Papers by VAMSHIKRISHNA DOMALA
Journal of Computational Design and Engineering
Maritime Autonomous Surface Ships are in the development stage and they play an important role in... more Maritime Autonomous Surface Ships are in the development stage and they play an important role in the upcoming future. Present generation ships are semi-autonomous and controlled by the ship crew. The performance of the ship is predicted using the data collected from the ship with the help of machine learning and deep learning methods. Path planning for an autonomous ship is necessary for estimating the best possible route with minimum travel time and it depends on the weather. However, even during the navigation, there will be changes in weather and it should be predicted in order to reroute the ship. The weather information such as wave height, wave period, seawater temperature, humidity, atmospheric pressure, etc., is collected by ship external sensors, weather stations, buoys, and satellites. This paper investigates the ensemble machine learning approaches and seasonality approach for wave data prediction. The historical meteorological data are collected from six stations near P...
A research note on a study of motion characteristics of tension leg spar
Journal of Offshore Structure and Technology, 2017
The present research note, reports a study on the dynamic motion analysis of a tension leg spar (... more The present research note, reports a study on the dynamic motion analysis of a tension leg spar (TLS). In the research note the time domain analysis is done using USFOS *TM software for a tension leg spar supporting a ‘National Renewable Research Laboratory (NREL)’ 5MW wind turbine at an operating depth of 320m to determine the dynamic responses of tension leg spar subjected to sea state 11 ( =15m and =16sec). Motion characteristics such as surge, pitch and heave as well as the combined effect of the above are discussed at length. Non-linear effect is introduced in the spar due to the tension leg. The nonlinear effects include combined-frequency effect such as double natural pitch and surge frequencies as well as sum of frequencies. The reported study is only limited to wave induced motions and no aerodynamic forces are taken into account. Hydrodynamic loads are based on a combination of the Morison formula and the pressure integration method. The response for the base case is compared with available result from the literature. Furthermore, to achieve a proper understanding of the response of the floating concept, parametric studies are carried out by varying parameters such as draft, pretension and position of ‘center of gravity (COG)’. The results highlight the variation in platform responses caused by changing these parameters. The analyses are carried out for combination of parameters in order to find a configuration having the least response for the above sea state. Keywords: Tension leg spar, Coupled motion characteristics, Time domain analysis, Dynamic response, Parametric study. Cite this Article Yadav K, Vamshikrishna Domala, Sharma R. A Research Note on a Study of Motion Characteristics of Tension Leg Spar. Journal of Offshore Structure and Technology . 2017; 4(3): 1–20p.
Ocean systems engineering, 2019
This paper presents the comparison between SFT response with linear and nonlinear cables. The dyn... more This paper presents the comparison between SFT response with linear and nonlinear cables. The dynamic response analysis of submerged floating tunnel (SFT) is presented computationally with linear and nonlinear tension legs cables. The analysis is performed computationally for two wave directions one at 90 degrees (perpendicular) to tunnel and other at 45 degrees to the tunnel. The tension legs or cables are assumed as linear and nonlinear and the analysis is also performed by assuming one tension leg or cable is failed. The Response Amplitude Operators (RAO‟s) are computed for first order waves, second order waves for both failure and non-failure case of cables. For first order wavesthe SFT response is higher for sway and heave degree of freedom with nonlinear cables as compared with linear cables. For second order waves the SFT response in sway degree of freedom is bit higher response with linear cables as compared with nonlinear cables and the SFT in heave degree of freedom has hi...
An experimental study on vortex-induced vibration response of marine riser with and without semi-submersible
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2017
This article presents an experimental study on ‘vortex-induced vibrations’ of marine riser that i... more This article presents an experimental study on ‘vortex-induced vibrations’ of marine riser that is mounted on a semi-submersible. The marine riser is considered as a flexible cylindrical member made of Stainless Steel Braided Flexible Hose that is fixed at both the ends. Our experimental conditions are carefully chosen to represent real world applications, and Stainless Steel Braided Flexible Hose riser acts as both the drilling and catenary riser. We report the experimental studies conducted in the current flume for three cases: Stainless Steel Braided Flexible Hose as drilling riser by tensioning, Stainless Steel Braided Flexible Hose as catenary riser, and Stainless Steel Braided Flexible Hose as catenary riser with semi-submersible. Our aspect ratio (length to diameter) of Stainless Steel Braided Flexible Hose drilling riser is 86 and Stainless Steel Braided Flexible Hose catenary riser is 157 (effective ratio till touchdown point), and Reynolds’s number is up to 5000. The experimental conditions are as follows: for Case 1 – tension of 43 N with empty pipe, with water, with drilling mud conditions and effective length decreased with water and increasing the tension up to 67 N with water; for Case 2 – catenary Stainless Steel Braided Flexible Hose with empty pipe condition and with water; for Case 3 – Stainless Steel Braided Flexible Hose catenary riser with semi-submersible at 0 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , and 90 ∘ current directions. The accelerometer signals are filtered and integrated to get the displacements, and the isolation of low frequencies obtained from semi-submersible is implemented to get the pure displacement of Stainless Steel Braided Flexible Hose. We report the results for transverse vibration and our results show that the maximum response for Stainless Steel Braided Flexible Hose drilling riser occurs at around reduced velocity of 6 and for Cases 2 and 3 at around reduced velocity of 9. Also, the Stainless Steel Braided Flexible Hose drilling riser with water shows higher response as compared to other cases (with and without drilling fluid), and increasing the tension results into increase of the natural frequency and decreased response when compared to other cases (with and without drilling fluid). Furthermore, for the same amplitude of vibration, Stainless Steel Braided Flexible Hose drilling riser with drilling fluid shows higher equivalent lift coefficients. The Stainless Steel Braided Flexible Hose catenary riser without fluid shows a minimum transverse response compared with fluid, and Stainless Steel Braided Flexible Hose’s response with semi-submersible is minimum compared with individual Stainless Steel Braided Flexible Hose riser with water. Finally, we show that the reported results offer meaningful deep insights into the vortex-induced vibration response of marine riser for real world applications.
A research note about a study of an anti-vibration device for jacket structure
Computer aided design model for integrated casing while drilling system for deepwater applications
International Journal of Oil, Gas and Coal Technology, 2015
ABSTRACT
An experimental study on vortex-induced motion responses of a moored semi-submersible with and without riser
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2020
This article presents an experimental study on the “vortex-induced motion” responses of a moored ... more This article presents an experimental study on the “vortex-induced motion” responses of a moored “semi-submersible without catenary riser” and “semi-submersible with catenary riser.” An eight-point catenary mooring system is adopted for the study in which eight rollers are installed on the pontoons for guiding the mooring lines and the semi-submersible design is of two rectangular pontoon and two circular columns on each of the pontoons. To replicate the real-world scene, the experiments are conducted in wave-cum-current flume with five directions of current (i.e. 0°, 30°, 45°, 60°, and 90°) to study the vortex-induced motion under the surge and sway degrees of freedom at high dimensionless reduced velocities (i.e. 6< Urs<50.86). Along with the surge and sway degrees of motion, the roll and pitch degrees of motion are investigated too with their paths for semi-submersible (i.e. amplitude traces). A “stainless steel flexible braided hose” with an aspect ratio of 157 till the to...
2014 Oceans - St. John's, 2014
The study of motion response of offshore structures is important in design and operation of offsh... more The study of motion response of offshore structures is important in design and operation of offshore structures. Primarily, the motion response of a semi-submersible depends upon centre of gravity, meta-centric height, geometric dimensions, arrangement and shape of the structural elements such as columns and pontoons, and operating draft of the structure. This paper reports a numerical study on the effect of geometric dimensions, shape and arrangement of columns and pontoons on the hydrodynamic response of a semi-submersible. In this paper five design configurations of a semi-submersibles with different dimensions are studied numerically using a commercially available software (i.e. ANSYS-AWQA *TM ) and in semi-submersible design the geometric dimensions, shape and arrangement of columns and pontoons are varied and a 'time domain analysis' is performed for head and beam sea conditions with an eight point moorings for 1000 m depth with an angle of 45 º between each set of mooring lines for regular waves and also for different sea state conditions. In the numerical study, the potential flow diffraction analysis is used and the viscous damping is suitably assumed from the available results from literature and that is given as an 'input' in the numerical simulation.
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Papers by VAMSHIKRISHNA DOMALA