• Earthquakes and Structures
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• 제14권1호
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• pp.1-10
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• 2018

Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.

• Smart Structures and Systems
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• 제19권2호
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• pp.115-126
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• 2017

In this paper, size dependent bending and free flexural vibration behaviors of functionally graded (FG) nanobeams are investigated using a nonlocal quasi-3D theory in which both shear deformation and thickness stretching effects are introduced. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present theory incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a hyperbolic variation of all displacements through the thickness without using shear correction factor. The material properties of FG nanobeams are assumed to vary through the thickness according to a power law. The neutral surface position for such FG nanobeams is determined and the present theory based on exact neutral surface position is employed here. The governing equations are derived using the principal of minimum total potential energy. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and dynamic responses of the FG nanobeam are discussed in detail. A detailed numerical study is carried out to examine the effect of material gradient index, the nonlocal parameter, the beam aspect ratio on the global response of the FG nanobeam. These findings are important in mechanical design considerations of devices that use carbon nanotubes.

• 환경위생공학
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• 제9권1호
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• pp.67-75
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• 1994

Formaldehyde has been in widespread industrial use since World War II . Numerous sources of formaldehyde are present in the indoor environment. Additionally, the current trend toward tighter, more energy efficient buildings with lower ventilation rates has led to increase concentrations of this and other pollutants generated indoors. In this paper, the field survey was carried out once a month from January to MarctL 1994 to measure indoor and outdoor formaldehyde concentration in several underground locations in Seoul. The results could be summarized as follows : 1. At Yang- jae underground shopping center, the mean formaldehyde concentration was 77.8ppb for indoor and 68.4ppb for outdoor. At Ban- po underground shopping center, it was 175.8ppb for indoor and 127.3ppb for outdoor. At Jam- shil underground shop ping center, it was 135.2ppd for indoor and 34.6ppb for outdoor. Indoor the No.2 sub way line, it was 105.6ppb. The formaldehyde concentration using Berge equation was as follows : At Yang- jae underground shopping center, the mean formaldehyde concentration was 85.99ppb for indoor and 72.75ppb for outdoor At Ban- po underground shopping center, it was 254. 17ppb for indoor and 138.14ppb for outdoor. At Jam- shil underground shopping center, it was 249.13ppb for indoor and 36.87ppb for outdoor. Indoor the No.2 subway line, it was 131.73ppb. 3, The result of correlation analysis indicated that the relationship between temperature and formaldehyde concentration is very high( $\gamma $= 0.831 ∼ 0.974). 4. Also, the relationship between humidity and formaldehyde concentration is variant ($\gamma $ = 0.246 ∼0.999). 5. The mean formaldehyde concentration indoor and outdoor Ban- po underground shop ping center and indoor Jam- shil underground shopping center and indoor the No.2 sub way line exceed the American Society of Heating, Refrigeration, Air- conditioning Engineers( ASHRAE) stflndard of 100ppb(120 $\mu $g/m$^{3}$).

• 대한의용생체공학회:의공학회지
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• 제28권3호
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• pp.348-354
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• 2007

Polymer actuators, which are also called as smart materials, change their shapes when electrical, chemical, thermal, or magnetic energy is applied to them and are useful in wide variety of applications such as microelectromechanical systems (MEMS), machine components, and artificial muscles. For this study, Polyaniline/carbon-nanotube polymer actuator that is one of electroactive polymer actuators was prepared. Since the nonlinear phenomena of hysteresis and a step response are essential considerations for practical use of polymer actuators, we have investigated the movement of the Polyaniline/carbon-nanotube polymer actuator and have developed an integrated model that can be used for simulating and predicting the hysteresis and a step response during actuation. The Preisach hysteresis model, one of the most popular phenomenological models of hysteresis, were used for describing the hysteretic behavior of Polyaniline/carbon-nanotube polymer actuator while the ARX method, one of system identification techniques, were used for modeling a step response. In this paper, we first expain details in preparation of the Polyaniline/carbon-nanotube polymer then present the mathematical description of our model, the extraction of the parameters, simulation results from the model, and finally a comparison with measured data.

• Advances in aircraft and spacecraft science
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• 제4권5호
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• pp.529-541
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• 2017

Landing phase is one of the crucial and most important phases during robotic aerospace explorations. It concerns the impact of the landing module of a spacecraft on a celestial body. Risks and uncertainties of landing are mainly due to the morphology of the surface, the possible presence of rocks and other obstacles or subsidence. The present work quotes results of a computational analysis direct to investigate the stability during the landing phase of a lander on Phobos, a Mars Moon. The present study makes use of available software tools for the simulation analyses and results processing. Due to the nature of the system under consideration (i.e., large displacements and interaction between several systems), multibody simulations were performed to analyze the lander's behavior after the impact with the celestial body. The landing scenario was chosen as a result of a DOE (Design of Experiments) analysis in terms of lander velocity and position, or ground slope. In order to verify the reliability of the present multibody methodology for this particular aerospace issue, two different software tools were employed in order to emphasize two different ways to simulate the crash-box, a particular component of the system used to cushion the impact. The results show the most important frames of the simulations so as to provide a general idea about how lander behaves in its descent and some trends of the main characteristics of the system. In conclusion, the success of the approach is demonstrated by highlighting that the results (crash-box shortening trend and lander's kinetic energy) are comparable between the two tools and that the stability is ensured.

• 한국해양공학회지
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• 제22권4호
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• pp.65-71
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• 2008

In many cases, open-type plate breakwaters use plates with multiple holes; the holes serve as energy dissipaters and weight reducers. Because of the multi-holes configuration, stress concentration should be considered during the design process. Among several design loading conditions, the loads from a possible collision with a man-made vessel or other unexpected events many damage a multi-perforated steel plate. In that case, the structural behavior of a multi-perforated steel plate is quite significant, and is not well understood. This study presents a collision analysis for a multi-perforated steel plate. First, four different perforation topologies (three with circles and one with squares) were selected to investigate the effect of different hole shapes on the structural response. Second, the wave force at a specific site was calculated and loaded onto a steel plate as a static load. The static stresses were used for reference values. Third, two rigid body impacters (cubical & cylindrical) were applied to the steel plates to investigate the transient stress responses. In addition, two different impacting angles ($45^{\circ}\;&\;90^{\circ}$) were selected to investigate the angle effect. From the collision analysis, the significance of the transient stresses was emphasized.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.353-353
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• 2011

Titanium dioxide is a suitable material for industrial use at present and in the future because titanium dioxide has efficient photoactivity, good stability and low cost [1]. Among the three phases (anatase, rutile, brookite) of titanium dioxide, the anatase form is particularly photocatalytically active under ultraviolet (UV) light. In fabrication of photocatalytic devices based on catalytic nanodiodes [2], it is challenging to obtain a photocatalytically active TiO2 thin film that can be prepared at low temperature (< 200$^{\circ}C$). Here, we present the synthesis of a titanium dioxide film using TiO2 nanoparticles and sol-gel methods. Titanium tetra-isopropoxide was used as the precursor and alcohol as the solvent. Titanium dioxide thin films were made using spin coating. The change of atomic structure was monitored after heating the thin film at 200$^{\circ}C$ and at 350$^{\circ}C$. The prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microcopy, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy (UV-vis), and ellipsometry. XRD spectra show an anatase phase at low temperature, 200$^{\circ}C$. UV-vis confirms the anatase phase band gap energy (3.2 eV) when using the photocatalyst. TEM images reveal crystallization of the titanium dioxide at 200$^{\circ}C$. We will discuss the switching behavior of the Pt /sol-gel TiO2 /Pt layers that can be a new type of resistive random-access memory.

• 한국자동차공학회논문집
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• 제19권5호
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• pp.134-142
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• 2011

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Exhaust pipes with circular fin were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NOx), carbon dioxide ($CO_2$) and carbon monoxide (CO). In addition, $O_2$ concentration in the exhaust was measured. The designs adopted in this study were about exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe technique. The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10 nm), surface forces are increasingly important. Nano particles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nano size. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^4$ by free convection and Re=$3.36{\times}10^4$ by forced air furnace.

• 대한화학회지
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• 제36권1호
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• pp.44-50
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• 1992

착물들의 자기성과 스펙트라의 성질은 d 궤도 함수의 퇴화에 대한 분열과 자외선 가시 분광학적 방법으로 비수용액 속에서 조사하였다. 10Dq의 에너지 크기는 착물들의 스펙트라와 결합에너지 그리고 스핀상태로부터 얻어졌다. 전기화학적 거동은 순환전압 전류법에 의해 측정하였다. 이들의 환원 피크는 Ag/AgCl 전극으로 20mV/s에서 $[(C_6H_5)3_P]_2Pd(II)(CH_3COO)_2$는 $E_{pc1} = -1.32 V,\;E_{pc2} = -1.56 V$이고, 그리고 $[(C_6H_5)_3Pd]_2Pd(II)Cl_2$에서는 $E_{pc1} = -1.74 V,\;E_{pc2} = -1.88 V$로 일전자 비가역적인 과정이었다. 그러나 $Ni^{2+}$ 착물에서는 환원성으로 되지 않았다.

• Earthquakes and Structures
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• 제9권3호
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• pp.657-671
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• 2015

The level of ductility is determined by depending on the intended use of the building, the region's seismic characteristics and the type of structural system when buildings are planned by engineers. Major portion of seismic energy is intended to be consumed in the plastic zone in structural systems of high ductility, so the occurrence of damages in load bearing and non-load bearing structural elements is accepted in planning stage under severe earthquakes. However, these damages must be limited among specific values in order not to endanger buildings in terms of the bearing capacity. Isolators placed between the basement and upper structure make buildings behave elastically by reducing the effects of seismic loads and improving seismic performance of building significantly. Thus, damages can be limited among desired values. In this study, the effectiveness of seismic isolation is investigated on both fixed based and seismic isolated models of a hospital building with high ductility level with regard to lateral displacements, internal forces, structural periods and cost of the building. Layered rubber bearings are interposed between the base of the structure and foundation. Earthquake analysis of the building are performed using earthquake records in time domain (Kocaeli, Loma Prieta and Landers). Results obtained from three-dimensional finite element models are presented by graphs and tables in detail. That seismic isolation reduces significantly the destructive effects of earthquakes on structures is seen from the results obtained by seismic analysis.