• Journal of Mechanical Science and Technology
• /
• 제19권3호
• /
• pp.826-835
• /
• 2005

Exposed-type steel column bases are used widely in low-rise building construction. Numerous researchers have examined methods to identify their stiffness and strength, but those studies have heretofore been restricted to in-plane behaviors. This paper presents an experimental investigation of inelastic behaviors of square hollow section (SHS) steel column bases under biaxial bending. Two types of failure modes are considered : anchor bolt yielding and base plate yielding. Different pinching effects and interaction surfaces for biaxial bending are observed for these two modes during bi-directional quasi-static cyclic loading tests. Differences are elucidated using limit analyses based on a simple analytical model.

• Computers and Concrete
• /
• 제17권4호
• /
• pp.541-551
• /
• 2016

Asphalt pavements are exposed to complex weather conditions and vehicle traffic loads leading to crack initiation and crack propagation in asphalt pavements. This paper presents the impact of weather conditions on fracture toughness of an asphalt concrete, prevalently employed in Ardabil road networks, under tensile (mode I) and shear (mode II) loading. An improved semi-circular bend (SCB) specimen was employed to carry out the fracture experiments. These experiments were performed in two different weather conditions namely fixed and cyclic temperatures. The results showed that consideration of the impact of temperature cycling resulted in decreasing the fracture toughness of asphalt concrete significantly. Furthermore, the fracture toughness was highly affected by loading mode for the both fixed and cyclic temperature conditions studied in this paper. In addition, it was found that the MTS criterion correctly predicts the onset of fracture initiation although this prediction was slightly conservative.

• 환경위생공학
• /
• 제14권4호
• /
• pp.172-179
• /
• 1999

In this research, biological treatability test was conduced using seawater flocculated tannery wastewater by fixed biofilm reactor. During one cycle, the removal efficiency of organic corbon obtained with fixed biofilm process for treating tannery wastewater was considerably greater than that with activated sludge process. As the hydraulic retention time increased form 0.5day to 4day, removal efficiency of organic carbon was increased from 72% to 87.3%. Attached biomass in media increased with influent organic loading up to 29g MLSS/L, that could reduce the specific organic loading rate. The continual measurement of attached biomass was possible for the operation of the biofilm reactor. Equal and low nitrication rates were observed in both suspended growth activated sludge process and fixed biofilm process, despite commercial nitrifier was seeded. Through the process of treating the tannery wastewater, EC50 values which is measured by the use of Ceriopdaphnia dubia, were decreased to the extent of 50% after treatment of seawater flocculation and of 83% after biological treatment, respectively, compared to those of the untreated wastewater.

• KSTLE International Journal
• /
• 제4권2호
• /
• pp.66-72
• /
• 2003

This paper presents the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existing investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal choices of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high-speed spindle. In this paper, The pressure behavior in theory of air film in high speed region of journal according to the eccentricity of journal and the source positions analyzed. The theoretical analysis has been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high-speed milling.

• The Journal of the Acoustical Society of Korea
• /
• 제16권1E호
• /
• pp.29-34
• /
• 1997

Numerical prediction of aerodynamic noise radiated by subsonic rotors are carried out. A computer program has been developed which incorporates both the discrete frequency noise as well as the broadband noise arising from the ingestion of turbulence. Acoustic analogy is used in conjunction with Homicz's formulation of turbulence ingestion noise. Formulation 1A of Farassat is used to enhance the numerical analysis performance of Ffowcs-Williams Hawkings equation by eliminating the numericla time differentiation. Homicz's trubulence ingestion noise prediction technique is used to understand the characteristics of broadband noise radiated by isotropic trubulence in gestion. Numerical predictions are carried out for a number of rotor configurations and compared with experimental data. Monopole consideration of transonic rotor agrees well with both the experimental data and the linear theory. Noise radiation characteristics of rotor at lifting hover are investigated utilizing simple blade loading obtained by thin wing section theory. By incorporating discrete noise prediction of steady loading with broadband spectrum, much better agreement with experimental data is obtained in the low frequency region. The contributions from different noise mechanisms can also be analyzed through this method.

• 산업기술연구
• /
• 제37권1호
• /
• pp.5-11
• /
• 2017

The purpose of this research is to propose an efficient loop line operation plan for customer transportation in a new theme park. Based on the expected customer arrivals, customer loading/unloading methods, and scheduled/non-scheduled departure schemes, movement time between stations etc., we have performed indepth analyses and derived the best optimal policy. Our results show that, over all, the operation with separate loading/unloading doors and scheduled departure is preferred to the other options. We then derived the optimal number of trains and cars meeting minimal customer unsatisfaction with low cost for each season.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 추계 학술발표회 논문집
• /
• pp.197-204
• /
• 2002

The resent earthquakes in worldwide have caused extensive damage to highway reinforced concrete bridge piers. It has been observed in the Korean Peninsula that the number of minor or low earthquake motions have increased year by year. Since the concern about the earthquake hazards is increased, the objective of this research is to evaluate the damage of reinforced concrete bridge piers subjected to probable earthquake motions. Experimental investigation was conducted to study the seismic performance of the full-scale specimens in size D=1.2m H=4.8m, which were constructed with different longitudinal lap splice and loading pattern, through the quasi-static test and the pseudo-dynamic test. It is thought that this result could contribute to establish the retrofit decision-making and disaster planning of reinforced concrete bridge piers in earthquake regions. And it could be also possible to quantify the damage of reinforced concrete bridge piers under cyclic loading

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 추계학술대회논문집 I
• /
• pp.529-535
• /
• 2001

A centrifugal fan design code was developed and packaged together with iDesignFan／sup TM／ as new models. This code generate centrifugal forward curved and backward curved bladed impeller optimally. It also predicts the aerodynamic performance and the overall sound pressure level of the rotating fan by assuming steady blade loading. The overall sound pressure level is used as an input parameter from the third loop of the designing process to acquire the most silent fan for the given aerodynamic performance parameters. With this kind of inverse design concept used in the code, the period of designing a fan is significantly shortened. A centrifugal fan design code, developed in this study and included in iDesignFan／sup TM／, predicts the aerodynamic performance such as design flow rate and static pressure. The aerodynamic performance in the design and off-design conditions is calculated by using the mean line analysis. For the steady loading calculation, the lift force distribution in a blade is used.

• 한국정밀공학회지
• /
• 제15권1호
• /
• pp.51-59
• /
• 1998

The purposes of the paper are to consider the failure phenomenon based on delamination and crack when the encapsulant of plastic IC package under hygrothermal loading in the IR soldering process is on elastic and viscoelastic behavior due to the temperature and to show the optimum design using fracture mechanics. The model for analysis is the plastic SOJ package with a dimpled diepad. The package model with the perfect delamination between chip and diepad is chosen to estimate the resistance to fracture by calculating J-integrals in low temperature and C(t)-integrals in high temperature with the change of the design under hygrothermal loading. The optimum design to depress the delamination and crack in the plastic IC package is presented.

• 한국지하수토양환경학회:학술대회논문집
• /
• 한국지하수토양환경학회 2002년도 추계학술발표회
• /
• pp.366-369
• /
• 2002

Subsurface biobarrier technology has potential applications to contain contaminated groundwater and/or to degrade toxic pollutants in groundwater. Most biobarrier studies were conducted under aerobic condition, however there were several obstacles to make aerobic condition. Thus, In this study, we examined biobarrier formation under denitrifying condition by using nitrate as an electron acceptor. Experiments were performed with a sand column inoculated with activated sludge from the nearby WWTP. The substrate medium was pumped to the sand column in an upflow mode. During the low substrate loading rate period, the extent of reduction rate in hydraulic conductivity was found similar throughout the column, and permeability became relatively stable after couple of days. However, during the high substrate loading rate period, the column demonstrated a gradient of permeability reduction, with the greatest reduction in sections nearest the column inlet. Rapid growth of microorganisms near the column inlet resulted in the unbalanced reduction of hydraulic conductivity throughout the sand column. As a result, at this denitrifying condition the thickness of biobarrier could be controlled by adjusting the medium conditions of microbial growth.