粗集料级配对多孔混凝土性能的影响研究

采用连续级配粗集料和单一粒级粗集料配制多孔混凝土,研究了集料级配对多孔混凝土的表观密度﹑抗压强度﹑空隙率﹑透水系数的影响。试验结果表明,在相同集灰比情况下,采用单一粒级的粗集料配制的多孔混凝土能获得较高的空隙率(大于22%),且抗压强度达15MPa,可满足对护坡工程所用生态混凝土提出的要求。

青铜灌区古灌渠河床渗透系数空间变异性研究

渗透系数影响地表水与地下水之间的水量交换,其大小具有空间效应。通过竖管法(单管法)、多孔介质垂向渗透系数测量仪法(双管法)测定了银川平原青铜峡市灌区汉延、惠农两条古灌渠18个试验点位的渗透系数,每个试验点进行了3组试验,共得到54组试验数据,另采取了16组原状土样进行颗粒分析。通过对试验数据的统计分析得出,研究区2条灌渠的渗透系数在0.1~1.1 m·d-1之间变化,渗透系数值总体服从正态分布,总体变异系数大小为0.441,属于中等程度变异;汉延渠河床渗透系数平均值比惠农渠稍大,但变异程度较惠农渠略小。且从上游至下游,河床渗透系数值总体变化呈下降趋势;颗粒直径是造成本研究区河段渗透系数变异的一个主要因素,但河床渗透系数的大小不仅仅受颗粒直径的影响,河床生物扰动、水化学特征变化等也可能会造成河床渗透系数发生明显变化。

温室滴灌系统支管水力性能影响因素试验研究

通过室内试验研究分析了入口压力、支管长度、毛管间距3个因素对滴灌系统中支管水头损失及沿程压力分布的影响。结果表明:支管上的水头损失随着支管长度和入口压力的增大而增大,随毛管间距的增大而减小,但入口压力增大也同时使得支管沿线压力分布更为均匀。毛管间距0.6、0.9和1.2m条件下,满足水力偏差要求的支管最大铺设长度分别为20、40和60m。支管沿程压力分布曲线服从三次多项式关系,R2均在0.99以上。对支管上水头损失的构成进行了分析,表明局部与沿程水头损失之比fc随支管长度的增加、毛管间距的减小而增加,部分工况下fc会超过1;fc随首部压力的变化较为复杂,与具体的管网铺设s条件相关。多孔系数与来流条件有关,利用克里斯钦森公式计算出的多孔系数比实际值略微偏大,入口雷诺数从22 707增加至50 846时,克里斯钦森公式计算值与实测值之比从1.107降至1.068,表明入口雷诺数越大,克里斯钦森公式的计算精度越高。

Sintering preparation of porous sound-absorbing materials from steel slag

Porous sound-absorbing materials were prepared from steel slag using waste expanded polystyrene（EPS） particles as pore former.The influences of the experimental conditions such as fly ash content,sintering temperature,sintering time,and pore former addition on the performance of the porous sound-absorbing materials were investigated.The results show that the porosity of the specimens can reach above 50.0%;the compressive strength and average sound-adsorption coefficient of the sintered specimens are above 3.0 MPa and 0.47,respectively.The optimum preparation conditions for the steel slag porous sound-absorbing materials are as follows：mass fraction of fly ash 50%,waste EPS particles 3.6 g,sintering temperature 1100℃,and sintering time 7.5h,which are determined by considering the properties of the sound-absorbing materials,energy consumption and cost.

塑料薄膜毛管微孔泄流的水力计算

本文根据塑料薄膜毛管水力学试验成果,提出了针对毛管滴、喷孔孔径很小、流量不大条件下毛管流态的判别及水力计算方法,同时结合试验资料进行验证并给出了计算例题。

EXPERIMENTAL STUDY OF HTC FOR FILM COOLING OF PARALLEL-INLET HOLES

The parallel-inlet holes with one-row, two-row and three-row film hole arrangements and different di- ameters are proposed to experimentally study their cooling characteristics. Detailed experimental processes and results are described and carried out. Results indicate that heat transfer coefficient （HTC） is increased with the increase of blowing ratio. When the blowing ratio is lower, the distribution of HTC along the heated wall can be divided into three regions. For larger blowing ratio or diameter, the cooling characteristics oi parallel-inlet film holes are similar to those of convective heat transfer around flat. Furthermore, when hole diameter is deter- mined, the arrangement patterns of film hole and the blowing ratio take a great influence on HTC.

A Multi-Domain Boundary Element Method to Analyze the Reflection and Transmission of Oblique Waves From Double Porous Thin Walls

In the present paper, we examine the performance of an efficient type of wave-absorbing porous marine structure under the attack of regular oblique waves by using a Multi-Domain Boundary Element Method(MDBEM). The structure consists of two perforated vertical thin barriers creating what can be called a wave absorbing chamber system. The barriers are surface piercing, thereby eliminating wave overtopping. The problem of the interaction of obliquely incident linear waves upon a pair of perforated barriers is first formulated in the context of linear diffraction theory. The resulting boundary integral equation, which is matched with far-field solutions presented in terms of analytical series with unknown coefficients, as well as the appropriate boundary conditions at the free surface, seabed, and barriers, is then solved numerically using MDBEM. Dissipation of the wave energy due to the presence of the perforated barriers is represented by a simple yet effective relation in terms of the porosity parameter appropriate for thin perforated walls. The results are presented in terms of reflection and transmission coefficients. The effects of the incident wave angles, relative water depths, porosities, depths of the walls, and other major parameters of interest are explored.

Experimental study of a simple pressure loss coefficient model for multi-hole orifice

A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） were designed for the throttling experiment to compare the throttling effect using the equivalent diameter ratio （RED） and diameter ratio （RD ） as key parameters, respectively. Meanwhile, effective metrical conditions were provided for experimental accuracy. The throttling model form was determined according to the theoretical throttling model of SO. Then the unknown parameters involved were identified by experimental data. A good concordance between the modeling computation and experimental results shows a validation of the MO throtting model.

Wind Force Coefficients for Designing Porous Canopy Roofs

Wind force coefficients for designing porous canopy roofs have been investigated based on a series of wind tunnel experiments. Gable, troughed and mono-sloped roofs were tested. The roof models were made of 0.5 mm thick perforated duralumin plates, the porosity of which was changed from 0 to about 0.4. Overall aerodynamic forces and moments acting on the roof model were measured in a turbulent boundary layer with a six-component force balance for various wind directions. The results indicate that the wind loads on canopy roofs generally decrease with an increase in porosity of the roof. Assuming that the roof is rigid and supported by the four corner columns with no walls, the axial forces induced in the columns are regarded as the most important load effect for discussing the design wind loads. Two loading patterns causing the maximum tension and compression in the columns are considered. Based on a combination of the lift and moment coefficients, the design wind force coefficients on the windward and leeward halves of the roof are presented for the two loading patterns as a function of the roof pitch and porosity. The effect of porosity is taken into account as a reduction factor of the wind loads.

A Research Note on the Adsorption of CO2 and N2

Experiments were made for the adsorption of CO2 and N2 on typical adsorbents to investigate the effects of porous structure and surface affinity of adsorbents as well as those of adsorption temperature and pressure that might cause the variation of adsorption mechanism. It is shown that polar surface tends to enlarge the adsorption difference between CO2 and N2, and the difference is more sensitive to temperature than the adsorbents with non-polar surface. The adsorbents with non-polar surface are not much sensitive to the effect of water vapor, though the water vapor interferes the separation remarkably. The separation coefficient linearly increases with the micro- pore volume per unit surface area of activated carbons, but no rule is shown on mesoporous silicon materials. The function of adsorption mechanism on the separation is not as much as expected.

Analysis of multi-dimensional SAR for determining the thickness of thin sea ice in the Bohai Sea

Flat thin ice (<30 cm thick) is a common ice type in the Bohai Sea, China. Ice thickness detection is important to offshore exploration and marine transport in winter. Synthetic aperture radar (SAR) can be used to acquire sea ice data in all weather conditions, and it is a useful tool for monitoring sea ice conditions. In this paper, we combine a multi-layered sea ice electromagnetic (EM) scattering model with a sea ice thermodynamic model to assess the determination of the thickness of flat thin ice in the Bohai Sea using SAR at different frequencies, polarization, and incidence angles. Our modeling studies suggest that co-polarization backscattering coefficients and the co-polarized ratio can be used to retrieve the thickness of flat thin ice from C- and X-band SAR, while the co-polarized correlation coefficient can be used to retrieve flat thin ice thickness from L-, C-, and X-band SAR. Importantly, small or moderate incidence angles should be chosen to avoid the effect of speckle noise.

Experimental Study of Dissolved Oxygen Transport by Regular Waves Through a Perforated Breakwater

The perforated breakwater is an environmentally friendly coastal structure, and dissolved oxygen concentration levels are an important index to denote water quality. In this paper, oxygen transport experiments with regular waves through a vertical perforated breakwater were conducted. The oxygen scavenger method was used to reduce the dissolved oxygen concentration of inner water body with the chemicals Na2SO3 and COC12. The dissolved oxygen concentration and wave parameters of 36 experimental scenarios were measured with different perforated arrangements and wave conditions. It was found that the oxygen transfer coefficient through wave surface, K1α1, is much lower than the oxygen transport coefficient through the perforated breakwater, K2α2. If the effect of K1α1 is not considered, the dissolved oxygen concentration computation for inner water body will not be greatly affected. Considering the effect of a permeable area ratio a, relative location parameter of perforations 6 and wave period T, the aforementioned data of 30 experimental scenarios, the dimensional analysis and the least squares method were used to derive an equation of K2α2 （K2α2=0.0042aσ56δ2T1）. It was validated with 6 other experimental scenarios data, which indicates an approximate agreement. Therefore, this equation can be used to compute the DO concentration caused by the water transport through perforated breakwater.

Wave Interaction with a Partially Reflecting Vertical Wall Protected by a Submerged Porous Bar

This study gives an analytical solution for wave interaction with a partially reflecting vertical wall protected by a submerged porous bar based on linear potential theory. The whole study domain is divided into multiple sub-regions in relation to the structures. The velocity potential in each sub-region is written as a series solution by the separation of variables. A partially reflecting boundary condition is used to describe the partial reflection of a vertical wall. Unknown expansion coefficients in the series solutions are determined by matching velocity potentials among different sub-regions. The analytical solution is verified by an independently developed multi-domain boundary element method(BEM) solution and experimental data. The wave run-up and wave force on the partially reflecting vertical wall are estimated and examined, which can be effectively reduced by the submerged porous bar. The horizontal space between the vertical wall and the submerged porous bar is a key factor, which affects the sheltering function of the porous bar. The wave resonance between the porous bar and the vertical wall may disappear when the vertical wall has a low reflection coefficient. The present analytical solution may be used to determine the optimum parameters of structures at a preliminary engineering design stage.

Saint-Venant Fractional Equation and Hydraulic Gradient

The overall objectives to support analytically the mathematical background of hydraulics, linking the Navier-Stokes with hydraulic formulas, which origin is experimental but have wide and varied application. This, leads us study the inverse problem of the coefficients of differential equations, such as equations of the porous medium, Saint-Venant, and Reynolds, and accordingly with the order of derivatives. The research led us to see that the classic version suffers from a parameter that reflects the fractal and non-local character of the viscous interaction. Motivated by the concept of spatial occupancy rate, the authors set forth Navier-Stokes＇s fractional equation and the authors obtain the fractional Saint-Venant. In particular, the hydraulic gradient, or friction, is conceived as a fractional derivative of velocity. The friction factor is described as a linear operator acting on speed, so that the information it contains is transferred to the order of the derivative, so that the same is linearly related to the exponent of the friction factor. It states Darcy＇s non-linear law. The authors take a previous result that describes the nonlinear flow law with a leading term that contains a hyper-geometric function, whose parameters depend on the exponent of the friction factor and the exponent of the hydraulic radius. It searches the various laws of flow according to the best known laws of hydraulic resistance, such as Chezy and Manning.

The Porous Ramie Fabric＇s Heat-Moisture Comfort

This paper in the light of the structure parameters of the ramie fabric to research and evaluation it＇s heart-moisture comfort. Selected 15 kinds of ramie fabric to test the average density, the thickness, the tightness, the heat rate, the heat transfer coefficient, the Clo, the air permeability, the water vapor permeability and other performance index, used SPSS factor analysis to explore the main influence factors of porous ramie fabric＇s heat moisture comfort. Results shows that： the main influence factors of ramie fabric＇s heat-moisture is the heat preservation material, the air permeability and the moisture permeability, get the equation of porous ramie fabric＇ s heat-moisture comfort： F=0.45855y1＋0.30588y2＋0.13549y3, evaluated and sorted the sample fabric＇ s heat-moisture comfort.

Measurement and modeling of the effective thermal conductivity for porous methane hydrate samples

The effective thermal conductivities of gas-saturated porous methane hydrates were measured by a single-sided transient plane source (TPS) technique and simulated by a generalized fractal model of porous media that based on self-similarity.The density of porous hydrate,measured by the volume of the sample in the experimental system,was used to evaluate the porosity of methane hydrate samples.The fractal model was based on Sierpinski carpet,a thermal-electrical analogy technique and one-dimensional heat flow assumption.Both the experimental and computational results show the effective thermal conductivity of methane hydrate decreases with the porosity increase.The porosity of 0.3 can reduce the thermal conductivity of the methane hydrate by 25%.By analysis of the experimental data and the simulative result,the optimized thermal conductivity of the zero-porosity methane hydrate is about 0.7 W m-1K-1.

Local Stability for an Inverse Coefficient Problem of a Fractional Diffusion Equation

Time-fractional diffusion equations are of great interest and importance on describing the power law decay for diffusion in porous media. In this paper, to identify the diffusion rate, i.e., the heterogeneity of medium, the authors consider an inverse coefficient problem utilizing finite measurements and obtain a local HSlder type conditional stability based upon two Carleman estimates for the corresponding differential equations of integer orders.

The periodic unfolding method for the heat equation in perforated domains

We study the heat equation with non-periodic coefficients in periodically perforated domains with a homogeneous Neumann condition on the holes. Using the time-dependent unfolding method, we obtain some homogenization and corrector results which generalize those by Donato and Nabil(2001).