Rehan Khan

Underwater acoustic channel modeling using BELLHOP ray tracing method

In recent years, underwater acoustic technology has rapidly developed in the mean of civil and military usage. The majority of models in underwater communication undergo the following factors those are limited bandwidth, high attenuation, time varying, multipath propagation, dispersion of signal and slow rate signal transmission. In this study we have design a GUI to examine the behavior of an acoustic signal with transmission frequency band (9 K to 90 KHz) under the above mentioned factors. We have selected two different channels environments in Arabian Sea to show channel effect over an acoustic signal, BELLHOP tool is used to design underwater channel.

Pilots Updating Channel Compensation Base on Underwater MIMO-OFDM

The communication rate is limited extremely by the confined bandwidth source of UWA (underwater acoustic) channel. MIMO (Multiple-input Multiple-output) techniques can drastically improve the spectral efficiency, and have been a new hot spot in UWA commutation. To estimate the UWA channel STBC (space-time block code) technique is adopted, and the improved method of channel estimating is also given. A designed of complex coding MIMO-OFDM is provided.The validity and the dependability of the scheme are verified by Monte Carlo simulations.

Study on the Effect of Containment Performance on Lodine Source Term

In this paper, the iodine source term is studied with the containment performance in normal, isolation, and emergency state of containment. For this study, a MATLAB computer-based program is developed, which simulates the iodine source term with time. The environmental iodine source term is determined with time normal, isolation and emergency state of containment. With the operation of Engineering Safety Features ESFs the effect on the iodine source term has been observed. From the results, it is observed that the iodine is strongly dependent on the exhaust rate and significantly reduced with ESFs operation.

Circlar Decoding and Sparse Channel Estimation for Underwater MIMO-OFDM

In UWA (underwater acoustic) communications, data rate is severely limited by the confined bandwidth source of aquatic channel. MIMO (Multiple-input Multiple-output) techniques can drastically improve the spectral efficiency, and have been a new point of reference in UWA commutations. For the estimation of UWA channel which is usually sparse, CS (compress sensing) along with STBC (space-time block code) is adopted with improved results. A design of mixing coding MIMO-OFDM is also presented in the proposed method. The validity and the dependability of this scheme are verified by Monte Carlo simulations.

OFDM with steering sinusoids for underwater acoustic communication

The underwater channel poses various challenges for the wireless information exchange as it offers complex communication design. OFDM, being a best viable solution for high rate and efficient underwater communication scheme, also faces signal degradation problems due to the dynamics nature of Sea. These non-uniform dynamics due to the wind or the platform motion are critical for the acoustic subcarriers (i.e. low frequency and low speed) and may cause inter-carrier interference which results distortion of the entire signal. In order to avoid these erratic distortions, proper tracking of relative change in terms of Doppler factor have to be incorporated in the design. The communication design must be capable enough to track aquatic variations and compensate the effects in an efficient way. In this article, a novel OFDM approach based on steering sinusoids is presented which may be able to trace and rectify the fast oceanic variations incurred with in a symbol length. The steering sinusoids are used to check the dynamic effects imposed by the channel and the recorded variations (either uniform or non-uniform) are further utilized to mitigate the Doppler spread. The algorithm is computationally very efficient and gives low latency period as compare to the two-step approach. The placement of the appended sinusoids among subcarriers is depended upon the measure of relative motion and the level of precise tracking i.e. tradeoff have to be considered. The proposed scheme is analyzed in the MATLAB simulation with self-induced Doppler and Bellhop ray tracing program is also executed to generate static multipath channel models. The simulation results endorsed the efficient performance of the proposed algorithm and suggested for the practical evaluation.

Kinetic Study of Containment Retention Factor (CRF) for Large Dry Containment Under Radiation Load

The Nuclear Power Plants (NPPs) have been built on the concept of Defense in depth. The severe accident causes the failure of fission product barriers and let the fission products to escape into environment. The containment is the last barrier to the fission products. Thus, the containment is installed with engineering safety features (ESFs) i.e. spray system, heat removal system, recirculation filtration system; containment filtered venting system (CFVS), and containment exhaust filtration system. In this work, kinetic study of the containment retention factor (CRF) has been carried out for a large dry PWR containment considering 1000 MWe PWR. The computational modeling and simulation have been carried out by developing a kinetic code in MATLAB, which uses the fractions of activity airborne into the containment after the accident. The Kinetic dependency of CRF on containment filtration systems, spray system with caustic and boric acid spray has been carried out. For noble gases, iodine and aerosols, the CRF increases with the increase in exhaust rate. While, CRF for iodine first increases then start reducing with containment spray flow rate. The Kinetic dependency of CRF has also been studied for boric and caustic spray.Copyright

Variability of channel response and acoustic system performance: Simulation study

Simulating realistic sonar data is essential for tuning detection and classification algorithms in active and passive sonar signal processing according to environment and acquisition characteristics. Robustness of performances estimation and prediction applications can be greatly enhanced if the real ocean environments can be placed as input data to the simulation. The Ocean environment presents a difficult channel for acoustic propagation because of its frequency dependent large and small-scale fading, signal spreading in time and frequency, and extended multipath. Its characteristics vary from place to place and with time over scales ranging from seconds to years. Any system that uses Acoustics in its operation is affected by this channel variability. System performance and availability for every condition of the channel thus requires that these should be evaluated and incorporated. In the present work data for the channel in terms of its bathymetry, SSP and sea surface winds have been taken for the year 2011 and the channel response on monthly averages have been calculated. Performance of a passive acoustic system has been evaluated by simulation on these and predictions of the system performance have been obtained for the full year. In this way system level design can be optimized for the prevailing channel conditions.

Study on Effect of Cycle Counting Correction Factors in Spectral Based Fatigue Computation

This paper investigates the effect of various cycle counting correction factors in spectral fatigue damage calculations. Spectral fatigue calculations are based on complex stress transfer functions established through direct wave load analysis combined with stress response analysis. Cycle counting correction factors are introduced in the computation process to cater swell’s effect and to reduce the conservatism in the results due to narrow band approximation for a wide band random process. In this study, fatigue life of a ship structural detail is predicted by spectral method utilizing ANSYS software along with 3D liner sea-keeping code AQWA. Cumulative fatigue damage is calculated by a MATLAB program based on direct calculation procedure of spectral fatigue using cycle counting correction factors proposed by Wirsching, Rice and Dirlik. The results show an overall decrease in the computed fatigue damage and a corresponding increase in the expected fatigue life of the structure.

Performance Evaluation of ZP-OFDM Scheme in Underwater Multipath Channel

One of the major problems while dealing with underwater acoustic communication (UWAC) is the occurrence of unwanted multipath having long delay spreads. Higher probability of reflections (from wavy sea surface, uneven sea bottom, other obstacles, etc.) and refraction of sound are the main causes of these grievous multipath signals. Multipath effects further offer severe degradation in the packet (s) and mutilation of entire signal in terms of inter-symbolic interference (ISI) is occurred. During last decade, multicarrier modulation in terms of OFDM was considered as one of the viable solutions to mitigate the multipath effect and provide high-rate communication. In this article, we are performing the practical evaluation of Zero-Padded Orthogonal Frequency Division Multiplexing (ZP-OFDM) based communication system. The data using various packet structures are used to demonstrate the effectiveness of ZP-OFDM scheme in the flat multipath channel of the water pool of acoustic lab, Harbin Engineering University. Satisfactory performance results are obtained even within high noisy environment. These results suggest that ZP-OFDM is a viable choice for high-rate communications over multipath induced underwater channels.

Mitigation of PWR In-Containment Iodine Source Term Under LOCA

Since, containment integrity is the main issue under accidental conditions. Radiological consequences of LWR under accident have the grievous impact on the reactor building and its surrounding environment. Iodine is one of the most hazardous fission product releases in the serious accidents. So in this paper, the iodine source term has been evaluated for two-loop PWR under severe accident initiated due to LOCA. The TMI-2 reactor is considered as the reference reactor. The modeling and simulations are carried out by developing a MATLAB base program that uses the post-accident conditions and core inventory as input. The containment response, in order to mitigate the environmental and in-containment iodine source term is studied in normal, emergency, and isolation states of containment. The In-containment iodine source term is calculated with, and without the operation of engineering safety features (ESFs). The mitigation is determined by the activation of ESF. The environmental iodine source term is calculated as the function of containment response. The iodine dependency on the containment retention factor is also studied in all said states of containment. Results indicate the weak sensitivity of Iodine with activation of ESF towards exhaust rate values, under ESFs Operation.Copyright