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Deepak Kumar
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Deepak Kumar
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Deepak Kumar
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Kumar, D.
Kumar, Deepak
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38 results
Now showing 1 - 10 of 38
- PublicationA prototype online database-enabled design framework for wind analysis/design of low-rise buildings(01-03-2016)
;Kwon, Dae Kun ;Kareem, Ahsan; Tamura, YukioThis study presents a development of an advanced cyberbased database-enabled design module for low-rise buildings (DEDM-LR) which provides estimation of the wind-induced responses for main wind force resisting frames by making direct use of pressure time histories measured at a large number of pressure taps over a suite of building models. These responses may be considered in lieu of code-specified load effects in which the overall accuracy may be influenced by the inherent simplifications in codes. In addition, this new automated approach is particularly attractive and advantageous as it allows a web-based online analysis/design via intuitive user-friendly interfaces for both the input and output in terms of familiar web-style forms that are nowadays very common in most of web-based services. Presently, the DEDM-LR hosts an aerodynamic database developed by the Tokyo Polytechnic University (TPU), Japan for a variety of building configurations like flat, gable, and hip roofs under suburban terrain flow condition with immediate application to other databases. The paper shows the efficacy and validity of the DEDM-LR by walking through its details and examples on selected gable-roofed buildings. The architecture of DEDM-LR platform offers the ability to pool resources by hosting other databases that may become available in the near future. - PublicationRMS control of response of jacket structure using tuned liquid column ball gas damper under random ocean waves(01-01-2021)
;Jothinathan, SatheeshJacket structures are one of the most important offshore structures for extracting oil and gas. The fatigue life is affected due to the continuous dynamic wave force experienced by the structure. Generally, the structure is designed so that the dynamic response is small, which increases the cost. So, controlling its response is a good alternative to increase its life span. In this work, a simplified jacket structure under a random sea state is controlled for its response using a tuned liquid column ball gas damper (TLCBGD). The jacket structure in a water depth of 60m is modeled in a surge degree of freedom. The parameters of TLCBGD are optimized using a genetic algorithm for achieving better control in response quantities. For the analysis purpose, the wave is considered stochastic and presented by Pierson-Moskowitz (PM) spectrum of significant wave height 10m. In such a case, the jacket structure response can be presented using the root mean square (RMS) values obtained from the Lyapunov technique. Based on the random vibration analysis theory, the Lyapunov method can be employed to obtain the RMS of the system driven directly without solving the governing differential equation. This method requires the system to be driven by white noise. So, in this study, filters are developed to get the required narrow banded ocean spectrum. It is noticed that the response quantity is highly sensitive to the filter parameters. This is because a slight change in excitation parameters and a change in filter parameters near the system's natural frequency affect the response significantly. Further, it is seen that the use of the genetic algorithm for tuning the TLCBGD gives very good control on the response quantity of the jacket structure. - PublicationStability of TLP tether using a stochastic averaging technique(15-05-2016)
; Datta, T. K.Tension Leg Platforms (TLPs) are popular deep water platforms for extracting oil and gas. TLPs are connected to the sea bed by pretensioned tethers. If fluctuating tension in tethers is sizable compared to the pretension, many dynamic stability problems may arise which also affects the platform motion. In this paper, stochastic stability of TLP tethers in transverse oscillations is investigated using stochastic averaging technique and the probability flow of the reduced Fokker-Plank equation. Stochastic averaging is used to obtain drift and diffusion coefficients independent of time. Onset of such transverse oscillations may be caused due to regular or random vortex shedding. The tension fluctuation of the tether due to random vertical wave forces on the platform induces multiplicative random excitation in the tether because of the presence of nonlinear drag. As a consequence, dynamic instability may become a significant problem. The tether is modeled as a simply supported uniform beam under initial tension assuming transverse oscillation to take place only in its fundamental natural mode. Thus, the problem is reduced to a single degree of freedom system. Fluid resistance is calculated by Morison's equation consisting of drag and inertia forces. A semi-analytical procedure combined with stochastic averaging technique is employed to obtain the drift and diffusion coefficients of the response in closed form. By examining the probability flow in terms of drift and diffusion coefficients at the two boundaries, the stability of the system is investigated. Stability of tethers of a TLP in 300 m water depth, for different pretensions, is studied for sea states of 21 m, 16 m and 8 m significant wave heights represented by PM spectrum. It is shown that for low values of pretension, stochastic stability of tether in transverse direction may take place for large wave heights. - PublicationStructural analysis of spherical pressure hull viewport for manned submersibles using biological growth method(18-08-2018)
;Pranesh, S. B.; ;Anantha Subramanian, V. ;Sathianarayanan, D.Ramadass, G. A.Manned submersibles are important platforms for exploration and research under the oceans. One of the most important components of the manned submersible is the viewport, which develops high stresses due to the nature of its design. The basic dimensions of the viewport window and its flange are determined using ASME PVHO-1. Analysis of the viewport for given basic dimensions, shows that the corners of the low-pressure face of the viewport window and the notch regions of the flange are subjected to high stresses. Using the fillet radius method at the notch region results in stress reduction by 64%. The biological growth method helps in getting the naturally optimised shape at the corner. The use of the biological growth method for structural shape modification reduces the stress acting on the acrylic viewport by 71%. The same method applied to the flange notch region reduces its sharpness and the stress there by a considerable amount. This also helps in increasing the number of cycles of operation. - PublicationSloshing dynamics of shallow water tanks: Modal characteristics of hydraulic jumps(01-07-2021)
;Gurusamy, Saravanan ;Sanapala, V. S.; The dynamics of slosh induced wave systems in shallow water tanks is analyzed for various excitation conditions. Shake table experiments have been systematically performed to understand the complex interaction of multi-wave system under harmonic excitation. From the experiments, it was observed that, for relatively large excitation amplitudes, the hydraulic jumps emanated around the resonance region. The hydraulic jump phenomenon is further explored for different tank aspect ratios, i.e, 2.5 ≤L∕B≤ 4.038. To establish the frequency bounds for hydraulic jumps, excitation amplitude and frequency are demarcated over the range of 0.841 ≤β≤ 1.628 and liquid depth range of 0.034 ≤h∕L≤0.069. The experimental bounds are juxtaposed with the theoretical bounds to analyze the margins present in hydraulic jumps. Although, the theoretical bound is independent of liquid depth, experimental observations clearly indicate a strong dependency. - PublicationExperimental study on nonlinear sloshing frequency in shallow water tanks under the effects of excitation amplitude and dispersion parameter(01-10-2020)
;Gurusamy, SaravananSloshing of liquid in partially filled tanks under high excitation amplitude is always a complicated phenomenon for shallow water condition. This complication arises due to nonlinear behaviour of liquid free-surface motion when the excitation amplitude is sufficiently large. Due to nonlinearity, the sloshing resonant frequency also gets affected and so the performance of several devices developed based on linear sloshing concept is disturbed. One widely studied and used such device is Tuned Liquid Damper (TLD). In the present study, a series of experiments has been conducted to investigate the nonlinear shallow water sloshing in detail. Experimental tests were carried out for tanks of different base-aspect ratios (length to width of tank), different water-depths, wide range of excitation amplitudes and frequencies. Nonlinear characteristics such as frequency jump-phenomenon, shift in resonant frequency, super-harmonic resonance, responses at higher harmonics and fractional harmonics of forcing frequency have been reported. It has been found that the resonant frequency is sensitive to the excitation amplitude and dispersion parameter (ratio of water-depth to tank-length). For a tank of large aspect-ratio under high excitation amplitude, it is also found that the resonance frequency increases about 45% in comparison to the linear sloshing frequency. - PublicationExperimental Study on Shallow Water Sloshing(01-01-2021)
;Gurusamy, SaravananSloshing of liquid in a partially filled container, subjected to higher amplitude of dynamic load, is a complex phenomenon. In shallow water conditions, the natural frequency of sloshing depends on the amplitude of excitation. Sloshing frequency tends to change with increase in amplitude of excitation. The change in natural frequency is critical if we use the sloshing tank as a passive damping device, such as Tuned Liquid Damper (TLD) for offshore structures or onshore structures. A small change in sloshing frequency in TLD may affect the structural vibration control significantly. Therefore, it is essential to comprehend the natural frequency of shallow water sloshing. Experimental study is one of the best ways to understand the physical insights of change in sloshing frequency. Experimental studies are conducted to study the jump in sloshing frequency at different excitation amplitudes. Several rectangular tanks (1163, 1064, 951, and 844 mm) under different water depths (60, 50, and 40 mm) are taken for the study to generalize the results. The liquid tank is mounted on a uni-directional horizontal shake table, which is subjected to simple harmonic motion. The amplitude of excitation varied from 5 to 50 mm. A single capacitance-type wave probe is used at the end of the tank wall to measure the wave surface elevation. The wave elevation increases as the excitation frequency reaches toward the natural frequency of sloshing. The measured liquid sloshing frequency, at the resonance condition, is considered as actual sloshing frequency of liquid in tank. This sloshing frequency changes with the amplitude of excitation and shows the sudden jump in frequency from a particular amplitude of excitation. The objective of this paper is to generalize the relation between the jump frequency ratio (ratio of jump frequency to linear frequency) and the non-dimensional amplitude of excitation. - PublicationStudy on effects of truncation and scaling of mooring lines of a FPSO(01-01-2022)
;George, Siddharth; FPSOs are widely used offshore structures, primarily due to their versatility and portability. The analysis of a FPSO is conducted in the realm of computer simulations and wave basin based model experiment studies. Although scaling down of a prototype to an experimental model is the crux of wave basin studies, most wave basins lack the necessary dimension in depth to handle it. So, the mooring lines need to be truncated first and then scaled down to suit the wave basin depth. In this paper, a typical FPSO of 300m length (with 3x3 mooring lines at 120° spacing) at a water depth of 1000m is considered as the prototype model. Then a corresponding truncated model is generated to suit a water depth of 300m. The dynamic analysis of the above two models (prototype and truncated-prototype) are carried out in ANSYS AQWA and their results are compared. To compare the experimental results obtained in a 3m deep wave basin, available at the Department of Ocean Engineering, IIT Madras, the truncated-prototype model details are scaled down by using 1:100 scale. - PublicationFrequency-bounds of sloshing wave systems in a square-base liquid tank(15-01-2021)
;Gurusamy, SaravananLiquid sloshing in square or nearly square-base tanks becomes more complex due to the emergence of three dimensional waves around resonance. Because of symmetrical base in a square tank, two predominant sloshing modes (along the plane of excitation and orthogonal to the excitation plane), simultaneously emerge even if the tank is resonantly excited in one direction. For relatively small liquid-depth, nonlinear effects shift the resonant sloshing frequency. So, the effectiveness of devices (Tuned Liquid Dampers) designed based on the linear theory will be affected. The present study investigates the existence of the sloshing wave systems and their frequency bounds with an extensive experimental data. The tank is subjected to horizontal harmonic excitation for a wide range of frequencies and amplitudes. Sloshing induces different wave systems which depend on excitation frequency, excitation amplitude and liquid-depth. The main focus is to determine the frequency bound of swirling waves for a range of excitation amplitudes and liquid-depths. It has been found that the frequency bound of swirling increases with excitation amplitude. - PublicationDesign and conception of a trailing edge morphing wing concept with bistable composite skin(01-01-2020)
;Mukherjee, Aghna; ; Arockiarajan, A.In the recent past, bistable laminates have been widely studied for their potential in wing morphing applications. The existence of multiple stable states makes them extremely viable as structural elements. However, for successful deployment, these laminates must be integrated into a larger mechanism. For integration, the bistable laminates are required to be clamped to a larger structure without the loss of bistability. In this work, an attempt has been made to understand the effect of integration (i.e., using different structural constraints and clamping) on the bistability and the snapthrough performance of a special class of hybrid bistable symmetric laminates (HBSLs). The structural analysis has been carried out using FEA software ABAQUS. Subsequently, a conceptual design of a morphing wing is proposed based on the insights gained from the numerical analysis that uses two HBSLs as skin with a corrugated core. Finally, using the analysis guidelines, two HBSL skins and a circular corrugated core are manufactured and integrated to show the possibility of using such bistable laminates as skin.