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地震栓波器是用来栓测竖向地震波的仪器.本文根据它的实际结构,提出了一个较精确的力学模型——双层三悬丝模型.把悬丝作为曲杆,用动力稳定性理论进行分析,揭示了地震仪栓波器由于竖向地震波以外的因素而产生输出的所谓假频现象产生的原因:位于悬丝所在水平面内的激励在一定条件下将导致悬丝在面外动力失稳而产生强烈振动,从而引起虚假输出.计算结果说明了影响假频的诸因素,为激励速度峰值、激励相对于栓波器的方向和曲杆面内振动的固有频率等的作用,并与实验值作了比较. 相似文献
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具有高固气比、低流速的挤压流型气固两相输送技术已在高技术领域的工程中得到应用.本文从实验和理论两方面研究了煤粉挤压流型的输送特性.试验的范围是:输送的固气比 m=280-770,空隙率8=0.37-0.58,单位面积管道煤粉输送流量 G_s/A=96-453g/s·cm~2.理论上用剪切应力模型进行分析,得到单位管长的压力降计算式.理论预测与实验结果是一致的. 相似文献
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煤粉在直管和弯管中输送的压力损失 总被引:1,自引:0,他引:1
本文是在分析颗粒运动的基础上,应用量纲分析,得到气粉在管内流动时的摩擦系数关系式.试验是在负压式气粉试验系统中进行,测量气粉在输送管道内的压差后,得到雷诺数在4.68×10~4-2.41×10~5、因气质量比在0.1—0.9的范围内,煤粉在垂直管、水平管和90°弯管内的摩擦系数λ_s 和压力降的经验计算式. 相似文献
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《固体力学学报》2017,(1)
利用实验研究与理论分析相结合的方法研究了泡沫铝填充金属薄壁圆管在准静态侧向压缩下的力学响应.基于能量法,建立了泡沫铝填充圆管和金属薄壁圆管在侧向均匀压缩时的瞬时侧向力、平均侧向力和总吸能的理论公式.对泡沫铝填充管与金属薄壁圆管进行了准静态侧向压缩实验,并且将实验结果与理论公式进行了对比,结果表明理论预测值与实验结果吻合较好.基于建立的理论分析模型,研究了管的几何尺寸以及泡沫铝材料的密度对结构的瞬时侧向力、平均侧向力、总吸能和比吸能的影响.结果表明,在准静态侧向压缩下,泡沫铝填充管的总吸能大于对应的金属薄壁圆管;泡沫铝填充管的侧向压缩力和总吸能随管长度、壁厚和直径的增加而增大;当填充材料泡沫铝密度增大时,填充管的总吸能与侧向压缩力均增加. 相似文献
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本文首先利用波函数展开法推导了弹性半空间中埋管的地基轴向阻抗函数计算公式.然后采用层状地基中无限长线激振荷载薄层法基本位移解,结合容积法求解了层状地基中埋管的地基轴向、垂直及水平阻抗函数.分别用两种方法计算了弹性全空间、弹性半空间地基内埋管的地基轴向阻抗函数,两者的计算结果符合良好,验证了用薄层法求解的可行性.本文还利用薄层法分析了弹性半空间内埋管的埋深对地基水平、垂直及轴向阻抗函数的影响;计算了弹性半空间内埋管的轴向刚度系数并与我国及日本的相关规范对比分析;计算分析了上海典型层状地基内地铁隧道的地基阻抗函数. 相似文献
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给出一种垂直上升油-气-水三相弹状流压力降的计算模型。该模型考虑弹状流中Taylor气泡周围下降液膜的变化历程。通过油-气-水弹状流的实验研究发现,该模型的数值模拟结果与低压工况下的实验值符合得较好。本模型是计算垂直油-气-水三相弹状流中液相的连续相为水相时的压力降的有效方法。 相似文献
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药筒发射应力和抽壳力的有限元分析 总被引:4,自引:1,他引:3
应用非线性有限元方法计算药筒的发射应力和抽壳力。结构分析分别采用轴对称和三维有限元计算模型。分析表明 :由于起膛线的作用 ,轴对称模型有比较大的误差。计算数据表明 :由于药筒为薄壁圆筒结构 ,膛压的作用导致药筒内部较高的等效应力和塑性变形 ;特别是膛压下降时 ,身管的收缩又使得药筒受到反向压力作用而再次屈服 ,并使等效应力达到最大值 ,并且维持在一个常值。因此抽壳力是必要的 ,而且开栓时间对抽壳力的影响很小。讨论了初始间隙等因素对发射应力和抽壳力的影响。 相似文献
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粘接多胞管三点弯曲实验与数值研究 总被引:1,自引:0,他引:1
基于实验和数值模拟方法,本文研究了一种易制备粘接多胞薄壁结构的弯曲性能,分析了粘接多胞管在横向三点弯曲加载下的变形和能量吸收性能。三点弯曲准静态实验表明:由于粘接的作用,通常情况下粘接多胞管的能量吸收性能高于其基本构成单胞管能量吸收的总和,但在某些情况下粘接可以带来70%的性能提升。借助于LSDYNA,我们计算模拟了三点弯曲实验,计算得到的粘接多胞管变形模式和力-位移曲线与实验结果吻合良好。此外,采用计算模拟方法,我还对三种不同接触条件下的结构响应进行了对比分析,结果表明:如果未出现明显的粘接脱开,则粘接多胞管的吸能特性与完整的多胞结构相当,否则其能量吸收性能会被严重削弱。 相似文献
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Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction, which limits their capability for increased predictive accuracy relative to experimental data. This is partly because of the nature of slug flow pneumatic conveying system, which, as a dynamic system, never becomes stable. By utilising conservation of mass (airflow), a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour. The rate of air permeation through slug, one of the important factors in the conservation model, is expressed as a function of a slug permeability factor. Other factors such as slug velocity, slug length and the fraction of stationary layer were also considered. Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model, showing good agreement between the model and experimental results. 相似文献
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Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction,which limits their capability for increased predictive accuracy relative to experimental data.This is partly because of the nature of slug flow pneumatic conveying system,which,as a dynamic system,never becomes stable.By utilising conservation of mass (airflow),a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour.The rate of air permeation through slug,one of the important factors in the conservation model,is expressed as a function of a slug permeability factor.Other factors such as slug velocity,slug length and the fraction of stationary layer were also considered.Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model,showing good agreement between the model and experimental results. 相似文献
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Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses.Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved.Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy.This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders.The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations.In particular,the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz.A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline.Furthermore,there was significant variation in gas pulse amplitude for different types of particulate material. 相似文献
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Kenneth C. Williams Mark G. Jones Ahmed A. Cenna 《Particuology》2008,6(5):301-306
Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses. Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved. Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy. This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders. The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations. In particular, the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz. A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline. Furthermore, there was significant variation in gas pulse amplitude for different types of particulate material. 相似文献
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《Particuology》2015
An accurate estimation of the total pressure drop of a pipeline is important to the reliable design of a pneumatic conveying system. The present paper presents results from an investigation into the modelling of the pressure drop at a bend in the pneumatic conveying of fly ash. Seven existing bend models were used (in conjunction with solids friction models for horizontal and vertical straight pipes, and initial acceleration losses) to predict the total pipeline pressure drop in conveying fly ash (median particle diameter: 30 μm; particle density: 2300 kg/m3; loose-poured bulk density: 700 kg/m3) in three test rigs (pipelines with dimensions of 69 mm inner diameter (I.D.) × 168 m length; 105 mm I.D. × 168 m length; 69 mm I.D. × 554 m length). A comparison of the pneumatic conveying characteristics (PCC) predicted using the seven bend models and experimental results shows that the predicted total pipeline PCC and trends depend on the choice of bend model. While some models predict trends that agree with the experimental results, other models predicted greater bend pressure drops for the dense phase of fly ash than for the dilute phase. Models of Pan, R. (1992). Improving scale-up procedures for the design of pneumatic conveying systems. Doctoral dissertation, University of Wollongong, Australia, Pan, R., & Wypych, P.W. (1998). Dilute and dense phase pneumatic conveying of fly ash. In Proceedings of the sixth International Conference on Bulk Materials Storage and Transportation (pp. 183–189), Wollongong, NSW, Australia and Chambers, A.J., & Marcus, R.D. (1986). Pneumatic conveying calculations. In Proceedings of the second International Conference on Bulk Materials Storage and Transportation (pp. 49–52), Wollongong, Australia reliably predicted the bend losses for systems conveying fly ash over a large range of air flows. 相似文献
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《Particuology》2015
In this study, experiments on fly ash conveying were carried out with a home-made long-distance positive-pressure pneumatic conveying system equipped with a high performance electrical capacitance tomography system to observe the transient characteristics of gas–solid two-phase flow. The experimental results indicated that solids throughput increased with increasing solids–gas ratio when the conveying pipeline was not plugged. Moreover, the optimum operating state was determined for the 1000 m long conveying pipeline with a throttle plate of 26 orifices. At this state the solids throughput was about 12.97 t/h. Additionally, the transportation pattern of fly ash gradually changed from sparse–dense flow to partial and plug flows with increasing conveying distance because of the conveying pressure loss. These experimental results provide important reference data for the development of pneumatic conveying technology. 相似文献
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《Particuology》2015,(4)
In this study,experiments on fly ash conveying were carried out with a home-made long-distance positive-pressure pneumatic conveying system equipped with a high performance electrical capacitance tomography system to observe the transient characteristics of gas-solid two-phase flow.The experimental results indicated that sol ids throughput increased with increasing solids-gas ratio when the conveying pipeline was not plugged.Moreover,the optimum operating state was determined for the 1000 m long conveying pipeline with a throttle plate of 26 orifices.At this state the solids throughput was about 12.97 t/h.Additionally,the transportation pattern of fly ash gradually changed from sparse-dense flow to partial and plug flows with increasing conveying distance because of the conveying pressure loss.These experimental results provide important reference data for the development of pneumatic conveying technology. 相似文献
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《Particuology》2018
During gas–solid mixture conveying in a dense phase, material is conveyed in dunes on the bottom of the pipeline, or as a pulsating moving bed. This phenomenon increases the pressure drop and power consumption. We introduce a new technique to reduce the pressure drop, which is termed the perforated double tube. To validate this new model, the gas–solid flow pattern and pressure drop were studied numerically and experimentally. The power consumption was also studied experimentally. Numerical studies were performed by the Eulerian–Lagrangian approach to predict gas and particle movement in the pipeline. Comparisons between the numerical predictions and the experimental results for the gas–solid flow patterns and pressure drop show good agreement. 相似文献
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Low-velocity pneumatic conveying in horizontal pipe for coarse particles and fine powders 总被引:3,自引:0,他引:3
First,the characteristics of low-velocity conveying of particles having different hardness are experimentally investigated in a horizontal pipeline in terms of flow pattern and pressure drop to show that the slug flow can be classified into two types depending on the settling of particles along the pipeline,and the period is small for slug flow without the settled layer,which is called solitary slug flow.The pressure drop for soft particles is shown to be larger than that for hard particles.Then,experimental results are presented on horizontal fluidized-bed conveying of fine powders to show that air release from the top surface of the conveying channel is an important factor for high mass flow rate of particles. 相似文献