Studies of the swallowing process are especially important for the development of care foods for dysphagia. However, the effectiveness of experiments on human subjects is somewhat limited due to instrument resolution, stress to the subjects and the risk of aspiration. These problems may be resolved if numerical simulation of swallowing can be used as an alternative investigative tool. On this basis, a numerical model is proposed to simulate the swallowing of a simple jelly bolus. The structure of the pharynx was modeled using a finite element method, and the swallowing movements were defined by pharynx posterior wall shift, laryngeal elevation and epiglottis retroflexion. The rheological characteristics of the jelly were investigated using an oscillatory rheometer and a compression test. A Maxwell three-element model was applied to the rheological model of the jelly. The model constants were obtained from compression tests because the mode of deformation and the stress level of the compression tests were similar to those of the swallowed jelly. The frictional relationship between the organs and the jelly was 5 Corresponding Journal of Texture Studies 40 (2009) 406-426. © 2009 estimated experimentally from some frictional measurements between the jelly and a wet sloping surface. The results of the simulations for the soft and hard jellies showed different patterns of swallowing that depended on their hardness, and the soft jelly produced faster swallowing because of its flexibility. PRACTICAL APPLICATIONSThe object of this study is to develop a numerical simulation model of swallowing. Numerical modeling is suitable for the quantitative analysis of the swallowing process and may also be expected to enable a systematic study of care foods that are safe and offer some degree of comfort to patients suffering from swallowing disorders. The computer simulation can be used for evaluation without dangerous risks to the patient.

In our previous study, in vitro hemolysis tests showed that collision flow against wall roughness had an effect on hemolysis when the flow velocity was more than 3 m/s and surface roughness was more than Ra = 1.54 microm. However, the specific portion of the flow on the wall that induced hemolysis was not clarified. Therefore, the purpose of this study was to present the relationship between flow behavior and hemolysis by means of in vitro tests and computational fluid dynamics (CFD) analysis. We investigated the relationship between the location of surface roughness and hemolysis. In CFD, we investigated the flow behavior on the wall. The highest rate of hemolysis was observed in a region around the center of the surface roughness on the bottom plate. On CFD analyses, the flow behavior included the highest wall shear stress (304 Pa) and the highest flow acceleration (2.8 m/s2) around the center of the bottom plate. Therefore, it is concluded that the causes of hemolysis during collision flow depend upon wall shear stress and flow acceleration.

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