Sharif Digital Repository

Conventional ships have been used for many years with usual body forms. But recent developments in high speed crafts have created many different alternatives. Therefore the selection of hull type becomes an important issue in the preliminary design stage. This selection should be based on performance comparisons and also other parameters such as building costs. Since planing monohulls and catamarans are very popular types of high speed crafts, in this paper their behaviors from resistance at high speeds are compared. The results may prove useful for designers at conceptual or preliminary design stages. © Shiraz University  

Interaction of freestream disturbances with high-speed inviscid flow over a blunt nose is simulated utilizing a shock-fitted spectral collocation method. The unsteady flow computations are made through solving the 2D Euler equations by virtue of such a dissipation-free numerical algorithm for precise unsteady flow simulations. A shock-fitting technique is employed to accurately compute the unsteady shock motions and its interaction with monochromatic freestream disturbances of different conditions. A symmetry condition is proposed to accurately model the both steady and unsteady characters of the symmetry boundary, which allows the use of halved geometries and avoids the extra computational... 

One of the main challenges for engineers in designing high-speed crafts is the evaluation of hydrodynamic loads during the impact of hull to wave’s surface. This paper presents an experimental investigation on the pressure distribution on three wedge-sections with 15°, 20° and 30° deadrise during water-entry. Assessment of pressure distribution on the effects of parameters such as drop heights, deadrise angles and the weights of the models had done. Time histories of impact pressure were recorded. It was showed that, the maximum pressure for 20° wedge had increased 2.4 times in comparison with 30° wedge while this number is 1.23 time for the 15° wedge. But the effects of weight and drop... 

The purpose of this paper is to study and identify suitable outflow boundary conditions for the numerical simulation of viscous supersonic/hypersonic flow over blunt bodies, governed by the compressible Navier-Stokes equations, with an emphasis motivated primarily by the use of spectral methods without any filtering. The subsonic/supersonic composition of the outflow boundary requires a dual boundary treatment for well-posedness. All compatibility relations, modified to undertake the hyperbolic/parabolic behaviour of the governing equations, are used for the supersonic part of the outflow. Regarding the unknown downstream information in the subsonic region, different subsonic outflow... 

The ride comfort of high-speed trains passing over railway bridges is studied in this paper. The effects of some nonlinear parameters in a carriage-track-bridge system are investigated such as the load-stiffening characteristics of the rail-pad and the ballast, rubber elements in the primary and secondary suspension systems. The influence of the track irregularity and train speed on two comfort indicators, namely Sperling's comfort index and the maximum acceleration level, are also studied. Timoshenko beam theory is used for modelling the rail and bridge and two layers of parallel damped springs in conjunction with a layer of mass are used to model the rail-pads, sleepers and ballast. A... 

The KASUMI block cipher is used for the cellular communications networks and safety of many wireless standards. Third generation cellular network technology (3G) permits to transmit information, voice and video at very high data rates never seen before that will revolutionize personal communications and information exchange. On the other hand, Residue Number System (RNS) is a modular representation and is evidenced to be serviceable equipment in many applications which need high-speed computations and high-performance components. RNS is a non-weighted and integer number system that can support secure, highspeed, low-power, parallel and carry-free arithmetic. For attaining the most... 

To investigate the factors affecting splashing in Peirce-Smith copper converters of Sarcheshmeh copper complex, South-East Iran, a laboratory scale model with dimensions one eighth of the actual converter was designed and assembled. The model was filled with water. Air was impinged onto the water. The sequence of events was subsequently recorded using high speed cameras. Factors affecting splashing such as blowing angle, volumetric flow rate of air, and the distance of the blowers from water surface were studied. Using a value of 2.65×10-11 for Morton dimensionless number, it was found that splashing may be reduced by 75% if the air speed in the tuyeres is reduced from 155 m/s to 30 m/s... 

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO2 laser beam at different scan rates ranging from 50 to 175 mm s-1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of... 

A low voltage high speed class AB op-amp with new structure is presented. The proposed op-amp has been designed to drive a large capacitive load as large as 10 pf dedicated for high-resolution high-speed pipelined analog to digital converters. Consuming comparatively low power about 6 mw, the proposed class AB op-amps has an output swing of 2.6 Vpp from a single supply of 1.5 volt. It has been observed that this op-amp can be suitable for a 1.5 volt 13-bit Pipelined A/D with sampling rate of 60 MS/S. This op-amp is to be fabricated in standard 0.18u CMOS technology  

High speed machine tools are required to operate in a wide range of spindle rotational speeds with high stiffness and high accuracy. The stiffness of the spindle is largely dependent on the axial preload of the angular contact bearings. A large preload is required at lower range of speeds to provide sufficient stiffness for vibration-free heavy cutting. However, at higher speeds, it results in rapid temperature rise and reduces the life of the bearing. For optimum performance, it is essential that the bearing preload is reduced as the rotational speed increases. In this paper, an automatic variable preload system is proposed that changes the preload on the bearings as a function of... 

In this study, a theoretical analysis is performed to assess the interaction of freestream disturbances with a plane normal shock considering real gas effects. Such effects are important in a field with high velocities and high temperatures. To perform the theoretical analysis, the downstream disturbances field is expressed as a mathematical function of the upstream one by incorporating real gas effects in the formulation. Here, the linearized one-dimensional perturbed unsteady Euler equations are used for the classification of the downstream/upstream disturbances field and the linearized one-dimensional perturbed Rankine-Hugoniot equations are applied to provide a relationship between the... 

This paper is Part II of a series of articles focusing on the disintegration of a cylindrical (Ø=0.60 mm diameter) water jet in a quiescent atmosphere, from Rayleigh to early atomization breakup regimes. Liquid fluorescence high-speed imaging is used here, instead of shadowgraphy, providing a more faithful representation of liquid jet breakup dynamics as described in Part I (Roth et al., 2021). Using these data, the aim of this article is to perform a temporal analysis of the primary breakup process and to investigate the variation of breakup length in the time-domain, under each breakup regime. The results indicate that the liquid jet velocity at the onset of primary breakup oscillates... 

The influence of deep cryogenic treatment on wear resistance and tool life of M2 HSS drills in high-speed dry drilling configuration of carbon steels was studied. The experimental results indicated 77 and 126% improvement in cryogenic-treated and cryogenic- and temper-treated drill lives, respectively. The results of wear rate test were in agreement with drill life test. Chemical composition of chips were also reported to show the onset of seizure in drilling test and the consequence of seizure in promoting dissolution wear by diffusion mechanism. Wear resistance improvement was mainly attributed to the resistance of cryogenically treated drills against diffusion wear mechanism, due to the... 

Cavitation phenomenon is defined as the process of rupturing any liquid by a decrease in pressure at nearly constant temperature. The cavities driven by the flow in a region of high pressure will implode and generate high pressure pulses leading eventually to erosion and vibration. But in supercavitation the bubbles produced by cavitation combine to form a large, stable bubble region around the supercavitating object. This phenomenon decreases the drag on the supercavitating body. Experimental testsware performed at 2-D unsteady flow for two wedge shaped bodies made before in laboratory and cavitation inception and its development were captured by a high speed camera. Then this cavitation... 

Nowadays networks-on-chip are emerging as a hot topic in IC designs with high integration. Much research has been done in this field of study recently, e.g. in routing algorithms, switching methods, VLSI Layout, and effects of resource allocation on system performance. On the other hand, three-dimensional integrated circuits allow a time-warp for Moore's Law. By vertically stacking two or more silicon wafers, connected with a high-density, high-speed interconnect, it is now possible to combine multiple active device layers within a single IC. In this paper, we examine performance and power consumption in a three dimensional network-on-chip structure under different types of traffic loads,... 

Dynamic stability of machine tools during operations is dependent on many parameters including the spindle speed. In high and ultra high speed machining, the gyroscopic effect on the spindle dynamics becomes more pronounced and can affect the borders of stability of the rotating system. In this paper, a finite element based model of spindle, tool holder and cutting tool is presented which uses Timoshenko beam theory to obtain the frequency response of the system when gyroscopic terms are included. Using this response, the stability of a high speed spindle system in the presence of gyroscopic effect is investigated. It is shown that the gyroscopic effects lower the critical depth of cut in...