Swimmers in nature use body undulations to generate propulsive and manoeuvring forces. The anguilliform kinematics is driven by muscular actions all along the body, involving a complex temporal and spatial coordination of all the local actuations. Such swimming kinematics can be reproduced artificially, in a simpler way, by using the elasticity of the body passively. Here, we present experiments on self-propelled elastic swimmers at a free surface in the inertial regime. By addressing the fluid–structure interaction problem of anguilliform swimming, we show that our artificial swimmers are well described by coupling a beam theory with the potential flow model of Lighthill. In particular, we show that the propagative nature of the elastic wave producing the propulsive force is strongly dependent on the dissipation of energy along the body of the swimmer.

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Passive elastic mechanism to mimic fish-muscle action in anguilliform swimming

The objectives of this study were to investigate the effect of trunk undulation on the swimming performance in underwater dolphin kick, and to clarify the ideal trunk undulation form. The reference swimming motion of an elite swimmer was firstly acquired from the video analysis, and input into the swimming human simulation model SWUM, which had been developed by the authors. The trunk motion was next optimized by the simulation for three objective functions: maximizing swimming speed, maximizing propulsive efficiency, and minimizing fluid force acting on hands. The following findings were obtained: In the case of maximizing swimming speed, the whole body forms a ‘C’ shape due to the in-phase trunk undulation. The swimming motion of maximizing propulsive efficiency and the reference swimming are considerably similar to each other. In both cases, the trunk moves as a seesaw with a node; whereas, the lower limbs form a traveling wave in the absolute space. The values of propulsive efficiency are around 0.2 in the cases of maximizing propulsive efficiency, minimizing fluid force on hands, and the reference swimming. The swimming motion in the case of minimizing fluid force on hands is almost the same as that of maximizing propulsive efficiency. The trunk undulation with the appropriate amplitudes and phases, especially bending at the chest, is important in realizing the swimming motion which maximizes propulsive efficiency.

https://www.jstage.jst.go.jp/article/jbse/4/1/4_1_94/_pdf

Simulation Analysis of the Effect of Trunk Undulation on Swimming Performance in Underwater Dolphin Kick of Human

There are many dynamical problems in front crawl swimming which have not been fully investigated by analytical approaches. Therefore, in this paper, standard six beat front crawl swimming is analyzed by the swimming human simulation model SWUM, which has been developed by the authors. First, the outline of the simulation model, the joint motion for one stroke cycle, and the specifications of calculation are described respectively. Next, contribution of each fluid force component and of each body part to the thrust, effect of the flutter kick, estimation of the active drag, roll motion, and the propulsive efficiency are discussed respectively. The following results were theoretically obtained: The thrust is produced at the upper limb by the normal drag force component. The flutter kick plays a role in raising the lower half of the body. The active drag coefficient in the simulation becomes 0.082. Buoyancy determines the primal wave of the roll motion fluctuation. The propulsive efficiency in the simulation becomes 0.2.

/pdf/mechanical-study-of-standard-six-beat-front-crawl-swimming-2vf0a0z2iw.pdf

Mechanical Study of Standard Six Beat Front Crawl Swimming by Using Swimming Human Simulation Model

This paper reviews unsteady flow conditions in human swimming and identifies the limitations and future potential of the current methods of analysing unsteady flow. The capability of computational fluid dynamics (CFD) has been extended from approaches assuming steady-state conditions to consideration of unsteady/transient conditions associated with the body motion of a swimmer. However, to predict hydrodynamic forces and the swimmer’s potential speeds accurately, more robust and efficient numerical methods are necessary, coupled with validation procedures, requiring detailed experimental data reflecting local flow. Experimental data obtained by particle image velocimetry (PIV) in this area are limited, because at present observations are restricted to a two-dimensional 1.0 m2 area, though this could be improved if the output range of the associated laser sheet increased. Simulations of human swimming are expected to improve competitive swimming, and our review has identified two important advances...

https://www.tandfonline.com/doi/pdf/10.1080/02640414.2015.1123284

Numerical and experimental investigations of human swimming motions

In this study, the optimal arm strokes in crawl swimming which maximize the swimming speed and propulsive efficiency were solved computationally. For this objective, an optimizing method which consisted of the random search and the PSO (Particle Swarm Optimization) algorithm was constructed. In order to consider the muscle strength characteristics of the swimmer as the constraint condition of the optimization, an experiment to measure the maximum joint torques was carried out for various joint angles and angular speeds. Using the measured experimental data as the reference values, a musculoskeletal simulation model was constructed. By the constructed musculoskeletal model, muscle strength characteristics in various conditions were investigated and used to create a database. Using this database, the optimizing calculation was finally conducted and the following results were obtained: In the optimization maximizing the swimming speed, the swimming speed became maximum when the stroke cycle was 0.9 s. A relatively I-shaped stroke was obtained in this case. In the optimization maximizing the propulsive efficiency, the propulsive efficiency became maximum when the stroke cycle was 1.3 s. A relatively S-shaped stroke was obtained in this case. Two strokes which respectively maximized the swimming speed and propulsive efficiency were very similar to each other when the stroke cycles were the same. The swimming speeds and stroke cycles obtained in the optimizing calculation were within reasonable ranges compared to the actual races.

https://www.jstage.jst.go.jp/article/jbse/7/2/7_2_102/_pdf

Optimizing Simulation of the Arm Stroke in Crawl Swimming Considering Muscle Strength Characteristics of Athlete Swimmers

The purpose of this study is to develop a swimming human simulation model considering rigid body dynamics and unsteady fluid force for the whole body, which will be utilized to analyze various dynamical problems in human swimming. First, the modeling methods and their formulations for the human body and the fluid force are respectively described. Second, experiments to identify the coefficients of the normal drag and the added mass are conducted by use of an experimental setup, in which a limb model rotates in the water, and its rotating angle and the bending moment at the root are measured. As the result of the identification, the present model for the fluid force was found to have satisfactory performance in order to represent the unsteady fluctuations of the experimental data, although it has 10% error. Third, a simulation for the gliding position is conducted in order to identify the tangential drag coefficient. Finally, a simulation example of standard six beat front crawl swimming is shown. The swimming speed of the simulation became a reasonable value, indicating the validity of the present simulation model, although it is 7.5% lower than the actual swimming.

Development of Swimming Human Simulation Model Considering Rigid Body Dynamics and Unsteady Fluid Force for Whole Body

Aging constants for efficient fracture toughness prediction of thermally aged GTAW/SMAW of 316L stainless steel

This paper describes a stress measurement from a welded part of an austenitic stainless steel using synchrotron X-rays. Observing the diffractions from a single crystal, coarse grained material and the welded part, the diffraction pattern of the welded part shows the feature of textured materials with large grains. Difﬁculty measuring the X-ray stress of the welded part is caused by the broadening of the diffraction spot in the radial and circumferential directions. The bending strains of the rectangular bar made of the welded part were measured using synchrotron white X-rays and the double exposure method. However, the results were not enough accuracy to obtain the strains. To improve the energy resolution, monochromatic synchrotron X-ray of 70 keV was used. The diffraction pattern showed the sharp arc like a pattern from texture material. The diffraction proﬁle was obtained from the integral of the diffraction intensity in the direction of the circumference. The diffraction angle was determined using the double exposure method. As a result, the distribution of the residual stresses of the welded part could be measured. 

A Study on Stress Measurement of Weld Part using Double Exposure Mehtod

Residual stresses in astresses in small-bore butt-welded pipe of austenitic stainless steel have never been measured. It is difﬁcult to obtain a detailed residual stress map of the root welded part, because the gauge volume in neutron diffraction is large. The stress evaluation of the welded part by synchrotron X-rays was also difﬁcult due to the dendritic structure. In this study, a double exposure method (DEM) with high-energy synchrotron X-rays was applied to measuring the details of the residual stress of the welded part, and we succeeded in obtaining the detailed axial and radial stress maps of the root welded part of the plate cut from the welded pipe, though the stress map was under the plane stress condition. The hoop stress map of the butt-welded pipe was obtained using the strain scanning method with neutrons under the triaxial stress state. The axial and radialradius stress maps under a triaxial stress state were made up using the complementary use of the synchrotron X-rays and neutrons. As a result, the detailed stress maps of the root welded part of the butt-welded pipe were obtained. The result of the actual stress analysis sufﬁciently explained the initiation and propagation of SCC. 

Yasufumi Miura

Papers

Development of Swimming Human Simulation Model Considering Rigid Body Dynamics and Unsteady Fluid Force for Whole Body

Development of Swimming Human Simulation Model Considering Rigid Body Dynamics and Unsteady Fluid Force for Whole Body

Aging constants for efficient fracture toughness prediction of thermally aged GTAW/SMAW of 316L stainless steel

A Study on Stress Measurement of Weld Part using Double Exposure Mehtod

Actual Stress Analysis of Small-Bore Butt-Welded Pipe by Complementary Use of Synchrotron X-Rays and Neutrons