A Comparative Study of Natural Gas and Biogas Combustion in A Swirling Flow Gas Turbine Combustor

In this study, non-premixed combustion of a traditional fuel-natural gas, and an alternative fuel-biogas, is simulated in a swirling flow industrial gas turbine combustor geometry which includes the combustor liner and the outside casing in order to replicate the flow and combustion in a real gas turbine combustor. The 3D combustion simulations are validated and the results for combustion of both gases are analyzed to compare and evaluate the viability of biogas as an alternative fuel for use in industrial gas turbine combustors. The combustion performance is evaluated based on multiple combustion performance optimization parameters, namely, the combustion efficiency, pattern factor, and pollutant emissions (CO and NO). The effects of two design parameters: swirl number and fuel injector diameter on the combustion performance optimization parameters are examined. The results have been analyzed to identify the best case for each combustion performance optimization parameter and a suitable trade-off case for both gases is proposed. Additionally, the comparison of the combustion performances of both gases revealed that despite possessing much lower methane and hence lower heating value (LHV), a combination of swirl number and fuel injector diameter for biogas of a specific composition results in a combustion performance comparable to natural gas along with lower NO emission, although at the expense of higher CO emission. Therefore, biogas can potentially be utilized as an alternative fuel in industrial gas turbine combustors, and methods for reducing CO emission can be devised.Peer ReviewedPostprint (published version

An Investigation of RANS Simulations for Swirl-Stabilized Isothermal Turbulent Flow in a Gas Turbine Burner

The presence of complex flow features in swirling flows have made it an essential part of many engineering applications. These features can only be accurately predicted by the DNS or LES type methods which are highly expensive in terms of resources and time. This fact established the RANS approach as the key method in the industrial arena because of its modest requirement of resources unlike LES. However, existing RANS investigations on swirl-stabilized isothermal turbulent flow are 2D and lack credibility on the question of predicting the prominent flow features which exist in swirling flows. The current study investigates the 3D RANS simulations in predicting a swirl-stabilized isothermal turbulent flow in a burner for a gas-turbine combustion chamber which possesses complex flow features such as bluff-body induced recirculation zone and Vortex Breakdown (VB) bubble. Current investigations also assess the establishment of 3D RANS simulations as a viable industrial alternative to the computationally expensive LES and the less accurate 2D RANS simulations. Furthermore, the influence of mesh quality, different turbulence models, discretization schemes on the accuracy of the predictions are examined. It was found that the multi-zonal mesh with hexahedron cells had the highest mesh quality and produced the best results, and the standard k-¿ model predicted all the flow features with default schemes in ANSYS-Fluent. The conclusions in the paper are valuable, practical and will save a lot of time and effort of practicing engineers during the numerical modelling setup selection stages for solving such complex three-dimensional flow problems. KEYWORDS: 3D RANS, industrial alternative, swirl, burner, recirculation, vortex breakdown, bluff-body, iso-thermal, turbulence.Award-winningPostprint (published version

Home Use of an Upper Extremity Exoskeleton in Children with SMA: A Pilot Study

Background: People with spinal muscular atrophy (SMA) often have arm weakness resulting in restricted independence and challenges with activities of daily living. An upper extremity (UE) orthosis, the Wilmington Robotic Exoskeleton (WREX), which augments arm movement by providing gravity assistance, was provided to a small cohort of subjects for 1 year. Resulting changes in the subjects’ performance were assessed. Method: Five subjects with SMA were asked to use the WREX system for 1 year. Data were collected at baseline and at 6-month intervals. Evaluation tools used were UE range of motion (ROM), the Box and Block Test, the Canadian Occupational Performance Measure (COPM), and the reachable surface area (RSA) using a Microsoft Kinect Sensor. Results: There were no significant changes in UE ROM without the device over time and no significant changes in dexterity after long-term use of the WREX. There were clinically meaningful changes in active ROM while wearing the device compared to without it and clinically meaningful changes in performance and satisfaction while wearing the device. The RSA software did not yield usable results for this population. Conclusion: Wearing bilateral WREX devices resulted in immediate improvements in ROM and function; however, the subjects experienced several barriers, which prevented consistent long-term use

Multiband split-ring resonator based planar inverted-F antenna for 5G applications

5G, the fifth generation of wireless communications, is focusing on multiple frequency bands, such as 6GHz, 10GHz, 15GHz, 28GHz, and 38GHz, to achieve high data rates up to 10 Gbps or more.The industry demands multiband antennas to cover these distant frequency bands, which is a task much more challenging. In this paper, we have designed a novel multiband split-ring resonator (SRR) based planar inverted-F antenna (PIFA) for 5G applications. It is composed of a PIFA, an inverted-L parasitic element, a rectangular shaped parasitic element, and a split-ring resonator (SRR) etched on the top plate of the PIFA.The basic PIFA structure resonates at 6GHz. An addition of a rectangular shaped parasitic element produces a resonance at 15GHz. The introduction of a split-ring resonator produces a band notch at 8GHz, and a resonance at 10GHz, while the insertion of an inverted-L shaped parasitic element further enhances the impedance bandwidth in the 10GHz band. The frequency bands covered, each with more than 1GHz impedance bandwidth, are 6GHz (5–7GHz), 10GHz (9–10.8GHz), and 15GHz (14-15GHz), expected for inclusion in next-generation wireless communications, that is, 5G. The design is simulated using Ansys Electromagnetic Suite 17 simulation software package.The simulated and the measured results are compared and analyzed which are generally in good agreement

Conceptual framework for IFRS adoption, audit quality and earnings management : the case of Bangladesh

This study propose to explore the moderating role of audit quality on the relationship between IFRS adoption and earnings management as well as the effect of IFRS adoption on earnings management in the context of Bangladesh, as developing economy. Earlier literature document that the relationship among IFRS adoption, audit quality and earnings management are not conclusive. In case of IFRS adoption, it is incoherent which may be the result of difference in culture, practices and legal strength of the country. This study considers discretionary accruals as proxy of earnings management which is measured by the extended modified Jones model. Moreover, the influence of audit quality on the association between IFRS adoption and earnings management is also proposed to investigate. This study expects to explore the effect of IFRS adoption on earnings management in the context of developing country, like Bangladesh. It may be informative for the reader to understand the outcome of IFRS adoption, audit quality on earnings management in developing economy.peer-reviewe

Total Mercury Levels In The Coastal Environment Of Qatar (Arabian Gulf)

The levels of total Mercury (t-Hg) were determined in various segments of the marine environment of Qatar. Several coastal stations, both on the East as well as the West coast of Qatar were worked for t-Hg in seawater, sediments and biological matrices. Nearly 20 stations were worked within the EEZ of Qatar, on the east coast, wherein seawater samples were collected at different depths for t-Hg along with surface sediments and resident biota. Seawater samples were not filtered and results given are for total dissolved Hg. Sediment samples were analyzed for leachable as well as t-Hg contents. A wide range of 22-198 ng/L values were obtained for the seawater samples, 0.098-317 ug/g dry wt. in sediments and 0.008-0.093 ug/g dry wt. in biota were measured. The leachable fractions amounted to a range of 3-18% of the t-Hg in sediments. The results do not indicate any elevated levels but are discussed in the light of the geographical distribution of stations and sampling sites with respect to their location and possible input sources

THE ROLE OF GOLD PRICES, EXCHANGE RATE AND INTEREST RATE ON THE CONTINUITY OF INFLATION IN PAKISTAN

In this paper we investigated the role of gold prices, interestrate and exchange rate against inflation in Pakistan both in the longand the short run, utilizing time series data over the period of 1975-2013 under the Johansen co-integration and vector error correctionspecifications. The results suggest that gold prices and interest rateare significantly positively related with inflation in the long run inthe case of Pakistan, indicating that a rise in gold prices and interestwill result in increase in inflation in Pakistan. Whereas exchangerate is found to be insignificant to impact inflation over the length ofthis study. However exchange rate is found to have significantly andnegatively associated with inflation in the short run. That means thatappreciation in rupee (PKR) will result in decrease in inflation andvice versa

Millimetre-wave antennas and systems for the future 5G

Editorial of the special issue on Millimetre-Wave Antennas and Systems for the Future 5

Relações entre parâmetros geofísicos e geotécnicos com foco em resultados específicos de uma área de risco de escorregamentos

The population growth and extension of a settlement on a risky area have increased the impact of natural disaster. Slope failures, landslides and subsidence of foundation have been identified as the most commonly occurring natural disaster if such sensitive areas are not well monitored. On the other hand, a detailed analysis of the triggering factors is often hindered by the lack of information gathered from the field measurements. A survey investigation was performed in a possible landslide risk area, using the geotechnical, geophysical and geological mapping approaches. The geotechnical investigations included coring in order to obtain the lithological sequence and for sampling purposes. And standard penetration test (SPT) in-situ field tests of soil strength. Electrical resistivity tomography (ERT) and seismic refraction tomography investigations were executed in order to determine the hydrogeological characteristics and delineate the regions of weak and hard subsurface materials. The 2D inversion results of resistivity technique suggested the presence of a two-layer structure model. Moreover, the 'break' in the unit was apparent, indicative of the presence of weak zones, fractured zone and cracks. As also demonstrated clearly by the seismic refraction data, the depth to bedrock (a sharp boundary interface approximately at a depth of 15 m) varies, and such variation is mainly attributed due to the thickness of the overlying backfill material. Additionally, we examined the possible correlation (if any) between geophysical parameters and geotechnical parameters to establish the quantitative estimates of a particular geotechnical parameter (e.g., soil strength) from geophysical surveys. From this study, a good relationship between electrical property (resistivity) and geotechnical property (soil strength) with the empirical equation RS= 31.733 (N60) -165.88 and regression coefficient R2=0.77 was observed. Based on the correlation between elastic property and weathering profile, we divided the subsurface materials into three zones: the first zone is classified as Residual soil with p-wave velocity (300 – 900 ms-1), the second zone is classified as highly weathered granite with p-wave velocity (900 – 1800 ms-1), and the third zone is classified as moderately weathered granite with p-wave velocity (1800 – 3000 ms-1). All geophysical and geotechnical data suggest that a fairly weak/uncompact backfill materials underlying the bedrock are likely to provide a planar surface where the landslide mass would move/be triggered.El crecimiento de la población y la extensión de un asentamiento en un área de riesgo han aumentado el impacto de un desastre natural. Las fallas en la pendiente, los deslizamientos de tierra y el hundimiento de la fundación se han identificado como el desastre natural más frecuente si dichas áreas sensibles no están bien monitoreadas. Por otro lado, un análisis detallado de los factores desencadenantes a menudo se ve obstaculizado por la falta de información obtenida de las mediciones de campo. Se realizó una investigación en un área de riesgo de deslizamiento posible, utilizando los enfoques de mapeo geotécnico, geofísico y geológico. Las investigaciones geotécnicas incluyeron la extracción de muestras para obtener la secuencia litológica y para fines de muestreo. Tambien pruebas de penetración estándar (SPT), pruebas de campo in situ de la resistencia del suelo. La tomografía de resistividad eléctrica (ERT) y la tomografía de refracción sísmica se realizaron para determinar las características hidrogeológicas y delinear las regiones de materiales subsuperficiales débiles y duros. Los resultados de inversión 2D de la técnica de resistividad sugirieron la presencia de un modelo de estructura de dos capas. Además, la "rotura" en la unidad era aparente, indicativa de la presencia de zonas débiles, zona fracturada y grietas. Como también se demuestra claramente por los datos de refracción sísmica, la profundidad al lecho de roca (una interfaz de borde afilada aproximadamente a una profundidad de 15 m) varía, y dicha variación se atribuye principalmente debido al grosor del material de relleno suprayacente. Además, examinamos la posible correlación (si existe) entre los parámetros geofísicos y los parámetros geotécnicos para establecer las estimaciones cuantitativas de un parámetro geotécnico particular (por ejemplo, la resistencia del suelo) a partir de estudios geofísicos. En este estudio, se observó una buena relación entre la propiedad eléctrica (resistividad) y la propiedad geotécnica (resistencia del suelo) con la ecuación empírica RS = 31.733 (N60) -165.88 y el coeficiente de regresión R2 = 0.77. En función de la correlación entre la propiedad elástica y el perfil de intemperie, dividimos los materiales del subsuelo en tres zonas: la primera zona se clasifica como suelo residual con velocidad de onda p (300 - 900 ms-1), la segunda zona se clasifica como altamente meteorizada el granito con velocidad de onda p (900 - 1800 ms-1), y la tercera zona se clasifica como granito moderadamente degradado con velocidad de onda p (1800 - 3000 ms-1). Todos los datos geofísicos y geotécnicos sugieren que un material de relleno bastante débil / no compacto que subyace en el lecho de roca es probable que proporcione una superficie plana donde la masa de deslizamiento de tierra se movería o se activaría.O crescimento da população e a extensão de um assentamento em uma área de risco aumentaram o impacto de um desastre natural. Falhas na encosta, desmoronamentos e subsidência da fundação foram identificados como o desastre natural mais freqüente se essas áreas sensíveis não forem bem monitoradas. Por outro lado, uma análise detalhada dos gatilhos é muitas vezes dificultada pela falta de informações obtidas a partir das medições de campo. Foi realizada uma investigação em uma área de risco de escorregamento, utilizando as abordagens de mapeamento geotécnico, geofísico e geológico. As investigações geotécnicas incluíram a extração de amostras para obter a seqüência litológica e para fins de amostragem. Também testes de penetração padrão (SPT), testes de campo in situ de resistência do solo. Tomografia por resistividade elétrica (TRE) e tomografia de refração sísmica foram realizadas para determinar as características hidrogeológicas e delinear as regiões de materiais subsuperfície fracos e duros. Os resultados da inversão 2D da técnica de resistividade sugeriram a presença de um modelo de estrutura de duas camadas. Além disso, a "quebra" na unidade era aparente, indicando a presença de áreas fracas, área fraturada e rachaduras. Como também é claramente demonstrado por dados de refração sísmica, a profundidade do leito de rocha (uma interface de borda afiada a aproximadamente uma profundidade de 15 m) varia, e essa variação é atribuída principalmente devido à espessura do material de preenchimento sobreposto. Além disso, examinou-se a correlação possível (se algum) entre os parâmetros geofísicos e geotécnica parâmetros para estabelecer estimativas quantitativas de um determinado parâmetro geotécnica (por exemplo, a resistência do solo) a partir de levantamentos geofísicos. Neste estudo, foi observada uma boa relação entre a propriedade eléctrica (resistividade) e propriedade geotécnica (resistência do solo) com as equações empíricas RS = 31,733 (N60) e -165,88 coeficiente R2 = 0,77 regressão. Dependendo da relação entre a propriedade elástica e os elementos de perfil, que divide os materiais do subsolo em três zonas: primeira zona é classificada como solo residual com velocidade de onda de cisalhamento p (300-900 ms-1), a segunda zona classificada como granito altamente resistido com velocidade de onda P (900 - 1.800 ms-1), e a terceira área é classificada como moderadamente degradada velocidade da onda de granito p (1800-3000 ms-1). Todos os dados geofísicos e geotécnicos sugerem que um material de preenchimento bastante fraco / não compacto subjacente ao leito rochoso provavelmente fornecerá uma superfície plana onde a massa de escorregamento se moveria ou se ativaria