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Issue Info: 
  • Year: 

    2015
  • Volume: 

    17
Measures: 
  • Views: 

    145
  • Downloads: 

    70
Abstract: 

FULLY DYNAMIC ANALYSIS OF OFFSHORE STRUCTURES UNDER RANDOM WAVE LOADS IN TIME DOMAIN IS SOMETIMES NECESSARY FOR CALCULATING STRUCTURAL RESPONSES IN DESIGN ISSUES. SUCH ANALYSES ARE VERY TIME CONSUMING AND THEREFOR SIMPLIFIED METHODS FOR ESTIMATION OF ACCEPTABLE RESPONSE OF THESE STRUCTURES CAN BE VERY USEFUL IN INITIAL DESIGN. IN THIS PAPER AN INNOVATIVE METHOD TO OBTAIN RESPONSE SPECTRUM OF FIXED OFFSHORE STRUCTURES CAUSED BY EXTREME WAVES IS REPRESENT BASED ON CONCEPT OF IMPULSE RESPONSE SPECTRUM. FOR THIS PURPOSE THE STRUCTURAL SYSTEM IS CONSIDERED AS A SIMPLE ONE DEGREE OF FREEDOM STRUCTURE AND THE DIFFERENT SEA STATES ARE EQUALIZED TO DIFFERENT HALF SINUSOIDAL PULSES. RESPONSE SPECTRUM OF STRUCTURE IS DEFINED AS A PLOT OF STRUCTURAL RESPONSE TO THESE PULSES FOR DIFFERENT PERIODS. BY USING THIS METHOD THE COST OF COMPUTATIONS IS DECREASED SIGNIFICANTLY WHILE THE ACCURACY OF RESULTS WAS PRESERVED.

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Issue Info: 
  • Year: 

    1382
  • Volume: 

    5
Measures: 
  • Views: 

    345
  • Downloads: 

    0
Keywords: 
Abstract: 

The main objective of this study is to investigate the phenomenon of water impact underneath the decks of offshore structures due to propagating waves. The decks of offshore structures may be subjected to wave induced loads, which may be not accounted for in the original design. For safe design of offshore platforms, it is important that the hydrodynamic loads and the predicted accurately. In this report, a review of the previous work on this topic with a brief introduction to slamming theory together with a proposed procedure to predict the water impact underneath the decks of floating offshore structures will be presented. Meantime, three dimensional hydrodynamic analysis of a semi-submersible in sea waves has been performed by using the direct boundary element methods.

Yearly Impact:   مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Author(s): 

Issue Info: 
  • Year: 

    2021
  • Volume: 

    41
  • Issue: 

    10
  • Pages: 

    2769-2777
Measures: 
  • Citations: 

    1
  • Views: 

    37
  • Downloads: 

    0
Keywords: 
Abstract: 

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Writer: 

Haghighi Tadjvar P.

Issue Info: 
  • Year: 

    2016
  • Volume: 

    15
Measures: 
  • Views: 

    208
  • Downloads: 

    94
Abstract: 

THE PURPOSE OF THIS PAPER IS TO INVESTIGATE THE EFFECTS OF LOCAL HEAT ADDITION IN A SUPERSONIC (MACH 3) FLOW, UPSTREAM OF THE OBLIQUE SHOCK WAVE GENERATED BY A 5-PERCENT THICKNESS SYMMETRICAL CIRCULAR-ARC AIRFOIL IN ANGLE OF ATTACK 2O.THIS HEAT HAS A CYLINDRICAL SHAPE AND A GAUSSIAN DISTRIBUTION (THERMAL SPOT) AND CAN BE ACHIEVED BY AN ON-BOARD MICROWAVE RADIATION. THIS MICROWAVE SOURCE CAN PRODUCE A SQUARE WAVE SHAPED HEAT PULSE WITH A DURATION OF 10-4 SEC AND GENERATES A POWER ABOUT 250 KW. MODIFICATION IN FLOW FIELD BY LOCAL HEAT ADDITION DEPENDS ON MANY PARAMETERS; IN THIS WORK EFFECTS OF LOCATION ARE INVESTIGATED. A NUMERICAL APPROACH HAS BEEN DEVOTED FOR THIS PURPOSE AND SIMULATIONS SHOW THAT THE INTERACTION AMONG THERMAL SPOT AND FLOW CAN GENERATE AN OBLIQUE SHOCK WAVE. THE LOCATION OF HEAT CENTER IS A KEY FACTOR IN DETERMINING THE COLLISION POINT OF THIS SHOCK WAVE. SIGNIFICANT MODIFICATION IN AERODYNAMIC COEFFICIENTS AND LIFT TO DRAG RATIO CAN BE OBTAINED BY SUITABLE COLLISION AND THEN REFLECTION OF THIS SHOCK WAVE FROM THE AIRFOIL.

Yearly Impact:   مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2009
  • Volume: 

    4
  • Issue: 

    2
  • Pages: 

    91-96
Measures: 
  • Citations: 

    0
  • Views: 

    329
  • Downloads: 

    238
Abstract: 

Background: Pulse wave velocity (PWV) is widely used for estimating the stiffness of an artery. Various invasive and non-invasive methods have been developed to determine PWV over the years. In the present research, the non-invasive estimation of the PWV of large arteries was used as an index for arterial stiffness. Methods: A dynamic model based on the Navier-Stokes equations coupled to elasticity equations was introduced for the PWV in arteries with elastic walls. This system of equations was completed by clinical information obtained from the Doppler ultrasound images of the carotid artery of 40 healthy male volunteers. For this purpose, the Doppler ultrasound images were recorded and saved in a computer; and subsequently center-line blood velocity, arterial wall thickness, and arterial radius were measured by offline processing. Results: The results from the analytic solution of the completed equations showed that the mean value of PWV for the group of healthy volunteers was 2.35 m/s when the mean arterial radius was used as the neutral radius and 5.00 m/s when the end-diastole radius was used as the neutral radius. It is noteworthy that the latter value closely complies with that reported by other researchers. Conclusion: By applying this method, a non-invasive clinical and local evaluation of the common carotid artery stiffness via a Doppler ultrasound measurement will be possible.

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Issue Info: 
  • Year: 

    2025
  • Volume: 

    16
  • Issue: 

    4
  • Pages: 

    229-234
Measures: 
  • Citations: 

    0
  • Views: 

    9
  • Downloads: 

    0
Abstract: 

Echocardiography is a noninvasive, highly sensitive method for evaluating heart disease in veterinary medicine, crucial for measuring cardiac structures and functions. Despite its importance, limited data exist on sheep, particularly the Ghezel breed, a significant breed in Iran. This study aimed to establish normal echocardiographic values for Ghezel sheep, providing reference data for both clinical and research applications. We evaluated 15 healthy Ghezel sheep with a mean age of 16.50 ± 1.80 months and a mean weight of 42.69 ± 4.73 kg. Comprehensive clinical exams, biochemical and hematological tests and color Doppler echocardiography were performed. Descriptive results from standard right and left parasternal views in both longitudinal and transverse planes were obtained and compared to existing studies. The study successfully established pulse wave Doppler reference values for the Ghezel breed. These findings could be used in diagnosing heart disease in Ghezel sheep and would be beneficial in future research particularly in sheep used as an animal model for translation in human cardiac studies.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2018
  • Volume: 

    23
  • Issue: 

    8
  • Pages: 

    0-0
Measures: 
  • Citations: 

    0
  • Views: 

    222
  • Downloads: 

    138
Abstract: 

Background: First‑ degree relatives (FDRs) of hypertensive (HT) are predisposed to hypertension (HTN) which accelerates cardiovascular aging. Same can be studied noninvasively by pulse wave analysis (PWA), encompassing central hemodynamics such as central blood pressure (cBP), cardiac output, and stroke work (SW) and vascular stiffness parameters such as pulse wave velocity (PWV) and augmentation index at HR 75 (AIx@75). We studied PWA‑ derived cardiovascular parameters in FDRs of HT compared to controls. Materials and Methods: We conducted a case– control study in 119 FDRs of HT and 119 matched controls. Oscillometric PWA was performed by Mobil‑ o‑ Graph (IEM, Germany) and cardiovascular parameters were compared. P < 0. 05 was considered statistically significant. Results: Groups were comparable with gender, age, height, weight, body mass index, and physical activity. FDRs of HT had significantly higher brachial and cBPs, SW (101. 41 ± 25. 44 vs. 88. 31 ± 20. 25, P = 0. 001), rate pressure product‑ 119. 40 ± 25. 34 vs. 108. 34 ± 18. 17, P < 0. 0001), PWV (5. 22 ± 0. 46, P < 0. 0001), and AIx@75 (31. 48 ± 9. 01 vs. 27. 95 ± 9. 4, P = 0. 002) than control. Dependent study variables correlated with brachial blood pressure more in magnitude and significance level than age or anthropometric variables. PWA results of FDR with maternal inheritance did not differ significantly from those with paternal inheritance. Conclusion: PWA reveals early cardiovascular aging in young FDRs of HTs. It clues to future cardiovascular disease including HTN itself, need for primary prevention, and further study for consolidation of these results.

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Author(s): 

DEBNATH P. | PANDEY K.M.

Issue Info: 
  • Year: 

    2017
  • Volume: 

    10
  • Issue: 

    2
  • Pages: 

    725-733
Measures: 
  • Citations: 

    0
  • Views: 

    226
  • Downloads: 

    278
Abstract: 

Detonation combustion based engines are more efficient compared to conventional deflagration based engines. Pulse detonation engine is the new concept in propulsion technology for future propulsion system. In this contrast, an ejector was used to modify the detonation wave propagation structure in pulse detonation engine combustor. In this paper k-ε turbulence model was used for detonation wave shock pattern simulation in PDE with ejectors at Ansys 14 Fluent platform. The unsteady Euler equation was used to simulate the physics of detonation wave initiation in detonation tube. The computational simulations predicted the detonation wave flow field structure, combustion wave interactions and maximum thrust augmentation in supersonic condition with ejectors at time step of 0. 034s. The ejector enhances the detonation wave velocity which reaches up to 2226 m/s in detonation tube at same time step, which is near about C-J velocity. Further the time averaged detonation wave pressure, temperature, wave velocity and vortex characteristics interaction are obtained with short duration of 0. 023s and fully developed detonation wave structures are in good agreement with experimental shadowgraph, which are cited from previous experimental research work.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2023
  • Volume: 

    26
  • Issue: 

    11
  • Pages: 

    642-646
Measures: 
  • Citations: 

    0
  • Views: 

    14
  • Downloads: 

    0
Abstract: 

Background: Various treatment methods are available for calcaneal spur, which can cause disability. Objective: To evaluate the efficacy of pulsed electromagnetic field therapy (PEMFT) added to extracorporeal shock wave therapy (ESWT) on pain and functional capacity in treating calcaneal spurs. Methods: Patients with calcaneal spurs who were recommended ESWT or ESWT+PEMFT and whose Foot Function Index (FFI) and visual analogue scale (VAS) values were available in their records were retrospectively analyzed. The two groups were ESWT (n=35) and ESWT+PEMFT (n=40). FFI and VAS scores were obtained from their records before treatment, after treatment, and in the third month after treatment. Results: The two groups were similar regarding their pre-treatment FFI and VAS scores. In intra-group evaluation, statistically significant decreases were found in terms of the FFI pain, disability, and activity limitation and VAS scores in both groups after treatment and in the third month after treatment compared to the pre-treatment period. In the comparison between the groups, the post-treatment and post-treatment third-month FFI pain, disability, and activity limitation and VAS scores were significantly lower in the PEMFT+ESWT group than the ESWT group (P<0.001). Conclusion: A calcaneal spur is a condition that can cause pain and functional limitation in patients. Various studies have demonstrated the efficacy of ESWT in the treatment of calcaneal spurs. In our study, we observed that PEMFT added to ESWT significantly improved the pain and functionality of the patients. Further studies are needed to evaluate the efficacy of PEMFT in calcaneal spurs.

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Author(s): 

MONTAHAEI M. | RIAHI M.A.

Issue Info: 
  • Year: 

    2005
  • Volume: 

    31
  • Issue: 

    2
  • Pages: 

    79-87
Measures: 
  • Citations: 

    0
  • Views: 

    697
  • Downloads: 

    0
Abstract: 

Mechanical and electromagnetic perturbations are coupled in a porous medium saturated with liquid. This coupling is such that, a seismic wave propagating through the mentioned medium will cause a relative movement between the solid and liquid. Then this movement will induce an electrical flux. When a seismic pulse propagates through a medium with specific chemical and elastic properties it causes an unbalance in the electrical flux. The unbalance in the electrical charge will separates the dipoles and multi-poles an both sides of an interface and that makes it possible to record the electromagnetic perturbations at the earth’s surface. In this paper, electroseismic wave propagation has been studied and simulated in a layered and porous medium saturated with liquid. For this purpose the governing equations of Pride (1994) and the coupled equations of the Biot and Maxwell were used. To calculate the electroseismic traces, the generalized reflection and transmission matrix method was applied.

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