Numerical Simulation of Ultrasonic Wave Propagation in FRP using Image-based Modeling

The use of fiber reinforced plastic (FRP) in industrial products and structural materials has been drastically increased in recent years. FRPs are made of a stack of plies, each of which is reinforced by fibers. The ply orientation, ply material, stacking sequence, and number of layers are designed depending on the mechanical requirement. When modeling wave propagation in the FRP for ultrasonic testing (UT), it is important to introduce three-dimensional mesoscopic and microscopic structures because the ultrasonic waves in the FRP are influenced by mechanical interaction between fibers and plastic. Although a numerical approach of full domain is a straightforward method, the discretization of the microscopic structure is not efficient in consideration of the wave length used in the UT. In this study, a finite element method using an image-based modeling [1] is applied to ultrasonic simulation in a carbon FRP (CFRP). Here, the elastic stiffness of a ply is determined with the homogenization method [2], and the three dimensional (3D) mesoscopic structure of the FRP is made by the image-based modeling. 3D finite-element simulations of ultrasonic waves are validated and compared with visualization results obtained with a laser scanning device. Figure 1 shows the results of wave propagation in a CFRP specimen with unidirectionally aligned fibers. The simulation results and measurements showed good agreement with respect to the velocity and spreading of pressure and shear waves

Numerical Simulation of Ultrasonic Wave Propagation in FRP using Image-based Modeling

The use of fiber reinforced plastic (FRP) in industrial products and structural materials has been drastically increased in recent years. FRPs are made of a stack of plies, each of which is reinforced by fibers. The ply orientation, ply material, stacking sequence, and number of layers are designed depending on the mechanical requirement. When modeling wave propagation in the FRP for ultrasonic testing (UT), it is important to introduce three-dimensional mesoscopic and microscopic structures because the ultrasonic waves in the FRP are influenced by mechanical interaction between fibers and plastic. Although a numerical approach of full domain is a straightforward method, the discretization of the microscopic structure is not efficient in consideration of the wave length used in the UT. In this study, a finite element method using an image-based modeling [1] is applied to ultrasonic simulation in a carbon FRP (CFRP). Here, the elastic stiffness of a ply is determined with the homogenization method [2], and the three dimensional (3D) mesoscopic structure of the FRP is made by the image-based modeling. 3D finite-element simulations of ultrasonic waves are validated and compared with visualization results obtained with a laser scanning device. Figure 1 shows the results of wave propagation in a CFRP specimen with unidirectionally aligned fibers. The simulation results and measurements showed good agreement with respect to the velocity and spreading of pressure and shear waves.</p

有明海における卵稚仔輸送過程の数値モデル

A hydrodynamic model was coupled to a particle tracking model to examine physical factors thatinfluence transport of the white croaker larvae in the Ariake Sea, Kyushu, Japan. The idealized particlesthat mimic the larvae of white croaker are tracked under various physical and biological conditions.Freshet reduces the possibility of particles that reach the nursery ground around the head of the bayby 7 % on average. Spring tide has a positive impact on the feeding migration of particles. Selective tidalstream transport (STST) mechanism dramatically changed particle trajectories. Particles tend to reachthe shallower nursery ground easier during ebb or low tide rather than high or flood tide, depending onwhether the STST is considered during the particle tracking experiment. In particular, the ratio of thenumber of particles that reach the nursery ground increases by approximately 24 % from flood tide tolow tide. When the sinking velocities of particles, ranging from 10-5 to 10-3 m/s, are considered during theparticle tracking experiment, majority of the particles stayed in the releasing area.海洋数値シミュレーションモデルと粒子追跡モデルを用いて，物理的要因が有明海の仔魚輸送に及ぼす影響について調べた。モデルにおいて仔魚は仮想的流体粒子として表現される。河川水の出水は生育場へ輸送される粒子数を７%減少させる。大潮時に潮流流速が増すことによって，生育場へ輸送される粒子数は増加する。稚魚の鉛直移動の効果（Selective tidal stream transport）によって，粒子の輸送過程は大幅に変化する。干潮時や下げ潮時に投入された粒子は，より生育場へ到達しやすくなる傾向がある。10-5から10-3m/sの範囲で粒子の沈降速度を加味した場合，粒子は放流地点付近にとどまる傾向が強くなる