Numerical simulation of molten pool dynamics in high power disk laser welding

A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed.     

Bubble Growth Rates and Nucleation Site Densities in Saturated Pool Boiling of Water at High Pressures

Experiments were carried out to observe boiling behaviors of water on horizontal and vertical surfaces at pressures from 0.35 to 5 MPa. The growth curves of the primary bubbles are well described by the t^1/2 variation over the whole range of pressures. The growth rates of primary bubbles are proportional to the square root of the Jakob number, and agree with the correlation by Labuntsov with the arbitrary constant β = 3. The conventional correlations of bubble growth rates, which are directly proportional to the Jakob number, predict slower growth rates at higher pressures. The coalescence behaviors of the primary bubbles were also measured on the vertical surface at 3.66 MPa. The coalesced bubbles, which were formed by the coalescence of two primary bubbles, grow at rates similar to the rates of the primary bubbles. The nucleation site densities measured on the vertical surface at pressures up to 5 MPa increase in proportion to about the 1.5th power of the pressure under equivalent heat flux conditions. The dependence of the nucleation site densities on the heat flux is very similar to the results obtained near atmospheric pressure where the nucleation site density is proportional to the 1.5th power of the heat flux. The nucleation site densities measured in the range of pressures of 0.35 to 5 MPa and at heat fluxes of 0.05 to 0.35MW/m² agree fairly well with the available correlations.     

Partial aggregation of users for biometric scores normalization

In this paper, we analyze a new method to deal with users' biometric data, by incorporating them in an incomplete aggregation framework, to make an optimal decision for the normalization process. This latter invokes the experts' opinions concept, where the opinions are represented by the user-specific scores. This aggregation of opinions needs more experts for a trusted and informative partial consensus. The key idea of this new approach is based upon the employment of a convex mixture of users' score dispersion. This procedure is used to revise the users' scores, then to update specific statistical parameters which are the principal elements of our score normalization formula. Applying this concept to various scenarios gives an interesting outcome compared to other alternatives. The main contribution of this work for aggregation framework on native space is to introduce this new user-specific concept of scores' normalization, followed by a thorough evaluation of the performance. The validation of this approach is ensured by using a unique modality followed by the exploitation of the fusion of different modalities, to achieve a viable reliability of the final decision. The benchmarking was conducted under Nist2005, Biosecure DS2, and XM2VTS score databases.     

Assessment of chemical and microbiological parameters of indoor swimming pool atmosphere using multiple comparisons

The aim of this study was to evaluate the air quality of an indoor swimming pool, analyzing diurnal and seasonal variations in microbiological counts and chemical parameters. The results indicated that yeast and bacteria counts, as well as carbon dioxide (CO₂), nitrogen oxides (NO_x) and O₃ concentrations, showed significant diurnal difference. On the other hand, temperature, relative humidity (R.H.), yeast counts and concentrations of CO₂, particles, O₃, toluene, and benzene showed seasonal differences. In addition, the relationship between indoor and outdoor air and the degree of correlation between the different parameters have been calculated, suggesting that CO₂, fine particles and NO_x would have indoor origin due to the human activity and secondary reactions favored by the chemical and environmental conditions of the swimming pool; while O₃, benzene and toluene, would come from outside, mainly. The overall results indicated that indoor air quality (IAQ) in the swimming pool building was deficient by the high levels of CO₂ and microorganisms, low temperatures, and high R.H., because frequently the limits established by the legislation were exceeded. This fact could be due to the poor ventilation and the inadequate operation of heating, ventilation, and air‐conditioning systems.     

谈混凝土植筋技术在污水处理工程的应用

结合实际工程介绍了混凝土植筋技术在污水处理工程中的应用,对混凝土植筋技术的施工特点、优缺点等进行了分析,并指出植筋技术在污水处理工程的应用越来越多,有全面取代水工构筑物各种预埋件的趋势。     

基于SWMM的雨水调蓄池容积研究

雨水调蓄池作为城市内涝防治的一种重要措施,其有效容积的确定在设计过程中极为重要。以云南省某市为例,采用传统公式法计算与SWMM软件模拟2种方法得到调蓄池有效容积,对2种方法的结果进行比较分析,结果表明在低重现期下公式法计算值要大于软件模拟值,而在高重现期下软件模拟值将大于公式计算值。     

液层厚度比对环形腔内双层液体的热毛细对流稳定性的影响

为了了解微重力条件下、水平温度梯度作用时,上部为固壁的环形腔内双层流体系统中液层厚度比对流动稳定性的影响,采用隐式重启Arnoldi方法(IRAM)对环形池内5cSt硅油/HT-70双层流体的热对流过程进行了线性稳定性分析,获得了不同液层厚度比下的临界Marangoni数、临界波数、临界相速度,并通过计算特征向量,得到了临界Marangoni数附近液-液界面的热流体波形态。     

A comparative study of correlations of critical heat flux of pool boiling

Nucleate pool boiling is desirable for many engineering systems. One challenge task for designing a system with nucleate pool boiling is to estimate the critical heat flux (CHF), which needs an accurate pool boiling CHF correlation. A few evaluations of pool boiling CHF correlations were reported, which used limited experimental data or covered limited correlations, resulting in inconsistent results. Therefore, it is difficult to determine which one is more appropriate for a given application. In this paper, a database containing 600 data points of pool boiling CHF of 12 pure liquids on plain surfaces having orientation angles of 0°?180° is compiled from 40 published papers. The reduced pressure is from 0.0001 to 0.98, and the 13 fluids are water, helium, nitrogen, hydrogen, R113, FC-72, FC-87, HFE-7100, ethanol, benzene, hexane, pentane, and methanol. With the database, 21 pool boiling CHF correlations are assessed. The most accurate one has a mean absolute deviation of 27.1%, indicating a need for developing more accurate correlations for engineering applications. Besides, the factors affecting the accuracy of correlations are analyzed and some valuable conclusions are obtained. The work lays a valuable foundation for the further study of pool boiling CHF correlations and provides a guide for choosing proper correlations for given applications. Several topics worthy of attention for future studies are suggested.     

某食品加工企业腌泡池智能清洗车设计的方案探讨

针对某食品加工企业上百个大型腌泡池的经常性清洗任务需求,基于现代机电控制技术,提出智能清洗车的解决方案,重点探讨这种清洗车的型式及结构、液压系统与电气控制部分的设计.     

Measuring overall thermal comfort to balance energy use in sports facilities

A study for the development of a monitoring methodology that includes thermal comfort in a smart metering system for sports facilities is presented. The scope of this system is to obtain meaningful information on how energy is used in relation to the level of comfort perceived, so as to allow fully informed management operations. The main problem to be addressed is the accurate quantitative measurement of the thermal comfort inside indoor sports areas (e.g. swimming pools, fitness rooms, etc.), which in this work is estimated through the PMV (Predicted Mean Vote) index. The paper describes what needs to be dynamically measured, which parameters are required, which critical uncertainty factors may arise and how to estimate the indicators. A sensitivity and uncertainty analysis for the PMV measurement in this specific application is performed to develop a simplified approach. The results obtained from the measurement campaigns made in two different sports areas are presented to validate the approach. Finally, a simulation of swimming pool data is used to preliminarily demonstrate the feasibility and effectiveness of the global monitoring system proposed.