Rajiv Sharma

The design of 'Autonomous Underwater Vehicles (AUVs)' is mission specific and it is getting more and more complex with time because of higher demands of range, endurance, payload, operation flexibility, navigational capabilities for deep and restricted water depths, energy efficiency and special mission requirements as placed by the user agencies. These requirements of design are primarily conflicting in nature and hence they can be efficiently satisfied or at least a best design suiting a set of requirements can be computed with the application of optimization techniques. At present, the design process for AUVs is dominated by 'ad-hoc' approaches or empirical formulations. Recent developments in computational science and engineering, optimization techniques and 'Computational Fluid Dynamics (CFD)' have the capability to enable the designer to compute better estimates of the drag and other parameters that are important in design. This premise has motivated the present work and in this paper we present a design optimization framework for design of an AUV. In the proposed model, 'Computer Aided Geometric Definition (CAGD)' is integrated with the CFD along with the optimization framework for optimizing a given parameter (i.e. resistance). In our work, CFD is used in place of empirical formulations for the estimation of drag as with CFD one can accurately estimate the drag and thus increasing the fidelity of the optimization model. Furthermore, the use of CFD by integrating it with CAGD and optimization method allows the study of parametric hull form generations and analysis. With the genetic algorithm driven optimization technique, CFD simulation, the automatic generation of geometry based on the design parameters, automatic generation of mesh and automatic analysis of fluid flow, the objective function is computed and optimized efficiently and the results are presented in this work. In this paper, one of the most popular genetic algorithm, 'Non-dominated Sorting Genetic Algorithm NSGA-II' is implemented with MATLAB∗TM and the CFD analysis is implemented with SHIPFLOW∗∗TM. And, in the design process GA and CFD are integrated and used to optimize the design variables for minimization of an objective function (i.e. viscous resistance) and finally, we present a design example motivated by the real world applications and show that the integration of NSGA-II with CFD and CAGD is effective for AUV hull form optimization. Furthermore, the effectiveness of the design variables considered for the optimization process on the design of the low drag hull forms for the design of AUVs is critically examined in this work.

Economie and efficient energy resources are keys to a nation's development. Because of their low cost and advancement in drilling and exploration technologies oil and gas based energy systems are most widely used in practice throughout the world. The inexpensive oil and gas based energy systems are used for everything from transportation of goods and people to the harvesting of crops for food to being able see at night. As the energy demand continues to rise, this is pushing further the demands for inexpensive energy solutions. Since, available reservoirs of energy rich fossil fuels at shallow and moderately deep waters have been exploited already, the fossil fuel exploration and production is being forced to move into extremely deep waters. At deep water the expenses associated with fixed production platforms are no longer feasible, and that makes a floating production platform design a far more economical choice. This paper presents a critical parameter driven optimum conceptual design of an ultra-low motion semisubmersible floating oil and gas production system. The design is carried to satisfy the given parameter of weights and dimensions of the platform topsides required for production and drilling, water depth location, and low motion requirements. The proposed design process is highly iterative process of altering the key dimensions of a ' n -column ring' pontoon, and it meets applicable regulations and customer requirements while minimizing costs and satisfying the chosen parameters. The chosen parameters are classified into groups depending upon the scientific and technological requirements, and they are: GAaOHD - general arrangement and overall hull design, WaCL - wind and current loading, LaGL - local and global loading, WBS weight/buoyancy/stability, HMaL - hydrodynamic motion and loading, SaSD - strength and structural design, M - mooring, and EaC economics and cost. Overall, this paper introduces a novel design process for an ultra-low motion semi-submersible that covers the complete life cycle of the structure. Finally, we discuss one design example motivated by real world applications to show the effectiveness, usability and efficiency of our proposed model. Copyright © 2010 by The International Society of Offshore and Polar Engineers (ISOPE).

This paper presents a 'Computer Aided Design (CAD)' model for energy efficient design of offshore structures. In the CAD model preliminary dimensions and geometric details of an offshore structure (i.e. semi-submersible) are optimized to achieve a favorable range of motion to reduce the energy consumed by the 'Dynamic Position System (DPS)'. The presented model allows the designer to select the configuration satisfying the user requirements and integration of Computer Aided Design (CAD) and Computational Fluid Dynamics (CFD). The integration of CAD with CFD computes a hydrodynamically and energy efficient hull form. Our results show that the implementation of the present model results into an design that can serve the user specified requirements with less cost and energy consumption.

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 modular and integrated optimisation model for the design of underwater vehicles is presented. In the proposed optimisation model two modules (i.e. low fidelity and high fidelity) are incorporated and the basic geometric definition of computer aided design (CAD) is integrated with computational fluid dynamic (CFD) analysis. The hydrodynamic drag is considered as single objective with constraints on the geometric parameters of dimension, space and volume. The CAD model is implemented in MATLAB∗™ and CFD model is implemented in Shipflow∗∗™. A real-world design example of an existing underwater vehicle is presented. The applicability of proposed optimisation model is shown. The presented results show that within given set or sets of constraints the application of optimisation model in design results into an efficient hull form.

This paper will provide a broad high-level comprehensive review of various high-density completion fluids (HDCF) for the high pressure and high temperature (HPHT) reservoir. The goal is to explain the advantages and disadvantages of various high-density completion fluids over conventional completion fluids. Existing completion fluids solutions are low to mid-density range, expansive, limited availability, corrosion issues, and not suitable for all types of reservoir formations. Solids-free high-density completion fluids differ from conventional completion fluids in several key aspects such as high density, solids-free, low viscosity, alkaline pH, less corrosive, minimum formation damage, and thermal stability. The desired requirements from a high-density completion fluid system include insignificant solids, providing rheological stability, fulfilling environmental conditions, and reducing reservoir damage. A suitable completion fluid system can provide sufficient density for well control while eliminating solid weighting materials which are potentially formation damaging.

We explore a novel ‘High-Density Nano based Completion Fluid (NBCF) formulation using Magnesium Bromide and copper oxide (CuO) NPs in the aqueous medium. Our work mainly focuses on investigating variation in the rheological properties due to the influence of using CuO NPs on the behavior of MgBr2 based base completion fluid at different ranges of temperature (80 °F to 192 °F). Formulated NBCF density has shown maximum density of 1.80 s g at ambient temperature. This result clearly gives a breakthrough on the density limit of base completion fluid (BCF) (s.g. 1.61). Developed NBCF has shown with improved a reasonably solid free/clear fluid as there is no settling of particles is observed at the bottom of sample and also exhibits a high value of specific gravity which will results in suitable CF. Prepared NBCF pH value are in alkaline region (pH 8.2), which is one of the requirements of completion fluid. BCF brine usually exhibits a favorable viscosity performance from 1 to 20 mPas, and following close to Bingham plastic model. NBCF has a maximum viscosity of 67 mPas with a density of 1.8 g/cm3 at 190 °F. The Herschel Bulkley model had shown a better rheological data fitting of the CuO NPs based CF than the Bingham plastic model. This study offers a broad experimental interpretation of High density completion fluids. The copper oxide NPs has shown good potential to enhance completion fluid properties and suitable for providing productive completion processes with minimal formation damage in formation.

Product life-cycle management (PLM) has become something like "a magic wand" for various industries because of its capability to integrate different productmodules via online network through the product's complete life cycle and hence to provide one-window access, thereby making the whole processes of product conception, design, manufacturing, delivery, maintenance, and disposal integrated with a reduction in product development time and cost. However, heavy industries (i.e., shipbuilding and shipbreaking) are different from consumer product industries because of high customization in design process and engineering software, widely varying scales of operations, and less compatibility between different design and production processes, for example, ship production is planned in activity-driven network scheduling system, in general, and is assumed to be more of a construction process or assembly process rather than a production process. In this paper, we present the conceptual development and the basic building concepts for a logic-based PLM system for the shipbuilding industry. Our logic bases consist of modularization, standardization, geographical zoning, and functional zoning. The logic bases of modularization and standardization are used in the ship design and production processes, and the logic bases of geographical zoning and functional zoning are used in "logically grouping" the on-board activities in the ship production process. Overall, this paper introduces a logic-driven methodology for PLM: planning and integration of ship design and production processes. Finally, in our implementation we show that by developing a logic-based PLM system the ship design and production processes become more streamlined and better planned and executed.

This paper adopts Genetic Algorithm (GA) -driven optimisation framework to solve the design optimisation problem of an autonomous underwater vehicle that aims to minimise the delivered power under the constraints on the geometric parameters that define the hull shape. The GA and computational fluid dynamics (CFD) solvers are seamlessly integrated into a single code so that it becomes an effective computational tool for optimisation. Adopting a hull and a ducted propeller, for which some experimental data are available for CFD validation, the optimisation is done for the shape of the hull for a single velocity, leading to significant reduction in delivered power. The hull shape is described by a 5-parameter axisymmetric form. Delivered power minimisation problem is compared with the corresponding drag minimisation problem of the chosen hull.