Autonomous control and membrane maintenance optimization of photovoltaic reverse osmosis systems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from department-submitted PDF version of thesis.Includes bibliographical references (p. 97-102).The supply of clean water in remote and off-grid areas has been a major global challenge for humanity. Over 780 million people lack access to clean water [1]. However, a significant fraction of these people have access to undrinkable surface, brackish or sea water. A promising solution to this problem is to use photovoltaic powered reverse osmosis (PVRO) systems to purify this unsafe water to produce clean drinking water. However, high initial capital costs and a lack of commercial viability have prohibited these systems for commercial and daily use. For this approach to be feasible and reach large-scale commercial viability, PVRO systems need to be energy efficient and cost-competitive compared with reverse osmosis systems powered by conventional sources, such as diesel engines or electricity from the grid. The costs and energy consumption in a PVRO system can be significantly decreased by maximizing water production and minimizing the effects of membrane degradation to extend system life. The membrane degradation considered here is the fouling phenomenon in which suspended solids and dissolved substances collect on the surface and within the pores of the membrane thereby reducing its permeability This thesis describes an innovative approach to autonomously controlling and optimizing community scale PVRO systems by controlling membrane degradation due to fouling, using a self-optimizing condition based maintenance algorithm. Additionally, by exploiting the energy compliance of PVRO elements and actively controlling the individual components of the system, water production can be maximized. The compliance in a PVRO system has been found to significantly affect PVRO performance by reducing system efficiency and resulting in long startup delays in producing clean water. In this thesis, a controllable recovery ratio concept system has been presented. By actively controlling the PVRO system, an improvement of 47% over the existing performance of a fixed recovery ratio system has been shown in simulations. Use of condition based maintenance strategies show an improvement of over 10% in cumulative clean water production compared to scheduled quarterly maintenance and 58% over 1 year in cumulative clean water production compared to the case without any maintenance. This is interesting since typical community scale and point of use systems can be and are operated without periodic maintenance [2]. Combining the optimal power control and condition-based maintenance strategies, an improvement in water production of 85 % is shown for a July day in Boston over the MIT PVRO system. Finally, a self-optimizing condition based maintenance algorithm is proposed as the optimal solution to control membrane degradation due to fouling.by Aditya Sarvanand Bhujle.S.M

Saptarshi’s visit to different Nakshatras:

Summary In several ancient Indian texts a mention is made of the movement of the Saptarshi constellation (Big Bear or Big Dipper) in the sky, visiting each nakshatras for 100 years. Saptarshi is said to visit a nakshatra if the nakshatra is in the middle of the stars in the first part of Saptarshi. Since astronomical objects except planets are more or less stationary in the sky, this is generally considered a fanciful statement devoid of astronomical meaning. We show that this may not be so. We show that the visit of Saptarshi to different nakshatras may be a very significant astronomical observation. The transition is not a constant of time since it depends on the proximity of the Saptarshi to the North Pole, which changes due to Earth"s precession and relative sizes of different nakshatras. We show that since 8000 BC, Saptarshi has visited 5 different nakshatras and for one of them, the transition happening in the span of roughly 100 years. We show that this interpretation allows dating of this belief which is consistent with other evidences of the Harappan civilisation and date different Saptarshi Era with calendar dates

Novel Speed-Up Strategies for Non-Local Means Denoising With Patch and Edge Patch Based Dictionaries

In this paper, a novel technique to speed-up a non-local means (NLM) filter is proposed. In the original NLM filter, most of its computational time is spent on finding distances for all the patches in the search window. Here, we build a dictionary in which patches with similar photometric structures are clustered together. Dictionary is built only once with high resolution images belonging to different scenes. Since the dictionary is well organized in terms of indexing its entries, it is used to search similar patches very quickly for efficient NLM denoising. We achieve a substantial reduction in computational cost compared with the original NLM method, especially when the search window of NLM is large, without much affecting the PSNR. Second, we show that by building a dictionary for edge patches as opposed to intensity patches, it is possible to reduce the dictionary size; thus, further improving the computational speed and memory requirement. The proposed method preclassifies similar patches with the same distance measure as used by NLM method. The proposed algorithm is shown to outperform other prefiltering based fast NLM algorithms computationally as well as qualitatively

Efficient non-local means denoising for image sequences with dimensionality reduction

The aim of this paper is to improve both accuracy and computational efficiency of non-local means video (NLMV) denoising algorithm. A technique of principal component analysis (PCA) is used to reduce the heavy dimensionality of patches. A pre-processing step of shot boundary detection is used to split the video sequence into different shots having content-wise similar frames. Further PCA is computed globally for these shots. To speed-up the denoising process, weights are computed in reduced subspace. In the proposed method, we modify the original histogram difference (HD) technique such that content-wise similar frames are separated more systematically and accurately. We have achieved improvement with respect to accuracy and computational speed compared to standard NLM. Moreover, qualitative and quantitative comparisons show that the proposed method is consistently superior compared to that of NLM and some of its variants

Effects of Simmer Current on Flashlamp Impedance and Their Combined Influence on the Output of a Quasi-CW Nd : YAG Laser

This paper reports the results of investigations carried out on the influence of simmer current on flashlamp impedance and performance of a flashlamp-pumped Nd:YAG laser operating in the quasi-CW mode. A pulse power source with an adjustable output pulsewidth (1-20 ms) and an adjustable simmer current source (30 mA to 6 A) developed specifically for the study were used. It is found that the simmering of the lamp reduces the impedance factor of the lamp, increases the correct are diameter, and reduces the peak current density of the flashlamp discharge. It improves the efficiency of the flashlamp pump source and, hence, the efficiency of the Nd:YAG laser also. An appropriate choice of the simmer current, using the results obtained, can lead to higher efficiency of the Laser and increased life of the lamp