In the Great East Japan Earthquake that occurred in March 2011, it was reported that mechanical structures were damaged due to tsunami wave pressure on the structures, and impact of debris that flowed along with the tsunami on the structures.If an industrial facility located on the coast is assumed to be flooded by a tsunami, it is necessary to have a method of evaluating the wave pressure of tanks, piping, and other equipment of the industrial facility and the debris impact. However, studies on debris impact for mechanical structures are not sufficient. Then, for the purpose of establishing a structure evaluation method for debris impact of outdoor tanks, debris impact test and dynamic and static analysis simulating debris impact were carried out. As a result of the experiment, the behavior data of the thin cylinder in the collision of drifting object was obtained. Dynamic analysis simulating the experiment was also carried out, and it was confirmed that the response was similar to the experiment. In addition, an evaluation equation of displacement and reaction force at debris impact using static incremental analysis was proposed.
We investigate the critical size of ferroelectricity in monolayer tin telluride (SnTe) nanoribbon by using ab initio (first-principles) density functional theory calculations. The edge of SnTe nanoribbon tends to suppress the ferroelectricity and the edge effect ranges within the 4 unit cells (~1.8 nm) from the edge. In nanoribbons, ferroelectric polarizations decrease monotonically with decreasing nanoribbon width. Ferroelectricity finally disappears in nanoribbons with 4 unit-cell width or less. This signifies that the ferroelectric critical size of SnTe nanoribbon is 4 unit cells (1.8 nm) due to the edge effect. However, the ferroelectricity of nanoribbon below the critical width is restored under uniaxial tensile strain along the  direction. Thus, the critical width of ferroelectric disappearance can be eliminated by tensile strain. Our results indicate that the lattice width ferroelectric material can be mechanically realized by tensile strain.
An evaluating equation to present the influence of thermal properties of workpiece and cutting tool on the cutting temperature is derived by the dimensional analysis. Turning experiments are carried out in order to confirm the propriety of the equation. Ti-6Al-4V, Inconel718, SUS304, S50C, 6/4 Brass, Aluminum and AZ80 are used as workpiece materials, and Al2O3, Si3N4, Cemented Carbide, CBN and Bidemics as tool materials. Cutting temperature is measured by two-color pyrometer with an optical fiber which is developed by the authors. The phenomenon of chip combustion is used to estimate the cutting temperature in turning of Ti-6Al-4V. As a result, the equation derived in this paper is useful and convenient to evaluate the overall influence of cutting conditions, thermal properties of workpiece materials and those of tool materials on the cutting temperature. The equation consists of the factors of cutting speed, depth of cut, feed rate, specific cutting energy, thermal diffusivity of workpiece and that of cutting tool. Moreover, experimental result suggests that the specific cutting energy of the workpiece material is estimated using only its volumetric specific heat and melting point.
In the initial design stage of vehicle development, it is important to estimate the strength of the structure against various loads. It is known that buckling occurs in thin-shell structures before yielding as the load increases, and that the structures can withstand loads even after buckling. The load acting on the beam constituting the vehicle structures may be not only a compressive force and a bending moment but also a torsional torque. Due to this torsion torque, a shear stress acts on the thin shell constituting the beam. In this paper, after shear buckling of a rectangular plate, the approximate expression of buckling deformation presented by Timoshenko as an out-of-plane displacement is used, and the relationship between the out-of-plane displacement amplitude (maximum out-of-plane displacement) and the shear force is determined based on Karman's effective width theory. Using the obtained out-of-plane displacement amplitude, three stress distributions and the maximum value of Mises equivalent stress are derived as a function of shear force. Then, the derived expressions are compared with the computation results of the finite element method (FEM) using shell elements under the boundary condition that does not constrain the in-plane displacement of both sides in the longitudinal direction, and the applicability is examined. As a result, it turned out that the derived relations between the out-of-plane displacement amplitude, the maximum value of Mises stress, and the shear load are less than the absolute value error within 10% in the discussed load range, compared to the FEM computation results. Therefore, the derived expressions are sufficiently effective in determining the yield strength based on the Mises stress.
In this paper, we propose a shock wave generation method through laser rupture that can control the timing and condition with high accuracy using a simple mechanism. We also evaluate the response performance, structure, and propagation characteristics of the shock wave generated using this method. When laser-irradiated from the outside through the window, the laser hole in the film shock-tube diaphragm is opened momentarily. As a result, the diaphragm bursts, and a shock wave is generated. First, we investigated the best combination of laser rupture using various laser and diaphragm materials. For the combination of a continuous wave (CW) laser with a lower output but longer adjustable irradiation time and an oriented polypropylene (OPP) film with a high tensile strength and a low tear resistance, the shock wave was generated at almost the same time with the laser irradiation. Subsequently, by investigating the fracture response time using the OPP film and CW laser, it was found that the shock wave generation timing with an accuracy of 100 μs order can be controlled. Furthermore, when compared with a metal diaphragm through natural rupture, the initial opening rate of the OPP film through laser rupture was high, and it was believed to form an ideal shock front. In contrast, compared to the natural rupture of a cellophane film, which burst and spread over the entire separation surface of the diaphragm when over-pressurized, the laser rupture using the OPP film diaphragm formed a curved shock shape because a spherical shock wave was formed from the opening start point. However, Shock wave became flat with propagation and was propagated at almost the theoretical velocity.
Steam is widely used as a medium for thermal energy transport in industry, such as in heat supply and drying processes. It is therefore important to evaluate precisely the steam flow rate at the demand end from the viewpoint of energy management. The state of steam in the steam piping of industrial facilities without the superheating process is usually wet steam resulting from causes such as heat loss, heat supply, and work. It is well known that steam wetness often causes measurement error of the steam flow meter. However, there has been no established standard for estimating the measurement error since it is difficult to evaluate the effects of steam wetness quantitatively in plants and factories. A clamp-on ultrasonic steam flow meter is suitable for use in factories since pipe processing is unnecessary. We conducted experiments to clarify characteristics of the measurement error of a clamp-on ultrasonic flow meter owing to steam wetness considering the influence of pipe diameter. The total mass flow rate of the steam through the test section was measured using a calibrated Coriolis flow meter downstream of the condenser to obtain a reference value. The measurement error of the clamp-on ultrasonic flow meter was estimated by comparison with the reference value. The flow rate difference between these two flow meters was found to increase with increasing steam wetness. Moreover, the clamp-on ultrasonic flow meter measurement was almost the same as the flow rate of only the gas phase in the wet steam flow. From the experimental results, we proposed a correction method for measurement using the clamp-on ultrasonic flow meter in a wet steam flow by correcting the density in the flow rate calculation. Moreover, we clarified the applicability of the clamp-on ultrasonic flow meter in piping of various diameters.
The present paper describes the performance of a micro undershot water wheel for the power generation in a snow drainageway with the Froude number of 2 to 3. In order to optimize the installation conditions of the undershot water wheel and its arc blade, the effects of blade inlet angle β and the submerged blade height hc on the performance of the undershot micro water wheel has been investigated by field test at Shiramine district in Ishikawa Prefecture. Furthermore, two-dimensional computational fluid dynamics (CFD) has been performed using ANSYS Fluent to be shown clearly the flow of inside and outside of the undershot water wheel and its power. The water wheel has a diameter of D = 600 mm and a width of W = 410 mm. In the snow drainageway, the Froude number is Fr = 2.15 to 2.42. The CFD result of the change of the maximum power coefficient CPmax with the blade inlet angle of β agrees with the experimental one qualitatively. In the case of the submerged blade height hc/D = 0.10, the blade inlet angle β has little influence on the power coefficient CP. In the case of hc/D = 0.20 and 0.29, the peak value of the maximum power coefficient is CPmax = 0.37 and 0.27 at β = 18° and 24°, respectively. The relation between the flow in the water wheel and the generation of torque has been clarified by CFD. The negative torque generates at the rotation angle of water wheel θ = 0 ~ 40° because the separated flow from the tip of blade collides against the back of the blade. The positive torque generates at θ = 45 ~ 110° to apply the drag force by the main flow. The positive torque also generates by the water flow passing through the blades for θ = 135 ~ 210°.
The flow and performance of a rotor of a Savonius hydraulic turbine provided with a shield plate were analyzed by the two-dimensional simulations. The rotor diameter DR is 142 mm, and the Reynolds number based on the velocity of the main flow U0, U0DR/ν, is 1.1×105. The shield plate with a length of 0.5DR is installed upstream of the rotor, perpendicular to the main flow. The comparative experimental studies have visualized the flow and clarified that the shield plate increases the power output of the rotor. The vortex in cell method combined with the volume penalization method was applied to the flow simulation, and the torque acting on the rotor was computed with a custom method by the authors. The simulated flows around the shield plate and rotor agreed with the experimentally visualized ones. The simulation successfully revealed the effect of the shield plate on the flow and power output of the rotor. These demonstrate the applicability of the present simulation method for the performance prediction of the rotor of Savonius hydraulic turbines provided with a shield plate.
The penetration of DME spray is shorter than that of diesel fuel when the same injection system is used because DME cannot be injected at high pressure like diesel fuel due to its high compressibility. Chris reported that supercritical gasoline spray has a wider spray angle and has increased penetration. Therefore, there is possibility that supercritical DME spray has increased penetration. However, there is no observation on the shape, development process, combustion of supercritical DME spray. In this study, the spray and combustion characteristics of supercritical DME in an optically accessible constant volume vessel were observed under turbo charged engine-like ambient condition. Parallel light shadow graph and diffused light shadow graph method were applied to image the liquid and vapor phase behavior. Moreover, the spray angle of supercritical spray was compared with that of subcritical one under the same ambient condition to confirm the influence of fuel temperature. The results show that there is no significant difference in spray shape between supercritical and subcritical spray under turbo charged engine-like ambient condition. Moreover, the spray angle of supercritical spray was bigger than that of subcritical one under relatively low pressure ambient conditions. These can be explained by p - v diagram. The reasons are as follows the difference in specific volume between liquid and vapor is small at ambient pressure near critical pressure. The ignition timing of the supercritical spray was slightly earlier than the subcritical spray.
The purpose of this research is to suggest tendon placement generation rules for folding transformation into multiple shapes. As a method to propose how to generate tendon placement, a method combining trial production, geometric interpretation, and algorithm development was used. Firstly, trial production and its analysis were carried out. As a result, it was found to be possible to drive consecutive folding operations and to drive the folding transformation into multiple shapes from the same panel by using the method that the tendon was penetrated the overlapping of plates in the shape after the folding transformation. And the rule that tendon placement can be generated by repeating primary transformation of starting point of tendon placement was extracted. Secondly, tendon placement generation algorithm based on the tendon placement generation rules, and state transition diagram generation algorithm were developed. Thirdly, experimenting the motion of the panels with tendon placement generated by the algorithm mounted, the operation of the algorithm was confirmed and the behavior of the panels was investigated. Finally, by examining the experimental results, the effective range of the algorithm was found to be folding transformation composed of up to two folding operations. From this, it was found that the applicable range of the extracted rules were folding transformation composed of up to two folding operations. By referring trial tendon placement generated for folding transformation composed of three folding operations, rules were modified. Therefore, it turned out that driving of the origami panel using the discovered tendon placement was realized by the mechanism of bringing all overlapping points closer by pulling the tendon, and the extracted rules were found to be effective for realizing driving of folding transformation from the same panel into multiple shapes.
In this paper, we proposed a sampling mechanism with flicking motion for chemical plume tracing (CPT). CPT stands for a task to locate a chemical source according to the chemical in the air. Capability of CPT by an autonomous robot is highly demanded because that can be applicable for rescue surveys, security inspections, and resource searching, yet that was difficult for an individual robot due to the complex behavior of airflow. From the viewpoint of bio-inspired systems, we focused on the flicking of an insect, by which it swings its antennae (chemical sensors) depending on situations. We expected the flicking provided variable sampling resolutions according to searching phases. We first design and implemented a variable air sampling mechanism that gave flicking ability to an autonomous mobile robot. Then, we introduced the flicking to a common CPT algorithm inspired by the programmed behavior of a silkworm moth, which was composed of three action phases. For the action phases, we tested the all combinations of wide or narrow range of the sampling system. We verified CPT performance with the proposed device through experiments. The results indicated that the flicking could improve success ratio of CPT tasks without extending needed time for a search.
Labyrinth seals have been used as non-contacting sealing devices for rotors such as on turbo machines. In recent years, an improvement of the sealing performance of labyrinth seals has been required due to the increasing pressure of turbo machines. In this paper, it is suggested that new type pump labyrinth seals (Radial labyrinth type) have high sealing performance on pump wear rings in the radial direction of fundamental labyrinth grooves seals. This study was carried out by CFD analysis. First, radial labyrinth seals were tested in an actual double suction pump. Subsequently, it became clear that pump radial labyrinth seals have an effect of increasing pump efficiency by reducing leakage compared to general plain wear ring seals. It was also confirmed by various experiments that the radial labyrinth seals have the effect of increasing pump suction specific speed. Furthermore, it was demonstrated that the rotor-dynamics coefficients of radial labyrinth seals are smaller than plain seals.
In sound-absorbing poro-elastic media, the energy of incident sound wave is dissipated through the following three mechanisms: the viscous dissipation arising the vicinity of the boundary between the solid and fluid phases due to the viscosity of air, the thermal dissipation, and the viscoelastic dissipation due to the damping property of the material used in the solid phase. Contribution of these three dissipated energies are not clear, although the incident energy is considered to be mainly dissipated by the viscous dissipation. In order to evaluate numerically these three dissipated energy separately in the finite element method, one needs to access element matrices, which is generally not easy in commercial softwares. Thus, in the study presented here, we evaluate the dissipated energies by using the analytical solutions for one-dimensional wave equations assuming that the sound is incident normal to the poro-elastic material. Moreover, we analyze the characteristics of the frequency spectrum of the sound-absorbing coefficient by using the relationship between the viscous dissipation and the particle velocity relative to the velocity of the constructed elastic material.
Pen comfort is an important factor in selection of pen for handwriting. In handwriting, a pen receives an impact when it contacts to paper placed on a desk. To hold the pen, fingers have to resist the impact. The greater impact, the grater mechanical workload on fingers associated with the grip strength to hold. Therefore, time series data of pen pressure is supposed to indicate the physical workload in handwriting task. As a preliminary step for the pen comfort evaluation, this study aims to evaluate the physical workload in handwriting tasks using time series of pen pressure. To judge whether pen tip contacts with paper, a probabilistic analysis method of time-series pen pressure was built first. Next, several indices of impacts such as average pen pressure and duration per stroke, and number of touchdowns per second were calculated. Finally, the product of the indices was defined as the normalized physical workload. For multiple four-character idioms with different stroke counts, pen pressure was recorded and the indices and the evaluation value were calculated. The results indicate that the normalized physical workload was larger in writing idioms with longer duration per stroke. In holding and moving a pen against the paper, it is considered that keeping pen pressure requires larger workload than resisting fluctuation of the pen pressure.
In previous papers, the author presented motion analysis methods of multibody systems. In the presented methods, the null space matrix for the constraint Jacobian is obtained by solving a differential equation, then the Lagrange multipliers are eliminated from the equation of motion with the obtained null space matrix.This enables us to perform efficient computation. The elimination of the Lagrange multipliers, however, may become drawback for analysis of constraint forces/moments since the Lagrange multipliers correspond to the constraint forces/moments for the considered constraints. In this report, a new method which can analyze constraint forces/moments efficiently with keeping advantage of the methods presented in the previous papers is developed. First, governing equations which involve the constraint forces/moments explicitly are derived by introducing relative displacements that violate the constraints, called anti-constraint relative displacements. Then a procedure to determine the constraint forces/moments with eliminating the Lagrange multipliers is presented. In addition, extension of the presented method to systems with redundant constraints is given. Finally, validity of the presented method is verified by some numerical examples.
Driving at resonance point of the large degree of freedom and large damping vibration system is difficult because of crowd of natural frequencies and decreased peak of gain of transfer characteristics. To solve this problem, the multi-point excitation is effective. Centralized control as the general control method for multi-point excitation is the method to adjust the amplitude and frequency of all actuators and the phase difference between the adjacent actuators to suit modal shape of natural vibration. Therefore, to grasp the natural frequency, vibration mode of natural vibration is necessary. In this paper, the expansion to the large degree of freedom and large damping vibration system of the proposed decentralized control is proposed. Firstly, the difficulty of the driving at resonance point of large degree of freedom and large damping vibration system by centralized control and conventional decentralized control is explain. The self-excited vibration is generated at the frequency that has the highest peak gain of a loop transfer function. In the condition of crowd of natural frequencies, this method can excite only the particular natural vibration. Secondary, the cross feedback control is to excite the arbitrary natural vibration. The phase adjusting modal shape of natural vibration is fed back to adjacent actuator. Lastly, the adaptability for the change of damping caused by environment using damping element is verified. The influence of damping of the system in a loop transfer function is decrease by local feedback control as the active damping control. As the result, the amplitude of system maintains against the increase of damping.
This paper proposes a method of airspeed measurement using ultrasonic waves for control of micro UAVs. Measurement by pitot tube sensor generally used for aircraft control does not show high resolution and responsiveness in low speed flight. The proposed method employs the phase difference method to overcome the drawback of low resolution in the measurement. The efficiency of this method is demonstrated through flight experiments to estimate the angle of attack and the angle of side slip of a micro UAV from measured airspeed.
Synthesis of cable-configurations of a novel redundant planar cable-driven parallel robot “SEIMEI” is discussed in this paper. This robot has the endless-pulley embedded inside the moving part as an additional rotational degrees of freedom (dof) for enlarging the rotational workspace. The four-dof moving part is driven by five cables, and the hand attached to the endless-pulley is controlled by four-dof mechanism. So SEIMEI has the actuation and kinematic redundancies simultaneously. Firstly, mechanical features and kinematics of SEIMEI are discussed. Next, hybrid analytical-numerical approach to determine the cable-configurations which satisfy the wrench-closure condition (WCC) is introduced. The cables can only be pulled but not pushed, so all cables must have positive tension value. The WCC defines the condition which the cables can receive any external wrench with positive cable tensions. By using new approach, cable-configurations which satisfy the WCC of SEIMEI was derived. Finally, derived cable-configurations were verified by numerical simulations.
This paper deals with seismic isolation system with nonlinear characteristics for vertical ground motion. The vertical seismic isolation system consists of a rhombus shaped link mechanism, a tension coil spring, and a leaf spring. The restoring force of the system is obtained by the sum of the restoring force of the buckling deformation of leaf spring and the restoring force of the rhombus shaped link. The purpose of this paper is to create design guidelines for seismic isolation system. Random waves were input to the experimental model with nonlinear restoring force, and the reduction effect was about 0.1 times. In addition, the validity of the analytical model was confirmed by comparing the experimental results with the calculated results. By setting dimensionless parameters and performing analysis, combinations of parameters with high seismic isolation effect were clarified. When the seismic isolation object was determined, a guideline on how to design it was given to make the seismic isolation design easier.
As one of the approaches to problem of variability in the thermal deformation of steel products after rapid cooling in the quenching process, a new computational method to evaluate the sensitivity to temperature concerning chemical composition of steel is described in this paper. The phase transformation and heat conduction interaction problems were solved by the finite element method. To calculate the sensitivity, parameterization of all necessary quantities was carried out not only for heat conduction analysis but also for prediction of phase transformation using time-temperature-transformation diagram and phase fraction. The sensitivity to the temperature through each parameter was calculated with respect to chemical composition within the range of variability defined for JIS SCr420 steel. One of the findings in this study lies in the significant differences in temperature, strain and deformation after the appearance of bainite phase due to small fluctuation in chemical composition. Moreover, the above sensitivity values were calculated as a function of time. It was found that the influences of Si on temperature through density, thermal conductivity and phase fraction were larger than those before bainite transformation. After the appearance of bainite, the influence of Si through phase fraction decreased, but the sensitivities concerning Mn and Cr increased.
Molecular gas film lubrication (MGL) equation, which is derived based on linearized Boltzmann equation, is the reliable means to analyze the molecular gas flow in the narrow channel, whose thickness is as thin as the molecular mean free pass. Though, the application limit of MGL equation against the surface roughness exists. Because the equation is available under the condition that the local surface curvature is sufficiently large, as in the case of Reynolds equation. This paper describes the effects of surface roughness on the lubrication characteristic and the application limit of MGL equation. The lubrication characteristics affected by surface roughness, such as the pressure, the shear force and the mass flow rate, are calculated by using two methods, direct simulation Monte Carlo (DSMC) method and MGL equation. DSMC method is free from the restriction by surface configuration and is expected to give the correct solution for molecular flow. The calculations are performed against the simple two-dimensional channel, which consists of the moving smooth plate and the stationary flat slider possessing the triangular roughness. No pressure difference exists between the ends of slider. It is clarified that the difference of resulted characteristics by two methods expands as the roughness slope increases, indicating the application limit of MGL equation. It is suggested that the relation between the mass flow rate and the roughness slope could be the index of the application limit of MGL equation.
Vacuum carbonitriding has recently been attracting attention as a heat treatment to reduce the size and weight of power transmissions. In this study, all of the chromium molybdenum steel test gears were vacuum carbonitrided after hobbing. The roughness of test gears was finished by a gear grinding machine to about 3 μmRz on tooth profile. These gears were called Gear G. Additionally, fine particle shot peening was applied on some of Gear G to improve the bending strength by providing work hardening and compressive residual stress on tooth flank. These gears were named Gear GS. Their load carrying capacity was investigated through running tests using a gear testing machine. The endurance limit of Gear G was about 2150 MPa in maximum Hertzian stress at the pitch point. This is an improvement of about 25 % over that of the carburized gear. However, the endurance limit of Gear GS was lower than that of Gear G. In order to investigate this factor, each of the surface topology were observed using a laser microscope. Comparatively, the rate of contact area was decreased after shot peening. This means that the surface topology of Gear GS must be improved, since failure occurs in shorter cycles on Gear GS. In order to simulate the surface roughness finished by the gear lapping technology which has been developed by the authors, some of Gear GS were polished to about 1 μmRz on tooth profile. These gears were called Gear GSP. According to running tests of Gear GSP, the fatigue life was longer than those of Gear G and GS, because the rate of contact area was improved by polishing. It is concluded that if the vacuum carbonitrided gear was treated by grinding, fine particle shot peening and the gear lapping in turn, the appropriate load carrying capacity may be obtained.
A new methodology to assess and adapt cutting conditions for machining operation planning is proposed in this study. In order to automate machining operation planning, the method to reuse cutting conditions in the past previous machining operations has been proposed in the previous study. However, the assessment and adaptation of cutting conditions are required to apply the referred cutting conditions to the different situation. For the assessment of cutting conditions, an acceptable area to select cutting conditions (AACC) is calculated. The AACC is restricted by several constraints such as spindle power capacity and maximum feed speed of machine tools, torsional and bending strength of cutting tools and so on. In the case that the referred cutting conditions keep in the AACC, the referred cutting condition can be applied to the situation without any revision. In the case that the referred cutting conditions keep out the AACC, the referred cutting conditions cannot be applied to the situation and should be adapted for the objective machining operation. In this study, the referred cutting conditions are adapted so as to keep the machining efficiency such as machining time, tool life and cusp height. This study considers that these three aspects are essential for skillful operators to determine the cutting conditions. The feasibility of this methodology is demonstrated in the case study and cutting experiments. This methodology can assess and adapt the referred cutting conditions for the objective machining operation.
The time history response and its variance of physical system are analyzed based on the functional model converted from physical domain to time-constant domain. Since a base unit of the model in time-constant domain is time, the relationship between the model and its time history response may be apparent for analysis of the response. This approach is firstly applied to the theoretical 1st and 2nd order system in time-constant domain and to give results: (1) a ratio of time-constant to input time of 1st and 2nd order system is an explanatory variable of the time history response and its variance, and thus (2) increasing the ratio can reduce the variance of time history response. This approach is then applied to a real system called the impact excitation system which converts input electrical energy to solenoid armature movement to excite a target plate. The measured time history responses of the system such as a current, armature velocity and impact force are analyzed by the corresponding functional model in time-constant domain and give results: (3) the rapid change of time history response and its variance of armature velocity and impact force at impacting on the target can be explained as a small time-constant of armature mass and contact stiffness relative to the input time, and thus (4) it is verified that the proposed approach can provide the insight for analysis and designing the time history response and its variance of physical system in an intuitive way.
In this research, we investigated the effect of allowance time on driver behavior when the Request-To-Intervene (RTI) at nighttime driving. We also analyzed driver behavior at RTI using the concepts of Situation Awareness (SA) and the behavioral analysis description method. The experiment was performed using a driving simulator, and a RTI occurs when the subjects was driving using level 3 of automated driving at night. After that, the subjects operate the steering wheel to avoid obstacles. As a result of the experiment, the lighting area of the driving beam was limited at night, so the obstacles moved out of the lighting area when Time-To-Collision (TTC) exceeded 7 seconds. Therefore, the driver was unable to responds to RTI driving behavior because no obstacles were detected. On the other hand, it was found that if TTC is shorter than 5 seconds, there is a high possibility of inducing a sudden operation the driver, and there is not enough time to confirm driving safety, so we think this driving condition is not suitable for RTI timing. Therefore, we think 7 seconds is enough for RTI timing at night. If this timing is secured, safety operation to avoid the collision to the obstacle is possible.