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Purpose This study elucidated the effect of an inclined spring arrangement on the flow-induced vibration of a circular cylinder to understand if the effect enhances the harnessing of the energy of fluid flows. Method An experiment was conducted on a circulating water channel. A circular cylinder was partially submerged. It was elastically supported by two springs whose longitudinal directions were varied. With the speed of the water flow varied, the vibrations of the circular cylinder were measured. The measured vibrations were interpreted by la linear dynamic model. Results and discussion In a few cases, a jump in response amplitudes from zero to the maximum was observed with the spring inclination at reduced velocities of 6 to 7, whereas gradually increasing response amplitudes were observed in other cases. The inclined spring arrangement achieved greater velocity amplitudes than in cases without spring inclination. A theoretical evaluation of the measured responses indicates that the effect of the inclined springs was caused by geometric nonlinearity; the effect would be more prominent by employing a longer moment lever.
Koki Yamada; Yuga Shigeyoshi; Shuangjing Chen; Yoshiki Nishi. Spring-Arrangement Effect on Flow-Induced Vibration of a Circular Cylinder. Journal of Vibration Engineering & Technologies 2021, 1 -12.
AMA StyleKoki Yamada, Yuga Shigeyoshi, Shuangjing Chen, Yoshiki Nishi. Spring-Arrangement Effect on Flow-Induced Vibration of a Circular Cylinder. Journal of Vibration Engineering & Technologies. 2021; ():1-12.
Chicago/Turabian StyleKoki Yamada; Yuga Shigeyoshi; Shuangjing Chen; Yoshiki Nishi. 2021. "Spring-Arrangement Effect on Flow-Induced Vibration of a Circular Cylinder." Journal of Vibration Engineering & Technologies , no. : 1-12.
To facilitate sustainable energy development, one has to understand the limited availability of nonrenewable energy resources, and the ability of the earth to renew or recover. Emergy is an instrument that measures environmental loading, ecological economics, and regional sustainable development. In this study, emergy indicators are calculated to investigate the sustainability of solar updraft tower (SUT). SUT produces energy from the hot air, utilizing a combination of a solar collector, central tower, and air turbines. The results demonstrate that the sustainability of SUT grew as the size of the plant increased. Further, emergetic ternary diagrams are drawn to facilitate the comparison between SUT and various technologies. The resources-use efficiency of wind energy and SUT, 200 MW is found to be the lowest among all energy technologies presented in this research. Scenario analysis is performed to explore the future optimization directions. The results demonstrate that the development direction of SUT systems should mainly focus on reducing the materials demanded by the manufacturing and construction of its solar collectors. This study aims to demonstrate the value of emergy as a powerful instrument for drawing long-term sustainable strategies in energy markets for a greener tomorrow.
Islam Elsayed; Yoshiki Nishi. Emergy and Sustainability Ternary Diagrams of Energy Systems: Application to Solar Updraft Tower. Sustainability 2020, 12, 10546 .
AMA StyleIslam Elsayed, Yoshiki Nishi. Emergy and Sustainability Ternary Diagrams of Energy Systems: Application to Solar Updraft Tower. Sustainability. 2020; 12 (24):10546.
Chicago/Turabian StyleIslam Elsayed; Yoshiki Nishi. 2020. "Emergy and Sustainability Ternary Diagrams of Energy Systems: Application to Solar Updraft Tower." Sustainability 12, no. 24: 10546.
This study estimated the amount of bilge water spilled from ships during normal operation and identified the contributing factors of the discharge by building a statistical model. To build the statistical model, we collected as much information as possible about the amount of bilge water in ships, then used the collected information to formulate a probability distribution of the discharge amount according to Bayesian statistics, and determined the parameters included in the model by applying a Markov Chain Monte Carlo method. The analysis of those parameters shows that the integrated bilge treatment system (IBTS) primarily contributes to reductions in the discharge amount, and that the container-type ship is involved with especially large discharge amounts.
Munekazu Motoyoshi; Yoshiki Nishi. Statistical Modeling of Bilge Water Discharge from Ships During Normal Operation. Journal of Marine Science and Engineering 2020, 8, 320 .
AMA StyleMunekazu Motoyoshi, Yoshiki Nishi. Statistical Modeling of Bilge Water Discharge from Ships During Normal Operation. Journal of Marine Science and Engineering. 2020; 8 (5):320.
Chicago/Turabian StyleMunekazu Motoyoshi; Yoshiki Nishi. 2020. "Statistical Modeling of Bilge Water Discharge from Ships During Normal Operation." Journal of Marine Science and Engineering 8, no. 5: 320.
Hamid Arionfard; Yoshiki Nishi. Erratum to “Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Vorticity dynamics” [J. Fluids Struct. 82 (2018) 505–519]. Journal of Fluids and Structures 2020, 95, 102969 .
AMA StyleHamid Arionfard, Yoshiki Nishi. Erratum to “Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Vorticity dynamics” [J. Fluids Struct. 82 (2018) 505–519]. Journal of Fluids and Structures. 2020; 95 ():102969.
Chicago/Turabian StyleHamid Arionfard; Yoshiki Nishi. 2020. "Erratum to “Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Vorticity dynamics” [J. Fluids Struct. 82 (2018) 505–519]." Journal of Fluids and Structures 95, no. : 102969.
In this study, the mechanics of an axially moving cable that is used to acquire mineralresources from the seafloor are theoretically and numerically investigated by focusing on the extentto which a load of buckets affects the cable deflection. In particular, we construct the theoreticalmodel of a cable, and its solutions are numerically determined using the mode expansion method.The results of the simulations performed using a varying number of buckets show that the cabledeflects in response to the passage of each bucket. As the total number of buckets increases, the loadof buckets acts as a continuous load. An increase in the total number of buckets naturally leads toan increase in the total load on the cable, resulting in the deviation of the paths of the buckets froma path under the zero-load state. These properties should be considered while designing cables.
Daiki Itoh; Yoshiki Nishi; Itoh. Linear Analysis of the Static and Dynamic Responses of the Underwater Axially Moving Cables to Bucket Loads. Journal of Marine Science and Engineering 2019, 7, 301 .
AMA StyleDaiki Itoh, Yoshiki Nishi, Itoh. Linear Analysis of the Static and Dynamic Responses of the Underwater Axially Moving Cables to Bucket Loads. Journal of Marine Science and Engineering. 2019; 7 (9):301.
Chicago/Turabian StyleDaiki Itoh; Yoshiki Nishi; Itoh. 2019. "Linear Analysis of the Static and Dynamic Responses of the Underwater Axially Moving Cables to Bucket Loads." Journal of Marine Science and Engineering 7, no. 9: 301.
In this paper, a numerical computation method is proposed to simulate tides in coastal regions. The proposed method is based on the hyperbolic form of governing equations and employs a semi-Lagrangian scheme to ensure the accuracy and stability of numerical computations. Open and wall boundary conditions can be treated universally by combining them with the semi-Lagrangian scheme. Furthermore, the method is applied to some benchmark problems of shallow water to examine its performances in wave propagation, wave transparency through open boundaries, and tides in semi-enclosed bays. The results obtained demonstrate that the proposed method can be utilized as a practical tool to investigate tidal dynamics in coastal regions.
Yoshiki Nishi; Eiki Taniguchi; Lisa Niikura; Eitetsu Shibata. Semi-Lagrangian numerical simulation method for tides in coastal regions. Journal of Marine Science and Technology 2019, 25, 675 -689.
AMA StyleYoshiki Nishi, Eiki Taniguchi, Lisa Niikura, Eitetsu Shibata. Semi-Lagrangian numerical simulation method for tides in coastal regions. Journal of Marine Science and Technology. 2019; 25 (3):675-689.
Chicago/Turabian StyleYoshiki Nishi; Eiki Taniguchi; Lisa Niikura; Eitetsu Shibata. 2019. "Semi-Lagrangian numerical simulation method for tides in coastal regions." Journal of Marine Science and Technology 25, no. 3: 675-689.
A solar thermal wind tower (STWT) is a low-temperature power generation plant that mimics the wind cycle in nature, comprising a flat plate solar air collector and central updraft tower to produce thermal wind that drives turbines to generate electricity. The development of power generation systems toward a sustainable future needs to be made taking into account the balance between environmental impact and economic feasibility. We examine the sustainability of STWT power generation technology using the inclusive impact index light (Triple I-light), which estimates whether it is good to do the project, including both the negative environmental impact and the economic aspect. Environmental disadvantages are discussed by performing a CO2 inventory analysis for the life-cycle of the STWT power plant. Evaluation of the economic feasibility is done by calculating the levelized electricity cost (LEC), which is the cost per unit of electricity generated. From the calculations, it is found that overall system efficiency is increased by enlarging the capacity, the negative environmental impact by the STWT plant comes mainly from manufacturing stage (more than 60%), and the levelized electricity cost is dramatically decreased by enlarging the capacity of the system (about 50% reduction). A negative value of Triple I (meaning it is sustainable) can be achieved for high power generation capacity (above 100 MW). Moreover, this paper discusses the implementation and the potential of constructing offshore STWTs.
Islam Elsayed; Yoshiki Nishi. A Feasibility Study on Power Generation from Solar Thermal Wind Tower: Inclusive Impact Assessment Concerning Environmental and Economic Costs. Energies 2018, 11, 3181 .
AMA StyleIslam Elsayed, Yoshiki Nishi. A Feasibility Study on Power Generation from Solar Thermal Wind Tower: Inclusive Impact Assessment Concerning Environmental and Economic Costs. Energies. 2018; 11 (11):3181.
Chicago/Turabian StyleIslam Elsayed; Yoshiki Nishi. 2018. "A Feasibility Study on Power Generation from Solar Thermal Wind Tower: Inclusive Impact Assessment Concerning Environmental and Economic Costs." Energies 11, no. 11: 3181.
In this study, the performance of a double cylinder flow-induced vibration (FIV) energy converter is experimentally investigated. The central aim is to take advantage of drag force and gap flow to enhance the vibration. The cylinders are free to rotate around a pivot and located in different configurations including both cylinders on the downstream, both on the upstream, a cylinder on each side and one cylinder on the pivot. Each configuration is represented by the gap ratio between the two cylinder (G = gap/cylinder diameter) and center of gravity ratio (CG = gravity center/cylinder diameter). Locating the cylinders in different positions made it possible to activate a wide range of vibration mechanisms including: Vortex excitation (VE), wake–induced vibration (WIV), galloping and gap–switching–induced vibration (GSIV). The most efficient vibration mechanisms are: (1) GSIV for CG=0 and G=0.9 (2) VE where CG=0 and G≥3.9 (3) drag–assisted vibration where one cylinder is on the pivot point and another one on the upstream side, (4) WIV where one cylinder is on the pivot point and another one on the downstream side, (4) both cylinders on the downstream side with no gap and (5) both cylinders on the upstream side with no gap.
Hamid Arionfard; Yoshiki Nishi. Experimental investigation on the performance of a double-cylinder flow-induced vibration (FIV) energy converter. Renewable Energy 2018, 134, 267 -275.
AMA StyleHamid Arionfard, Yoshiki Nishi. Experimental investigation on the performance of a double-cylinder flow-induced vibration (FIV) energy converter. Renewable Energy. 2018; 134 ():267-275.
Chicago/Turabian StyleHamid Arionfard; Yoshiki Nishi. 2018. "Experimental investigation on the performance of a double-cylinder flow-induced vibration (FIV) energy converter." Renewable Energy 134, no. : 267-275.
This paper presents the results of an experimental investigation on the vibration mechanisms of two connected circular cylinders that are free to rotate around a pivot in different arrangements including both cylinders on the downstream, both on the upstream and a cylinder on each side of the pivot point. The Reynolds number is varied during the test to find the maximum possible displacement amplitude for each configuration. Four main mechanisms of vibration are identified. The cylinders experience galloping if both located on the upstream of the pivot and the gap between them is zero. Vortex excitation (VE) is observed in two configurations and referred to as VEfStVEfSt and VEfNVEfN. VEfStVEfSt occurs when both cylinders are located on the downstream of the pivot while the gap is zero. The frequency responses lock into the Strouhal frequency in this case. VEfNVEfN occurs when the center of gravity (cg ) is on the pivot and the gap ratio (G=gap∕cylinderdiameter) between the cylinders is G >> 3.9. In this case, the frequency response locks into the natural frequency of the system. If one cylinder is located on the center of the rotation and the other cylinder is on the downstream, wake-induced vibration (WIV) takes place. While for G << 1.4 the response is a typical wake galloping, for G >> 1.4 two vibration modes are recognizable as ‘combined vortex resonance and galloping’. For all configurations with G >> 0, gap-switching-induced vibration (GSIV) is observed especially for 1.9 << G << 2.4. However, GSIV is the dominant mechanism of vibration if cg is on the pivot point. In cases where cg is not close to the pivot, the drag force may enhance the vibration if the Reynolds number is not large enough to suppress the motion.
Hamid Arionfard; Yoshiki Nishi. Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Characteristics of vibration. Journal of Fluids and Structures 2018, 80, 165 -178.
AMA StyleHamid Arionfard, Yoshiki Nishi. Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Characteristics of vibration. Journal of Fluids and Structures. 2018; 80 ():165-178.
Chicago/Turabian StyleHamid Arionfard; Yoshiki Nishi. 2018. "Flow-induced vibrations of two mechanically coupled pivoted circular cylinders: Characteristics of vibration." Journal of Fluids and Structures 80, no. : 165-178.
This study examined the influence of the oscillatory time variation in the attitude angle of compound parabolic concentrator (CPC) on the thermal performance of CPC. Two experimental CPC models were constructed, one of which was fixed and the other one was provided with two rotational motions (pitch and roll) under sunlight irradiance. By comparing the temperatures of thermal collectors in the two CPCs, the influence by the oscillation was evaluated. Experimental results demonstrated that the oscillation can decrease or increase the temperatures depending on the centre and amplitude of oscillation. To see in more detail the influence of oscillation, exergy budgets were analysed. It is found that the rotational motions of CPC tend to decrease the exergy efficiency by a few percentages, whereas it can improve the efficiency by a few percentages by minimising the incident angles of solar irradiance around the noon.
Yoshiki Nishi; Yusuke Tokui. Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator. International Journal of Exergy 2018, 27, 311 .
AMA StyleYoshiki Nishi, Yusuke Tokui. Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator. International Journal of Exergy. 2018; 27 (3):311.
Chicago/Turabian StyleYoshiki Nishi; Yusuke Tokui. 2018. "Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator." International Journal of Exergy 27, no. 3: 311.
Yusuke Tokui; Yoshiki Nishi. Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator. International Journal of Exergy 2018, 27, 311 .
AMA StyleYusuke Tokui, Yoshiki Nishi. Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator. International Journal of Exergy. 2018; 27 (3):311.
Chicago/Turabian StyleYusuke Tokui; Yoshiki Nishi. 2018. "Influence of rotational oscillation on exergy efficiency of compound parabolic concentrator." International Journal of Exergy 27, no. 3: 311.
Yoshiki Nishi; Yuta Ueno; Takuma Miyamoto. Energy Harvesting Using Wake-Induced Vibration: Experiment in Circulating Water Channel. Journal of Ocean and Wind Energy 2015, 2, 1 .
AMA StyleYoshiki Nishi, Yuta Ueno, Takuma Miyamoto. Energy Harvesting Using Wake-Induced Vibration: Experiment in Circulating Water Channel. Journal of Ocean and Wind Energy. 2015; 2 (4):1.
Chicago/Turabian StyleYoshiki Nishi; Yuta Ueno; Takuma Miyamoto. 2015. "Energy Harvesting Using Wake-Induced Vibration: Experiment in Circulating Water Channel." Journal of Ocean and Wind Energy 2, no. 4: 1.
Yoshiki Nishi; Phan Viet Doan. Distribution of damping device on riser pipe in sheared currents. Ocean Engineering 2015, 104, 489 -499.
AMA StyleYoshiki Nishi, Phan Viet Doan. Distribution of damping device on riser pipe in sheared currents. Ocean Engineering. 2015; 104 ():489-499.
Chicago/Turabian StyleYoshiki Nishi; Phan Viet Doan. 2015. "Distribution of damping device on riser pipe in sheared currents." Ocean Engineering 104, no. : 489-499.
Yusuke Tokui; Hitoshi Moriguchi; Yoshiki Nishi. Comprehensive environmental assessment of seawater desalination plants: Multistage flash distillation and reverse osmosis membrane types in Saudi Arabia. Desalination 2014, 351, 145 -150.
AMA StyleYusuke Tokui, Hitoshi Moriguchi, Yoshiki Nishi. Comprehensive environmental assessment of seawater desalination plants: Multistage flash distillation and reverse osmosis membrane types in Saudi Arabia. Desalination. 2014; 351 ():145-150.
Chicago/Turabian StyleYusuke Tokui; Hitoshi Moriguchi; Yoshiki Nishi. 2014. "Comprehensive environmental assessment of seawater desalination plants: Multistage flash distillation and reverse osmosis membrane types in Saudi Arabia." Desalination 351, no. : 145-150.
Luis Antonio Rodrigues Quadrante; Yoshiki Nishi. Amplification/suppression of flow-induced motions of an elastically mounted circular cylinder by attaching tripping wires. Journal of Fluids and Structures 2014, 48, 93 -102.
AMA StyleLuis Antonio Rodrigues Quadrante, Yoshiki Nishi. Amplification/suppression of flow-induced motions of an elastically mounted circular cylinder by attaching tripping wires. Journal of Fluids and Structures. 2014; 48 ():93-102.
Chicago/Turabian StyleLuis Antonio Rodrigues Quadrante; Yoshiki Nishi. 2014. "Amplification/suppression of flow-induced motions of an elastically mounted circular cylinder by attaching tripping wires." Journal of Fluids and Structures 48, no. : 93-102.
Yoshiki Nishi; Yuta Ueno; Masachika Nishio; Luis Antonio Rodrigues Quadrante; Kentaroh Kokubun. Power extraction using flow-induced vibration of a circular cylinder placed near another fixed cylinder. Journal of Sound and Vibration 2014, 333, 2863 -2880.
AMA StyleYoshiki Nishi, Yuta Ueno, Masachika Nishio, Luis Antonio Rodrigues Quadrante, Kentaroh Kokubun. Power extraction using flow-induced vibration of a circular cylinder placed near another fixed cylinder. Journal of Sound and Vibration. 2014; 333 (10):2863-2880.
Chicago/Turabian StyleYoshiki Nishi; Yuta Ueno; Masachika Nishio; Luis Antonio Rodrigues Quadrante; Kentaroh Kokubun. 2014. "Power extraction using flow-induced vibration of a circular cylinder placed near another fixed cylinder." Journal of Sound and Vibration 333, no. 10: 2863-2880.
The exergy budget in a solar collector has thus far been estimated under the condition of steady solar radiation intensity. In reality, solar radiation temporally varies depending on weather conditions. In particular, it remains to be elucidated to what extent cloud cover affects an exergy budget. To develop a method to evaluate the exergy efficiency with consideration of cloud cover, we studied the exergy budget of a three-dimensional compound parabolic concentrator (CPC) by constructing a model representing the heat budget of the CPC and by measuring temperatures at a few points in the CPC under a variety of cloud circumstances. We found reasonable validity in the thermal model through comparisons of the simulation with measurements. The temperature of the collector fluctuated owing to the appearance and disappearance of clouds, and in response, the input and output rates of the exergy temporally varied during cloudy days. By integrating the rates of exergy over a period including noon, we computed net input and output exergies. The exergy efficiency estimated was maximally 12%. The method developed in this study is also useful in quantifying the thermal performance of other types of solar collectors and improving their design.
Yoshiki Nishi; Tomokazu Sema. Estimation of exergy efficiency of compound parabolic concentrator under time-varying cloud cover condition. Solar Energy 2013, 98, 341 -348.
AMA StyleYoshiki Nishi, Tomokazu Sema. Estimation of exergy efficiency of compound parabolic concentrator under time-varying cloud cover condition. Solar Energy. 2013; 98 ():341-348.
Chicago/Turabian StyleYoshiki Nishi; Tomokazu Sema. 2013. "Estimation of exergy efficiency of compound parabolic concentrator under time-varying cloud cover condition." Solar Energy 98, no. : 341-348.
Yoshiki Nishi; Phan Viet Doan. Hybrid boundary condition combined with data assimilation for simulations of free surface flows using lattice Boltzmann method. Computers & Fluids 2013, 88, 108 -114.
AMA StyleYoshiki Nishi, Phan Viet Doan. Hybrid boundary condition combined with data assimilation for simulations of free surface flows using lattice Boltzmann method. Computers & Fluids. 2013; 88 ():108-114.
Chicago/Turabian StyleYoshiki Nishi; Phan Viet Doan. 2013. "Hybrid boundary condition combined with data assimilation for simulations of free surface flows using lattice Boltzmann method." Computers & Fluids 88, no. : 108-114.
This study investigates the two-dimensional static mechanics of an axially moving cable used in a two-ship continuous line bucket (CLB) system for exploiting mineral resources deposited on the sea floor. The aim of this study is to formulate a theory for estimating the grounding length of the cable. The theory is governed by the relation for the static equilibrium of forces acting on the cable and geometrical conditions imposed on the submerged length of the cable and on the distance between the two ships supporting the cable. Two algorithms involving a couple of iterations are developed for obtaining the grounding length. The calculation using the algorithm shows that the grounding length varies in response to changes in the rate of collection by the bucket and the bucket interval. The calculation also demonstrates that the maximum grounding length is determined on the basis of the geometry of the submerged part and that the grounding length ranges from zero to the maximum depending on the distance between the two ships.
Yoshiki Nishi. Determining the grounding length of an axially moving cable in a two-ship continuous line bucket system. Applied Ocean Research 2013, 40, 42 -49.
AMA StyleYoshiki Nishi. Determining the grounding length of an axially moving cable in a two-ship continuous line bucket system. Applied Ocean Research. 2013; 40 ():42-49.
Chicago/Turabian StyleYoshiki Nishi. 2013. "Determining the grounding length of an axially moving cable in a two-ship continuous line bucket system." Applied Ocean Research 40, no. : 42-49.
This study presents a thermal model for the optimum design of the three-dimensional compound parabolic concentrator (CPC) considering the maximisation of exergy delivery. The model in this study has been validated by comparing the computed collector temperature with the measured one. A good agreement has been confirmed. The optimum temperatures of the collector and the thermal medium are calculated. Reduction of heat loss from the collector to ambient air can enhance the maximum exergy, but it is accompanied by shift of the optimum temperature. The heat extraction process has been examined by assuming that it is composed of two steps of heat flow: the first from the collector to the medium and the second from the medium to the final objective. The analysis shows how the exergy efficiency varies in response to the design change in the second step and where the overall optimised design can be found in a diagram between heat transfer coefficient and temperature.
Yoshiki Nishi; Qi Xie. Exergy analysis on solar heat collection of three-dimensional compound parabolic concentrator. International Journal of Exergy 2013, 13, 260 .
AMA StyleYoshiki Nishi, Qi Xie. Exergy analysis on solar heat collection of three-dimensional compound parabolic concentrator. International Journal of Exergy. 2013; 13 (2):260.
Chicago/Turabian StyleYoshiki Nishi; Qi Xie. 2013. "Exergy analysis on solar heat collection of three-dimensional compound parabolic concentrator." International Journal of Exergy 13, no. 2: 260.