Prasanta Sahoo

Tribological Performance Optimization of Al-7.5% SiCp Composites Using the Taguchi Method and Grey Relational Analysis

The present study considers an experimental study of tribological performance of Al-7.5% SiCp metal matrix composite and optimization of tribological testing parameters based on the Taguchi method coupled with grey relational analysis. A grey relational grade obtained from grey relational analysis is used as a performance index to study the behaviour of Al-7.5% SiCp MMC with respect to friction and wear characteristics. The tribological experiments are carried out by utilizing the combinations of tribological test parameters based on the L27 Taguchi orthogonal design with three test parameters, namely, load, speed, and time. The material Al-7.5% SiCp metal matrix composite is developed by reinforcing LM6 aluminium alloy with 7.5% (by weight) SiC particle of 400 mesh size (~37 μm) in an electric melting furnace. It is observed that sliding time has a significant contribution in controlling the friction and wear behaviour of Al-7.5% SiCp MMC. Furthermore, all the interactions between the parameters have significant influence on tribological performance. A confirmation test is also carried out to verify the accuracy of the results obtained through the optimization problem. In addition, a scanning electron microscopy (SEM) test is performed on the wear tracks to study the wear mechanism.

EFFECTS OF HEAT TREATMENT ON TRIBOLOGICAL BEHAVIOR OF ELECTROLESS Ni–B COATING AT ELEVATED TEMPERATURES

The present work investigates the effects of heat treatment on friction and wear behavior of electroless Ni–B coatings at elevated temperatures. Coating is deposited on AISI 1040 steel specimens and subjected to heat treatments at 350∘C, 400∘C and 450∘C. Coating characterization is done using scanning electron microscope, energy dispersive X-Ray analysis and X-Ray diffraction analysis. Improvement in microhardness is observed for the heat treated deposits. Further, the effect of heat treatment on the tribological behavior of the coatings at room temperature, 100∘C, 300∘C and 500∘C are analyzed on a pin-on-disc setup. Heat treatment at 350∘C causes a significant improvement in the tribological behavior at elevated temperatures. Higher heat treatment temperatures cause deterioration in the wear resistance and coefficient of friction. The wear mechanism at 100∘C is observed to be predominantly adhesive along with abrasion. While at 300∘C, abrasive wear is seen to be the governing wear phenomenon. Formation of mechanically mixed layers is noticed at both the test temperatures of 100∘C and 300∘C for the coatings heat treated at 400∘C and 450∘C test temperature. The predominant wear mechanisms at 500∘C are abrasive and fatigue for as-deposited and heat treated coatings, respectively.

Practical evaluation of resistance of high-speed catamaran hull forms—Part I

Abstract Although catamaran configuration has been around for a longtime, it is only in the recent past that such hull forms have seen unprecedented growth in the high-speed ferry industry. One of the design challenges faced by naval architects is accurate prediction of the hydrodynamic characteristics of such vessels primarily in the areas of resistance, propulsion and seakeeping. Even though considerable amount of research has been carried out in this area, there remains a degree of uncertainty in the prediction of calm water resistance of catamaran hull forms. This paper attempts to present the research work carried out so far and what needs to be undertaken in future for a reasonably accurate prediction of catamaran resistance characteristics. The authors have examined the deep water wave resistance characteristics of a series of transom stern, semi-displacement slender catamaran hull forms of round bilge as well as single chine hull forms, which are of utmost importance to the high-speed ferry industry. The accuracy of the established regression equation has been seen to deviate appreciably by various sources of uncertainties. Verification of the equation with experimental database is also lacking to a certain extent. Further research is, therefore, needed to refine the accuracy as well as to complete the selection of crucial parameters employed. However, the results obtained have shown considerable promise, and a regression equation for predicting wave resistance of catamarans in calm water can be seen as achievable.

EFFECT OF TiO2 PARTICLES ON MICRO-HARDNESS, CORROSION, WEAR AND FRICTION OF Ni–P–TiO2 COMPOSITE COATINGS AT DIFFERENT ANNEALING TEMPERATURES

The present study investigates the effect of titania particles on the micro-hardness, wear resistance, corrosion resistance and friction of electroless Ni–P–TiO2 composite coatings deposited on mild steel substrates at different annealing temperatures. The experimental results confirmed that the amount of TiO2 particles incorporated in the coatings increases with increase in the concentration of particles in the electroless bath. In presence of TiO2 particles, hardness, wear resistance and corrosion resistance of the coating improve significantly. At higher annealing temperature, wear resistance increases due to formation of hard Ni3P phase and incorporation of titania particles in the coated layer. Charge transfer resistance and corrosion current density of the coatings reduce with an increase in TiO2 particles, whereas corrosion potential increases. Microstructure changes and composition of the composite coating due to heat treatment are studied with the help of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) analysis.

A case study: theoretical and experimental analysis of motion characteristics of a trimaran hull form

Abstract Vessel motion is an aspect of design that requires a high degree of consideration with regard to passenger comfort. Within the last two decades, extensive research work has resulted in development of numerical and analytical methods for the prediction of heave and pitch motions of catamaran hull forms. However, in the recent past, there appears to be a strong interest in the development of trimaran hull forms. Investigations have shown that little research has been conducted on such hull forms to reduce their motions in heave and pitch. In this article, we investigate the effects of the (longitudinal) stagger of the sidehulls on the motions in heave and pitch of a representative trimaran hull. To quantify the effects of longitudinal stagger of the sidehulls (outriggers) with respect to the centrehull, experimental investigations were undertaken at the Australian Maritime College Ship Hydrodynamic Centre. A round-bilge high-speed hull form model of the Australian Maritime Engineering CRC systematic series was constructed and subjected to extensive experimental analysis as well as computer simulations (HYDROS) for four different longitudinal stagger positions. The investigations demonstrated that this variation and the resulting variation in the radius of gyration could have a significant effect on the heave and pitch motions. The literature survey indicated that, to date, investigations on trimaran hull forms have been confined to determining the effects of transverse and longitudinal positions of the sidehulls only on the resistance characteristics. The investigations undertaken within the scope of this article provide a starting point to investigate the effect of the trimarans sidehull position on the motions of the vessel.

TRIBOLOGICAL BEHAVIOR OF ELECTROLESS Ni–P COATINGS IN VARIOUS CORROSIVE ENVIRONMENTS

The present paper deals with the study of tribological characteristics, viz. friction and wear, of electroless Ni–P coating in corrosive environments (brine, acidic and alkaline) by varying different coating process parameters as well as varying the tribological testing parameters, viz. applied load and speed. The optimized results of coating process parameters for minimum friction and wear performance of the coating are presented. Moreover, a detailed study of the tribological behavior of the coating is undertaken individually for the three corrosive environments. The results obtained are compared among each other and also with the dry condition test of the coating. It is found that the friction coefficient of Ni–P coating decreases with increase in load for all environments. In case of wear, the wear rate of Ni–P coating gradually increases with increase in load for all mediums but the same decreases after 40N in brine and alkaline mediums. However, for acidic solution, the wear rate shows a continuous increasing trend. It is observed that alkaline and brine environments are favorable from friction and wear point of view of the coating, respectively. Microstructure study of the coatings is also performed and the coating is found to be of cauliflower-like morphology. The coating also exhibits amorphous structure in as-deposited condition, which gradually turns crystalline with heat treatment.

Determination of Roll Motion for a Floating Body in Regular Waves

This paper deals with the mathematical modelling of the roll motion of a floating body in regular waves in beam seas for non-restrained conditions. The hydrodynamic forces are computed with the application of strip theory, and frequency dependent sectional added mass moment of inertia and damping are integrated over the length of the body by using the Frank close fit method. The governing equation that arises after balancing the hydrodynamic and exciting forces is reduced to non-dimensional form prior to converting it into the frequency domain by applying the Laplace transform technique. Numerical experiments have been carried out for a vessel of 19 190 t displacement under the action of a small amplitude sinusoidal wave of 11.2 s periodicity to obtain the roll response. This has been done in order to check the roll response computed numerically by developing a numerical model, SHIPMOT-R, where the Runge-Kutta-Gill method is adopted. A good agreement has been achieved between the time histories of roll motions computed numerically and derived analytically for zero and nonzero forward speeds. It is observed that the roll amplitude increases with the increase of vessel speed. This modelling technique would be very useful for ascertaining a vessels safety requirements in the early stages of design.

Numerical study of hydrodynamic response of mooring lines for large floating structure in South China Sea

In this paper, an attempt has been made to numerically model the responses of mooring lines on large floating structures (LFS) deployed in South China Sea. In this paper, a preliminary study has been undertaken to locate the mooring form and determine the mooring hydrodynamic response characteristics when LFS are deployed in water depths of under 1000 m. In addition, studies have also been carried out on the overall influence of dynamic response with different mooring lengths and angle between mooring lines.

A simplified method to calculate trim and resistance of a two-stepped planing hull

ABSTRACT In a creative design process of planing craft, stepped hulls could fill a gap in the planing craft industries in response to low drag and high speed demands. However, there exists a need for new computational tools for performance prediction of such hulls. Therefore, in the current work, an attempt has been made to develop a mathematical model for performance prediction of two-stepped hulls. Savitskys mathematical model has been modified, and in conjunction with linear wake theory, a new mathematical model has been proposed, which would enable prediction of trim, resistance and other parameters related to planing hulls with transverse steps. To validate the proposed model, existing experimental data have been used. The obtained results are in good agreement with experimental data. As such, developed mathematical model can be used in conceptual design phase of stepped hulls with transverse steps.

Numerical simulation of unsteady cavitating flows of pumpjet propulsor

In this study, an attempt has been made to study the cavitating flows of a pumpjet propulsor. A numerical study based on the unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics method of homogeneous multiphase using structured grids and the shear stress transport (SST) k–ω turbulence model has been carried out. Considering the effects of non-condensable gas (NCG) on the cavitation performance, the Schnerr–Sauer cavitation model has been applied and improved by introducing the NCG. The numerical calculations of non-cavitating and cavitating flows for the marine propeller E779A are carried out with different advance ratios at several cavitation numbers to verify the numerical simulation method. Results show that the thrust, the torque, and the cavitation performance, such as the cavitation location and shape, are in good agreement with experimental data. Furthermore, numerical predictions for a pumpjet propulsor on an unmanned underwater vehicle are made with different non-cavitating and cavitating flow conditions. The numerical simulations accurately predict the propulsor efficiency changes and the cavitation inception and extension on the suction side of rotor blades. The circumferential distributions of velocity components in different regions along the axial direction have different characteristics. The pressure distributions around rotor and stator blades are reasonable and consistent with the cavitation phenomenon. Additionally, the existence of a tip vortex and tip clearance cavitation leads to a further loss in efficiency of cavitating flows.