Insulation effect of air cavity in sand mold using 3D printing technology

The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.

地下圆形衬砌洞室对SH波的散射(Ⅰ):3-D级数解

针对地下圆形衬砌洞室对入射平面SH波的散射问题,采用波函数展开法,研究了不同频率入射波作用下,圆形衬砌洞室散射的三维级数解.结果表明:当入射波所在平面与圆形衬砌洞室Z轴互相垂直时,该级数解退化为半无限二维空间中的结果.级数解为定量研究圆形衬砌洞室对不同入射角度和入射波长下的SH波的散射引起的地震动的影响提供了理论依据.

基于3-D打印技术的新型微波/毫米波无源波导器件

综述了近年来基于多种3-D打印工艺的微波直至太赫兹频段无源波导器件的发展研究现状,并介绍了作者所在小组研制的多个基于立体光刻3-D打印工艺的滤波器(包括基于新型高Q值单模和双模球形腔体谐振器的X频段带通滤波器以及基于裂缝波导和紧凑片上结构的W频段带通滤波器).这些滤波器射频性能的测量与仿真结果吻合良好.与相同形状的铜制器件相比,采用非金属材料的3-D打印器件的重量减轻了80%以上,并保持了优良的射频性能.

Sound absorption characteristic of micro-helix metamaterial by 3D printing

We present the design of micro-helix metamaterial supporting high sound absorption characteristic by 3D printing. The sample structure which is fabricated out of polylactide （PLA） material, many micro-helix are arranged by periodic arrays on XY plane. Experiment measurement results show that different geometrical dimensions of helix vestibule and cavity depth have a great effect on sound absorption coefficient. Physical mechanism depends on the friction and viscosity between the air and the helix vestibule. This work shows great potential of micro-structure metamaterial in noise control applications require light weight and large rigid of sound absorption.

Forced and Natural Vibrations of an Orthotropic Pre-Stressed Rectangular Plate with Neighboring Two Cylindrical Cavities

Forced and natural vibrations of a rectangular pre-stressed orthotropic compositeplate containing two neighboring cylindrical cavities whose cross sections are rectangularwith rounded-off corners are investigated numerically. It is assumed that all the end surfacesof the rectangular pre-stressed composite plate are simply supported and subjected to auniformly distributed normal time-harmonic force on the upper face plane. The consideredproblem is formulated within the Three-Dimensional Linearized Theory of Elastic Waves inInitially Stressed Bodies (TDLTEWISB). The influence of mechanical and geometricalparameters as well as the initial stresses and the effect of cylindrical cavities on the dynamicalcharacteristics of the rectangular orthotropic composite plate are analyzed and discussed.

Effects of Loess Cavity on Soil Moisture Movement: Revealed by Soil Column and HYDRUS Model

The purpose of this study is to advance our current understanding of soil moisture storage in subsurface and water infiltration rate in loess soil. Therefore, a set of experiments was conducted on two soil columns filled with silty clay loam, with and without applying cavity technical method. For the soil column applied with loess cavity, the ponding infiltration was simulated using HYDRUS-2D/3D, version 2.x and the simulated results were verified by those of observation. The results show that 1) the loess cavity significantly decreased the infiltration rates when the flux permeated through it (varying from 0.358 to 0.208 cm·min-1) as compared with no cavity soil column (varying from 0.408 to 0.241 cm·min-1);2) similarly, the total cumulative infiltration and at the termination of wetting front advancement of soil column with cavity were 66 cm and 69 cm lower than that of no cavity soil column (76 and 78 cm), respectively. Consequently, the soil moisture at the subsurface and surrounding the loess cavity was effectively ameliorated;3) the model was capable of predicting water infiltration processes in the soil column with loess cavity, and the root mean square error of simulated water contents, wetting front advancements, cumulative infiltrations, and infiltration rates were from 0.22 to 3.63 cm3·cm-3, 1.6 to 3.63 cm, 3.44 cm, and 0.026 cm·min-1, respectively. Overall, the findings in this study indicate that loess cavity can effectively increase soil moisture storage at shallow surface and the HYDRUS-2D/3D model is capable of simulating and predicting scenarios to help achieve stable shallow soil surface with loess cavity.

3D阶梯模板在SMT特殊制程及器件上的应用技术

在当前的SMT生产制程中，由于某些电子产品SMD凹腔电路板（CarityPCB）设计、元器件高密度组装与特殊构造需要，以及通孔回流焊（Through—HoleReflow）器件、混合制程器件（HybridProcessComponent）、正反表面焊接连接器（DoubleSurfaceReflowSolderingDevice）等问题，令焊锡膏或胶的印刷与涂覆工艺，变得日益复杂与多样化。而一直来最具主流的普通平面型印刷模板（2DScreenStencil），便难以满足日新月异复杂工艺需求，于是非共面性阶梯模板（3DStencil）应运而生，它为解决SMT特殊制程及异型器件的焊锡或胶的印刷涂覆问题，正发挥着日益重要的作用。3DStencil的设计多种多样且用途广泛，它适宜各种较为复杂的PCBA组装工艺需求，可用在各种较为前端的特殊而复杂的工艺产品上。传统的非共面性3D模板，通常有局部减薄模板（Step—downstencil）、局部加厚模板（Step—upstencil）或两种工艺同时在一块模板上应用，模板的局部加厚或减薄的阶梯高度，通常需依据PCB板面的凹陷或凸起高度以及元器件的特点灵活应对，且加厚或减薄的阶梯既可放在模板装锡膏的印刷面，也可放在模板的底面。而时下的精密特制3D阶梯型模板，其模板钢片厚度与普通2D模板无异，但阶梯高度可达N20mm它足以避让底部多数己组装的SMD器件或AI器件剪脚后的高度。这种模板通常称之为VectorGuard3DStencil，由于它能够对己贴片组件展示出全方位的立体屏蔽保护而得名。3D阶梯模板在设计制作过程中，需重点关注其脱模性能与模板的使用寿命，力求使其既有良好的印刷效果又能经久耐用。在各种模板的制作工艺中，电铸成形模板和激光切割／电抛光模板的印刷性能较好，而以激光切割加电抛旋光性价比最高；对于印刷工艺的优化，模板的设计是关键的一环。为了使焊锡膏的脱模性能达到最好，模板上的开孔尺寸比率以及开孔性能应当按照行业标准设计，其开口的宽厚比、面积比、开孔梯度、开口侧壁的光洁度等方面都有严格要求。多半情况下，通过3D阶梯模板能够解决的SMT特殊制程及器件的工艺难题，也能通过非接触式喷印（JetPrinting）或针头点涂（Dispenser）的工艺方式解决。不过机器喷印或点涂的方式，不仅前期设备投资巨大，而且它们对于高密度设计的PCB和精细间距器件（FinePitchTechnology），在组装精度、质量和效率等诸多方面都还受到限制，很多时候还不及3D模板实用有效。

大间隙速调管输出腔支撑杆的3维设计

利用3维高频软件对大间隙速调管输出腔及其同轴提取波导金属支撑杆进行了高频分析,建立了带双排金属支撑杆的大间隙输出腔3维结构模型,采用3维PIC程序对该输出腔的提取效果进行了粒子模拟。研究结果表明:作为输出腔同轴提取波导支撑的第二排支撑杆,和兼作输出腔腔壁的第一排支撑杆,都会影响输出腔的高频谐振特性,因此必须结合大间隙输出腔进行一体化设计;此时同轴提取波导支撑杆设计的基本原则不以追求最高的TEM模式传输效率为目的,而是通过控制双排支撑杆的散射特性,得到合适的外部品质因数和间隙电场强度。在注入电功率约2.9GW,束流调制深度90%时,设计的带双排支撑杆的3.6GHz大间隙输出腔结构,可提取约1.06GW的平均功率,效率约36.5%。

基于二维、三维地质雷达快速探测城市地下灾害——以长沙某道路为例

采用新一代三维地质雷达Raptor45联合二维地质雷达,在湖南长沙某道路开展了地下灾害快速探测研究,快速有效分辨出地下管线、人工构造物等地下结构物和地下疏松体、脱空、空洞等城市道路地下灾害。研究结果为新一代三维地质雷达进一步应用于道路塌陷、地下空洞、地面疏松等地下灾害探测提供了示范案例。

Analysis of Heat Transfer Phenomena inside Concrete Hollow Blocks

During both hot and cold seasons,masonry walls play an important role in the thermal performance between the interior and the exterior of occupied spaces.It is thus essential to analyze the thermal behavior at the hollow block’s level in order to better understand the temperature and heat flux distribution in its structure and potentially limit as much as possible the heat transfer through the block.In this scope,this paper offers an experimental and numerical in-depth analysis of heat transfer phenomena inside a hollow block using a dedicated experimental setup including a well-insulated reference box and several thermocouples and fluxmeters distributed at the boundaries and inside the hollow block.The block was then numerically 3D modelled and simulated using COMSOL Multiphysics under the same conditions,properties,and dimensions as the experimentally tested block.The comparison between the numerical and experimental results provides very satisfactory results with relative difference of less than 4%for the computed thermal resistance.

Solving generalized lattice Boltzmann model for 3-D cavity flows using CUDA-GPU

The generalized lattice Boltzmann equation(GLBE),with the addition of the standard Smagorinsky subgrid-stress(SGS) model,has been proved that it is more suitable for simulating high Reynolds number turbulent flows when compared with the lattice BGK Boltzmann equation(LBGK).However,the computing efficiency of lattice Boltzmann method(LBM) is too low to make it for practical applications,unless using a massive parallel computing clusters facility.In this study,the massive parallel computing power from an inexpensive graphic processor unit(GPU) and a typical personal computer has been developed for improving the computing efficiency,more than 100 times.This developed three-dimensional(3-D) GLBE-SGS model,with the D3Q19 scheme for simplifying collision and streaming courses,has been successfully used to study 3-D rectangular cavity flows with Reynolds number up to 10000.

高密度电法勘探数据三维处理技术及城市勘察中的应用

在以往的高密度数据反演解释过程中,将地质结构简化成二维,通过地电断面图、切片图进行分析。实际上,地质体具有三维地电结构,二维反演难免会受到旁侧效应的影响,二维图件也不能清晰直观地反映地质体的空间分布情况。本文以某陶瓷厂空洞探测为例,利用实测资料构建三维数据场,在反演参数优化的基础上,选择基于最小二乘法的三维反演技术对数据场进行处理,将反演结果利用三维可视化技术显示出来,对采空区位置及空间形态给出结论。研究结果显示,三维处理技术能够从空间上,多手段、多视角分析物探数据,有效地消除了旁侧效应的影响;物探结果直观清晰地呈现出空洞的分布位置、范围以及空间特征,与钻探结果吻合较好。

激光扫描在鼻腔三维重建及测量中的初步应用

目的:通过激光扫描建立0至12岁汉族儿童各年龄段正常鼻腔的三维重建模型,并揭示鼻腔随年龄发育的规律。方法:在全麻状态下对60例0至12岁的进行分组并制取鼻腔模型,用激光扫描仪扫描鼻腔形态,通过计算机工程软件进行模型重建。结果:此法可准确扫描鼻腔内部形态,并通过三维重合重建每组理想的鼻腔内部形态,并可以分析鼻腔随年龄增长的变化情况。结论:激光扫描三维分析方法是分析正常儿童鼻腔形态的理想方法,应用此模型可重建各个年龄段理想的鼻腔内部形态,并可量化分析正常儿童随生长发育而变化的鼻腔形态。

高压输电线塔基煤矿采空区的高密度电阻率法探查研究

煤矿采空区的塌陷与变形对高压供电线塔基的稳定构成了极大的威胁.使用高密度电法对塔基附近的地质结构进行了探测,应用二维和准三维反演方法确定了地下电阻率分布形态,以此为基础推断解释了塔基附近煤矿采空区的位置和形态,并对塔基的加固处理提出了建议.

平面SH波在弹性半空间中三维洞室周围的散射

结合弹性均匀半空间中力源格林影响函数,采用一种间接边界积分方程法求解了弹性半空间中三维洞室对入射平面SH波的散射问题。通过与已有结果的比较,验证了方法的计算精度。在此基础上,以半空间中圆球形洞室为例,对洞室附近地表位移响应和洞周应力集中特征进行了分析,并与二维模型进行了比较。研究表明:三维和二维模型对平面波的散射在整体上存在相似性,但也存在显著差别;二维模型的地表位移峰值均大于三维情况,前者地表位移空间分布更为复杂,动力响应更为剧烈;三维模型的洞室表面应力峰值则普遍大于二维情况,并且在峰值位置上存在显著差异,且随着频率增大,差异愈加明显。

湍流粉碎机吸入腔流场的数值模拟

应用三维粘性流动计算软件NUMECA对湍流粉碎机的吸入腔进行了定常三维紊流流场的数值模拟,得到了吸入腔内部流场的压力、速度分布,直观显示了吸入腔内部的流动现象,为后续阶段的整机联算奠定了基础。

基于PCL与HOOPS的空区点云处理系统的设计与开发

三维激光扫描技术在空区探测中得到了越来越多的应用,但是获取的点云数据往往需要经过多个软件的联合处理与分析,消耗大量的计算处理时间,多个软件在操作上的复杂性也限制了后期数据的利用。针对上述问题,在VS2010编程平台下,利用PCL和HOOPS技术,自主开发了空区点云处理系统。该系统由点云数据管理模块、三维显示模块、点云过滤模块、剖切和实体建模模块及应用模块组成,采用模块化设计的思路,功能易于扩展。根据空区处理精度的要求,能够进行点云的过滤与精简,既满足工程需求,又加快了后期空区三维建模与显示的处理速度;系统集成了三维建模、剖切、体积计算等常用的空区处理机能,显示直观,易于使用,为现场技术人员的决策提供了方便。系统为空区治理方案的选择、参数的优化提供指导和科学依据,对于促进采空区处理的可视化、科学化具有积极的意义。

三维方腔流的混合有限分析解

本文建立了三维对流扩散方程的混合有限分析八点隐格式，并证明了它的基本数学性质。应用原函数法和交错网格技术给出了三维Ｎ—Ｓ方程的混合有限分析解法，计算了雷诺数Ｒｅ＝２０、５０和１００三种情况下的三维方腔内的流场，结果与已有计算成果一致。

三维N-S方程混合有限分析多重网格方法

提出了一种求解三维定常不可压Ｎ－Ｓ方程的混合有限分析多重网格方法（ＨＦＡ－ＦＭＧ）。以三维方腔流动作为算例，计算表明提出的数值格式能极大地节省计算工作量且稳定有效。三维方腔流动的模拟成果较好地表现方腔内复杂的流动特征并和其他成果吻合。

掺气坎角度对溢流坝阶梯面掺气空腔的影响

在宽尾墩+阶梯溢流坝+消力池一体化消能工中利用前置掺气坎连接WES曲面与阶梯溢流坝,能有效增加阶梯面掺气,避免阶梯遭受空化空蚀破坏。主要引用水气两相流VOF方法的RNG k-ε模型,采用几何重建方式对水气面附近进行插值以及利用PISO算法和非定常流算法进行数值模拟,模拟前置掺气坎角度8°,10°和11.3°时阶梯溢流坝上坎后掺气空腔长度及阶梯面压力分布,模拟范围从库区至消力池尾部。为验证模拟计算的可靠性,对阶梯溢流坝坎后掺气空腔进行模型试验,通过坎后空腔长度模拟值与实测值的对比分析,发现两者吻合较好,最大偏差为7.9%。模拟结果表明,掺气空腔长度随前置掺气坎角度的增加而增加,阶梯近壁面最大负压绝对值及压力随前置掺气坎角度的增加而增加且负压分布范围逐渐扩大。