Impact Of Flow Field Research Articles

Displacement Reliability Analysis of Submerged Multi-body Structure’s Floating Body for Connection Gaps

Abstract Aiming at the problem of systems’ dynamic characteristics’ randomness caused by connection gaps of submerged multi-body structures, a stochastic and uncertainty dynamical model were formulated for connection gaps and dynamic elongation of mooring cables. This model considered sag effect caused by light, soft and low damping characteristics of mooring cables and their dynamic elongation under the impact of flow field and connection gaps. The equivalent elastic modulus method was used to modify the sag effect. The Newmark-β method was used to solve the problem. Calculation results showed that the average value and peak value of floating body displacement caused by uncertainty of gap contact states are larger than those of ideal articulated states. The reliability of floating body’s displacement with gap contact will be reduced to different extents and the reliability of displacement in velocity direction changes greatly, especially perpendicular to flow field. When studying multi-body structures, randomness of contact state should be considered to reduce the dispersion of clearance and improve dynamic performance.

Experimental investigation of temperature-dependent interfacial heat transfer mechanism with spray quenching for 22MnB5 steel

The mechanical properties of heat treatable high strength 22MnB5 steel will become much more excellent after high pressure spray quenching through controlling process parameters. The contact between hot parts and fluid medium is a complex two-phase flow quenching process, which can affect the microstructure and mechanical properties directly. A main objective of this paper is to investigate the influence factors on temperature-dependent interfacial heat transfer coefficient (T-IHTC) law during spray quenching process for 22MnB5 high strength steel. The impact of flow field and boiling stages were analyzed based on single-point spray experimental platform. The Beck’s non-linear estimation method was used to calculate the fluid-solid contact T-IHTC between blank and fluid medium. The influence of different process factors, including injection air and water pressure, spray height, initial quenching temperature and oxide layer, were discussed. The results showed that the peak of T-IHTC appears in nucleate boiling stage, the T-IHTC correlates highly with injection pressure by a positive power function, and inverse correlation with the initial quenching temperature and the spray height. In addition, surface oxide layer also has a significant impact on T-IHTC, which impedes the contact between steel and fluid medium, leads to the weakening of heat transfer efficiency.

Multidimensional modeling of the effect of EGR (exhaust gas recirculation) mass fraction on exergy terms in an indirect injection diesel engine

In this investigation, the energy and exergy analyses are carried out for a Lister 8.1 IDI (indirect injection) diesel engine at four different EGR (exhaust gas recirculation) mass fractions (0%, 10%, 20% and 30%) and at 50% load operation. The energy analysis is performed during a closed cycle by using a three-dimensional CFD (Computational Fluid Dynamics) code. For the exergy analysis, an in-house computational code is developed, which uses the results of the energy analysis at different EGR mass fractions. The cylinder pressure results for baseline engine are compared with the corresponding experimental data that shows a good agreement. With crank position at different EGR mass fractions, various exergy components and the cumulative exergy are identified and calculated separately. It is found that at 50% load operation, as EGR mass fraction increases from 0% to 30% (in 10% increments), exergy efficiency decreases from 31.74% to 25.38%. Also, the cumulative irreversibility related to the combustion chamber decreases from 29.8% of the injected fuel exergy to 25.5%. This work demonstrates that multidimensional modeling can be used to simulate the effect of various EGR mass fractions and gain more insight into the impact of flow field on combustion process in IDI engines from the second law perspective.