• Structural Engineering and Mechanics
• /
• 제86권2호
• /
• pp.167-180
• /
• 2023

This work applies a four-known quasi-3D shear deformation theory to investigate the bending behavior of a functionally graded plate resting on a viscoelastic foundation and subjected to hygro-thermo-mechanical loading. The theory utilizes a hyperbolic shape function to predict the transverse shear stress, and the transverse stretching effect of the plate is considered. The principle of virtual displacement is applied to obtain the governing differential equations, and the Navier method, which comprises an exponential term, is used to obtain the solution. Novel to the current study, the impact of the viscoelastic foundation model, which includes a time-dependent viscosity parameter in addition to Winkler's and Pasternak parameters, is carefully investigated. Numerical examples are presented to validate the theory. A parametric study is conducted to study the effect of the damping coefficient, the linear and nonlinear loadings, the power-law index, and the plate width-tothickness ratio on the plate bending response. The results show that the presence of the viscoelastic foundation causes an 18% decrease in the plate deflection and about a 10% increase in transverse shear stresses under both linear and nonlinear loading conditions. Additionally, nonlinear loading causes a one-and-a-half times increase in horizontal stresses and a nearly two-times increase in normal transverse stresses compared to linear loading. Based on the article's findings, it can be concluded that the viscosity effect plays a significant role in the bending response of plates in hygrothermal environments. Hence it shall be considered in the design.

• Computers and Concrete
• /
• 제19권6호
• /
• pp.625-630
• /
• 2017

In this paper, 54 pull-out specimens and 36 cubic specimens with different replacement ratios of fly ash in the concrete (i.e., 0%, 20%, 30%, 40%, 50%, 60%) were fabricated to evaluate the bond at the interface between fly ash concrete and steel rebar. The results showed that the general shape of the bond-slip curve between fly ash concrete and steel rebar was similar to that for the normal concrete and steel rebar. The bond strength between fly ash concrete and the steel rebar was closer to each other at the same rebar diameter, irrespective of the fly ash replacement percentage. On the basis of a regression analysis of the experimental data, a revised bond strength mode and bond-slip relationship model were proposed to predict the bond-slip behaviour of high volume fly ash concrete and steel rebar.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• 제19권6호
• /
• pp.9-16
• /
• 2020

This study aims to assess the effects of specimen thickness (ST) on fatigue crack growth in the early stages of crack propagation and near failure in magnesium alloys. The analysis of variance (ANOVA) method was adopted because fatigue crack propagation in magnesium alloys exhibits statistical behavior. The equality of variance test and residual diagnostics were performed on the grown cracks to confirm the validity of ANOVA by verifying the normal distribution and mutual independence of the residuals and their homoscedasticity. ANOVA confirmed that ST heavily impacts crack growth; i.e., when ST is smaller, cracks grow faster in the early crack propagation stage and break more quickly before the formation of larger cracks. We found that ST significantly affects fatigue crack growth in the early crack propagation stage and near the failure stage in magnesium alloys. The regression model was also used to predict crack formation near the failure stage.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• 제20권8호
• /
• pp.2626-2636
• /
• 1996

A study of soot deposition and reentrainment was carried out both theoretically and experimentally to understand behavior of soot formed by incomplete combustion in a diesel engine. Theoretically, soot deposition on engine cylinder wall and/or piston head was studied with a stagnation point flow approximation. Soot reentrainment occurred upon exhaust gas blowdown was also studied by assuming a long-normal shear velocity distribution. Experimentally, a LPG$O_2/N_2$ flame impinging on a disk, produced by a concentric tubular burner, was chosen as deposition configuration and a shear flow unit with compressed air was installed for the study of reentrainment. For selected flame configuration, soot deposition measurements were conducted and showed that the dominant deposition mechanism was thermophoresis. Distributions of gas temperature and soot number density were estimated by combining data obtained by a B-type thermocouple with a thermophoretic transport theory. Disk temperature distributions were directly measured using a K-type thermocouple. Soot size and morphology were estimated from a TEM photograph. Ratios of soot deposit to reentrained amount were measured for a wide range of shear flow velocities, which showed that the reentrainment model was reasonable.

• Environmental Analysis Health and Toxicology
• /
• 제18권2호
• /
• pp.155-163
• /
• 2003

Fluoranthene, a common polycyclicaromatic hydrocarbon (PAH), exhibits phototoxicity which may affect aquatic organisms. The eventual goal of this study is to develop a biomarker of Japanese medaka (Oryzias latipes) used in monitoring hazardous chemicals in the ecosystem. In this study we investigated neural toxicity of fluoranthene in Japanese medaka (Oryzias latipes) along with comparative analysis of corresponding behavioral response. The untreated individuals shooed normal behavioral characteristics (i. e., smooth and linear movements). The treated fish, however, showed stopping and abrupt change of orientation (100 ppb), and severely reduced locomotive activity and enhanced surfacing activity (1,000 ppb). Treatment of the medaka fish with fluoranthene caused a significant suppresson of acetycholine esterase (AChE) activities in the body portion but not in the head portion. When fish were exposed to 1,000 ppb of fluoranthene for 24 hr, the body AChE activities decreased from 126.${\pm}$31.89 (nmoles substrate hydrolyzed per min per mg protein) to 49.51${\pm}$11.99. Expressions of tyrosine hydroxylase (TH) protein in the different organs from both head and body portions were comparatively analyzed using an immunohistochemical technique. Five organs of the medaka fish showing a strong TH protein expression were the olfactory bulb, hypothalamus, optic lobe, pons and myelencephalon regions. This study provides molecular and neurobehavioral bases of a biomonitoring system for toxic chemicals using fish as a model organism.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
• /
• pp.419-424
• /
• 2002

The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial criticality In February, 1995. Many experiments should be safely performed to activate the utilization of the HANARO. A flow simulation facility is being developed for the endurance test of reactivity control units for extended life times and the verification of structural integrity of those experimental facilities prior to loading in the HANARO. This test facility is composed of three major parts; a half-core structure assembly, flow circulation system and support system. The flow circulation system is composed of a circulation pump, a core flow pipe, a core bypass flow pipe and instruments. The system is to be filled with de-mineralized water and the flow should be met the design flow to simulate similar flow characteristics in the core channel of the half-core test facility to the HANARO. This paper, therefore, describes an analytical analysis to study the flow behavior of the system. The computational flow analysis has been performed for the verification of system pressure variation through the three-dimensional analysis program with standard k-$\epsilon$ turbulence model and for the verification of the structural piping integrity through the finite element method. The results of the analysis are satisfied the design requirements and structural piping integrity of flow circulation system.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• 제26권2호
• /
• pp.234-242
• /
• 2002

A shape optimal design of synthetic intervertebral disc prosthesis is performed using a three-dimensional finite element method. Geometric parameters are introduced to model the cross-sectional geometry of the intervertebral disc. It is assumed that the total strain energy in the intact intervertebral disc is minimized under the normal load conditions, as often cited in other references. To calculate the stain energy density, both the nonlinear material properties and the large deformations are taken into account. The design variables of the annulus fiber angle and the area ratio of the nucleus pulposus are calculated as 31°and 30%, respectively, which complies well with the intact disc. Thus, the same optimization procedure is applied to the design of the synthetic intervertebral disc prosthesis whose material properties are different from the intact disc. For the given synthetic material properties, the values of 67°and 24% for the fiber angle and the area ratio are obtained.

• International Journal of Automotive Technology
• /
• 제4권4호
• /
• pp.165-172
• /
• 2003

This article deals with the spin loss analysis of friction drive CVTs, especially for the cases of S-CVT and SS-CVT. There are two main sources of power loss resulting from slippage in the friction drive CVT, spin and slip loss. Spin loss, which is also a main design issue in traction drives, results from the elastic contact deformation of rotating bodies having different rotational velocities. The structure and operating principles of the S-CVT and SS-CVT are first reviewed briefly. And to analyze the losses resulting from slippage, we reviewed previous analyses of the friction mechanism. A modified classical friction model is proposed, which describes the friction behavior including Stribeck (i.e., pre-sliding) effect. It is also performed an in-depth study for the velocity fields generated at the contact regions along with a Hertzian analysis of deflection. Hertzian results were employed to construct the geometric parameters and normal pressure distributions of the contact surface with respect to elastic and plastic deformations. With analytic formulations of the relative velocity field, deflection, and friction mechanism of the S-CVT and SS-CVT, quantitative analyses of spin loss for each case are carried out. As a result, explicit models of spin loss were developed.

• Journal of Power Electronics
• /
• 제11권2호
• /
• pp.163-172
• /
• 2011

Oxidation models of a rotor bar and end ring segment in an induction motor are presented to simulate the behavior of an induction machine working with oxidized rotor parts which are modeled as rotor faults in progress. The leakage inductance and resistance of the rotor parts arc different from normal values because of the oxidation process. The impedance variations modify the current density and magnetic flux which pass through the oxidized parts. Consequently, it causes the rotor asymmetry which induces abnormal harmonics in the stator current spectra of the faulty machine. The leakage inductances of the oxidation models are derived by the Ampere's law. Using the proposed oxidation models, the rotor bar and end ring faults in progress can be modeled and simulated with the motor current signature analysis (MCSA). In addition, the oxidation process of the rotor bar and end ring segment can motivate the rotor asymmetry, which is induced by electromagnetic imbalances, and it is one of the major motor faults. Results of simulations and experiments are compared to each other to verify the accuracy of the proposed models. Experiments are achieved using 3.7 kW, 3-phase, and squirrel cage induction motors with a motor drive inverter.

• Journal of Korean Society of Steel Construction
• /
• 제16권4호통권71호
• /
• pp.453-461
• /
• 2004

Since there are no specifications in Korea regarding the design of steel column baseplates that are subjected to concentric axial load, this paper proposes a more accessible stress design method for baseplates based on AISC specifications and guidelines.Some designs included in this paper were: (1) a full area ofconcrete bearing pressure under normal axial load and subsequent failure in external cantilevers at 0.95 d or 0.8 bf, and (2) a partial area of the pressure under a light axial load and subsequent failure as an internal cantilever model.