技术进步与建筑界面形态的演变

技术进步正大跨步地改变着人们的生产方式、生活习惯,亦影响着人们的审美观念,尤其是迅猛发展的高新技术给社会带来巨大变革的同时,也对建筑领域产生了极大的影响。建筑材料类型的丰富、建筑结构技艺的更迭、建筑设备性能的升级都直接或者间接地牵制着建筑形态。本文通过对技术变革剧烈的近现代时期典型建筑界面形态在结构技术及计算技术两个层面的解析,厘清其在技术演进路线上的演绎步进,探讨建筑界面发展趋势,以及对其产生影响的各种技术因素的内在联系。     

海控国际广场超高空屋顶空间网架施工技术

海控国际广场项目建筑高度249.7m,其结构标高213.700～ 249.700m为拱形空间异形网架结构.该部分结构体系复杂,单拱最大跨度36.2m,最大高度36m,且处于超高空施工,受环境条件影响大,决定采用无胎架支撑安装方法.通过对施工过程的模拟分析,证明该方法可行,并将施工监测数据与施工模拟结构进行对比分析,及时反馈,保证施工安全性.对比实施方案证明无胎架施工减少了施工措施投入,施工更加经济、快捷.     

基于结构重叠网格的栅格翼导弹流场数值仿真

采用结构重叠网格方法对栅格翼导弹的粘性流场进行了数值仿真计算,相对于单一结构网格而言,该方法不但降低了网格生成难度,提高了网格质量,而且大幅度降低了网格数量,计算结果表明该方法是可靠有效的。     

网架结构固有振动分析的分解刚度法

把矩形平面网架结构简化为夹层板,采用考虑剪切变形的具有三个广义位移的平板弯曲理论进行分析。基于分解刚度的思想提出了网架结构固有频率的计算方法,给出了八种网架结构(正放四角锥网架、两向正交正放网架、正放抽空四角锥网架、三角锥网架、三向网架、抽空三角锥网架、两向正交斜放网架和斜放四角锥网架)各阶频率的统一计算公式,对八种网架进行了固有振动分析,并与有限元分析结果进行了对比。作为一种简化的计算方法,该方法不仅计算公式简单,而且其精度比较高,误差基本在10%以内,可以为网架结构分析与设计作参考。     

Study on the influence of three-grid assembly thermal deformation on breakdown times and an ion extraction process

In order to study the influence of three-grid assembly thermal deformation caused by heat accumulation on breakdown times and an ion extraction process,a hot gap test and a breakdown time test are carried out to obtain thermal deformation of the grids when the thruster is in 5 k W operation mode.Meanwhile,the fluid simulation method and particle-in-cell-Monte Carlo collision(PICMCC) method are adopted to simulate the ion extraction process according to the previous test results.The numerical calculation results are verified by the ion thruster performance test.The results show that after about 1.2 h operation,the hot gap between the screen grid and the accelerator grid reduce to 0.25–0.3 mm,while the hot gap between the accelerator grid and the decelerator grid increase from 1 mm to about 1.4 mm when the grids reach thermal equilibrium,and the hot gap is almost unchanged.In addition,the breakdown times experiment shows that 0.26 mm is the minimal safe hot gap for the grid assembly as the breakdown times improves significantly when the gap is smaller than this value.Fluid simulation results show that the plasma density of the screen grid is in the range 6?×10~(17)–6?×?10~(18) m~(13) and displays a parabolic characteristic,while the electron temperature gradually increases along the axial direction.The PIC-MCC results show that the current falling of an ion beam through a single aperture is significant.Meanwhile,the intercepted current of the accelerator grid and the decelerator grid both increase with the change in the hot gap.The ion beam current has optimal perveance status without thermal deformation,and the intercepted current of the accelerator grid and the decelerator grid are 3.65 m A and 6.26 m A,respectively.Furthermore,under the effect of thermal deformation,the ion beam current has over-perveance status,and the intercepted current of the accelerator grid and the decelerator grid are 10.46 m A and 18.24 m A,respectively.Performance test results indicate that the breakdown times increase obviously.The intercepted current of the accelerator grid and the decelerator grid increases to 13 m A and 16.5 m A,respectively,due to the change in the hot gap after 1.5 h operation.The numerical calculation results are well consistent with performance test results,and the error comes mainly from the test uncertainty of the hot gap.     

Study of the key factors affecting the triple grid lifetime of the LIPS-300 ion thruster

In order to ascertain the key factors affecting the lifetime of the triple grids in the LIPS-300 ion thruster,the thermal deformation,upstream ion density and component lifetime of the grids are simulated with finite element analysis,fluid simulation and charged-particle tracing simulation methods on the basis of a 1500 h short lifetime test.The key factor affecting the lifetime of the triple grids in the LIPS-300 ion thruster is obtained and analyzed through the test results.The results show that ion sputtering erosion of the grids in 5 kW operation mode is greater than in the case of 3 kW.In 5 kW mode,the decelerator grid shows the most serious corrosion,the accelerator grid shows moderate corrosion,and the screen grid shows the least amount of corrosion.With the serious corrosion of the grids in 5 kW operation mode,the intercept current of the acceleration and deceleration grids increases substantially.Meanwhile,the cold gap between the accelerator grid and the screen grid decreases from 1 mm to 0.7 mm,while the cold gap between the accelerator grid and the decelerator grid increases from 1 mm to 1.25 mm after 1500 h of thruster operation.At equilibrium temperature with 5 k W power,the finite element method(FEM)simulation results show that the hot gap between the screen grid and the accelerator grid reduces to 0.2 mm.Accordingly,the hot gap between the accelerator grid and the decelerator grid increases to 1.5 mm.According to the fluid method,the plasma density simulated in most regions of the discharge chamber is 1?×?10~(18)-8?×?10~(18)m~(-3).The upstream plasma density of the screen grid is in the range 6?×?10~(17)-6?×?10~(18)m~(-3)and displays a parabolic characteristic.The charged particle tracing simulation method results show that the ion beam current without the thermal deformation of triple grids has optimal perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 5.5?×?10~(-14)kg s~(-1)and 4.28?×?10~(-14)kg s~(-1),respectively,while after the thermal deformation of the triple grids,the ion beam current has over-perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 1.41?×?10~(-13)kg s~(-1)and 4.1?×?10~(-13)kg s~(-1),respectively.The anode current is a key factor for the triple grid lifetime in situations where the structural strength of the grids does not change with temperature variation.The average sputtering rates of the accelerator grid and the decelerator grid,which were measured during the 1500 h lifetime test in5 k W operating conditions,are 2.2?×?10~(-13)kg s~(-1)and 7.3?×?10~(-13)kg s~(-1),respectively.These results are in accordance with the simulation,and the error comes mainly from the calculation distribution of the upstream plasma density of the grids.     

一种跟踪电网频率的新方法

基于正交变换,提出了一种新的电网频率跟踪方法.针对两种模型进行仿真,表明该方法能够较为精确与快速地跟踪电网频率,尤其针对突变频率的信号,具有较好的跟踪效果;同时算法克服了同步采样条件的限制,通过迭代,在不同初始频率下均具有较好的收敛性.     

基于支持向量机的复杂地质分形特征自动提取

为了提升勘探工作效率,准确提取复杂地质分形特征,提出一种支持向量机的复杂地质分形特征自动提取方法.在两种线性可分情况下,将最佳的分类面简化为最佳分类直线,获得最佳分类平面;考虑噪声及其它干扰因素造成线性不可分的状况,得到广义的最佳分类面;基于两点可以得出支持向量机内积;通过抽取异常重磁分维数的频率域角度获得分维值,反映...     

板栅连铸结晶器传热模型分析

传热过程决定着板栅连铸结晶器能否连续稳定地生产出合格质量的连铸板栅,根据热力学第一定律和傅里叶定律(热传导定律)对板栅连铸结晶器的热量传递进行了研究。依据板栅连铸结晶器实际结构简化模型,分别建立了冷却油、端盖以及空气稳态复合传热模型,高温铅液、连铸动模外筒以及冷却油的稳态复合传热模型,连铸动模内部冷却油的放热计算模型,进而建立了板栅连铸结晶器传热动态平衡方程;为了指导生产实际,建立了运行过程操作函数。通过板栅连铸结晶器传热过程的分析研究,对提高板栅连铸的连续稳定生产并实现板栅连铸结晶器的全自动温度控制具有一定的指导意义。     

不同网格中导热方程的精确解和数值解

用基元有限容积方法求解热传导问题,结构化网格和非结构化网格同时采用,并和精确解相比较.虽然从两种网格形式,都能得到满意的结果,但结构化网格在规则区域更精确一些.对于非结构化网格,二次扩散项对提高精度是十分重要的.