Open Square Research Articles

Numerical analysis of MHD natural convection in a partially open cavity with internal energy source

In this paper, the problem of MHD natural convection in a partially open square cavity in the presence of internal energy source has been studied numerically. The bottom and vertical walls are isothermally heated and cooled by different constant temperatures. The top wall of the cavity has been opened in three different positions namely, left, middle and right whereas the remaining unopened part is thermally insulated. The governing nonlinear partial differential equations are solved by SIMPLE algorithm where the discretitation is followed by finite volume method. The influence of various pertinent parameters such as internal Rayleigh number, external Rayleigh number and Hartmann number are discussed via graphs and tables. It is found that the fluid flow and heat transfer are strongly depends on the internal and external Rayleigh numbers, Hartmann number and three different opening positions of the top wall.

CO2 emissions and energy consumption of loaders in woodchip loading operation

Woodchip is the most widespread form of wood biomass used in power stations because it guarantees homogeneous sizes and high load densities. From an environmental point of view, woodchip production has been studied from many aspects (comminution wood, transportation.), but no experimentations have focused on loading operations. The goal of this work was to evaluate the energy consumption and CO2 emissions of four types of loader used in woodchip loading. A knuckle-boom loader and three front loaders were tested. In the trials, a different woodchip pile position (near a wall and in an open square) was considered. Higher values on energy consumption were obtained by a mechanical shovel equipped with a standard bucket (5.59 and 5.01 MJ m−3, for woodchip stored in piles sited near a wall and in an open square, respectively), whereas lower values were observed during the use of telescopic loaders (1.89 and 2.09 MJ m−3, for piles sited in an open square and near a wall, respectively). The same results were also observed for CO2 emissions, where the best performances were obtained by the telescopic handler (58.6 kg h−1), with the worst by the mechanical shovel (118.4 kg h−1). The study pointed out that in woodchip loading, telescopic handlers equipped with a hinged bucket are able to reach a higher working efficiency with lower energy consumption and CO2 emissions in all working conditions.

Magneto-hydrodynamic Marangoni flow in bottom-heated lid-driven cavity

The paper presents fluid and heat flow in an open square cavity where the free, forced and Marangoni convection are taking place simultaneously in presence of external magnetic field. Free convection induces from bottom heating, whereas forced convection is imposed by the motion of two sidewalls. Thermal interaction through open surface at top is also taken into account invoking Marangoni convection. The development of thermal-hydraulic flow physics is addressed systematically through both transient and steady analyses using an in-house CFD code. The results reveal the distinct flow-patterns using the pertinent parameters like Marangoni number (Ma=0–1000), Biot number (Bi=0–10), Reynolds number (Re=10–500), Richardson number (Ri=0.1–100) and Hartmann number (Ha=0–100). The impact of the mutual strengths of three convection modes on a liquid metal (Pr=0.054) in the presence of uniform magnetic field is explored exhaustively to extract the useful data relevant for practical applications. The thermal mixing behavior of the liquid is also assessed. The novelty of this work is it addresses magneto-hydrodynamic (MHD) flow that couples with simultaneous Marangoni, free and forced convection, as first time.

The effect of an urban park on the microclimate in its vicinity: a case study for Antwerp, Belgium

ABSTRACTAn urban park can exhibit a cooling effect not only in the park itself, but also in its wake with respect to the prevailing wind. This study investigates the cooling potential of an urban park in Antwerp, Belgium focusing on two parameters: (1) intensity of the cooling effect, indicating the maximum reduction in air temperature and (2) range of the cooling effect, indicating the maximum horizontal distance where a minimum of 0.1 °C cooling effect is present. Computational fluid dynamics (CFD) simulations are performed using the three‐dimensional unsteady Reynolds‐averaged Navier–Stokes equations. Coupled simulations of wind flow and heat transfer consider all the conductive, convective and radiative heat transfer processes but not the long‐wave radiation heat exchange between buildings, trees and ground. The vegetation model used in this study is evaluated with experimental data from an earlier study. Moreover, the simulated air temperatures inside the Antwerp city center are compared with available measurement data. Following the fairly‐good predictions from CFD simulations, results from the following cases are compared: (1) base case with the park, (2) a case with an open square instead of the park, and (3) a case with representative buildings instead of the park. The results indicate a maximum daytime intensity and range of the cooling effect of 3.4 °C and 498 m at 1500 LST (UTC + 2, Central European Summer Time). Further analysis shows that the cooling effect is more profound closer to the ground. Apart from the daytime cooling effect, the park investigated has the potential to lower wind velocities, resulting in increased air temperatures during the night‐time (at 0000 LST) by 0.9 °C, although this number might be slightly different given the neglect of long‐wave radiation heat exchange between buildings, trees and ground.

Gamma Putty shielding effect in megavoltage photon beam

Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation therapy. Lately, another shielding material called Gamma Putty has emerged. The objective of this report is to examine its dosimetric and shielding characteristics in megavoltage photon beam. Methods: All measurements were carried out in a dual energy linac. Data were collected using a calibrated ionization chamber. Percent transmission, linear attenuation, and field size dependence were evaluated for open square fields (4 × 4 cm 2 to 10 × 10 cm 2 ) defined by collimator jaws and for different Gamma Putty thicknesses (t = 0, 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm) at 6 and 18 MV photon beams. The measurements were performed both in air using appropriate acrylic buildup cap and in solid water. Results: The Gamma Putty tray factor (GPTF) increased steadily with field size for both 6 and 18 MV. It was characterized by a half value thickness (HVT) of 2.513 ± 0.101 and 2.855 ± 0.024 cm for 6 and 18 MV, respectively. The reduction in surface dose was about 6%, 14.5%, 22%, 36.37%, and 54% for 6 MV and 2.75 %, 9.36 %, 16.25 %, 28.95 %, and 44.47 % for 18 MV for Gamma Putty thicknesses of 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm. Conclusion: The result of Gamma Putty shielding on the photon beam output increases with thickness, beam energy, and field size. Therefore, clinical use of Gamma Putty tray factors should be tailored for all thicknesses, beam energies, and field sizes.

Multi‐layer EBG slab waveguide based on open square rings

A novel guiding channel that is electromagnetic bandgap (EBG) based is presented. The structure is formed in a two-dimensional slab of a square lattice of multi-layer metallic open square rings. Dispersion diagrams and eigenfield distributions of the in-gap-guided mode are shown. The channel guide offers many advantages such as easy and flexible design for band-select applications while retaining its electromagnetic properties, simple fabrication (no drilling through the substrate) and compatibility with integrated circuit technology. Two EBG waveguide configurations with a feeding structure on a circuit board (PCB) were designed, fabricated and tested. It is shown experimentally that the length of the EBG guide does not impact the insertion loss significantly, which establishes low insertion loss of the guide.

Design of a Novel Wideband and Dual-Polarized MagnetoElectric Dipole Antenna

A wideband antenna with ±45° dual polarization is proposed. The antenna is mainly comprised of four printed trapezoidal metal walls standing on a ground plane that forms a 3-D open square aperture cavity structure with tapered cut on the four wall edges. The metal walls are fed by two orthogonally positioned (±45°) feeding networks, forming two pairs of dipole arms. Because of the excited magnetic-electric resonances, wide bandwidth can be achieved. The proposed antenna is fabricated, and the measured results show that it has an impedance bandwidth of 56% (1.62–2.87 GHz) for VSWR < 1.5. In addition, isolation of larger than 30 dB is also exhibited across the bandwidth between the two feeding ports. Because the proposed antenna has a hollow inside structure, it is a good candidate for multiband sharing aperture antenna element. Furthermore, it has a simplified fabrication process and is suitable for outdoor base station antennas that require VSWR < 1.5.

과부하 4방향 사각형 합류맨홀에서의 에너지 손실 저감을 위한 실험 연구

과부하 맨홀에서의 에너지 손실은 도심지의 침수피해를 가중시키는 요인이 된다. 그러므로 과부하 4방향 합류맨홀에서 에너지 손실의 저감을 위한 흐름특성 분석이 필요하다. 본 연구에서는 현황조사 결과를 고려하여 수리실험 장치를 제작하였으며, 사각형 맨홀 및 연결관은 하수도시설 기준을 준용하여 1/5로 축소 제작하였다. 또한 과부하 4방향 사각형 합류맨홀에서 에너지 손실을 저감 시킬 수 있는 인버트 형상 조건을 도출하기 위하여 Fluent 6.3모형으로 수치모의를 실시하였다. 선정된 수리실험 조건인 유출유량(<TEX>$Q_{out}$</TEX>)에 대한 측면 유입유량(<TEX>$Q_{lar}$</TEX>)의 비(<TEX>$Q_{lat}/Q_{out}$</TEX>)와 유출유량(2.0, 3.0, 4.0, 4.8 l/sec) 및 인버트 형상 변화 조건(십자형, 개선형)을 변화시키며 수리실험을 실시하였다. 십자형 인버트는 과부하 4방향 합류 맨홀의 배수능력 향상에 영향이 미미한 것으로 분석되었다. 그러나 개선된 직사각 개거형 인버트와 정사각 개거형 인버트는 각각 평균적으로 약 7%, 28%의 손실계수가 감소하여 배수능력을 개선하는 것으로 분석되었다. 따라서 도시 관거 시설의 배수능력을 증대시키기 위하여 본 연구에서 제시된 개선형 인버트의 설치 및 활용이 가능할 것으로 판단된다. Energy loss at manholes under surcharged flow is considered as one of the major causes of inundation in urban area. Therefore, it is necessary to analyze the flow characteristics to reduce the energy loss in the surcharged four-way combining manhole. In this study, hydraulic experimental apparatus was constructed considering the results of the present survey. Square manholes and pipe diameters were reduced to 1/5 by applying sewer facility standards. Numerical simulations were carried out with the Fluent 6.3 model to derive the invert condition which can reduce the energy loss in the surcharged four-way combining square manhole. The hydraulic experiments were carried out according to the various conditions of the lateral flow rate(<TEX>$Q_{lat}/Q_{out}$</TEX>), discharge of outflow pipe (2.0, 3.0, 4.0, 4.8 l/sec), and invert shape (rectangle and square open conduit type). The crossed invert was not found to improve the drainage capacity of the surcharged four-way rectangular combining manhole. However, the improved rectangle open conduit type invert and square open conduit type invert were analyzed to improve the drainage capacity by reducing the head loss coefficients by about 8% and 28%, respectively. Therefore, in order to increase the drainage capacity of urban facilities, it is possible to install and use the improved invert proposed in this study.

Thermohydrodynamic analysis and tribological optimization of a curved pocket thrust bearing

Texture patterns implemented on thrust bearing surfaces have been proven very beneficial in terms of load carrying capacity and friction coefficient. In the present study, the potential of thrust bearings with a curved pocket stator geometry is investigated for realistic operating conditions. Bearing performance is quantified by means of Computational Fluid Dynamics (CFD) simulations based on the numerical solution of the Navier-Stokes and energy equations for incompressible flow, taking into account conjugate heat transfer at the bearing stator and rotor. After defining a reference slider design, optimization problems are formulated and solved, to arrive at optimal curved pocket designs. Here, the slider convergence ratio, as well as the pocket size, shape and depth, are defined in terms of proper design variables, whereas the load carrying capacity and friction coefficient constitute the problem's objective functions. The present results illustrate a superior performance of the curved open pocket slider designs in comparison to corresponding open square pocket sliders. Optimal solutions are characterized by parallel slider geometries. The improved performance of optimal designs can be attributed to reduced side leakage, in comparison to open square pocket geometries. The good performance of a thrust bearing with a corresponding curved pocket geometry is verified. Overall, the present optimal geometries are rather easy to manufacture, which makes them an attractive choice for the design of thrust bearings operated in a wide range of rotor speeds.

Refuerzo de fustes de columna en la arquitectura monumental de &lt;em&gt;Italica&lt;/em&gt; (prov. &lt;em&gt;Baetica&lt;/em&gt;). Aplicación de nuevas tecnologías para la reconstrucción de una práctica singular

Esta investigación tiene por objeto presentar los trabajos en curso en torno a un conjunto de fustes procedente de los órdenes arquitectónicos del conocido como Traianeum de Itálica (provincia Baetica, actual Santiponce, Sevilla), complejo de templo central y pórtico perimetral levantado en la ciudad a comienzos del siglo II d. C. En ellos se observan las huellas dejadas por toda una serie de recursos técnicos tales como grapas, espigas metálicas y cavidades para parches marmóreos, asociada con medidas preventivas de refuerzo de piedra eventualmente quebradiza. Para ello, dado su estado fragmentado y fragmentario, se ha recurrido a la aplicación de técnicas fotogramétricas que permitan la obtención de modelos tridimensionales de las piezas, con el fin de reconstruir el funcionamiento y finalidad mecánica de los citados recursos. En último término, se trata de profundizar en aspectos relacionados con una singular capacidad tecnológica selectiva y con la economía y organización de las obras.

A Sr2+-metal-organic framework with high chemical stability: synthesis, crystal structure and photoluminescence property.

Metal-organic frameworks (MOFs) are typically built by assembly of metal centres and organic linkers, and have emerged as promising crystalline materials in a variety of fields. However, the stability of MOFs is a key limitation for their practical applications. Herein, we report a novel Sr 2+: -MOF [Sr4(Tdada)2(H2O)3(DMF)2] (denoted as NKU- 105: , NKU = Nankai University; H4Tdada = 5,5'-((thiophene-2,5-dicar bonyl)bis(azanediyl))diisophthalic acid; DMF = N,N-dimethylformamide) featuring an open square channel of about 6 Å along the c-axis. Notably, NKU- 105: exhibits much outstanding chemical stability against common organic solvents, boiling water, acids and bases, relative to most MOF materials. Furthermore, NKU- 105: is an environment-friendly luminescent material with a bright cyan emission.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.

Effect of Prandtl Number and Inclination Angle on MHD Natural Convection in Inclined Open Square Cavity

Effect of Prandtl Number and Inclination Angle on MHD Natural Convection in Inclined Open Square Cavity

A Novel Multilayer Electromagnetic Bandgap Structure Composed of Square Rings as Microwave Guiding Structures

This paper presents a novel electromagnetic bandgap (EBG) structure composed of stacked U-shaped 3-D lattice of metallic open square rings and its potential application to selected waveguide configurations. Five key geometrical parameters are shown to impact the bandgap and modal structure of the EBG. Using this insight, we demonstrate two different configurations for line defect that realize guiding through the structure at Ku-band. The proposed EBG structure overcomes the fabrication complexity of conventional 2-D EBGs that are composed of dielectric rods or holes in a dielectric material. Selected EBG waveguide configurations with transitions to conventional microwave guiding structures are fabricated and tested.

A cluster-based mesoporous Ti-MOF with sodalite supercages.

The cooperative assembly of a hexagonal column shaped [Ti6O6][iPrO]66+ cluster and rhomboid Cu2I2 dimers using isonicotinic acid results in an unprecedented three-dimensional (3D) highly crystalline cluster-based Ti-MOF that features both giant sodalite cages with an inner diameter of 2.8 × 3.2 nm2 and 3D open square channels.

Influence of the Distance between Nanoparticles in Clusters on the Magnetization Reversal Process

Fourfold magnetic nanoparticles, created from nanowires or in the form of an open square, offer the possibility of creating quaternary memory devices with four unambiguously distinguishable stable states at remanence. This feature, however, has been simulated for single magnetic nanoparticles or clusters with interparticle distances similar to the nanoparticle dimensions. For the possible use in bit-patterned media, it is important to understand the scaling behavior of the stability of the additional intermediate states with the interparticle distance. The paper investigates exemplarily nanoparticles of two shapes which were found to be optimum to gain four states at remanence. For clusters of these particles, the probability of reaching the additional intermediate states in all particles in the same field region is strongly reduced with decreased interparticle distance. The differences between both shapes indicate possible solutions for this problem in the form of new nanoparticle shapes.

Natural convection on an open square cavity containing diagonally placed heaters and adiabatic square block and filled with hybrid nanofluid of nanodiamond - cobalt oxide/water

A finite difference based two dimensional simulations on laminar natural convection inside the open square cavity containing diagonal heaters and a central adiabatic square block is presented by vorticity – stream function approach. The enclosure is filled with hybrid nanofluid of Nanodiamond - Cobalt Oxide/Water. The top and bottom walls are considered as adiabatic and the vertical walls have diagonal heaters. The inlet port is placed on the left end of the top wall and the outlet is placed at the bottom of the right wall. The variables considered are Rayleigh number (104 to 106) and volumetric fraction of Nanodiamond - Cobalt Oxide (0 to 6%) particles. The results of fluid flow with single phase model are elucidated with streamlines, Isotherms and Average Nusselt number. The strength of the primary vortex depreciated with the increasing percentage of nano composites for all the Rayleigh numbers. Intensity of heat transfer is high in the right wall than the left wall.

Near limit premixed flamelets in Hele-Shaw cells

In this paper, we report a preliminary attempt to stabilize near limit premixed flamelets in Hele-Shaw cells. As a quasi-two-dimensional analog of flame balls, the flamelet is sustained by diffusive transport alone, with fuel supplied from the open ends of the Hele-Shaw cell, and heat dissipated to the ambient environment through conduction; radiative heat losses from both phases are neglected. Following Spalding’s “one-dimensional idealization” approximation, we construct a 2-D model to account for the heat and mass transfer processes in both the gas and the solid phases, with the gap height as a parameter controlling the heat exchange rate between the two phases. For each of the three kinds of wall materials considered, two steady solution branches are obtained as a function of the gap height, one corresponding to large flames and the other to small flames. The large flame branch is critically dependent on the boundary and is therefore of little physical value. Linear stability analysis shows that the small flame branch is unstable to random perturbations. 2-D time dependent numerical simulations indicate that a slightly perturbed steady state on the small flame branch either evolves into a single flamelet drifting to the boundary as a whole, or splits into two drifting to the boundary along opposite directions. A partially open square Hele-Shaw combustor has been proposed and is shown to be able to support stabilized flamelets for a certain range of the degree of opening.

C-SATS: Assessing Surgical Skills Among Urology Residency Applicants.

We hypothesized that surgical skills assessment could aid in the selection process of medical student applicants to a surgical program. Recently, crowdsourcing has been shown to provide an accurate assessment of surgical skills at all levels of training. We compared expert and crowd assessment of surgical tasks performed by resident applicants during their interview day at the urology program at the University of California, Irvine. Twenty-five resident interviewees performed four tasks: open square knot tying, laparoscopic peg transfer, robotic suturing, and skill task 8 on the LAP Mentor™ (Simbionix Ltd., Lod, Israel). Faculty experts and crowd workers (Crowd-Sourced Assessment of Technical Skills [C-SATS], Seattle, WA) assessed recorded performances using the Objective Structured Assessment of Technical Skills (OSATS), Global Evaluative Assessment of Robotic Skills (GEARS), and the Global Operative Assessment of Laparoscopic Skills (GOALS) validated assessment tools. Overall, 3938 crowd assessments were obtained for the four tasks in less than 3.5 hours, whereas the average time to receive 150 expert assessments was 22 days. Inter-rater agreement between expert and crowd assessment scores was 0.62 for open knot tying, 0.92 for laparoscopic peg transfer, and 0.86 for robotic suturing. Agreement between applicant rank on skill task 8 on the LAP Mentor assessment and crowd assessment was 0.32. The crowd match rank based solely on skills performance did not compare well with the final faculty match rank list (0.46); however, none of the bottom five crowd-rated applicants appeared in the top five expert-rated applicants and none of the top five crowd-rated applicants appeared in the bottom five expert-rated applicants. Crowd-source assessment of resident applicant surgical skills has good inter-rater agreement with expert physician raters but not with a computer-based objective motion metrics software assessment. Overall applicant rank was affected to some degree by the crowd performance rating.

Microclimatic differences and their influence on transpirational cooling of Tilia cordata in two contrasting street canyons in Munich, Germany

Urban trees can help to mitigate the urban heat island through evapotranspiration. However, growing conditions in cities are heterogeneous and micrometeorological conditions in street canyons can have a large impact on a tree’s transpiration. Here we investigated a common urban street tree species Tilia cordata of different ages and sizes, planted in two contrasting street canyons in a densely built neighbourhood within the centre of Munich, Germany: Bordeaux Platz, an open green square (OGS), and Pariser Platz, a circular paved square (CPS) with similar aspect ratio≈0.5. The experiment was carried out during the exceptionally hot and dry summer of 2015. The open green square showed significantly higher wind speed and vapour pressure deficit but lower soil temperature, less negative soil moisture potential and also a smaller wind tunneling effect compared to the circular paved square. All these variables showed strong relationship with the sapflux density (Js) of trees grown at these two sites. They explain almost 78% of the variation in Js. On average Js values of the trees at Bordeaux Platz peaked to 0.30–0.35mlcm−2min−1 during the day compared to the peak values of 0.20–0.23mlcm−2min−1 for trees at Pariser Platz. Consequently, trees grown at the open green square showed higher peak cooling of 2.3kWtree−1 or 82wm−2 than at the circular paved square (1.9kWtree−1). Interestingly, nocturnal cooling was higher for trees at the circular paved square with 18% of daytime transpiration compared to 2% for trees at the open green square. The study gave new insights into the cooling benefits of urban trees planted in open green squares compared to closed and paved squares and its temporal variation.

Effect of Bulky Cations on the Stability and Properties of Anion Exchange Membranes

Alkaline anion exchange membrane fuel cells are widely investigated recently as promising alternative to well-established proton exchange membrane fuel cells. Anion exchange membranes, using as solid electrolytes, are required to be thermally, chemically and mechanically stable in base at the operation temperature and humidity, as well as have an efficient OH- transport along the membrane across two electrodes. This study aims at studying AEMs functionalized with three different bulky cations. They are 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalized polyphenylene oxide (Figure 1(a)) [1], tris(2,4,6-trimethoxyphenyl) phosphonium functionalized PPO (Figure 1(b)) [2], and phenylene cobaltocenium functionalized norbornene (Figure 1(c)). Degradation study on 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalize PPO and unsubstituted imidazolium PPO by soaking both two membranes into 1 M sodium hydroxide at 80°C indicates attachment of 2,4,6-trimethoxyphenyl group efficiently improve OH- stability due to the enhanced volumetric steric and basicity of the central cation. Super hydrophobic and bulky phosphonium cation attached by three 2,4,6-trimethoxyphenyl groups has the chemical stability surpassing benzyl trimethyl ammonium by 30% after degrading in 1 M KOH at 80°C for 20 days. The cobaltocenium cation, which has 18 valance electrons further improve the chemical stability by 60% higher than trimethyl ammonium after treating in 1 M NaOH/CH3OH at 80°C for 20 days (Figure 2). Besides enhanced chemical properties from these bulky cations, their influence on the other polymer properties include thermal stability, water uptake, conductivity as well as transport property are also discussed. Figure 1. Structure of 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium functionalized PPO (a), tris(2,4,6-trimethoxyphenyl) phosphonium functionalized PPO (b) and phenylene cobaltocenium functionalized norbornene (c). Figure 2. Degradation studies performed at 80°C on 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl) imidazolium (solid diamond, 1 M KOH), tris(2,4,6-trimethoxyphenyl) phosphonium (solid square, 1 M KOH), phenylene cobaltocenium (solid triangle, 1 M NaOH/CH3OH) and benzyl trimethyl ammonium (open square, 1 M KOH; open triangle, 1 M NaOH/CH3OH). Reference [1] Y. Liu, J. Wang, Y. Yang, T.M. Brenner, S. Seifert, Y. Yan, M.W. Liberatore, A.M. Herring, J. Phys. Chem. C 118 (2014) 15136-15145. [2] Y. Liu, B. Zhang, C.L. Kinsinger, Y. Yang, S. Seifert, Y. Yan, C.M. Maupin, M.W. Liberatore, A.M. Herring, J. Membr. Sci. 506 (2016) 50-59. Figure 1