Ahmed Sayed - Academia.edu (original) (raw)
Papers by Ahmed Sayed
The nearshore wave conditions around Salalah coast were investigated using the REFDIF 1 numerical... more The nearshore wave conditions around Salalah coast were investigated using the REFDIF 1 numerical model. The input wave conditions to REFDIF 1 covered the extreme conditions that happen during the three seasons of wave climate in the area, namely the SouthWestern Monsoon, the NorthEastern Monsoon and the transition period between them. The input wave data to the model was obtained from ships' observations that covered a period of 18 years, and the extreme conditions were calculated using the three parameter Weibull distribution. To make sure that REFDIF 1 will provide acceptable results for the studied area, few runs were carried out by both REFDIF 1 and the more sophisticated and reputable model SWAN. The results of both models were comparable, and then REFDIF 1 was used to determine the wave conditions at the nearshore region of Salalah for different wave conditions. The study results showed that the wave heights for the 1 year and 100 years wave conditions in the nearshore ar...
Lagos and Lekki lagoons in Nigeria are water body in the heart of the Lagos metropolis. The two l... more Lagos and Lekki lagoons in Nigeria are water body in the heart of the Lagos metropolis. The two lagoons are interlinked by a waterway. Lagos State is naturally protected by Lekki and Victoria Islands/barrier against wave and tidal action of the Atlantic Ocean. In addition, it is frequently exposed to seasonal rainfall storms that lead to increased water level (retained water depth) of the lagoon due to relatively long residence times and eventually inundation of low-lying and swamp areas. The Nigerian authorities do not permit any breach in the natural barrier to directly release rainfall storm waters into the ocean except the existing Lagos Lagoon outlet. Outfalls are merely permitted around Lagos and Lekki Lagoons. The drainage of rainfall storm water into the lagoons shall result in water volume retention leading to potential increase in water level. The question of how much water level rise due to rainfall storm water discharges requires an answer since there are ongoing and fut...
Journal of Environmental Protection, 2012
The Gulf of Aqaba (GOA) is unique as it contains significant percentage of the world's natural ma... more The Gulf of Aqaba (GOA) is unique as it contains significant percentage of the world's natural marine biodiversity. This unique environment is potentially vulnerable to pollution particularly at its northern tip. One of the major activities affecting the environment of the gulf is the man-made desalination plants that abstract sea water and dispose desalinated brine. In this context, the paper discusses the impact of the abstract and disposal activities on the GOA environment. A 3D hydrodynamic model was developed to cover the GOA. Relevant data were collected for 3D hydrodynamic modeling construction. Delft-3D model developed by Deltares was applied in this study. The 3D model reliability was confirmed since the model results have revealed the existence of a structure of primary eddies along the axis of the Gulf which was previously reported by different researchers. Further numerical simulations were carried out by incorporating various alternatives of seawater abstraction and desalinated brine disposal off the north and north east coast of the GOA. The developed GOA hydrodynamic model, at the present stage, is preliminary where the results provide qualitative assessment on the potential impacts on the water circulation. Accordingly, this study is considered a pace ahead for a better model development and validation in the future studies.
Coastal Engineering Journal, 2001
Abstract: The behavior of the bottom boundary layer of a natural rippled bed and plane bed is inv... more Abstract: The behavior of the bottom boundary layer of a natural rippled bed and plane bed is investigated utilizing PIV technique. An enhanced approach of the PIV is developed on the basis of the Minimum Quadratic Difference (MQD), which is better compared with the ...
Coastal Engineering Journal, 2003
Abstract: Experiments with uniform sediments of different grain sizes were performed and net tran... more Abstract: Experiments with uniform sediments of different grain sizes were performed and net transport rates were measured. A comparison between four existing models to predict the net transport rate of uniform sediments was achieved. The prediction of offshore ...
Coastal Dynamics 2005, 2006
An X-band marine radar system was employed in the vicinity of Hazaki Oceanographical Research Sta... more An X-band marine radar system was employed in the vicinity of Hazaki Oceanographical Research Station (HORS) located at Ibaraki prefecture of Japan. The nearshore region around HORS exhibited a complicated morphological feature represented by a barred beach as a result of frequent exposure to large storm events. The radar system provides subsequent wave images having a clear variation of wave pattern during a storm event. These images were analyzed with an improved approach based on spectra analysis and PIV technique. Both wave period and spatial distribution of wave celerity vectors were determined based on a refined approach to Bell (1999). A linear bathymetric inversion algorithm was initially examined and then applied to derive the nearshore bathymetry around HORS. The computed beach profile showed an appropriate agreement with the measured ones. However, there is a discrepancy existed due to ignorance of nearshore currents.
ABSTRACT Although the stilling basin is one of the most important components of many hydraulic st... more ABSTRACT Although the stilling basin is one of the most important components of many hydraulic structures provided with a spillway, the analytical solutions are still open to discussion due to simplifying hypothesis accepted in deriving the equations of the rapidly varied flow. For a long period, the scale studies to decide the best final design solution were used. The scale studies continues to be used nowadays in the engineering practice for designing the stilling basins attached to important structures, although it is widely recognized that most of the model studies involve simplifying assumptions with regard to the variables to be considered that could raise several questions. There are problems related to free surface flow in which viscous, inertial, and gravitational forces are all important, so the design and use of such models requires considerable attention on using the results. Even if the number of assumptions is frequently less significant than accepted for mathematical models, they nevertheless introduce some uncertainty in the model design. The rapid development of the numerical methods in the last decades provided the designer with indispensable tool used in an ever-increasing range of problems, including the design of the stilling basin. There are however, several questions related to the use of mathematical models such as: How reliable are the numerical models applied to study the flow motion in stilling basin? To what extend the numerical models used for the design of the stilling basin can replace the physical models. What are the main parameters affecting the sensitivity of the model? What are the advantages and constraints of the numerical models? The paper presents the conclusions of the authors to some of these questions by comparing the results obtained in the study of a selected stilling basin by using physical models and mathematical models studies. A comparison between use of 1-D, 2-D and 3-D mathematical models is also presented. Due attention is given to analyzing the sensitivity of the grid selection for the case of 3-D models and to consequences due to simplifying the model.
Oceans '04 MTS/IEEE Techno-Ocean '04 (IEEE Cat. No.04CH37600)
... Ahmed'Sayed Mohamed Ahmed, Littoral Drift Division Marine Environment and Engineering De... more ... Ahmed'Sayed Mohamed Ahmed, Littoral Drift Division Marine Environment and Engineering Department, Port and ... leave from Hydraulics Research Institute, Egypt) E-Mail Address:ahmed@Rari.clo ... I. El-Desouky, deputy director, of the Hydraulics Research Institute (HRI, Egypt ...
The nearshore wave conditions around Salalah coast were investigated using the REFDIF 1 numerical... more The nearshore wave conditions around Salalah coast were investigated using the REFDIF 1 numerical model. The input wave conditions to REFDIF 1 covered the extreme conditions that happen during the three seasons of wave climate in the area, namely the SouthWestern Monsoon, the NorthEastern Monsoon and the transition period between them. The input wave data to the model was obtained from ships' observations that covered a period of 18 years, and the extreme conditions were calculated using the three parameter Weibull distribution. To make sure that REFDIF 1 will provide acceptable results for the studied area, few runs were carried out by both REFDIF 1 and the more sophisticated and reputable model SWAN. The results of both models were comparable, and then REFDIF 1 was used to determine the wave conditions at the nearshore region of Salalah for different wave conditions. The study results showed that the wave heights for the 1 year and 100 years wave conditions in the nearshore ar...
Lagos and Lekki lagoons in Nigeria are water body in the heart of the Lagos metropolis. The two l... more Lagos and Lekki lagoons in Nigeria are water body in the heart of the Lagos metropolis. The two lagoons are interlinked by a waterway. Lagos State is naturally protected by Lekki and Victoria Islands/barrier against wave and tidal action of the Atlantic Ocean. In addition, it is frequently exposed to seasonal rainfall storms that lead to increased water level (retained water depth) of the lagoon due to relatively long residence times and eventually inundation of low-lying and swamp areas. The Nigerian authorities do not permit any breach in the natural barrier to directly release rainfall storm waters into the ocean except the existing Lagos Lagoon outlet. Outfalls are merely permitted around Lagos and Lekki Lagoons. The drainage of rainfall storm water into the lagoons shall result in water volume retention leading to potential increase in water level. The question of how much water level rise due to rainfall storm water discharges requires an answer since there are ongoing and fut...
Journal of Environmental Protection, 2012
The Gulf of Aqaba (GOA) is unique as it contains significant percentage of the world's natural ma... more The Gulf of Aqaba (GOA) is unique as it contains significant percentage of the world's natural marine biodiversity. This unique environment is potentially vulnerable to pollution particularly at its northern tip. One of the major activities affecting the environment of the gulf is the man-made desalination plants that abstract sea water and dispose desalinated brine. In this context, the paper discusses the impact of the abstract and disposal activities on the GOA environment. A 3D hydrodynamic model was developed to cover the GOA. Relevant data were collected for 3D hydrodynamic modeling construction. Delft-3D model developed by Deltares was applied in this study. The 3D model reliability was confirmed since the model results have revealed the existence of a structure of primary eddies along the axis of the Gulf which was previously reported by different researchers. Further numerical simulations were carried out by incorporating various alternatives of seawater abstraction and desalinated brine disposal off the north and north east coast of the GOA. The developed GOA hydrodynamic model, at the present stage, is preliminary where the results provide qualitative assessment on the potential impacts on the water circulation. Accordingly, this study is considered a pace ahead for a better model development and validation in the future studies.
Coastal Engineering Journal, 2001
Abstract: The behavior of the bottom boundary layer of a natural rippled bed and plane bed is inv... more Abstract: The behavior of the bottom boundary layer of a natural rippled bed and plane bed is investigated utilizing PIV technique. An enhanced approach of the PIV is developed on the basis of the Minimum Quadratic Difference (MQD), which is better compared with the ...
Coastal Engineering Journal, 2003
Abstract: Experiments with uniform sediments of different grain sizes were performed and net tran... more Abstract: Experiments with uniform sediments of different grain sizes were performed and net transport rates were measured. A comparison between four existing models to predict the net transport rate of uniform sediments was achieved. The prediction of offshore ...
Coastal Dynamics 2005, 2006
An X-band marine radar system was employed in the vicinity of Hazaki Oceanographical Research Sta... more An X-band marine radar system was employed in the vicinity of Hazaki Oceanographical Research Station (HORS) located at Ibaraki prefecture of Japan. The nearshore region around HORS exhibited a complicated morphological feature represented by a barred beach as a result of frequent exposure to large storm events. The radar system provides subsequent wave images having a clear variation of wave pattern during a storm event. These images were analyzed with an improved approach based on spectra analysis and PIV technique. Both wave period and spatial distribution of wave celerity vectors were determined based on a refined approach to Bell (1999). A linear bathymetric inversion algorithm was initially examined and then applied to derive the nearshore bathymetry around HORS. The computed beach profile showed an appropriate agreement with the measured ones. However, there is a discrepancy existed due to ignorance of nearshore currents.
ABSTRACT Although the stilling basin is one of the most important components of many hydraulic st... more ABSTRACT Although the stilling basin is one of the most important components of many hydraulic structures provided with a spillway, the analytical solutions are still open to discussion due to simplifying hypothesis accepted in deriving the equations of the rapidly varied flow. For a long period, the scale studies to decide the best final design solution were used. The scale studies continues to be used nowadays in the engineering practice for designing the stilling basins attached to important structures, although it is widely recognized that most of the model studies involve simplifying assumptions with regard to the variables to be considered that could raise several questions. There are problems related to free surface flow in which viscous, inertial, and gravitational forces are all important, so the design and use of such models requires considerable attention on using the results. Even if the number of assumptions is frequently less significant than accepted for mathematical models, they nevertheless introduce some uncertainty in the model design. The rapid development of the numerical methods in the last decades provided the designer with indispensable tool used in an ever-increasing range of problems, including the design of the stilling basin. There are however, several questions related to the use of mathematical models such as: How reliable are the numerical models applied to study the flow motion in stilling basin? To what extend the numerical models used for the design of the stilling basin can replace the physical models. What are the main parameters affecting the sensitivity of the model? What are the advantages and constraints of the numerical models? The paper presents the conclusions of the authors to some of these questions by comparing the results obtained in the study of a selected stilling basin by using physical models and mathematical models studies. A comparison between use of 1-D, 2-D and 3-D mathematical models is also presented. Due attention is given to analyzing the sensitivity of the grid selection for the case of 3-D models and to consequences due to simplifying the model.
Oceans '04 MTS/IEEE Techno-Ocean '04 (IEEE Cat. No.04CH37600)
... Ahmed'Sayed Mohamed Ahmed, Littoral Drift Division Marine Environment and Engineering De... more ... Ahmed'Sayed Mohamed Ahmed, Littoral Drift Division Marine Environment and Engineering Department, Port and ... leave from Hydraulics Research Institute, Egypt) E-Mail Address:ahmed@Rari.clo ... I. El-Desouky, deputy director, of the Hydraulics Research Institute (HRI, Egypt ...