EFFECT OF AXIAL SPACING ON COMPRESSOR STABILITY

Experimental studies are carried out at a low speed axial compressor with five different rotor/stator gaps. Analysis of the effect of axial spacing of two successive blade rows on the measured mean flow coefficient at stall inception and on the flow range of compressor under multi-cell rotating stall operating conditions proves that the stator can suppress the flow disturbance in the compressor and strengthen the stability of the compressor. Experimental data show that the stall flow coefficient decreases by reducing the axial spacing of successive blade rows. Moreover, by reducing the axial spacing, the stall pattern transition pace from multi-cell stall to single-cell stall can be shifted. And the compressor directly slips into single-cell stall at 21.0% CR axial spacing. By analyzing the pressure fluctuation closed to the surge line, it can be known that there exists an eigenfrequency where the amplitude of the oscillating pressure suddenly and dramatically increases as the compressor runs close to the surge line and this pressure disturbance is relevant to the compressor instability.

Numerical and Experimental Studies on the Effect of Axial Spacing on Hydrodynamic Performance of the Hybrid CRP Pod Propulsion System

The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST k ？？ turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically and experimentally. It shows that RANS with the sliding mesh method and SST k -ω turbulence model predicts accurately the hydrodynamic performance of the hybrid CRP pod propulsion system. The axial spacing has little influence on the hydrodynamic performance of the forward propeller, but great influence on that of the pod unit. Thrust coefficient of the pod unit declines with the increase of the axial spacing, but the trend becomes weaker, and the decreasing amplitude at the lower advance coefficient is larger than that at the higher advance coefficient. The thrust coefficient and open water efficiency of the hybrid CRP pod propulsion system decrease with the increase of the axial spacing, while the torque coefficient keeps almost constant. On this basis, the design principle of axial spacing of the hybrid CRP pod propulsion system was proposed.

3D FE Analysis of Effect of Ground Subsidence and Piled Spacing on Ultimate Bearing Capacity of Piled Raft and Axial Force of Piles in Piled Raft

The effects of ground subsidence and piled spacing on axial force of piles in squared piled rafts were investigated using numerical analysis. Two cases of piled rafts in soft clay including case 1 (s = 2d) and case 2 (s = 4d) with s and d were piled spacing and piled diameter respectively were considered in this study. Undrained (without ground water pumping) and drained (with ground water pumping) conditions were applied in each case in order to evaluate variations of ultimate bearing capacity of piled raft and axial force of the piles in piled raft. The results showed that ultimate bearing capacity increased about 25% for undrained condition and about 32% for drained condition when piled spacing increased from 2d to 4d. In the same piled spacing, axial force of the piles increased about 9% for piled spacing of 2d and 7% for piled spacing of 4d when drained condition was applied. When piled spacing increased 2 times (2d to 4d), the axial force of piles increased about 7% for undrained condition and about 5% for drained condition.

Effect of Pre-Swirling Flow on Performance and Flow Fields in Semi-Opened Axial Fan

In this study, we tried to improve the performance by giving a pre-swirling flow to the radial inflow that occurred in the semi-opened axial fan. In addition, the flow fields of rotor outlet were clarified experimentally, and the effect of pre-swirling flow was considered. The experiment was carried out using a performance test wind tunnel with a square cross section of 880 mm. Three types of casings were prepared, in which the blade tip protruded 0%, 20%, and 40% of the meridional chord length. They were called R25, R15, and R05, respectively, in the casing bellmouth model code. Guide blades for generating a pre-swirling flow were installed on the vertical wall surface of the casing. In addition, a vertical wall was installed 60% upstream of the meridional chord length as an obstacle to prevent axial inflow. The velocity fields of the rotor outlet were measured using a hot-wire anemometer. From the results, the pre-swirling flow did not significantly affect the fan performance. When there was no obstacles wall upstream, there was a partial increase in efficiency, but the difference was not so large. When there was an obstacle wall upstream, the efficiency increased overall in the case of R15, but in the case of R05, the efficiency increased only in the low flow rate region, and conversely decreased in the high flow rate region. By observing the blade outlet flow fields when the performance was improved, it was confirmed that the influence of the tip leakage vortex was weakened.

空间运动刚体加速度瞬轴位置的分析

针对空间运动刚体的加速度分析,本文提出了在各种情况下确定空间运动刚体加速度瞬轴(或动轴)位置的方法。研究结果表明,对于空间运动的刚体,当角速度矢与角加速度矢平行时,存在加速度瞬轴(或动轴),此时,刚体可视为绕加速度瞬轴(或动轴)作转动,即用加速度瞬轴(或动轴)法求解刚体上任一点的加速度。用这种方法分析空间运动刚体上各点加速度的时候更加方便快捷。

ANALYTICAL SOLUTION OF AXIAL SYMMETRICAL WALL TEMPERATURE DISTRIBUTION FOR HOLLOW CYLINDER

Using the variable transformation method,the formulae of the axial symmetrical wall temperature distribution during steady heat conduction of a hollow cylinder are derived in this paper.The wall temperature distribution and the wall heat flux distribution in both axial and radial direction can be calculated by the temperature distribution of the liquid medium both inside and outside the cylinder with temperature changing in axial direction.The calculation results are almost consistent with the experience results.The applicative condition of the formulae in this paper consists with most of practice.They can be applied to the engineering calculation of the steady heat conduction.The calculation is simple and accurate.

混凝土芯水泥土复合桩竖向承载特性分析方法

基于Euler梁理论和状态空间法,建立了综合考虑非线性芯桩-水泥土-桩周土界面作用的双层叠合直梁分析模型及其状态方程,推导了成层土中不同组合形式的复合桩截面内力与变形的统一解析解,有效地考虑了复合桩分析中土与结构相互作用、结构局部参数发生变化等难点。通过与已有文献中现场试验和数值计算结果对比,验证了该方法的有效性,并讨论了桩径比、芯长比和水泥土弹性模量对桩承载特性的影响。研究结果表明:(1)桩径比增大,可提供的桩侧摩阻力和桩端阻力增大,复合桩竖向承载力基本呈线性增长;(2)芯长比增大,复合桩竖向承载力的增长幅度逐渐增大;(3)水泥土弹性模量对于桩竖向承载力影响较小。

管道非对称双腐蚀缺陷相互作用极限间距

管道长期运行过程中会产生形态不一的腐蚀缺陷,相邻腐蚀缺陷间存在相互作用,从而影响管道的失效压力。然而,针对非对称腐蚀缺陷管道的相互作用极限间距尚还没有系统的研究。有鉴于此,采用有限元方法对含非对称双腐蚀缺陷管道相互作用极限间距进行研究。首先,验证了Benjamin爆破试验中多腐蚀缺陷有限元建模的可靠性。在此基础上,对轴向方向上长度非对称腐蚀缺陷和深度非对称腐蚀缺陷进行研究,同时对环向方向上长度非对称腐蚀缺陷和深度非对称腐蚀缺陷进行研究。研究结果表明:对于含非对称腐蚀缺陷的管道,本文得出的非对称腐蚀缺陷的相互作用极限间距在评价非对称腐蚀缺陷时要更加准确。

对旋轴流通风机轴向间距对性能影响分析

以FBDCZ-8-NO27型对旋轴流通风机为例,模拟分析了轴向间距对旋轴流通风机性能的影响。首先,将通风机规格尺寸、材料特性等参数录入到CFD软件内,由该软件自动构建出通风机及流体的有限元模型,并根据研究需求划分网格,然后以此为基础,分别从稳态与非稳态两个方面出发,模拟分析了三种轴向间距条件下通风机性能的变化情况,以设计出最佳的通风机轴向间距,提升通风机性能,使其在煤矿生产作业中发挥出更大的作用。

大跨度下基坑支护结构体系受力及变形分析

以中国科学院临床研究医院为工程背景,采用排桩与斜支撑相结合的支护体系,运用ABAQUS有限元软件建立本构模型,重点分析医院基坑施工过程中桩顶水平位移与斜支撑轴力的变化规律,并改变其斜支撑间距,分析对其造成的影响。首先模拟得到桩顶水平位移与斜支撑轴力,发现桩顶水平位移与斜支撑轴力均随着基坑开挖深度的增大而增大,最大值均发生在基坑开挖深度10 m处,桩顶水平位移的最大值为24.13 mm,斜支撑轴力最大值为600.85 kN,均未超过预警值;再对比现场监测数据,发现两者变化规律基本一致,验证了数值分析的有效性;最后改变其斜支撑间距,分别设置为6、8、10 m,并与原斜支撑间距进行对比,通过分析,发现原工程方案斜支撑间距设置最为合理。

Effects of axial static stress on stress wave propagation in rock considering porosity compaction and damage evolution

A wave equation of rock under axial static stress is established using the equivalent medium method by modifying the Kelvin-Voigt model.The analytical formulas of longitudinal velocity,space and time attenuation coefficients and response frequency are obtained by solving the equation using the harmonic method.A series of experiments on stress wave propagation through rock under different axial static stresses have been conducted.The proposed models of stress wave propagation are then verified by comparing experimental results with theoretical solutions.Based on the verified theoretical models,the influences of axial static stress on longitudinal velocity,space and time attenuation coefficients and response frequency are investigated by detailed parametric studies.The results show that the proposed theoretical models can be used to effectively investigate the effects of axial static stress on the stress wave propagation in rock.The axial static stress influences stress wave propagation characteristics of porous rock by varying the level of rock porosity and damage.Moreover,the initial porosity,initial elastic modulus of the rock voids and skeleton,viscous coefficient and vibration frequency have significant effects on the P-wave velocity,attenuation characteristics and response frequency of the stress wave in porous rock under axial static stress.

Effective Curvature Matrices and Mixed Moments of General Pulsed Paraxial Beams

On the basis of the space-time Wigner distribution function, we use the least-squares fitting method to derive the relationship between effective wavefront curvature matrices and second-order mixed moments of quasimonochromatic and polychromatic pulsed paraxial beams. The expressions here are valid for both completely coherent and partially coherent light in the three-dimensional space. Finally, the fitting method is extended to the higher-order situation;from this, a novel technique for characterizing the beam phase from the moments and their derivatives is presented.

空间任意运动刚体速度瞬轴位置的分析

针对刚体空间任意运动的速度分析,本文提出了“轴向速度投影定理”。基于该定理,本文分析了空间任意运动刚体速度瞬轴位置的情况。研究结果表明,对于空间任意运动的刚体,有时候存在速度瞬轴,有时候不存在速度瞬轴。存在速度瞬轴的时候,刚体绕速度瞬轴作转动或瞬时转动;不存在速度瞬轴的时候,它存在一根速度动轴,刚体沿速度动轴方向作螺旋运动或瞬时螺旋运动。在此基础上,分析空间任意运动刚体上各点速度的时候就更加方便快捷。

轴向间距对FBCDZ-10-No20型对旋风机失速过程的影响

对旋风机在小流量工况运行时容易出现失速甚至喘振等不稳定现象,为研究轴向间距对对旋风机失速起始及其发展与传播过程的影响,采用Shear Stress Transport(剪切应力输运)k-ω湍流模型,对一台FBCDZ-10-No20型对旋风机全通道内的非定常流动进行数值模拟,探究了2种轴向间距下对旋风机的失速发展过程。结果表明:轴向间距对对旋风机失速起始及发展过程具有显著影响。在失速起始阶段,当对旋风机两级叶轮的轴向间距为170 mm时,失速起始扰动首先发生于后级叶根吸力面的尾缘区域,之后扰动沿径向从叶根向叶顶发展,沿周向向某个叶片通道聚集,导致该叶片通道堵塞,从而引起对旋风机失速;当轴向间距为70 mm时,失速起始扰动先后发生于前、后级的叶顶区域,之后扰动逐渐增强,最终发生失速。在完全失速阶段,轴向间距对于失速涡团沿周向、轴向及径向的传播都具有显著影响。轴向间距为170 mm时对旋风机进入单涡团全叶高失速,失速涡团沿轴向传播范围限于后级叶轮区域,沿周向以33.3%的后级转速旋转;轴向间距为70 mm时对旋风机进入多涡团部分叶高失速,失速涡团先后在两级叶轮叶顶区域产生,沿轴向向上、下游传播,沿径向分散于各叶片通道的70%叶高以上区域。由于两级叶轮轴向间距的改变,引起了对旋风机的失速起始扰动类型发生了由“局部喘振型”向“突尖型”的转变。

轴向间距对矿用旋风机旋转失速性能的影响

矿用对旋风机在小流量工况运行时极易出现旋转失速现象,严重影响其运行稳定性。采用SST k-ω湍流模型,对FBCDZ-10-No20型对旋风机在5种轴向间距下全流道内的非定常流动进行数值模拟,研究了轴向间距对矿用对旋风机失速过程的影响,揭示了不同轴向间距时的失速起始与发展机理。结果表明:轴向间距对失速起始扰动的首发位置、表现形式和发展过程都具有显著影响。对于70、100 mm两种轴向间距,失速起始扰动均首发于前级叶顶,随后在两级叶轮之间的动−动干涉作用下,后级叶顶也出现失速起始扰动,但与70 mm的轴向间距相比,当轴向间距为100 mm时,动−动干涉效应相对较弱,使得后级出现失速起始扰动需要更长的时间。对于140、170、225 mm三种轴向间距,失速起始扰动均是首先发生在后级叶根区域,不同的是140 mm间距时,前级叶顶泄漏流不能完全随主流流出通道,而是形成了局部叶顶堵塞区;而对于170、225 mm两种间距,前级叶顶则几乎没有堵塞区,最终仅在后级形成了成熟的失速涡团。随着轴向间距的增大,由前级叶顶泄漏流发生前缘溢流及尾缘反流形成的堵塞区逐渐缩小,而由后级叶根吸力面径向涡流形成的堵塞区则逐渐增大,当前级叶顶泄漏流无法形成堵塞区时,失速类型就由前级叶顶泄漏流诱发的“突尖型”转变为由后级叶根径向涡流诱发的“局部喘振型”。

TBM掌子面力学模型与滚刀破岩力推力预测

以掌子面岩体破坏前状态建立了滚刀推力作用的双集中力模型,采用弹性半空间理论的Boussinesq解答和叠加原理,给出了双滚刀协同作用下岩体应力分布的解析解。根据应力分布的特点和TBM破岩要求,提出了TBM破岩的必要条件;采用单轴强度理论和多轴强度理论,分别给出了滚刀破岩推力的预测公式。工程实例表明,采用本文提出的基于多轴强度理论的预测公式计算出的滚刀破岩推力与TBM工作时实际使用的推力非常吻合。

沙漠砂混凝土空间边节点抗震性能有限元分析

为了研究沙漠砂混凝土空间边节点的抗震性能,利用ABAQUS有限元软件建立7个空间边节点和1个平面边节点模型,通过破坏现象、滞回曲线、骨架曲线和延性性能等,分析材料类型、节点形式、轴压比和配筋率对节点抗震性能的影响。结果表明:等效塑性应变最大值位置出现在梁柱交接处的柱子侧面和梁侧面,此处混凝土最容易脱落,钢筋最容易发生断裂。沙漠砂混凝土空间边节点比普通砂混凝土空间边节点的初始刚度和延性分别大约15%和18%,可以作为普通砂混凝土的替代材料。空间节点比平面节点的屈服荷载和极限荷载分别小约3%和2%,但延性系数比平面节点大约16%。轴压比从0增加到0.6时,空间节点的初始刚度和耗能分别增大约42%和12%,但延性降低约2.41%。配筋率从1.54%增加到3.08%时,试件的极限承载力、初始刚度和延性分别增大约15%、20%、29%,但建议节点设计时柱子纵筋不仅要满足承载力,且应对称与均匀配筋。

沙漠砂混凝土梁柱空间中节点抗震性能有限元分析

为得到沙漠砂混凝土梁柱空间中节点的抗震性能,利用ABAQUS软件建立7个沙漠砂混凝土和1个普通混凝土空间中节点有限元模型,通过得到的结构破坏现象、滞回曲线、骨架曲线、延性性能等研究了混凝土材料、加载制度,轴压比及配箍率等对梁柱空间中节点抗震性能的影响。结果表明:沙漠砂混凝土与普通砂混凝土节点的屈服荷载、极限载荷、屈服点至极限点承载力余量、初始刚度与延性系数相近,且屈服点至极限点变形能力储备比普通砂混凝土节点约大23%;双轴加载与单轴加载空间节点的平均屈服荷载、平均极限荷载和屈服点至极限点承载力余量相近,而屈服点至极限点变形能力储备比单轴加载空间节点小约13%;随着轴压比从0增加至0.6,试件的屈服荷载逐渐增大,屈服点至极限点承载力余量逐渐减小;随着配筋率从1.54%增加至3.08%,试件的屈服荷载和极限荷载逐渐增大,屈服点至极限点承载力余量逐渐减小;沙漠砂混凝土空间节点的破坏位置位于梁柱交界处柱子的四角,钢筋的屈服位置位于节点的柱纵筋处。

基于轴线模型的医院公共空间交通组织优化设计研究

基于空间句法理论,运用Depth Map X软件对医院案例进行测算,分析得出数值图谱,归纳说明了综合医院平面轮廓、空间布局、路径网络等因素对可达性和使用者路径选择的影响,进而对综合医院功能布局、交通组织提出优化策略。研究过程证明了轴线分析方法对提高医院空间设计的科学性有显著的帮助。

沙漠砂混凝土框架空间角节点抗震性能分析

为得到沙漠砂混凝土空间角节点的抗震性能,利用ABAQUS有限元软件建立6个沙漠砂混凝土空间角节点、1个沙漠砂混凝土平面角节点和1个普通砂混凝土空间角节点模型,通过滞回曲线、骨架曲线、耗能和延性系数等,研究了不同材料、不同节点形式、不同轴压比与配箍率对梁柱节点抗震性能的影响。研究结果表明:沙漠砂混凝土角节点的初始刚度与延性系数比普通混凝土节点均大约7%和9%。平面节点与空间节点的初始刚度、延性系数和屈服点至极限点承载力余量相近,但极限载荷与变形能力储备比空间节点分别小约3%和9%。轴压比从0增加至0.6,试件平均初始刚度增大约42%。柱子的配筋率从1.54%增加至3.08%时,试件的平均屈服荷载、平均极限荷载和变形能力储备分别增加约13%、21%和35%。节点破坏位置发生在梁柱交界处柱子的四角,此处混凝土最容易脱落。