For the mass production of astatine-211, a promising radiopharmaceutical for cancer treatment, we have proposed the innovative “Liquid Bismuth Target System.” The target window in this system must be made from a material that resists the highly corrosive liquid bismuth environment. To meet this requirement, a promising target window material was selected in corrosion experiments performed in stagnant liquid bismuth. Based on knowledge of corrosion in liquid lead-bismuth eutectic gained during the development of fast reactors and accelerator-driven subcritical systems, FeCrMo alloy, FeCrAl alloy and austenitic stainless steel (as a reference) were selected as the specimen materials. Experiments were carried out under saturated dissolved oxygen and low oxygen conditions, and the corrosion behaviors of the specimens were evaluated, mainly by scanning electron microscopy. The FeCrAl alloy exhibited the most excellent corrosion resistance, followed by FeCrMo alloy. Both materials are suitable candidates for the target window. Although austenitic stainless steel was less corrosion resistant than the former two materials, it is a likely applicable for the target window under appropriately limited operation conditions (such as irradiation current and exposure time) of the liquid bismuth target system.

The high temperature gas-cooled reactors (HTGRs) are the next-generation reactors with high safety, because the cores of HTGRs would not melt. But it is important to improve the oxidation resistance of the fuel in case of a huge oxygen ingress into the core to further improve the safety of HTGRs, because most of the volume of the core of the HTGRs consists of graphite. Coated fuel particles (CFPs), of which the diameter is around 1 mm, are used in HTGRs. A small sphere containing fissile materials is sealed up with ceramics coating layers to form a CFP. A mixture of CFPs and starting materials of binding material (matrix) is sintered to form fuel compact. Currently the matrix is graphite, which would easily oxidized in case of a huge oxygen ingress into the core. In this study, the development of oxidation resistant fuel compact, of which the matrix is a mixture of SiC and graphite, has been carried out. Simulated CFPs (alumina particles) and starting materials of matrix (Si powder, graphite powder and resin) were molded and hot-pressed into simulated fuel compacts. In order to maintain the structural integrity of fuel elements for HTGR under accident conditions, not only oxidation-resistant but also high-strength fuel compacts should be further developed. Hot press conditions such as pressure would be one of the factors affecting the strength of the HTGR fuel elements. In order to identify the optimal hot press conditions for preparing the high-strength fuel elements, the effect of the hot press conditions on the mechanical strength properties of the HTGR fuel elements should be evaluated quantitatively. In the present study, the response surface model, which represents the relationship between the hot press conditions and the mechanical strength properties, has been constructed by introducing statistical design of experiments (DOE) approaches, and the optimal hot press conditions were estimated by the model.

Two-phase pressure drop in the debris has been studied by many researchers concerning the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow patterns on interfacial drag and pressure drop. Usually, it would not be easy to visualize such two-phase flow behavior in a randomly packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates a two-dimensional network of porous structures, was fabricated to avoid overlapping bubbles. The two-phase flow pattern in the porous structure has been identified by high-speed imaging of the two-dimensional network model. The flow regime map based on the flow pattern visualization results is applied to the pressure drop evaluation and it could reduce the overestimation of experimental values. The experimental results suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model.

A direct reactor auxiliary cooling system (DRACS) under natural circulation (NC) conditions with a dipped-type direct heat exchanger (D-DHX) in the upper plenum of a reactor vessel (RV) has been investigated for enhancing the safety of sodium-cooled fast reactors. Studies of the past have revealed that core-plenum interactions, which consists of penetration of the coolant from D-DHXs into the subassemblies and the narrow gap between them (IWF: inter-wrapper flow), and the heat transfer through a wrapper tube among subassemblies (radial heat transfer), occurred and increased core cooling performance during the DRACS operation. Therefore, a multidimensional thermal-hydraulics analysis model in the RV using a computational fluid dynamics (CFD) code (RV-CFD model) was developed to evaluate the core cooling performance. For the design study, the RV-CFD model must simulate reasonable calculation costs while maintaining accuracy. In this study, the subchannel analysis method using the CFD code for fuel subassemblies (subchannel CFD model) was applied to the RV-CFD model. In the subchannel CFD model, the porous media approach was used to consider local geometry in the fuel subassembly, and the effective heat conductivity coefficients in a diffusion term of the energy equation were set to fit the actual radial thermal diffusion between subchannels. Two numerical simulations were compared to the experimental data obtained from the sodium experimental apparatus PLANDTL-1. In the first case, the focus was only the radial heat transfer without the D-DHX operation. In another case with the D-DHX operation, the IWF noticeably occurred, and the focus was on the core-plenum thermal interaction. The calculated sodium temperature in the core correlated well with the experimental results. The RV-CFD with subchannel CFD model was validated for core-plenum interactions during the DRACS with the D-DHX operation under NC conditions.

In order to improve the thermal performance of natural draft wet cooling tower under crosswind, a three-dimensional numerical model for heat and mass transfer of cooling towers was established. The comparison with the design parameters of the cooling tower shows that this model satisfies the requirements of the thermal performance computation of cooling tower. According to the numerical calculation of the cooling tower and the analysis of the temperature, humidity and velocity field under various crosswinds velocities, a scheme of partition water distribution of cooling tower was proposed to deal with the effect of crosswind. Using this scheme, the influence of various spray water density ratio k on the thermal performance of cooling tower were researched, and the results show that the heat transfer performance of the cooling tower can be effectively improved under a certain comparing with uniform water distribution. When the cross wind speed is in the range of 2-6 m/s and this partition water distribution scheme is applied, maximum reduction of the outlet water temperature will reach 1.01K comparing with uniform water distribution.

In solid-fuel fired boilers, ash deposition on heat-transfer surfaces can cause operational problems. It is important to predict ash-deposition properties based on the ash composition of the solid fuel in advance. However, general prediction methods do not always agree with actual ash deposition under conditions of actual combustion. In this study, we first developed a new sampling system that can collect ash particles during the combustion of mixed bituminous coal samples in a boiler; the composition of the sampling ash was evaluated, and the composition that affect ash-deposition properties were identified. Next, the ash composition of the coal samples was evaluated as a mineral with CCSEM. These results were summarized in order to identify which mineral particles were strongly related to ash-deposition properties, and a new prediction method for ash deposition based on the actual combustion state was investigated. The main conclusions were drawn as follows: (1) Iron was condensed in the early-stage ash deposition of the secondary superheater tube area, and there were differences in the amount of iron between the sampling-ash deposition and the ash in the bituminous coal. (2) The amount of iron in the ash deposition could be predicted with high accuracy by using the amount of included iron oxide, pyrite, Fe-Si (iron silicate), and pyrrhotite. (3) The method developed in this study can be applied to boilers with various solid fuels such as coal, woody biomass, and/or waste. This will contribute to improving the prediction accuracy of ash-deposition properties.

Some ash particles in municipal and industrial waste adhere to heat exchanger tube surfaces, which causes problems such as heat-transfer inhibition, high temperature corrosion and low utilization in Waste-to-Energy (WtE) plants. The objective of this study is to develop new surface treatment materials and techniques which can decrease the ash deposition and the corrosion, and to provide further understanding of ash deposition mechanisms for various metal surfaces in WtE plants. First, the adhesion force between an ash pellet, which was made of ash sampled from a WtE plant, and an alloy specimen was measured to investigate the mechanisms that increase ash deposition. Second, the adhesion interfaces of the specimens were analyzed after the adhesion force measurement. The result was that the adhesion forces of all specimens increased with the interface temperature, and there was a clear temperature dependency on the force. The adhesion force of the ash pellet to stainless steel AISI 430 and 304 were larger than to 310S or to a surface-modified AISI 304 due to a lower Cr content. In particular, there was a correlation between Ni + Cr content in the surface of the alloy specimens and the adhesion force. Moreover, the analysis of AISI 304 with SEM-EDS have shown that the active oxidation involved in interface reactions. In addition, analysis of the adhesion interface and the thermodynamic equilibrium calculation supported the results of the adhesion measurements. Specifically, results of the calculations were that partial pressure of Fe-chloride gases are higher than that of Ni or Cr-chloride gases.

Experimental absorption refrigeration equipment with a generator driven by waste heat was manufactured and tested, with 2,2,2-trifluoroethane/1-methylpyrrolidine as the working fluid pair. A plate generator was used to reduce the heat transfer distance and to decrease the start-up time. However, the flow paths of the plate generator were not large enough to separate the refrigerant vapor from the two-phase flow. Therefore, a gas-liquid separator was introduced, and a cooling coil was embedded as a partial condenser in the separator to cool the refrigerant vapor and to condense the absorbent contained within it, thus increasing the concentration of the refrigerant vapor. The separator successfully separated the refrigerant from the solution in all tested conditions. The cooling rate of the partial condenser was varied from 143 to 222 W by changing the flow rate of cooling water. Then, a calculation model for the partial condenser was constructed to analyze its characteristics. In the calculation model, the helical coil partial condenser was modeled by being divided into 10 horizontal columns. It was assumed that only the solution phase had the concentration distribution from the bulk flow to the liquid-vapor interface. We show that a heat and mass transfer area of 0.04 m² is needed to achieve an outlet vapor concentration of 0.95.

To achieve the global goal of decarbonization, use of hydrogen in place of fossil fuels is expected to increase worldwide. In this study, to establish a hydrogen combustion technology of boilers for a safe, low NOx and low cost, a combustion test of a hydrogen burner was carried out in a large model furnace, and it was confirmed that supplying hydrogen fuel to the burner at a high pressure that has never been used before reduces NOx. In addition, the mechanism of NOx reduction by increasing the supply pressure was newly clarified by the numerical analysis (LES) of hydrogen combustion field. The high-pressure hydrogen supply was also effective for the cost reduction, and the prospect of the application to the actual use of the hydrogen burner was obtained.

Biomass fuel is promoted toward a target of net GHG zero emissions in 2050 that Japanese government announced last October 2020. Using biomass pellets in pulverized coal fired power plants are recently increasing. IHI has supplied the co-firing power plants of 30cal% or more biomass pellets with coal. The biomass particles after pulverization by biomass mills are transported to the burners through the fuel pipes by air. Deposition of the biomass particles in a fuel pipe on the way to a burner make a serious impact on the stable combustion and boiler operation. It is important to understand conditions of occurring deposition in order to prevent the deposition of the biomass particles in the fuel pipe. However, various types of pellets are used, and conditions of occurring deposition is depending on the size and shape of the biomass particles. In this test, the transportation of two types of biomass particles is observed by using a transparent horizontal pipe with 30m length. This result suggests that conditions of occurring deposition is different depending on the shape of biomass particles.

Carbon capture and storage (CCS) is an important technology to reduce CO₂ emissions from power and industry. To accelerate large-scale CCS deployment, further reduction of the cost to implement the full technology chain is necessary. Full chain CCS cost depends on multiple technological, market, and societal factors. Therefore, case-specific cost analysis is important. This study estimates the CCS cost in Japan, which can be considered as a case study for specific countries where offshore sites are more suitable for CO₂ storage than onshore sites regarding geological reasons and barrier reduction of public/political acceptance. With the phasedown of unabated coal power, retrofitting amine-based post-combustion CO₂ capture system is a realistic way for pulverized coal-fired power plants. Capture cost was determined by the process simulation of coal-fired power plant retrofits. Current political realities in Japan suggest that CO₂ transport will be done by ship. Transport cost was estimated via a bottom-up analysis of each sub-process. Injection and monitoring cost was based on the values reported by the Tomakomai demonstration project, which are applicable to onshore injection into an offshore storage site. We find the full chain CCS cost to be 99-111 USD/t-CO₂. Though changing the solution in the CO₂ capture process from monoethanolamine to the blend of 2-amino-2-methyl-1-propanol and piperazine reduces the regeneration energy by 0.85 GJ/t-CO₂, the CCS cost was only reduced by ~9 USD/t-CO₂. Likewise, even when the regeneration energy was reduced to 2.0 GJ/t-CO₂ using a hypothetical amine solution embedded in a highly optimized PCC system, the CCS cost was still ~93 USD/t-CO₂. Considering that capital expenditure accounts for ~65% of capture cost, downsizing capture facilities may provide further cost reduction. Since transport and storage costs were roughly equivalent to capture costs, full chain CCS implementation is likely necessary to reduce costs through learning-by-doing, scale-out, and market effects.

At a combined cycle power plant, gas turbine cooling air flowrate data is required for operation and maintenance because it is an important for analyzing not only the temperature of both stators and blades but also plant efficiency. However, it is very difficult to measure the data. An ultrasonic flowmeter cannot be used since the measurement position becomes hot, usually exceeding 300 degrees centigrade. An insert type flowmeter is also difficult to use as it requires additional pipe processing for installation and also causes a pressure loss. Accordingly, we tried to use the heater method, which we proposed and validated in our previous papers. In this method, a circumferential heater is attached to the outside of a pipe and then the axial temperature distribution along the outside of the pipe, which is influenced by the fluid velocity in the pipe, is measured by thermocouples. The velocity is analyzed on the basis of the temperature distribution along the pipe. Measurements were conducted for two kinds of cooling air pipe at an advanced combined cycle power plant. In one, cooling air is extracted from the 13^th stage of a compressor and supplied to the 2^nd stators of the gas turbine; in the other, cooling air is extracted from the 9^th stage of the compressor and supplied to the 3^rd stators of the gas turbine. As a result, it was clarified that the cooling air flowrate had a positive dependence on atmospheric temperature at the plant. The dependence was also compared to that of a tit 1,600 degrees centigrade-class combined cycle power plant, with a power output of 700 MW.

In high-chromium ferrite heat-resistant steel pipe welds, which are often used in ultra-supercritical pressure boilers in Japan, a large number of Type IV creep voids occur in the region deep beneath the outer surface of the pipe and then develop into cracks. When a crack is detected, the main piping of the power plant is judged to have zero remaining life. Since the damage occur in deep areas of the material and there is no non-destructive evaluation (NDE) method for dense creep voids prior to crack formation, NDE methods cannot be used for plant-maintenance planning. The authors selected the water-immersion acoustic-imaging method, which has the highest measurement resolution among the ultrasonic-measurement methods that can be expected to be applied to actual equipment, and searched for a measurement method that greatly exceeds the existing measurement resolution. And we focused on the reception characteristics of ultra-high-focused acoustic lens. For that purpose, we designed an aspherical, angled acoustic lens that can be applied to the welded part of the actual piping. We also developed a new measurement system that can mechanically scan this probe with high accuracy. As a result, using the developed measurement system, changes in the scattered wave amplitude could be observed depending on the presence or absence of Type IV creep void density in the deep region of the material, which led to the evaluation of the void density area.

Supercritical carbon dioxide (S-CO₂) energy system has gained extensive attention recently, while design of its turbine is one of the most crucial tasks. In this research, we establish a data-driven model for the physical field prediction of a S-CO₂ turbine. This method can be applied to real-time prediction of physical fields in design and operation process of turbine. Firstly, a brief outline is presented, including previous computation efforts of S-CO₂ turbine and academic progress on applying deep learning in physical field prediction. Then, a specific S-CO₂ system is defined with details of blade profile geometry and operating conditions. Generation of the training data with CFD method is also covered. Next, the structure of the proposed neural network and its training strategies are formulated. To balance the prediction accuracy and the time cost, we build our model by basic multi-layer perceptron (MLP) model, with various depths of the hidden layers. Finally, accuracy of the predictive models under different training parameters are evaluated and compared to each other. The result demonstrates that the proposed framework is capable of predicting whole physical fields of the S-CO₂ turbine efficiently with overall mean square error (MSE) on test dataset as low as 3.187×10^-4, which implies its great potential in design and maintenance of S-CO₂ turbines.

Superheaters are critical components in a coal-fired power plant because they sustain the highest tube wall (metal) temperature point in the boiler. The pressurized steam flowing in superheater tubes is mainly heated via the thermal radiation and convection from the combustion gas in the radiant zone. To prevent the bursting of superheater tubes caused by the high-temperature creep, corrosion, and thermal fatigue for proper plant operation and maintenance, accurately predicting complex heat transfer characteristics, estimating the local temperature, and assessing the heat flux of the superheater are essential. In this study, a computational fluid dynamics model of the boiler and the superheater in a coal-fired power plant was developed using radiation and turbulence models. The local metal temperature and heat flux of the superheater were evaluated by calculating the heat exchange between the combustion gas and pressurized steam flows in the tubes. The calculated values of the steam outlet temperature accurately matched the values measured using the equipment at the plant, and thermal radiation was confirmed to be dominant in the boiler. The metal temperature and heat flux of the superheater at the outermost heat transfer tubes, which receive the maximum thermal radiation, were larger than those of the superheater at the inner tubes. Therefore, the outermost tubes were determined to be under the most severe thermal conditions despite having a higher mass flow rate of steam. Additionally, the heat fluxes on the center lines of superheater tube panels were higher due to the large gap between the adjacent heat transfer tubes at the bent part.

The operation of gas turbines under off-design conditions is becoming more frequent to absorb the power supply fluctuations from renewable power. By operating gas turbines at the off-design point, the flow rates of cooling air through the nozzle guide vanes (NGVs) and blades can be varied. It is necessary to understand the influence of the flow rate change of cooling air on the deterioration of aerodynamic components in gas turbines to realize suitable maintenance work. We conducted conjugated heat transfer simulations of the 1st stage nozzle with flow simulation of the following stages. The numerical method was validated by comparison with the operation data from a working power plant. It was found that the deteriorated NGV was damaged around the leading edge near the hub-side end wall due to corrosion. The numerical results showed that the entire wall cooling efficiency of the NGV increased as the flow rate of cooling air increased, excepting for the leading edge near the hub-side end wall. This was because the pressure upstream the NGV is too high to increase the cooling air flow rate. The results also showed that the gas turbine performance was maintained regardless the flow rate change of the cooling air.

Hysteresis in so-called ‘microbubble emission boiling (MEB)’ in a pool is investigated experimentally. Correlation among the heat transfer characteristics, the behavior of the vapor bubbles over the horizontal circular heat-transfer surface, and the induced boiling sound is indicated under various highly subcooled conditions for the processes of increasing and decreasing the power input to the heaters. Variations of the boiling sound is depicted by monitoring the spectrogram. Spatio-temporal variation of the vapor bubbles’ oscillation and their synchronous behavior in the MEB are illustrated. It is indicated that the variation of the fundamental frequency of the vapor bubbles’ oscillation almost coincides in the increasing and decreasing processes of the power input to the heaters, whereas the heat transfer characteristics becomes worse in the decreasing process in the MEB regimes.

Carbonization or torrefaction is performed to promote the fuel efficiency of biomass as a renewable energy source by increasing the biomass energy. Carbonized biomass is manufactured in large-scale furnace, and technology to measurement the carbonized biomass fuel characteristics is required in manufacturing plants because the best fuel is produced under the optimal conditions. Herein, we proposed a method of evaluating fuel characteristics by measuring the hue value of the carbonized biomass. In this study, a carbonization experiment on the raw biomass was conducted, and the characteristics of the carbonized biomass in terms of elements, heating value, lightness L* and chromaticity a* and b* were evaluated. As the results, a positive correlation was observed between the color difference ΔE and the heating value of the carbonized biomass. Moreover, changes in the lightness L*, and the chromaticity a* and b* of cellulose and xylose affected the carbonized biomass, whereas such changes in lignin a limited effect on the carbonized biomass. The color difference ΔE between the raw biomass and the carbonized biomass could be used as an indicator of the optimal production of carbonized biomass.

In recent years, the importance of hydraulic power generation has further increased because of the movement toward decarbonization and the need to control floods in Japan. For this reason, demand for dam discharge valves has been increasing. However, it is necessary to improve the reliability of valve systems due to their complicated two-phase flows. Therefore, in this study we attempt to apply a link-sleeve valve (LSV), which is usually used for public water supply, as a dam discharge valve. In general, to prevent cavitation erosion, vibration, and noise, air is injected into the downstream pipe of a dam discharge system. Since LSVs are designed to operate in a pressured water supply system, however, the characteristics of air‒water two-phase flows in LSVs have not been investigated. To clarify the characteristics of air entrainment by water jets in an LSV, experiments were conducted using a small-scale LSV model. The results showed that this entrainment is analogous to that which occurs with a jet pump or an ejector at a high water flow rate, while air suction behavior shows complicated characteristics at low water flow rates. This means that air entrainment occurs due to the water jet and that air reverse flow occurs due to the positive pressure gradient in the pipe at a high water flow rate. The present findings could be useful for improving the potential use of LSVs as a lower-maintenance alternative to dedicated dam discharge valves.

To reduce both the platform motion and dynamic loads of floating offshore wind turbine-generator systems, feedforward control for high wind speed regions is developed by combining with the wind speed previewed by a nacelle-mounted lidar. First, the wind speed preview using a nacelle-mounted lidar was simulated by considering the floating platform velocity and the temporal difference of laser casting. Feedforward control, in which the blade pitch is manipulated according to the preview wind speed so as to maintain the rated generator speed, is combined with gain-scheduling feedback control of the generator speed. This feedforward control is characterized by employing the first-order lag filter with the delay compensator for the preview wind speed. The effectiveness of the developed feedforward-feedback controller is analyzed through an aero-elastic-hydro-control coupled nonlinear dynamic simulation of a 5-MW floating offshore wind turbine-generator system under turbulent wind fields and irregular wave height variations. The feedforward-feedback controller provides the stabilization of the platform pitching motion and the reduction in the dynamic load variations at the blade root and drivetrain as well as the tower base in comparison to the conventional gain-scheduling feedback control of the generator speed. Moreover, the sensitivity of the settings of the first-order lag filter and the delay compensator in the wind speed preview is clarified for their optimal design.

Cross-flow boiling in horizontal tube bundles occurs in kettle type evaporators. Convective heat transfer due to the motion of vapor bubbles is an important factor for boiling heat transfer in the evaporator under low heat flux conditions. To clarify the liquid agitation effect on heat transfer, the local heat transfer around a tube in in-line and staggered tube bundles was investigated in two-phase flows under adiabatic and atmospheric pressure conditions. Air and tap water were used as the working fluids. The test section was a vertical duct with inner dimensions of 90 × 90 mm². In-line and staggered tube bundles each containing eight rows and five columns, were used as test sections. For both bundles, the tube diameter, d, was 18 mm, and the tube pitch, p, was 22.5 mm (p/d = 1.25). The local heat transfer had the highest values around θ = ± 90° where the liquid velocities were high in single-phase, bubbly and intermittent flows for both in-line and staggered arrays. A significant improvement in the heat transfer caused by the bubble motion was present for the in-line array as compared to the staggered array. Owing to the fluctuation of the liquid velocity, the heat transfer coefficient fluctuated significantly under intermittent flow conditions. In the bubbly flow at p/d = 1.25, the average heat transfer coefficient around a tube for the in-line array was higher than that for the staggered array. In contrast, the heat transfer coefficient of the staggered array was high under intermittent flow at a lower gas flow rate. This tendency is different from the results at p/d = 1.5. With a decrease in the relative size between the bubble diameter and the tube gap, there was a high improvement in the heat transfer coefficient due to the liquid agitation in the bubbly flow.

Solid Expandable Tubular (SET) has been proven a promising technology in overcoming several unresolved challenges like isolating unwanted substances, sidetracking, well repair, and patching in horizontal wells. A novel multistage expansion system of SET is found to be an efficient way of reducing expansion cost while conserving tubular structural integrity. However, due to the complexity of multistage system, an estimation of post-expansion properties of tubular, especially in variable physical conditions, becomes a challenge in making the technology viable and cost-effective. In the current work, numerical modeling is utilized to evaluate the effects of multiple physical conditions, tubular-mandrel contact and tubular's boundary conditions on the post-expansion properties of tubular. Initially, a finite element model of multistage tubular-mandrel system is developed using the real well conditions in finite element software ABAQUS. The real boundary conditions of tubular at the field, fixed-free and fixed-fixed, are incorporated in finite element model. Moreover, a nonlinear material model, using the experimental results of uniaxial tensile tests, is used to model tubular's material behavior, while mandrel is considered as rigid body. A surface-to-surface contact conditions are defined through Coulomb’s friction law with varying coefficient of friction. The finite element simulation results are compared with the experimental observations of single-stage tubular-mandrel system and found to be in good agreement. Finally, further simulations are performed to evaluate the deformation behavior of tubular using contact pressure, equivalent stress, tubular thickness variation, length shortening, and equivalent plastic strain. It is observed that the contact and boundary conditions of tubular have significant effects on tubular post-expansion properties.

It is generally known that the temperature and mixture concentration in the combustion chamber influence knock intensity. It is assumed that the distribution of temperature and mixture concentration in the end-gas region of a two-stroke engine differs depending on the ignition position. Therefore, this study investigated the effect of the ignition position on knock behavior in a spark-ignition engine. A two-stroke air-cooled single-cylinder gasoline test engine was used to investigate autoignition and abnormal combustion behavior based on in-cylinder pressure analysis, in-cylinder visualization of combustion and frequency analysis of in-cylinder pressure waveforms. Six ignition positions were defined, considering the distribution of temperature and gas concentration in the cylinder. The results revealed that the ignition position influenced localized autoignition development behavior and knock intensity owing to the related distribution of temperature and fuel concentration. It was observed that knock was relatively weak when a large quantity of high-temperature residual burned gas was present in the end-gas region because it suppressed a sharp pressure rise. Knock was also relatively weak in the presence of a large quantity of fresh charge in the end-gas region because the flame was able to propagate sufficiently. Strong knock occurred when the fresh charge and residual gas were both present in the end gas-region because the high-temperature residual gas easily autoignited and autoignition developed rapidly in the new charge that readily burned. Accordingly, it was found that conditions tending to induce strong knock were present when a distribution of high-temperature areas conducive to autoignition and a distribution of high fuel concentration conducive to combustion occurred in the end-gas region. In addition, the dominant knock vibration mode was the 1,0 mode regardless of the ignition position, although it was observed that the resonant frequency varied depending on the end-gas distribution.

In this study, we proposed a structural health monitoring and diagnostic method for layered structures using the transmissibility function. This method belongs to the primary diagnosis one, and its purpose is to identify the location of abnormality quickly after abnormality detection. It focuses on the following fact. When the ceiling or foundation of the first floor is excited in the horizontal direction, the transmissibility function of the top floor is constructed with only the characteristics of the top floor, and in the case of descending to the lower floor, only the characteristics of the floor of interest are unknown parameters. In the diagnosis of an actual structure, there may be a difference between the actual vibration characteristics and those obtained from the mathematical model. We also proposed a method for predicting the resonance and peak frequencies in an abnormal condition based on the difference between the actual measurement and the mathematical model under a normal condition. First, we considered a three-layered structure as a numerical example and verified the validity of the proposed method. When the method was applied to the three types of abnormal conditions, it was shown that the abnormal diagnosis could be performed correctly. Next, we constructed an experimental model of a three-layered structure, and verified the applicability of the proposed method. We realized three types of abnormal states similar to the numerical examples and showed that correct abnormal diagnosis was possible. As described above, the validity and applicability of the proposed method were clarified.

Stability and buckling have attracted extensive attention in the design of structural elements, especially in the design of thin-walled structures since they may naturally have poor stability and be prone to buckling failure. This paper proposes a level-set based topology optimization (TO) method that can maximize the lowest linear buckling load under a mean compliance constraint. First, we conduct the linearized buckling analysis and formulate the optimum design problem. Second, we derive the design sensitivity and revisit the reaction-diffusion equation-based level-set topology optimization. Finally, we solve several two-dimensional benchmark problems and the design results are presented to validate the proposed method.