Mustafa Taşkin

Purpose: The purpose of this paper is to parametrically investigate the vibration and damping characteristics of a functionally graded (FG) inhomogeneous and porous curved sandwich beam with a frequency-dependent viscoelastic core. Design/methodology/approach: The FG material properties in this study are assumed to vary through the beam thickness by power law distribution. Additionally, FG layers have porosities, which are analyzed individually in terms of even and uneven distributions. First, the equations of motion for the free vibration of the FG curved sandwich beam were derived by Hamilton's principle. Then, the generalized differential quadrature method (GDQM) was used to solve the resulting equations in the frequency domain. Validation of the proposed FG curved beam model and the reliability of the GDQ solution was provided via comparison with the results that already exist in the literature. Findings: A series of studies are carried out to understand the effects on the natural frequencies and modal loss factors of system parameters, i.e. beam thickness, porosity distribution, power law exponent and curvature on the vibration characteristics of an FG curved sandwich beam with a ten-parameter fractional derivative viscoelastic core material model. Originality/value: This paper focuses on the vibration and damping characteristics of FG inhomogeneous and porous curved sandwich beam with frequency dependent viscoelastic core by GDQM – for the first time, to the best of the authors' knowledge. Moreover, it serves as a reference for future studies, especially as it shows that the effect of porosity distribution on the modal loss factor needs further investigation. GDQM can be useful in dynamic analysis of sandwich structures used in aerospace, automobile, marine and civil engineering applications.

Underwater explosions are tremendously hazardous for floating structures and human life inside. When compared to an air blast, an underwater blast is more effective due to the effect of the fluid domain. Therefore, the design of marine structures with high strength to underwater explosions is a difficult subject as well as important. With the rapid progression of material technology, composite materials are widely preferred over metals in fields of marine and defense industries due to low density, high elasticity and high strength in their nature. In this study, a sandwich panel with a soft-core was modelled using the finite element method, and the dynamic behavior of the panel subjected to an underwater blast load is investigated. In the validation study of the model and method, firstly, the dynamic responses of the carbon epoxy composite plate structure subjected to underwater explosion load were confirmed with the results available in the literature. In this part, ALE (Arbitrary Lagrangian-Eulerian) and Load_SSA (Sub Sea Analysis) methods were used to simulate the dynamic response of the plate and a very good agreement was observed by using the ALE method. Then, the composite sandwich panels with a soft-core (foam) were investigated by the finite element-based ALE method. Finally, the maximum deflection results of the plate structure subjected to underwater explosion loads were examined with parametric studies. Increasing core layer thickness caused a decrease in plate deflections and an increase in post-explosion oscillation frequency under the same blast conditions.

The goal of this study is to develop a computational fluid dynamics (CFD) modeling approach to better estimate the blood flow dynamics in the bundles of the hollow fiber membrane based medical devices (i.e., blood oxygenators, artificial lungs, and hemodialyzers). Three representative types of arrays, square, diagonal, and random with the porosity value of 0.55, were studied. In addition, a 3D array with the same porosity was studied. The flow fields between the individual fibers in these arrays at selected Reynolds numbers (Re) were simulated with CFD modeling. Hemolysis is not significant in the fiber bundles but the platelet activation may be essential. For each type of array, the average wall shear stress is linearly proportional to the Re. For the same Re but different arrays, the average wall shear stress also exhibits a linear dependency on the pressure difference across arrays, while Darcy's law prescribes a power-law relationship, therefore, underestimating the shear stress level. For the same Re, the average wall shear stress of the diagonal array is approximately 3.1, 1.8, and 2.0 times larger than that of the square, random, and 3D arrays, respectively. A coefficient C is suggested to correlate the CFD predicted data with the analytical solution, and C is 1.16, 1.51, and 2.05 for the square, random, and diagonal arrays in this paper, respectively. It is worth noting that C is strongly dependent on the array geometrical properties, whereas it is weakly dependent on the flow field. Additionally, the 3D fiber bundle simulation results show that the three-dimensional effect is not negligible. Specifically, velocity and shear stress distribution can vary significantly along the fiber axial direction.