Biomechanics Analyses and Application of Freshwater Snails Sinotaia quadrata, Semisulcospira libertina, and Thiara granifera for Channel Ecological Engineering Design

淡水螺是台灣水質的重要生物指標，同時也是螢火蟲的主要食物來源。對於水中生物而言，水流可以增加營養物質的傳輸與新陳代謝，但是同時也會施加應力在生物體上。生物力學可以幫助我們瞭解及量化生物體與其物理環境間的交互關係。本研究中將針對石田螺、川蜷與瘤蜷的型態、阻力、升力、吸附力與衝落流速進行量測。根據所量測的結果，求得流體力學、形態與機械特性的關係。 由本實驗的結果可以發現在高流速下流線型的螺殼將可以減少阻力與昇力，流線型的螺殼型態使得瘤蜷在減少水中應力上表現較川蜷與石田螺佳。理論上，瘤蜷應較川蜷與石田螺更能抵擋水流的沖落，但是衝落實驗的結果並非如此，衝落瘤蜷所需的流速最低(67cm/s)，石田螺次之(72cm/s)，衝落川蜷所需流速最高(107cm/s)。實驗所得的衝落流速與由衝落模式計算所得的結果是相符合的。經過衝落模式的分析可以將淡水螺的沖落機制分成兩個部分：衝落機制，包括阻力、升力與浮力；及抵抗衝落機制，包括吸附力與重力。總而言之，水流作用力主要是由螺殼的型態所決定，吸附力則可減緩水流直接的作用力，而衝落流速則是由水流作用力與生物力的交互作用下而決定。石田螺擁有最強的吸附力，但最差的螺殼型態；瘤蜷則擁有最佳的螺殼型態，但最弱的吸附力；瘤蜷則在這兩方面擁有均衡的能力。川蜷抵抗阻力的機制，包含流線型螺殼型態、方位角與攻角的改變與富有彈性的肌肉。 生物力學上分析所得的結果可提供渠道生態工法設計上的參考依據。設計流速可以由衝落累積機率函數的平均值與標準差求得，以保育原生螺類或控制有害螺類。設計流速可由渠道的坡度、底質的粗糙度與渠道斷面所決定，其中底質的粗糙度亦同時會影響到螺的吸附力。Freshwater snails are important biological indicators of water quality and the primary source of sustenance for firefly larvae in Taiwan. Currents may promote the transport of nutrients and the metabolism of aquatic organisms. However, they may simultaneously exert stresses on organisms. Biomechanics helps us to understand and quantify the interaction between an organism and its physical environments. In this study, the morphology, drag, lifts, adhesive forces and dislodgment velocities of Sinotaia quadrata, Semisulcospira libertina, and Thiara granifera were measured. The relationships among hydrodynamics, morphology and mechanical characteristics were derived from the results of the measurements. An analysis using the dislodgment model was conducted. The results indicated that the streamline shell could reduce drag and lift under high current velocity. The morphology of T. granifera was better than those of S. quadrata and S. libertina for resisting hydrodynamic stresses because it is streamlined. Theoretically, T. granifera should be better able to resist dislodgment than S. quadrata and S. libertina; however, the results of the dislodgment experiment did not confirm this expectation but showed that the experimental dislodgment velocity of T. granifera was the slowest (67cm/s); that of S. quadrata was middle (72cm/s); that of S. libertina was the fastest (107cm/s). The experimental dislodgment velocities of freshwater snails were tally with the calculated dislodgment velocities obtained by dislodgment model. The analysis of the dislodgement model showed that the mechanism of dislodgment of freshwater snails consists of two parts - the actual dislodgment mechanism, involving drag, lift, and buoyancy, and the dislodgment-resistance mechanism, involving adhesive force and weight. In conclusion, the hydrodynamic forces were determined primarily by the morphology of the shell, and the adhesive forces served as a buffer of the direct effects of hydrodynamic forces. The dislodgment velocity was determined by the interaction between hydrodynamic and biological mechanisms. The adhesive force of S. quadrata was the strongest but its morphology was the worst; the morphology of T. granifera was the best but its adhesive force was the weakest. S. libertina had balance performance on both of adhesive force and morphology. The drag load on S. libertina is reduced by: the slender, streamlined shape of shell, the change of orientation and attacking angle, and the flexibility of the muscle. The analysis of biomechanics provides a valuable reference for ecological engineering design. The design velocities can be determined by the mean and standard deviation of the normal cumulative probability function obtained in the dislodgment experiment to conserve the ecology of native freshwater snails and control the harmful ones. The design current velocity could be determined by controlling the roughness of the substrate, the channel section and the slope of the riverbed. In addition, the substrate material influences the adhesive force simultaneously.ABSTRACT 1 摘 要 3 CHAPTER 1 INTRODUCTION 5 1.1 Biomechanics and Ecological Engineering 5 1.2 The Environment Factors of Freshwater Snails 7 1.3 The Schemes for Adapting to Current 9 1.4 Purpose 10 CHAPTER 2 THEORY AND MODEL 11 2.1 Orientation and Attacking Angle 11 2.2 Reynolds Number 14 2.3 Drag and Lift 16 2.4 Dislodgment Model 18 CHAPTER 3 MATERIALS AND METHODS 21 3.1 Species 21 3.1.1 Sinotaia quadrata 21 3.1.2 Semisulcospira libertina 21 3.1.3 Thiara (Tarebia) granifera 22 3.2 Morphology 24 3.3 Orientation and Attacking Angle 27 3.4 Adhesive and Shear Forces 29 3.5 Drag and Lift 31 3.6 Dislodgment Experiment 32 CHAPTER 4 RESULTS 33 4.1 Morphology 33 4.2 Orientation and Attacking Angle 36 4.3 Adhesive and Shear Forces 39 4.4 Drag and Lift 41 4.5 Dislodgment Experiment 46 4.6 Calculation of Dislodgment Model 49 CHAPTER 5 DISCUSSIONS 54 5.1 Effect of Shell Shape on Hydrodynamic Force 54 5.2 Dislodgment Experiment and Dislodgment Model 55 5.3 Application in Channel Ecological Engineering Design 57 5.4 The Schemes for Decreasing Drag 60 LIST OF SYMBOLS 65 REFERENCES 68 APPENDIX: RESUME 7