Soil disturbance and force mechanics of vibrating tillage tool

Experiments were conducted with vibrating tillage tools in a sandy loam soil. It was observed that during oscillating operation, initially draft increased slightly with an increase in forward speed but later it decreased. For the non-oscillating operation, draft increased continuously with increase in forward speed. The ratio of draft from oscillating to non-oscillating mode varied from 0.63 to 0.93. The total power required for oscillating operation was 41–45% more than the power required for non-oscillating operation. The soil surface was cracked due to tool motion showing the characteristics of lifting up of soil clods during the oscillating operation, whereas it showed the characteristics of soil flow during non-oscillating operation. The soil was pulverized more due to oscillating than non-oscillating operation. The reduction in dry bulk density of soil mass in the oscillating operation was about 70–270% more than that during the non-oscillating mode.     

Determination of the soil pressure distribution around a cone penetrometer

The objective of this paper was to investigate the pressure distribution around a cone penetrometer using a pressure sensing mat under laboratory conditions. The investigation was conducted under (1) constrained conditions using cylindrical split pipe molds and (2) unconstrained conditions using a soil box. These tests were conducted in Capay clay and Yolo loam soil containing two different moisture conditions and two compaction levels.In the constrained tests, a maximum radial pressure of 111 kPa was observed in the Capay clay soil with 3.4–4.3% d.b. moisture content and three blows of compaction (cone index value of 2040 kPa) when using the 41 mm diameter split pipe mold. These pressure levels decreased to 82 and 22 kPa, respectively, when 65 and 88 mm diameter molds were used. In both the Capay clay and Yolo loam tests, the average radial pressure and average cone index values showed similar trends.In the unconstrained tests, a maximum pressure of 9.0 kPa was observed in the Capay clay with 4.5% d.b. moisture content and three blows of compaction (cone index value of 550 kPa) at a horizontal distance of 25.4 mm from the vertical axis of the cone penetrometer and minimum pressure levels in the range of 0.2–0.3 kPa when the horizontal distance of the penetrometer was in the range of 56.8–66 mm. The pressure levels are much smaller than the ones obtained in the constrained tests and may suggest that the pressure distribution under field conditions is small at a distance of 25.4 mm or higher from the tip of the cone.The experimental data were statistically analyzed to identify significant factors. The results of the analysis for the constrained test indicated that the mold diameter and number of blows significantly increased the pressure readings within the soil mass. Increasing the mold diameter led to a decrease in the average radial pressure and increasing the number of blows contributed to an increase in the average radial pressure. In the unconstrained test, the average radial pressure distribution at a given point were significantly influenced by the horizontal distance of the point from the vertical axis passing through the center of the penetrometer shaft, soil type, and soil moisture content. Higher pressure values were obtained in the Capay clay tests compared to the Yolo loam tests. In all cases, the pressure levels were greater for the drier soil than for the moist soil.     

Effect of hydrodynamic forces on capillary pressure and relative permeability

Because of the influence of hydrodynamic forces, the capillary pressure measured at static equilibrium may be different from that which pertains during flow. If such is the case, it may not be permissible to use steady-state relative permeabilities to predict unsteady-state flow. In this paper, the idea that the total flux of a given phase may be partitioned into several individual fluxes, together with a new pressure difference equation, is used to explore the possible impact that the hydrodynamic forces might have on capillary pressure and, as a consequence, relative permeability. This exploration reveals that, provided the pressure difference equation is implemented properly, capillarity has no impact on the relative permeability curves for the homogeneous, water-wet porous media considered. Moreover, it is demonstrated that, if the hydrodynamic effects are neglected, very little error is introduced into the analysis.     

Hydrodynamics of a flexible cylinder under modulated vortex-induced vibrations

Both amplitude modulation and frequency modulation of Vortex-induced Vibration (VIV) are observed in a recent model test of a flexible cylinder under oscillatory flow, but its hydrodynamics has not yet been broached in detail. This paper employs the Forgetting Factor Least Squares (FF-LS) method for identification of time-varying hydrodynamics of a flexible cylinder under modulated VIV. The FF-LS method’s applicability to accurately identify time-varying hydrodynamic coefficients is demonstrated through an elastically mounted rigid cylinder under flow with a given modulated motion. Furthermore, we propose a framework to predict instantaneous amplitude (envelope) and frequency using time-varying hydrodynamic coefficients to establish their analytical relationship. This prediction method is further extended to a highly tensioned flexible cylinder through Fourier series expansion in the spatial domain. By performing the identification procedure for all sampled data of a flexible cylinder undergoing oscillatory flow, we obtain the corresponding time-varying hydrodynamics in the cross-flow direction considering the amplitude and frequency modulation. The results show that, under modulated VIV, hydrodynamic coefficients of the flexible cylinder also show time-varying characteristics. We further investigate differences between identified hydrodynamic coefficients and those obtained from the database of a cylinder with modulated motion under flow. Prediction results using these identified time-varying coefficients reveal that the time-varying excitation coefficients mainly influence the amplitude modulation, and the time-varying added-mass coefficients contain the major information of frequency modulation. These results further suggest including the temporal derivative of the instantaneous amplitude as one determining parameter in building databases to improve the prediction of modulated VIV.     

Grip pressure distribution under static and dynamic loading

The dynamic response of a vibrating handarm system is strongly related to the grip force. While the relationship between total grip force and vibration characteristics of the hand-arm system has been extensively studied, no attempts have been made to investigate the distribution of grip pressure at the hand-handle interface. The local grip-pressure distribution may be more closely related to the finger blood flow, fatigue and loss of productivity than total grip force. In the present study, distribution of static and dynamic forces at a hand-handle interface is investigated using a grid of pressure sensors mounted on the handle. The pressure distribution is acquired for different values of static and dynamic grip forces in the range of 25–150 N. The dynamic measurements were conducted at various discrete frequencies in the 20–1000 Hz range with peak acceleration levels of 0.5 g, 1.0 g, 2.0 g and 3.0 g. The grip-pressure distribution under static loads revealed a concentration of high pressures near the tips of the index and middle fingers, and the base of the thumb. This concentration of high pressures shifted towards the middle of the fingers under dynamic loads, irrespective of grip force, excitation frequency and acceleration levels. These local pressure peaks may be related to impairment of blood flow to finger tips and the possible causation of vibration white finger. Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 8–11.     

平屋盖风压分布的数值模拟

基于Reynolds时均N-S方程和RSM模型对平屋面的风压分布进行了数值模拟,在此基础上系统研究了风向角、跨高比、地面粗糙度、风速等因素对屋面风压分布的影响,探讨了结构周围流场的绕流特性,最后根据屋面的结构形式及风压分布特点将屋面进行分区,给出了屋面在不同风向角下的分区风载体型系数以供工程设计参考。     

Stress state of a hollow round cylinder with side holes under different pressure and temperature impact

The stress–strain state of a hollow cylinder (pipe) with lateral holes is considered. The pipe is under the action of internal and external hydrostatic pressures P₁ and P₂ and also a temperature effect. Such a pipe is used in oil–gas recovery, rocket engineering, chemical machinery industry and etc. There is no detailed analytic solution of this problem in literature to date. The number of holes through which a liquid or gas can flow into the pipe interior (and vice versa) depends on the loads, the size of the cross-section and the material of the pipe. The proper selection of the arrangement of holes and their diameters is determined from an analytic solution. In addition, the maximum boundary loads (of pressures) at which the pipe cracks is also found.     

An investigation of pressure under wheeled vehicles

This paper reviews methods currently used to predict the pressure exerted by a wheeled vehicle on the ground. It describes a programme of experiments designed to measure the pressure at a certain depth in a soil mass, the surface of which is traversed by a number of different vehicles in a range of loading conditions. Methods for inferring the surface pressure from underground measurements are described and compared. The inferred surface pressures are then compared with predicted values. A discussion is given on the usefulness and validity of ground pressure characterisation for wheeled vehicles.     

复合射孔压力加载下铜柱测压计测试实验和数值分析

进行基于铜柱测压和实测压力时间曲线的石油井射孔压裂实验,建立铜柱测压计的数学模型,并采用交互式计算方法得出其作用过程的解析解。分析结果表明,井下射孔压裂过程中,压力上升沿很陡,活塞在外部压力达到峰值时,速度很大,会继续压缩铜柱直到速度为零。活塞的运动可以分为加速和减速撞击2个过程。活塞的最大速度决定了铜柱测压计最终测试值,且与速度成正比。射孔脉冲压力加载过程中铜柱测压计的误差取决于压力上升时间、脉冲宽度、峰值压力等影响因素。火炮膛压加载下铜柱测压计误差较小。     

大型户外广告牌面板极值风压分布的试验研究

大型户外广告牌作为城市典型的风灾易损性结构,在强风作用下的毁坏倒塌发生频繁,存在巨大的安全隐患.本文针对大型户外独立柱广告牌结构设计的薄弱环节,即广告牌面板的极值风压破坏,通过开展三种湍流度不同的风场的测压试验,考虑面板风压时程的高斯/非高斯特性,使用三种不同的极值风压计算方法,给出了极值风压与风场之间的联系,同时也比...     

低层房屋风压分布特性的模拟与分析

基于Reynolds时均N—S方程和标准κ-ε双方程封闭模型,对一类带挑檐的低层双坡屋面房屋在不同风向角下的表面风压进行了敷值模拟,模拟结果与风洞试验结果作了比较。在此基础上,根据模拟结果对房屋各表面及挑檐处的风压分布特性和规律进行了分析和计算,获得了不同风向角下各表面的风载体型系数,为该类房屋的工程抗风设计提供了依据。     

Changes in some mechanical properties of a loamy soil under the influence of mechanized forest exploitation in a beech forest of central Belgium

Modification of some soil mechanical properties (penetration resistance and consolidation pressure) induced by vehicle compaction during mechanized forest exploitation was studied in an acid and loamy leached forest soil of the loessic belt of central Belgium. In situ penetration tests and laboratory Bishop–Wesley cell tests were undertaken for the two main soil horizons of a beech high-forest, i.e. the eluvial E horizon (5–30 cm depth) and the underlying clay-enriched B_t horizon (30–60 cm depth). Both undisturbed and wheel-rutted soil areas were studied (E and B_t horizons vs. E_g and B_tg horizons).

Results show that: The experimental overconsolidation pressure of the eluvial reference horizon (E) is about 50 kPa higher than the value calculated from soil overburden pressure; this probably results from suction action during dry periods. The clay-enriched reference horizon (B_t) shows the same trends. In wheel-rutted areas, seven years after logging operations, the E_g horizon memorizes only 14.5% of the wheel induced stress due to forest machinery.

In the compacted B_tg horizon, the experimental overconsolidation pressure represents 96% of the exerted theoretical stresses due to harvesting actions. The good recording of the exerted stresses, after seven years, can be explained by: (1) The B_tg depth which keeps it from seasonal variations i.e. from desiccation–moistening or freeze–thaw cycling; (2) amorphous and free iron accumulation inducing a “glue” effect of the B_tg soil matrix, which could stabilize the soil structure and prevent recovery to initial conditions. These results provide clear evidence that on loessic materials, soil compaction due to logging operations leads to modifications in both physical (bulk density, total porosity) and mechanical (penetration resistance and consolidation pressure) soil properties.     

幂律型浆液扩散压力环向分布模型

为研究幂律型浆液注浆时注浆压力的变化情况,考虑盾尾断面新注入浆液与已注入浆液间阻碍作用,假设壁后注浆时盾尾形成三维环形空隙,提出了幂律型浆液扩散压力环向分布模型,并利用流体力学理论推导了幂律型浆液扩散压力环向分布式,分析了公式适用范围以及各参数的实际意义。与实际工程数据对比,验证了模型和计算式的正确性。结果表明,计算式可以反映注浆时环向分布各个位置压力值的大小;当公式中稠度系数n=1时,该式即为牛顿流体计算式,环向压力扩散模型同样适用,且幂律型流体环向扩散压力小于牛顿流体;受浆液自重影响,注浆孔注浆时向上表现为减压,向下表现为加压;压力环向分布断面呈现出上窄下宽的不规则环形;同一注浆孔幂律型浆液水灰比越大,浆液扩散压力越小。     

Effects of reduced inflation pressure and vehicle loading on off-road traction and soil stress and deformation state

Field experiments on off-road vehicle traction and wheel–soil interactions were carried out on sandy and loess soil surfaces. A 14 T, 6 × 6 military truck was used as a test vehicle, equipped with 14.00-20 10 PR tyres, nominally inflated to 390 kPa. Tests were performed at nominal and reduced (down to 200 kPa) inflation pressures and at three vehicle loading levels: empty weight, loaded with 3.6 and 6.0 T mass (8000, 11,600 and 14,000 kg, respectively). Traction was measured with a load cell, attached to the rear of the test vehicle as well as to another, braking vehicle. Soil stress state was determined with the use of an SST (stress state transducer), which consists of six pressure sensors. Soil surface deformation was measured in vertical and horizontal directions, with a videogrammetric system. Effects of reduced inflation pressure as well as wheel loading on traction and wheel–soil interactions were analyzed. It was noticed that reduced inflation pressure had positive effects on traction and increased stress under wheels. Increasing wheel load resulted in increasing drawbar pull. These effects and trends are different for the two soil surfaces investigated. The soil surface deformed in two directions: vertical and longitudinal. Vertical deformations were affected by loading, while longitudinal were affected by inflation pressure.     

Normal stress difference in liquid lubricants sheared under high pressure

Although normal stress differences in liquids have conventionally been associated with polymers, aspects of rheological behavior in lubricated concentrated contacts suggest that normal stress difference may be significant in even low molecular weight liquids sheared under high pressure and high shear stress. A torsional flow rheogoniometer was constructed for use at high (300 MPa) pressure. Four typical liquid lubricants were investigated, including one polymer/mineral oil solution. Shear stress and N ₂-N ₂ are reported as functions of shear rate. The effect of pressure variation is reported for two liquids. Results are compared with predictive techniques and a molecular dynamics simulation. Simple low molecular weight lubricant base oils can generate measurable and significant normal stress differences when sheared at high shear stress.     

Experimental and numerical analysis of high pressure diesel spray–wall interaction

The interaction between impacting and splashed droplets and air motion plays a fundamental role on the mixture formation process, which is a crucial aspect for the correct operation of modern DI Diesel engines as it greatly influences the combustion process and the exhaust emissions. A complete understanding of spray impingement is quite complex. A mixed numerical–experimental approach is proposed in this paper.     

围压状态下的混凝土本构模型

利用已有不同围压下的混凝土三向压缩试验, 分析研究不同围压条件对混凝土强度和应力-应变关系的影响。试验表明, 把混凝土简单视为脆性材料的观点并不符合实际情况, 塑性特征也是混凝土材料主要力学特征。由热力学定律出发, 本文提出了多次方形式的屈服函数和与围压状态相关联的损伤标准化函数, 提出了考虑围压状态的混凝土本构模型。试验结果与数值计算比较表明, 该本构关系可以很好地描述混凝土在不同围压状态下的力学损伤发展和脆-塑性转换力学特征, 也可以描述拉伸作用下的应力-应变关系, 具有一定的普遍意义。     

电子测压器与铜柱测压器在膛压测试中结果差异分析

火炮膛压作为火炮和弹药的内弹道重要参数,在研制、生产、交付、存储校验等环节都需要测量。针对当前同时采用放入式铜柱测压器和电子测压器测量某一批弹药时,电子测压器峰值出现散布较大,而铜柱测压法一致性好的问题,在分析两种测压法测压原理的基础上,利用铜柱动态校准数据作用到其ANSYS模型上修正了铜柱的Johnson-Cook模型参数;分析发现出现差异时电子测压器测量的压力变化率时程曲线不同,铜柱实际测试形变量与施加压力时程曲线作用于模型得到的形变量一致。研究表明：同时测量某一批弹药时,电子测压器比铜柱测压器出现压力峰值散布大的原因是由膛压上升过程变化率不同导致铜柱的应变率不同造成的。

     

考虑流固耦合作用的充气膜结构风压分布研究

充气膜结构是典型的风敏感型柔性结构,风荷载经常起关键的控制作用。本文利用ANSYS14.5程序中的workbench平台,考虑流固耦合作用,研究矩形平面气承式充气膜结构的风压系数分布。其中,选用基于雷诺时均模拟法的RNGk-ε湍流模型进行风场模拟,采用弱耦合分析方法模拟流固耦合风荷载效应。分析的参数选择风向角、结构内压、矢跨比和平面长宽比。针对矢跨比分别为1/4,1/3和1/2,长宽比分别为5/3,2/1和3/1的柔性充气膜结构模型,计算不同内压及不同风向角作用下的结构响应。结果表明,考虑流固耦合作用时,充气膜结构的风压体型系数比不考虑流固耦合作用的刚性模型明显偏大,其影响因子在1.25~1.5之间;充气膜结构的风压系数分布受风向角、内压、长宽比及矢跨比的影响较大。     

冲击荷载作用下粘土孔隙水压的数值分析

为了分析冲击荷载作用下粘土的孔隙水压力的增长规律,为分析粘土介质的动态响应、动力固结加固提供理论依据,将冲击瞬态荷载简化为三角形荷载,通过编制瞬变动态弹塑性有限元程序,对冲击荷载作用下粘土孔隙水压的动态响应进行了模拟,得出了冲击荷载作用下粘土孔隙水压的增长规律,发现孔隙水压力峰值无论是随水平距离还是随深度的增加均呈指数形式衰减,和实际工程施工中孔隙水压的监测数据相吻合。