There are many marine animals that employ a form of jet propulsion to move through the water, often creating the jets by expanding and collapsing internal fluid cavities. Due to the unsteady nature of this form of locomotion and complex body/nozzle geometries, standard modeling techniques prove insufficient at capturing internal pressure dynamics, and hence swimming forces. This issue has been resolved with a novel technique for predicting the pressure inside deformable jet producing cavities (M. Krieg and K. Mohseni, J. Fluid Mech., 769, 2015), which is derived from evolution of the surrounding fluid circulation. However, this model was only validated for an engineered jet thruster with simple geometry and relatively high Reynolds number (Re) jets. The purpose of this manuscript is twofold: (i) to demonstrate how the circulation based pressure model can be used to analyze different animal body motions as they relate to propulsive output, for multiple species of jetting animals, (ii) and to quantitatively validate the pressure modeling for biological jetting organisms (typically characterized by complicated cavity geometry and low/intermediate Re flows). Using jellyfish (Sarsia tubulosa) as an example, we show that the pressure model is insensitive to complex cavity geometry, and can be applied to lower Re swimming. By breaking down the swimming behavior of the jellyfish, as well as that of squid and dragonfly larvae, according to circulation generating mechanisms, we demonstrate that the body motions of Sarsia tubulosa are optimized for acceleration at the beginning of pulsation as a survival response. Whereas towards the end of jetting, the velar morphology is adjusted to decrease the energetic cost. Similarly, we show that mantle collapse rates in squid maximize propulsive efficiency. Finally, we observe that the hindgut geometry of dragonfly larvae minimizes the work required to refill the cavity. Date Received: 10-18-2019, Date Accepted: 99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822.

中文翻译：

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喷射动物的瞬态压力建模。

有许多海洋动物采用喷射推进的形式在水中移动，通常通过扩大和收缩内部流体腔来产生喷射。由于这种运动形式的不稳定性质和复杂的主体/喷嘴几何形状，标准建模技术证明不足以捕捉内部压力动态，从而捕捉游泳力。这个问题已通过预测可变形射流产生腔内压力的新技术得到解决（M. Krieg 和 K. Mohseni, J. Fluid Mech., 769, 2015），该技术源自周围流体循环的演变。然而，该模型仅针对具有简单几何形状和相对较高雷诺数 (Re) 喷气机的工程喷射推进器进行了验证。这份手稿的目的有两个：(i) 演示如何使用基于循环的压力模型来分析与推进输出相关的不同动物身体运动，对于多种喷射动物，(ii) 并定量验证生物喷射生物（通常是以复杂的腔几何形状和低/中 Re 流为特征）。以水母 (Sarsia tubulosa) 为例，我们表明压力模型对复杂的腔几何结构不敏感，可应用于低 Re 游泳。通过分解水母以及鱿鱼和蜻蜓幼虫的游泳行为，根据循环产生机制，我们证明了管状袋鼠的身体运动针对脉动开始时的加速进行了优化，作为一种生存反应。而在喷射快结束时，会调整软膜形态以降低能量消耗。同样，我们表明鱿鱼的地幔坍塌率使推进效率最大化。最后，我们观察到蜻蜓幼虫的后肠几何形状最大限度地减少了重新填充腔所需的工作。收到日期：10-18-2019，接受日期：99-99-9999 *kriegmw@hawaii.edu, UHM Ocean and Res Eng, 2540 Dole St, Honolulu, HI 96822。