A numerical study of the effects of bell pulsation dynamics and oral arms on the exchange currents generated by the upside-down jellyfish Cassiopea xamachana

Abstract

SUMMARYMathematical and experimental studies of the flows generated by jellyfish have focused primarily on mechanisms of swimming. More recent work has also considered the fluid dynamics of feeding from currents generated during swimming. Here we capitalize on the benthic lifestyle of the upside-down jellyfish (Cassiopea xamachana) to explore the fluid dynamics of feeding uncoupled from swimming. A two-dimensional mathematical model is developed to capture the fundamental characteristics of the motion of the unique concave bell shape. Given the prominence of the oral arms, this structure is included and modeled as a porous layer that perturbs the flow generated by bell contractions. The immersed boundary method is used to solve the fluid-structure interaction problem. Velocity fields obtained from live organisms using digital particle image velocimetry were used to validate the numerical simulations. Parameter sweeps were used to numerically explore the effects of changes in pulse dynamics and the properties of the oral arms independently. Numerical experiments allow the opportunity to examine physical effects and limits within and beyond the biologically relevant range to develop a better understanding of the system. The presence of the prominent oral arm structures in the field of flow increased the flux of new fluid from along the substrate to the bell. The numerical simulations also showed that the presence of pauses between bell expansion and the next contraction alters the flow of the fluid over the bell and through the oral arms. Supplementary material available online at

Reconfiguration and the reduction of vortex-induced vibrations in broad leaves

“…The immersed boundary method has been used successfully to model a variety of problems in fluid dynamics where the interactions between an incompressible viscous fluid and a deformable elastic boundary are significant. Some examples of biological problems that have been studied with the immersed boundary method include lamprey swimming (Tytell et al, 2010), jellyfish feeding (Hamlet et al, 2011), flow-through heart valves (Griffith et al, 2009) and ciliary-driven flows (Grünbaum et al, 1998). In the immersed boundary framework, the Navier-Stokes equations (Eqn4) are solved on a fixed Cartesian grid.…”

Bases morfo-funcionais da alimentação e o papel trófico de iLychnorhiza lucerna (Scyphozoa, Rhizostomeae)

“…9). The utility of bell pulsations as a particle transfer mechanism in ephyrae is thus very limited, since vortices of bell pulsations quickly dissipate after leaving bell margin (Hamlet et al 2011). As medusae grow, dissipation of vortices takes longer and vortices become increasingly important to fluids transport toward oral arms.…”

“…translates through the oral arms (Hamlet et al 2011;Santhanakrishman et al 2012). The position of the millimeter scale mouthlets also changes among species of Rhizostomeae.…”

“…Embora tenha se atribuído um papel relevante dos movimentos natatórios na produção de correntes alimentares em éfiras Gordoa et al, 2014), os baixos números de Reynolds (Re<100) em seu ambiente fluido viscoso sugerem que o transporte de fluidos (e presas) seja pouco eficiente neste estágio. Éfiras não criam vórtices circulatórios através das pulsações da umbrela (Feitl et al, 2009), e quando o fazem os mesmos são rapidamente dissipados em indivíduos juvenis (Hamlet et al, 2011). O uso da técnica da velocimetria por imagem de partículas no presente trabalho demonstrou que toda a aceleração dos fluidos gerada pela pulsação umbrelar é rapidamente dissipada em éfiras (6 mm de diâmetro umbrelar) sendo ineficiente para o transporte de presas para suas superfícies distais nos braços orais.…”

“…Tais diferenças afetam o modo de interação entre os vórtices produzidos pelas pulsações umbrelares e os braços orais, portanto afetando o modo pelo qual presas são retidas. Em Cassiopea sp., que possui braços orais de maior projeção lateral em relação ao eixo de simetria, todo o vórtice adentra os braços orais (Hamlet et al 2011;Santhanakrishman et al 2012 ii-peneiramento, em que o fluido que adentra o centro do braço oral pela região proximal, tanto durante a expansão quanto durante a contração da umbrela, flui em direção ao exterior e as presas maiores do que os poros filtradores são retidas.…”