ON SOME RECURSION RELATIONS FOR HORN'S HYPERGEOMETRIC FUNCTIONS OF THREE VARIABLES

P. Agarwal,A. SHEHATA,S. I. MOUSTAFA,K. CHAKRABORTY 장전수학회 2021 Proceedings of the Jangjeon mathematical society Vol.24 No.2

The principal aim of this paper to study the recursion formulas for the Horns hypergeometric functions of three variables. Earlier in [Shehata, A.; and Moustafa, S.I. Some new results for Horn's hypergeometric functions Γ1 and Γ2. Journal of Mathematics and Computer Science, (2021), 23 (1), 26{35.], and Pathan et al. [Pathan, M.A.; Shehata, A.; and Moustafa, S.I. Certain new formulas for the Horns hypergeometric functions. Acta Uni- versitatis Apulensis, (2020)] have studied the new results for Horns hypergeometric functions. Motivated by the above works here we will derive some contiguous relation for the families of Horn hypergeometric functions GA, GB, GC, GD and G C of three variables. After that we will establish the differential reclusion relations and differential operators for GA, GB, GC, GD and G* C of three variables, respectively.

Failure analysis of a transmission tower during a microburst

Shehata, A.Y.,El Damatty, A.A. Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.3

This paper focuses on assessing the failure of one of the transmission towers that collapsed in Winnipeg, Canada, as a result of a microburst event. The study is conducted using a fluid-structure numerical model that was developed in-house. A major challenge in microburst-related problems is that the forces acting on a structure vary with the microburst parameters including the descending jet velocity, the diameter of the event and the relative location between the structure and the jet. The numerical model, which combines wind field data for microbursts together with a non-linear finite element formulation, is capable of predicting the progressive failure of a tower that initiates after one of its member reaches its capacity. The model is employed first to determine the microburst parameters that are likely to initiate failure of a number of critical members of the tower. Progressive failure analysis of the tower is then conducted by applying the loads associated with those critical configurations. The analysis predicts a collapse of the conductors cross-arm under a microburst reference velocity that is almost equal to the corresponding value for normal wind load that was used in the design of the structure. A similarity between the predicted modes of failure and the post event field observations was shown.

Use of right lobe graft with type IV portal vein accompanied by type IV biliary tree in living donor liver transplantation: report of a case

Shehata, Mahmoud Refaat,Kim, Dong-Sik,Jung, Sung-Won,Yu, Young-Dong,Suh, Sung-Ock The Korean Surgical Society 2014 Annals of Surgical Treatment and Research(ASRT) Vol.86 No.6

<P>Anatomic variations of the portal vein (PV) and bile duct (BD) are more common on the right lobe as compared with left lobe grafts in living donor liver transplantation (LDLT). We recently experienced a case of LDLT for hepatocellular carcinoma combined with liver cirrhosis secondary to hepatitis B virus and hepatitis C virus infection. The only available donor had right lobe graft with type IV PV associated with type IV BD. The patient underwent relaparotomy for PV stenting due to PV stenosis. Percutaneous transhepatic biliary drainage was done for a stricture at the site of biliary reconstruction. Thereafter, the patient was discharged in good health. Our experience suggests that, the use of right lobe graft with type IV PV accompanied by type IV BD should be the last choice for LDLT, because of its technical difficulty and risks of associated complications.</P>

Seismic response evaluation of fixed jacket-type offshore structures by random vibration analysis

Shehata E. Abdel Raheem,Elsayed M. Abdel Aal,Aly G.A. AbdelShafy,Mohamed F.M. Fahmy 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.2

Offshore platforms in seismically active areas must be designed to survive in the face of intense earthquakes without a global structural collapse. This paper scrutinizes the seismic performance of a newly designed and established jacket type offshore platform situated in the entrance of the Gulf of Suez region based on the API-RP2A normalized response spectra during seismic events. A nonlinear finite element model of a typical jacket type offshore platform is constructed taking into consideration the effect of structure-soil-interaction. Soil properties at the site were manipulated to generate the pile lateral soil properties in the form of load deflection curves, based on API-RP2A recommendations. Dynamic characteristics of the offshore platform, the response function, output power spectral density and transfer functions for different elements of the platform are discussed. The joints deflection and acceleration responses demands are presented. It is generally concluded that consideration of the interaction between structure, piles and soil leads to higher deflections and less stresses in platform elements due to soil elasticity, nonlinearity, and damping and leads to a more realistic platform design. The earthquake-based analysis for offshore platform structure is essential for the safe design and operation of offshore platforms.

Behaviour of guyed transmission line structures under downburst wind loading

Shehata, A.Y.,El Damatty, A.A. Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.3

Past experience indicates that the majority of failures of electrical transmission tower structures occurred during high intensity wind events, such as downbursts. The wind load distribution associated with these localized events is different than the boundary layer wind profile that is typically used in the design of structures. To the best of the authors' knowledge, this study represents the first comprehensive investigation that assesses the effect of varying the downburst parameters on the structural performance of a transmission line structure. The study focuses on a guyed tower structure and is conducted numerically using, as a case study, one of the towers that failed in Manitoba, Canada, during a downburst event in 1996. The study provides an insight about the spatial and time variation of the downburst wind field. It also assesses the variation of the tower members' internal forces with the downburst parameters. Finally, the structural behaviour of the tower under critical downburst configurations is described and is compared to that resulting from the boundary layer normal wind load conditions.

Dynamic characteristics of hybrid tower of cable-stayed bridges

Shehata E. Abdel Raheem 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.17 No.6

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/ concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

Seismic pounding effects on adjacent buildings in series with different alignment configurations

Shehata E. Abdel Raheem,Mohamed Y.M. Fooly,Aly G.A. Abdel Shafy,Yousef A. Abbas,Mohamed Omar,Mohamed M.S. Abdel Latif,Sayed Mahmoud 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.3

Numerous urban seismic vulnerability studies have recognized pounding as one of the main risks due to the restricted separation distance between neighboring structures. The pounding effects on the adjacent buildings could extend from slight non-structural to serious structural damage that could even head to a total collapse of buildings. Therefore, an assessment of the seismic pounding hazard to the adjacent buildings is superficial in future building code calibrations. Thus, this study targets are to draw useful recommendations and set up guidelines for potential pounding damage evaluation for code calibration through a numerical simulation approach for the evaluation of the pounding risks on adjacent buildings. A numerical simulation is formulated to estimate the seismic pounding effects on the seismic response demands of adjacent buildings for different design parameters that include: number of stories, separation distances; alignment configurations, and then compared with nominal model without pounding. Based on the obtained results, it has been concluded that the severity of the pounding effects depends on the dynamic characteristics of the adjacent buildings and the input excitation characteristics, and whether the building is exposed to one or two-sided impacts. Seismic pounding among adjacent buildings produces greater acceleration and shear force response demands at different story levels compared to the no pounding case response demands.

Improved Power Control of DFIGs Driven by Wind Turbine under Unbalanced Grid Voltage

Shehata E. G. 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.1

Undesired oscillation components appear in active and reactive powers, electromagnetic torque and DC-link voltage of doubly fed induction generators (DFIGs) connected to unbalanced grid voltage. These components oscillate at double source frequency as a result of negative sequence components in voltage and current. Diferent direct power control (DPC) techniques were studied in literatures to damp these oscillations. However, these techniques require sequence decomposition process, axes transformation of stator voltage/current and estimation of diferent power components which complicate the overall control system. This paper presents a simplifed DPC of DFIGs in stationary reference frame under normal and unbalanced grid voltage. Decomposition process, axes transformation and compensation power terms are totally eliminated. Vector proportional- integral (VPI) controllers are designed to regulate stator active and reactive powers. The performance of the proposed DPC scheme using VPI and proportional-integral-resonant (PIR) controllers is analyzed and compared under different operating conditions. Bode diagram of open loop and closed loop control using VPI and PIR are studied to illustrate stability, steady state and transient response of the two controllers. Also, the performance of proposed technique and previous DPCs designed in synchronous reference frame is compared to prove the validity of proposed one. The results show that proposed DPC using VPI has superior performance in steady state and transient conditions with simple implementation. Undesired oscillation components appear in active and reactive powers, electromagnetic torque and DC-link voltage of doubly fed induction generators (DFIGs) connected to unbalanced grid voltage. These components oscillate at double source frequency as a result of negative sequence components in voltage and current. Different direct power control (DPC) techniques were studied in literatures to damp these oscillations. However, these techniques require sequence decomposition process, axes transformation of stator voltage/current and estimation of different power components which complicate the overall control system. This paper presents a simplified DPC of DFIGs in stationary reference frame under normal and unbalanced grid voltage. Decomposition process, axes transformation and compensation power terms are totally eliminated. Vector proportional- integral (VPI) controllers are designed to regulate stator active and reactive powers. The performance of the proposed DPC scheme using VPI and proportional-integral-resonant (PIR) controllers is analyzed and compared under different operating conditions. Bode diagram of open loop and closed loop control using VPI and PIR are studied to illustrate stability, steady state and transient response of the two controllers. Also, the performance of proposed technique and previous DPCs designed in synchronous reference frame is compared to prove the validity of proposed one. The results show that proposed DPC using VPI has superior performance in steady state and transient conditions with simple implementation.

Ileo-uterine fistula in a degenerated posterior wall fibroid after Caesarean section

Shehata, Ayman,Hussein, Naglaa,El Halwagy, Ahmed,El Gergawy, Adel,Khairallah, Mohamed The Korean Society for Reproductive Medicine 2016 Clinical and Experimental Reproductive Medicine Vol.43 No.1

Uterine fibroids are benign tumors of the myometrium with a diverse range of manifestations. Fibroids can dramatically increase in size during pregnancy due to the increase in estrogen levels. After delivery, the fibroids usually shrink back to their pre-pregnancy size. Uterine myomas may have many complications, including abnormal uterine bleeding, infertility, pressure on nearby organs, degeneration, and malignant transformation. No previous reports have indicated that a fistula may develop between a uterine fibroid and the bowel loops, although previous studies have documented the occurrence of fistulas from the uterus to the bowel following myomectomy or uterine artery embolization performed to treat a myoma. In our case report, we document the rare complication of a fistula occurring between a degenerated myoma in the posterior wall and the ileum 1 week postoperatively in a patient who underwent a Caesarean section but did not have a history of uterine artery embolization.

Numerical analysis for structure-pile-fluid-soil interaction model of fixed offshore platform

Raheem, Shehata E. Abdel,Aal, Elsayed M. Abdel,AbdelShafy, Aly G.A.,Mansour, Mahmoud H.,Omar, Mohamed Techno-Press 2020 Ocean systems engineering Vol.10 No.3

In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil-structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads.