TRIP steel is an advanced high strength type steel and good performance for structural application in industries including high temperature products such as automobile and transportation. To optimize costs, the desired material must be selectively placed. In the current study, TRIP steel and mild steel are joined by friction stir welding under the optimal conditions. The fatigue strength of dissimilar joints is evaluated relative to the fatigue strength of the monolithic and FSWed base metal. Fatigue crack growth in the dissimilar joints was also studied to determine specific fatigue behavior by employing digital image correlation technology.

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This study aims to solve effector of coupling’s tensile strength and temperature measurement on tip of tool. This joining produce friction heat by pushing spinning tool to Al alloy, and adhere insert material into Al alloy and CFRP by friction heat and plunging force. This joining use tool made of SKD61. Tool’s diameter is 12mm. Tool’s rotating speed is 750rpm. Tool’s indentation speed is 5.0mm/min. Tool’s indentation hold time is 5.0s. Sample materials are Al alloy(A5052-H34) and CFRP. Insert material is Polyethylene terephthalate(PET). PET is held by Al alloy and CFRP, and pushed by spinning tool from Al alloy side. Tensile shear test is conducted in the atmosphere. Cross head speed is 0.5mm/min. Use load cell in plunging load measurement. Establish thermocouple into hollow tool, and use in temperature measurement. As a result of measurement, identified that coupling’s tensile strength increase by joining area’s size and indentation force’s volume. PET’s molten state is affect to tensile strength because temperature occurred by joining isn’t over PET’s melting temperature in 0.3mm and 0.5 mm.

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In this study, we investigated the effect of carbon fiber laminate structure on peel strength of Al alloy / CFRP adhesive joint. Four types of CFRPs with different lamination configurations were manufactured and bonded to Al alloy to produce test specimens. In order to perform the peel test, we made a jig for reducing the force acting on the test piece in the longitudinal direction of the Al alloy. The peeling test was performed using a test machine AG-250kN / 300kN Xplus manufactured by Shimadzu Corporation. Attach the jig to the tester and fix the test piece to the jig table. The experimental results showed that the larger the maximum test force, the larger the fracture energy. Fracture is divided into three stages: instantaneous rupture of part, gradual rupture, and instantaneous rupture of the rest. Since there are various factors such as the maximum test force, the test force after the first break, and the stroke, it is difficult to simply perform the strength evaluation.

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A reactor core isolation cooling (RCIC) system of the Fukushima Dai-ichi Nuclear Power Plant Unit 2 (1F2) was continued to operate even after the loss of power supply. However, the fact that water injection by the RCIC system is continued was still unknown. On the other hand, from the predicted results with the severe accident analysis codes, the RCIC system was speculated that had been driven by two-phase flow of water and vapor. In order to contribute to the clarification of the unexplained events related to the RCIC system of 1F2, distributions of void fraction, mixture velocity, etc. based on the flow rates of water and vapor and the number of rotation of the wheel in the RCIC turbine were predicted numerically. In the simulations, the structure of the current RCIC turbine was simply simulated and the two-dimensional analytical domain was considered. From the present study, it was found that the torque against a shaft of the wheel increases with increasing the accumulated water in the RCIC turbine and prevents the rotation.

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Clarifying thermal-hydraulic characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. With progress of a technology on Computational Fluid Dynamics (CFD), development of analysis methods to predict numerically complicated phenomena between liquid and gas phases is performed by atomic research institutes and universities in each country. The objective of this study is to clarify the prediction performance of a two-phase flow analysis code TPFIT which was developed by JAEA. In order to validate predicted results, the bubbly flow in a subchannel with/without a grid spacer were measured under the water-air two-phase flow condition. Bubble dynamics in the simulated subchannel with an obstacle were investigated experimentally and numerically and the spacer effect to the bubbly flow behavior was clarified.

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The Best-Estimate Plus Uncertainty (BEPU) is applied as Deterministic Approach for safety analysis of Nuclear Power Plant using the system analysis code such as Relap5. Thus, it is necessary to verify the applicability of a system analysis code that is able to predict accurately the two-phase flow such as interfacial shear between two phases: liquid and gases. It is also important to know the prediction uncertainty due to the constitutive relation in order to close the twofluid model equation. In PWR’s Small-Break LOCA (SB-LOCA) accident, the loop-seal clearing is important phenomena where liquid inventory going into the reactor core from Steam Generator known as the inherent safety feature of PWR. The prediction of thermal-hydraulic system code is necessary to be verified. In order to investigate this phenomenon, the experimental data is used to compare with simulation results in order to validate the computer code. In this work, the UPTF-TRAM simulated the counter-current flow between vapor and liquid in Loop-seal during SB- LOCA which is used to verify the applicability of Relap5/Mod3.3. Moreover, the uncertainty of simulation results is also quantified by using the statistical method. Therefore, the uncertainty quantification of interfacial shear stress is reported for loop-seal clearing phenomena.

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Regarding the storage of fuel debris accompanying the decommissioning of the Fukushima Daiichi Nuclear Power Plant, management of hydrogen gas generated by radiolysis of water is indispensable. For this reason, it is important to maintain the concentration of hydrogen in sealed vessels below the explosion limit in order to improve the safety of long-term waste storage containers. Then, it was considered that the generated hydrogen is combined with oxygen by the passive autocatalytic recombiner (PAR) and return to water. Basic experiments and analyses were performed to investigate the controlling factors for reducing the hydrogen concentration in a fuel debris storage container with PAR. The present study shows the effects of the PAR quantity, PAR installation position and hydrogen flow rate on the reduction of hydrogen concentration.

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After the big earthquake in Fukushima Prefecture in March 11 and following by the Fukushima Daiichi Nuclear Power Plant accident, Japanese regulator system has been reinforced by requesting the additional safety scale in order to enhance the nuclear safety. The nuclear regulatory has requested strictly not only s safety measures of nuclear facility but also the safety awareness of human who is involved in the facility operation and safety management. However, the conventional approach in educating has some disadvantages in developing the practical programs, especially in nuclear energy field where the exercises is not so popular to be implemented. Hence, the human resource development on nuclear energy field has been upgraded the education and training programs in strengthening the quality of personnel in nuclear engineering field. Therefore, in accordance with new system of nuclear regulatory requirement, the practical education program is developed in parallel with lectures at Nagaoka University of Technology. Accordingly, the Accelerators facility such as Tandem 2MeV is used as an important part of radiation safety awareness and the nuclear safety is given by simulating a Nuclear Power Plant on the Work-station platform.

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Thermoacoustic system using thermoacoustic self-excited oscillation which is mutual conversion between heat and sound waves has been proposed as a means to effectively utilize waste heat from factories and automobiles. In thermoacoustic systems, it is important to estimate the critical temperature ratio at which self-oscillation with the desired pressure amplitude occurs for system evaluation and improvement design. Our propose is to estimate the critical temperature ratio for looped-tube traveling wave thermoacoustic systems based on steady-state oscillation control. Considering the effect of the fluctuation of pressure amplitude during self-oscillation on the estimation of the temperature ratio, the relationship between the sound source position and the estimation result was investigated in more detail using the temperature ratio near the critical temperature ratio. As a result, (i) It is possible to estimate the temperature ratio at which the desired pressure amplitude may be obtained regardless of the sound source position, (ii) It shows that the temperature ratio at which the average of the pressure amplitude becomes the desired value can be estimated with accuracy of two decimal places regardless of the location of the sound source. Furthermore, it is shown that the more the estimation is performed using a temperature ratio far from the critical temperature ratio, the more likely the estimation result differs depending on the sound source position, and that it is necessary to reproduce the amplitude ratio of the traveling wave pressure component during self-excited oscillation.

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Thermoacoustic systems utilizing the thermoacoustic phenomena are one of means for recovering waste heat from factories and automobiles. In the practical application of thermoacoustic systems, it is important to estimate the steadystate pressure amplitude for thermoacoustic self-excited oscillation at the system design stage. In this paper, we propose a frequency response measurement method with large amplitude excitation using the resonance characteristics of the measurement tube by steady-state oscillation control. The oscillation frequency is determined automatically by the resonance frequency which depends of the tube length without using a sinusoidal reference signal. It is shown that the frequency response obtained by the proposed method agrees well with the one obtained using a sinusoidal reference signal. Furthermore, the pressure amplitude for thermoacoustic self-excited oscillation of thermoacoustic engine was estimated with in about 10% error.

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Vibration energy harvester is a technology of converting vibration energy into electric power. The final purpose of this research is to develop a vibration generator that keeps the maximum power generation efficiency by adaptively changing the natural frequency of the vibrator to track the unknown frequency of vibration source. In this paper we consider a simple case where the frequency of the vibration source is constant being equal to the natural frequency of the generator, and the vibrator’s amplitude is to be controlled to meet a target value. In the previous studies, the steady-state oscillation control was proposed to solve the problem by which the charging current of capacitors was dynamically varied by a resistor, allowing a energy dissipation of the resistor. In this study, we propose a similar oscillation control system but without resistor for current control, by utilizing the charge/discharge cycle of capacitors as the control input. Experimental results show that the vibrator’s amplitude can be maintained at a target value by setting PI gains appropriately in the proposed system.

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In general-purpose servo motors, notch filters are used to suppress resonance in the equipment. When using a notch filter, it is necessary to know the resonance frequency of the system to be controlled. we have presented a method for estimating of resonance frequency based on steady-state oscillation control that keeps the amplitude of the motor speed constant at a target value by self-exciting the resonance. In this paper, the proposed method was experimentally verified by changing the cutoff frequency of LPF in the control system. As a result, it was found that the stability condition of the control system depends on the cutoff frequency , which is consistent with the previously reported result for steady-state oscillation control.

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Recently, upon creating microstructure on a workpiece surface, manufacturing high value-added parts with superior characteristics such as wettability is required. These parts are machined using ultra-precision machine tools. In this case, the ultra-precision machine tools need to be equipped with a high-speed aerostatic spindle that shaft diameter is small e.g., 10 mm. Using a small diameter shaft is decreased the bearing stiffness because of decreasing the bearing area. There are many studies shown to be effective. However, it is difficult to apply to the traditional aerostatic bearing because it needs to put a special mechanism in bearings in the design phase. Therefore, the purpose of this study was to develop a feedback displacement control system that the spindle shaft can be maintained in a uniformed position. And also, we evaluated the control performance of this system against external constant loads. As a result, we found that the displacement control system has high performance.

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In recent years, the automobile industry has been required to reduce the weight of vehicles due to environmental issues. While reducing the weight of the vehicle has advantages such as improved fuel efficiency, it has an effect on driving performance due to a decrease in rigidity. In this study, vehicle dynamics analysis was performed for a solar car by changing the suspension stiffness. From the analysis results, the relationship between suspension stiffness and steering stability was evaluated using the stability factor, an index of steering stability. As a result, it was found that the steering stability was greatly affected not only by the stiffness of the entire suspension but also by the stiffness ratio of the components. Therefore, we aim to evaluate the suspension stiffness and steering stability so as not to be affected by the suspension geometry by examining the differences between the vehicle running test, analysis and theoretical formula.

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In recent years, the automotive industry has emphasized fuel efficiency and safety with weight saving. However, it is said that they are in conflicting relation and difficult to achieve both. In order to solve this problem, this research focuses on the side of the vehicle and examines an energy absorbing member for a vehicle that is superior in side collision. First, the shape of the member with high energy absorption is devised by using the collision analysis. Currently, reinforcements called side door beams are used on the side of automobiles. Many of these reinforcements are made of metal, and we focus on aluminum and CFRP hybrid materials to achieve weight reduction.

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In the recent automotive industry, more and more vehicles are equipped with ventilation systems on their seats to improve passenger comfort. Since the centrifugal fan mounted on this system needs to blow air into a narrow space between the occupant and the seat, the pressure loss increases and the operation is performed at a low flow rate region. General centrifugal fans are operated under free inflow conditions because they have a space at the suction. In the seat ventilation system, which is the target of this research, the air flows into the blower through a narrow air flow path between the seat surface and the occupant, so that the inflow direction is limited to the radial direction. In this report, first, the effects of the radial inflow on the fan and the effects of the suction resistance installed upstream on the fan were examined by experiments. Next, fluid simulation was performed and compared with experimental data.

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A passive noise control technique for the flow-induced noise using a porous media was studied experimentally. The purpose of this study was to decrease the aerodynamic sound using porous media that permeated only sound and clarify that reduction mechanism. In experiment, flow-induced noises emitted from two types of rectangular cylinders was measured in a low-noise wind tunnel. One cylinder was made of four aluminum plates and the other was two aluminum and porous media plates each. Measurement results show that the frequency of the distinct tonal noise was different between two cylinders, that frequency was higher for using porous media. It was also found that the sound pressure level of the noise was also different and that of the cylinder using porous media plate was 25 dB smaller at maximum. Velocity field around cylinders were examined by the PIV measurement and that showed that time and space scale of separation vortex street around cylinder were smaller for using porous media. It is assumed that the change of aerodynamic sound was caused by that change in velocity field.

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