Sharif Digital Repository

Paramecium or other ciliates have the potential to be utilized for minimally invasive surgery systems, making internal body organs accessible. Paramecium shows interesting responses to changes in the concentration of specific ions such as K+, Mg2+, and Ca2+ in the ambient fluid. Some specific responses are observed as, changes in beat pattern of cilia and swimming toward or apart from the ion source. Therefore developing a model for chemotactic motility of small organisms is necessary in order to control the directional movements of these microorganisms before testing them. In this article, we have developed a numerical model, investigating the effects of Ca2+ on swimming trajectory of... 

In this paper, hydrodynamic simulation of fish-like swimming for two types of aquatic animals including tuna fish and giant danio is presented. We employ an unsteady three-dimensional inviscid boundary element method including time stepping algorithm to capture the wake sheet and flow features around swimming fish in a straight course. At each time step, an unsteady Bernoulli equation was used to find the pressure distribution and thrust generated by the animal. To couple fluid solver with kinematic equations of flexible body, undulating motions of backbone were defined using a prescribed continuous function. Although the flexible motion mechanism controls the fish swimming but no structural... 

Swimming microrobots have a variety of applications including drug delivery, sensing, and artificial fertilization. Their small size makes onboard actuation very hard, and therefore an external source such as the magnetic field is a practical way to steer and move the robot. In this paper, we have designed a novel microrobot steered by magnetic paddles. We have also discussed design parameters where, based on the conducted simulation, the robot speed reaches 520 um/s. It is shown that the microrobot speed depends on the robot paddle dimensions. According to the microrobots motion characteristics and their different reactions to the same input, we have designed a steering strategy for... 

Experimental hydrodynamics imaging of four Pangasius sanitwongsei were considered. A quantitative characterization of caudal fin is presented in this article. Steady swimming of four P. sanitwongsei with different total length was studied experimentally and taped by high-speed digital video, and undulatory movement of each fish at different velocity was revealed. The pattern of body undulatory movement of the fish was drawn from the video images. Three main factors that determine the fish swimming behavior are Reynolds number, Strouhal number and shape. In this study, Lf/L was chosen as a characteristic of shape, where Lf was the distance from the start of the head to the end of the head.... 

In recent years, a number of patents have been devoted to designing micro robots for minimally invasive therapies inspired by Paramecium. Paramecium changes its swimming direction due to application of an external magnetic or electric field. Changing ciliary beat direction and frequency have been identified as possible methods for maneuvering through water; however, effects of variations in ciliary spacing on swimming trajectory have been poorly studied. In this work, it is aimed to analyze the effects of adjusting the ciliary spacing on swimming trajectory. For determining the swimming trajectory, Paramecium membrane is discretized to boundary elements with length of 15μm on which there are... 

Efficient mixing, typically characterised by chaotic advection, is hard to achieve in low Reynolds number conditions because of the linear nature of the Stokes equation that governs the motion. Here we show that low Reynolds number swimmers moving in quasi-periodic orbits can result in considerable stretching and folding of fluid elements. We accurately follow packets of tracers within the fluid domain and show that their trajectories become chaotic as the swimmer's trajectory densely fills its invariant torus. The mixing process is demonstrated in two dimensions using the Quadroar swimmer that autonomously propels and tumbles along quasi-periodic orbits with multi-loop turning trajectories.... 

In certain types of biomimetic surgery systems, micro robots inspired by Paramecium are designed to swim in a capillary tube for gaining access to internal organs with minimal invasion. Gaining insight into the mechanics of Paramecium swimming in a capillary tube is vital for optimizing the design of such systems. There are two approaches to modeling the physics of micro swimming. In the envelope approach, which is widely accepted by researchers, Paramecium is approximated as a sphere, self-propelled by tangential and normal surface distortions. However, not only is this approach incapable of considering the specific geometry of Paramecium, but it also neglects short range hydrodynamic... 

Aims Previous reports on the possible effects of Extremely Low Frequency Magnetic Fields (ELF MF) on mood have been paradoxical in different settings while no study has yet been conducted on animal behavior. In addition, it was shown that ELF MF exposure makes an increase in brain nitric oxide level. Therefore, in the current study, we aimed to assess the possible effect(s) of ELF MF exposure on mice Forced Swimming Test (FST) and evaluate the probable role of the increased level of nitric oxide in the observed behavior. Main methods Male adult mice NMRI were recruited to investigate the short term and long term ELF MF exposure (0.5 mT and 50 Hz, single 2 h and 2 weeks 2 h a day). Locomotor... 

Microrobots with their promising applications are attracting a lot of attention currently. A microrobot with a triangular mechanism was previously proposed by scientists to overcome the motion limitations in a low-Reynolds number flow; however, the control of this swimmer for performing desired manoeuvres has not been studied yet. Here, we have proposed some strategies for controlling its position. Considering the constraints on arm lengths, we proposed an optimal controller based on quadratic programming. The simulation results demonstrate that the proposed optimal controller can steer the microrobot along the desired trajectory as well as minimize fluctuations of the actuators length. ©... 

Manta ray swimming or bio-inspiration propulsion system, as a special type of marine propulsion system, is used for submersible vehicles that require high-speed maneuverability and stability, such as glider and AUV. In a manta ray swimming, the thrust force is generated by a couple of undulation and oscillation of wing, so that the direction of undulation wave and oscillation is upright and perpendicular to the direction of thrust force, respectively. It is possible to combine these two movement modes (flapping motion) on the three-dimensional model without considering the effects of wing twisting and flexibility to simplify and better understand the physical behaviors or special study of... 

It has always been a human challenge to inspire natural configurations and phenomena and benefit from their merits in improving the performances of man-made proposed aero/hydro vehicles. For example, the manta rays are known for their great swimming performances. To design and fabricate an underwater robot based on the manta ray geometry and its kinematic characteristics, it is important to initially study its hydrodynamic behavior and possibly arrive at some key design parameters, which can remarkably help to figure out an optimum geometry with high swimming performances. The main objective of this study is to focus on the merits of gliding motion inspired by the manta ray fish considering... 

Although medical advancements have successfully helped a lot of couples with their infertility by assisted reproductive technologies (ART), sperm selection, a crucial stage in ART, has remained challenging. Therefore, we aimed to investigate novel sperm separation methods, specifically microfluidic systems, as they do sperm selection based on sperm and/or the female reproductive tract (FRT) features without inflicting any damage to the selected sperm during the process. In this review, after an exhaustive studying of FRT features, which can implement by microfluidics devices, the focus was centered on sperm selection and investigation devices. During this study, we tried not to only point to...