RELAP5 code post-test analysis was performed on one of abnormal transient tests conducted with the ROSA/large scale test facility (LSTF) simulating a PWR station blackout (SBO) transient with the TMLB' scenario in 1995. The TMLB' scenario involves prolonged complete loss of alternating current power and unavailability of turbine-driven auxiliary feedwater as well as malfunction of primary- and secondary-system relief valves. The LSTF test revealed core uncovery by core boil-off took place a little after hot leg became empty of liquid while the primary pressure was kept high. The RELAP5 code predicted well the overall trend of the major phenomena observed in the LSTF test, and indicated remaining problems in the predictions of reverse flow U-tubes in steam generator (SG) during long-term single-phase liquid natural circulation. Sensitivity analyses were performed further to clarify effectiveness of depressurization of and coolant injection into SG secondary-side as accident management measures for core cooling, based on the RELAP5 post-test analysis. SG secondary-side depressurization was initiated by fully opening the safety valve in one of two SGs with the incipience of core uncovery. Coolant injection was done into the secondary-side of the same SG at low pressures considering availability of fire engines. The peak cladding temperature was dependent on the onset timing and flow rate of the SG coolant injection as well as the onset timing of the SG depressurization after core uncovery. The SG depressurization with the SG coolant injection was found to well contribute to maintain core cooling by the actuation of accumulator system during a PWR SBO (TMLB') transient.
This study is aimed to obtain fundamental data of transient heat transfer and clarify transient heat transfer process between the surface of solid and the neighboring helium gas in Very High Temperature Reactor (VHTR). Such studies are important for both of the academic knowledge on the complex transient phenomena and the safety assessment of severe nuclear reactor accidents such as power burst, rapid depressurization and withdraw of control rods. In this paper, a series of flat plates with different widths under different pressures inside a circular channel have been experimental tested and numerical analyzed for forced convection transient heat transfer for helium gas flowing over the plate. The heat generation rate of the plate was increased with a function of Q0exp(t/τ) (where t is time and τ is period of heat generation rate or e-fold time). The plates were made of platinum with a thickness of 0.1 mm and widths of 2 mm, 4 mm and 6 mm. Based on the experimental data and our previous research (Liu, et al. 2008a), we found that when the period τ is longer than around 1 second the heat transfer coefficients approach the quasi-steady-state values but when the period is shorter than around 1 second the heat transfer coefficients become higher as the period decreases. In this paper, we found that the conductive heat transfer becomes predominant for the period less than around 1 second and the heat transfer is mainly governed by convection heat transfer in the quasi-steady-state for the period larger than around 1 s. A semi-empirical correlation of surface temperature difference for plate heater was obtained based on the experimental data and analytic results. A 3-dimensional numerical simulation was carried out for the purpose of obtaining the plate temperature changes with time at various periods and velocities. The numerical solutions agree well with the experimental data within 6% differences.
The international fusion materials irradiation facility (IFMIF) presents an intense neutron source to develop fusion reactor materials. The liquid metal Lithium (Li) jet with a free surface is planned as a target irradiated by two deuteron beam to generate intense neutrons and it is thus important to obtain information on the surface wave characteristic for the safety and the efficiency of system in the IFMIF. We have been studying on surface wave characteristics experimentally using the liquid metal Li circulation facility at Osaka University and numerically using computational fluid dynamics (CFD) code, FLUENT. The CFD simulation has been used in order to establish the mechanism of the formation and development of the surface wave of the liquid Li jet. The introduction of a two-staged contraction nozzle is planned in the IFMIF. This nozzle has a concave wall at each contraction part, and it was then predicted that Görtler vortices in the boundary layer inside the nozzle was generated and flowed out from the nozzle exit at the high velocity condition in our previous simulation. The Li free surface flow simulation including the flow inside the nozzle set in our Li loop was conducted to compare simulation results with experimental results. In this simulation, large eddy simulation and volume o fluid models are used as turbulence model and interface tracking method, respectively. Our simulation result indicates that both transverse vortices due to gas-liquid shear stress and longitudinal vortices induced by Görtler vortices downstream the nozzle exit contribute to the formation of three-dimensional wave of the Li free surface flow at the jet velocity of 15 m/s. It was found that the vortex structure and the flow pattern under the free surface due to the flow inside the nozzle strongly contributed the development of the surface wave of the liquid Li jet.
In a nuclear power plant, one of the important issues is evaluation of the safety of reactor core and its pipes when an earthquake occurs. Many researchers have conducted studies on constructions of plants. Consequently, there is some knowledge about earthquake-resisting designs. However the influence of an earthquake vibration on thermal fluid inside a nuclear reactor plant is not fully understood. The aim of this study is to clarify the influence of vibration of construction on bubbly flow structure. In order to investigate it, we visualize changing of bubbly flow structure in pipeline on which sine wave is applied. Bubbly flow is produced with injecting gas into liquid flow through a horizontally circular pipe. In order to vibrate the test section, the oscillating table is used. It was clarified that the behavior of liquid phase and bubble through horizontal circular pipes was affected by an oscillation. And it was indicated that the velocity field around bubble when the oscillation was added showed different behavior from the oscillation was not added. Moreover as compared with two-phase flow simulation code with an advanced interface tracking method TPFIT results, the experimental result showed good coincidence.
The study is one on the series of the study on two-phase flow under earthquake, in which the two-phase flow behavior under the seismic vibration is systematically investigated by using both an experimental method and a numerical situation. The present study focuses on a bubbly flow behavior in a horizontal pipe under flow rate fluctuations. The periodical flow rate fluctuation was added to the bubbly or plug flow in a horizontal pipe, and the flow behavior was mainly measured by using image processing and PIV (particle image velocimetry). In the result of the image processing, the characteristic bubble deformation near the pipe wall was observed and the bubble deformation was synchronized with the flow rate fluctuation. The velocity field obtained by PIV showed the characteristic shear flow under the deformed bubble. The motion of both the liquid and the bubble responded to the pressure gradient fluctuation under the flow rate fluctuation, but the response of the bubble motion to the pressure gradient was slightly faster than that of the liquid motion. It indicated that the relative velocity between the bubble and the liquid changed with time. Therefore, the shear flow under the bubble was caused by the relative velocity between the bubble and the liquid, and the bubble was deformed by the shear flow due to the flow rate fluctuation. The numerical simulation code for the gas-liquid two-phase flow with an advanced interface tracking method, TPFIT, also showed the same mechanism of the bubble deformation, i.e., the shear flow under the bubble caused by the flow rate fluctuation.
This study describes the achievements of a program that provides technology education about radiation to develop practical core engineers, then the effects of the programed were discussed. An education program starting at an early age and continuous and consistent educational agendas through seven years of college has been constructed in collaboration with regional organizations. Subjects relating to atomic energy or nuclear engineering were regrouped as “Subjects Related to Atomic Power Education” for most grades in each department. These subjects were included in the syllabus and the student guide book to emphasize a continuous and consistent policy throughout the seven-year period of college study, comprising the five-year system and the additional two-year advanced course. Furthermore, the content of lectures, experiments, and internships was enriched and realigned in collaboration with the Japan Atomic Energy Agency (JAEA), Okayama University, and Chugoku Electric Power Co., Inc. Additional educational materials were developed from inspection visits by teaching staff to atomic energy facilities were also used in the classes. Two student experiment textbooks were developed to promote two of the subjects related to atomic energy: “Cloud Chamber Experiment” and “A Test of γ-ray Inverse Square Law.” In addition to the expansion and rearrangement of atomic power education, research on atomic power conducted for graduation thesis projects was undertaken to enhance educational and research activities. Some examples are as follows: “Study on the Relation between γ Dose Rate and Rainfall in Northern Okayama Area,” “Remote Sensing of Radiation Dose Rate by Customizing an Autonomous Robot,” and “Nuclear Reaction Analysis for Composition Measurement of BN Thin Films.” It should be noted that an atomic-energy-related education working group has been in place officially to continue the above activities in the college since 2011. In consequence, although government subsidy has been decreasing, both human and material resources have been enhanced, and many students with a satisfactory understanding of atomic energy are being developed.
On March 11th, 2011, the Great East Japan Earthquake which is one of the largest earthquakes in japan occurred and the maximum acceleration in observed seismic wave in the HTTR exceeded the design value in a part of input seismic motions. Therefore, a visual inspection, a seismic analysis and a performance confirmation test of facilities were carried out in order to confirm the integrity of facility after the earthquake. The seismic analysis was carried out for the reactor core structures by using the response magnification factor method. As the results of the evaluation, the generated stress in the graphite blocks in the reactor core at the earthquake were well below the allowable values of safety criteria, and thus the structural integrity of the reactor core was confirmed. The integrity of reactor core was also supported by the visual inspections of facilities and the operation without reactor power in cold conditions of HTTR.
Studies on the self-leveling behavior of debris bed are crucial in the assessment of core disruptive accident (CDA) that could occur in sodium-cooled fast reactors (SFR). To clarify the mechanisms underlying this behavior, several series of experiments were elaborately designed and conducted within a variety of conditions in recent years, under the close collaboration between Japan Atomic Energy Agency (JAEA) and Kyushu University (Japan). The current contribution, including knowledge from both experimental analyses and empirical model development, is focused on a recently developed comparatively larger-scale experimental facility using gas-injection to simulate the coolant boiling. Compared to the previous investigations, this facility can achieve a much wider range of gas velocities (presently up to a flow rate of around 300 L/min). Based on the experimental observation and quantitative data obtained, influence of various experimental parameters, including gas flow rate (～ 300 L/min), water depth (180 mm and 400 mm), bed volume (3 ～ 7 L), particle size (1 ～ 6 mm), particle density (beads of alumina, zirconia and stainless steel) along with particle shape (spherical and non-spherical) on the leveling is checked and compared. As for the empirical model development, aside from a base model which is restricted to predictions of spherical particles, the status of potential considerations on how to cover more realistic conditions (esp. debris beds formed with non-spherical particles), is also presented and discussed. This work, which gives a large palette of favorable data for a better understanding and an improved estimation of CDAs in SFRs, is expected to benefit future analyses and verifications of computer models developed in advanced fast reactor safety analysis codes.
It has been pointed out that high concentration dissolved hydrogen is one of the important factors of PWSCC (primary water stress corrosion cracking) in the primary systems of pressurized water reactors. Application of a substitution for hydrogen may be a fundamental countermeasure of PWSCC. The authors are developing a new water chemistry technology of a hydrogen alternative to suppress PWSCC. In the present paper, corrosion tests of Zircaloy-4 were performed in deaerated 5x10-3 mol dm-3 methanol solution at 320 °C in the absence and presence of gamma-irradiation. The nominal absorbed dose of the test water was 100 kGy. After the immersion tests, the specimens were analyzed. Weight gain per unit surface area, thickness of oxide film and hydrogen storage were measured. In addition, Raman spectroscopy was carried out, to investigate possible deposition of organic compounds on surface of the specimens. The corrosion behavior of Zircaloy-4 without irradiation agreed with literature data. It was concluded that the presence of methanol did not affect the corrosion behavior of Zircaloy-4. The corrosion behavior of Zircaloy-4 hardly depended on 100 kGy gamma-irradiation. On the Raman spectra of the specimens after the immersion tests, the Raman peaks ascribed to polyethylene or graphite were not found. The deposit of decomposition products of methanol would be negligible if any. It seems that polymerization is not the major process in thermal decomposition and radiolysis of methanol, but methanol decomposes into CO2 or carboxylic acids.
The postulated core disruptive accidents (CDAs) are regarded as particular difficulties in the safety analysis of liquid-metal fast reactors (LMFRs). In the CDAs, the self-leveling behavior of debris bed is a crucial issue, which greatly affects the relocation process and heat-removal capability of molten core. SIMMER-III is a fast reactor safety analysis code and successfully applied to a series of the CDA assessments. It is a 2D, multi-velocity-field, multiphase, multicomponent, Eulerian, fluid dynamics code coupled with a fuel-pin model and a space- and energy-dependent neutron kinetics model. However, strong interactions between solid particles, as well as particle characteristics, in multiphase flows with particles are not taken into consideration in SIMMER-III. In this article, a hybrid method is developed by coupling the discrete element method (DEM) with the multi-fluid model of SIMMER-III, and the numerical simulation of a simplified self-leveling experiment is presented. In the coupling algorithm, the governing equations of gas and liquid phases are solved by a time-factorization (time-splitting) method. Contact forces between particles and interactions between particles and fluid are considered in the DEM. Reasonable agreement between simulation results and corresponding experimental data can demonstrate the validity of the present method in simulating the self-leveling behavior of debris bed.
In this study, to develop the predictive technology of two-phase flow dynamics under earthquake acceleration, a detailed two-phase flow simulation code with an advanced interface tracking method TPFIT was expanded to perform two-phase flow simulations under seismic conditions. In the expansion of the TPFIT, the oscillating acceleration attributed to the earthquake motion was introduced into the momentum equation of the two-phase flow as body force. Moreover, to simulate fluctuation of the flow rate and a shear force on a pipe wall, time dependent boundary conditions can be added in the numerical simulations. The bubbly flow in a horizontal pipe excited by oscillation acceleration and under the fluctuation of the liquid flow was simulated by using the modified TPFIT. Furthermore, predicted velocity distribution around the bubbles and shapes of bubbles were compared with measured results under flow rate fluctuation and structure vibration. In the results of numerical simulation, periodical change of shapes of bubbles was observed. In addition, velocity distribution around bubbles also changed in accordance with flow rate fluctuation or structure vibration. Predicted results almost agreed with measured results. In the results, it was confirmed that the modified TPFIT can predict time dependent velocity distribution around the bubbles and shapes of bubbles qualitatively. The main cause of bubble deformation observed from the measured and predicted results is large shear stress at the lower part of the bubble, and this large shear stress is induced by the velocity difference between the liquid phase and bubble. Moreover, by using the predicted results, we discussed about the difference between both effects of flow rate fluctuation and structure vibration on two-phase flow. In the results, bubble acceleration of the structure vibration case was larger than that of the flow rate fluctuation case. Finally, it was concluded that unsteady shear stress induced by vibration of the pipe wall was one of the main driving forces of bubble motion in structure vibration case.
As revealed by Fukushima Daiichi nuclear disaster, countermeasures against severe accident in nuclear power plants are an urgent need. In particular, from the viewpoint of protecting a containment and suppressing the diffusion of radioactive materials, it is important to develop the device which allows a filtered venting of contaminated high pressure gas. In the filtered venting system that used in European reactors, so called Multi Venturi Scrubbers System is used to realize filtered venting without any power supply (Lindau, 1988) (Rust, et al., 1995). The system operates with any power supply and high pressure gas filled in the containment. This system is able to define to be composed of Venturi Scrubbers (VS) and a bubble column. In the VS, scrubbing of contaminated gas is promoted by both gas releases through a submerged VS and gas-liquid contact with splay flow formed by liquid suctioned through a hole provided by the pressure difference between inner and outer parts of a throat part of the VS. This type of the VS is called self-priming ones. However, the scrubbing mechanism of the self-priming VS including effects of gas mass flow rate and shape of the VS are understood insufficiently in the previous studies. In this study, to understand the VS operation characteristics for the filtered venting, we discussed the mechanisms of the self-priming phenomena and the hydraulic behavior in the VS. In this paper, we conducted a visualized observation of the hydraulic behavior in the VS and measured liquid flow rate of the self-primming. As a result, it is shown that there is the possibility that the VS decontamination performance falls low level with no self-priming.
Calcium silicate hydrate (CSH) is a main component of cement-based material required for constructing the geological repository. As in many countries, since the repository in Japan is constructed below water table, we must consider the interaction of radionuclide with cement materials altered around the repository after the backfill. Using fluorescence emission spectra, so far, the authors have investigated the interaction of Eu(III) (as a chemical analog of Am(III)) with CSH gels as a secondary mineral formed without drying process, considering a condition saturated with groundwater. However, in such fluorescence emission behaviors, a deexcitation process of OH vibrators of light water and a quenching effect caused by Eu-Eu energy transfer between Eu atoms incorporated in the CSH gel must be considered. This study examined the fluorescence emission behavior of Eu(III) sorbed on CSH gels, by using La(III) (non-fluorescent ions) as a diluent of Eu(III). Furthermore, CSH samples were synthesized with CaO, SiO2, and heavy water (D2O) as a solvent in order to avoid the obvious deexcitation process of OH vibrators of light water. In the results, the peak around 618 nm was split into two peaks of 613 nm and 622 nm in the cases of Ca/Si=1.0 and 1.6. Then, the peak of 613 nm decreased with increment of Eu(III)/La(III) ratio. This means that the relative intensity of 613 nm is useful to quantify the amount of Eu(III) incorporated in CSH gel. Besides, the decay behavior of the fluorescence emission did not depend on the Eu/La concentration ratio. That is, such a quenching effect is neglectable. Additionally, the fluorescence emission spectra of Eu(III) showed that the state of Eu(III) depended on Ca/Si ratio of CSH. This suggested that there was several sites in CSH to incorporate Eu(III). When CSH is altered, whole cementitious material in repository must be altered forming cracks and leaching some calcium compositions. Therefore, the adsorptive capacity of CSH might also play a key role to retard the migration of nuclides released from the waste body. This study mentioned the fundamental behaviors on the interaction of radionuclides and the altered CSH around the repository.
This paper describes experimental analyses using SIMMER-III and -IV, which are respectively two- and three-dimensional multi-component multi-phase Eulerian fluid-dynamics codes, for the purpose of integral code validation. Two topics of key phenomena in core disruptive accidents of sodium-cooled fast reactors are presented in this paper: duct-wall failure and fuel discharge/relocation behavior. To analyze the duct-wall failure behavior, the SCARABEE BE+3 in-pile experiments were selected. The SIMMER-III calculation was in good agreement with the overall event progression; which was characterized by coolant boiling, clad melting, fuel failure, molten pool formation, duct-wall failure, etc.; observed in the experiment. The CAMEL C6 experiment investigated the fuel discharge and relocation behavior through a simulated control rod guide tube, which is important in evaluating the neutronic reactivity. SIMMER-IV well simulated fuel-coolant interaction, sodium voiding, fuel relocation behavior observed in the experiment. These experimental analyses indicated the validity of the SIMMER-III and -IV computer code for the duct wall failure and fuel discharge/relocation behavior.
Compressive residual stresses induced by peening techniques improve the strength properties of steels, such as fatigue and stress corrosion cracking. However, the compressive residual stress might be reduced owing to thermal and mechanical loading in-service. In this study, the behavior of surface and internal residual stresses of a laser-peened ferritic steel under quasi-static tensile loading was investigated by X-ray and neutron diffraction. The complementary use of these diffraction techniques provided decisive experimental evidence for elucidating the relaxation process. As the applied tensile stress increases, the inside of the sample yields before the surface yielding at the critical applied stress (the applied stress for the onset of relaxation of the surface residual stress). The internal yielding causes the redistribution of residual stress, resulting in the relaxation of the surface compressive residual stress. Therefore, the relaxation of the surface compressive residual stress under tensile loading starts before the surface yielding. The critical applied stress of peened samples subjected to a tensile loading can be estimated from the von Mises yield criterion with the maximum tensile residual stress inside the sample. The FWHM of X-ray diffraction profile of the sample surface was increased by laser-peening, and it was further increased by further plastic deformation after peening.
For real-time load monitoring, we present a new smart lighting protection skin using resistive touchpad techniques that covers measuring objects with a flexible sheet composed of multiple tiny sensors. We measured loading from off-plate direction, including quasi-static indentation and dynamic impact. We believe our method is suitable for load monitoring of composite aircraft structures. A metal film or mesh coving the fiber composite components of our system acts as both the load sensor and wiring, and a lightning protection shield (LPS). The sheet consists of an upper LPS layer and a lower layer, with multiple pressure-sensitive elastomer pills arranged between layers. The lower layer is a grid consisting of high-electrical-resistance nichrome wires and low-resistance copper wires. The pressure-sensitive pill becomes conductive when compressed. When the sensor sheet is indented, a compressed pill creates a new electrical path between the two layers and the electrical potential equalizes at that point. This event triggers the application of a potential across the nichrome wires that form the x axis, enabling measurement of the x coordinate. The orthogonal potential gradient is then applied to the lower layer so that the y coordinate can be measured. The x and y coordinates are recorded quickly and describe the quasi-static load point with an error of 29 mm or less. Additionally, we can estimate the peak value of the impact load by measuring the electrical resistance of the pressure-sensitive pill with an error of 17 %.
Fiber reinforced thermoplastic composites has poorer matrix resin impregnation to fiber reinforcements, because of extreme high viscosity of molten thermoplastics. Fabrication method of intermediate materials using micro-braiding technique has been developed to overcome these difficulties. In this study, resin impregnation behavior in textile composites fabricated by micro-braiding technique was investigated. In order to predict the impregnation behavior, a simple model was proposed based on the Darcy's law and the continuity equation. Textiles composite plates were fabricated under various fabrication conditions using micro-braided yarn and the resin impregnation behavior in fiber yarn was investigated experimentally. The impregnation in single-ply textile composites is improved compared with that of multi-ply composites because single-ply composites have flatter fiber yarns which result in shorter impregnation distance. The numerical predictions calculated by boundary element method are in good agreement with the experimental results. This result suggests the effectiveness of the analysis proposed.
Nanotechnology devices with strong adhesion strength are required due to the miniaturization and reduction of the thickness of electronic devices. This paper describes a technique to select a silane coupling agent effective for obtaining the strong adhesion with copper by use of a density functional theory (DFT) in addition to an experimental peel test. We calculated the adhesion energy at the interface between three candidate silane coupling agents, aminoethyl-aminopropyltrimethoxysilane (AEAPS), mercaptopropyltrimethoxysilane (MPS), and aminopropyltrimethoxysilane (APS), and the copper in order to evaluate the adhesion strength at the interface. The adhesion energy obtained from DFT simulations increased in the order of AEAPS/copper > MPS/copper >APS/copper. The peel strength obtained from an experimental peel test increased in the same order as the adhesion energy obtained from the DFT simulation. Thus, AEAPS was selected as an effective coupling agent for obtaining the strong adhesion with copper. The selection method with the DFT simulation in addition to a peel test is considered to be effective for selecting the best material with the highest adhesion strength.
Water hydraulics is increasingly used in industrial application because of its inherent advantages including environmental friendliness, high safety against fire hazards, running cost reduction, and easy availability. However, water hydraulics remains two restrictions to make it popular in real application; higher price of water hydraulic devices and larger energy loss than conventional one. Thus, finding a suitable water hydraulic system that can reduce the price and save energy is one of the most important requirements for water hydraulic society. A water hydraulic fluid switching transmission (FST) and a water hydraulic pump motor transmission (PMT) that use cheap devices and can recover energy in deceleration process are good solutions for these difficulties. This study aims to compare two most important performances that are velocity response and energy saving of water hydraulic FST and PMT systems, in particular, focusing on detail analysis of energy saving performance. A method to estimate the relative wasted energy of FST in comparison with PMT system is also proposed. The PMT system has revealed many advantages such as reducing noise because of smooth operation, lengthening the duration of life of the devices, and especially the drastic reduction in both steady state errors in working phase and energy consumption.
This paper describes a tactile display for reproducing stiffness distributions based on magnetorheological (MR) fluid. This display can represent stiffness distribution by controlling the applied magnetic field locally. Computed tomography (CT) and endoscopy are currently used to diagnosis intravital conditions. However, CT cannot detect tumors smaller than 5 mm, and endoscopy can only diagnosis the tissue surface. Since tumors are stiffer than normal tissue, endoscopic palpation may be effective for detecting tumors smaller than 5 mm located beneath the tissue surface. To perform such palpation, a tactile display that can reproduce the spatial stiffness distribution of tissue is strongly required. For intravital tissue, the display must be capable of creating stiffness values ranging from about 200 to about 600 kPa with a spatial resolution of less than 5 mm. In the present study, a tactile display is proposed that exploits the ability of a MR fluid to change its stiffness in a magnetic field. In the proposed device, the MR fluid is encapsulated in an acrylic chamber covered by a thin flexible membrane. We first characterized the mechanical properties of the device and then, conducted sensory experiments with five subjects to verify that the device could display stiffness distribution. The magnetic field was produced by a cylindrical permanent magnet with a diameter of 5 mm, and the applied field strength was controlled by varying the separation between the magnet and the display. The experimental results indicated that the proposed display could successfully recreate the stiffness distribution including stiffness of tumor tissue under a local magnetic field of 200 mT. The device was then evaluated using five subjects, who were asked to touch the device with their index fingers and estimate the size of the stiff spot. Although the results varied among subjects, all were capable of perceiving spots smaller than 5mm.
Environmental problems related to wetlands have attracted strong concern around the world during past decades. Mobile mechanisms of many kinds have been developed to satisfy demands of environmental investigation of wetlands. However, few researchers have studied spiral propulsion mechanisms. Our previous work showed that the spiral can move forward between gaps of plants, giving only very slight damage to plants. It is introduced to be used to carry measurement devices in wetlands when investigating the current state of wetlands. This paper addresses the development and performance analysis of spiral driving units, which rotate the spiral by gripping its circumference and moving it forward or backward. A method to analyze the attitude angle and traveling distance of the spiral without a center axle is proposed. The kinematic relations between the driving unit and spiral are established on the premise of data from a motion capture system. Experimental results for driving units of two kinds are discussed, with emphasis on attitude stability, technical feasibility, and repeatability. Results show that the proposed driving units can drive the spiral to rotate forward along the desired direction as expected.
This paper presents an advanced parallel two-wheel vehicle that has an underslung vehicle body. In the proposed parallel two-wheel vehicle, since large wheels which its diameter is 1.05[m] are applied, and the battery, the actuators and the controller are placed at the lower position in the vehicle body, the gravity center of vehicle body with a passenger can be assigned at the lower position than the wheel axis. Therefore, the vehicle has a pendular structure that enables the vehicle body with the passenger to always maintain the stable posture, even if the vehicle is in the power-off or control-off condition. A 2-DOF joystick that has operation in pitching and yawing is applied to the proposed vehicle. The elderly or handicapped passenger can operate easily and intuitively the vehicle by this joystick. Moreover, in order to suppress the sway of the vehicle on the pitch axis of the vehicle body while vehicle is driven, the sway suppression control system with an active mass system is proposed in this paper. The control system of the active mass system is designed by a backstepping method. The effectiveness of the proposed pitch sway suppression control system with the active mass system is verified by the experiments using the proposed parallel two-wheel vehicle with an underslung vehicle body.
This work analyzes the influence of steering angle saturation to the convergent property in the Path-generating Regulator (PGR) under the feedback gain switching strategy for car-like robots. The PGR control method carries out asymptotic convergence to a given path function group. It has been extended to car-like robots, and its convergent region has been expanded by the feedback gain switching strategy. However, under this strategy, when the robot restarts after the feedback gain switches, the command of the steering angle tends to be close to ±π/2 rad, which might exceed the maximum steering angle. This phenomenon causes steering angle saturation. The robot then drives along the minimum turning circle. In this paper, the convergent property of the robot under steering angle saturation is investigated first. Results show that the convergent property is related strongly to the number of singular points, which depends on the center location of the minimum turning circle. Then the convergent properties at different locations are clarified through region division. Moreover, an extended feedback gain switching strategy method is proposed to change the convergent property in the specific region. Based on simulation and experiment results, we summarize the convergent property related to the region and verify the proposed method.
Integration of bioactuators in engineered microstructures is expected to be beneficial to further miniaturize and functionalize microelectromechanical systems. However, it is difficult to achieve reciprocation of micro-objects with common biological motors, although reciprocating movement is an important mechanism in constructing micromechanical systems. The ciliate protozoan Vorticella convallaria possesses a contractile filamentous stalk approximately 100 μm long, of which the contraction-extension cycle has the potential of being used as a linear reciprocating machine. In this study, we used polylysine (PLL) to attach micro-objects to Vorticella convallaria with the purpose of reciprocating the objects by contracting and extending the Vorticella cells. Two types of micro-objects, namely, polystyrene microspheres and glass grits, were coated with positively charged PLL and attached by electrostatic interaction to negatively charged V. convallaria. We characterized the adhesive performance and analyzed the movement of the objects by optical microscope observation. Microspheres of diameter 21 μm were moved back and forth by the contraction and extension of V. convallaria. Comparison of the adhesiveness of PLL-coated and COOH-terminated spheres confirmed the effectiveness of our attachment and actuation method. The grits were actuated in various ways depending on their size, the point of attachment to V. convallaria, and the number of cells. The typical motions were linear and rotational and were propelled by a few cells. V. convallaria cells displaced thin glass grits of thickness up to tens of micrometers. The adhesive force and the drag forces were estimated hydrodynamically. The implemented reciprocating motion can be applied to biohybrid microfluidic systems.
We have been investigating applications of a topology optimisation method with the level set method. In this study, to further enhance the applicability of the method, we investigate a topology optimisation method for three-dimensional scalar wave scattering problems which can be defined in an unbounded domain. To this end, the fast multipole boundary element method (FMBEM), which can deal with the unbounded domain accurately and efficiently, is implemented in the proposed optimisation method. A detail of the algorithm of the topology optimisation with the level set method and the FMBEM is presented. Also, a rigorous derivation of the topological derivative, which characterises the sensitivity of the objective function when an infinitely small spherical object appears, using spherical functions is presented. After validating the topological derivatives with approximated ones, we show the efficiency of the proposed optimisation method with a numerical benchmark. Through these numerical experiments, we conclude that the proposed topological optimisation with the level set method and the FMBEM can be applied to scattering problems in acoustics.
Much effort has been made to experimentally fabricate acoustic metamaterials that display novel properties, such as single or double negativity, negative refractive index. The novel properties displayed by acoustic metamaterials and their deep subwavelength nature, whereas the size of phononic crystals is in a comparable scale to wavelength, facilitate the development of real-world applications, from sound attenuation to superlenses, and acoustic cloaking. Compared with a conventional trial and error method, a systematic structural design methodology such as topology optimization is useful to achieve optimal designs of acoustic metamaterials. This paper proposes a topology optimization method for the design of acoustic metamaterials with the property of negative mass density. We consider mass-in-mass system that consists of a solid inclusion coated with a soft materials embedded in matrix material to produce a local dipole resonance that demonstrate negative mass density. The optimization is conducted to find optimal configurations of a locally resonant unit cell structure which achieves negative mass density at a certain desired frequency. The S-parameter retrieval method is efficaciously applied to describe the acoustic metamaterial according to its effective mass density. A level set-based method is employed to obtain the optimal configurations that have clear boundaries without gray scales, which would otherwise limit fabricability of the obtained acoustic metamaterial designs. The sensitivity analysis is performed by the adjoint variable method, and a reaction-diffusion equation is used to update the level set function. Several numerical examples are provided to demonstrate how the algorithm works, and the obtained optimal configurations illustrate the achievement of acoustic metamaterials that have negative mass density at certain prescribed frequencies.
One of the key aspects of developing gossamer space structures is the prediction of wrinkles and slacks in the material. Wrinkles, which essentially refer to elastic buckling, have been analyzed numerically using finite element methods (FEMs) with shell elements, but at a high computational cost. Therefore, membrane elements, which ignore bending stiffness and consider only in-plane stress, have been employed to reduce the computational cost. However, the compressive stiffness of the membrane cannot be ignored when predicting wrinkle regions precisely in membrane structures. Some previous studies have employed membrane elements considering small, constant non-zero values of compressive stiffness; these membrane elements can predict the distribution of principal stress as the wrinkle regions. However, none of these traditional methods can determine the value of compressive stiffness, and some parts of the principal stress distribution in slack areas do not correspond to the actual phenomenon. Therefore, in order to determine compressive stiffness logically and uniquely, we propose a new numerical calculation model, the modified-stiffness reduction model (Mod-SRM), which is based on the stretchable elastic theory. Moreover, by comparison with the other FEM models, we confirm that Mod-SRM represents the slack region more accurately than the traditional models.