Influence of Hip Joint Flexion Angle on the Submerged Dolphin Kick Stroke Based on Numerical Simulation of Multi-Body Motion / 医用生物力学

Objective To explore characteristics of flow field around the athletes, change of net flow force, and influences of hip flexion angles at the end of extension kick on the submerged dolphin kick stroke. Methods The body shape data of a swimmer were obtained by three-dimensional (3D) scanning, and the data were reversely reconstructed to obtain the swimmer model. The joints of the swimmer model were separated, and each segment of the athlete was divided into independent rigid body, and simulation of the submerged dolphin kick stroke was realized by controlling movement of each independent rigid body. The computational fluid dynamics (CFD) software package ANSYS Fluent was used as the solver for calculation and solution. Results The vortex structures were shed off from the surface of the swimmer’s body in the area with a large velocity gradient in flow field, and the shedding of vortex structures was different at the stage of extension kick and flexion kick. Propulsion was mainly generated during extension kick phase. At the end of extension kick, the drag decreased as the hip flexion angle increased from 20° to 30°. Conclusions To some extent, increasing flexion angle of the hip joint at the end of extension kick will reduce the drag force and increase the swimming speed in process of the submerged dolphin kick stroke.

Mechanical characteristics of the spirochete flagella in 2D micro-periplasmic space / 医用生物力学

Objective To investigate mechanical characteristics of the spirochete flagella with tight-fitting ribbon configuration in micro-periplasmic space. Methods The 2D model of two parallel plates was used to simplify the periplasmic space, and the effects of flagellum spacing and eccentricity on force and torque acted on the spirochete flagella, and wall shear stress acted on the spirochete protoplasmic cylinder were studied by using numerical simulation method. Results (1) The relationship between the flagellum horizontal force and eccentricity was presented as a parabolic curve, and the peak value of the flagellum horizontal force was mainly caused by the gradual increase of pressure difference at two sides of the cylinder and the resistance viscous force as well. Flagellum spacing had no significant influence on flagellum horizontal force. (2) The relationship between the flagellum torque and eccentricity was presented as an exponential curve, and smaller flagella spacing would cause bigger flagella torque. (3) Flagellum spacing had no significant effect on wall shear stress of the protoplasmic cylinder, but it would be increased with the number of flagella and the eccentricity increasing. Conclusions Numerical simulation results in this study can qualitatively reflect mechanical characteristics of the spirochete flagella, and also provide references for further understanding the morphology of spirochete as well as its kinematic mechanism and pathogenic characteristics.

Preliminary observation on the interstitial fluid pressure of low hydraulic resistance channel along meridians / 医用生物力学

Objective To measure the interstitial fluid pressure (IFP) on low hydraulic resistance channel along meridians and observe the difference and fluctuation. Method Low hydraulic resistance points (LHRP) and non LHRP were measured on anesthetized mini pigs by a scanning hydraulic resistance measuring device. The IFP was then measured by wick in needle method on these two regions. Results The stomach meridian, kidney meridian and conceptual vessel meridian on mini pigs were measured. The IFP were significantly lower than non LHRP region on the above three meridians(P<0.05), the differences of which were 1.06，0.70，3.69 mmHg respectively with the total pressure difference of 1.44 mmHg and pressure gradient of 1.44~2.88 mmHg/cm（1 mmHg=0．133 kPa）. Conclusions Among the peripheral subcutaneous tissues, there exists a difference of IFP toward the meridian which may drive the flow of interstitial fluid toward the meridians.

Conceitos de física básica que todo cirurgião cardiovascular deve saber: parte I: mecânica dos fluídos / Concepts of basic physics that every cardiovascular surgeon should know: part I: mechanics of fluids

A atividade profissional que o cirurgião cardiovascular executa é muito mais do que um simples gesto mecanizado de operar um coração doente. Há em cada ato do intraoperatório mais noções de fisiologia e física do que geralmente nos damos conta. O presente trabalho discorre, à luz da matemática, acerca da dinâmica dos fluídos, ou seja, do sangue, com enfoque nas medidas invasivas de pressão arterial, do efeito do diâmetro do vaso sobre sua resistência interna e do fluxo que passa por ele, na conversão de diversas unidades de medidas de pressão e resistência, viscosidade sanguínea e suas relações no vaso, hemodiluição, diferenças de fluxo laminar e turbulento, velocidade e pressão do sangue e a tensão da parede após uma estenose e a origem do aneurisma pós-estenótico. O objetivo do trabalho não é de habilitar o leitor no conhecimento da física, mas apresentá-la como ferramenta útil na explicação de fenômenos conhecidos na rotina do cirurgião cardiovascular.

The professional activity that the cardiovascular surgeon performs is much more than a simple gesture to mechanically operate the patient's heart. There is in every act of intraoperative most notions of physiology and physics than we generally realize. This paper discusses, in the light of mathematics, on the dynamics of fluids, ie blood, focused on invasive measurements of blood pressure, the effect of vessel size on its internal resistance and the flow passing through it in conversion of various units of measurements of pressure and resistance, blood viscosity and its relationship to the vessel, hemodilution, differences in laminar and turbulent flow, velocity and blood pressure and wall tension after a stenosis and the origin of poststenotic aneurysm. This study is not to enable the reader to the knowledge of all physics, but to show it as a useful tool in explaining phenomena known in the routine of cardiovascular surgery.

A simple model to describe dimple dynamics / Un modelo sencillo para la descripción de la dinámica de un dimple / Um modelo simples para a descrição da dinâmica de um dimple

A model based on the hydrodynamics equations that allows to describe the dynamics of a dimple, once it has formed, is proposed. The Navier-Stokes equations are considered, and two fundamental approaches are used to simplify the mathematical treatment of the hydrodynamics equations. Certain conditions are considered that must be fulfilled at the interface, which serve to close the system of differential equations and lead to an evolution equation that describes the interfacial film dynamics. With the intention of solving this equation, the method of finite differences has been used.

Se propone un modelo que permite la descripción de la dinámica de una depresión superficial (dimple) una vez que se ha formado. Las ecuaciones de Navier-Stokes son consideradas, y dos enfoques fundamentales son utilizados para simplificar el tratamiento matemático de las ecuaciones hidrodinámicas. Se consideraron ciertas condiciones que deben cumplirse en la interfase, las cuales sirven para completar el sistema de ecuaciones diferenciales y llevan a una ecuación de evolución que describe la dinámica de la película interfacial. A fin de resolver la ecuación se utilizó el método de diferencias finitas.

Propõe-se um modelo que permite a descrição da dinâmica de uma depressão superficial (dimple) após ter se formado. As equações de Navier-Stokes são consideradas, e dois enfoques fundamentais são utilizados para simplificar o tratamento matemático das equações hidrodinâmicas. Consideraram-se certas condições que devem cumprir-se na interfase, as quais servem para completar o sistema de equações diferenciais e conduzem a uma equação de evolução que descreve a dinâmica da película interfacial. A fim de resolver a equação se utilizou o método de diferenças finitas.

Film drainage between two drops: Vortex formation in thin liquid films / Drenaje de la película interfacial entre dos gotas: Formación de vórtices en películas líquidas delgadas / Drenagem da película interfacial entre duas gotas: Formação de vórtices em películas líquidas delgadas

In this study, a mathematical formalism that takes into account the surfactant effect on the drainage of the interfacial film between two drops is considered. The effects of thermal perturbations and van der Waals forces are neglected. In the mathematical formalism the Navier-Stokes equations within the lubrication approximation are coupled to a diffusion-convection equation leading to an evolution equation for the interfacial film. This last equation is solved by using the numerical method of lines coupled with an implicit Runge-Kutta method for the integration with respect to time. As a result of the inclusion of interfacial tension gradients a non oscillating dimple arises, even beginning with an initial condition corresponding to a plane interfacial film.

En este estudio se desarrolla un formalismo matemático que toma en consideración el papel del surfactante en el drenaje de la película interfacial entre dos gotas. No se consideran los efectos de perturbaciones térmicas y fuerzas de van der Waals. En el formalismo matemático se acoplan las ecuaciones de Navier-Stokes (dentro de la aproximación de lubricación) con la ecuación de difusión-convección, lo cual conduce a una ecuación de evolución para la película interfacial. Esta última ecuación es resuelta utilizando el método numérico de líneas junto con un método implícito de Runge-Kutta para la integración con respecto al tiempo. Como resultado de la inclusión de los gradientes de tensión interfacial surge una depresión superficial (dimple) no oscilatoria, inclusive comenzando con una condición inicial correspondiente a una película interfacial plana.

Neste estudo se considera um formalismo matemático que toma em consideração o efeito surfactante na drenagem da película interfacial entre duas gotas. Não se consideram os efeitos de perturbações térmicas e forças de van der Waals. No formalismo matemático as equações de Navier-Stokes dentro da aproximação de lubrificação se acoplam a uma equação de difusão-convecção, o qual leva a uma equação de evolução para a película interfacial. Esta última equação é resolvida utilizando o método numérico de linhas junto com um método implícito de Runge-Kutta para a integração relativa ao tempo. Como resultado da inclusão de gradientes de tensão interfacial surge uma depresão superficial (dimple) não oscilatoria, inclusive começando com uma condição inicial correspondente a uma película interfacial plana.