基于有限元的管道凹陷回弹与回圆分析

为了明确回弹与回圆行为对管道结构完整性的影响,解决不同约束状态下管道凹陷适用性评价结果的差异性问题,建立模拟3种管型在2类压头作用下凹陷成型-回弹-回圆全过程的三维有限元模型,系统地探讨管型、管径、壁厚、压头类型、压头尺寸、凹陷位置、螺距等对凹陷回弹率和回圆率的影响,采用非线性回归函数拟合得出不同类型管道回弹系数和回圆系数经验公式。研究结果表明:凹陷的回弹与回圆行为受管道结构刚度、凹陷形貌、尺寸、位置及内压等多因素影响,导致不同约束状态下凹陷变形历程和评价保守性差异;误差分析显示拟合预测精度较好。研究结果可用于基于内检测的凹陷深度的预测与评价。

基于全尺寸试验的管道凹陷回弹回圆行为研究

回弹回圆行为直接影响管道凹陷深度和应力应变状态。为了明确凹陷回弹回圆行为对管道结构完整性的影响,建立回弹与回圆修正系数,估算内检测报告的非约束凹陷成形时的最大深度以及受约束凹陷去除约束回弹回圆后的最小深度,对2种管径、3种壁厚的X70螺旋钢管开展了全尺寸凹陷回弹与回圆试验。试验结果表明,凹陷回弹回圆受管道径厚比、压头形状与尺寸、凹陷位置和深度等多种因素的影响。零内压下所有凹陷的平均回弹率达到23%、最大达到38.4%,内压产生的环向应力为50%管材规定的最小屈服强度(SMYS)时的平均回圆率达到29.6%、最大达到49.6%,而凹陷变形全过程平均回弹+回圆率达到了54.6%,导致不同约束状态下的凹陷评价结果差异很大。采用非线性回归方法拟合了凹陷回弹与回圆系数公式,误差分析显示拟合预测精度较高,能够满足凹陷回弹与回圆前后的深度估算,可以更精确地评估含凹陷管道的结构完整性。

长输管道凹陷提压回圆评价方法

为了解决长输管道深凹陷所导致的清管器及内检测器难以通过的工程问题,基于局部提高管道内压可使凹陷回圆、深度减小以达到清管器或检测器可通过深度门槛值的思想,建立了内压作用下管道凹陷回圆过程非线性有限元模型;提出了管道凹陷回圆系数的定义;通过应力应变响应分析对凹陷回圆过程的安全性进行论证;对回圆系数的影响因素进行分析,探讨径厚比、管材、凹陷尺寸、初始内压、回圆压力等参数对回圆系数的影响;基于有限元计算算例,采用非线性回归的方法拟合了凹陷回圆系数工程计算公式。研究结果表明:在极限回圆压力工况下,凹陷回圆过程中管道未发生二次塑性损伤;误差分析显示拟合所得公式预测精度较好,可用于长输管道凹陷的回圆评价。

4,4'-(1-氢-1,2,4-三唑-1-亚甲基)双苯甲腈的晶体结构

用四圆 X-射线衍射研究了来曲唑的晶体结构 ,结果表明 ,来曲唑晶体属于单斜晶系 ,空间群为 P2 1/n,晶胞参数 a=7.0 30 ( 1 4) ,b=1 6.1 70 ( 3) ,c=1 3.360 ( 3) ,β=1 0 4 .80°,V=1 468.3( 5 ) 3 ,Z=4。

Study on Hysteretic Bond Mechanisms of Plain Round Bar

Plain round bars were commonly used as main bars in the design of RC （reinforced concrete） buildings prior to the 1970s. According to previous research investigating the seismic performance of reinforced concrete members constructed with plain round bars, the strength of those members did not reach the calculated flexural strength due to bond slippage of main bars before yielding. It is important, therefore, to investigate the hysteretic bond mechanisms of plain round bars in concrete. In this research, analytical models were proposed to predict hysteretic bond-slip mechanisms between plain round bar and concrete depending on the results of experiments performed by the authors. In addition, the energy absorption capacity and the equivalent viscous damping factors obtained from the experimental results and analytical models are discussed. As a result of comparisons between the experimental data and the analysis models, good agreements were obtained.

New empirical model to evaluate groundwater flow into circular tunnel using multiple regression analysis

There are various analytical, empirical and numerical methods to calculate groundwater inflow into tun- nels excavated in rocky media. Analytical methods have been widely applied in prediction of groundwa- ter inflow to tunnels due to their simplicity and practical base theory. Investigations show that the real amount of water infiltrating into jointed tunnels is much less than calculated amount using analytical methods and obtained results are very dependent on tunnel＇s geometry and environmental situations. In this study, using multiple regression analysis, a new empirical model for estimation of groundwater seepage into circular tunnels was introduced. Our data was acquired from field surveys and laboratory analysis of core samples. New regression variables were defined after perusing single and two variables relationship between groundwater seepage and other variables. Finally, an appropriate model for estima- tion of leakage was obtained using the stepwise algorithm. Statistics like R, R2, R2e and the histogram of residual values in the model represent a good reputation and fitness for this model to estimate the groundwater seepage into tunnels. The new experimental model was used for the test data and results were satisfactory. Therefore, multiple regression analysis is an effective and efficient way to estimate the groundwater seeoage into tunnels.

On Quadratric Rotational Curved Surface

In this paper,a deterministic theorem is proposed for quadratic rotational curved surface.The relationship between invariants for quadratic rotational curved surface is established.In addition we give each type of equitions for rotational curved surface using the invariant.

Modeling and prediction of daily gas concentration variation at a mining face based on the elliptic orbit model: A case study

Monitoring and analysis of daily gas concentrations at a mining face is a vital task on safety production and security management in the coal-mining industry. This study addresses modeling and prediction of daily gas concentration variations based on the elliptic orbit model. The model describes the hourly variation in daily gas concentration by mapping its time-series into the polar coordinates to create its elliptic orbit trace for further analysis. Experiments show workability of the proposed method that daily gas concentration variation at a mining face of one coal mine in China is well described by the elliptic orbit model. Result analysis and performance comparison of the proposed elliptic orbit model with the classical AR model on the same prediction tasks indicate potentiality of the proposed elliptic orbit model,which presents a vivid approach for modeling and forecasting daily gas concentration variations in an intuitive and concise way.

Bias Correction in Wind Direction Forecasting Using the Circular-Circular Regression Method

Wind direction forecasting plays an important role in wind power prediction and air pollution management. Weather quantities such as temperature, precipitation, and wind speed are linear variables in which traditional model output statistics and bias correction methods are applied. However, wind direction is an angular variable; therefore, such traditional methods are ineffective for its evaluation. This paper proposes an effective bias correction technique for wind direction forecasting of turbine height from numerical weather prediction models, which is based on a circular-circular regression approach. The technique is applied to a 24-h forecast of 65-m wind directions observed at Yangmeishan wind farm, Yunnan Province, China, which consistently yields improvements in forecast performance parameters such as smaller absolute mean error and stronger similarity in wind rose diagram pattern.

Cylindrical coordinate measuring machines: probe offset and workpiece clamping error

A cylindrical coordinate measuring machine for the detection of large-size rotational parts is introduced. The measuring machine can simultaneously measure the geometrical dimensions, form and position errors of the inner and outer surfaces. Since the maximum length of the workpiece can reach 2 000 mm , it is difficult to be clamped and adjusted and easy to produce clamping error. The eccentricity can be up to 1.5 mm, which has an interaction effect with the probe mounting offset. We mainly study the probe offset of the measuring machine and the influence of the workpiece clamping error on the measurement. A method of controlling the offset of the measuring probe is proposed. The effect of the clamping error is eliminated through the space coordinate transformation of the workpiece axis, and the axis is fitted by the least square method. Finally, a common fixture can be realized to meet the clamping requirements of the workpiece.

Cryogenic springback of 2219-W aluminum alloy sheet through V-shaped bending

A V-shaped bending device was established to evaluate the effects of temperature and bending fillet radius on springback behavior of 2219-W aluminum alloy at cryogenic temperatures.The cryogenic springback mechanism was elucidated through mechanical analyses and numerical simulations.The results indicated that the springback angle at cryogenic temperatures was greater than that at room temperature.The springback angle increased further as the temperature returned to ambient conditions,attributed to the combined effects of the “dual enhancement effect” and thermal expansion.Notably,a critical fillet radius made the springback angle zero for 90° V-shaped bending.The critical fillet radius at cryogenic temperatures was smaller than that at room temperature,owing to the influence of temperature variations on the bending moment ratio between the forward bending section at the fillet and the reverse bending section of the straight arm.

Exact free vibration analysis of open circular cylindrical shells by the method of reverberation-ray matrix

This paper is concerned with the free vibration analysis of open circular cylindrical shells with either the two straight edges or the two curved edges simply supported and the remaining two edges supported by arbitrary classical boundary conditions. Based on the Donnell-Mushtari-Vlasov thin shell theory, an analytical solution of the traveling wave form along the simply supported edges and the modal wave form along the remaining two edges is obtained. With such a unidirectional traveling wave form solution, the method of the reverberation-ray matrix is introduced to derive the equation of natural frequencies of the shell with different classical boundary conditions. The exact solutions for natural frequencies of the open circular cylindrical shell are obtained with the employment of a golden section search algorithm. The calculation results are compared with those obtained by the finite element method and the methods in the available literature. The influence of length, thickness, radius, included angle, and the boundary conditions of the open circular cylindrical shell on the natural frequencies is investigated. The exact calculation results can be used as benchmark values for researchers to check their numerical methods and for engineers to design structures with thin shell components.