Masoud Arabghahestani

In this paper, transverse vibration analysis of rotating micro-beam is investigated based on the modified couple stress theory. The simply-supported micro-beam is modeled utilizing Euler-Bernoulli and Timoshenko beam theories. The system is rotating around a fixed axis perpendicular to the axial direction of the beam. For the first time, displacement filed is introduced as a coupled field to the translational field. In other words, the mentioned rotational displacement field is expressed as a proportional function of translational displacement field using first (axial), second (lateral), and third (angular or rotational) velocity factors. Utilizing Hamilton’s approach as a variational method, dynamic-vibration equations of motion of the proposed model are derived. Galerkin’s method is adopted to solve the equation corresponding to the Euler–Bernoulli and Timoshenko beams. For the case considering shear deformation effects, Navier method is chosen. For evaluation of current results and models, they are compared with those available at the benchmark. In this paper; effects of slenderness ratio, axial, lateral, and angular velocity factors, and rotations of the beam on the frequency are reported. Based on the results presented, mentioned factors should be counted in the analysis and design of such rotating micro-systems.

In this work non-equilibrium molecular dynamics (MD) simulations were performed to investigate the liquid argon flow passing a stationary carbon nanotube and to estimate kinetic energy of the flow and flow forces exerted on the nanotube. Effects of different factors were also investigated. CFD simulations of flow around a circular cylinder were also performed to compare the results with those of MD around the carbon nanotube. In molecular dynamics simulation, the fluid forces on the body are calculated directly from the summation of the molecular forces exerted on solid atoms by fluid atoms. In this work, this method is used to investigate the effects of different flow parameters such as flow velocity, flow temperature on the flow behavior over the carbon nanotube, atom positioning around the nanotube and forces exerted on it. The simulation is 3D, and the computational domain consists of a maximum of 33,700 liquid argon atoms as the fluid and 240 atoms of carbon which represent the solid nanotube. A single-walled carbon nanotube is simulated as a rigid body of fixed carbon atoms, and both argon-argon and argon-carbon interactions are modeled by the standard Lennard-Jonnes potential function. Flow is driven by rescaling fluid particles velocities at the inlet region with a length of 3% of the domain length in that direction every 50-time steps. Based on the information given, a parallel code was developed, and investigations have been conducted using this code. Results show that among all the parameters which were investigated in this paper, the flow velocity has the most significant effects on the exerted forces and kinetic energy on the carbon nanotube and the drag force is increased with an increment of the flow inlet velocity in all cases. Lift fluctuates around zero in all cases of the stationary carbon nanotube. Inlet flow velocities and temperatures have also changed atoms positioning in the vicinity of the nanotube and so atomic density in the nearby bins which is used to further clarify the difference in the drag force.

Recently, remarkable developments have taken place, leading to significant improvements in microfluidic methods to capture subtle biological effects down to single cells. As microfluidic devices are getting sophisticated, design optimization through experimentations is becoming more challenging. As a result, numerical simulations have contributed to this trend by offering a better understanding of cellular microenvironments hydrodynamics and optimizing the functionality of the current/emerging designs. The need for new marketable designs with advantageous hydrodynamics invokes easier access to efficient as well as time-conservative numerical simulations to provide screening over cellular microenvironments, and to emulate physiological conditions with high accuracy. Therefore, an excerpt overview on how each numerical methodology and associated handling software works, and how they differ in handling underlying hydrodynamic of lab-on-chip microfluidic is crucial. These numerical means rely on molecular and continuum levels of numerical simulations. The current review aims to serve as a guideline for researchers in this area by presenting a comprehensive characterization of various relevant simulation techniques.

In this study, we evaluated the fundamental physical behavior during droplet formation and flow from a rotary bell spray in the absence of an electrostatic field. The impact of a wide range of operating parameters of the rotary bell sprayer, such as flow rates, rotational speeds, and spatial positioning, on droplet sizes and size distributions using a three-dimensional (3-D) mapping was studied. The results showed that increasing the rotational speed caused the Sauter mean diameter of the droplets to decrease while increasing flow rate increased the droplet sizes. The rotational speed effect, however, was dominant compared to the effect of flow rate. An increase in droplet size radially away from the cup was noted in the vicinity of the cup, nevertheless, as the lateral distances from the cup and rotational speed were increased, the droplet sizes within the flow field became more uniform. This result is of importance for painting industries, which are looking for optimal target distances for uniform painting appearance. Furthermore, the theoretical formulation was validated with experimental data, which provides a wider range of applicability in terms of environment and parameters that could be tested. This work also provides an abundance of measurements, which can serve as a database for the validation of future droplet disintegration simulations.