Sodium fire is one of risk factors for containment failure in a sodium-cooled fast reactor in case of sodium spray from the top of a reactor vessel due to a power excursion during a severe accident. Modifications of multi-dimensional sodium fire analysis code AQUA-SF have been carried out so as to investigate the sodium fire under the severe accident condition inside a reactor containment. The GGDH (Generalized Gradient Diffusion Hypothesis) turbulence model and a radiation model for sodium droplets were newly implemented to the AQUA-SF code. A validation study has been conducted through a benchmark analysis of an upward spray combustion experiment. This paper describes detailed influencing factors in the benchmark analysis. Reasonable temperature distribution is obtained in turbulence analyses although a laminar analysis shows an upward high temperature jet which was not observed in the experiment. The temperature distributions are almost the same between the analyses with the previous and GGDH turbulence models because there is no significant difference in the balance of production and dissipation of turbulence energy between them. The radiation model for sodium droplet increases heat transfer to structure and hence gas temperature and pressure decrease. Consequently, it has been confirmed that the experimental results is simulated reasonably by the newly introduced models in the AQUA-SF code. This means the improved AQUA-SF code is applicable for investigation of sodium fire under the severe accident condition. In addition, because the improved models on turbulence and radiation are applicable for various sodium fire events, general validity for various cases would be confirmed by additional validation activities.
Critical heat flux is one of the most important key parameters for various boiling systems, such as nuclear reactors and conventional boilers. Thus, many investigations have been reported, but most of these are concerned with the upward flow condition, and the phenomena under downward flow condition have not been fully understood. In this series of studies, the critical heat flux under the downward flow condition was classified into four mechanisms, i.e. dryout of falling liquid film, critical heat flux caused by the flooding, critical heat flux caused by the hydraulic instability and the liquid film dryout in annular flow regime. In addition, evaluation models of CHF were presented for each mechanism. Although these explanations showed the features of CHF under downward flow condition adequately, they were not suitable to explain the characteristics of CHF caused by the hydraulic instability. In this investigation, CHF of this region was formulated by two different models based on the comparison of the data in the experimental results obtained by using the tube with heated length of 200 mm and that of 400 mm. As a result, the model based on the Kelvin-Helmholtz instability was found to be suitable for relatively low mass flux condition. Under relatively high mass flux condition, the modified model of the departure from nucleate boiling (DNB) is proposed. These models show good agreement with the experimental results.
Dual fuel engines (DFE) suffer from considerably high total hydrocarbon emissions and low thermal efficiency due to its poor combustion at low loads. Also, further improvement of thermal efficiency is needed at high loads. Therefore, in this study, the effect of double diesel fuel injection on the combustion and exhaust emission characteristics of DFE using town gas 13A (natural gas) was investigated in the experiments and injection strategy was developed. The experiments were conducted using a single-cylinder engine and with a common rail injection system, varying the number of fuel injection and injection timings. In lower loads, the combustion of natural gas was activated by the double injection and both THC emissions and thermal efficiency were improved. By advancing the second injection timing, CA50 was shifted toward the top dead center and hence the thermal efficiency was improved. On the other hand, at higher loads, although the thermal efficiency slightly improved by the double injection, NOx emissions increased. It was suggested that the injection interval of double injection was appropriately selected and the injection timing was retarded so that the NOx emission can be suppressed while keeping the thermal efficiency high.
Wastage on adjacent tubes (target-wastage) arise from water/steam leak in steam generators of sodium-cooled fast reactors (sodium-water reaction). Target-wastage is likely to be caused by liquid droplet impingement erosion (LDI) and Na-Fe composite oxidation type corrosion with flow (COCF) in an environment marked by high temperature and high-alkali (reaction jet) due to sodium-water reaction. In the previous study, the authors quantitatively evaluated the effect of material temperature and fluid velocity on COCF rate, and revealed that COCF was sodium-iron composite oxidation type corrosion from metallographic observation and element assay. It was confirmed that Heymann’s equation was adaptable to LDI in a nonreactive environment. The authors derived new wastage correlations from COCF and LDI equations based on the material conversion coefficient and relaxation coefficient due to liquid film. In this study, the applicability of new wastage correlations was confirmed for each tube in sodium-water reaction test with straight vertical tube bundle under practical steam generator operation condition. The authors established that the new wastage correlations were applicable to each tube of tube bundle in the above test, and the time progress of wastage was qualitatively investigated for the two penetrated tubes in the period including the water and/or steam blowdown.
700°C class A-USC (Advanced Ultra Super Critical) thermal power plant is one of the solutions to reduce carbon dioxide (CO2) emission. In order to meet the design requirement, which is capable to be operated under 700°C steam condition, the development of Ni-based superalloys is essential. Fundamental research and demonstration of mock-up plants have been driven by national project in Japan, US, Europe and China, to confirm the reliability of Ni-based superalloys. One issue of superalloys reported by others is the stress accelerated grain boundary oxidation (SAGBO), leading to the deterioration of creep rupture properties during service. We newly manufactured the test apparatus which enables to creep test under high temperature steam environment, and evaluated the grain boundary oxidation behavior of Ni-based rotor material, TOS1X-2, under various stresses and atmosphere. Microstructure observation after creep tested at 750°C for 2,500h, found that thin layer of Cr-rich and Al-rich oxides form at all stress and atmosphere condition. Detail studies revealed that the Al-rich oxide were formed at fine, recrystallized grain boundary, which is driven by initially induced strain by machining. The quantitative analysis of microstructure showed that steam atmosphere slightly accelerates the grain boundary oxidation. On the contrary, effect of applied stress on oxidation depth was not observed. The grain boundary oxidation observed in this study was very small, suggesting that TOS1X-2 exhibits good oxidation and creep rupture properties in 700°C A-USC operating condition.
The authors develop a small and simple steam-reforming reactor in a home-use size for such various heavy-hydrocarbons fuels as n-octane, n-decane, n-tetradecane and n-hexadecane in addition to n-dodecane. Under the thermal condition controlled by electric heaters and a gas burner with a thermal diffuser, measurements are conducted on the inside-temperature profile and the hydrogen molar fraction, together with the molar fractions of other main gas components such as methane, carbon monoxide and carbon dioxide. As a result, the authors successfully achieve suitable inside-temperature profiles. And, the effects of the liquid-hourly space velocity upon the molar fractions, a conversion ratio and reforming efficiencies for various heavy-hydrocarbons are revealed. This suggests the common upper limit of liquid-hourly space velocity for the practically-suitable operation.
Energy management is systematic activity to improve energy performances of target system, and it has already been introduced in the industrial field. Energy management system is expected to solve operational planning problem and report or suggest opportunities for performance improvement. In recent years, CO2 heat pump water heater is attracting attention as one of the high-efficiency devices to meet domestic hot water demand. Energy management in residential and commercial sector is one way to keep the system operation efficient. However, few studies have been reported based on the thermodynamically-sound model of CO2 heat pump for energy management. Since the heat pump model based on Japanese energy conservation law (ECL) is designed for calculating daily performance, it is not appropriate for deriving an operational planning in shorter period, such as several tens of minutes’ intervals. In this paper, we will propose a heat pump model suitable for solving day-ahead operational planning problems in energy management in a time scale of several minutes. The CO2 heat pump model is simply composed of Lorentz efficiency and theoretical maximum coefficient of performance (COP) for trans-critical heat pump cycle. The Lorentz efficiency is identified by a series of experimental data for typical residential hot water demand with variation of ambient temperature, inlet/outlet water temperature at gas-cooler of the heat pump unit. Comparing with the base model derived by ECL model, we confirmed that the proposed model is preferable with the viewpoint of its simplicity and robust performance for wide temperature range.
Flow accelerated corrosion (FAC) is one of the causes for wall thinning mechanisms in carbon steel pipes. Prediction of geometry factor is the key elements for estimation of FAC. Geometry factor is defined as the ratio of wall mass transfer coefficient in the piping systems such as elbow to that in a straight pipe. In this study, geometry factor of the elbow pipe is computed by using large eddy simulation (LES) for Re=45000, 180000 and 540000. Mass transfer coefficient is evaluated based on the calculations simulating the heat transfer phenomena, instead of the mass transfer. Geometry factors obtained from the heat transfer coefficient by LES are good agreement with experimentally measured values by electrochemical method at Re=45000. Geometry factors on the outer side of the elbow are affected by strong shear flow and decrease with increase of Re. Geometry factors on inner side become large due to the unsteady swirling flow and they slightly depend on Re. The maximum of geometry factors are found on inner side near elbow outlet and their values are 2.38, 2.04, 1.76 for Re=45000, 180000, 540000, respectively.
In the in-service inspection of sodium cooled fast reactors, an examination by continuous leak monitoring will be applied for components constituting sodium boundaries. The continuous leak monitoring examinations are premises in a LBB (leak before break) being established. In previous LBB evaluation, the axial crack of the elbow flank has been evaluated, because in the piping system of the fast reactor with high thermal expansion, high stress is generated in the elbows flank. However, the LBB evaluations for circumferential cracks are important in the point of continuous leak monitoring in the in-service inspection. In this study, the load conditions in the LBB assessments for circumferential cracks were examined and LBB characteristics of class 1 pipes of the prototype fast breeder reactor "Monju" were evaluated as an example. Additionally, in order to research the relationship between pipe condition and LBB, many pipes were evaluated with actual conditions. As results, following conclusions were obtained. It was demonstrated that LBB characteristics are established at class 1 pipes in “primary heat transport system” and “cooling system for maintenance” of “Monju”. LBB characteristics are correlated with pipe diameter and thickness.
Due to energy shortage and environmental protection, reduction of energy consumption and CO2 emissions has been demanded. A smart home system is now expected as one of the solutions to satisfy these demands by using various home-energy devices such as cogeneration system, electric vehicle, and stationary battery in cooperation with each other. This paper analyzes the time-series dataset of the optimized home-energy device control, which minimize energy cost including initial investment and CO2 emission on a sunny winter day, by the proper orthogonal decomposition (POD). POD extracts specific rules that discharging a stationary battery in the daytime with higher power unit price and operating a cogeneration system in the time when electricity and heat demands exist are significant for energy cost reduction. Thus, POD helps to consider universal rules which will be effective anytime for home energy management.
A Very High Temperature Reactor (VHTR) is a next generation nuclear reactor system. From a view point of safety characteristic, a passive cooling system should be designed for the VHTR as a best way of a reactor vessel cooling system (VCS). Therefore, a gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Japan Atomic Energy Agency (JAEA) is advancing a technological development of the VHTR using the HTTR and is now pursuing design and development of commercial systems such as the 300MWe gas turbine high temperature reactor (Gas Turbine High Temperature Reactor 300 for Cogeneration, GTHTR300C). The objective of this study is to investigate heat transfer characteristics of natural convection in a vertical rectangular channel inserting porous materials with high porosity. It is also to examine heat transfer characteristics of natural circulation in one side heated vertical rectangular channel in order to apply to the passive cooling system of the VCS of the VHTR. This paper describes the heat transfer coefficient and the amount of removed heat in the proposed channel. To enhance heat transfer, a porous material was inserted into the vertical channel with high porosity. From the analytical results, it was found that the amount of removed heat by this method was larger than that of the channel without the porous material.
The filtered venting system has the functions of preventing the overpressure breakage of a primary containment vessel of a reactor and reducing the release amount of the radioactive materials to the environment. One of the filtered venting systems is a Venturi scrubber to remove small particles of the radioactive materials. However, the physics of the two-phase flow in the Venturi scrubber has not been clarified. In this study, the experimental results of the water-vapor two-phase flow in a Venturi tube are reported. As the gas flow rate increased, the supply amount of scrubbing water decreased and eventually stopped because the pressure at the throat increased with increasing the gas density. This phenomenon was caused by the gas compressibility. By visualizing the two-phase flow in the Venturi tube, we cannot measure the spraying from the water supply port, which is considered to affect decontamination of the Venturi scrubber. However, it was confirmed that the water film on the wall at the diverging part of the Venturi tube, and the dispersed water droplets were formed intermittently from the water film. In addition, generation of the liquid at the divergent area was observed even though scrubbing water-supply stopped.
In recent years, CCS (CO2 Capture and Storage), which capture CO2 from CO2 emission source and storage it in ocean, for mitigation of global warming has been expected. Especially, the method using depression region in seabed that can be stored huge amount of CO2 and reduce the influence on surrounding environment is required to practical use. In this method, hydrate is formed at the interface of liquid CO2 and seawater, but the diffusion behavior of CO2 with the hydrate film is not clear. Therefore, this paper aimed to measure CO2 concentration distribution and estimate effective diffusion coefficient. We visualized pH distribution in timeseries using bromophenol blue as a pH indicator in a pressure resistance visualization apparatus under hydrate formable conditions. As a result, pH concentration in water due to CO2-dissolving was verified by variation of colors of water including pH indicator, and saturated solution of CO2 represents pH 2.9. The diffusion process of CO2 was evaluated by calculated line of pH 3.0 from diffusion equation with the hydrate. We compared the experimental results and calculated results from diffusion equation, and the calculated results with larger diffusion coefficient than the conventional knowledge corresponds with experimental results. We compared experiment results with calculation results estimated by the diffusion equation of surface renewal model and small eddy model, and we confirmed that acceleration of diffusion can be explained by these models.
When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of sodium-cooled fast reactors, a high-velocity and high-temperature jet with sodium-water chemical reaction may cause wastage on the adjacent tubes. To evaluate the effect of the reacting jet to the adjacent tubes, a computational fluid dynamics code SERAPHIM, in which a compressible multicomponent multiphase flow with sodium-water chemical reaction is computed, has been developed. The multiphase flow under the tube failure accident is calculated by the multi-fluid model considering compressibility. The chemical reaction between liquid sodium and water vapor is considered under the assumption of an infinite reaction rate. The original SERAPHIM code is based on the finite difference method. In this study, unstructured mesh-based numerical method was developed and introduced into the SERAPHIM code to advance a numerical accuracy for a complex-shaped domain including multiple heat transfer tubes. Validity of the unstructured mesh-based SERAPHIM code was investigated through the analysis of an under-expanded jet experiment, which is a key phenomenon in the tube failure accident. The calculated pressure profile showed good agreement with the experimental data. Numerical analysis of water vapor discharging into liquid sodium was also performed. The calculated temperature field agreed with the existing experimental knowledge. It was demonstrated that the proposed numerical method could be applicable to evaluation of the sodium-water reaction phenomenon.
This study investigates the effects of mixing vane (MV) attached to a grid spacer on pressure drop for air-water annular flows in a vertical circular pipe of 16 mm I.D. In order to know the effects of MV, grid spacers with or without MV were installed in the test pipe. Three types of grid spacers with MV which has four MVs inclined 20, 30 degree from the vertical flow axis (4-MV20, 4-MV30) and two MVs inclined 30 degree (2-MV30) were used. In addition, two liquid injection methods (wall and center jet injections) are adopted to control liquid droplet entrainment faction in gas core. In the experiment, pressure drop along the channel upstream and downstream from the spacer was measured with a pressure transducer. In the analysis, the correlation of the pressure drop across the spacer is newly developed based on the present data.
Fatigue damage is a problem in the stable operation of thermal power plants. Especially in coal-fired thermal power plant boilers, grooving corrosion in water wall tubes caused by thermal fatigue combined with sulfide corrosion may occur. Since this grooving corrosion may cause breakage of a water wall tube, various costly repairs are conducted. Some design guidelines for power plants (e.g.: ASME Boiler Pressure Vessel Code Section III SS-NH) propose a method using FEA for evaluating thermal stresses causing fatigue. However, thermal and mechanical boundary conditions are changeable with time and uncertain, and therefore performing FEA for complex boundary conditions is not straightforward. Hence, we propose a method to easily evaluate thermal stresses and fatigue life consumption by monitoring temperature data of an actual water wall tube, without performing FEA. Furthermore, we analyzed the monitoring temperature data of actually taken from a boiler with the proposed method. We also observed the trend of fatigue damage.
Thermal efficiency is commonly applied in the power plants for the purpose of evaluating heat engines. However, the maximization of the thermal efficiency does not lead the maximization of the available power output from ocean thermal energy conversion (OTEC), which converts the finite thermal energy stored between different temperature seawaters into work. The maximum work efficiency based on the theoretical maximum work from the ideal heat engine has been identified for evaluation; however, the implication in the available thermal energy has not yet been substantially identified. This paper theoretically reveals the available thermal energy from the ocean thermal gradient and the effective energy, which is known as the exergy, using the reference of the equilibrium temperature as the dead state. By employing the finite-time thermodynamics, the available energy and the exergy calculation methods for OTEC are obtained. For the evaluation of the systems, the normalized thermal efficiency is proposed instead of the conventional thermal efficiency and the exergy efficiency for OTEC is proposed as well. The results indicated that increases in the normalized thermal efficiency increase the power output from the OTEC system and the maximum normalized thermal efficiency conditions correspond to the maximum power output heat balance. They also showed the effectiveness of the proposed exergy for OTEC derived by entropy generation minimization.
While the efforts to control global warming are being strengthened all over the world, expectations for CO2 Capture, Utilization and Storage (CCUS) technology for coal fired power plants are increasing. IHI has been working on development of oxyfuel-combustion technology since 1989 with the aim of easily capturing and storage CO2 emitted from coal fired power plants. For the demonstration of oxyfuel-combustion technology, IHI participated in the Callide Oxyfuel Project with collaboration between Australian and Japanese under the financial support of Australian, Queensland state and Japanese governments. In the project, the oxyfuel-combustion process was applied to the existing coal power plant in Queensland, Australia, and demonstration was carried out and successfully completed without any significant technical barrier to commercialization in March, 2015. In Oxyfuel-combustion, the coal-fired boiler is operated with an inlet O2 content of 27 vol% in order to achieve the same furnace heat transfer as in conventional air-firing. The first outcome of oxyfuel-combustion is a significant reduction in NOx production, typically 60% reduction, measured in mgNOx/MJcoal. The second outcome of oxyfuel-combustion is a reduction in the actual volumetric flow of flue gas, typically a 60% to 70% reduction in gas flow measured as m3/h, and a proportionate increase in the CO2 content of the flue gas from ~ 15 vol% (dry) in airfiring mode to 70 to 80 vol% (dry) in Oxyfuel mode. In addition, CO2 product from the Callide Oxyfuel Project was injected into the Paaratte formation in the Otway Basin (Victoria) to investigate the geochemical effects of CO2 (normal product) and CO2 with added impurities. The recent research and development about characteristics of roller mill and electrical precipitator using combustion test facilities for the flexibility of plant design and the current commercialization activities of oxyfuel power plant are introduced in this paper.
Microbubble emission boiling (MEB) is an interesting phenomenon because of extremely high heat flux over the CHF. However, the mechanism of occurrence and the heat transfer characteristics are still unknown. We carried out the experimental observation of bubble behaviors on the heating surface by using a platinum wire and a planar copper surface. The MEB was not observed in the subcooled boiling on the wire, but we found the similar behavior to the MEB on the planar surface. In the experiment, the huge coalesced bubbles were observed intermittently on the planar heat transfer surface, showing higher heat flux than the CHF. Because such large bubble was not formed on the fine wire, we are considering that the formation of the large coalesced bubbles has an important role on the occurrence of MEB. We also applied the prediction of heat transfer by the microlayer model and we have a good agreement with experiments for nucleate boiling before the MEB.
Hamaoka Nuclear Power Station (NPS) has always embraced the most up-to-date knowledge in its effort to enhance safety. Following the accident at TEPCO’s Fukushima Daiichi Nuclear Power Station, we have been implementing voluntary countermeasures for tsunami and severe accidents countermeasures, and introducing additional measures in light of the New Regulatory Requirements so as to build up our safety. While reinforcing facility measures, Hamaoka NPS is also making all-out efforts to ‘strengthen the frontline response capabilities' as it is humans who can handle those facilities to make the measures function effectively. Strengthening collaboration with local communities to enable a coordinated response in case of nuclear emergency is also essential. “No More Fukushima Daiichi Accidents”, with this firm resolve, Hamaoka Nuclear Power Station is making all-out efforts for safety.
An anode-supported honeycomb SOFC gives high volumetric power density and improves thermo-mechanical durability at high temperatures. We have so far fabricated and tested a honeycomb cell with a cathode layer of LSM and an electrolyte layer of 8YSZ on a porous anode honeycomb substrate of Ni/8YSZ. The anode-supported honeycomb cell exhibited promising volumetric power densities. In the present study, current-voltage and current-volumetric power density characteristics of the cells having different flow channel arrangements of the anode and cathode are measured under various inlet hydrogen fuel flow rates to show the effect of three-dimensional transport and distribution of the fuel in the porous anode substrate on the cell performance. We measure ohmic resistances of the honeycomb cells by current interruption method, and indicate the impact of nickel catalyst re-oxidation in the anode substrate by the fuel depletion with the flow channel arrangements resulting in high ohmic resistances and deactivation of the nickel catalyst. In low inlet fuel flow rate, smaller number of the anode flow channel is thereby advantageous, while larger number of the anode flow channel is advantageous in high inlet fuel flow rate. We also discuss suitable flow channel arrangements depending on inlet fuel flow rate to choose an appropriate operation mode.
This study analyzes cost-minimum combination of long-term introduction of technologies for the given targets of integrated CO2 emissions from 2010 to 2050. The area covers all sections of power generation, industry, home & office, transportation, and others. The analysis was made with MARKAL MODEL, a linear programing model, modified to be available for renewable energies with daily and seasonal fluctuation. Input data are given from variety of official statistics. The results show the relationship between the CO2 reduction amount and the increased cost: for example, the maximum limit of the integrated CO2 reduction for the period is 38%, when the integrated total cost increases 18% compared to the case with no CO2 limitation. When the CO2 limitation becomes 20%, increased cost changes to 3%. The number itself changes in some extent depending on the input data, but it gives ideas of the trends in the total relationship. As the CO2 reduction rate increases, coal power plants are gradually replaced by combined cycle of natural gas, and then by wind and solar. The influence of the CO2 limitation is large in the home & office sector and the industry sector due to the increased cogeneration system and electricity from lower CO2 power plants. However, the CO2 emission from steel and paper industries and transportation sector remains almost same. This result in transportation sector is due to the reason that the hybrid cars take share similarly regardless of the CO2 limitation, and that electric and fuel cell cars take little share in this analysis conditions.
This study proposes nondestructive long-range inspection for axial cracks appearing at the inner surface of a metal pipe using microwave. Numerical simulations were conducted to design a mode converter that converts TEM into TE mode that is necessary to detect axial cracks. The simulations confirmed that situating coaxial cables circumferentially enables to propagate microwaves in TE mode inside a pipe. The results also revealed that the number and positions of coaxial cables affect the frequency range where microwaves propagate as TE01 mode dominantly. A mode converter with four coaxial cables was fabricated according to the results of the simulations aiming at the propagation of microwaves as TE01 mode. Experimental verification was conducted using a brass pipe with a total length of 11.6 m and an inner diameter of 19.0 mm, and having the mode converter at the center. The results showed significant difference between the signals with and without an artificial slit simulating a crack. This study also proposed a signal processing method to compensate for the dispersion of microwaves with an aid of a window function. The signal processing method gave the clearer signals corresponding to the slits to determine the predict position of the slit quantitatively using the time-of-flight of the signals.
Fatigue crack propagation in a polycrystalline Ni-base superalloy was experimentally investigated at room temperature. Fatigue crack propagation tests were conducted under a constant ΔK condition to clarify the effect of grains crystal orientation, grain size and grain boundary, employing CT specimens with different grain size and grains orientations. A series of experiments revealed that crack propagation modes within the grain were roughly categorized into the shearing and opening mode, depending on crystal orientations and grain size. Crack propagation rate in the shearing mode was affected by the primary and secondary crystal orientation of grains and its fundamental mechanism could be explained by the findings for the single crystal material in our previous study. The crack propagation rate in the opening mode was affected by both Schmid factor and Young's modulus, which increased with reduction of the crack length relative to the grain size. It was also found that the grain boundary caused the crack retardation depending on the crack propagation modes in both grains across the boundary. In case the crack propagated in the shearing mode in two adjacent grains, the crack retardation became more pronounced due to the discontinuity and transition of the crack planes.
Ammonia is regarded as one of the alternative fuels because CO2 is not emitted during the combustion process of ammonia. The physical properties of ammonia are suitable for transportation and storage as a “hydrogen carrier”. Also, a large amount of ammonia can be easily produced through the Haber-Bosch process with low price. To use ammonia as a fuel, it is necessary to understand the fundamental combustion characteristics of ammonia. Flammability of ammonia coaxial jet diffusion flame is important to know for developing the industrial furnace. Ammonia laminar diffusion flame is difficult to be stable under atmospheric oxidizer (O2 21%) of room temperature. In this study, therefore, the oxygen-enriched combustion is applied to make the stable ammonia laminar diffusion flame. In this study, effects of the fuel velocity and the oxidizer velocity on the ammonia laminar diffusion flame are investigated in detail under the conditions of O2 volume fraction of 24% and 25% at the burner rim thickness of 6.0 mm. Results showed that there were three regions with different extinction mechanism of the ammonia coaxial jet diffusion flame under the relatively higher fuel velocity. Particularly, the flame extinction also occurred under the low fuel velocity under the condition of O2 volume fraction of 24%.
In this paper, we introduce practical design and hardware implementation issues of an adaptable crawler mechanism for a mobile robot, enabling it to maintaining its constant desired pose when moving. For this purpose, a novel multi-legged adaptable crawler (MLAC) prototype is proposed by utilizing a spring and a rack-and-pinion unit. More specifically, the MLAC prototype allows changing of the crawler configuration in order to adapt to a local surface topology. When the MLAC prototype is mounted under the mobile robot, even though the robot might encounter ascending/descending slopes and thresholds, the mechanism allows it to preserve its locomotive pose continuously. The design and performance of the MLAC prototype is explained in detail. As a result, the effectiveness of the crawler was verified through extensive experiments. Although the robot equipped with the proposed crawler encountered ascending/descending slopes and thresholds, it could preserve its desired locomotive pose continuously. Moreover, we investigated the technical features by comparing the proposed crawler and a typical crawler through experiments.
This paper presents an optimal control design approach for LNT aftertreatment system in diesel engines. First, based on the observation of physics of the system, a dynamical model is constructed to represent the NOx reduction behavior under the air-fuel ratio changes. Then, the optimal control problem is formulated as a nonlinear dynamics-constrained optimization problem with a cost function that targets the NOx reduction with trade-off between fuel consumption and emission reduction. A numerical approximation algorithm is proposed to solve the optimization problem. Finally, the validation results with the simulation model with the identified physical parameters are illustrated to compare with the conventional rule-based approach.
The purpose of this research is measurement in plain forest using a 3D-LIDAR. Point clouds of standing trees are acquired by a mobile 3D-LIDAR that is brought by a human who keeps walking in the forest. We have developed the mobile 3D-LIDAR that has wide field of view. 3D forest maps can be generated by LOAM. LOAM is a method of 6DOF matching with rotating 2D scans. Diameters at breast height and trunk locations are measured from the 3D forest map. We consider a way to prevent the error of matching by LOAM from affecting measuring precision of diameters at breast height and trunk locations of each standing tree. At first, a central axis of the trunk is obtained by cylinder fitting to the point clouds of the trunk. Next, scanned points on the trunk of the one scan are projected onto a plane that has a normal vector parallel to the central axis. Finally, the diameters and the central points are obtained by circle fitting to the projected points, and averages of diameters and central points at the same trunk are calculated for diameters at breast height and trunk locations. In experiment, we have evaluated precision of measured diameters at breast height and distances between standing trees among three walking paths for the measurement in plain forest. Target accuracy of diameters at breast height is achieved for 12 out of 14 standing trees. Target accuracy of distances between standing trees is achieved for all standing tree pairs. It takes approximately 30 minutes in a range of 30 m × 10 m area for ten times measurements by the proposed method. This time is shorter than the conventional manual method. Proposed method can make forest measurement more efficient.
Because of using interference of sound wave, it is difficult to control in whole three-dimensional acoustic field by Active Noise Control (ANC). Instead, around-head-control is investigated in this paper. In this system, two error microphones are set near ears, and noise is reduced around evaluation points locally. This system requires fast adaptation speed of controller following movement of head, and a problem still remains that the control effect during movement becomes worse. Against this problem, we propose Modified Reference signal Method (MRM). This method improves adaptation speed during movement, by modification of filtering of input signal in Filtered-x. The secondary path model that controller requires is interpolated by the method Ohno et al. proposed. There is modeling error of secondary path caused by interpolation and measuring error of it, and this modeling error causes divergence of controller. In this paper, suppression method of divergence is also investigated. Suppression of divergence is executed by addition of penalty term to evaluation value, and it is equivalent to ridge regression mathematically. Proposed method requires a large number of matrix calculations, therefore reducing method of computational complexity according to acoustic characteristics is also investigated in this paper. The validity of the proposed method is shown by numerical simulation and experiment.
House-collapsing simulation using a physics engine is an effective method for acquiring structural data regarding collapsed houses with the aim of understanding the properties of destroyed or disordered structures for designing and operating rescue-robots. However, the simulation needs a lot of time since a house model consists of a large number of rigid bodies and joints. In order to find an appropriate configuration of computer hardware and software for accelerating house-collapsing simulations, this study evaluates the performances of four major physics engines, namely Open Dynamics Engine, Bullet Physics Library, PhysX 2.8.1 and PhysX 3.4, by comparing the processing time about two sample structures including only rigid bodies or rigid bodies constrained by joints. Results of the experiments show that the use of multi-core CPU and GPU, especially high-speed GPU, on PhysX 3.4 has the best performance since it can process a large number of rigid bodies and joints in parallel. Based on the results, an existing simulation system has been improved and the collapsing process of one-house, which consists of about 7,500 rigid bodies and 15,000 joints, can be simulated in real-time using multi-core CPU and GPU. Moreover, this study estimates the size of GPU memory which is required for simulating the large-scale field on PhysX 3.4 to enlarge the scale of simulation. Consequently, the collapsing process of thirty-houses which includes interactions between collapsed houses can be simulated.
This paper investigates the forced vibrations of double beams, consisting of upper and lower beams, which are discretely connected by N sets of springs and dashpots, when the upper beam is subjected to harmonic excitation. In the theoretical analysis, the orthogonality conditions of the vibrational modes of the system are derived and allow ones to obtain the modal equations of motion. Then, the solutions of the forced vibrations for the two beams can be theoretically obtained by summing up the results for the vibrational modes. In the numerical calculation, two cases, Cases A and B, are examined. In Case A, the two beams are connected by a single set of a spring and a dashpot, while in Case B they are connected by two sets of them. In Case A, when the two beams have identical materials and dimensions, the resonant peaks for the odd-order vibrational modes are independent of the connecting spring and dashpot because they are not stretched. However, the resonant peaks for the evenorder vibrational modes are influenced by the spring and dashpot. In Case A, when the two beams have different dimensions, the lower beam may vibrate at amplitudes lower than those of the upper beam due to the changes of the vibrational mode shapes. In Case B, the amplitudes of the even-order vibrational modes for the lower beam may be increased because increasing the number of connecting springs and dashpots results in the changes of the vibrational mode shapes and modal forces. The validity of the theoretical analysis was confirmed by comparing the theoretical results with the results obtained by the FEM analysis when the damping coefficients of the dashpots are comparatively small.
In the field of regenerative medicine, cell processing operation mainly depends on manpower. Moreover, it requires a large amount of labor and cost, and its efficiency needs to be improved. Automatic cell culture apparatuses equipped with a vertical articulated robot have recently been proposed. However, automating all tasks of cell processing complicates the system constitution. This study aims to develop a simple and rational cell processing system by combining the tasks performed by a robot and a human. Herein, we first analyze each task in the cell processing operation, verify whether a task can be efficiently performed by a robot and automated equipment, and judge sharing with a human. In this study, we examined the improvement in the efficiency of the discarding task of spent culture media in a flask using a robot arm in a media change process. We conducted task analysis on the discarding task performed by a cell processing expert and beginner and conducted experiments using a robot on the discarding task based on the analysis results. We proposed an optimum condition of the discarding task considering the dripping risk owing to the characteristics of the culture media and showed that a robot could perform the discarding task more efficiently than a human; the dripping risk could also be reduced using a robot.
This paper describes the results of the static loading tests using half-scale thick rubber bearings to investigate the fundamental characteristics such as horizontal and vertical restoring force applied for a Sodium-cooled-Fast-Reactor (SFR). The thick rubber bearings, which have a rubber layer roughly two times thicker than conventional rubber bearings, have developed by the authors to ensure seismic safety margins for the components installed reactor building, and to reduce the seismic response not only horizontal direction but also vertical direction. The applicability of design formula to take into account an inner hole for the thick rubber bearing is demonstrated by compared with the results of static loading test, and indicates the non-linear restoring force under beyond-design-basis ground motions. In addition, a new type of hysteresis models that can predict the non-linear characteristics in horizontal and axial direction are proposed, and presents the seismic response results, including beyond-design-basis ground motions, obtained by response analysis using the proposed hysteresis models.
With a view to application to micro-macro decoupled multiscale simulations, a method of isogeometric homogenization analysis (IGHA) is proposed to characterize the in-plane macroscopic material behavior of dry woven fabrics in consideration of microscopic frictional-contact between fiber bundles. The microstructure of dry woven fabrics having periodicity only in in-plane directions, which is identified with the representative volume element to realize in-plane macroscopic deformations, is referred to as an in-plane unit cell in this study and is regarded as a virtual specimen in numerical plate testing (NPT). NURBS basis functions are utilized for discretization to accurately solve micro-scale frictional contact problems of fiber bundles and the knot-to-surface (KTS) and mortar-based KTS algorithms are employed to evaluate the contact- and friction-related variables. The initial state of an in-plane unit cells, which is supposed to be obtained by a weaving process, is determined as a solution of the bending problem of two fiber bundles contacting with each other and is in reality subjected to in-plane tension. Several numerical examples are presented to demonstrate the performance and capability of the proposed IGHA for conducting NPT of dry woven fabrics involving with microscale frictional-contact to characterize the geometrical-nonlinearity-induced material nonlinearity especially in response to macroscopic shear deformations.
This paper presents a topology optimization based on a covariance matrix adaptation evolution strategy (CMA-ES) for acoustic cloaks rendering a scattering object acoustically invisible. The cloaks are designed by minimizing the scattering of acoustic waves around the object and the objective function is defined as the integrated intensity of the scattered wave. CMA-ES is employed to search the optimal set of level set functions as design variables during a topology optimization for minimizing the objective function regularized by a perimeter constraint. Level set functions express structures with its structural boundaries clearly without grayscales during the optimization process. In the best case in our simulation, we succeed to obtain an optimal configuration which can reduce the amount of acoustic scattering to 0.81% of that in the absence of cloaking.
The sound quality design of consumer electronics spans multiple design processes, from requirement definition to functional and structural design. It is difficult to reflect customer demands depending on situations to physical design. In this paper, we introduce the evaluation grid method that assumes use cases to clarify customer demands for camera shutter sound depending on situations. To define the sound quality target, customer demands according to use cases are derived from clustering analysis of the evaluation grid test for camera shutter sound. Using domain mapping matrix, we define the relationships between use cases and requirement clusters, requirement clusters and evaluation words for sensory test, evaluation words and tonal factors. By this method, it is possible to evaluate the customer requirements depending on use cases, and define the sound quality target. In order to solve a problem in which relationship among customer requirements, functional and structural design are not clear, we propose an MDM-based representation to show the design information management from requirement definition to functional and structural design. In the requirement definition process, sound quality targets depending on use cases are defined using tonal factors. In order to systematically connect to sound quality metrics in the functional design process and to engineering metrics in the structural design process, DSM and DMM were used. The method was applied to camera shutter sound design and shows its effectiveness.
As represented by energy and/or environmental issues, modern technologies are facing with a lot of difficult problems that must be solved urgently for sustainable development. Concerning with anyone of those problem-solving, however, we often come across such a situation that requires us to consider multiple goals conflicting with each other. To deal with such complicated and difficult problem, multi-objective optimization has been highly required and supported agile and flexible decision-making. Accordingly, we developed a novel method termed MOON2R/MOON2 and demonstrated its effectiveness through various applications. To enhance its usefulness, in this paper, we have proposed a unique procedure for multi-objective optimization and its post-optimal analysis. Actually, it is deployed in co-operation with our elite-induced multi-objective evolutionary algorithms (MOEA) and a new idea named downsizing NSGA-II together with a technique to solve single-objective optimization problem using MOEA. After preliminarily examining some properties of the idea, a practical benchmark problem on multiple car structure design has been solved to discuss the significance of the proposed idea. Eventually, the proposed idea makes multi-objective optimization more practical toward recent qualified decision-making.
This paper deals with the onset and development of wavy wrinkling of a web caused by a roller tilt using a FEM commercial software. The simulation model mainly used is composed of two rigid rollers and a web (a rectangular sheet) divided by a membrane element with four nodes. After applying tension to the web, both end parts of the web are fixed to the rollers and then the one roller is inclined gradually. The main results are summarized as follows. (1) The wavy wrinkling suddenly occurs at a tilt angle β of the roller. A pitch, amplitude and slope of the wavy wrinkles are larger in the loose side of the web comparing with those in the tight side. The number of wavy wrinkles of the web decreases exponentially with increase in β. A slack area is approximately estimated as an area where the von Mises stress is smaller than a certain value. (2) The number of wavy wrinkles becomes larger when Young's modulus or a thickness of the web decreases, or when the web tension increases, comparing at the same β. (3) The onset of the wavy wrinkling is strongly affected by the imperfection of the tensile strain distribution and of the web position relative to the rollers in the tension process. (4) Another wavy wrinkling simulation method is proposed, which makes a membrane buckle by applying a small out-of-plane displacement.
For the medical treatment of damage or ruptures in the flexor digital tendon, finger flexor tendon suture surgery is utilized. In previous studies, various core suture methods have indicated that important factors affect biomechanical properties, including the number of suture strands. In many suture methods, Fore-strands core suture and Six-strands core suture are used. Recently, asymmetric sutures have been reported to be effective in the gap formation. However, what has not been studied is the optimal asymmetry or required degree of asymmetry. Therefore, this study was aimed to evaluate the strength in asymmetric core sutures under cyclic load testing. Porcine flexor tendons were used in this study. We sutured porcine flexor tendons using combinations of six-strands Pennington suture and interlocking cross-stitch peripheral suture. This study looked at one symmetrical and five types of asymmetrical six-strands Pennington suture. In reference to the suture standard suture length (10 mm) from the end of the porcine flexor tendon, an asymmetric suture was shifted 1 mm, 2 mm, 3 mm, 4 mm and 5 mm from the reference position, respectively. This experiment was performed under cyclic load testing using an evaluation simulator our research group developed. A 2 N preload was applied to each of the sutured tendons. Tendons were tested with an initial load of 10 N for 500 cycles. If no evidence of failure was noted after the 500 cycles, the force was increased by 5 N for each additional 500 cycles. This procedure was continued until rupture. The sutured tendons were pulled at a constant distraction rate of 300 mm/min. As a result, tendons with 2 mm or more asymmetry had significantly greater the number of cycles to rupture than tendons with symmetry and with 3 mm or more asymmetry had significantly greater the number of cycles to rupture than tendons with asymmetry 1 mm. Tendons with 3 mm or more asymmetry had significantly less gap formation than tendons with symmetry. Furthermore, tendons with asymmetry 3 mm and 4 mm had significantly less gap formation than tendons with asymmetry 1 mm. Asymmetry 3 mm was the highest in both number of cycles to rupture and fatigue strength. Furthermore, it had the smallest value in the gap formation. Therefore, our results support that asymmetry 3 mm produces better beneficial had results compared to the others.
Many women undergo lumbopelvic pain (LPP) during pregnancy. The main factors for LPP are the physical stress related with change of posture and muscle relaxing around pelvis. Also it is thought that movement patterns during daily activity are associated with LPP. Therefore, this paper attempts to investigate the characteristic of movement patterns that have affect LPP during pregnancy. For this purpose, an experiment was conducted to measure standing up and sitting down of pregnant women using inertial sensor unit (IMU), which is simple device and is able to measure motions such as vibration or rotation quantitatively. Then movement evaluation parameters were calculated from measured data of lumber angular velocity. As the movement evaluation parameters, Maximum peak, Minimum peak, Peak to peak (PP: Range between Maximum peak and Minimum peak), Time of PP, PP divided by Time of PP, Root mean square of each parameter, and each parameter divided by Body mass index variation (BMIV) were calculated during both of standing up and sitting down for each of roll, pitch, and yaw angles. Finally, we consider whether there is any relevance between LPP and movement characteristics by comparing the movement evaluation parameters of LPP group with these of non-LPP group. As a result, it appears that Maximum peak, PP and PP/Time of PP of pitch angle during standing up have some relevance to LPP. Additionally, particular features of LPP group in roll and yaw angles and during sitting down were founded by accounting for BMIV to the proposed parameters.
A novel method to measure the deformation of a urethane-foam object using an X-ray computed tomography (X-ray CT) technique was proposed and examined. The proposed method is made up of following two steps. First, X-ray sensitive ‘contrast media’ were drawn in lattice-like manner on top and bottom surfaces and internal planes of urethane-foam, which enabled visualization of the drawn positions in CT images. Second, position data of contrast media were then converted into the numerical values in a prescribed coordinate to measure the deformation. It was found that the contrast media successfully visualized outer and internal displacement with the urethane-foam deformation, and the comprehensive error of measurement was 0.3 mm in root mean square. As a trial for further practical purpose, the deformation of the urethane-foam mattress with a human-body model on it was measured using this method. A urethane-foam mattress with contrast media was prepared, a human trunk model was set on the mattress, and the mattress with the model was subjected to X-ray CT. The deformation state at surface of, and especially inside of, the mattress could be visualized and measured. We concluded that the proposed method could bring us an information on deformation state of the urethane-foam and the urethane-foam mattress as numerical values.
In an axle journal bearing of railway vehicles, it is required to reduce the fretting wear caused by the very slight relative slip between the contact surface of the inner ring and the backing ring. Up to now, we have found that an uneven contact pressure distribution between the inner ring and the backing ring affects the fretting wear. In this work, we have proposed the backing ring which is provided with grooves in the circumferential direction on its oil seal sliding surface in order to obtain the even contact pressure distributions in the radial direction between the inner ring and the backing ring of the axle journal bearing. To confirm the effect of providing backing ring with grooves, we have investigated the contact pressure distributions between the inner ring and the backing ring, and conducted a rotational test using the full-scale railway axle journal bearing. It has been found out that the maximum contact pressure is reduced and the contact pressure distribution in the radial direction becomes even by grooving the oil seal sliding surface of the backing ring in the circumferential direction, and further that the fretting wear of the backing ring with grooves becomes smaller than that of the existing backing ring without grooves. Therefore, there is a possibility that the fretting wear is decreased by bringing the radial contact pressure distribution close to being even.
Vibration suppressors are used to resolve the problem of collisions and entanglement to the hoistway equipment caused by the rope sway due to the resonance of the building and the elevator rope. To gain an understanding of rope sway, the free vibration analysis of the rope with vibration suppressors has been studied. However, the vibration of the rope equipped with vibration suppressors encounters geometric nonlinearity, and hence, its characteristics have been studied under a few conditions. In the case in which the vibration suppressors are located except for both ends part of the rope, exact solution has been obtained when the gap between rope and vibration suppressor is zero. In this paper, an exact solution to the free vibration of the rope with vibration suppressors located except for both ends part is presented in the case where the gap between rope and vibration suppressor is not zero and center position of the rope is pulled. The rope is modeled with string. The natural frequency of this case was obtained as a function of the gap. Finite difference analysis of the rope vibration with vibration suppressors is also performed. The calculated results of the finite difference analyses are in good agreement with those of the exact solution.
Environmental test for space hardware is one of the effective way to verify their design and quality. The level of environmental test has been decided empirically based on the development experience of government procurement large satellite of each space agency. However, this test level may not necessarily be the optimal solution in some cases due to diversification of missions and spacecraft design in recent years. In order to solve this problem, we propose a new model which optimizes the environmental test level from the viewpoint of minimizing the total costs related to the environmental test: replacement or repair cost due to failure in the test and the loss cost due to failure in the flight environment. By using this model, it is possible to find the optimum test level according to the importance of a mission, single mission or multiple missions applied hardware. Furthermore, the proposed method will support the quantify assessment of the cost reduction effects when either increasing design margin or reducing strength variation in production.