Volume 10 (2010): Issue 4 (January 2010)

The accurate determination of the flow rate of the low flow season is a very important factor in setting and running a water resources development plan. Because South Korea undergoes a lot of flood damage due to localized heavy rain during the summer season, flow rates are measured mostly according to flood management, and this allows for a lack in research in understanding low flow season flow rates. In order to estimate the accurate flow rate of a low flow season, the present study has used the Parshall flume that has been used widely in flow measurements, and has reviewed the applicability. A Parshall flume was installed in an actual river and the measured flow rate that was obtained from the flow rate formula and velocity measurements, that were suggested by the ISO and the USBR, were found to be very accurate when compared to the flow rate computation results by the Parshall flume. By using the state-discharge rating curve equation that is most commonly used at the level gauging station, the flow rate was estimated and compared with the flow rate by the Parshall flume. The results showed an approximate 14% error with the estimation from the state-discharge rating curve equation. Therefore, using the Parshall flume to estimate the flow rate of low flow season is more effective than the state-discharge rating curve equation.

Functional magnetic resonance imaging (fMRI) is a quickly developing method for non-invasive dynamic brain studies. It uses swift acquisition sequences like echo planar imaging (EPI) that are very sensitive to susceptibility artifacts. These artifacts relate to magnetic field inhomogeneities and may cause geometric distortions. Many methods for correcting these distortions are currently used. Most common are the field mapping methods that use the map of field strength. To create a field map, different approaches can be used and different data must be acquired for each method. This paper compares a commonly used conventional gradient echo (GE) field mapping method with a 3EPI phase images based method. Although the EPI method is more sophisticated and was expected to perform better, the GE field maps showed better results in distortion correction. The cause of this is not in the method's principle itself, but in its high requirements.

This paper aims at studying the effect of the dynamic errors on surface measurements using three different types of touch trigger probes attached to a bridge-type-CMM. Unforeseeable dynamic root errors of a ductile touch trigger probing system have been characterized theoretically and experimentally as well. The results were employed in validating a developed analytical two-dimensional-model (2DM) of stylus tip to be developed to demonstrate the capability of such approaches of emphasizing the root error concept, and to evaluate the accuracy of the CMM measurements. A set of experiments was conducted; the results were analyzed in order to investigate the effect of the dynamic root errors in the light of probe scanning speed at different stylus tip radii. Variations in the mass and geometry of the stylus have their consequent effects on its inherent intrinsic dynamic characteristics that in turn would cause relevant systematic root errors in the resulting measurements. 3D bore cylindrical surface form undulations were measured by employing a probe on the trajectory of internal surface diameter for the standard reference test gauge ring. Regression analysis was applied on the results of measurement density distribution; uncertainty of measurement repeatability was then evaluated and graphically presented. The results were investigated and optimum strategic measurement parameters could thus have been derived to ensure foreseeable accurate and precise results.

Several commercial instruments are available for pressure measurements. As per ISO stipulations, whenever such instruments are used for precise and accurate pressure measurements, it is obligatory on the part of measurement authority to indicate the quality of results. Stability of the pressure measuring instruments over the years is one of the important parameters in defining the quality of results quantitatively. Also, it helps the users to decide the optimum calibration interval of the particular instrument. In the present investigation, we have studied a number of analogue / digital pressure transducers / transmitters / calibrators and pressure dial gauges. The present paper describes the results of the studies carried out on several pressure dial gauges and transducers in the pressure range up to 500 MPa, calibrated several times over the years, as examples. A new approach is proposed for the establishment of measurement uncertainty for such instruments by characterizing the data obtained during calibration over the years using curve fitting.

Measurements in production must be rapid, robust and automated. In this paper a new method is proposed to automatically extract features and parameters of screw threads via Hough transformation from 2D point clouds acquired from profile measuring machines. The described method can be used to automate many operations during screw thread prealignment and drastically reduce operator's influence on the measurement process resulting in lower measurement times and increased repeatability.

This paper presents a simplified system for measuring geometric profiles of end mills. Firstly, a CCD camera was used to capture images of cutting tools. Then, an image acquisition card with the encoding function was adopted to convert the source of image into an USB port of a PC, and the image could be shown on a monitor. In addition, two linear scales were mounted on the X-Y table for positioning and measuring purposes. The signals of the linear scales were transmitted into a 4-axis quadrature encoder with 4-channel counter card for position monitoring. The C++ Builder was utilized for designing the user friendly human machine interface of the measuring system of tools. There is a cross line on the image of the interface to show a coordinate for the position measurement. Finally, a well-known tool measuring and inspection machine was employed for the measuring standard. This study compares the difference of the measuring results by using the machine and the proposed system. Experimental results show that the percentage of measuring error is acceptable for some geometric parameters of the square or ball nose end mills. Therefore, the results demonstrate the effectiveness of the presented approach.