超燃冲压发动机凹腔内补氧的强化点火试验

在超燃冲压发动机扩张型燃烧室中,对凹腔内局部补氧的点火强化方法进行了试验研究。采用高速摄影手段研究了不同的补氧方式对凹腔内火焰分布特征和燃烧强度的影响,并针对并联双凹腔燃烧室构型,研究了在单侧凹腔补氧条件下向异侧凹腔的火焰传播过程。试验结果表明,采用凹腔内补氧的方式能调节凹腔内的燃料浓度分布、改善凹腔内的燃烧过程,控制燃烧放热强度;稳态燃烧情况下,观察到凹腔驻留火焰的两种存在特征,分别表现为:由回流区热量反馈机制作用下的凹腔局部驻留火焰和燃烧室全局压力反馈影响下的凹腔剪切层火焰。只有在单侧凹腔燃烧建立了全局压力反馈的条件下才能实现凹腔火焰的异侧传播。      

Numerical study on the cavity characteristics and impact loads of AUV water entry

The high-speed water entry process of an autonomous underwater vehicle (AUV) has a strong impact nonlinearity, and a cavity formed by air and water will often be generated as part of the entry process. The shape of the water-entry cavity plays an important role in the load characteristics and stability of the water-entry trajectory. In this paper, a numerical model for describing the cavity and impact load characteristics of a high-speed water-entry AUV is established. The simulation results such as cavity shape and impact load are compared with experimental data. The good agreement between the numerical results and those of the experiments reveals the accuracy and capability of the numerical algorithm. Subsequently, the arbitrary Lagrange-Euler (ALE) numerical algorithm is used to simulate and analyse the variation laws of the cavity characteristics and impact loads with different head shapes, water-entry velocities, water-entry angles and angles of attack. The results obtained in this study can provide a good reference for the trajectory control and structural design of the AUV.     

基于腔减相移光谱技术测量大气气溶胶消光系数的应用研究

基于腔减相移光谱(CAPS)技术检测灵敏度高、光源性价比好、容易控制和有效吸收光程长等优点,搭建了一套基于CAPS技术的连续测量大气气溶胶消光系数的监测系统。测试系统高反射镜片反射率约为0.9999,对应有效光程约为4.4 km;通过Allan方差测试分析系统最佳积分时间约为80 s,对应消光系数检测极限为0.06Mm-1;将系统应用于实际大气气溶胶消光系数的12个周期和48 h连续监测,显示空腔相移基本稳定,样品测量相移偏移明显,反演得到的大气能见度结果稳定可靠。由此表明,研制的基于CAPS技术的大气气溶胶消光系数连续测量系统应用于实际的测量是完全可行的。     

XCC pile installation effect in soft soil ground: A simplified analytical model

This paper presents a simplified analytical model: the X-shaped cylindrical cavity expansion method (XCEM), which can be used to interpret and predict the displacement, stress, and excess pore pressure caused by the X-section cast in place concrete (XCC) pile installation in soft soil. Analytical solutions for the displacement and strain field are obtained with a streamlined solution, base on the strain path method (SPM). The stress and excess pore pressure can then be subsequently determined with the assumption of the elastic-perfectly plastic soil behavior. A positive agreement was found when the theoretical prediction of the displacement, stress, and excess pores pressure was compared against the field measurements. The proposed XCEM improves the conventional cavity expansion method (CEM) and offers a framework for understanding the non-circular cross-section penetrator problem, which is different from the conventional circular penetrator problem.     

Experimental and numerical investigation of a freefall wedge vertically entering the water surface

Experiments and numerical methods are developed to investigate the water entry of a freefall wedge with a focus on the evolution of the pressure on the impact sides (the side contacting water) and the top side (the dry side on the top of the wedge), evolution of the global hydrodynamic loads, evolution of the air–water interface, and wedge motion. It is found that a typical water entry of a freefall wedge can be divided into slamming, transition, collapse and post-closure stages. A single-fluid numerical model is presented to simulate the first three stages. The results are compared to experiments and good agreements are obtained. A two-fluid BEM is proposed to investigate the influence of the air flow before the closure of the cavity created on the top of the wedge. It is found that for the closure of the 2D cavity, the air flow starts to play an important role just before closure but due to the short duration, the influence of air flow on the body velocity and configuration of the air–water interface is limited.     

High pressure jet-grouting column installation effect in soft soil: Theoretical model and field application

This paper presents a theoretical model for investigating the installation effect of high pressure jet grouting column in soft clay. The model is formulated by assuming the installation process as a series of pressure-controlled spherical cavity expansion in semi-infinite soil, of which the approximate solutions are derived by combining use of two fundamental solutions of spherical cavity expansion in finite spherical symmetry soil and displacement-controlled spherical cavity expansion in semi-infinite soil. The approximate solutions are then validated by comparing the predictions with FEM results as well as published results. The comparison results show that the presented approximate solutions are suitable for the problem of pressure-controlled spherical cavity expansion in semi-infinite soil, particularly in evaluating the limit expansion pressure as well as the expansion pressure-ground surface displacement relation. Subsequently, the proposed approximately solutions are applied to interpret the limit injection pressure and the grouting pressure-ground surface displacement during the installation process of HPJ-GC. Some parametric studies are also conducted. Furthermore, an instrumented field test study of HPJ-GC is conducted in the thick soft soils comprising quaternary alluvial and marine deposits of the Lianyungang-Yancheng Highway located in Jiangsu Province, China. The measured ground heave is compared with the analytical predictions using the proposed theoretical model. Reasonable agreement is achieved.     

高密度电法勘探数据三维处理技术及城市勘察中的应用

在以往的高密度数据反演解释过程中,将地质结构简化成二维,通过地电断面图、切片图进行分析.实际上,地质体具有三维地电结构,二维反演难免会受到旁侧效应的影响,二维图件也不能清晰直观地反映地质体的空间分布情况.本文以某陶瓷厂空洞探测为例,利用实测资料构建三维数据场,在反演参数优化的基础上,选择基于最小二乘法的三维反演技术对数据场进行处理,将反演结果利用三维可视化技术显示出来,对采空区位置及空间形态给出结论.研究结果显示,三维处理技术能够从空间上,多手段、多视角分析物探数据,有效地消除了旁侧效应的影响; 物探结果直观清晰地呈现出空洞的分布位置、范围以及空间特征,与钻探结果吻合较好.     

Modelling the Cone Penetration Test in sand using Cavity Expansion and Arbitrary Lagrangian Eulerian Finite Element Methods

The paper considers two techniques to model the Cone Penetration Test (CPT) end resistance, q_c in a dense sand deposit using commercial finite element programmes. In the first approach, Plaxis was used to perform spherical cavity expansion analyses at multiple depths. Two soil models, namely; the Mohr–Coulomb (MC) and Hardening Soil (HS) models were utilized. When calibrated using simple laboratory element tests, the HS model was found to provide good estimates of q_c. However, at shallow depths, where the over-consolidation ratio of the sand was highest, the relatively large horizontal stresses developed prevented the full development of the failure zone resulting in under-estimation of the q_c value. The second approach involved direct simulation of cone penetration using a large-strain analysis implemented in Abaqus/Explicit. The Arbitrary Lagrangian Eulerian (ALE) technique was used to prevent excessive mesh deformation. Although the Druker–Prager soil model used was not as sophisticated as the HS model, excellent agreement was achieved between the predicted and measured q_c profiles.     

Cone penetration-induced pore pressure distribution and dissipation

The excess pore water pressure distribution (u) induced by the penetration of a piezocone into clay and its dissipation behaviour have been investigated by laboratory model tests, theoretical analysis and numerical simulation. Based on the results of the tests and the analysis, a semi-theoretical method has been proposed to predict the piezocone penetration-induced pore pressure distribution in the radial direction from the shoulder of the cone. The method can consider the effect of the undrained shear strength (s_u), over-consolidation ratio (OCR) and rigidity index (I_r) of the soil. With a reliably predicted initial distribution of u and the measured curve of dissipation of pore water pressure at the shoulder of the cone (u₂), the coefficient of consolidation of the soil in the horizontal direction (c_h) can be back-fitted by analysis of the pore pressure dissipation. Comparing the back-fitted values of c_h with the values directly estimated by a previously proposed method indicates that the previously proposed method can be used reliably to estimate c_h values from non-standard dissipation curves (where u₂ increases initially and then dissipates with time).     

A general semi-analytical solution for consolidation around an expanded cylindrical and spherical cavity in modified Cam Clay

This paper presents a general semi-analytical solution for undrained cylindrical and spherical cavity expansion in Modified Cam Clay (MCC) and subsequent consolidation. The undrained cylindrical and spherical cavity expansion response in MCC model is obtained through the similarity solution technique. Then, the subsequent consolidation process around the cavity is governed by the classical partial differential equation for consolidation. Finite Difference Method (FDM) is selected for solving the consolidation equation numerically. The proposed semi-analytical solution is validated by comparing the prediction of the dissipations of the pore pressure with Randolph’s closed-form solution for elastic-perfectly plastic soil. Parametric study shows that G₀/p₀′, R and M have significant influence on the cavity wall excess pore pressure dissipation curve, while it is not sensitive to the value of ν′. It is also found that the negative pore pressure generates around the expanded cylindrical and spherical cavity wall during the consolidation process when R > 5 for typical Boston blue clay. The developed solution has potential applications in geotechnical problems, such as the pile foundation, in-situ test, tunnel construction, compaction grouting, and so forth.