Department of Ocean Engineering

Evaluation of maneuverability of a ship at the early design stages is necessary for ensuring safety of its voyage. IMO recommends the test speed or approach speed for the maneuvering predictions as 90-100% of the service speed of the vessel. The confined model tests for ship maneuvering assessment are usually conducted at low speeds and the hydrodynamic derivatives obtained from these tests are used in the equation of motion even when vessel operates at much higher speeds. But the hydrodynamic derivatives and consequently the trajectory predicted using these derivatives differ substantially from the actual maneuvering conditions. Hence the dependency of the derivatives on vessel speed needs to be understood properly to get the correct estimate of the vessel trajectory prediction. This paper investigates the effect of vessel speed (Fn) on hydrodynamic characteristics of a container ship. Straightline test and horizontal planar motion mechanism (HPMM) tests are conducted for a container ship model for different speeds in a CFD environment.

In this paper, the performance of caisson embedded in a soft marine clay has been brought out through the results obtained from tests carried out on model caissons subjected to both static and cyclic loading. The load-ground level deflection curves and the variations in lateral earth pressure with depth are presented and discussed for the cases of static, cyclic and post cyclic static lateral loading for the load eccentricity ratio (e/D) of 2 and caisson embedment ratios (L/D) of 2,3 and 4. Under cyclic loading with cyclic load ratios (CLR) up to 0.6, the lateral capacity of caisson is governed by static loading. With the increase in cyclic load ratio, there is in an increase in the lateral passive earth pressure. However, at higher cyclic load ratios, there is a significant increase in the lateral deflections. Based on the results of the investigation, it is suggested that the seawalls can be formed out of contiguous caissons installed in a line and these walls can be designed for cyclic load ratios up to 0.6 with suitable embedment ratios.

This paper addresses the parametric studies on the impact response of offshore triceratops subjected to low-velocity impact. Triceratops is the object of the present impact study which is one of the new generation offshore complaint platforms with three buoyant legs connected to deck by ball joints. The innovative geometric form and compliant characteristics distinguish triceratops from conventional offshore platforms. The buoyant legs in triceratops are usually designed as orthogonally stiffened cylindrical shell structures. Numerical studies are carried out using Ansys Explicit analysis solver to predict the impact response and local damage of buoyant leg of triceratops. From the impact force time history obtained through explicit analysis, the hydrodynamic time response analysis is carried out in Ansys Aqwa to predict the response of deck and buoyant legs. Parametric studies are mainly focussed on the effect on the location of the indenter, size of the indenter, type of indenter, number of stiffeners and strain-rate definition. Force displacement curves are reported along with detailed numerical observations.

Conventional floating breakwaters are examined and the feasibility of developing a cage floating breakwater is explored. Earlier studies on floating breakwaters reveal that, to achieve a transmission coefficient (Kt) less than 0.5, the breakwater width to wave length ratio (W/L) should necessarily be greater than 0.4 for most of the configurations. Recent studies on cost-effective floating breakwaters indicate that by fixing a row of pipes below the floating body, the W/L requirement can be reduced to 0.15 without any compromise in the performance. This concept has been adopted in developing a new configuration to serve as: (1) a floating breakwater; and (2) as a possible shallow water cage culture unit. Experiments were conducted to study the performance of the cage floating breakwater under wave and wave-current environment. The results on transmission and reflection coefficients are presented and compared with those reported in the literature. The variation of water surface oscillations and velocities within the cage, the effect of mooring line stiffness, and initial tension on transmission characteristics are also discussed.

The measured wave elevation and the corresponding two horizontal velocity components of in-line and transverse directions at eight different locations across a bar in a groin field off the East Frisian Island off Norderney at the North Sea Coast have been analysed. The variation of the wave and the velocities spectra within the groin field is reported. The waves and their kinematics are seldom linear in nearshore waters. In this paper, the results obtained through an attempt to study the asymmetries in the wave elevation and the in-line velocity time histories are reported. The probability density of the asymmetries are drawn along with theoretical Rayleigh and Weibull distributions. The variation of the different asymmetry factors within the groin field is discussed. © 1994.

This study aims to explore the site-specific impact of coastal structures on the stability of the shoreline. For this study, the shoreline data were collected with higher-order accuracy along a few vulnerable stretches of the coast in the vicinity of hard structures such as Seawalls, Groyne, Breakwater, and Training walls along the southeast and southwest coasts of India. All the field collected shoreline data were analysed with statistical measures using DSAS (Digital Shoreline Analysis System) tool of ArcGIS software. The presence of shore connected coastal structures dictates the sedimentation process in its purlieu. The observed average rate of erosion and accretion in the adjoining coastlines are −5.7 m/yr and +4.92 m/yr, respectively. The field measurements from the present study would provide an effective base for the planning and implementation of coastal structures near the studied area, as well as to adopt a better methodology for coastal impact assessment. Most of the well-planned and executed hard engineering structures have yielded desirable results and benefit for the local coastal communities.

The aim of the current work is to find out the effects of tubercles on the blade and wake of the turbine, which could be used in situations, where interaction among the array turbines is inevitable. Steady simulations are performed on a linear cascade setup of modified and unmodified infinite span NACA 63421 section blade, at Reynolds numbers 5×105 and 106 at inboard (low radial location) spacing. The tubercles used are at the scale of the boundary layer. The study showed that the boundary layer scale tubercles are advantageous only at higher Re and deeper stall regimes.

This 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.

Composite materials are a superior class of material used in almost every field of engineering like construction, military, aerospace, ocean structures, communication, and various other high-performance applications owing to their high specific strength and modulus, increased design flexibility, desirable thermal expansion characteristics good resistance to fatigue and corrosion, and economic efficiency. However, their ply-by-ply nature makes them susceptible to delamination, which originates from the propagation of microcracks in the weak resin-rich layers. Many attempts have been made to address the lack of mechanical properties of this weak interlaminar region. A particularly promising approach involves the incorporation of nanofibers between the reinforcement layers as the composite is laid up. This work involves studying the property improvements in carbon fiber epoxy composite by interleaving electrospun polyacrylonitrile (PAN) nanofibers. Experimental testing involving Tensile, Izod, Charpy and high velocity impact tests showed improved material properties for the PAN nano-interleaved composite. These improvements achieved by nanofiber interleaving shows a greater potential in addressing major concerns for critical application of composite materials in future.

The offshore platforms are generally designed with sufficient vertical clearance from the maximum predicted wave crest elevations. This vertical clearance is termed as 'air gap'. However, due to compelling reasons of hydrocarbon processes and also due to the increase in water levels due to climatic changes or seabed subsidence due to reservoir subsidence, the lower decks may become vulnerable to wave action due to reduction in air gap. The structural elements in the lower decks may become prone to wave-induced loads caused by high wave crests. The assessment of such wave-induced loads on the lower deck and supporting structures, especially in the existing platforms, becomes very essential for the continued safe operations. In the case of wave slamming on a structure, these supporting structural members will also be prone to large loads. Circular sections are commonly used for substructures due to their hydrodynamic efficiency; however, for deck structure, it is very common to use non-circular sections for supporting superstructure loads. The non-circular sections used in the lower decks get exposed to wave-induced loads. The imposed loads could be of higher magnitude compared with the circular sections due to the flat surface of the sections. A review of the literature indicates that the previous studies focused mainly on the circular sections and not much information is available on the non-circular shapes, especially in the case of wave slam and slap. The current study was focused on the measurement of wave-induced slam and slap loads on an array of non-circular sections in a laboratory wave flume and the estimation of force coefficient based on drag-based empirical equations. The studies revealed that the slam and slap coefficients for non-circular shapes are greater than those for circular shapes. © 2013 Copyright Taylor and Francis Group, LLC.