The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in the stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the SMA tape in the tension test. The results obtained are summarized as bellows. (1) In the loading process, temperature increases due to the exothermic martensitic transformation (MT) till the holding strain under a constant stress rate and thereafter temperature decreases during holding the strain constant, resulting in stress relaxation due to the MT. (2) In the unloading process, temperature decreases due to the endothermic reverse transformation till the holding strain under a constant stress rate and thereafter temperature increases during holding the strain constant, resulting in stress recovery due to the reverse transformation. (3) Stress varies markedly in the initial stage followed by gradual change during holding the strain constant. (4) If stress rate is high till the holding strain in the loading and unloading processes, both stress relaxation and stress recovery are large. (5) It is important to take account of these behaviors in the design of SMA elements since the force of SMA elements can vary under constant strain even if temperature is kept constant around SMA elements.
Present titanium plates for implants have the problems like too heavy and excessive elastic modulus compared with natural bones. In this study, Titanium mesh plates with higher 3-demensional flexibility were developed to improve such problems. Fundamental mesh patterns were designed through three dimensional CAD tools from higher flexibility and strength points of view. Based on the designed mesh patterns, sample specimens of Titanium mesh plates with different design variables like plate thickness, mesh line width were manufactured through wire-cut discharge processing. Mechanical properties of the Titanium mesh plates like volume density, tensile elastic modulus and bending stiffness were experimentally and analytically evaluated. Experimental results showed that such Titanium mesh plates had much higher flexibility and their mechanical properties could be controlled to close to the natural bones. More details on the mechanical properties of meshed plates including compression, torsion and durability will be executed in future study.
The dynamic contact angle, the angle between the surfaces of the liquid and the solid at a moving contact line, is one of the primary conditions for the dynamics of the liquid surface confined by solid wall. It has been commonly modeled as a function of the velocity of the contact line relative to the solid surface under steady state condition. Some situations, such as the impact of a drop on a solid surface or sudden release of a contact line stuck on an edge of solid, however, involve a transient motion of the contact line, which would lead to a deviation of the dynamic contact angle from the steady one. In this study, dynamic contact angle for an accelerating or decelerating contact line advancing on glass surface is measured in two experimental systems different with other, i.e. one with a rapid meniscus formation after contact of a descending rod with the liquid surface, and the other with accelerating advance of liquid column in a circular tube. The experimental results revealed that the contact angle is increased with the (positive) acceleration of the contact line relative to the solid and vice versa. The critical condition for the appearance of the deviation of the contact angle brought with the acceleration is also discussed.
Fluctuating force induced by upward gas-liquid two-phase flow on 90 degree pipe bend was investigated. From the previously developed database comprised of dynamic force signals and two-phase flow parameters such as volumetric fluxes, area averaged void fraction and pressure fluctuations, the study was conducted to develop a model which is capable of predicting the force fluctuation magnitudes. The model was fundamentally developed from the local instantaneous two-fluid model applied on the control volume of 90 degree elbow. The force fluctuation of two-phase flow is caused by momentum and pressure fluctuations. For slug flow regime, however, it was found that impact force caused by the collision of liquid slug against the structure boundary produces “water-hammer” like impact. In order to avoid discontinuity due to flow regime transition, interfacial area concentration correlation was utilized using two-group approach. The newly developed model is capable of predicting two-phase flow induced force fluctuation and dominant frequency range with satisfactory accuracy.
Dynamic response of the fluid force acting on an axially oscillating balance piston was numerically investigated. The balance piston of a rocket engine turbopump was modeled and forced to oscillate in the axial direction. The flow field around the rotor was simulated using unsteady CFD simulation changing the oscillation frequency. The dynamic characteristics of the fluid forces acting on the front and on the back shrouds were estimated and compared. From the analysis of these coefficients, it was found that the dynamic characteristics of the fluid force on the back shroud with a balance piston dominated that of the whole rotor. The dependency of damping coefficients on the frequency of the axial oscillation seemed to be related to the unsteady flow structure such as vortices caused by the oscillation of the rotor.
The Rotating instability, abbreviated to RI, in a centrifugal blower with shrouded impeller is investigated by experiments and CFD analyses. The RI occurs in a partial-flow operation of the blower prior to stall with mild fluctuations of impeller-discharge velocity and radiated noise, and appears in the power spectra as a gradual hump at almost half of the blade-passing frequency. The cause of the RI is supposed to be unsteady vortices rotating along the impeller periphery and the irregular change of the vortex rotating speed may generate the gradual hump in the power spectra. The RI noise is generated by the impingement of the impeller-discharge flow with unsteady vortices. Fundamental characteristic and structure of the unsteady vortices are investigated supplementary by detailed measurements using a double-phase-locked averaging method and also CFD analyses.
The gradient diffusion hypothesis for turbulent mass fluxes of reactive scalar is investigated by using direct numerical simulations (DNS) of a planar jet with a second-order chemical reaction A+B→R. Reactants A and B are separately supplied in the jet and ambient fluids, respectively. DNS is performed at three different Damköhler numbers, i.e, Da=0.1, 1, and 10. Eddy diffusivity and turbulent Schmidt number of reactive species are calculated from the DNS results. The results show that the longitudinal (x-direction) eddy diffusivity of reactant A near the jet centerline is always positive, whereas the longitudinal eddy diffusivities of reactant B and product R can be negative near the jet centerline. Near the jet centerline, the lateral (y-direction) eddy diffusivity of reactant A, DtA,y, becomes small, but the lateral eddy diffusivity of reactant B, DtB,y, becomes large because of the chemical reaction. In the outer region of the jet flow, the chemical reaction has the opposite effect on DtA,y and DtB,y, and the chemical reaction makes DtA,y large, but DtB,y small. It is concluded that the gradient diffusion hypothesis is largely affected by the chemical reaction, and this effect of chemical reaction should be taken into account when the gradient diffusion model is used to estimate turbulent mass fluxes of reactive scalar.
In order to clarify unsteady flow structure’s behavior that improves vehicle’s high-speed stability during steering input, on-road analysis was conducted. The analysis was conducted on two vehicles’ aerodynamic specifications which were produced by configuring two different shapes from a single vehicle. During high speed driving while steering input in sinusoidal waveform was being applied, these two vehicles were analyzed focusing on the relationships between dynamic movements, unsteady forces affecting on vehicle’s body surface and unsteady behavior of flow structure. As a result, it was clarified that there existed a unsteady behavior of flow structure that aerodynamically control to stabilize vehicle’s steering response motion in vertical and yawing direction. It was also clarified that this aerodynamic force that control to stabilize vehicle’s steering response motion was caused by behaviors of flow structure beside body just behind front tire which reduced and expand its vertical scale during high-speed driving with steering input. Furthermore, it was shown that this behavior of flow structure was caused by weakening vortex structure which came out and separated from the gap between the upper rear side of the front wheel and the front wheel arch.
Turbulent energy transport mechanism involved with large-scale coherent structures in a self-similarity region of a turbulent plane jet is investigated experimentally. First, simultaneous multipoint measurements of two velocity components and pressure are performed by using the “combined probe” which consists of a pressure probe and an X-type hot-wire probe. Then, Proper Orthogonal Decomposition (POD) is applied to both velocity and pressure fields to extract the coherent structure in the jet. Further, the complementary techniques of POD and Linear Stochastic Estimation (LSE) are used to reconstruct spatiotemporal velocity and pressure fields of the dominant POD mode. As a result of reconstruction, we observe the coherent structure with the counter-rotating vortices staggering with respect to the jet centerline: it contains approximately 42 % of the total energy. Finally, the turbulent energy transport is evaluated by using reconstructed velocity and pressure data. The results show that the production and pressure diffusion of the turbulent energy in the jet are mainly caused by the coherent structure.
Spherical motor is a multi-degrees of freedom actuator which can be rotated in various directions. However, the control method of the completely arbitrary direction was not fully established in the conventional research. This study develops a controlling method of a spherical motor that can rotate to all directions and can be fixed to arbitrary postures. In the 1st. report, the torque generating method to the arbitrary directions from arbitrary rotor postures that used a torque-map was shown. However, in order to generate the torque towards the desired direction from arbitrary postures and to stop with a target posture, monitoring of the present rotor posture is indispensable. In this report, the rotor posture detecting system using the information of two optical mouse sensors is shown. The detection technique of the rotor posture using the information from the sensors installed in the arbitrary position is described in detail. The experimental results of the mouse sensor system are shown. Based on this current rotor posture and the target posture, the feedback control algorithm that can position the rotor into the target posture is also explained. And experimental results of the feedback control are shown. The experiment shows that the rotor can be moved and positioned to the target posture by using the feedback control.
This paper deals with an active acoustic enclosure for preventing vibration of precision measuring equipment, e. g. Scanning Probe Microscope (SPM) and Scanning Electron Microscope (SEM) etc., due to surrounding sound noise. In our previous work, an effective actuation method in an active sound transmission control was proposed and the high performance of the method was demonstrated both theoretically and experimentally. Moreover, the acoustic enclosure using the proposed actuation method and piezoelectric film sensors has been developed. In this study, the practical acquisition method of the reference signal for the acoustic enclosure is investigated experimentally. In order to get reference signal of the sound waves with every incident angles so that the causality of the control system can be satisfied, the reference microphone is placed above the center of the each panel and the signals from a number of reference microphones are used for controlling the vibration of one panel, which constitutes the Multi Input Single Output feedfoward control system. The relation between the distance from the reference microphone to the panel and the angle of the incident sound wave which can be sensed by the reference microphones is clarified. The experiments in the case that multiple noise sources existed around the enclosure were performed. A control effect of about 10 dB was obtained up to 122 Hz even when the three noise sources existed, which suggests that in this case the weight of the panel of the enclosure can be reduced about one-third according to the mass law.
The acoustic material has been used inside ducts as a countermeasure of the self-sustained tone generated from heat exchangers and boilers. However the effects of the amount of acoustic material and its patching position in a lined duct on the acoustic damping in its duct have not been established. It can be expected that we can suggest the guideline of absorbing treatment at the design stage to avoid the generation of the self-sustained tone. In this study, the experiment and the analysis are carried out to clarify the problems mentioned above. First the usefulness of the analytical method by BEM is shown by comparing experimental results referring to the acoustic damping in the duct. Next, the effects of the amount of acoustic material and its patching position relative to the noise source on the acoustic damping in the duct are examined by BEM analysis. As a result, it was confirmed that the analytical method due to BEM was useful to predict the acoustic damping because the analytical results of acoustic damping were in good agreement with the experimental ones. And the acoustic damping was also clarified to be affected strongly by the positional relation between the noise source and the acoustic material. In addition, it was effective to patch the acoustic material near the noise source.
In this paper, we investigate gathering control of autonomous multiple agents by single mobile robot. This work was motivated by so-called sheepdog harnessing, in which a mobile robot is developed to gather a flock of ducks or sheep and maneuver them to a specified goal position. Based on discrete model of sheepdog system, we apply two different types of control methods to the system. After defining some evaluation indices (harness time, dispersion of flock), we analyze relationship among the parameters of the robot, the sheep and the control algorithms (center-targeting control, tangent-targeting control) by numerical simulations. Moreover, we propose an improved control method to maneuver separate groups of sheep to a goal position based on on-line clustering.
This paper presents a non-parametric, or a node-based, shape optimization method for designing the optimal geometry of a space frame structure for a natural frequency problem. For a frame structure composed of arbitrarily curved linear elastic members, a natural frequency maximization problem for a specified mode subjected to a volume constraint is formulated as a distributed-parameter shape optimization problem. With the eigenvalue of a specified mode as the objective functional and the assumption that each frame member varies in the out-of-plane direction to the centoroidal axis, the shape gradient function and the optimality conditions are theoretically derived by the Lagrange multiplier method and the material derivative method. An optimal geometry is determined by applying the negative shape gradient function as fictitious external forces to the frame members and analyzing an optimal variation that minimizes the objective functional. This methodology was developed by the authors as the free-form optimization method for frame structures, which is a gradient method in a Hilbert space. For achieving the eigenvalue of a specified mode to be maximized, multiple root problem is avoided by tracking the specified mode through the optimization process using Modal Assurance Criterion (MAC). The effectiveness of the proposed method were verified through several design problems.
Damping material is usually applied on the steel panel of a vehicle to reduce vibration level. On the other hand, the weight reduction is also required to improve fuel consumption. Therefore, modal loss factors induced by damping material on the steel panel of a vehicle body structure need to be maximized with a given volume. In this paper we propose a practical design method to maximize modal loss factors by optimizing the material distribution of damping material under a volume constraint. The modal loss factor of an eigen mode can be written as the ratio of the strain energy stored in the damping material over the total strain energy in the system under consideration. In the proposed method, we assume the eigenvectors are almost the same as the eigenvectors when damping material is removed. The modal loss factor can then be represented by using a corresponding eigenvalue where the mass density of the damping material is ignored whereas the stiffness is taken into account. Several numerical examples are provided to show the optimal distribution of the damping material by using a flat panel. Damping material is distributed in the domain where the strain energy is stored, which agrees well with our experiences. Moreover, by applying a sensitivity filter that utilizes a weighted average of design sensitivities over local area, damping material can be distributed collectively in a single domain to meet practical requirements for manufacturing,
This paper presents stress singularity analysis using three-dimensional Akin singular element. In case that Akin singular element is employed, it is necessary to know order of singularity before stress analysis. However, in case of three-dimensional model, it is not easy to obtain order of singularity comparing to 2-dimensional model. Therefore, a finite element eigen analysis is applied to obtain order of singularity in 3-dimensional bonded structure model, and the obtained order of singularity is applied to Akin singular element. This analysis is frequently applied to obtain 3-dimensinal order of singularity. Consequently, it was found that order of singularity obtained by least square approximation is close to that obtained by the finite element eigen analysis comparing to that in case of normal element. Furthermore, it was found that convergence process in conjugate gradient method is almost same between normal and singular elements in case that course mesh is used around singular point. On the other hand, it was found that it takes a lot of iterations in case of use of singular element if fine mesh is employed around singular point.
We investigate the influence of non-glide stresses on the Peierls energy of screw dislocation by using Nudged-Elastic-Band method. The influence of the applied non-glide stress fields on the Peierls energy of a screw dislocation is clearly observed. Moreover, we find that the stress field dependence of the Peierls energy is changed by the moving direction of the screw dislocation under a specific applied stress field. Geometrical parameters, which can measure the atomic elastic deformation around the screw dislocation core, are introduced to explain the stress field dependence of the Peierls energy. Finally, the cross slip of a screw dislocation around a precipitate with a misfit strain is discussed by combining the analytical solution of stress fields around the precipitate with the geometrical parameters obtained by our atomic simulations.
Vehicle pedal operations are classified as acceleration, transfer between the brake pedal and the accelerator, clutch operation, and braking. This paper deals with the first three without feeling factors. In terms of leg motion, these operations are classified as ankle movement, leg movement and pedal-change movement. In the study reported here, pedal characteristics were analyzed experimentally to clarify the mechanical properties of the leg and related effects on muscle activity. Ankle joint movement is involved in fine adjustment of the accelerator, leg movement is involved in the large motion of depressing the clutch, and ankle joint movement is involved in switching between the brake and the accelerator. The results highlighted three points in particular: (1) Ankle joint movement depends on the force used to depress the accelerator, and involves comprehensive consideration of joint movement, leg muscle activity and seat pressure distribution. (2) Leg movement for the application of foot force to operate the clutch is the greatest in the region of the maximum point near the pedal force. These are easy to operate and a lower burden is placed on the leg. (3) Pedal-change movement can be implemented more precisely when the accelerator-brake pedal transfer path is low and the lateral position of the accelerator is an appropriate distance from the operator’s body center. Comprehensive consideration of these results is expected to be useful in the design of vehicle pedals.