A swinging arm calibration method for low velocity hot-wire probe calibration

This paper describes a swinging arm calibration facility for the calibration of hot-wire probes at low velocities. During the motion of the probe the anemometer signal is recorded digitally using pre-set angle positions for the start and stop of the data acquisition. The evaluation method described in this paper is based on an integral procedure over a fixed, known probe path length. Tests in the velocity range 1 to 6 m/s demonstrated a high degree of repeatability of the calibration results. Furthermore, the test facilities can easily be adjusted for other low velocity ranges.     

Multiple hot-film sensor array calibration and skin friction measurement

A method for the calibration of closely spaced multiple hot-film sensor (MHFS) arrays of nickel-on-polyimide-substrate type was presented in this paper. The hot-film sensors were calibrated individually and in situ against the values of the wall-shear stresses determined from boundary-layer velocity profiles (developed on the front portion of a circular cylinder) through a specially designed wall-mounted hot-wire probe. The accuracy and feasibility of the present method was examined through the subsequent measurements of the skin-friction distributions on a circular cylinder (including the removal and bonding of the calibrated MHFS from a 10-cm diameter calibration cylinder and onto the surface of a 8-cm diameter test cylinder) and comparison of their consistency with the published results. The present MHFS calibration method is important in the non-intrusive multipoint measurements of the mean skin friction along the surfaces of two-dimensional aerodynamic objects of interest.     

A simple pendulum technique for the calibration of hot-wire anemometers over low-velocity ranges

A method for low velocity calibration of hot-wire anemometers, in which the probe is mounted on a pendulum arm, is presented. The calibration constants are determined from recorded traces of the anemometer signal obtained in the forward swing of the pendulum with the probe mounted at two different radii along the arm. Typical calibration results are presented and the use of a modified King's law in the low Reynolds number range is discussed.List of Symbols A, B, n calibration constants in King's law - E anemometer voltage output - E ₀ anemometer voltage output for zero flow velocity - Re Reynolds number - r radius along the pendulum arm - T period of oscillation of the pendulum arm - t time - U velocity - y ⁺ non-dimensional distance from the wall Greek Symbols root mean square of the velocity difference in half the forward swing - angular position of pendulum - angular velocity of pendulum arm Financial support for this work was provided by the Natural Sciences and Engineering Research Council of Canada and by the Atomic Energy of Canada Limited.     

Two-component hot-film probe for measurements of wall shear stress

A two-component, hot-film probe has been developed, to measure the wall shear stress as a vector quantity in time-dependent flows. The probe has been applied for the measurements of the bottom shear stress in a flow generated by combined waves and current in a water basin where the magnitude and the direction of the bottom shear stress varied periodically with respect to time. The probe has also been used to measure the bottom shear stress around a vertical cylinder exposed to water waves generated in a wave flume.     

Optimal seeding for long pathlength multi-component laser Doppler anemometers

There are optimal combinations of size and number density of seed particles which can maximize the processed data rate of laser Doppler anemometers (LDAs). When optical pathlengths are long, as in large scale water facilities, the choice and density of seeding particles determines the balance between the scattered-light intensity at a measuring volume and its extinction along the rest of the optical path, and so its intensity at a photodetector. These considerations must generally be coupled with knowledge of particle arrival statistics, detector performance, processor characteristics and signal conditioning to optimize data rate. However, in multicomponent LDAs, coincidence requirements in data arrival times enforce a close approximation to a Poisson distribution in the processed data rate as a function of the number density of seed particles. This result leads to simple models for optimal number densities for seeding as a function of optical pathlength and related parameters.     

An approximate amplitude attenuation correction for hot-film shear stress sensors

A correction method, based on experimental results, has been developed to remedy the amplitude attenuation that occurs when statically calibrated hot-film shear stress sensors are used in air. The correction method is necessary in applications where typically two-dimensional arrays of measurement points are needed and other sensors, such as hot wires, cannot be employed. The method was developed with a primary aim of obtaining the correct power spectral density of an ensemble-averaged signature from an array of hot-film shear stress sensors. The hot-film sensors are corrected by comparing their individual power spectral densities to a reference spectrum obtained with a single hot wire, slightly elevated but within the viscous sublayer of the turbulent boundary layer. The method is verified by comparing the corrected hot film’s turbulence statistics, power spectral density, and correlation coefficients with the corresponding results from the hot wire. Published online: 19 December 2002     

Second or third order control theory for constant-temperature hot-wire anemometers?

 It is shown that only a third order control theory is capable of describing dynamically optimized modern constant-temperature hot-wire anemometers. Second order theories or approximations contain serious errors in judgment. Received: 31 January 1997/Accepted: 19 February 1997     

A method for the analysis of hot-film anemometer signals in two-phase flows

The authors discuss the application of hot-film anemometers in gas-liquid two-phase flow. Having stored the digitized record of the anemometer output signal on magnetic tape, methods are discussed that permit the identification of the vapour-phase using electronic computer programs. Methods are described to identify large vapour slugs and small bubbles. The authors propose an extension of these methods to the treatment of two-phase flows containing both large and small bubbles.     

A characteristic length for dilute drag reducing polymer solutions: Measurement using hot film anemometers

Summary This paper emphasizes that a length characterizing the fluid must be used to write realistic constitutive equations for some flows of high molecular weight polyethylenoxide solutions. The onset velocityu _c of anomalous heat transfer about submerged cylinders and the characteristic timet _c of the solutions have been measured using hot film sensors and total head pressure tubes. Measurements made for several cylinder diameters, solution concentrations, solvents and polymer molecular weights produce a characteristic length which actually looks like the fully extended length of the macromolecules.

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Zusammenfassung Diese Untersuchung stellt heraus, daß eine die Flüssigkeit charakterisierende Länge benötigt wird, wenn man für gewisse Strömungssituationen bei hochmolekularen Polyäthylenoxid-Lösungen realistische Stoffgleichungen angeben will. Die Einsatzgeschwindigkeitu _c für die anomale Wärmeübertragung bei eingetauchten Zylindern und eine für die Lösung charakteristische Zeitt _c werden mit Heißfilmsonden und Staurohren gemessen. Die mit verschiedenen Zylinderdurchmessern, Lösungskonzentrationen, Lösungsmitteln und Molgewichten durchgeführten Messungen ergeben eine charakteristische Länge, die der Größenordnung nach mit der Länge der voll ausgestreckten Makromolekeln übereinstimmt.

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With 3 figures and 2 tables     

Evaluation of flush mounted hot-film sensors for skin friction reduction measurements in viscoelastic polymer solutions

The purpose of this investigation was to evaluate the performance of flush mounted hot-film sensors for mean wall shear stress measurement in turbulent flows of dilute drag reducing polymer solution. A series of pipe flow expriments were conducted over a range of Reynolds numbers and polymer solution concentrations to compare the level of skin friction drag reduction measured by hot-film sensors with values calculated from pipe pressure drop. It is shown that water calibrated hot-film sensors consistently underestimate the wall shear stress suggesting that Reynolds analogy is not valid in dilute polymer solutions. The Newtonian form of the relationship between the wall shear stress and the heat transfer remains valid in dilute polymer solutions. However, multiplicative and additive factors in the relationship are shown to increase linearly with the logarithm of the polymer concentration.     

捷联惯导系统的空中标定方法

从工程实用和维护的角度出发,提出了一种针对机载捷联式系统的空中标定方法。该方法依据捷联惯导系统级标定的基本原理,使用卡尔曼滤波作为估计手段,惯性器件常值漂移、刻度系数误差及惯导系统基本误差项作为状态量,依据外部GPS信息作为观测基准,通过设定的飞行机动动作对各待标定误差项进行激励。仿真卡尔曼滤波结果表明,依据飞机实际运动过程设计的简单飞行轨迹即可以实现对所有误差项的有效激励,各误差项随飞行过程进行逐步收敛。这种系统级空中标定方法不需要飞机作特殊的机动动作,在实际工程中易于实现,且经过一个架次的飞行就可以对惯导系统进行一次标定补偿。     

一种激光陀螺惯性测量单元混合标定方法

针对采用低精度转台标定高精度激光陀螺惯性测量单元(IMU)的方法进行了研究。提出一种不依赖转台精度的静态解析与Kalman滤波估计混合的新型高精度标定方法。首先采用多位置静态解析法粗标定出IMU系统参数的低精度初始值;然后根据惯性导航算法基本误差方程,建立以IMU系统参数粗标定结果的残差为估计对象,以IMU速度误差为观测量的扩展Kalman滤波器,估计出系统参数残差,进一步修正粗标定结果。实验结果表明,该方法能够利用低精度转台获得与高精度转台相当的参数标定精度,降低了惯导系统的标定成本,满足高精度激光陀螺IMU的使用需求。     

近钻头测斜器最优八位置标定法

近钻头测斜器(ABI)用于石油钻井中随钻测量实际井眼轨迹,是实现钻井设备自动化和智能化的重要部件。但由于其现场标定条件限制,只能用定制双轴转台进行标定,不适合采用常规的十二位置翻滚标定法,故在分析标定原理的基础上,针对现场标定条件提出了近钻头测斜器最优八位置标定法,并定义了该方法最小二乘估计的信息矩阵,而后通过数值计算对其行列式进行优化设计,求出使其行列式最大的位置参数,确定了其最优值。通过标定实验算出近钻头测斜器最优八位置标定法得到的标定参数,并将其与常规十二位置标定法的结果进行对比,验证了该方法的精度,标度因数和零偏的相对误差在10-5量级以下,而失准角误差也在2″以内,完全能够满足实际应用需要。     

一种新的激光陀螺惯性测量组合标定方法

根据激光陀螺和石英加速度计的简化输出模型，推导并提出了一种新的激光陀螺惯性测量组合标定方法。该方法首先建立了一个与转台无关的机体坐标系，然后利用惯性测量组合绕6个不共面轴转动的输出值求解出激光陀螺的比例因子和安装方位；与此同时，根据6个转轴在竖直向上和竖直向下位置时的惯性测量组合输出值来确定加速度计在同一机体坐标系下的比例因子、安装方位和漂移。理论分析表明，与传统的标定方法不同，新方法对激光陀螺的标定结果受转台精度的影响较小，可以克服减震装置变形对激光陀螺标定的影响，从而实现中等精唐转合对惯性测量组合的高精唐标定。     

激光捷联惯导系统的一种系统级标定方法

根据陀螺和加速度计的输出误差模型,从惯性导航基本方程出发推导了捷联惯导系统的系统级标定的一种误差参数标定模型,明确了该模型成立的条件,分析了该模型下惯性仪表24项误差参数的可辨识性,从而解释了已有文献未将惯性仪表24个误差参数完全辨识的原因,完善了该理论的完整性,并且提出了设计多位置翻滚实验的位置编排原则,给出了能够辨识出惯性仪表24项误差参数的标定方法.根据该位置编排原则可以找到多组可行的位置编排使得惯性仪表误差参数是可辨识的.该标定方法简单易行.     

激光陀螺捷联惯导系统外场快速标定新方法

针对激光陀螺具有标度因数稳定、漂移误差变化小的特点,建立了适合激光陀螺捷联惯导系统的陀螺及加速度计组件简化误差参数模型,推导出了适合激光陀螺捷联惯导系统外场快速自标定的误差模型,设计了激光陀螺捷联惯导系统9位置系统级标定方法,并通过试验验证了该方法可快速准确的标定出加速度计组件的标度因数、安装误差、零偏及激光陀螺安装误差等15个主要参数,方法简单易行。     

惯性测量组件整体标定技术

研究了惯性测量组件中陀螺与加表的标度系数、零偏、安装耦合误差等的标定问题。建立了陀螺与加表的输入输出模型,提出了在三轴摇摆转台上利用六位置试验法对加表标度系数、零偏、耦合误差进行标定的方法;提出了在三轴摇摆转台上利用正负对称的多组速率试验法以及最小二乘法对陀螺标度系数、零偏、耦合误差进行标定的方法,以及利用六位置试验对陀螺与g有关量进行标定的方法。详细介绍了组件输出参数的测量方法并推导误差计算公式。理论分析表明,该方法可在三轴转台上通过位置与速率试验一次性标定出测量元件的相关误差,具有一定的工程应用价值。     

Design of aluminium boom and arm for an excavator

The aim of this work is to study the boom and the arm of an excavator in order to replace the material, which they are usually made of, with another material. In particular, the study wants to substitute the steel alloy for an aluminium alloy. This change lightens the components of the arm, allows to increase the load capacity of the bucket and so it is possible to increase the excavator productivity per hour.For this purpose many different load conditions have been studied numerically on the original excavator in order to estimate a safety factor and the deformability or flexibility of each component. These parameters have been used in order to design a new arm.The excavator which has been analyzed is composed of three elements and the load conditions assumed, in order to evaluate the stress, are five (lifting at the maximum and minimum distance from the axis of rotation, maximum load induced by hydraulic cylinders, spin of the arm of the excavator and collision with an obstacle, etc.).As regards to the safety factor and deformability in order to maintain the original value the new geometry of the arm involves an increase of the dimension and so the lightness is not correlate only to the variation of the material density.The weight of the final geometry of the aluminium arm is 1080 kg whereas the one of the steel arm is 2050 kg and consequently it has been possible to increase the capacity of bucket from 1 m³ to the 1.35 m³.With reference to the manufacturing cycle of the aluminium arm with the new pins, the price increased about € 2.500-3.000 and this aspect could be justified if we consider that the productivity per hour increased about 35%.