Coupled hydroelastic vibrations of an elliptical cylindrical tank with an elastic bottom

An exact three-dimensional analysis based on the linear potential theory and the elaborated method of eigenfunction expansion in elliptic coordinates are presented to study the free coupled elasto-hyrodynamic characteristics of an upright non-deformable cylindrical container of elliptical planform with a flexible bottom plate, filled to an arbitrary depth with an inviscid incompressible liquid. Extensive numerical data are presented in an orderly fashion for the first few symmetric/anti-symmetric coupled hydroelastic natural frequencies as a function of fluid depth parameter for two plate aspect ratios. Also, selected hydrodynamic and structural deformation modes shapes are presented in graphical form. The effects of liquid level, bottom plate elasticity, and cross sectional aspect ratio on the sloshing frequencies and hydrodynamic pressure modes are examined. The validity of the results is examined through computations using a commercial finite element package as well as by comparison with the data available in literature.     

Microstructural and mechanical assessment of transient liquid phase bonded commercially pure titanium

Diffusion joining of commercially pure titanium was successfully prepared via transient liquid phase bonding in vacuum environment. The process was carried out using AMS 4772 silver-based filler alloy at 900–1000°C for various holding time under the vacuum of 6?×?10^?7?Torr. Optical and scanning electron microscopy equipped with an EDS analyzer was conducted for microstructural evaluations. Mechanical properties were also investigated by shear test, fractographic assessment and X-ray diffraction analyses. The tendency to achieve isothermally solidified joint increased by increasing bonding time. No sign of athermal solidification was detected of sample bonded at 1000°C for 90?min. Consequently, the bonding condition of a high quality joint was obtained. Elemental analyses revealed that filler alloy’s elements (Ag, Cu) distributed more uniformly in fully isothermal solidified bond, whereas the aggregation of these elements is considerable in athermally solidified bond. Shear test results represented that the highest shear strength attributed to the sample bonded in isothermal solidified condition (bonded at 1000°C for 90?min).     

Production planning: a DEA-based approach

In organizations with a centralized decision making environment, production usually involves the participation of more than one individual unit, each contributing in part to the total production. The planning problem involves determining the number of products to be produced by all individual units in the next season when demand changes can be forecasted. This paper introduces a data envelopment analysis approach to making future production plans in a centralized decision making environment when demand changes can be forecasted in the next production season. The approach proposed in this paper takes the size of operational units into account so that the planned production for each unit becomes proportionate to the ability of the units. A real world data set is used to illustrate the applicability of the approach.     

Comparison of optical properties between ladder and lambda-type EIT medium with Er3+ ion concentration in Er3+:YAG crystal

The effect of Er³⁺ doped ion concentration on optical properties of two type three-level schemes in 35 nm Er³⁺:YAG (yttrium aluminum garnet) crystal is studied. It is found that intensity threshold of optical bistability and multistability can be changed by Er³⁺ doped ion concentration. Moreover, switching from optical multistability to optical bistability can be done differently by Er³⁺ concentration in two types of three-level schemes. The steady-state and transient behaviors of absorption, dispersion and group index of weak probe field in two schemes are also discussed. In this study, we will report an initial study on optical properties in Er³⁺:YAG crystal and propose a basis for selecting the suitable concentration to carry out experimental investigations in the future.     

Influence of case hardening on wear resistance of a sintered low alloy steel

PM technique has been applied for some products in the autoindustries due to unique functions and cost saving. The wear resistance of PM steel parts is one of the most significant surface properties. Nitriding and carburizing processes consist of exposing metallic materials to nitrogen and carbon to improve their surface hardness and wear resistance. In this research, the partially diffusion prealloyed powders, Ultrapac LE, containing Fe-4Ni-1.5Cu-0.5Mo with 0.2% graphite and two different densities were sintered at 1120 °C for 30 min. Depending on the applied pressures during cold pressing, two different porosities of 14.11 and 10.26 vol.% were obtained. Some specimens were carburized and some others were nitrided in cyanate liquid salt bath. The pin-on-disc wear test and hardness test were used to evaluate the surface behavior of specimens. The results showed that the wear resistance increased by nitriding and carburizing processes and the effect of nitriding is more than carburizing on wear resistance. In the case of materials studied, except for 4 h nitrided specimens, other specimens with higher porosity level showed better wear resistance. In these specimens, large pores entrapped the wear debris and created a densified layer. It prevented the formation of large abrasive agglomerates. For the carburized specimens, wear mechanisms were affected by the brittle fracture caused by abrasive wear. So, wear resistance did not increase significantly. In this investigation, abrasive, plastic deformation and oxidation wear were observed as wear mechanisms.     

An investigation on the sensitivity analysis of the parameters of proposed wax precipitation model

Reservoir hydrocarbon fluids contain heavy paraffins that may form solid phase of wax at low temperatures. Formation of solid phases is highly unwanted in oil production assemblies, pipelines and in process equipments. A predictive technique is crucial to the solution of wax formation to alleviate this problem.The effect of different parameters to predict the conditions under which wax precipitation takes place using the proposed model of Sahand University of Technology and other models has been investigated. The proposed model uses regular solution theory to describe solid phase (wax) non-ideality and the liquid and gas phases are being described by an equation of state.In order to evaluate the reliability of the proposed model, wax appearance temperatures (WAT's) were calculated for several mixtures at different compositions and compared with different models. The proposed model predictions had very good agreement with experimental data over a wide range of compositional distributions in comparison with other models. Solid wax content was also calculated at different temperatures below WAT in several synthetic systems made up of a solvent (decane) and a paraffinic heavy fraction. The results of calculating the amount of wax precipitation showed very good agreement with experimental data. Effect of different parameters including fusion temperature (T^f), Enthalpy of fusion (Δh^f), solubility parameter (δ^S), and binary interaction parameters (BIP) in predicting the WAT and the amount of wax precipitated for different oil mixtures have been evaluated using the proposed model and compared with other models. The results showed that the T^f is the most sensitive parameter while δ^S shows the least sensitivity in matching the WAT. Even though using Δh^f could provide the same results as tuning T^f, but the required changes are much higher and sometimes not practical. Also using BIP as the tuning parameter, requires a fairly large coefficient that makes it unsuitable to be considered as the tuning parameter.