The analysis of underwater structure vibration and noise control has been paid more attention now. The problem about propeller exciting force transfers from shafting, the bearing supporting to structure, causing structure radiated noise is less studied. It is necessary to study the characteristic of coupled system for solving such problem. In this paper, the characteristic of shafting and underwater structure coupled system vibration power flow is analyzed by numerical method and experimental method. The finite element method was adopted to build the analysis model. The force transfer ratio at each bearing supporting are calculated. The transfer function from propeller force to structure response are studied. The vibration characteristics of coupled system are got by numerical method and experimental method. The results show that the coupling vibration effect of shafting and shell are significantly especially at low frequency. The whole coupled system can be excited by propeller force. Some methods should be proposed to reduce this kind of vibration.
In general, marine propellers have complicated geometries and as a consequence complicated flow around propeller. The aim of this work is to find an appropriate method and assess the turbulence model to approach the open water hydrodynamic characteristics of the marine propellers. In this work, a numerical modeling using a finite volume commercial code (FVM) for different turbulence models has been applied on the well known conventional screw propeller DTRC P4119. The 3-D solid model of P4119 is established using pro/E software and for the mesh generation ANSYS-ICEM has been used. Steady Reynolds-Averaged Navier Stokes (RANS) simulations are accomplished using FLUENT software with unstructured mesh in the rotating computational domain and structured mesh for the rest of the domain. The open water performance coefficients, thrust (KT), torque (KQ) and efficiency (η) have been calculated and compared with available experimental data to assess the applicability of different turbulence models for the open water study of propeller. This paper shows that, the accuracy of the CFD based on RANS equations is dependent on the used turbulence model and the RNG K-epsilon turbulence model yields to provide the most accurate results. Also, all the turbulence models via FLUENT software behave the same behavior for the total span of the advance coefficient (J) with two types of result accuracy. All the turbulence models shows high accuracy at low advance coefficient and this accuracy decreases but with an acceptable error till it decreases suddenly at the maximum advance coefficient.
In recent years, diesel engine is developing rapidly in the direction of high power and super long stroke, which requires higher strength of its key moving parts. Connecting rod is one of the key moving parts of diesel engine which is subjected to complex alternating load during the working process. This loading condition has a great influence on its structural strength and reliability. In the proposed study, the strength and fatigue of a low-speed diesel engine con-rod made of 42CrMoA are analyzed. The 3-D model of the con-rod assembly built in the proposed study. The stress distribution and deformation of the con-rod assembly under the maximum explosive pressure are presented and studied. In the present paper, fatigue safety factor of all parts of con-rod assembly under the maximum explosive pressure condition is checked. According to the results carried out from the proposed work, the corresponding alternating stress is 340MPa, while the fatigue limit of 42CrMo material is above 430-540MPa, which means that the con-rod parts work under the alternating stress far below the fatigue limit. The kirasushvili method is adopted in the present paper as the standard of safety factor evaluation of con-rod. According to the allowable safety factor table of kirasushvili method, the minimum safety factor of the big and small ends of the con-rod and rod body can meet the requirements without fatigue damage.
In this work, both steady and unsteady Reynolds-Averaged Navier Stokes (RANS) simulations have been used via FLUENT software to calculate the induced 3-D hydrodynamic forces and moments of marine propeller. Marine propeller is excited by variation of hydrodynamic loading due to its operation in non-uniform wake field. The induced hydrodynamic forces and moments are calculated for single blade and for all blades at low Reynolds number under two operating conditions. The first one, uniform inflow is considered at the inlet. The second one, non-uniform inflow is considered at the inlet (under the wake effect of the ship) to represent the propeller-ship interaction. Unsteady results show that, due to non-uniform inflow every single blade is suffering from periodic forces and moments with fluctuation amplitude and harmonies higher than that applied on the propeller shaft but with lower frequency. The moments in vertical and transversal directions My and Mz are higher than the axial moment Mx. This study shows that, using Computational Fluid Dynamics (CFD) to solve RANS equation is a reliable tool for calculating the hydrodynamic characteristics and estimating the excited hydrodynamic forces due to propeller-ship interaction.
The present paper focused on both turbulent flow and laminar flow at low Reynolds number in a curved duct. The finite volume method on unstructured grid and SIMPLEC algorithm were adopted here and the computation program was design with these methods. Good agreement was achieved between the numerical result and experimental data in the literature, and it shows that the method is reasonable and the program works well. The numerical method was also used to flow simulation with different attack angle and side angle, and numerical results were consistent with conclusion in the literature. Finally, the numerical method used for cases with different Reynolds number at the inlet. Secondary flow phenomena have been researched in the curved duct and some conclusions were derived.
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