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Deep sea mining is mineral retrieval process that takes place on the ocean floor wherein global industries are actively exploring and experimenting of different techniques in this relatively new concept of mining for extracting it economically from depths of 5000–5500 m below the ocean’s surface. National Institute of Ocean Technology (NIOT), India has been working on a mining concept for ∼6000 m water depth where a crawler based mining machine collects, crushes and pumps nodules to the mother ship using a positive displacement pump through a flexible riser (umbilical) system. The umbilical also serve as the weight supporting member for the miner and pump. In this paper, static and dynamic analysis of the umbilical system in steep wave configuration and the miner is carried out using ORCAFLEX for launching and touchdown conditions. Three different materials are considered and the best suitable material for umbilical is selected as the first step based on the tension. Then umbilical with Single Miner System is analyzed for the launching and touchdown conditions. Based on the analysis the optimum number and spacing of buoyancy tanks that will keep the stresses within the allowable limits in the umbilical cable are recommended.

Tension Leg Platforms (TLPs) are one of the best options for offshore industry in deep waters due to proven motion response characteristics. These are water depth sensitive structures and the motion responses in vertical plane motions (heave, roll and pitch) are critical for a TLP. Tension Based TLP (TBTLP) is a new concept and finds application in much deeper waters. A provision of a tension base at mid-depth results in an economical design of TLP. In fact, the TLP installed at a certain depth without any modifications can be made to be deployed in much deeper water depths by means of a tension base. In this paper, the concept of TBTLP is highlighted and hydrodynamic analysis of the chosen platform has been carried out using ANSYS AQWA package. The motion responses in terms of Response Amplitude Operators (RAOs) of TBTLP with one Tension Base in surge, heave and pitch have been obtained and compared with a TLP without a tension base.

Drinking water is a precious commodity with growing demand, motivating the researchers to explore innovative and cost effective measures to augment the available resources. Low Temperature Thermal Desalination (LTTD) is one among the ideas that utilizes the ocean thermal gradient for the production of freshwater. The cold water from deep sea is drawn and transported to the coast or to a floating platform to aid the conversion of surface seawater to fresh water. The behavior of this cold water pipeline in open waters is to be studied through analytical, numerical and experimental studies before actual field implementation. This paper presents the preliminary analysis of a flexible cold water pipe made up of High Density Polyethylene (HDPE) catering for an island based desalination plant. The water is drawn at a depth of 400 m and transferred to the shore. The site with coral reef demands an inverted catenary profiled pipeline to minimize damages and is connected to sump at the shallow end and a clump weight at the deep end. Preliminary hydrodynamic analysis of the cold water pipeline is carried out using OrcaFlex software under regular waves. Obtaining the effect of flexible pipeline under regular waves besides carrying out vortex induce vibration analysis and modal analysis forms the scope of this study. Variation of VonMises stresses, and effective tension at salient points (top end, middle and bottom end) are included.

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