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Practical estimation of veering effects on high-rise structures: a database-assisted design approach
Yeo, DongHun Techno-Press 2012 Wind and Structures, An International Journal (WAS Vol.15 No.5
Atmospheric boundary layer winds experience two types of effects due to friction at the ground surface. One effect is the increase of the wind speeds with height above the surface. The second effect, called the Ekman layer effect, entails veering - the change of the wind speed direction as a function of height above the surface. In this study a practical procedure is developed within a database-assisted design (DAD) framework that accounts approximately for veering effects on tall building design. The procedure was applied in a case study of a 60-story reinforced concrete building, which also considered the dependence of veering effects on the orientation of the building. Comparisons are presented between response estimates that do not account for veering, and account for veering conservatively. For the case studied in this paper veering effects were found to be small.
Tall Building Database-assisted Design: a Review of NIST Research
Yeo, DongHun,Potra, Florian A.,Simiu, Emil Council on Tall Building and Urban Habitat Korea 2019 International journal of high-rise buildings Vol.8 No.4
The purpose of this review paper is to briefly describe main the features of novel procedures developed by the National of Standards and Technology (NIST) for the design of tall buildings. Topics considered in the paper include: the division of tasks between wind and structural engineers; the determination of wind effects with specified mean recurrence intervals by accounting for wind directionality; the risk-consistent design of structures subjected to multiple wind hazards; iterative dynamic analyses and member sizing, including the use of modern optimization approaches; and commonalities of and differences between Database-assisted Design (DAD) and Equivalent Static Wind Loads procedures. An example of the application of the DAD procedure is presented for a reinforced concrete structure. Also included in the paper is an introduction to ongoing research on the estimation of wind load factors or of augmented design mean recurrence intervals commensurate with the uncertainties in the factors that determine the wind effects.
Practical estimation of veering effects on high-rise structures: a database-assisted design approach
DongHun Yeo 한국풍공학회 2012 Wind and Structures, An International Journal (WAS Vol.15 No.5
Atmospheric boundary layer winds experience two types of effects due to friction at the ground surface. One effect is the increase of the wind speeds with height above the surface. The second effect, called the Ekman layer effect, entails veering - the change of the wind speed direction as a function of height above the surface. In this study a practical procedure is developed within a databaseassisted design (DAD) framework that accounts approximately for veering effects on tall building design. The procedure was applied in a case study of a 60-story reinforced concrete building, which also considered the dependence of veering effects on the orientation of the building. Comparisons are presented between response estimates that do not account for veering, and account for veering conservatively. For the case studied in this paper veering effects were found to be small.
Yeo, Byung Chul,Kim, Donghun,Kim, Hyungjun,Han, Sang Soo American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.42
<P>An efficient propylene/propane separation is a very critical process for saving the cost of energy in the petrochemical industry. For separation based on the pressure-swing adsorption process, we have screened similar to 1 million crystal structures in the Cambridge Structural Database and Inorganic Crystal Structural Database with descriptors such as the surface area of N-2, accessible surface area of propane, and pore-limiting diameter. Next, grand canonical Monte Carlo simulations have been performed to investigate the selectivities and working capacities of propylene/propane under experimental process conditions. Our simulations reveal that the selectivity and the working capacity have a trade-off relationship. To increase the working capacity of propylene, porous materials with high largest cavity diameters (LCDs) and low propylene binding energies (Q(st)) should be considered; conversely, for a high selectivity, porous materials with low LCDs and high propylene Q(st) should be-considered, which leads to a trade-off between the selectivity and the working capacity. In addition, for the design of novel porous materials with a high selectivity, we propose a porous material that includes elements with a high crossover distance in their Lennard-Jones potentials for propylene/propane such as In, Te, Al, and I, along with the low LCD stipulation.</P>
Kim, Donghun,Yeo, Byung Chul,Shin, Dongbin,Choi, Heechae,Kim, Seungchul,Park, Noejung,Han, Sang Soo American Physical Society 2017 Physical Review B Vol.95 No.4
<P>Recent studies on crystal facet manipulation of anatase TiO2 in photocatalysis have revealed that reduction and oxidation reactions preferably occur on (100)/(101) and (001) facets, respectively; however, a fundamental understanding of their origin is lacking. Here, as a result of first-principles calculations, we suggest that a dissimilar trend in the anisotropy of electron vs hole bulk transport in anatase TiO2 can be a dominant underlying mechanism for the difference in photochemical activity. Photoexcited electrons and holes are driven to different facets, i.e., electrons on (100)/(101) and holes on (001), leading to the observed preference for either reduction or oxidation. This trend of electrons vs holes found in pure TiO2 applies even for cases where a variety of dopants or defects is introduced.</P>
Advances in the design of high-rise structures by the wind tunnel procedure: Conceptual framework
Simiu, Emil,Yeo, DongHun Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5
This paper surveys and complements contributions by the National Institute of Standards and Technology to techniques ensuring that the wind tunnel procedure for the design of high-rise structures is based on sound methods and allows unambiguous inter-laboratory comparisons. Developments that enabled substantial advances in these techniques include: Instrumentation for simultaneously measuring pressures at multiple taps; time-domain analysis methods for estimating directional dynamic effects; creation of large simulated extreme directional wind speed data sets; non-parametric methods for estimating mean recurrence intervals (MRIs) of Demand-to-Capacity Indexes (DCIs); and member sizing based on peak DCIs with specified MRIs. To implement these advances changes are needed in the traditional division of tasks between wind and structural engineers. Wind engineers should provide large sets of directional wind speeds, pressure coefficient time series, and estimates of uncertainties in wind speeds and pressure coefficients. Structural engineers should perform the dynamic analyses, estimates of MRIs of wind effects, sensitivity studies, and iterative sizing of structural members. The procedure is transparent, eliminates guesswork inherent in frequency domain methods and due to the lack of pressure measurements, and enables structural engineers to be in full control of the structural design for wind.
β-CuGaO<sub>2</sub> as a Strong Candidate Material for Efficient Ferroelectric Photovoltaics
Song, Seungwoo,Kim, Donghun,Jang, Hyun Myung,Yeo, Byung Chul,Han, Sang Soo,Kim, Chang Soo,Scott, James F. American Chemical Society 2017 Chemistry of materials Vol.29 No.17
<P>We propose a recently discovered material, namely, beta-CuGaO2 [T. Omata et al., J. Am. Chem. Soc. 2014, 136, 3378] as a strong candidate material for efficient ferroelectric photovoltaics (FPVs). According to first-principles predictions exploiting hybrid density functional, beta-CuGaO2 is ferroelectric with a remarkably large remanent polarization of 83.80 mu C/cm(2), even exceeding that of the prototypic FPV material, BiFeO3. Quantitative theoretical analysis further indicates the asymmetric Ga 3d(z)(2)-O 2p(z) hybridization as the origin of the Pna2(1) ferroelectricity. In addition to the large displacive polarization, unusually small band gap (1.47 eV) and resultantly strong optical absorptions additionally differentiate beta-CuGaO2 from conventional ferroelectrics; this material is expected to overcome critical limitations of currently available FPVs.</P>
Lee, Hong Woo,Jung, Hyun,Yeo, Byung Chul,Kim, Donghun,Han, Sang Soo American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.36
<P>Black phosphorus has recently attracted significant attention as an anode material for sodium-ion batteries (SIBs); however, the material suffers from a severe volume change during charge/discharge processes, leading to poor cycle life. To overcome this drawback of black phosphorus, a phosphorene/graphene (P/G) heterostructure was recently proposed, but no atomistic understanding of the sodiation mechanism has yet been reported. In this work, we report an atomistic mechanism for the sodiation of the P/G hybrid material based on first-principles calculations. The layered structure of P/G is maintained up to the composition of Na<SUB>0.25</SUB>P/G, which can be referred to as an intercalation process; however, above that composition, further sodiation leads to the dissociation of P−P bonds and the formation of an amorphous Na<SUB><I>x</I></SUB>P/G structure where the graphene layers are not broken and no Na atoms intercalate into the spaces between two graphene layers, which is referred to as an alloying process. According to our first-principles calculation, the graphene layers in the P/G material provide a buffer layer to accommodate the volume expansion of the material during sodiation (30% lower than that in the case of black phosphoros) without sacrificing the specific capacity. On the basis of calculations of carrier effective masses based on the band structures calculated by a hybrid density functional theory at the HSE06 level, the P/G material exhibits electrical conductivity superior to that of black phosphorus, in which graphene layers in the P/G can provide an electrical conducting channel even at a high sodiation level because the graphene layers are maintained up to full sodiation. Moreover, first-principles molecular dynamics simulations demonstrate that graphene layers in the P/G provide facile diffusion channels for Na atoms in highly sodiated Na<SUB><I>x</I></SUB>P/G, although the effect is not significant during the intercalation process. On the basis of these results, we can expect that the P/G heterostructure has superior cycling properties and high rate capabilities and that the P/G hybrid material can indeed be a promising material for the anode of practical SIBs.</P> [FIG OMISSION]</BR>