http://hdl.handle.net/20.500.12228/51 2026-04-07T16:51:28Z 2026-04-07T16:51:28Z Khan, Md. Salman http://hdl.handle.net/20.500.12228/515 2019-05-05T21:00:15Z 2019-03-01T00:00:00Z

Study on Sensitivity of Microphysics for the Simulation of Rainfall for the Month of May 2015 over Bangladesh using High Resolution WRF Khan, Md. Salman In the present study, the Advanced Research WRF (ARW) model v3.8.1 has been used to simulate the rainfall for the month of May 2015 all over Bangladesh. The initial and boundary conditions are drawn from the global operational analysis and forecast products of National Center for Environmental Prediction (NCEP-FNL) available at 1˚×1˚ resolution. The model was configured in nested domain with 18 and 6 km horizontal grid spacing with 100 × 96 and 103 × 127 grids respectively in the east-west north-south directions with 30 vertical levels. Time step of integration is set to 90 and 30 seconds for maintaining computational stability as the model uses third-order Runge-Kutta time integration scheme. In this research, six different microphysics schemes such as Lin et al., WSM6, Thomson, Morrison Double-Moment (M-2M), Stony Brook University (SBU), and WDM6 coupling with Kain-Fritsch (KF) cumulus parameterization scheme has been used to simulate the monthly total rainfall, monthly heavy rainfall, monthly rainy days and monthly heavy rainy days for the month of May 2015 all over Bangladesh. The outputs obtained by using different microphysics are compared with the observed outputs at 33 meteorological stations of BMD and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) output. Standard deviation of all observed, PERSIANN and model simulated parameters have been analyzed and compared. The maximum monthly observed rain of May 2015 at Sylhet is 752 mm but WSM6, M-2M and WDM6 schemes have simulated 831, 788 and 742 mm for day 1 prediction; WSM6, WDM6 and SBU-Lin schemes have simulated 757, 916 and 981 mm for day 2 prediction and WSM6 and WDM6 schemes have simulated 741 and 925 mm for day 3 prediction, respectively and all other MPs have simulated much higher rainfall at domain (D1). The WDM6, M-2M and Lin et al. schemes have simulated 744, 807 and 923 mm for day 1 prediction, WSM6 and WDM6 schemes are 714 and 877 mm for day 2 predictions and WSM6, SBU-Lin and Lin et al. schemes are 802 and 913 and 998 mm, respectively for day 3 prediction at domain (D2). WDM6 scheme gives the better performance of rainfall and rainy days all over the country. This thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Science in Physics, March 2019.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 79-84).

2019-03-01T00:00:00Z Akter, Sharmin http://hdl.handle.net/20.500.12228/512 2019-04-25T21:00:12Z 2019-02-01T00:00:00Z

Investigation of the Structural, Magnetic and Transport Properties of Yttrium Substituted Ni-Zn Ferrites Akter, Sharmin The present research work is focused on Yttrium (Y) doped Ni-Zn ferrites. The ferrite samples of the composition Ni0.25Zn0.75YxFe2-xO4 [where x= 0.00, 0.02, 0.04, 0.06 and 0.08] were synthesized by conventional solid state reaction method. As a part of synthesis the samples were pre-sintered at 850°C for 2 hours and sintered at 1150°C for 3 hours. The effect of rare earth Y3+ substitution on the structural, magnetic and electrical properties of the Ni-Zn ferrites was studied. The phase identification and lattice parameter determination were carried out by using X-ray diffraction (XRD). XRD patterns show that all the samples consisted of the single phase cubic spinel structure with an extra peak in x=0.08. The lattice parameters gradually increases with increasing Y content but it slightly decreased for x=0.08. The bulk density suddenly decrease for x=0.02 then increases with increasing rare earth Y3+ ion and again slightly decreased for x=0.08. The X-ray density increases continuously with increasing x-content. The microstructural analysis was done by Scanning Electron Microscopy (SEM). The SEM images show that the samples exhibit uniform surface morphology with well-defined spherical grains. The average grain size was calculated using Image J software and it can be observed that the average grain size gradually increased with Y content except x=0.08 where it decreases suddenly. The complex permeability, loss tangent and dielectric properties were investigated as a function of frequency range 1 KHz to 120 MHz by using an impedance analyzer. The initial permeability was found in steady state to a higher order of frequency range from 103 Hz - 50 MHz. Continuous decrease of the dielectric constant with the increasing frequency and remains almost constant at higher frequency range has been observed. The magnetic properties have been studied by Vibrating Sample Magnetometer (VSM). The saturation magnetization(Ms), coercivity(Hc), remanent magnetization(Mr) and the ratio of remanent magnetization and saturation magnetization have been calculated from the M-H loop at room temperature. The values of Ms were decreases with increasing Y3+ content. Moreover, coercivity decreases with increasing Y content. Doping of Y ion lowers the conduction and subsequently an increase in resistivity is observed. The characteristics of electromagnetism, excellent chemical stability, mechanical hardness, high coercivity, and moderate saturation magnetization have made Y doped Ni-Zn ferrite a good candidate for synthesizing and investigation to contribute in science and technology. This thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Masters of Science in Physics, February 2019.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 78-83).

2019-02-01T00:00:00Z Nahar, Kamrun http://hdl.handle.net/20.500.12228/511 2019-04-25T21:00:11Z 2018-11-01T00:00:00Z

Eff'ect of Lanthanum Substitution on the Structural, Magnetic and Transport Properties of Cu-Zn Ferrites Nahar, Kamrun This thesis work is acquainted with the study of lanthanum (La) doped Cu-Zn ferrite. The composition of the sample is Cu0.15Zn0.85LaxFe2-xO4 where it was prepared for x = 0.00, 0.02, 0.04, 0.06 and 0.08 content of La by Solid State Reaction method. The samples were pre-sintered at 800oC for 3hours and sintered at 1150oC for 3 hours. The substitution of La for various ratio have remarkable effects on the structural, magnetic and electrical properties of Cu-Zn ferrite. The phase identification has carries out by using X-ray diffraction (XRD). The XRD analysis revealed that undoped in Cu-Zn ferrite shows formulation of cubic single phase (fcc) spinel structure without any impurity peak but other four La doped Cu-Zn ferrites are shows additional peaks manifested the formation of secondary phase presumably LaFeO3. The values of lattice parameter have the trend of increasing with the increase of x. The bulk density also has a trend of increasing with the increase of La content where the X-ray density decreases. In morphological study, SEM image exhibit uniform surface morphology with well defined spherical grain. The average grain size was calculated using Image J Software and it was observed that, the average grain size decreases with increasing La content. The magnetic properties were studied by investigating M-H curves that was obtained by vibrating sample magnetometer (VSM). The magnetic properties demonstrated a strong dependence of the variation of x. With the increase of x, saturation magnetization (Ms) decreases while remanent magnetization (Mr) and coercivity (Hc) increases. The hysteresis curve for samples of various ratio of La showed the ferromagnetic behavior. The decrease of Ms with increasing of La substitutions has been explained as the effect of dilution of Fe3+ magnetic moment by nonmagnetic La3+. The complex permeability, loss tangent, dielectric properties were investigated as a function of frequency upto 120MHz by using impedance analyzer. The initial permeability slightly increases with the increase of La substation while imaginary permeability decreases. Moreover the dielectric constant decreases rapidly with the increase in frequency at lower frequencies and slowly at higher frequency and almost constant exhibiting normal behavior of ferrites. Dielectric constant decreases with increases of La content in Cu-Zn ferrites. The electrical DC resistivity has a trend of increasing with the increase of La content. The variation of electrical and dielectric in La doped Cu-Zn ferrites are explained on the basis of Fe2+/Fe3+ ionic concentration with affect La ions as well as the electronic hopping frequency between Fe2+ and Fe3+ ion. This thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Masters of Science in Physics, November 2018.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 66-73).

2018-11-01T00:00:00Z Ahammed, Md. Razu http://hdl.handle.net/20.500.12228/491 2019-01-20T21:00:19Z 2018-12-01T00:00:00Z

Study on Convective and Non-Convective Rain of Different Heavy Rainfall Events in the Monsoon Season using WRF-ARW Model Ahammed, Md. Razu In the present study the Advanced Research WRF (ARW) model v3.8.1 have been used to simulate the convective and non-convective rain during 3-5 July 2017, 19-20 July 2017 and 23-24 July 2017, when heavy rain observed in different areas of Bangladesh. The initial and boundary conditions are drawn from the global operational analysis and forecast products of National Center for Environmental Prediction (NCEP) Final reanalysis (FNL) data available at 1o ×1o resolution. The model was configured in nested domain with 18 km and 6 km horizontal grid spacing 100×96 and 103×127 grids in the east-west and north-south directions with 28 vertical levels. In this research 12 Cumulus parameterization (CP) schemes in combination with WDM6 microphysics (MP) scheme has been used to identify the convective and non-convective rain of different heavy rainfall (HR) events. The CP schemes used in this research are Kain-Fritsch (KF), Betts-Miller-Janjic (BMJ), Grell-Freitas (GF), Old simplified Arakawa-Schubert (OSAS), Grell-3 (G3), Tiedtke, Zhang-McFarlane (ZM), Multi-scale KF (MSKF), New SAS, New Tiedtke (NTD), New SAS-HWRF (NSH) and Grell-Devenyi (GD). The model simulated rainfall mainly convective for KF, GF, OSAS, G-3, TD, ZM, NTD, NSH and schemes and mainly non-convective for BMJ, MSKF and NS schemes during all over Bangladesh during 3-5 July 2017. BMJ, MSKF and NS schemes have simulated higher non convective rain (NCR) and all other cumulus parameterization schemes have simulated higher convective rain (CR) all over Bangladesh during 19-20 July 2017. OSAS and NSH schemes have simulated higher convective rain and all other cumulus parameterization schemes have simulated higher non-convective rain all over Bangladesh during 23-24 July 2017. It is also seen that during the two simulation periods (i.e., 3-5 and 23-24 July 2017) the CR is found to decrease continuously and NCR increased during the period and opposite in case of 19-20 July 2017. GF and G-3, GF and MSKF schemes give the better performance for daily and 48 hour prediction respectively on the basis of Threat Score, Equivalent Threat Score and Bias Score during 3-5 July 2017. On the basis of Threat Score, Equitable Threat Score and Bias Score for the prediction of HR KF and MSKF schemes during 19-20 July 2017, TD and KF schemes during 23-24 July 2017 give the better performance. This thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Science in Physics, December 2018.; Cataloged from PDF Version of Thesis.; Includes bibliographical references (pages 110-116).

2018-12-01T00:00:00Z