Spatial distribution of soil forces on moldboard plough and draft requirement operated in silty-clay paddy field soil

Spatial distribution of soil forces on the surface of plough is an important aspect that can help engineers for improving efficiency of tillage implement. It was analyzed at eleven different points of the moldboard plough with the help of sensors accompanied with the virtual instrument developed in LabView software with the aid of other supporting instruments. It was observed that soil forces increased with an increase in speed and depth. Depth changed soil forces more at upper parts than lower parts whereas speed affected rear parts more than the front part of the plough. Draft forces followed almost similar trend and least value of 308.17 N experimental draft force was found at 1 m/s speed and 5 cm depth under 33% moisture content. Cumulative soil forces found too smaller than the draft as they represented the force spatial distribution of specific parts of plough. It was observed that sensor technology provided real time picture of force variation during tillage process that could save time and effort.     

Effects of tyre inflation pressure and forward speed on vibration of an unsuspended tractor

Relationships among intensity of vibrations, tractor speed, soil moisture content and tyre inflation pressure are important for the design of tractor suspension systems. This study was designed to evaluate the effect of tyre inflation pressure and forward speed on tractor vibration in the paddy fields of Southern China by using a two-wheel-drive unsuspended tractor with different combinations of forward speed, tyre inflation pressure and soil moisture content. During experiments, the vertical vibration accelerations in front and rear axles and triaxial vibration accelerations of the tractor body were measured using three accelerometers. Fourier analysis was applied to determine root mean square acceleration values in the low frequency range from 0.1 to 10 Hz. The results of the study indicate that tractor vibration is strongly affected by changing forward speed and tyre inflation pressure, and especially by changing forward speed and rear tyre inflation pressure. The research also shows the variation in the pattern of vibration intensity especially at the tractor’s front axle when field soil moisture content is changed.     

微悬臂梁生化传感系统的性能分析

在基于光杠杆原理检测微悬臂梁变形的生化传感实验系统中,液体折射率的变化会导致PSD上光斑的位移,从而影响系统的检测信号。本文从理论上分析了在不同检测光束的入射角度、微梁的放置角度等参数条件下,液体折射率的变化对系统检测信号的影响。结果表明：在传统的光路下,液体折射率改变10-3引起的光斑位移与一般的生化反应引起的位移相当,即液体折射率的改变严重影响系统的检测信号。通过理论分析还发现在适合的参数配置下,可以忽略折射率变化对系统检测信号的影响。同时,参数的改变不影响系统的检测灵敏度。理论分析的结果得到了实验验证。     

绞合式光纤应变传感器

研究了一种可用于工程结构状态监测的本征型强度调制光纤应变传感器,由两根以上多模光纤相互绞合形成,分析了该传感器的应变传感原理,得到其既能测量拉应变,又有测定压应变的结论,传感器对应变的响应具有良好的线性和重复性、灵敏度高、无迟滞现象,对钢筋拉应变、混凝土压就矿业的实验结果与理论分析一致,表明该传感器是适合土木工程测量、结构状态监测等方面的较为理想的光纤传感器。     

导电混凝土传感器的热变形与机敏性研究

论文设计了具有不同灵敏度的水泥基传感器.测试了传感器的热变形特征与机敏性规律.验证了传感器埋入混凝土进行结构变形检测的可行性.热膨胀系数测定实验发现:与传统认为的受热膨胀不同,添加了碳纳米管的传感器具有热胀-热缩特性.通过对比传感器单独加载与埋入混凝土中加载,发现了大掺量的碳纳米管传感器的压阻效应更易受到混凝土干缩应力...     

Das Eindringen von Feuchtigkeit in ein ungesättigtes,poröses Medium auf Grund von periodischen Temperaturschwankungen

An analysis has been made which describes the moisture migration in an unsaturated semi-infinite porous medium under the influence of periodic variation of the surface temperature. For the case of constant transport properties, this combined heat and mass transfer problem is governed by only one dimensionless group — the Luikov number K/α_s. Numerical solutions of the energy and moisture conservation equations yielded temperature and moisture fields. The presentation of results provides the distributions of the dimensionless moisture content as a function of dimensionless distance measured from the surface of the semi-infinite medium and time with the Luikov number as a parameter. This parameter was varied in the range of 0.1 to .004. Because of an error in the pictorial presentation of the temperature field in the literature, these results were reproduced. It was found that the moisture fluctuations penetrate to a considerably smaller depth in the porous material than the temperature fluctuations, and that this penetration depth increases with increasing value of the Luikov number. An example demonstrates that the annual temperature fluctuations cause only small fluctuations of the moisture content in a sandy soil. The penetration depth of the moisture is also smaller than that of the temperature.     

温度对季节性冻土水分迁移的影响研究

寒区季节性冻土冻胀性质对工程实际影响很大。为了了解温度对水分迁移现象的影响,本文通过地温测试仪对野外不同深度处的土层温度进行测量,并在不同时间相应深度取土样,测其含水率,通过比较不同时间不同深度处的含水率的变化情况来分析温度变化对水分迁移现象的影响。在气温回升之前,当地表温度降低时,温度随深度的降低而升高; 随着地表温度不断降低,各深度处的温度也不断下降,温度梯度增加,各深度处地层的含水率变化大,即温度梯度的增加促进了季节性冻土区水分迁移现象的发生。     

Performance of coated floats in different soils

Experiments were conducted in a laboratory soil bin to evaluate the performance of coated floats in different soils. Two coating materials were studied, namely enamel and Teflon, and three soil types, namely clay, loam and sandy soil were used for testing. The forces required to overcome the drag of the floats and pull them over the soil surface were measured. The normal loads were varied to 25, 44 and 64 N. The effect of moisture content (db) was evaluated by varying the soil moisture from 21.2 to 62.4% for clay soil, 16.6 to 36.1% for loam soil and 0.7 to 13.8% for sandy soil. All tests were conducted at a constant speed of 0.20 m/s. The performance of the enamel coated float was superior to Teflon and uncoated floats in all soil conditions. In clay and loam soils, the drag force increased initially until the soil moisture content reached the plastic limit. The drag forces showed a decreasing trend once soil moisture exceeded the plastic limit. In sandy soil, the drag force increased with increase in moisture content. The overall reductions for the enamel coated float compared to uncoated float were from 4 to 64% in clay soil, 16 to 46% in loam soil and 26 to 45% in sandy soil. Besides this superior performance, the enamel coated float compared to the other floats showed excellent resistance to wear due to abrasion and superior scouring.     

The determination of plough draught—Part II the measurement and prediction of plough draught for two mouldboard shapes in three soil series

The draught of a 3-furrow reversible plough fitted with two types of bodies was measured at five separate test sites. Each site was ploughed on four different days to provide a range of soil moisture contents. The plough was operated at three different speeds in sequence for each type of body. The horizontal and vertical forces transmitted to the tractor were measured on a three-point linkage dynamometer. Tachogenerators monitored tractor wheel speed and fifth wheel ground speed. Cone index and soil specific weight were recorded at 30 mm intervals throughout the top-soil profile. Cone index at median plough depth was found to be a satisfactory measure of soil strength for the prediction of plough draught. Characterising specific plough draught by soil cone index, specific weight, moisture content, plough mouldboard tail angle and ploughing speed provided predicted values in closer agreement with measured draught compared with earlier equations. The sensitivity of cone index to soil moisture content supports the use of the cone penetrometer as a practical monitor of soil conditions in the field and as a management tool for judging the opportune times for agricultural tillage operations.     

光纤光栅传感器在大体积混凝土基础温度监测中的应用

光纤光栅传感器具有体积小、质量轻、灵敏度高、耐腐蚀、抗电磁干扰、传输频带较宽、易于进行分布式测量等诸多其他传感器所不具备的优点,更适用于现场的长期健康监测。大体积混凝土在施工过程中的温度问题如处理不当将会引起混凝土开裂。利用温度计、热电耦等作为传感器的传统的检测手段已经大大的制约了数据的准确性与精度。寻求一种高精度温度检测手段已经成为用于现场结构监测的前提。本文结合具体的工程实例介绍了光纤光栅传感器在基础混凝土温度监测中的应用,介绍了监测系统的组成,传感器的构造和标定,并利用实测温度预测基础混凝土底板中温度应力,及时采取措施防止混凝土的开裂。     

Validation of the GeoWATCH soil moisture model and proposed bias correction method

The US Army is required to be a good steward of the land per US Army regulation AR 200-1. Based on this regulation, Army installations need to manage lands, to reduce potential damage and impacts to water quality and habitat that may occur from training. Maneuver training does impact the vegetation and soil and this damage is directly related to soil moisture. Soil moisture is an important factor for understanding the potential for soil surface disturbance due to vehicle impacts and predicting soil resilience to vehicle traffic, however, producing accurate estimates of the spatial and temporal variation of soil moisture has historically been elusive. GeoWATCH, which stands for Geospatial Weather-Affected Terrain Conditions and Hazards (formerly DASSP), simulates soil moisture world-wide, at relatively small spatial and temporal scales. GeoWATCH uses a physics-based downscaling approach that uses weather-scale land surface model estimates of soil moisture and land surface water and energy fluxes, with high resolution geospatial data. GeoWATCH soil moisture outputs coupled with vehicle impact models, are anticipated to be useful for near-real-time estimation of ground disturbance, but will require ground validation. To validate GeoWATCH soil moisture estimates, we utilized Soil Climate Analysis Network (SCAN) gauge network soil moisture data from 127 sites across 34 states. Statistical analysis of the raw GeoWATCH output indicated the model performs statistically better in certain soil textures. Model bias is largest for sandy soils, whereas clayey soils were least biased. As a result, bias correction models were applied to the raw GeoWATCH simulated values using linear regression to predict correction factor (CF) values based on physical site characteristics. The bias correction models significantly improved the performance of the GeoWATCH soil moisture model in terms of average performance statistics and number of statistically cally unbiased sites. This process could easily be incorporated into GeoWATCH, allowing for a capability to rapidly estimate vehicle impacts and determine rehabilitation requirements by installation land managers.     

A calculation method of track shoe thrust on soft ground for splayed grouser

Thrust of track shoes on soft ground is affected by soil moisture content, shear rate and structure parameters of track shoes. A lack of comprehensive consideration of these factors exists for normal calculation methods. A method to predict thrust for track shoes on soft ground with splayed grouser was established based on experimental results and theoretical derivations. Model track shoe traction experiments were conducted for verification and correction of the thrust formula. It was observed that the thrust for the track shoes decreased with the increase in moisture content of the soil. Increases in shear rate, grouser height, and grouser splayed angle resulted in greater tractions. Effect of grouser thickness and grouser draft angle on tractions was not obvious. A corrected thrust formula allowed accurate prediction of thrust for a single track shoe on soft ground.     

Experimental investigation of impact of environmental temperature and optimal baseline for thermal attenuation in structural health monitoring based on ultrasonic guided waves

Structural health monitoring (SHM) of any mechanical component is compulsory for its efficient and long-term performance. One of the major challenges to apply SHM technique in real-time inspections is variation in environmental and operating conditions (EOCs). Sometimes the effect of this variation in EOCs is so severe that it influences the SHM system’s response and reduces the accuracy of the inspection process. The goal of current research is to investigate experimentally the impact of environmental temperature on the ultrasonic guided wave signal during damage detection. According to the characteristic of breathing phenomenon of fatigue crack caused by the applied temperature (30 °C–180 °C) under operation condition, behavior of reflection and transmission signal is analyzed in terms of amplitude and group velocity. Based on experiment findings, a wave velocity function has been generated in the Matlab® environment to compute the velocity of acquired signal considering the effect of both temperature and excitation frequency. A corresponding sequence curve is drawn which illustrates that the proposed function is valid when the operating temperature is less than 130 °C because sensor bonding’s characteristics are affected by the further increment in temperature and consequently it would become difficult to illuminate the sole impact of temperature on damage detection results. Impact of temperature on examined material properties and sensor’s bonding strength is also observed in the current study. Analysis of dispersion curves is performed to examine the individual behavior of S0 and A0 wave modes with temperature and to determine the temperature invariant points to reduce the influence of environmental temperature in SHM. Hence current study not only evaluates the impact of temperature on damage detection but also provides an optimal baseline for thermal attenuation in real-time ultrasonic guided wave inspections.     

超声振动对纳米二氧化硅(n-SiO2)添加剂减摩抗磨性能的影响

在有和无超声振动条件下,分别考察了含不同质量百分数n-SiO2添加剂的减摩抗磨性能,初步探讨了超声振动下纳米二氧化硅(n-SiO2)添加剂的润滑机理.结果表明:超声振动通过减小纳米微粒所受的正压力、促进纳米微粒滚动及增加摩擦表面的活性3种方式改善摩擦表面的润滑状态.超声振动使n-SiO2润滑下的磨痕深度下降,表面硬度降低,磨损表面Si元素含量增加,有效地改善了摩擦表面的润滑状态.在试验范围内,超声振动对0.5%n-SiO2添加剂的减摩抗磨性能影响效果最显著,摩擦副间的摩擦系数和45#钢表面的磨损体积量分别降低了12%和34%.     

Dynamics of a powered disk in clay soil

Experiments were conducted with a single powered disk in a laboratory soil bin containing Bangkok clay soil with an average moisture content of 18% (db) and 1100 kPa cone index. The disk was 510 cm in diameter and 560 mm in radius of concavity. During the tests the disk angle was varied from 20° to 35°, ground speed from 1 to 3 km/h and rotational speed from 60 to 140 rpm. The working depth was kept constant at 12 cm. The vertical, horizontal and lateral reactions of the soil were measured by force transducers. The forward and rotational speeds were recorded. It was observed that disk angle, rotational speed and ground speed had significant effects on soil reactive forces and power requirement. With a small disk angle, low ground speed, and high rotational speed, the soil longitudinal reactive force was a pushing force and became a resistive one at larger disk angles and ground speeds. The soil transverse reactive force increased with an increase of rotational and ground speed but decreased with the increase of disk angle, whereas the vertical relative force increased only with the increase of ground speed but decreased with the increase of rotational speed and disk angle. It was found that the powered disk required the least power at a disk angle of 30° and rotational speed between 80 and 100 rpm. Increase in ground speed from 1 to 3 km/h increased the total power requirement by 31.8%. Upon driving the disk forward, the draft reduced considerably compared to that of the free-rolling disk. By driving the disk in the reverse direction, the draft reduced slightly. At a disk angle of 30°, rotational speed of 100 rpm, and ground speed of 3 km/h, the total power requirement of the forward-driven disk was 65% higher than that of the free-rolling disk. The predicted engine power of the forward-driven disk, however, was only 21% higher than that of the free-rolling one owing to the more efficient power transmission through the PTO, as opposed to the drawbar. The effects of reverse driving and free rolling of the disk were also studied.     

A comparison of ground vehicle mobility analysis based on soil moisture time series datasets from WindSat,LIS, and in situ sensors

Soil moisture is a key terrain variable in ground vehicle off-road mobility. Historically, models of the land water balance have been used to estimate soil moisture. Recently, satellites have provided another source of soil moisture estimates that can be used to estimate soil-limited vehicle mobility. In this study, we compared the off-road vehicle mobility estimates based on three soil moisture sources: WindSat (a satellite source), LIS (a computer model source), and in situ ground sensors (to represent ground truth). Mobility of six vehicles, each with different ranges of sensitivity to soil moisture, was examined in three test sites. The results demonstrated that the effect of the soil moisture error on mobility predictions is complex and may produce very significant errors in off-road mobility analysis for certain combinations of vehicles, seasons, and climates. This is because soil moisture biases vary in both direction and magnitude with season and location. Furthermore, vehicles are sensitive to different ranges of soil moistures. Modeled vehicle speeds in the dry time periods were limited by the interaction between soil traction and the vehicles’ powertrain characteristics. In the wet season, differences in soil strength resulted in more significant differences in mobility predictions.     

Multi-Functional Measurement Using a Single FBG Sensor

This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size.     

Optically interrogated MEMS pressure sensor array

A novel pressure measurement technique is presented for wireless recording of time-averaged surface pressure distributions in wind tunnel surveys. An array of silicon micro-plate resonators acts as pressure sensing element. The pressure is recorded by measuring the sensor diaphragms’ resonance frequency using optical interferometry. Dependent on the quasi-static deflection caused by a pressure load, the resonance frequency varies with an average pressure sensitivity of 3 Hz/Pa in a frequency range between 30 and 150 kHz. A smart-pixel CMOS camera, narrow-band acoustic noise excitation and a specific sensor surface structure allow for the interrogation of a large number of sensors in parallel without the need for alignment between sensor and detector. Experimental tests reveal increased sensing performance with acoustic excitation of the higher vibration modes.     

定子表面织构对超声电机性能的影响

针对超声电机摩擦材料磨损严重和温升高的问题,采用在定子表面加工微织构的方法,提高了电机机械特性并降低了摩擦材料磨损. 首先,用显微镜测量超声电机定子表面摩擦材料黏着区域,设计出三种不同密度的凹坑织构,采用激光的方法加工在定子表面;然后,测试超声电机负载特性、效率特性和温升特性并观察定子表面. 结果表明:3-凹坑织构定子电机空载转速最高,相比光滑定子电机高出12.1%,5-凹坑织构定子电机堵转转矩和最大效率最高,分别高于光滑定子电机13.04%和17.1%,同时电机的温升也有所降低. 通过观察定子表面发现,凹坑织构有大幅降低摩擦材料黏着的作用,这种作用可以增加电机接触界面能量转换效率,提高了电机的性能并降低了摩擦材料的磨损.      

Reconstruction of Scalar Source Intensity Based on Sensor Signal in Turbulent Channel Flow

We consider a turbulent channel flow, where a scalar point source with a time-harmonic intensity releases a substance that can be modeled as a passive scalar. With the source location known, our objective is to estimate the time history of the source intensity based on sensor measurements at different locations downstream of the source by adopting an adjoint approach. It is shown that the proposed algorithm reproduces the original coherent sinusoidal wave of the scalar source accurately from the chaotic scalar signals measured by our sensors. By systematically changing the source-sensor distance and the pulsation frequency of the source, we clarify how these two factors affect the estimation accuracy. The proposed scheme is also applicable to estimation with multiple sensors. We demonstrate that increasing the number of sensors improves the estimation greatly when the scalar is released from a source away from the wall, where large-scale eddies dominate the scalar dispersion. In contrast, the estimation performance remains poor even with multiple sensors when the scalar source is located near the wall, where the source information is quickly lost due to the strong turbulence activity and the scalar diffusion in the near-wall region.