In turbomachinery, such as turbine, pump, and valve, components damage caused by collapsing cavitation bubbles has been a critical issue that needs a proper solution. For this reason, investigation on the cavitation erosion behavior of materials as well as the life prediction techniques has been extensively conducted. Moreover, a number of repairing techniques, such as by a surface coating of polymeric materials, has been established. However, in real operation, cavitation is actually not the only load acquired by the components. Other external loads, such as centrifugal force and hydraulic pressure, may also affect the generation of damage. Therefore, its effect on the lifetime needs to be considered carefully. In this paper, the behavior of cavitation damage of epoxy resin specimens subjected to uniaxial tensile loading is reported. A self-developed testing device was used to conduct a cavitation test based on ASTM G32 while at the same time exerting a constant uniaxial tensile load to the specimen. Using this device, various levels of tensile stress effect on the cavitation damage was examined. As a result, besides erosion damage, we revealed that the specimens demonstrated fracture when a certain tensile load was applied. Furthermore, as the tensile load was increased, the time to fracture was shortened significantly, indicating the pronounced effect of tensile stress on the damage formation. The crack growth mechanism was then analyzed by fractography. The result indicated that the crack propagation under a mixed condition of cavitation and tensile loads was most likely driven by the combination of creep deformation and fatigue-like crack growth. Finally, a mathematical relationship between tensile stress and cavitation damage life was proposed. The relationship is important to enhancing the existing theory of cavitation damage evaluation in e.g. turbomachinery application.
The nonlinear bending equation for a slender, tapered cantilever beam made of axially functionally graded material (FGM) with a transverse load applied at the tip, undergoing large deflections, is solved by the Runge-Kutta method. Solutions are obtained for round cross-sections, for varying degrees of both taper and Young's modulus and are compared with existing values obtained in previous research. Sets of deflection and stress curves are also obtained, from which the deflection and stress at any point in the beam may be computed.
We propose a simple tensile test with which to identify the parameters that constitute the failure criterion of an adhesive in a multiaxial stress state. In this paper, we define the failure criterion as the proportional limit of load-displacement curves obtained from experiments. We first introduced the failure criterion based on the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor. To determine the unknown parameters of the failure criterion, two experiments were performed. The first was a tensile shear test for bonded plate structures to obtain the strength of the adhesive material in simple shear deformation and assess how the strength depends on the strain rate and adhesion layer thickness. We subsequently performed a uniaxial tensile test for circular pipe specimens bonded by the same adhesive. The pipe specimens had inclined cutting surfaces for the purpose of measuring adhesive failure points in a multiaxial stress state. Using the failure criterion with the developed tensile test, we next evaluated the adhesive strength of the pipe specimens with reference thickness of h* ~ 0.4 mm. Formulating a scale function δ as a reference of h*, we calculated the failure magnitudes of pipe specimens with different thicknesses h. As a result, we obtained the power law of δ ∝ h−0.79, which allows us to extend the failure criterion to different thicknesses of the adhesive layer.
In this paper, we present the relationship between printing parameters of a 3D gel printer "Soft and Wet Intelligent Matter-Easy Realizer (SWIM-ER)" and mechanical properties of the fabricated gel objects by SWIM-ER. The printer is able to fabricate hydrogel objects by scanning of ultra-violet (UV) light irradiation (photopolymerization). Various hydrogels objects were printed with different scanning velocity of UV light. We measured the water content and mesh sizes of gel objects utilizing Scanning Microscopic Light Scattering (SMILS). Furthermore, we also printed the gel objects with multiple scan rates with constant UV light irradiation energy, and measured sizes of gel objects, and performed the compression test. It was observed that the physical properties of printed hydrogel objects are strongly related with 3D printing parameters (scan velocity and number of scans-scan rate) due to difference in crosslinking density of polymer network.
A series of study is presented to develop a prediction method for pipe wall thinning in power plants in order to improve the maintenance management for piping system. In the first report, experiments for flow-accelerated corrosion (FAC) of carbon steel specimens were conducted and basic data of FAC rate were obtained by setting temperature from 50 to 150 ℃ and pH from 7.0 to 9.8 as main parameters. As this second report, the experimental data of FAC rate were compared with the prediction method. Effective mass transfer coefficient correlation was proposed and implemented into the prediction method considering combining effect of local average and turbulent velocity in the near-wall region calculated by computational fluid dynamics (CFD) simulation code. Fairly good agreement was confirmed between experimental and predicted FAC rate profile, quantitatively. Continuously, prediction method was applied to actual power plant piping systems, and some elbow components were chosen for evaluation in detail. Comparison of measured and predicted FAC rate also showed good agreement with data mostly evaluated conservatively in sense of maintenance management. As a whole, presented FAC prediction method including effective mass transfer coefficient was confirmed to predict measured FAC rate data of power plant pipe component with fairly good accuracy and reasonable conservatism, at least for the subjected temperature and pH conditions.
In this research, we investigated an energy supply system based on hydrogen derived from renewable energy. We modeled the energy flow and efficiency of a system using the MCH-toluene-hydrogen reaction cycle (MTHR) by methylcyclohexane (MCH, C6H11CH3) and toluene (C6H5CH3). Electric power storage by the MTHR and energy transport by a hydrogen infrastructure were investigated using numerical analysis. The energy flow of the whole system was investigated by cooperation of the numerical model of each component. The rate of input and output based on the calorific value of hydrogen defines the efficiency of each component and the system. When the electric power output of the renewable energy source was set to 100%, the maximum energy efficiency based on the calorific value of the hydrogen supplied from the hydrogenation facilities was 53.6%. Conversely, the electric power and thermal efficiency based on the rating of the dehydrogenation facilities were 29.9% and 6.8%, respectively. The maximum total power generation efficiency of the MCH-toluene-hydrogen reaction cycle was 16.0%; however, when thermal power was taken into account this rose to 16.7%. A case study was also conducted using a 1 MW wind farm combined with MTHR for Hokkaido in Japan.
Throwing an object by a powered robotic system is an effective way for object manipulation in long distance. The focus of the throwing is on the accuracy of the landing point with respect to model uncertainties or disturbances. A robust controller is often designed, however, the motion will be finished before the controller produces its effects because throwing is fast and highly dynamic. Moreover, the robot system sometimes has zero adjustment error in the initial position on its joint angle. This error cannot be overcome by a robust controller. So far, we have proposed a dynamic sensitivity analysis method of throwing for a feed-forward controlled manipulator. The sensitivity of the landing point with respect to zero adjustment error has been calculated, and robust throwing with small sensitivity has been designed. In this paper, the conventional method is applied to a feed-forward/back controlled manipulator in the real world, and evaluations are executed by using a prototyped three-link manipulator. The effectiveness of the proposed method is evaluated based on the sensitivity and variance of the landing point, and a robust throwing with small sensitivity is designed.
An optical disc drive uses an optical pickup to read and write data by focusing a laser beam on the data plane of a rotating disc. The pickup is required to keep the beam spot on the current track. The latest trend of replacing metal pickup housing with plastic easily excites elastic deformation modes of the pickup housing. Optical components mounted on the housing are vibrated at the mode frequencies of the housing as well. These vibrations tilt the incident angle of a laser beam entering the objective lens and results in the displacement of the beam spot on the data plane. Our purpose in this paper is to improve the accuracy of a vibration model for optical pickups by considering the effect of the elastic deformation modes of the housing in addition to the commonly used mechanical dynamics of an objective lens actuator in order to predict stability in a tracking servo system. The effect of the elastic deformation modes of the housing was formularized as the incident angle deviation and was calculated by adding and subtracting the products of a ray transfer matrix chain representing the transfer from each optical component to the objective lens with its small displacement and tilt vector. This new vibration model reproduced an increased gain around a frequency of 20 kHz in the measured open-loop transfer function of the tracking servo system with 4% error in frequency, which was entirely unexpected in the context of existing vibration models for optical pickups. The calculated results also identified the most influential vibration modes of the housing and estimated the effectiveness of stiffening the housing with 17% error.
We herein propose a liquid encapsulation method for a submillimeter-size polydimethylsiloxane (PDMS) membrane. We selected a magnetorheological (MR) fluid as the liquid to be encapsulated in the membrane, the stiffness of which is tuned by an external magnetic field. The proposed method consists of two steps. First, a PDMS bump was made to contact a MR fluid, and a MR fluid droplet was formed on top of the bump. Next, the droplet was dipped in a PDMS casting solution and fully covered with a PDMS casting solution layer. Finally, the droplet was encapsulated in the membrane after curing. We experimentally confirmed that the radius of the PDMS bump and the viscosity of the MR fluid were variable parameters that could determine the height of the structure. We also evaluated the stiffness characteristics of the structure. The calculated Young's modulus indicated that the stiffness varied from 70 kPa to 180 kPa in the presence of an external magnetic field. The results indicated that the structure could emulate relatively soft materials and could be applied to a tactile display used in palpation.
The objective of this study was to solve the theoretically ideal arm stroke for a swimmer with hemiplegia by using the optimizing simulation. The method of optimizing simulation for non-disabled swimmers was extended to a swimmer with hemiplegia. In order to evaluate the arm strokes in the optimizing calculation, the swimming human simulation model SWUM was employed. As the design variables, the joint angles in the three time frames, in which the arm was performing underwater strokes, were used. The objective function was the swimming speed. Three constraint conditions including the maximum joint torque characteristics were imposed on the optimizing calculation. The swimming motion of an actual swimmer with hemiplegia was measured and put into the simulation as the original motion. In the simulation, significant increase in the swimming speed was obtained in the case of the optimized stroke with the actual swimmer's wrist motion at the slower stroke cycle. From the comparison between the optimized stroke and the actual swimmer's stroke, several differences were found as follows. First, at the entry phase in the fastest optimized stroke, the left elbow was more extended than the actual swimmer's stroke. Second, at the catch phase in the fastest optimized stroke, the forearm in the side view was more tilted with respect to the vertical line, while that in the actual swimmer was almost vertical. Third, at the pull and finish phases in the optimized stroke, the hand pushed the water sufficiently to the end, while that in the actual swimmer went out from the water earlier. Overall, it was found that the optimized stroke effectively utilized the joint torque at the shoulder and elbow to the maximum extent, by selecting the more natural positions and the slower stroke cycle.
In recent years, the design of footballs, including the number and shape of the panels forming the surface of footballs, has undergone a significant change. However, panels of varied shapes and seams are combined in complex ways to form the surface shape of footballs, and almost nothing is known about the effect of these surface shapes on the football drag characteristics. The present study used a wind tunnel to study the relationship between the critical Reynolds number and the length, depth, and width of the panel joints (seams) of 10 most recent football types used in matches in recent years. The results show the tendency that the drag coefficient in the super-critical regime (30 m/s) of a football increases as the panel joint length increases. Moreover, the depth of the panel joint indicates the highest correlation with the critical Reynolds number (r = -0.71, p < 0.01) and is considered to be a strong and convenient indicator that expresses the roughness (large scale) of the football surface. This study reveals the drag characteristics of the latest footballs and enables some degrees of prediction of the critical Reynolds number for the latest football types and those that will be developed in the future.
The effects of the point angle of a metal anchor and the angle between the target and the plane perpendicular to the direction of travel of the anchor (target angle) on the docking state of the anchor in a satellite structure were experimentally and numerically evaluated. Projectile experiments were conducted using test plates at target angles of 0°, 30°, 45°, and 60° and two metal anchors with conical tips with different point angles (60° and 90°) to investigate the effects of the anchor point angle and the target angle and determine the minimum penetration velocity in each case. The experimental results indicate that the minimum penetration velocity increases as the target angle increases. Because of the limitations of the experimental equipment, performing experiments at certain target angles is difficult; thus, an accurate numerical simulation model was developed based on the experimental results to enable a more detailed investigation. The simulation results obtained using a bilinear isotropic hardening model and three Johnson-Cook models with different sets of parameters were compared with the experimental results to evaluate their applicability. Besides, the applicability of the numerical simulation model are also evaluated by experiments with different metal anchor shape and target plate thickness. It was confirmed that Johnson-Cook models can be used to effectively simulate the docking state and minimum penetration velocity of a metal anchor projection at different target angles. The effects of the point and target angles on the docking state of the metal anchors were investigated more quantitatively through numerical analysis. The numerical analysis results indicate that the minimum penetration velocities of the metal anchor with the smaller point angle (60°) are smaller than those of the metal anchor with the larger point angle (90°) when the angle of attack, which is the angle complementary angle to the target angle, is larger than half of the anchor point angle. When the angle of attack is smaller than this critical value, the metal anchor passes through the target at the minimum penetration velocity, and the conditions are not suitable for docking. The experimental and numerical simulation results indicate that a metal anchor with a smaller point angle can more easily penetrate a target plate and the angle of attack should be larger than half of the anchor point angle to achieve an adequate docking state.