Influence of wavelength-to-excavation span ratio on ground motion around deep underground excavations

Accurate estimation of ground motion around excavations is important for dynamic rock support design in deep civil tunnels and underground mines. Among the influencing factors, the wavelength-to-excavation span ratio (λ/D) has a large effect on ground motion. Using an advanced wave propagation simulation tool, we performed two series numerical experiments to study the effect of the λ/D ratio on ground motion near excavation boundaries. The modeling results reveal that the wave field becomes more complex as the λ/D ratio decreases. The absolute PPV (Peak Particle Velocity) values around an excavation are closely related to the intensity of the seismic source but the relative PPV value depends on the λ/D ratio. Amplification factors, defined as the PPV in the excavation model to the PPV in the background model without any excavation, are calculated for each case. The amplification factor around the excavation increases significantly as the λ/D ratio decreases. When the λ/D ratio is greater than 30, the wave amplitudes are less affected by the excavation and a seismic wave loading can be considered as “quasi-static.” When the λ/D ratio is less than 20, significant wave interaction occurs and the wave loading needs to be considered as “dynamic.” The numerical results provide additional insights into the ground motion behavior around excavations under both “quasi-static” and “dynamic” loading conditions.     

齿面相对滑动速度和诱导法曲率变化对剃齿精度的影响

本文分析了剃齿加工中齿面相对滑动速度的变化以及齿面诱导法曲率的变化对被剃齿轮齿形中凹的影响.在此基础上,提出了某些与提高剃齿精度有关的结论.     

内外单螺带—锚搅拌槽中粘弹性流体的流速分布和混合时间

本文用照相法测定了内外单螺带锚搅拌槽中高粘牛顿流体和粘弹性流体的流速分布,用示踪粒子法和脱色法分别测定了循环时间和混合时间,结果发现: (1)在低Re~*数下,对于同一转速,粘弹性流体的切向速度大于牛顿流体,而轴向速度则小于牛顿流体。 (2)在槽中的低剪切区,两种流体的剪切率分布相差不大,而高剪切区的剪切率和全槽平均剪切率都是粘弹性流体的大。 (3)粘弹性流体的混合时间NT_M和循环流量N_q与牛顿流体和假塑性流体相比分别增加一倍和降低70％右左。     

关于速度空间中的积分变分原理

本文提出了速度空间中的两种积分变分原理,讨论了存在驻值原理的条件及极值性质,最后讨论了速度空间中的变分原理在弹性动力学中的应用。     

微动力测试仪原理及应用

微动力测试是指：被微机构的动态微力矩Ｍ，微力矩所作的微功Ａ，瞬时微功率Ｐ，以及它们的最大值和一些相关参数的测量，其测量方法和测试仪器的原理包括了应变式微力传感器和力－力矩转换机构，本文给出了微力传感器设计、实验的推导以及实验数据；针对微动力测试的特点独特设计了速度模拟系统的工作原理；测试仪器的整体的结构原理；最后给出了一些微型精密机构的实测结果。     

An analysis for AlGaN/GaN modulation doped field effect transistor using accurate velocity-field dependence for high power microwave frequency applications

An analytical model of Al_0.15Ga_0.85N/GaN modulation doped field effect transistor (MODFET), which uses an accurate velocity field relationship and incorporates the dominant effect of piezoelectric polarization induced charge at the AlGaN/GaN interface is presented. The effect of traps has also been taken into account. The calculated DC characteristics are in excellent agreement with the measured data. The model is extended to predict the microwave performance of the device. High current levels (>500 mA/mm), large transconductance (160.83 mS/mm) and a high cutoff frequency (9.6 GHz) have been achieved analytically and are in close agreement with the experimental data.     

印花糊料透网性评价

本文用印浆试验法和滤浆试验法测定了若干糊料的透网性能。结果指出,印浆量和网目相关性值适用于纯净的糊料,而浆料滤过速度更能正确地反映糊料在生产使用中的透网性能。     

用声速法在线测量强酸溶液的浓度

超声波技术为化工溶液浓度的测量提供了可能。由于强酸中超声波速度在一定浓度上存在着极值现象，因此超声波测量溶液浓度的技术只适用于某些浓度范围。作者根据超声波速度与强酸溶液浓度的关系提出了一种用声速法测量强酸浓度的方法，该法特别适用于化工厂生产液的在线测量。     

COMPUTATION OF THE FLOW FIELD IN A RECIRCULATING TURBULENT GAS JET

As part of an overall investigation of flash-smelting processes, numerical computations were performed for the turbulent recirculating flow field of a gas jet in a confined cylindrical system. The two-equation (k - e) model was used to describe turbulence. The two-dimensional elliptic partial differential equations cast into finite difference forms were solved by the TEACH code (Gosman and Pun, 1973), and the pressure field was computed by the SIMPLER method (Patankar, 1980). Various correlations for the dissipation rate of turbulent kinetic energy at the inlet were tested, and the relation yielding the best results was obtained as E= C_μK^1.5/(0.015d_e where d_e = 4 x hydraulic radius. Extensive comparisons have been made between the computed results using the proposed form of e at the inlet and experimental data taken from the literature. Much better predictions than previously possible have been obtained     

The analysis of flow-induced vibration and design improvement in KSNP steam generators of UCN #5, 6

The KSNP Steam Generators (Youngkwang Unit 3 and 4, Ulchin Unit 3 and 4) have a problem of U-tube fretting wear due to Flow Induced Vibration (FIV). In particular, the wear is localized and concentrated in a small area of upper part of U-bend in the Central Cavity region. The region has some conditions susceptible to the FIV, which are high flow velocity, high void fraction, and long unsupported span. Even though the FIV could be occurred by many mechanisms, the main mechanism would be fluid-elastic instability, or turbulent excitation. To remedy the problem, Eggcrate Flow Distribution Plate (EFDP) was installed in the Central Cavity region of Ulchin Unit 5 and 6 steam generators, so that it reduces the flow velocity in the region to a certain level. However, the cause of the FIV and the effectiveness of the EFDP was not thoroughly studied and checked. In this study, therefore the Stability Ratio (SR), which is the ratio of the actual velocity to the critical velocity, was compared between the value before the installation of EFDP and that after. Also the possibility of fluid-elastic instability of KSNP steam generator and the effectiveness of EFDP were checked based on the ATHOS3 code calculation and the Pettigrew’ s experimental results. The calculated results were plotted in a fluid-elastic instability criteria-diagram (Pettigrew, 1998, Fig. 9). The plotted result showed that KSNP steam generator with EFDP had the margin of Fluid-Elastic Instability by almost 25%.