Numerical Study of Flow Features Around Submerged Circular and Square Piles at Flat and Scoured Beds Using OpenFOAM

Elucidating the flow features around piles in local scouring processes is crucial for studies of local scouring mechanisms and scour depth estimates.This study details the flow turbulence characteristics of two submerged piles that are determined by solving the Navier-Stokes equations with the improved delayed detached eddy simulation model.This model is verified by comparing experimental and numerical results for hydrodynamic parameters with the literature for both square-crossing piles(SCPs)and circular-crossing piles(CCPs).Original topographies of flat and scoured beds(i.e.,the initial and equilibrium scouring stages)are based on experimental results obtained by the authors in the present paper.SCP and CCP flow features in the scouring process are discussed.The results indicate that during the scouring process,the time-averaged drag coefficient and root mean square(rms)of the lift coefficient increase linearly in the CCP test,while the rms of the lift coefficient in the SCP test decreases linearly.Moreover,the minimum pressure coefficient is always located in the upstream corners in the SCP case but moves from 72.5°to 79.5°when the scour hole is completely developed in the CCP case.Downward flow behind the pile,which is generated by separated boundary layers above the top face of the pile,can reach the sand bed and turn the separated shear layers into patches of small vortices in the near-wake regions.Thus,the high shear stress zones are mainly at the scour edges under scoured-bed conditions.

Experimental observation of Fermi-level flat band in novel kagome metal CeNi_(5)

Kagome materials are a class of material with a lattice structure composed of corner-sharing triangles that produce various exotic electronic phenomena,such as Dirac fermions,van Hove singularities,and flat bands.However,most of the known kagome materials have a flat band detached from the Fermi energy,which limits the investigation of the emergent flat band physics.In this work,by combining soft x-ray angle-resolved photoemission spectroscopy(ARPES)and the first-principles calculations,the electronic structure is investigated of a novel kagome metal CeNi_(5) with a clear dispersion along the kz direction and a Fermi level flat band in theΓ–K–M–Γplane.Besides,resonant ARPES experimental results indicate that the valence state of Ce ions is close to 4^(+),which is consistent with the transport measurement result.Our results demonstrate the unique electronic properties of CeNi_(5) as a new kagome metal and provide an ideal platform for exploring the flat band physics and the interactions between different types of flat bands by tuning the valence state of Ce ions.

Layered kagome compound Na_(2)Ni_(3)S_(4)with topological flat band

We report structural and electronic properties of Na_(2)Ni_(3)S_(4),a quasi-two-dimensional compound composed of alternating layers of[Ni_(3)S_(4)]^(2-)and Na^(+).The compound features a remarkable Ni-based kagome lattice with a square planar configuration of four surrounding S atoms for each Ni atom.Magnetization and electrical measurements reveal a weak paramagnetic insulator with a gap of about 0.5 eV.Our band structure calculation highlights a set of topological flat bands of the kagome lattice derived from the rotated dxz-orbital with C_(3)+T symmetry in the presence of crystal-field splitting.

Observation of flat-band localized state in a one-dimensional diamond momentum lattice of ultracold atoms

We investigated the one-dimensional diamond ladder in the momentum lattice platform. By inducing multiple twoand four-photon Bragg scatterings among specific momentum states, we achieved a flat band system based on the diamond model, precisely controlling the coupling strength and phase between individual lattice sites. Utilizing two lattice sites couplings, we generated a compact localized state associated with the flat band, which remained localized throughout the entire time evolution. We successfully realized the continuous shift of flat bands by adjusting the corresponding nearest neighbor hopping strength, enabling us to observe the complete localization process. This opens avenues for further exploration of more complex properties within flat-band systems, including investigating the robustness of flat-band localized states in disordered flat-band systems and exploring many-body localization in interacting flat-band systems.

Laser-induced breakdown spectroscopy as a method for millimeter-scale inspection of surface flatness

A non-contact method for millimeter-scale inspection of material surface flatness via Laser-Induced Breakdown Spectroscopy(LIBS)is investigated experimentally.The experiment is performed using a planished surface of an alloy steel sample to simulate its various flatness,ranging from 0 to 4.4 mm,by adjusting the laser focal plane to the surface distance with a step length of 0.2 mm.It is found that LIBS measurements are successful in inspecting the flatness differences among these simulated cases,implying that the method investigated here is feasible.It is also found that,for achieving the inspection of surface flatness within such a wide range,when univariate analysis is applied,a piecewise calibration model must be constructed.This is due to the complex dependence of plasma formation conditions on the surface flatness,which inevitably complicates the inspection procedure.To solve the problem,a multivariate analysis with the help of Back-Propagation Neural Network(BPNN)algorithms is applied to further construct the calibration model.By detailed analysis of the model performance,we demonstrate that a unified calibration model can be well established based on BPNN algorithms for unambiguous millimeter-scale range inspection of surface flatness with a resolution of about 0.2 mm.

Evaluation of the seismic behavior of reinforced concrete structures with flat slab-column gravity frame and shear walls through nonlinear analysis methods

This paper presents an investigation of the seismic behavior of reinforced concrete(RC)structures in which shear walls are the main lateral load-resisting elements and the participation of flat slab floor systems is not considered in the seismic design procedure.In this regard,the behavior of six prototype structures(with different heights and plan layouts)is investigated through nonlinear static and time history analyses,implemented in the OpenSees platform.The results of the analyses are presented in terms of the behavior of the slab-column connections and their mode of failure at different loading stages.Moreover,the global response of the buildings is discussed in terms of some parameters,such as lateral overstrength due to the gravity flat slab-column frames.According to the nonlinear static analyses,in structures in which the slab-column connections were designed only for gravity loads,the slab-column connections exhibited a punching mode of failure even in the early stages of loading.However,the punching failure was eliminated in structures in which a minimum transverse reinforcement recommended in ACI 318(2019)was provided in the slabs at joint regions.Furthermore,despite neglecting the contribution of gravity flat slab-column frames in the lateral load resistance of the structures,a relatively significant overstrength was imposed on the structures by the gravity frames.

A More Accurate Determination of the Magnitude of Cosmic Inflation in the Big Bang Model

According to our hypothesis, at the very beginning of the Big Bang, a hyperenergetic spherical wave was created. We described its characteristics in our previous work, and the present work is based on them. Logically, we saw that in cosmic inflation the frequency of such a wave would decrease sharply. Based on the temperature that prevailed immediately after inflation according to the hot Big Bang model, we determined a measure of the size of the inflation in this model, in accordance with our hypothesis.

Thermodynamic Analysis and Optimization of Flat Plate Solar Collector Using TiO_(2)/Water Nanofluid

To research solar energy's efficiency and environmental benefits,the thermal efficiency,exergy,and entropy of solar collectors were calculated.The experiment involved two glass-topped collectors,fluid transfer tubes,and aluminum heat-absorbing plates.Glass wool insulation minimized heat loss.A 0.5% TiO_(2)/Water nanofluid was created using a mechanical and ultrasonic stirrer.Results showed that solar radiation increased thermal efficiency until midday,reaching 48.48% for water and 51.23% for the nanofluid.With increasing mass flow rates from 0.0045 kg/s to 0.02 kg/s,thermal efficiency improved from 16.26% to 47.37% for water and from 20.65% to 48.76% for the nanofluid.Filtered water provided 380 W and 395 W of energy in March and April,while the nanofluid increased it to 395 W and 415 W during these months.Mass flow generated energy,and the Reynolds number raised entropy.The noon exergy efficiency for nanofluids was 50%-55%,compared to 30% for water.At noon,the broken exergy measured 877.53 W for the nanofluid and 880.12 W for water.In Kirkuk,Iraq,the 0.5% TiO_(2)/Water nanofluid outperformed water in solar collectors.

Changes of coastline and tidal flat and its implication for ecological protection under human activities: Take China’s Bohai Bay as an example

The change processes and trends of shoreline and tidal flat forced by human activities are essential issues for the sustainability of coastal area,which is also of great significance for understanding coastal ecological environment changes and even global changes.Based on field measurements,combined with Linear Regression(LR)model and Inverse Distance Weighing(IDW)method,this paper presents detailed analysis on the change history and trend of the shoreline and tidal flat in Bohai Bay.The shoreline faces a high erosion chance under the action of natural factors,while the tidal flat faces a different erosion and deposition patterns in Bohai Bay due to the impact of human activities.The implication of change rule for ecological protection and recovery is also discussed.Measures should be taken to protect the coastal ecological environment.The models used in this paper show a high correlation coefficient between observed and modeling data,which means that this method can be used to predict the changing trend of shoreline and tidal flat.The research results of present study can provide scientific supports for future coastal protection and management.

How the Flat Space Cosmology Model Correlates the Recombination CMB Temperature of 3000 K with a Redshift of 1100

This paper shows how the Flat Space Cosmology model correlates the recom-bination epoch CMB temperature of 3000 K with a cosmological redshift of 1100. This proof is given in support of the recent publication that the Tatum and Seshavatharam Hubble temperature formulae can be derived using the Stephan-Boltzmann dispersion law. Thus, as explained herein, the era of high precision Planck scale quantum cosmology has arrived.

Product Development of High Strength and Toughness Spring Flat Steel

With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.

Experimental Study of Temperature and Humidity Variations in an Incubator Fitted with a Flat-Plate Collector

In Burkina Faso, where livestock farming is widely practiced, particularly in rural areas without access to electricity, solar energy offers a viable alternative due to the country’s abundant sunshine. To support poultry farmers in increasing their production, we developed a solar-powered incubator equipped with a flat-plate collector, requiring no grid electricity. This is a new approach that we want to experiment with because the incubators on the global market operate either with the electricity grid, photovoltaic, gas or oil and not a solar thermal concentrator. This solar concentrator represents the heat source of the device during the day. We plan to look for rocks with high thermal inertia in order to heat them during the day using another flat solar concentrator and then introduce them into the incubator at night to continue the incubation process. In 2022, we conducted a simulation to study temperature variation inside the incubator. In this work, we built a prototype to experimentally evaluate key hydrothermal properties such as air temperature and humidity. Furthermore, we will not introduce rocks into the incubator overnight but will let the system run overnight to see how the hygrothermal properties vary. The findings revealed temperature fluctuations from 25˚C to 65˚C, instead of the desired 36˚C to 38˚C, and humidity levels ranging from 15% to 57%, instead of the target 55% to 75%. Solutions have been proposed to enhance the system’s performance.

免耕播种机勒洛三角形镇压轮设计与试验

针对免耕播种机镇压轮在地表有残茬时,作业阻力大、作业后种沟土壤平整度差的问题,设计了一种勒洛三角形刚性镇压轮。以镇压轮的定宽高度和宽度为试验因素,以工作阻力、土壤平整度、土壤下陷量为指标,采用中心复合表面试验设计(Central Composite Face-centered design, CCF)进行离散元仿真优化试验。对试验数据进行分析并得出回归模型,获得镇压轮最优结构参数。仿真结果表明:镇压轮定宽高度为274.75 mm、宽度为78.49 mm时,作业性能最优;此时,工作阻力为32.73 N、种沟土壤平整度为2.64 mm、土壤下陷量为14.25 mm。与传统镇压轮进行田间对比试验,结果表明:勒洛三角形镇压轮作业后,土壤密度为1.16 g/cm^(3),满足农作物生长所需条件;勒洛三角形镇压轮作业阻力比传统镇压轮减少9.1%、地表平整度提高15.3%。该研究为免耕播种机镇压轮的设计提供新的思路和借鉴。

不同栅氧退火工艺下的SiC MOS电容及其界面电学特性

SiC MOS电容的电学特性和栅氧界面特性是评价和改进SiC MOS器件制造工艺的重要依据。通过依次测试SiC MOS器件的氧化物绝缘特性、界面态密度、偏压温度应力不稳定性(偏压温度应力条件下的平带电压漂移)、氧化物陷阱电荷密度和可动电荷密度的方法,对分别经过氮等离子体氧化后退火(POA)处理、氮氢混合等离子体POA处理、氮氢氧混合等离子体POA处理、氮氢氯混合等离子体POA处理的SiC MOS电容的电学特性和栅氧界面特性进行了分析。结果表明,该方法可以系统地评价SiC MOS电容电学特性和栅氧界面特性,经过氮氢氯混合等离子体POA处理的SiC MOS电容可以满足高温、大场强下长期运行的性能指标。

平房仓准低温储藏稻谷温度场的演变规律

通过实验研究与数值模拟相结合的方法,研究了平房仓准低温储藏稻谷温度场的时空分布。通过对平房仓准低温储藏稻谷进行了为期14个月粮温实验,得到了稻谷温度场的演变规律;同时构建了准低温储藏稻谷温度场的数值模型,对其进行模拟,并与实验结果对比验证了数值模型的有效性;最后,利用本文模型对26个月内的稻谷温度场进行预测。研究表明:在为期14个月平房仓准低温储藏的实验过程中,稻谷的整体平均温度低于17℃,最高值是15.57℃、最低值是11.32℃;依据模型对平房仓准低温储藏26个月进行模拟,在整个模拟过程中稻谷整体平均温度呈上升趋势,平均粮温仍处于17℃以下;月平均最高粮温均出现在每年的九月份,第一年和第二年分别为14.85℃、15.34℃,表层粮温最高值同样出现在九月份分别为15.3℃、15.8℃。本文探究的稻谷温度场演变规律,可为稻谷平房仓准低温储藏提供应用支持。

老旧小区综合整治实践与建议——以北京某中央国家机关小区改造为例

中央国家机关老旧小区综合整治与地方存在一定差异,产权单位在项目申报、改造和居民协调过程中发挥重要作用。本文以北京某中央国家机关小区为例,介绍了“12121”居民协调模式等经验做法,并提出了扁平化管理等思考建议,以期为其他类似项目提供可参考的借鉴和思路。

Nanogrinding of SiC wafers with high flatness and low subsurface damage

Nanogrinding of SiC wafers with high flatness and low subsurface damage was proposed and nanogrinding experiments were carried out on an ultra precision grinding machine with fine diamond wheels. Experimental results show that nanogrinding can produce flatness less than 1.0μm and a surface roughness Ra of 0.42nm. It is found that nanogrinding is capable of producing much flatter SiC wafers with a lower damage than double side lapping and mechanical polishing in much less time and it can replace double side lapping and mechanical polishing and reduce the removal amount of chemical mechanical polishing.

Feasible Rate of Tidal Flat Reclamation——Jiangsu Mud Coast as a Case Study

Reclamation of tidal flat is one of the main ways to get a dynamic balance of the total amount of plowland. With the development of social economy and the increasing demand for plowland, the contradiction between tidal flat reclamation and environment protection becomes more and more outstanding. However, tidal flat reclamation should also follow the dynamic balance of total amount of tidal flat amount. The paper analyzed the history of reclamation and development of Jiangsu mud coast, and calculated the feasible rates of tidal flat reclamation on different stretches respectively, and pointed out that both the economic social benefits of reclamation and the natural erosion-accretion conditions of the coasts should be taken into consideration in deciding the intensity of tidal flat reclamation, so as to satisfy demands on both reclamation and protection of tidal flat resource.

The Submanifolds with Parallel Mean Curvature Vector in a Locally Symmetric and Conformally Flat Riemannian Manifold

In the present paper we obtain the following result: Theorem Let M^R be a compact submanifold with parallel mean curvature vector in a locally symmetric and conformally flat Riemannian manifold N^(n+p)(p>1). If then M^n lies in a totally geodesic submanifold N^(n+1).

SI-FLAT板形仪激振频率设定

SI-FLAT板形仪是国内宽带钢冷连轧机首次采用的非接触式工业用板形仪,但实际使用过程中发现,对于常轧规格的带钢,其激振频率设定始终为同一固定值,激振力仅随张应力的变化而变化,导致板形控制不稳定,激振频率的设置严重影响着板形检测的精度.本文在分析现场实际生产数据的基础上,提出了激振频率的设置应该遵循的两个基本原则,即振幅控制原则和检测间隔控制原则.为了对带钢振动进行固有频率和受迫振动振幅的分析和计算,采用大型有限元软件ANSYS12.0建立了带钢振动仿真模型,分析了带钢板形、宽度、厚度、张应力等因素所导致的带钢固有频率波动对带钢振幅的影响.研究发现,张应力和板形对带钢固有频率的影响较大.最后,基于振幅控制原则和检测间隔控制原则提出了可行性方案,即通过限制最小张应力,减小板形对测量结果的影响;同时为了控制最小检测间隔,便于对板形的在线控制,激振频率的大小应根据带钢速度进行调节设定.