小区供热外网改造设计中经济比摩阻值的确定

在机械循环热水采暖系统室外管网设计工作中,我们往往遵循《热力管道设计手册》中经济比摩阻值30～80pa/m来确定管道直径,但在小区供热管网增容改造设计中,如何确定管网的经济比摩阻值,使其在不增加电能消耗的条件下,尽量利用原有管道,增加供热面积,降低工程造价,尚无最佳数据。我公司90年夏季在张庄小区供热外网改造设计中,将外网干管的平均比摩阻值定为150pa/m左右。

后张预应力锚索摩阻试验研究

本文介绍了清江隔河岩工程压力引水隧洞后张预应力锚索摩阻值1:1模型试验情况。通过对两种不同结构的锚索进行的9次张拉测试,整理出各种张拉方式、锚固方式及不同孔道曲率情况下的孔道摩阻系数μ,探讨了锚索在张拉过程中的张力分布规律,初步分析了钢丝束内应力分布的不均匀性。研究表明:两种锚索的布置形式对实际工程均是适用的,其中由于HM锚摩阻损失较小,更适于在工程中采用。

压差密度仪在海上油田应用中的适应性探讨

受海上油田高产、井斜大、油管生产等影响,传统放射性流体密度仪的替代仪器压差密度仪应用初期测量效果较差。为此,在深入研究压差密度仪测井原理的基础上,探讨了影响压差密度仪测量效果的各类因素,并进行了实际测井资料分析研究。结果表明,摩阻、加速度、井斜及硅油等因素对测量值均有影响,其中摩阻是影响测量效果的最主要因素。结合海上油田生产状况,总结提出了考虑摩阻影响的仪器适用性图版,该图版对作业前压差密度仪的适用性分析有较好的指导意义。

Turbulence Model Investigations on the Boundary Layer Flow with Adverse Pressure Gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients （APGs） is conducted by using Reynolds-averaged Navier-Stokes （RANS） equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox （2006） k-co are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.

A simplified approach for negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge

A simplified approach was proposed to analyze the negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge. Based on the concentric cylinder shearing theory, considering the changes of pile shape(such as, taper angle and diameters of pile base, etc.), the load-transfer of special-shaped pile was built. The accuracy of the developed simplified approach was verified by numerical simulation model with the same condition. Then, the influence factors, such as, taper angles, the diameter of pile base, surcharge, and pile-soil interface parameters were analyzed and discussed. The results show that the developed simplified approach can calculate NSF of special-shaped pile under surcharge effectively. A limited parametric study indicates that in many practical situations special-shaped piles(such as belled wedge pile shown in this work) offer a design option that is more economical than traditional uniform cross-section piles.

Loading Sequence Effects on Dragload and Downdrag for Pile Foundation

Negative skin friction (NSF) is one of the important problems when designing a pile foundation. However, the influence of loading sequence on the dragload and downdrag for pile foundation is seldom studied. In this paper, a three-dimensional numerical model was established using FLAC3D. Compared with the results of model test, the established model could be used to study the NSF of pile foundation. The influencing factors were discussed including the length-diameter ratio of pile and the loading sequence of pile head load and surcharge. A case history was analyzed using FLAC3D. The calculated results are in good agreement with the measured results. It is concluded that the dragload and downdrag are remarkably influenced by the loading sequence of pile head load and surcharge. The dragload and downdrag reach the maximum values under the condition of surcharge after pile head load.

Accurate measurement of wall skin friction by single-pixel ensemble correlation

The present work deals with accurately estimating wall-skin friction from near-wall mean velocity by means of PIV measurement.The estimation accuracy relies on the spatial resolution and the precision of the resolved velocity profile inside the viscous sublayer,which is a big challenge for conventional window-based correlation method(K?hler C J,et al.Exp Fluids,2012,52:1641–1656).With the help of single-pixel ensemble correlation,the ensemble-averaged velocity vector can be resolved at significant spatial resolution,thus improving the measurement accuracy.To demonstrate the feasibility of this single-pixel ensemble correlation method,we first study the velocity estimation precision in a case of steady near-wall flow.Synthetic particle images are used to investigate the effect of different image parameters.It is found that the velocity RMS-uncertainty level of the single-pixel ensemble correlation method can be equivalent to the conventional window correlation method once the effective particle number used for the ensemble correlation is large enough.Furthermore,a canonical turbulent boundary layer is synthetically simulated based on velocity statistics resolved by previous Direct Numerical Simulation(DNS)work(Schlatter P,et al.J Fluid Mech,2010,659:116–126).The relative error of wall skin friction coefficient is shown to be one-order smaller than that of the window correlation method.And the optimization strategy to further minimize the measurement uncertainty is discussed in the last part.

Nonlinear dynamics of Kuroshio intrusion in the Luzon Strait

This study used a 1.5-layer reduced-gravity numerical model to investigate the nonlinear dynamics of Kuroshio intrusion into the Luzon Strait.The model results suggested that both basin-scale wind curl and lateral friction are the primary factors that control the transformation of the flow,although inertia also plays an important role.Using an idealized model,both the mechanism via which the flow pattern changes depending on the two primary factors and the occurrence of hysteresis were investigated.It was established that the transformation of the Kuroshio flow field between the four previously reported flow patterns(i.e.,leaping across,current looping,eddy shedding,and branch intruding) can be explained under a unified theoretical framework.A diagram is proposed to explain how the flow field transforms between the four patterns from a certain prior state when varying the values of the controlling factors.