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Journal Articles

Evaluation of local damage to reinforced concrete panels subjected to oblique impact by soft missile

Nishida, Akemi; Kang, Z.; Nagai, Minoru*; Tsubota, Haruji; Li, Y.

Nuclear Engineering and Design, 350, p.116 - 127, 2019/08

Many empirical formulas have been proposed for evaluating local damage to reinforced concrete structures caused by impacts of rigid missiles. Most of these formulas have been derived based on tests involving impact normal to target structures. Thus far, few tests with oblique impact onto target structures have been carried out. As a final goal of this research, we aim to propose a new formula for evaluating the local damage caused by oblique impact based on previous experimental and simulation results. In this study, we perform simulation analyses for evaluating the local damage to reinforced concrete panels subjected to oblique impacts with various angle by soft missiles under various impact velocities using a simulation method that was validated using the results of previous impact experiments. In this paper, the investigated results and obtained knowledges from them are shown.

Journal Articles

Impact assessment on local damage to reinforced concrete panels by different projectiles; Impact behavior for projectiles with hemispherical nose shape

Kang, Z.; Nagai, Minoru*; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08

Many empirical formulae have been proposed for evaluating the local damage to reinforced concrete (RC) structures caused by rigid projectile impact. The majority of these formulae aim at impact tests perpendicular to target structures, while few impact tests oblique to the target structure have been studied. The final objective of this study is to propose a new formula for evaluating the local damage to RC structures caused by oblique impact based on past experimental and simulation results. Up to now, we validated the analytical method by comparison with the experimental results and conduct the simulation analysis of impact assessment on RC panel by rigid/soft projectile with flat nose shape using the validated approach. In the part 1 of this paper, the same analytical method is used to simulate the local damage to RC panels caused by oblique impact of rigid/soft projectile with hemispherical nose shape. The results associated with penetration depth of RC structure, energy contribution ratio, etc. are presented.

Journal Articles

Uncertainty of different modeling methods of NPP building subject to seismic ground motions

Choi, B.; Nishida, Akemi; Shiomi, Tadahiko; Muramatsu, Ken*; Takada, Tsuyoshi*

Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 8 Pages, 2019/08

In this study, to clarify the influence of the uncertainty of the input seismic ground-motion response of a nuclear power plant (NPP) building, we examined seismic-response analysis results using two different methods of modeling buildings and then compared the results to evaluate effects related to differences between the models. The two methods we used are the three-dimensional (3D) finite-element (FE) model (mainly composed of shell elements) and the conventional sway-rocking (SR) model. Also, using features of the 3D FE model, we analyzed the spatial features of the response results. In this paper, we describe the differences in seismic response obtained by the 3D FE model and the SR model based on simulated input ground motions, and we discuss the influence of the characteristics of the input ground motion on the maximum-response acceleration of the modeled NPP building.

Journal Articles

Development of seismic counter measures against cliff edges for enhancement of comprehensive safety of nuclear power plants, 10; Avoidance of cliff edge for reactor vessel

Yamano, Hidemasa; Nishida, Akemi; Choi, B.; Takada, Tsuyoshi*

Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08

The objective of this study is to assess cliff edge effects, which are greatly important for nuclear power plants. Through assessments of failure probabilities (fragility), this study examined seismic margins of simulated two kinds of thin- and thick-walled reactor vessels by using response waveforms of the reactor building with/without a seismic isolation system obtained by seismic response analyses. The fragility analyses showed that the seismic isolation technology largely reduced the structural response effects nearly twice as much as that of the non-isolated plant. In focusing on uncertainty of response factor of components, the seismic isolation plant has a significant margin compared to the non-isolated plant even if factors from 0.5 to 2.0 are taken into account. This study concluded that the seismic isolation technology is effective to avoid cliff-edge effects.

Journal Articles

Development of seismic counter measures against cliff edges for enhancement of comprehensive safety of nuclear power plants, 8; Identification and assessment of cliff edges of NPP structural system

Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Itoi, Tatsuya*; Takada, Tsuyoshi*

Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 9 Pages, 2019/08

In this research, the seismic safety of a nuclear power plant (NPP) is treated as a system in which the various cliff edge effects are identified and quantified based on the concepts of risk and defense in depth. An aim of this research is to develop a methodology for avoiding these cliff edge effects. In order to examine how the cliff edge state specified and evaluated in the seismic response analysis of the building system, we investigated the seismic isolation mechanism related to physical cliff edges and the modeling effects of the building system related to knowledge oriented cliff edges. In particular, with regard to knowledge-oriented cliff edges, we quantitatively evaluated the uncertainty within the same floor which is evaluated by a three-dimensional building model and tried to reflect it on the fragility evaluation. This paper presents and discusses these results.

Journal Articles

Application of analysis for assembly of integrated components to steel member connections towards seismic safety assessment of plant structures

Nishida, Akemi; Murakami, Takahiro*; Satoda, Akira*; Asano, Yuya*; Guo, Z.*; Matsukawa, Keisuke*; Oshima, Masami*; Nakajima, Norihiro

Proceedings of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08

Exhaustive studies on external events that may pose a threat to the structures of nuclear facilities and evaluations of the structural integrities are critical to safety. One of the components that greatly influence the behavior of the plant structure is the connection of structural members. In particular, the modeling of the connections has relied on empirical methods, and been conservatively designed and evaluated by considering them as pinned or rigid connections. Therefore, in this research, we have aimed to develop a connection modeling method that reproduces more realistic behavior by utilizing a three-dimensional model of the connection. As the first step of this research, we planned to determine the stiffness of the connections of steel structural members. The results confirmed that the connection can be regarded as a partially-restrained connection depending on the connection specifications of the structure, and the prospects for realistic stiffness evaluation of the connection were determined.

Journal Articles

Simulation analysis on local damage to reinforced concrete panels subjected to oblique impact by different projectiles, 1; Comparison of impact behavior for rigid projectiles with flat and hemispherical nose shape

Kang, Z.; Nagai, Minoru*; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 9 Pages, 2019/05

Many empirical formulae have been proposed for evaluating the local damage to reinforced concrete (RC) structures caused by rigid projectile impact. The majority of these formulae aim at impact tests perpendicular to target structures, while few impact tests oblique to the target structure have been studied. The final objective of this study is to propose a new formula for evaluating the local damage to RC structures caused by oblique impact based on past experimental and simulation results. The finite element code LS-DYNA R7.1.2 is used to perform the numerical analysis by adopting Lagrangian finite elements and explicit time integration. So far, we validated the analytical method by comparison with the experimental results and conduct the simulation analysis of impact assessment on RC panel by rigid/soft projectile with flat nose shape using the validated approach. Results of reduction coefficient with respect to rigid/soft projectile and impact angle were obtained. Therefore, in this study, we focus on the impact problems caused by rigid projectile with hemispherical nose shape. The same analytical method is used to simulate the local damage to RC panels caused by oblique impact of rigid projectile with hemispherical nose shape. The results associated with penetration depth of RC structure, energy contribution ratio, etc. are presented. According to the comparison analysis of results of local damage to RC structure by rigid projectiles with flat and hemispherical nose shape, the influence of different nose shapes of rigid projectile on the local damage of RC panels caused by oblique impact is investigated.

Journal Articles

Simulation analysis on local damage to reinforced concrete panels subjected to oblique impact by different projectiles, 2; Comparison of impact behavior for soft projectiles with flat and hemispherical nose shape

Nagai, Minoru*; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05

In this study, the final purpose is to propose a new formula for evaluating the local damage caused by oblique impact based on past experimental results and previous research achievements. Up to now, we validated the analytical method by comparison with the experimental results and conducted simulation analysis associated with impact assessment on RC panel by soft/rigid projectile with flat nose shape using the validated approach. In the part 1 of this study, the same procedure of our previous work is followed to investigate the local damage to RC panel caused by rigid projectile with flat and hemispherical nose shape. In the part 2, we focus on the comparison analysis of simulation results of local damage to RC panel subjected to oblique impact by soft missile with flat and hemispherical nose shape. The structural damage of RC panel and projectiles, energy contribution ratio, etc. is studied for each case. The results indicate the difference of nose shape of projectile is of great importance to influence the penetration depth generated by oblique impact of soft projectile.

Journal Articles

Advanced analysis technology for new material and product development

Sasaki, Hirokazu*; Nishikubo, Hideo*; Nishida, Shinsuke*; Yamazaki, Satoshi*; Nakasaki, Ryusuke*; Isomatsu, Takemi*; Minato, Ryuichiro*; Kinugawa, Kohei*; Imamura, Akihiro*; Otomo, Shinya*; et al.

Furukawa Denko Jiho, (138), p.2 - 10, 2019/02

no abstracts in English

Journal Articles

Failure behavior analyses of piping system under dynamic seismic loading

Udagawa, Makoto; Li, Y.; Nishida, Akemi; Nakamura, Izumi*

International Journal of Pressure Vessels and Piping, 167, p.2 - 10, 2018/11

 Percentile:100(Engineering, Multidisciplinary)

It is important to assure the structural Integrity of piping systems under severe earthquakes because those systems comprise the pressure boundary for coolant with high pressure and temperature. In this study, we examine the seismic safety capacity of piping systems under severe dynamic seismic loading using a series of dynamic-elastic-plastic analyses focusing on dynamic excitation experiments of 3D piping systems which was tested by NIED. Analytical results were consistent with experimental data in terms of natural frequency, natural vibration mode, response accelerations, elbow opening-closing displacements, strain histories, failure position, and low-cycle fatigue failure lives. Based on these results, we concluded that the analytical model used in the study can be applied to failure behavior evaluation for piping systems under severe dynamic seismic loading.

Journal Articles

Evaluation of local damage to reinforced concrete panels subjected to oblique impact; Simulation analysis for evaluating perforation phenomena caused by oblique impact of deformable projectiles

Nishida, Akemi; Nagai, Minoru*; Tsubota, Haruji; Li, Y.

Mechanical Engineering Journal (Internet), 5(5), p.18-00087_1 - 18-00087_21, 2018/08

To date, oblique impact has not been studied and few experimental data on the local damage of reinforced concrete (RC) panels exist for oblique impact of deformable projectiles. The final purpose of this study is to propose a new formula for evaluating the local damage to reinforced concrete structures caused by oblique impact based on past experimental results and simulation results. As the first step of this final purpose, we validate the analytical method by comparison with the experimental results and simulate the damage caused by oblique impact using the validated method. First, we analyze and simulate the local damage of RC panel caused by a deformable projectile owing to an impact test normal to the target structure to verify the validity of the simulation analysis. Next, we perform simulation analyses for evaluating the perforation of RC panel due to oblique impact by the deformable projectile and present the results. Various response characteristics and perforation mechanisms to be the basis of examination of oblique impact evaluation were clarified in this paper.

Journal Articles

Development of seismic countermeasures against cliff edges for enhancement of comprehensive safety of nuclear power plants; Cliff edges relevant to NPP building system

Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Takada, Tsuyoshi*

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 11 Pages, 2018/07

This study identified and quantified possible cliff edge effects through a seismic safety evaluation of a nuclear power plant, based on the concepts of risk and defense in depth. Cliff edges of the both physical and knowledge-based type were considered in this study. We investigated a seismic isolation effect, etc., for physical cliff edges, and the modeling of the target structure, boundary conditions, etc., for knowledge-based cliff edges. Response analysis was performed using a sway-rocking (SR) model and a three-dimensional model of the target building. The seismic isolation effect of the base-isolated building was confirmed by comparison to the results of earthquake-resistant building. In the case of a collision with the retaining wall of the base-isolated building, the level of damage was found to depend on the modeling of the collision condition assumed. On the other hand, the study confirmed the differences between the results from the SR model and the three-dimensional model.

Journal Articles

Epistemic Uncertainty Quantification of Floor Responses for a Nuclear Reactor Building

Choi, B.; Nishida, Akemi; Li, Y.; Muramatsu, Ken*; Takada, Tsuyoshi*

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 9 Pages, 2018/07

After the 2011 Fukushima accident, nuclear power plants are required to take countermeasures against accidents beyond design basis conditions. In seismic probabilistic risk assessment (SPRA), uncertainty can be classified as either aleatory uncertainty, which cannot be reduced, or epistemic uncertainty, which can be reduced with additional knowledge and/or information. To improve the reliability of SPRA, efforts should be made to identify and reduce the epistemic uncertainty caused by the lack of knowledge. In this study, we focused on the difference in seismic response by modeling methods, which is related epistemic uncertainty. We conducted a seismic response analysis with two kinds of modeling methods; a three-dimensional finite-element model and a conventional sway-rocking stick model, by using simulated various input ground motions, which is related to aleatory uncertainty. And then we quantified the seismic floor response results of the various input ground motions of each modeling methods. For the uncertainty quantification related to different modeling methods, we further perform a statistical analysis of the floor response results of the nuclear reactor building. Finally, we discussed how to utilize the results from these calculations for the quantification of uncertainty in fragility analysis for SPRA.

Journal Articles

Evaluation of local damage to reinforced concrete panels subjected to oblique impact of rigid and soft missiles

Nishida, Akemi; Nagai, Minoru*; Tsubota, Haruji; Li, Y.

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 8 Pages, 2018/07

Many empirical formulas have been proposed for evaluating local damage to reinforced concrete (RC) structures caused by impacts of rigid missiles. Most of these formulas have been derived based on impact tests normal to the target structures. Up to now, few impact tests oblique to the target structures have been carried out. This study has been conducted with the purpose of proposing a new formula for evaluating the local damage caused by oblique impacts based on previous experimental and simulation results. In this paper, the results of simulation analyses for evaluating the local damage to a RC panel subjected to normal and oblique impacts by rigid and soft missiles, by using the simulation method that was validated using the results of previous impact experiments. Based on the results of these simulation analyses, the effects of the rigidity of the missile as well as the impact angle on the local damage to the target structures are clarified.

Journal Articles

Thermal-hydraulics technological strategy roadmap 2017; An Approach for continuous safety improvement of LWRs

Itoi, Tatsuya*; Iwaki, Chikako*; Onuki, Akira*; Kito, Kazuaki*; Nakamura, Hideo; Nishida, Akemi; Nishi, Yoshihisa*

Nippon Genshiryoku Gakkai-Shi, 60(4), p.221 - 225, 2018/04

no abstracts in English

Journal Articles

Engineering applications using probabilistic aftershock hazard analyses; Aftershock hazard map and load combination of aftershocks and tsunamis

Choi, B.; Nishida, Akemi; Itoi, Tatsuya*; Takada, Tsuyoshi*

Geosciences (Internet), 8(1), p.1_1 - 1_22, 2018/01

After the Tohoku earthquake in 2011, we observed that aftershocks tended to occur in a wide region after such a large earthquake. These aftershocks resulted in secondary damage or delayed rescue and recovery activities. However, it is difficult to evaluate the hazards of an aftershock before the main shock due to various uncertainties. For possible great earthquakes, we must make decisions based on such uncertainties, and it is important to quantify the various uncertainties. We previously proposed a probabilistic aftershock occurrence model that is expected to be useful to develop plans for recovery activities after future large earthquakes. In this paper, engineering applications of the proposed approach for probabilistic aftershock hazard analysis are shown for demonstration purposes. One application is to use aftershock hazard maps to plan recovery activities. Another application is to derive load combination equations of the load and resistance factor design (LRFD) considering the simultaneous occurrence of tsunamis and aftershocks for the tsunami-resistant design of tsunami evacuation buildings and nuclear facilities.

Journal Articles

Uncertainty evaluation of seismic response of a nuclear facility using simulated input ground motions

Choi, B.; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*

Proceedings of 12th International Conference on Structural Safety & Reliability (ICOSSAR 2017) (USB Flash Drive), p.2206 - 2213, 2017/08

In order to clarify the influence of the difference of modeling method on the variation of the result of seismic response analysis of nuclear facility, seismic response analysis using various simulated input ground motions was carried out and the sensitivity analyses of the variations in seismic response was conducted. In particular, we focused on the maximum acceleration response of reactor building shear walls, the effect of modeling method on response result and the factors of response variation were described and discussed.

Journal Articles

Evaluation of local damage to reinforced concrete panels subjected to oblique impact of soft missile

Nishida, Akemi; Ota, Yoshimi*; Tsubota, Haruji; Li, Y.

Transactions of 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08

Many empirical formulas have been proposed for evaluating local damage to reinforced concrete structures caused by impacts of rigid missiles. Most of these formulas have been derived based on tests involving impact perpendicular to target structures. Thus far, few tests with oblique impact onto target structures have been carried out. In this study, we aim to propose a new formula for evaluating the local damage caused by oblique impact based on previous experimental and simulation results. We performed simulation analyses for evaluating the local damage to reinforced concrete panels subjected to oblique impacts by soft missiles under various impact velocities by using a simulation method that was validated using the results of previous impact experiments. Based on the results of these simulation analyses, quantitative evaluation of the reduction in local damage and the differences in energy transfer process due to the difference in impact angle and impact velocity are investigated.

Journal Articles

Method for detecting optimal seismic intensity index utilized for ground motion generation in seismic PRA

Igarashi, Sayaka*; Sakamoto, Shigehiro*; Ugata, Ken*; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*

Transactions of 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08

For the purpose of improving the precision of probabilistic seismic PRA for NPPs, the authors developed the methodology for generating hazard-consistent ground motions based on stochastic fault models which include seismic-source uncertainties by Monte Carlo Simulation. The PRA with HCGMs would require a lot of computer power. The optimization of ground-motions generations is one of the most important subjects for practical application of the PRA method. For optimizing the ground-motions generations, seismic sources for the generations should be selected effectively, and this can be conducted by utilizing optimal seismic index in the hazard analysis. In this study, the method for detecting the optimal seismic intensity index which corresponds with damage probabilities of the target equipment system was developed, and the validity of the proposed method was confirmed for some equipment systems, which has different weak equipment with each other.

Journal Articles

Development of seismic countermeasures against cliff edges for enhancement of comprehensive safety of nuclear power plants, 2; Cliff edges relevant to NPP structure modeling

Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Takada, Tsuyoshi*

Transactions of 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 9 Pages, 2017/08

In this research, the seismic safety of nuclear power plants (NPP) is treated as a system in which the various cliff edge effects are identified and quantified based on the concepts of risk and defense in depth. A methodology is then developed for avoiding these cliff edge effects. The first step was to carry out a preliminary elastic-plastic analysis of the NPP building system. From the analysis, some knowledge was obtained for the modeling factor dependence of cliff edge effects. Next, a preliminary fragility evaluation of the reactor vessel and piping was carried out; it was found that introducing a horizontal seismic isolation system was very effective for avoiding the cliff edge.

252 (Records 1-20 displayed on this page)