Superheaters are essential components in a coal-fired power plant because they keep the highest tube wall temperature points in the radiant boiler. The pressurized steam flowing in the superheater tubes is heated via the thermal radiation and convection from the combustion gas. To prevent the bursting of superheater tubes caused by the thermal fatigue for stable and safe plant operation, precisely predicting complex heat transfer characteristics, and estimating the local temperature and heat flux of the superheater are necessary. In this study, a computational fluid dynamics model of the boiler and the second and third superheaters in a coal-fired power plant is developed using radiation model (DO model) and turbulence models (k-ε RNG model). In the second superheater installed near the burner, the influence of radiation from the combustion gas is strong, and the temperature and heat flux of the outermost tube are highest. In the third superheater, the tube wall temperature and heat flux becomes large in the upper and middle parts of the superheater, where the combustion gas flow velocity around the superheater is high, whereas those at the bottom of the superheater are significantly small due to the dead water region of the gas. Therefore, to consider the combustion gas flow is important for prediction of the heat transfer characteristics of the third superheater.

Japan has a huge geothermal resource with geothermal power generation capacity of about 550 MWe. The hot water geothermal resources in Japan are mostly in the range of 53-120 °C. Hot spring thermal energy conversion (STEC) can provide a stable power output so introduction of small-scale STEC based on organic Rankine cycle (ORC) is expected. Hybrid hot spring thermal energy conversion (H-STEC) is a combination of distillation and ORC; thus, it is able to produce electric power and water to supply the cooling tower simultaneously. H-STEC has a flash chamber to prevent scaling in heat exchangers due to the supersaturated Ca, Si, and so on. The system characteristics of H-STEC are such that power output and supplied water ratio can be clarified by using parametric analysis, however, there has been no significant research proving such in actual experiments. In this study, the system characteristics of H-STEC were clarified by using a small-scale demonstration equipment. Pumped hot spring water was used as the heat source of H-STEC where the hot spring water was delivered after heat utilization. To evaluate the available power for a power generation system using a finite heat source, the maximum power output and the maximum power efficiency were defined. The maximum power efficiency is the ratio of the gross power to the maximum power. The maximum gross power was 15.9 kW, and the maximum power efficiency was 22.1%. The condensed water from evaporator could supply 100% of the water consumption in the cooling tower.

High efficiency coal fired power plants are expected to operate at a certain rate due to low generated electricity costs. In coal fired power plants, coal mills are important machinery that pulverize the coal and supplies the coal powder to the boiler. To protect the bearings from coal dust, seal air is added. The seal air is supplied from one air compressor to each position of several coal mills at a target power station. An imbalance in its flowrate can lead to coal mill failures, thereby affecting the operation of coal fired power plants. In order to diagnose any problems with the operation of a coal mill immediately after maintenance, the heater method was used to measure the seal air at five locations from the outside of the supply pipes. The heater method is possible to measure the flow rate of compressed air and steam in the pipes from the outside of the pipes without any modification of the pipes, and has previously been applied to the measurement of cooling air flow in gas turbines. In the present case, three pipes out of five measuring points have curvature, so that a numerical analysis was carried out to verify whether the heater method is valid. Due to the effects of the corona disaster and other work, the measurement schedule at the power station was restricted and the installation, measurement and removal of instruments at five locations was carried out in a period of five days. As a result, it was confirmed that the seal air flowrate at each of the coal mill locations was normal value and that there were no problems with operation.

In high temperature gas-cooled reactors (HTGRs), Tri-isotropic (TRISO)-coated fuel particles are employed as fuel. In the high burnup coated fuel particle, stress due to fission gas pressure and irradiation-induced pyrolytic carbon (PyC) shrinkage is introduced into the coating layers and consequently the stress could cause failure of coating layers under high burnup irradiation condition. A failure model has developed to predict failure fraction of TRISO-coated particle under high burnup irradiation. In the model, failure probability is strongly dependent on the irradiation characteristics of PyC. This paper describes the outline of the failure model and evaluation result of high burnup fuel irradiation experiment by the model.

In recent years, attention has focused on the excellent mechanical properties of bones, teeth, and crustaceans. In particular, interlocking tissue is strongly interested as one of the characteristics of the microscopic structure of crustaceans. The interlocking structure has sutures like puzzle pieces, and friction slip in the pull-out process occurs at the sutures by subjecting to a tensile load. As a result, it is recognized that the toughness is apparently improved. By the way, in wooden houses in Japan, iron nails are not used, but the mortise-neck joints are used to fasten timbers together. The feature is that the fastening force can be freely controlled by adjusting the angle of the suture. Therefore, in this study, we simulate the bioinspired interlocking structure by these sickle joints and develop a mechanical model based on the pull-out mechanism for this structure. In order to verify the validity of the developed model, we compared it with the finite element analysis results. Furthermore, we investigated the effect of the suture shape on the relationship between load and displacement. It was clarified that the suture shape and interfacial friction coefficient affect the maximum load and elongation at break. Finally, the relationship between the fracture energy estimated from the relationship between load and displacement and these parameters was summarized as a map.

Direct fuel injection spray is used to improve thermal efficiency and environmental performance in SI engines. A mixture is formed through momentum exchange between fuel droplets and ambient gas, along with mixing accompanied by droplets evaporation and diffusion. Both the droplets development derived from the liquid fuel atomization and the entrainment ambient air predominate the mixture formation process. The purpose of this study is to elucidate the momentum exchange characteristics of the spray formed by a single-hole injector for direct injection gasoline engines. To clarify the momentum exchange characteristics of spray droplets, the spray was visualized by optical experiments and the spray development process was analyzed. The parameters are injection pressure and ambient density. A comparison of experimental results and a model analysis of a single droplet movement was conducted, and different of deceleration characteristics were evaluated. In the case of the fuel spray, the induced ambient air by the spray tip droplets decreases the relative velocity between the spray droplets and the spray internal flow. A model for predicting the temporal variation of the spray tip penetration from the different of momentum exchange characteristics between the spray and the droplet was proposed.

After massive earthquakes, many steel structures were built with frame welded joints of welded construction and welded base. Although steel structures are considered highly resistant to earthquakes, many were constructed using frame-welded joints of fillet welded construction and welded column bases. These weld joints could have a low capacity to absorb energy during earthquakes. Infrastructure built in the period of high economic growth in Japan is becoming deteriorated. Furthermore, it is an issue that costs are expensive because mandatory checking once every five years. Structural health monitoring for the maintenance of infrastructures is widely expected to be a new technology. In order to put such a new sensor to practical use, it is required to accumulate the measurement data and establish the evaluation methods to derive information about the states of structures. In this paper, we have proposed the development method for sensor measuring displacement by using composite piezoelectric film and glass. We are investigated relationship between the displacement of the structure and the output voltage from the piezoelectric joint sensor to recorded the sensor characteristics. Structural FEM analysis was also introduced to evaluate the sensor characteristics and assess the mechanisms and effects of various environmental factors on the structure's response.

NV (Noise and Vibration) performance is determined by the influence of all components constituting a whole structure. It is difficult to design NV performance efficiently because the structural modification of a certain component affects the performance of the whole structure. As one of the effective ways to design the performance, this paper presents an inverse method for structural modification that keeps the specified eigenfrequency and its modal vector of the whole structure the same. Firstly, the matrices for structural modification are calculated as dynamic stiffness matrix variation from the zero-divisors of a specified modal vector. Furthermore, it is possible to represent the calculated matrices redundantly by using an arbitrary non-zero weighting matrix. This makes it possible to obtain various solutions for structural modification. However, the matrices are generally calculated as fully populated and non-symmetric matrices. Therefore, with these matrices, it is difficult to feasibly find a symmetrical and sparse mass or stiffness matrix to use for structural modifications in applications that focus on designing specified regions of the whole structure. Secondly, we propose how to transform the matrices as the zero-divisors into the sparse matrix of reduced row echelon form in advance. This transformation simplifies building symmetric and sparse matrices for realizable structural modification. The sparse matrix, redundantly represented by a weighting matrix, allows a value analysis to select among alternative structural changes to lighten the product or simplify its complexity. Finally, the proposed method was applied to a numerical case study.

Natural angular frequencies and natural vibration modes of the three-dimensional orthotropic rectangular parallelepiped that is not made of layers are investigated. The natural angular frequencies and eigenmodes are calculated as the eigenvalues and eigenvectors of the frequency equation that is derived from the relationship between stress and strain in the x-, y- and z-axes, the equations of motion and the admissible functions of displacements. In the numerical examples, we investigate a three-dimensional orthotropic material and an isotropic material. In the relationship between the dimensions and the natural angular frequencies, there are three ranges where the natural angular frequencies vary linearly, they are almost constant and the intermediate range between them regardless the type of the materials. In the case of the three-dimensional orthotropic material, two natural angular frequencies were almost the same only in the range where the natural angular frequencies vary linearly. All eigenmodes are changed in the intermediate range and are unchanged in the other ranges regardless the type of the materials. In the case of the isotropic material, there is always only one dominant component of eigenvectors, while in the case of the three-dimensional orthotropic material, there are sometimes two.

In recent years, research and development of robots that exist in the same space as humans and can collaborate with humans have been actively carried out. If the body of a robot is made of a hard material, it may cause injury. Therefore, attempts have been made to make a robot with a soft body using rubber or resin. In order to accelerate such research on soft robotics, it is necessary to establish fast and stable simulation algorithm for robots containing viscoelastic bodies such as rubber and resin. Therefore, in this study, we consider to approximate viscoelastic bodies with finite rigid body segments and connect them with joints and linear viscoelastic elements such as Voigt model, Maxwell model and generalized Maxwell model to approximate viscoelastic properties. The recursive dynamics algorithm is used to speed up the calculation, and the generalized-α method is used to stabilize the numerical integration. In particular, we propose a new method on how to incorporate the Maxwell model and generalized Maxwell model into recursive dynamics algorithm and generalized-α method. The effectiveness of the proposed method is confirmed by some numerical examples. In addition, the effectiveness of the proposed method is verified on a real system by applying Particle Swarm Optimization (PSO) to identify the dynamic parameters in linear viscoelastic elements.

Laser slicing technology is a new processing technology to fabricate optical glass lenses by focusing ultrashort laser pulse laser into the glass to form a modified layer. Crack propagation can be generated by forming a modified layer with residual stresses, and three-dimensional machining can be achieved by controlling the crack propagation. The purpose of this study was to elucidate the crack propagation mechanism by the laser slicing of glass. The stress around the modified layer were evaluated using microscopic birefringence evaluation device under various laser irradiation conditions. As a result, it was clarified that crack propagation occurs according to the tensile stress in the modified layer due to volume expansion. The tensile stresses were stronger when the modification layer was densely formed. Using this knowledge, we attempted to fabricate a spherical lens with a diameter of 30 mm and a radius of 100 mm. The stress concentration at the crack edge due to warpage promoted self-crack propagation and successfully produced a spherical lens with a mirror surface.