However, it is not easy to analyze how factors such as the fiber content and porosity affect the tensile strength of LFTs. With this motivation, we investigate the relationship between fiber content, porosity, and tensile...
Since most of the floating offshore wind turbines are in the hurricane’s path, it is essential to analyze the dynamic safety caused by the hurricane. At extreme wind speeds, the influence of hydrodynamic loads is relatively increased because the turbine is idling. In addition, the semi-submersible offshore wind turbine (FOWT) causes a slow drift mo...
The method proposed in this study is to determine the welding sequence to suppress welding de-formation using the strain directed as boundary (SDB) method. Welded joints are modeled by constructing tack welds and gaps as kinematic constraints in shell models. In addition, the SDB method considering the elastoplastic properties is used to evaluate t...
The wind tower block is welded with the flange to assemble the wind tower. The inherent strain due to local heating and cooling of the weld affects the flatness of the flange. Therefore, line heating is performed to satisfy the design criteria of the flange flatness, but the work variables depend on the operator’s empirical judgment. This study pro...
The aim of this work is to propose a new multiphysics mode synthesis (MMS) for the thermomechanical vibration problem. The present thermomechanical model is based on a state-space formulation, which consists of displacement, velocity, and temperature shift. The state-space based thermomechanical formulation is symmetric unlike a conventional non-sy...
Increases in energy demand and waste are a major cause of natural resource depletion and environmental pollution, and technology capable of processing waste to convert it into energy is required to mitigate this issue. Hydrothermal carbonization (HTC) is an example of this technology that can convert waste into energy, and various studies have been...
The mechanical properties of polyamide 6 glass fiber (PA6/GF) long-fiber-reinforced thermoplastic (LFT) composites were characterized by studying the process conditions in terms of manufacturing methods (direct extrusion and pultrusion) and material characteristics (void content and fiber volume fraction). The LFT composites prepared through the pu...
This study aims to analyze the effects of dynamic motion and structural response of semi-submersible floating offshore wind turbine structures (FOWTs) in waves generated in hurricane environments. The extreme environment utilizes numerical simulation data of hurricanes and is divided into low-frequency and high-frequency components based on wave-ag...
A composite neural network (NN) is a way to improve the reliability of a prediction field by implementing a multi-fidelity model when high-fidelity data are extremely limited. The reliability of the composite NN depends highly on the quantity and quality of low-fidelity data. Satisfying both issues simultaneously is difficult in engineering practic...
In the shipbuilding industry, welding is the main technique used to join steel structures. There is a lifting process, post-welding, that can eliminate the correction effect of line heating. Line heating is reperformed after the lifting process. This can significantly delay the ship assembly process. Herein, we present a design method for installin...
An interpolation multipoint constraints (MPCs) formulation with selection criteria of the additional degree of freedoms is proposed for the simulation of flexible multibody dynamics (FMBD). The proposed formulation, which addresses invertible condition problems, overcomes the limitations in the selection of dependent degrees of freedom (DOFs) in in...
The aim of this work is to propose a new multiphysics mode synthesis (MMS) for the thermomechanical vibration problem. The present thermomechanical model is based on a state-space formulation, which consists of displacement, velocity, and temperature shift. The state-space based thermomechanical formulation is symmetric unlike a conventional non-sy...
The accuracy of the reduced-order model (ROM) mainly depends on the selected basis. Therefore, it is essential to compute an appropriate basis with an efficient numerical procedure when applying ROM to nonlinear problems. In this paper, we propose an online adaptive basis technique to increase the quality of ROM while decreasing the computational c...
Abstract - This research analyzes the fluid pressure response acting on the inner wall of steel water tanks subjected to seismic actions including horizontal and vertical ground motion components using computational fluid dynamics. To achieve this aim, this research proposes a computational hydrodynamic modeling technique by validating the simulate...
In present study, laminates with the type of [±θ°]S and [0°2/±θ°]S are investigated in order to clearly show the effect of material shear nonlinearity, and then theoretical predictions are compared with experimental data. In the whole process of generating failure envelopes, secant shear modulus instead of initial shear modulus is used for accurate...
The purpose of this study is to optimize the processing conditions (temperature, pressure, process time, yield rate) for the conversion of biomass to a high-energy density biofuel. The hydrothermal polymerization (HTP) catalytic process has been developed for production of biofuel via hydrothermal processing using an acid-based catalyst. This study...
The present study conducted an analysis of waves and wind on the west coast of Jeju Island in South Korea to derive the loads for a structural analysis under operational, extreme, and survival conditions and then evaluated the structural strength of the DeepCwind semi-submersible platform of NREL for 5 MW wind turbine. As a floating structure is ex...
We analyzed the dynamic response characteristics of a floating offshore windturbine structure influenced by the wave energy under extreme metocean conditions. Wave energy consists of swell and wind sea components, and the wave age criteria method was used to separate each component of wave energy. We then applied a hydrodynamic load to the platform...
In this study, we analyzed the effect of the second hydrodynamic loads on mooring line response and damage equivalent fatigue by wave energy components under the extreme sea conditions. To examine this effect, the dynamic responses of offshore wind turbine structures were evaluated by separating each component and coupling it with a HydroDyn module...
This study aims at evaluating nonlinear hydrodynamic pressures on the inner wall of rigid cylindrical tanks, resulting from liquid sloshing due to the simultaneous action of two horizontal and one vertical ground motion components. For this purpose, the computational model that can predict realistic dynamic fluid responses is validated through comp...
A general formulation is presented to linear multipoint constraints, underlying that the linkages of mechanical system dynamics are governed by kinematic constraint conditions. Both rigid and interpolated multipoint constraints are then described in a formulation based on the Lagrange multiplier adjunction. The proposed formulation can directly off...
In the wave energy generated under an extreme sea condition, the swell in the low-frequency has a significant influence on the floating offshore wind structure behavior. If the mooring tension is calculated considering the hydrodynamic load acting on the floating structure in the first order, the response can be underestimated because it is smaller...
In this study, the simple analysis method for simulating weld thermal deformation is analyzed. The deformation caused by the welding of the thin plate shows the deformed shape mixed with the in plane deformation and the out of plane deformation, and the prediction by the simple analysis method has a time advantage in comparison with the prediction...
The wave energy generated by the occurrence of a tropical cyclone and hurricane is in a bi-modal form that is distinctly separated by the swell and wind sea. The wind sea influencing the local wind has a large change both in energy with time and in frequency, while the wave energy increases in the swell, but the swell has a small cycle variation. T...
Influence of material shear nonlinearity on multidirectional laminates in terms of failure envelopes was investigated. In applying classic laminate theory, elastic constants were employed in transverse and longitudinal directions, while initial shear modulus was substituted by the secant shear modulus, which was achieved by means of Ramberg-Osgood...
We present the prediction of nonlinear in-plane shear stress strain curves based on complementary strain energy density function. When the [0°] unidirectional laminates are subjected to a combination of shear stresses and axial stresses, the predicted shear responses of laminates are compared with measured experimental data for verifying this accur...
This paper presents the results of a simulation-based study aimed at evaluating the response of floating offshore wind structures in offshore environmental conditions during hurricanes. The marine environment data used in the study was obtained through simulation of hurricane scenarios using the University of Miami Coupled Model (UMCM), one of the...
This study examines earthquake-induced sloshing effects on liquid storage tanks using computation fluid dynamics. To achieve this goal, this study selects an existing square steel tank tested by Seismic Simulation Test Center at Pusan National University as a case study. The model validation was firstly performed through the comparison of shaking t...
A white-box friction draft gear model has been developed. All components of the draft gear are considered. The distinctive feature of the model, as compared to its predecessor, is the transitional characteristic, which accounts for the effect of elastic deformations of the draft gear housing on the position of the friction wedge system components u...
In this study, simulations of shunting impacts for groups of freight cars that include up to six cars are considered. The simulation technique employs a white-box improved dynamic model of friction draft gear considering all its components and detailed finite element models of the freight cars. The key differences between the one-to-one shunting im...
A solid tetrahedral finite element employing the absolute nodal coordinate formulation (ANCF) is presented. In the ANCF, the mass matrix and vector of the generalized gravity forces used in the equations of motion are constant, whereas the vector of the elastic forces is highly nonlinear. The proposed solid element uses translations of nodes as set...
In this study an efficient three-stage method for fatigue life assessment combining multibody dynamic analysis and finite element method is considered in the context of investigating the performance of a serial stilt sprayer. The proposed approach enables accurate simulation of dynamics for a vehicle subjected to real loads and finite element analy...
The principle of mass detection using carbon nanotube (CNT) resonators is based on the detection of the resonant frequency shift due to an attached mass. Although CNT resonators can easily show a nonlinear oscillation behavior, there is a lack of studies on the influence of the design parameters and the nonlinear dynamic behavior on the detection s...
Background:
Biaxial (BX) and triaxial (TX) composite laminates with ±45° angled plies have been widely used in wind turbine blades. As the scale of blades increases, BX and TX laminates with shallow-angled plies (i.e. off-axis ply angle <45°) might be utilized for reducing mass and/or improving performance. The compressive properties of shallow-an...
In the present study we carried out a dynamic analysis of a CNT-based mass sensor by using a finite element method (FEM)-based nonlinear analysis model of the CNT resonator to elucidate the combined effects of thermal effects and nonlinear oscillation behavior upon the overall mass detection sensitivity. Mass sensors using carbon nanotube (CNT) res...
In this paper, a new and simple optical technique to accurately measure the straightness errors of a linear stage is proposed. To improve the performance, including the measurement sensitivity and resolution of the measurement system, and to simultaneously measure two-dimensional straightness errors (2D straightness errors), an optical system was d...
The safety of vehicles has been studied in the past on the basis of the safety of passengers. Recently, pedestrian safety has also attracted attention. The pedestrian protection performance of vehicles has gradually improved but is still not sufficiently good. Devices such as the pop-up hood and the pedestrian protection airbag system are generally...
The bodies of many railway freight cars in many countries of the world are coupled to the running gear by means of a body centre plate that makes a friction pair with a centre bowl. During motion, the bogie is rotated and moved with respect to the car body. This leads to wear on the contact surfaces. Lubrication is inexpedient in this case because...
A mass sensor using a nano-resonator has high detection sensitivity, and mass sensitivity is higher with smaller resonators. Therefore, carbon nanotubes (CNTs) are the ultimate materials for these applications and have been actively studied. In particular, CNT-based nanomechanical devices may experience high temperatures that lead to thermal expans...
Frequency response analysis is an important computational tool to simulate and understand the dynamic behavior of structures. However, for more target frequency and/or larger scale structures, the runtime is greatly increased. Furthermore, increasingly complex degree of freedom problems intended to improve the accuracy of the analysis results is cr...
Accounting for surface roughness in contact simulation can significantly change the calculated values of contact stresses for many objects. This can be important for high-precision mechanisms where displacements of tens of micrometers are required, such as a machining attachment used to clamp machine elements during processing on high precision mac...
The problem of the evolution of a single spherical bubble in an infinite liquid is considered, as the result of a variation of the pressure in the liquid at an infinite distance from the bubble. It has been assumed the bubble is filled with vapor from the surrounding liquid or insoluble gas. The question of the fulfillment of the integral energy co...
The problem of the response of a single spherical vapor bubble is considered for the case of an abrupt increase of pressure in the surrounding infinite liquid. The mathematical model adopted is based on the assumption of the uniformity of pressure, temperature and density throughout the bubble volume. The temperature field around the bubble is calc...
Gallium oxide nanowires were synthesized via chemical vapor deposition of gallium/gallium oxide mixture and oxygen. The diameter of the nanowires is 30−80 nm with an average value of 50 nm. They consist of single-crystalline monoclinic crystal. While the nanowires grown without catalyst exhibit a significant planar defect, the nanowires grown with...
Porous structured GaN nanowires were synthesized with a large scale by chemical vapor deposition of Ga/Ga2O3/B2O3/C mixture under NH3 flow. The average diameter is 40 nm and the length is up to 1 mm. The porous GaN nanowires consist of the wurtzite single crystal grown with the [0 1 1] direction parallel to the wire axis. The size of pores is 5–20...
Gallium nitride nanorods were synthesized by a chemical vapor deposition using the reaction of gallium/gallium nitride with ammonia. All nanorods have, exclusively, a triangle cross section with an average diameter of 50 nm. They consist of single-crystalline wurtzite structure crystal grown with the [010] direction. X-ray diffraction and Raman spe...
A large quantity of GaN nanostructures (nanosaws) was produced by a chemical vapor deposition of Ga/Ga2O3/B2O3 mixture under NH3 flow. All of them have a single-edged sawlike configuration. The average width of the nanosaw is in the range 100 nm–1 μm and the thickness is about 1/10 of the average width. They consist of single-crystalline wurtzite s...
Nitrogen-doped gallium phosphide nanobelts were directly synthesized via a sublimation of ball-milled powders under ammonia flow. The average width of the nanobelts is 300 nm and the thickness is about 1/10 of the width. They consist of single-crystalline zinc blende structure crystal with the [111] direction parallel to the belt axis. Electron ene...
We present a novel method to synthesize high-density silicon nitride nanowires directly from the silicon substrates via a catalytic reaction under ammonia or hydrogen flow at 1200 °C. Gallium, gallium nitride, and iron nanoparticles deposited on the silicon substrate were used as catalysts. Gallium nitride can act as a nitrogen source under hydroge...
Aligned silicon carbide nanowires were synthesized directly from the silicon substrates via a novel catalytic reaction with a methane-hydrogen mixture at 1,100 degrees C, with a mean diameter of 40 nm and length of 500 microm; they consist of a single-crystalline zinc blende structure crystal in the [111] growth direction; X-ray diffraction, Raman,...
Bulk-quantity wurtzite structured gallium nitride nanobelts have been synthesized on a large area of the silicon substrate by a reaction of gallium/gallium oxide and ammonia using nickel and boron oxide as catalysts. The widths of the nanobelts are in the range from 100 nm to 1 μm and the thickness is about 1/10 of the width. They usually have an u...
Gallium phosphide nanowires were synthesized by sublimation of ball-milled powders and are straight, cylindrical, and smooth in surface, with mean diameter of 40 nm and length up to 300 μm; they have a single-crystalline zinc blende structure with [111] growth direction; X-ray diffraction and Raman spectroscopy reveal a high degree of crystallinity...
Single-crystalline wurtzite gallium nitride nanobelts were synthesized by thermal reaction of gallium, gallium nitride, and ammonia using iron and boron oxide as catalysts. The structure of nanobelts was investigated by high-resolution transmission electron microscopy with electron energy-loss spectroscopy. They have a distinctive triangle tip and...
Gallium nitride nanowires were synthesized on silicon substrates by chemical vapor deposition using the reaction of gallium and gallium nitride mixture with ammonia. Iron nanoparticles were used as catalysts. The diameter of nanowires is uniform as 25 nm and the lengths are 20–40 μm. The nanowires have single crystalline wurtzite structure with a f...
Bulk-quantity single crystalline wurtzite gallium nitride nanowires with a mean diameter of 25 nm were synthesized on silicon substrate using a catalyst-assisted reaction of gallium and gallium nitride mixture with ammonia. They exhibit a strong and broad photoluminescence in the energy range of 2.9-3.6 eV with no yellow band. X-ray diffraction and...
Collisional quenching of vibrationally excited methyl-substituted pyrazine and pyridine molecules by CO2 has been investigated using the infrared emission of C–H stretching vibrations in gas phase. The methyl substitution increases the collisional quenching efficiency, but its enhancement effect decreases as the number of methyl groups increases. T...
The collisional quenching of vibrationally excited methyl-substituted pyrazine series with an initial energy of 38000–39000 cm−1 by He, Ar, and Kr has been investigated using time-resolved infrared fluorescence of C–H stretching vibrations. The methyl group facilitates the quenching process, but its enhancement effect decreases as the number of met...
An approach for the automatic generation and refinement of finite element meshes over nonconvex domains subdivided by multibody connected, rigid body-movable subdomains has been developed. The basis of this method relies in order on (1) the automatic insertion of nodes on the digitized boundaries and within the interiors of movable subdomains, (2)...
An approach for the automatic generation and refinement of three dimensional finite element meshes subdivided by multiply connected, rigid body movable subdomains has been developed. A combination of computational geometry and geometric modeling techniques have been employed to implement parametric computer-aided design based on the finite element...
Thesis (D. Eng. Sci.)--Columbia University, 1991. Includes bibliographical references (leaves 131-142).
