Measurement of stress in bolts using resonant ultrasound spectroscopy

Stress affects the resonance properties of materials. A suitable technology and instrumentation for calculating stress in pre-installed oil pipeline bolts is developed and tested. The technology, Resonant Ultrasound Spectroscopy (RUS), relates the change in bolt resonances to bolt stress, using analysis software. A suitable instrumentation that excites the bolt over a band of frequencies through a broad band sweep and measures the response to compute resonances and bolt stress is developed. The instrumentation and the analysis software operate in a loop with minimum operator input to predict stress in the bolts. The project is primarily aimed at the oil and gas industry but has the potential to fit bolt-testing applications in aerospace, defence and manufacturing industries. The proposed testing method is new to Non Destructive Testing (NDT) of oil pipeline bolts and has no peers. A calibration data set is built using the resonance information extracted from a set of bolts. Test results are discussed and areas of future work explored. A stress prediction accuracy of = 20% has been achieved with a group of 10 B7 bolts. This project is a Knowledge Transfer Partnership (KTP) project and was done at Hedley Purvis Ltd., in association with Durham University

Evaluation of Satellite-Based Rainfall Estimates in the Lower Mekong River Basin (Southeast Asia)

Satellite-based precipitation is an essential tool for regional water resource applications that requires frequent observations of meteorological forcing, particularly in areas that have sparse rain gauge networks. To fully realize the utility of remotely sensed precipitation products in watershed modeling and decision-making, a thorough evaluation of the accuracy of satellite-based rainfall and regional gauge network estimates is needed. In this study, Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42 v.7 and Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) daily rainfall estimates were compared with daily rain gauge observations from 2000 to 2014 in the Lower Mekong River Basin (LMRB) in Southeast Asia. Monthly, seasonal, and annual comparisons were performed, which included the calculations of correlation coefficient, coefficient of determination, bias, root mean square error (RMSE), and mean absolute error (MAE). Our validation test showed TMPA to correctly detect precipitation or no-precipitation 64.9% of all days and CHIRPS 66.8% of all days, compared to daily in-situ rainfall measurements. The accuracy of the satellite-based products varied greatly between the wet and dry seasons. Both TMPA and CHIRPS showed higher correlation with in-situ data during the wet season (JuneSeptember) as compared to the dry season (NovemberJanuary). Additionally, both performed better on a monthly than an annual time-scale when compared to in-situ data. The satellite-based products showed wet biases during months that received higher cumulative precipitation. Based on a spatial correlation analysis, the average r-value of CHIRPS was much higher than TMPA across the basin. CHIRPS correlated better than TMPA at lower elevations and for monthly rainfall accumulation less than 500 mm. While both satellite-based products performed well, as compared to rain gauge measurements, the present research shows that CHIRPS might be better at representing precipitation over the LMRB than TMPA

Power Spectral Density Computation and Dominant Frequencies Identification from the Vibration Sensor Output under Random Vibration Environment

The objective of the modal and spectral analysis is to determine the vibration characteristics of structures such as natural frequencies, dominant frequencies and mode shapes. Such modal and spectral analyses have major relevance to the study of the dynamic properties of the structures undergoing dynamic vibration. Methods for the estimation of the power spectral density and identification of the dominant frequencies from the sensor responses under random vibrating environment are presented in this paper. Periodogram using FFT, Welch Method and MUSIC algorithm are used to analyse the known frequency sinusoids with additive white noise and output of the vibration sensor mounted on the test object. The resultant spectra obtained using the methods and their corresponding errors with the reference spectrum are analysed. The Welch method is further studied with three different windows, namely, Hann, Hamming and Blackman-Harris and with three different overlapping criteria viz. 0%, 25% and 50%. The same algorithm and methodology were adopted and compared in two different platforms: Mathematical Model Simulation and Hardware-In-Loop-Simulation. It is observed from the results that Welch Method with 25% overlap used in combination either with Hann or Blackman-Harris window yields more accurate results, compared to other combinations. Also, 25% overlap provides better execution time trade-off compared to 50% overlap

An Architecture for On board Frequency Domain Analysis of Launch Vehicle Vibration Signals

The dynamic properties of the airborne structures plays a crucial role in the stability of the vehicle during flight. Modal and spectral behaviour of the structures are simulated and analysed. Ground tests are carried out with environmental conditions close to the flight conditions, with some assumptions. Subsequently, based on the flight telemetered data, the on-board mission algorithm and the auto-pilot filter coefficients are fine tuned. An attempt is made in this paper to design a novel architecture for analysing the modal and spectral random vibration signals on-board the flight vehicle and to identify the dominant frequencies. Based on the analysed results, the mission mode algorithm and the filter coefficients can be fine tuned on-board for better effectiveness in control and providing more stability. Three types of windows viz. Hann, Hamming and Blackman-Harris are configured with a generalised equation using FIR filter structure. The overlapping of the input signal data for better inclusiveness of the real-time data is implemented with BRAM. The domain conversion of the data from time domain to frequency domain is carried out with FFT using Radix-2 BF architecture. The FFT output data are processed for calculating the power spectral density. The dominant frequency is identified using the array search method and Goldschmidt algorithm is utilised for the averaging of the PSDs for better precision. The proposed architecture is synthesised, implemented and tested with both Synthetic and doppler signal of 300 Hz spot frequency padded with Gaussian white noise. The results are highly satisfactory in identifying the spot frequency and generating the PSD array

Robust and Adaptive Attitude Control Of Spacecraft Using Solar Radiation Pressure

Satellites in orbit are expected to maintain a preset attitude either pointing towards Earth (in case of satellites for weather) or pointing towards space for the purpose of research and exploration. The satellite as a system though is extremely nonlinear and the system parameters are not easily available. The goal of this thesis is to develop robust and adaptive control laws that can be used to control the attitude of satellites in elliptic orbits. The attitude of the satellite is controlled by the use of Solar Radiation Pressure (SRP) on the solar panels of the satellite. The SRP is basically a mechanical pressure caused by the photons impinging on the solar panels. By deflecting the solar panels the area that is impinged by photons is varied and therefore the torque on the satellite is also varied. This torque is used to control the attitude of the satellite which is expected to be maintained at a preset orientation. In this work, different methods will be used to control the satellite under different conditions involving state and output feedback. For state feedback all the states of the system are assumed to be available. In this case the states would involve the pitch angle, angular velocity and acceleration of the satellite. However the information on these states may not be easily available. Output feedback is when the output alone of the system is used and only an estimation of other states is used. Simulation is used to project the results of the different types of controllers

A 3 year retrospective study on gestational trophoblastic disease in a government obstetrical tertiary care centre

Background: The aim of this study is to assess the post diagnostic outcome of Gestational Trophoblastic Disease, a heterogeneous group of disorders, in a government obstetrical tertiary care centre.Methods: The study was conducted in the Institute of Obstetrics & Gynecology, Madras Medical College as a retrospective study. A total of 75 cases were studied over a 3 year period from January 2012 to December 2015. The parameters which were studied included age group, antecedent pregnancy, beta hCG values, histopathological types and Treatment profile.Results: Of the 75 cases, 55 cases (73%) were in the 21-39 age group. The spectrum of disorders that were studied included 69 cases of complete mole, 2 cases of partial mole, 1 case of twin pregnancy with single live foetus and partial mole, 1 case of triplet pregnancy with two live foetuses and partial mole, 1 case of epithelioid trophoblastic tumour and 1 case of choriocarcinoma. Of the 75 cases, 16 cases underwent chemotherapy. No mortality was observed during the study period.Conclusions: Close monitoring and follow up with beta hCG values is of utmost importance in the management of Gestational trophoblastic disease. In cases of gestational trophoblastic neoplasia (GTN), WHO/FIGO scoring should be done and managed with chemotherapy according to the risk assessment

Site symmetry and internal strains

The determination of the internal strains on the coupling parameter approach becomes very involved particularly when the number of atoms per unit cell is very large. It is shown in this paper that a knowledge of the site symmetry of the atoms helps one in determining the number of non-vanishing internal strain coefficients easily. The internal strain coefficients of two symmetry connected atoms can also be related. Examples are shown to illustrate these ideas