A finite volume implicit time integration method for solving the equations of ideal magnetohydrodynamics for the hyperbolic divergence cleaning approach

A finite volume numerical technique is proposed to solve the compressible ideal MHD equations for steady and unsteady problems based on a quasi-Newton implicit time integration strategy. The solenoidal constraint is handled by a hyperbolic divergence cleaning approach allowing its satisfaction up to machine accuracy. The conservation of the magnetic flux is computed in a consistent way using the numerical flux of the finite volume discretization. For the unsteady problem, the time accuracy is obtained by a Newton subiteration at each physical timestep thereby converging the solenoidal constraint to steady state. We perform extensive numerical experiments to validate and demonstrate the capabilities of the proposed numerical technique.     

Modeling of pulsed spark discharge in water and its application to well cleaning

This paper presents a simulation model for the generation of strong pressure wave by means of pulsed spark discharge in water and its application to well cleaning. In the simulation model, one-dimensional time-dependent magnetohydrodynamic equations are coupled to a capacitive discharge circuit equation. A cylindrical conducting spark channel formed by electrical breakdown of water gap between a pair of electrodes is treated as a load of which resistance and inductance are allowed to change with time. For describing the spark channel properties accurately, precise calculations on thermodynamic properties and electrical conductivity are included in the simulation model. The simulation results show an excellent agreement with the experimentally measured shock pressure as well as the current and voltage waveforms. The simulation reveals that Joule heating of the spark channel during the very early phase of electrical discharge plays a key role in the formation of shock wave in water. The voltage on a capacitor at breakdown, the circuit inductance, and the resistance of the spark channel are found to be the most important parameters for the shock wave formation. With this technique, a pilot test for the cleaning of a clogged well has been performed in a water well which was constructed as a test-bed for riverbank filtration near the Anseong-cheon (river) in Korea. Well treatments have been carried out with an electrical energy of 510 J stored on a pulsed power system, at which the maximum shock pressure is measured to be around 7 MPa at the position of the well screen, i.e. 0.1 m away from the spark gap. A slug test shows 2.9 times improvement in the hydraulic conductivity of the well, which, combined with a visual inspection inside the well using an underwater camera, clearly demonstrates that the strong pressure wave generated by underwater spark discharge can effectively remove almost all incrustations formed in the well screen and thus improve well performance. Operating parameters for controlling the strength of shock pressure are discussed using the simulation model for extensive applications of the present technique to various types of water wells.     

Homogenization theory for designing graded viscoelastic sonic crystals

In this paper,we propose a homogenization theory for designing graded viscoelastic sonic crystals(VSCs) which consist of periodic arrays of elastic scatterers embedded in a viscoelastic host material.We extend an elastic homogenization theory to VSC by using the elastic-viscoelastic correspondence principle and propose an analytical effective loss factor of VSC.The results of VSC and the equivalent structure calculated by using the finite element method are in good agreement.According to the relation of the effective loss factor to the filling fraction,a graded VSC plate is easily and quickly designed.Then,the graded VSC may have potential applications in the vibration absorption and noise reduction fields.     

生物质燃烧碳烟的物化特性及生成机理研究

以棉花秸秆和木屑为研究对象,设定不同的燃烧工况,在管式炉中进行燃烧并采集碳烟物质,采用TEM、EDS、GC-MS等检测方法对生物质燃烧过程中生成碳烟的物化特性进行研究,并根据检测结果对碳烟生成机理进行分析和推测。检测及分析结果表明,碳烟颗粒典型形貌有胶囊状、球状、链状、网状等。燃烧工况影响燃烧过程使碳烟颗粒表现出不同的微观形貌。碳烟生长过程中伴随着颗粒的碰撞和凝并,形成形貌复杂的链状或网状颗粒聚团。生物质燃烧中碳烟主要由纤维素热裂解生成,成分包括糠醛类、酚类、醛类、呋喃、烷烃、烯烃等含碳化合物。推测碳烟生成机理为,在生物质燃烧过程中,纤维素发生化学键的断裂与重排,生成CO、CO₂和残炭分子碎片等,而残余碳基再通过重整、脱水、碳化、断键等反应生成各种醛类、酮类等产物,醛类、酮类化合物之间通过缩聚、环化反应生成苯环结构,再进一步转化为苯酚、甲苯等化合物。     

Using Surfactant System to Wash a Polluted Soil by Petroleum Derivatives in Egyptian Abu Madi Fields in Terms of Emulsification

The exploration and production activities of the natural gas in Abu Madi region (in middle delta) progressed in the last decade. The condensate hydrocarbon and formation water are bi‐products produced during the natural gas industry. The accompanied water contains 10–15% condensate (gasoline). This water with gasoline was drained into the Shehab El‐Din drain. The farmers were used this water to irrigate their fields. Great areas of the fields were out of order of planting as the result of gasoline pollution. This work concentrates on washing the polluted soil using locally prepared surfactant (LABSA‐Na) in the washing process. The soil sample was picked up from the Abu Madi field and was divided into pots (four pots for each treatment). The experiment was designed on the basis of polluting the soil by gasoline (condensate) from 1 to 10%. The washing process was carried out in presence of 0.1, 0.3, and 0.5% surfactant solutions. The control and blank sample were taken in consideration. The washed and the latent oil percentages were determined using the spectrophotometric method. After polluting and washing the soil, the pots were fertilized and planted by Zea Mays. The pots were irrigated twice a week. The length of plants was followed up. The obtained results cleared that, the efficiency of washing process increases with increasing of the pollutant percentage and also with increasing of surfactant concentration. The maximum washed oil (gasoline) was obtained at 10% gasoline and 0.5% surfactant concentration. The length of plants after 21 days of planting were; 0 (no planting), 24, 34, 39, 54, and 57 cm against polluted soil and planted (control) washed soil by water only; washed soil by 0.1%; washed soil by 0.3%; washed soil by 0.5% and no polluted soil (blank) respectively. These data revealed that, removing the hydrocarbon from the soil by washing using surfactants is the most effective method as the result of solubilization and emulsification of the hydrocarbon by surfactant which make it more removable.     

First principles study of gallium‐cleaning for hydrogen‐contaminated α‐Al2O3(0001) surfaces

The use of gallium for cleaning hydrogen‐contaminated Al₂O₃ surfaces is explored by performing first principles density functional calculations of gallium adsorption on a hydrogen‐contaminated Al‐terminated α‐Al₂O₃(0001) surface. Both physisorbed and chemisorbed H‐contaminated α‐Al₂O₃(0001) surfaces with one monolayer (ML) gallium coverage are investigated. The thermodynamics of gallium cleaning are considered for a variety of different asymptotic products, and are found to be favorable in all cases. Physisorbed H atoms have very weak interactions with the Al₂O₃ surface and can be removed easily by the Ga ML. Chemisorbed H atoms form stronger interactions with the surface Al atoms. Bonding energy analysis and departure simulations indicate, however, that chemisorbed H atoms can be effectively removed by the Ga ML. © 2013 Wiley Periodicals, Inc.     

铈铁锆三元复合氧化物上碳烟的催化燃烧

采用水热法制备了纯CeO₂、Fe₂O₃和系列Ce₀.5Fe₀.5-xZr_{xO2复合氧化物催化剂,采用XRD、Raman、H2-TPR和BET等方法对其进行了表征,并利用程序升温氧化反应(TPO)技术研究了其碳烟燃烧催化性能。结果表明,Zr⁴+完全进入CeO2晶格中形成了固溶体,而Fe³+较难进入CeO2晶格中,部分Fe2O3分散在固溶体表面。固溶体形成产生的氧空位和表面高度分散的氧化铁协同作用是铈铁锆三元复合氧化物具有较高碳烟燃烧催化性能的关键。同时,与单纯的铈铁二元复合氧化物相比,Zr⁴+的掺杂明显提高了催化剂的抗老化能力,使Ce0.5Fe0.5-xZrxO2复合氧化物显示出更好的应用前景。在系列样品中,Ce0.5Fe0.30Zr0.20O2样品由于形成了最多的固溶体并具有良好分散性的表面Fe2O3,显示出最好的催化活性和稳定性。其催化碳烟的起燃温度(ti)和峰顶温度(tp)分别为251℃和310℃,长时间高温老化后其ti和tp仍较低,分别为273℃和361℃。}     

Cavitation in a periodontal pocket by an ultrasonic dental scaler: A numerical investigation

Periodontal pockets are spaces or holes surrounded by teeth under the gum line. These pockets can become filled with infection-causing bacteria resulting in tissue, bone, and tooth loss. Cavitation produced by the oscillating tip of dental ultrasonic scalers plays a significant role in routine periodontal therapy to clean these areas. Numerical studies were conducted for a scaler vibrating in a periodontal pocket which was simplified to a hole, using ABAQUS based on the finite element method. The simulations consider the three-dimensional, nonlinear, and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation. The numerical model was validated by comparing results with experimental data for a scaler vibrating in an unbounded liquid, the displacement at the free end of the scaler and the cavitation pattern near the scaler tip displaying excellent agreement. A parametric study for a scaler vibrating in a hole has been carried out in terms of the volume of the hole, the taper ratio (the radius ratio between the circular opening and bottom of the hole), and the immersion depth of the scaler tip in the hole. The amount of cavitation generated is evaluated by the cavitation density (or the void fraction) which is the ratio of the volume of the cavitation occupied in the hole to the total volume of the hole. Numerical results indicate that the cavitation density in the hole increases with the decreasing hole volume and the increasing taper ratio. It is inferred that cleaning effects could be increased if some modifications to the scaler design could be made to increase the blocking effect of the hole during the cleaning process. Cavitation is observed in the hole even if the scaler is placed above the hole and increases with the immersion depth.     

轴对称含烟黑火焰非均匀温度与烟黑浓度分布同时重建模拟研究

对于非均匀吸收、发射、无散射的轴对称含烟黑火焰对象,常规双色法不再适用。本文基于烟黑辐射特性,提出并模拟研究了同时重建火焰温度与烟黑容积份额的新的辐射测量方法。从重建结果看,重建误差主要集中在火焰中心区域,这是观测路径上测量误差累积的结果。温度重建主要受火焰断面参数分布类型影响,而烟黑容积份额重建主要受测量误差的影响,这由它们与单色辐射强度的内在关系所决定。     

以虚拟仪器为平台的声学实验

基于计算机声卡和Adobe Audition软件制作了声学虚拟仪器,可实现示波器、信号发生器和频率计算仪器功能,并介绍了此声学虚拟仪器在双音多频信号DTMF的研究、声速的测量和变音钟实验中的具体应用.