• Wind and Structures
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• v.23 no.2
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• pp.127-142
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• 2016

Aerodynamic effects, such as drag force and flow-induced vibration (FIV), on civil engineering structures can be minimized by optimally modifying the structure shape. This work investigates the turbulent wake of a square prism with its faces modified into a sinusoidal wave along the spanwise direction using three-dimensional large eddy simulation (LES) and particle image velocimetry (PIV) techniques at Reynolds number $Re_{Dm}$ = 16,500-22,000, based on the nominal width ($D_m$) of the prism and free-stream velocity ($U_{\infty}$). Two arrangements are considered: (i) the top and bottom faces of the prism are shaped into the sinusoidal waves (termed as WSP-A), and (ii) the front and rear faces are modified into the sinusoidal waves (WSP-B). The sinusoidal waves have a wavelength of $6D_m$ and an amplitude of $0.15D_m$. It has been found that the wavy faces lead to more three-dimensional free shear layers in the near wake than the flat faces (smooth square prism). As a result, the roll-up of shear layers is postponed. Furthermore, the near-wake vortical structures exhibit dominant periodic variations along the spanwise direction; the minimum (i.e., saddle) and maximum (i.e., node) cross-sections of the modified prisms have narrow and wide wakes, respectively. The wake recirculation bubble of the modified prism is wider and longer, compared with its smooth counterpart, thus resulting in a significant drag reduction and fluctuating lift suppression (up to 8.7% and 78.2%, respectively, for the case of WSP-A). Multiple dominant frequencies of vortex shedding, which are distinct from that of the smooth prism, are detected in the near wake of the wavy prisms. The present study may shed light on the understanding of the underlying physical mechanisms of FIV control, in terms of passive modification of the bluff-body shape.

• Steel and Composite Structures
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• v.16 no.5
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• pp.491-506
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• 2014

Buckling-restrained braces (BRBs) have excellent hysteretic behavior while buckling-restrained braced frames (BRBFs) are susceptible to residual lateral deformations. To address this drawback, a novel self-centering (SC) BRB with Basalt fiber reinforced polymer (BFRP) composite tendons is presented in this work. The configuration and mechanics of proposed BFRP-SC-BRBs are first discussed. Then an 1840-mm-long BFRP-SC-BRB specimen is fabricated and tested to verify its hysteric and self-centering performance. The tested specimen has an expected flag-shaped hysteresis character, showing a distinct self-centering tendency. During the test, the residual deformation of the specimen is only about 0.6 mm. The gap between anchorage plates and welding ends of bracing tubes performs as expected with the maximum opening value 6 mm when brace is in compression. The OpenSEES software is employed to conduct numerical analysis. Experiment results are used to validate the modeling methodology. Then the proposed numerical model is used to evaluate the influence of initial prestress, tendon diameter and core plate thickness on the performance of BFRP-SC-BRBs. Results show that both the increase of initial prestress and tendon diameters can obviously improve the self-centering effect of BFRP-SC-BRBs. With the increase of core plate thickness, the energy dissipation is improved while the residual deformation is generated when the core plate strength exceeds initial prestress force.

• Fire Science and Engineering
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• v.11 no.1
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• pp.3-9
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• 1997

The objective of this research is to study on the formations of thermal stratification in a room in case of several furniture fires such as trashcan, carpet, sofa, mattress and wardrobe as a fire starter in a residential room by performing the experimental studies. The uniformly distributed fire in case of carpet showed that the ignition and the initial growth period were relatively short while the fully developed period was considerably long. The concentrated fires such as the mattress and wardrobe showed that the ignitions and the initial growth periods were relatively long. When fire spread to only direction, like the case for the trashcan with a regular shape, there was one peak of temperature profile, and for the irregular shaped furniture such as chair, sofa, mattress and wardrobe, there were two or more peaks. The interface heights for the furniture fires were around 1[m] maintaining constant state. However, at the time of the maximum temperature, the interface height was lowered to 0.25[m]-0.75[m] from the floor.

• Korean Journal of Ichthyology
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• v.19 no.2
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• pp.120-127
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• 2007

To investigate the skin of the flat-headed goby, Luciogobius guttatus, it was used 8 body regions such as the head, the upper and lower jaw, the chin, the back, lateral region, abdomen, and the operculum. The epidermis consisted of three layers: the outermost layer, middle layer and stratum germinativum (basal layer). The outermost layer consisted of rather flattened cells arranged in 1 to 4 layers and mucous cells. The middle layer consisted of large epidermal cells occupying the height of the epidermis with 1 to 10 layers, causing a web-shaped structure. Due to the large epidermal cells of the middle layer, L. guttaus had a thick epidermis. The large epidermal cell contains tonofilaments, lucent contents, and desmosome. The basal layer was comprised of a single layer having cuboidal cells. A large number of fine blood capillaries were found just under the basal layer. The dermis consisted mostly of stratum compactum with numerous blood capillaries but had no scale.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.202-209
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• 2004

Hydroxyapatite(HA)/TiO$_2$ composite powders were prepared by mixing of spherical TiO$_2$ (10-15 nm, 500 nm) and needle-shaped HA (50-70 nm, 120-250 nm) powders which had been synthesized through precipitation, sol-gel and hydrothermal methods. From the three types of starting composite powders (HA/TiO$_2$ wt% of 75/25, 50/50, and 25/75), dense $\beta$-TCP/TiO$_2$ composites were prepared by hot-pressing at 800-100$0^{\circ}C$ for 30 min under the pressure of 30 ㎫ in Af atmosphere. The $\beta$-TCP/TiO$_2$ composites showed different microstructures and sintering densities depending on their powder morphology, composition and sintering temperature. With increasing the sintering temperature and the content of TiO$_2$, sintered density was increased and microstructure became more homogeneous.

• Steel and Composite Structures
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• v.22 no.5
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• pp.937-974
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• 2016

While extensive efforts have been made in the past to develop finite element models (FEMs) for concrete-filled steel tubular columns (CFSTCs), these models may not be suitable to be used in some cases, especially in view of the utilisation of high strength steel and high strength concrete. A method is presented herein to predict the complete stress-strain curve of concrete subjected to tri-axial compressive stresses caused by axial load coupled with lateral pressure due to the confinement action in square and rectangular CFSTCs with normal and high strength materials. To evaluate the lateral pressure exerted on the concrete in square and rectangular shaped columns, an accurately developed FEM which incorporates the effects of initial local imperfections and residual stresses using the commercial program ABAQUS is adopted. Subsequently, an extensive parametric study is conducted herein to propose an empirical equation for the maximum average lateral pressure, which depends on the material and geometric properties of the columns. The analysis parameters include the concrete compressive strength ($f^{\prime}_c=20-110N/mm^2$), steel yield strength ($f_y=220-850N/mm^2$), width-to-thickness (B/t) ratios in the range of 15-52, as well as the length-to-width (L/B) ratios in the range of 2-4. The predictions of the behaviour, ultimate axial strengths, and failure modes are compared with the available experimental results to verify the accuracy of the models developed. Furthermore, a design model is proposed for short square and rectangular CFSTCs. Additionally, comparisons with the prediction of axial load capacity by using the proposed design model, Australian Standard and Eurocode 4 code provisions for box composite columns are carried out.

• ALGAE
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• v.24 no.3
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• pp.139-147
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• 2009

Microalgae using a submersible fluorescence probe in water column (up to 100 m) were measured during the austral summer of 2006 (February) in Prydz Bay, East Antarctica (triangular-shaped embayment in the Indian sector of Southern Ocean). Concurrently, environmental parameters such as temperature, salinity and nitrogen (nitrate, ammonium, urea) uptake rates were measured. The concentration of phytoplankton is relatively high due to availability of high nutrients and low sea surface temperature. Phytoplankton community is dominated by diatoms whereas cryptophytes are in low concentration. The maximum concentration of total chlorophyll is 14.87 ${\mu}g\;L^{-1}$ and is attributed to upwelled subsurface winter water due to local wind forcing, availability of micro-nutrients and increased attenuation of photosynthetically available radiation (PAR). Concentration of blue-green algae is low compared to that of green algae because of low temperature. Comparatively high concentration of yellow substances is due to the influence of Antarctic melt-water whereas cryptophytes are low due to high salinity and mixed water column. Varied concentrations of phytoplankton at different times of Fluoroprobe measurements suggest that the coastal waters of Prydz Bay are influenced by changing sub-surface water temperature and salinity due to subsurface upwelling induced by local winds as also melting/freezing processes in late summer. The productivity is high in coastal water due to the input of macro as well as micro-nutrients.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.829-837
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• 2012

Direct numerical simulations were carried out for turbulent channel flows with $Re_{\tau}$ = 180, 395 and 590 to investigate the turbulent flow structure related to the Reynolds shear stress. By examining the probability density function, the second quadrant (Q2) events with the largest contribution to the mean Reynolds shear stress were identified. The change in the inclination angle of Q2 events varies with wall units in $y^+<50$ and with the channel half height in y/h > 0.5. Conditionally averaged flow fields for the Q2 event show that the flow structures associated with Reynolds shear stress are a quasi-streamwise vortex in the buffer layer and a hairpin-shaped vortex in the outer layer. Three-dimensional visualization of the distribution of high Reynolds shear stress reveals that the organization of hairpin vortices in the outer layer having a size of 1.5~3 h is associated with large-scale motions with high Reynolds shear stress in the outer layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.839-847
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• 2012

Numerical simulations for channel flows with $Re_{\tau}$ = 180, 395 and 590 have been performed to investigate the hairpin packet formation process in wall-bounded turbulent flows. Using direct numerical simulation databases, the initial flow fields are given by the conditionally averaged flow field with the second quadrant event specified at the buffer layer. By tracking the initial vortex development, the change in the initial vortex to an ${\Omega}$-shaped vortex and th generation of a secondary hairpin vortex were found to occur with time scales based on the wall units. In addition, at the time when the initial vortex has grown to the channel center, the inclination angle of the hairpin vortex packet is approximately $12{\sim}14^{\circ}$, which is similar for all three Reynolds numbers. Finally, numerical simulations of the evolution of two adjacent hairpin vortices have been performed to examine the interaction between the adjacent vortex packets.

• Land and Housing Review
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• v.8 no.4
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• pp.223-232
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• 2017

The purpose of this study is to identify the supply status and planning trend of North Korean housing through analysis on the North Korean architecture specialized media data. The flat composition is changing and the living room is becoming the center of the houses. Also, in the urban areas, the standard apartment type is four apartments in a row and the plan form is getting diversified into circle type, Y type, and irregular type. On the other hand, in the rural areas, two houses in a row and single house are typical and the change in planning scale and space structure are not substantial. Since the 2000s, design changes have been made to emphasize the third dimensional structure of buildings such as the elliptical houses and L-shaped houses. Furthermore, 8~10 households are located on one floor which leads to the tendency of the building enlargement. In terms of house size, a square concept was introduced to replace the initial 2~3 room concept and the basic module of the room planning the 3 room house based on $3m{\times}3m$. However, there seems to be no standard house size, and the house size may differ depending on the social classandregion. In the early 1980s, when there was focus on the apartment complex construction, the high-rise apartment buildings of 30~40 floors was planned. However, during the Pyongyang redevelopment project, apartments of more or less than 10 floors were built and row-houses of more or less than 4 floors were built. In terms of the complex scale, a lot of small complexes of around 300 households are emerging after 2010. The construction projects are mainly limited to specific regions such as Pyongyang and Samjiyeon, and also limited to specific classes such as the workers and soldiers initially and the scientists lately. In addition, living boundary composition and ancillary facilities for sufficient green area ratio securement and the people of North Korea are maintained consistently. In recent years, the specialized floor planning such as solar house and the house for the disabled people, framework houses for redevelopment business, and multi-storied house construction technology are also emerging.