Tomoya Niho

Passive maintenance of high angle of attack and its lift generation during flapping translation in crane fly wing.

SUMMARY We have studied the passive maintenance of high angle of attack and its lift generation during the crane flys flapping translation using a dynamically scaled model. Since the wing and the surrounding fluid interact with each other, the dynamic similarity between the model flight and actual insect flight was measured using not only the non-dimensional numbers for the fluid (the Reynolds and Strouhal numbers) but also those for the fluid—structure interaction (the mass and Cauchy numbers). A difference was observed between the mass number of the model and that of the actual insect because of the limitation of available solid materials. However, the dynamic similarity during the flapping translation was not much affected by the mass number since the inertial force during the flapping translation is not dominant because of the small acceleration. In our model flight, a high angle of attack of the wing was maintained passively during the flapping translation and the wing generated sufficient lift force to support the insect weight. The mechanism of the maintenance is the equilibrium between the elastic reaction force resulting from the wing torsion and the fluid dynamic pressure. Our model wing rotated quickly at the stroke reversal in spite of the reduced inertial effect of the wing mass compared with that of the actual insect. This result could be explained by the added mass from the surrounding fluid. Our results suggest that the pitching motion can be passive in the crane flys flapping flight.

An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies.

The relative importance of the wings inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wings elastic and fluid forces is dynamically similar to that of the actual insect, while the wings inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wings elastic forces and the wings inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wings elastic and aerodynamic forces, while it will be enhanced by the wings inertial force.

Numerical instability of magnetic damping problem of elastic plate

Numerical instability occurs in an analysis of a vibration with magnetic damping, or an electromagnetic and structural coupled problem. In this paper, the numerical instability of the coupled analysis is examined by the finite element in time. It is confirmed that the simultaneous method is unconditionally stable even if the magnetic field and the time increment are large. For the staggered method, we obtain the conditions where the numerical instability occurs.

Failure detection and diagnosis of rotating machinery by orthogonal expansion of density function of vibration signal

The authors present a new robust failure detection and diagnosis method based on a statistical hypothesis on vibration characteristics of the rotating machines in good condition. The hypothesis is that if the machine is in good condition, its probability density function of the vibration signal follows the normal distribution in time domain. This method based on the hypothesis for characteristics of vibration of good condition can lead to high precision failure diagnosis without any prior knowledge concerning to vibration characteristics corresponding to specific failure to be detected.

Parallel electromagnetic-mechanical coupled analysis using combined domain decomposition method

Since the electromagnetic-mechanical coupled analysis requires large computation time, the development of parallel processing techniques is inevitable. In this paper, the parallel computing technique with the combination of the domain decomposition method and the domain partitioned conjugate gradient method is proposed. The method to evaluate the parallel performance is presented and discussed for the coupled problem using a workstation cluster. This method is efficient for a large scale coupled problem of a magnetic fusion device component.

Stability of augmented staggered method for electromagnetic and structural coupled problem

Numerical instability occurs in analyses of an electromagnetic and structural coupled problem or a magnetic damping problem when the matrix equations of structure and eddy current are solved alternately. In this paper, an augmented staggered method is proposed for the coupled analysis. The stability of this method is demonstrated for the magnetically damped vibration by finite element analyses. According to the characteristic equation obtained from the recurrence relation of this time integration scheme, it is confirmed that this method is unconditionally stable for the intensity of magnetic field and the size of time increment.

Simplified analysis method for vibration of fusion reactor components with magnetic damping

This paper describes two simplified analysis methods for the magnetically damped vibration. One is the method modifying the result of finite element uncoupled analysis using the coupling intensity parameter, and the other is the method using the solution and coupled eigenvalues of the single-degree-of-freedom coupled model. To verify these methods, numerical analyses of a plate and a thin cylinder are performed. The comparison between the results of the former method and the finite element tightly coupled analysis show almost satisfactory agreement. The results of the latter method agree very well with the finite element tightly coupled results because of the coupled eigenvalues. Since the vibration with magnetic damping can be evaluated using these methods without finite element coupled analysis, these approximate methods will be practical and useful for the wide range of design analyses taking account of the magnetic damping effect.

Evaluation method of magnetic damping effect for fusion reactor first wall

An evaluation method of the magnetic damping effect and a method to determine the conditions for a reduced scale magnetic damping test of fusion reactor first wall are described. The coupling intensity parameter is used for the evaluation method because it has the potential to evaluate the magnetic damping effect. The thickness and the steady magnetic field required in the reduced tests are obtained to maintain two parameters unchanged, namely the coupling intensity parameter and the ratio of time constants of eddy current and structure, using finite element analysis and the solution of the coupled eigenvalue. To verify the scaling method, experiments and numerical analyses of a plate are performed for various scale factors. Good agreement between the displacement responses of the original and reduced configurations is obtained. The steady magnetic field of the reduced scale test can be decreased using copper or aluminum alloy instead of austenitic stainless steel.

Electromagnetic and structural coupled analysis with the effect of large deflection

This paper describes a coupled finite element analysis for the eddy current and the structure. A formulation is presented considering the effect of the large deflection of shell structures by the total Lagrangian formulation. Both matrix equations for the eddy current and the structure are solved simultaneously using coupling sub-matrices. A coupled problem of a cantilever bending plate is analyzed. Based on the analysis results, the influence of the large deflection on the coupling effect is discussed. The condition that the large deflection analysis is required is examined through some parametric analyses.

Condition monitoring and diagnosis of rotating machinery by Gram-Charlier expansion of vibration signal

Here we present the new robust condition monitoring and diagnosis method based on the statistical hypothesis on vibration characteristics of the rotating machines in good condition. The hypothesis is that if the machine is in good condition, its probability density function of vibration signal follows the normal distribution in time domain. This method can lead to the robust failure diagnosis without any prior knowledge concerning vibration characteristics corresponding to specific failure to be detected.