Deformation and failure behavior of a Ni-base superalloy specimen with thermal barrier coating were investigated when it was subjected to external load under a graded temperature condition. The experimental results demonstrated that the crack density in the ceramic top coat was higher at lower temperature side than that at higher temperature side. It was also observed that the inelastic strain rate of the specimen was higher, compared with that of the laboratory creep test without temperature gradient. In order to get basic understanding on the above specific behaviors, a simple two-dimensional creep deformation model was proposed, taking account of the effect of temperature gradient. In the model the stress state was analyzed when the material is uniformly deformed associating with diffusion creep. The numerical calculation result predicted the following noteworthy phenomena: higher stress state would be build up at the lower temperature side than at the higher temperature side, and this state is promoted with time. Cumulative creep strain develops more quickly at the lower temperature side than at the high temperature side. These predictions provided some reasonable explanations to the experimental results.
Electroplated diamond tools are developed for grinding hard and brittle materials because of its low wear resistance. To improve the grinding performance of diamond tools, a single layer of diamond abrasives is electroplated on the tool body. The electroplating process delivers a homogeneous layer with diamonds embedded in nickel alloy at high speed. In order to facilitate the adhesion of diamond abrasives, the diamond abrasives are coated by nickel membrane. Therefore, the cutting edges of diamond abrasives are hidden and the grinding performance of diamond tools decreases. Moreover, a phenomenon of abrasive aggregation generates and leads to bad abrasive distribution. In this paper, in order to solve those problems, authors developed partially Ni-coated diamond abrasives, which were produced from the commercially available full Ni-coated diamond abrasives. The adhesion characteristics of partially Ni-coated diamond abrasives were discussed, too. The grind-abilities of diamond tools, which are fabricated with using non-coated diamond abrasives, Ni-coated diamond abrasives and partially Ni-coated diamond abrasives, have been evaluated. As the results, the problems when using non-coated diamond abrasives or Ni-coated diamond abrasives could be solved and the grind-abilities of electroplated tools were improved with using partially Ni-coated diamond abrasives.
The bimetal materials that sintered the powder of lead bronze on the base material (i.e. carbon steel) have the excellent performance as the bearing material. However, the nation or the society is moving on with the planning on the use restriction of lead and lead compound. Therefore, lead-free copper alloy is developed, and the practical applications of the alloy are advanced. However, the mechanical properties of the bimetal material that sintered the alloy powder have not sufficiently been grasped. In this study, the evaluation of the fracture mechanism and that types which arose in the materials was examined. As the results, it was possible to grasp or evaluate each fracture type by the frequency component of Acoustic Emission (AE) signal with Fast Fourier Transform (FFT) method, and the m value which is led from the amplitude distribution of the signal. By using the criterion for recognizing each type, it was proven that the proposed technique in this study can evaluate the fracture mechanism of each bimetal material which changed the type of the lining material.
The advanced phased array UT technique for SCC crack depth sizing in Ni-based alloy weld was developed. In previous study, authors proposed to the UT procedure for defect depth sizing by phased array UT in the inside inspection. The UT procedure was applied to the defect depth sizing in Ni-based alloy weld specimen with EDM notches. From these results, superior performance for defect depth sizing by phased array UT technique was shown. However, it is not clarified the performance of SCC crack depth sizing. And then, it is not established the fabrication method of Ni-based alloy weld specimen with artificial SCC crack. In this paper, the investigated results of fabrication method of Ni-based alloy weld specimen with axial SCC crack are shown. Furthermore, phased array UT technique for crack depth sizing was applied to the Ni-based alloy weld specimen with axial SCC crack. From the experimental results, good accuracy of SCC crack depth sizing by phased array UT in the inside inspection was shown. Therefore, it was clarified the effectiveness of the UT procedure for defect depth sizing in Ni-based alloy weld. Furthermore, main factors of crack depth sizing error were investigated, and then countermeasure for the decrease of those errors was also investigated.
In planar laser induced fluorescence (PLIF) measurement, temporally varying and fluctuating noises affect measured statistical profiles, significantly. In this study, the former φ is caused by a ratio of temporally varying quantum yield φ between measurement and reference images, and the latter sβI is mainly due to temporal fluctuations of a ratio of camera sensitively β and a ratio of incident laser I to excite a fluorescent dye, where sβI ≡ βI- 1. These noises can significantly affect statistical profiles of fluctuating concentration field. The aim of this study is to develop predictive formulas for the effects on fundamental statistical profiles. The effects of φ and sβI are reconstructed to mean of φ, αT/2, mean of sβI, SβI and intensity of fluctuation of sβI, <e2>, where α is rate of temporal change of φ, T is required time of the experiment, SβI = <sβI>, e = sβI, sβI = SβI + sβI and <> denotes ensemble average. Then, we show a series of the formulas to predict the effects on mean scalar, intensity of scalar fluctuation, 3rd-order statistics and 4th-order statistics of scalar fluctuation. The predictive formulas are validated by using experimental results of high-Sc-number scalar mixing layer in grid-generated turbulence measured by PLIF method, where the mesh Reynolds number was 2,500 and the Schmidt number was about 2,100, respectively. The effects of <e2> is analytically found to be the most significant among αT, SβI and <e2> by expanding the predictive formulas. In fact, the profile of <c2> is significantly affected by variation of <e2>. The predictive formulas can be used as formulas to correct the profiles when given values of the three parameter are appropriate.
Recently, reduction of CO2 emissions from automobiles is carried out in the world. The improvement in aerodynamics and reduced in CO2 emissions have been realized with passenger cars. However, there is still some room for improvement between trucks and trailers in aerodynamics. In this study, a wind deflector attached on the container of a truck was proposed to reduce the drag. To investigate the effects, the drag and flow patterns over a small-scale truck model were measured in a small wind tunnel. Furthermore, the drag, flow patterns, and pressure distributions of a full-scale truck model were examined at a highway driving condition by Computational Fluid Dynamics. It was found that the drag can be reduced without losing container space by the wind deflector attached on the container. The maximum decreasing ratio of drag was 3.4%. As the reason of the drag reduction, it was found that the wind deflector reduces size of wake flow and increases static pressure behind the vehicle.
In this experimental study, fluid dynamic response characteristics of wake galloping between two square prisms of same size in tandem and staggered arrangement to their relative position and free stream velocity were investigated. An immovable square prism of size d was fixed at upstream side and another vibratile square prism was placed at downstream side. The relative position of the vibratile downstream prism to the upstream prism was varied in the range from 1.6 d to 3.1 d in stream-wise direction, and in the range from 0.0 d to 2.1 d in cross flow direction. The vibratile prism at downstream side is elastically supported at it's both end and is ristricted to vibrate in only cross-flow direction. Instantaneous displacement of vibratile prism was measured by means of Laser Displacement Anemometer, and degree of vibration was evaluated by rms value of the fluctuating displacement. At first, response characteristics of wake galloping to relative position and flow velocity were investigated by free-vibration experiments in tandem and staggered arrangements using a wind tunnel. From the experiments, it was found that the response characteristics can be classified into three patterns in relation to relative positions and free stream velocities. Then the wake galloping phenomena occurred in the free-vibration experiments were reproduced by forced-vibration experiments in a water channel to conduct flow visualization. The visualization results well explained the phenomena observed in the wind tunnel experiment.
The complexity or randomness was examined with the aid of Kolmogorov complexity for the flow about a turbulence wedge developed from a single roughness element on a flat plate. Velocity data obtained from a hot-wire anemometer and its time derivative data were compressed using a compression program running on a Windows PC. Approximated Kolmogorov complexity, AK, and normalized compression distance, NCD, were obtained. Although the AK variation of fluctuating velocity and that of its time derivative do not completely agree with that of the fluctuating velocity and the intermittency factor, they do roughly. Therefore, the objective judgment of the laminar-turbulent transition progress based on the Kolmogorov complexity mostly supports the judgment by the conventional intermittency factor. With the aid of the AK we can distinguish the complexity within the turbulent region; on the other hand, the intermittency factor cannot. The AK distribution of fluctuating velocity and that of time derivative are similar, and this suggests the similarity in the differentiation of complexity. The AK in the turbulent flow is larger than that in the non-turbulent flow. The AK decreases when the coherent structure has occurred in the turbulent flow. This means that the length of the algorithm is short if a computer expresses the coherent structure detected by the conventional method. Although the hot-wire signal within the coherent structure is random in appearance, it is coherent in the algorithm view. The difference in NCD on the time derivative of the fluctuating velocity between the turbulent and non-turbulent flow is larger than the NCD on the fluctuating velocity itself. That is, the difference in complexity appears in the fluctuating vorticity more than in the fluctuating velocity.
Recently, dielectric barrier discharge (DBD) plasma actuator attracts attention as an active separation control device. This study is concerned with the flow control around airfoil when a DBD plasma actuator is mounted on the leading edge. The experiments are performed mainly in an external airflow of 10 m/s . DBD plasma actuator is installed at x/c=0.025 of 100mm chord and 150mm width of NACA0015 airfoil model. Aerodynamic force and velocity field around the airfoil are measured for the on and off modes of the plasma (pulse modulated drive). As a result, the on time per one period of pulse modulated drive affects a lift force, and the maximum lift angle increases by selecting optimum on time. On the other hand, drag force is nearly unaffected by the difference of on time. The faster the uniform flow velocity is, the shorter the most effective on-time length is, and non-dimensional effective time length is constant. When the actuator is driven with the most effective on-time, the strong vortex structure are formed in the shear layer and this vortex is maintained to the downstream.
Authors developed the flexible biomimetic fish-like robot for usage in narrow passage flow. The robot mainly consists of three sections: a control section, actuator section and flexible fin section. By using the shape memory alloy (SMA) actuators, downsizing and lightening has been achieved. At first, we constructed the fluid-body coupled model of robot fish for consideration of undulatory swimming and nonlinearity of SMA characteristics. We also constructed experimental model to confirm the validity of analytical model. It is known that dynamics of SMA actuator depends on ambient temperature. Therefore over-heating of SMA actuator may cause accumulation of heat in actuator section of the moving body, and decrease of the amplitude of the caudal fin and the thrust force. Thus, in this study, to improve the driving characteristics of actuator, we identified the relation between temperature and moment of SMA actuator. Next, we constructed the fluid-moving body interaction model which is considering the dynamics of actuator. We searched the local optimal input for SMA actuator based on optimization theory. As a result, it was found that for maintaining high thrust force SMA actuator needs to be driven keeping the temperature around 340[K].
We have investigated reconstruction of the pipe-undulation shape throughout the length of a pipe from the measured data of the interior profiles by using a laser-beam scanning sensor. This sensor has been studied for detailed noncontact mapping of the interior geometry of pipes. The sensor, which is based on the optical triangulation, employs a laser-beam scanner placed between a laser diode and a position sensor. In this article, we develop a model for calculating a curvature of ridgeline on an inner wall of a pipe, and derive a formula to compute the curvature form of the pipe. By using this formula, it is possible to lead the whole pipe-undulation shape of the measured pipe in an iterative manner. Then we apply it to an actual measurement of a pipe, which was constructed for experiment. We find that the reconstruction is successful for the short section (up to 7 m) with expected accuracy (within about 20%) and we could derive a rough shape for a whole length of the conduit.
In this paper, a self-powered active seismic isolation floor is proposed to solve safety concern about active control in case of an electricity shortage. The self-powered active seismic isolation floor is composed of two layers named Unit B and Unit T. This self-powered system is based on the idea of electric power regeneration. Two kinds of actuators act in it. The two actuators are controlled by different control methods; the two control methods are constructed as a distributed control. One actuator at Unit B acts as a generator during deceleration based on an energy optimal control that is superior in energy regeneration, and the other one at Unit T acts to control vibration using charging energy at Unit B based on conventional control method that is effective in vibration reduction. The control design method and its parameters are shown considering performance and energy. In addition, the displacement of the top layer which defines a required clearance of the two-layer seismic isolation floor can be reduced by allowing for large drift of the small layer between Unit B and Unit T. It is showed that the proposed system uses only charged battery at an initial state, and its control performance is superior to that of a two-layer passive seismic isolation floor by time-history analysis.
This paper presents a real-time simulation for coupled system with rigid body system and hydraulic system. The equations of motion for the rigid body are derived by transforming the rigid body motion to the linear element motion. The system equations can be presented as the ordinary differential equations of motion for the coupled system of the rigid body system and the hydraulic system without introducing the constraint conditions, describing the motions of the rigid body system using the linear element motion. Then, this modeling is useful for the real time simulation for the coupled system, as numerical stability is improved by carrying out coupled system simulation in one software package. Firstly, rigid body system driven by the linear element is formulated, coupled analysis theory with the hydraulic system is derived, and electric motor drive system is formulated. Finally, the actual digging simulations of a hydraulic excavator are implemented using the present technique. It is clarified that the real time simulation is successfully conducted.
We have developed a dynamic model for a coupled railway vehicle to evaluate the ride comfort of high speed train on curve section in the tunnel. This model was generated by using the mathematical software. First, the calculation code of the one vehicle model was transformed to a module. Secondly, the transformed modules were connected to expand a coupled train model in mathematical software, considering the inter-car suspension force and the aerodynamic force. High speed train model of five cars was composed. The numerical simulation on curve section with aerodynamics force was carried out to validate the coupled simulation model. It was shown that a developed model can be used for the evaluation of the lateral ride comfort in the tunnel with curve section
Recently, in order to improve the fuel consumption of a gasoline engine, a condition of mixed intake gas was varied to improve combustion efficiency. Besides, a transient state was increased in the test-mode of regulation. In order to purify the exhaust gas efficiently with a three-way catalyst, the AFR should be controlled within the window around a stoichiometric ratio. Therefore, a precise control system was required to control AFR to the target value under any intake gas condition. For a fast-response and highly robust control system, both a feed-forward(FF) controller and a feed back(FB) controller were required. And those controller were desirable to equip with a robustness or an adaptability. From this point of view, in order to add an adaptability to the model based FF controller, the error value was used to adjust the compensation value. And the feedback controller was designed using the backstepping method that was well known as a nonlinear adaptive controller. And both controller was operated as if those were fused in one-controller, then, a precise AFR control results were obtained. Then, Two sets of parameters in each controller were provided and an investigation was carried out as to which combination is superior for robustness regarding several initial starting engine speeds.
This paper describes the driving control system of a powered wheelchair using voluntary eye blinks. Recently, new human computer interfaces (HCIs) that take the place of a joystick have been developed for people with disabilities of the upper body. In this study, voluntary eye blinks are used as an HCI. However, the problem with this HCI is that the number of input directions and operations is smaller than that of a joystick, which causes inefficient movement. Therefore, assist systems are needed for efficient and safe wheelchair movement. This paper presents the system which is based on environment recognition and fuzzy theory. It can detect obstacles and passages in a real environment, and the velocity and direction are calculated automatically for obstacle avoidance or right/left turns. Simulations show the effectiveness and robustness for the driving position and position where an operation input is given. Furthermore, experiments were carried out and verified the effectiveness of the proposed method.
Parallel magnetic suspension has been proposed where multiple floators are controlled with a single power amplifier. The feasibility of voltage-controlled double parallel magnetic suspension with parallel connected coils has been already demonstrated in the previous work. This study focuses on the zero-power control in a voltage-controlled double parallel suspension system with parallel connected coils. In this system, there are three methods of achieving zero-power control: feeding back the control voltage, either or the sum of the coil currents. This paper shows the conditions for the system with each zero-power controller to be controllable, and compares their performances.
In this paper, a new method to evaluate performance of sound insulating plates in closed medium is investigated by using acoustic finite element method (FEM) under such two conditions that plates are having free ends and that plates are simply supported. The proposed method is able to compute sound transmission loss by using sound pressures at the small numbers of properly selected nodes considering acoustical symmetry of modal shapes in the closed medium, which is equivalent to the theoretical transmission loss without using all nodes existing in the medium. By the proposed method, the computed transmission loss does not depend on sizes or shapes of the medium; it is the unique transmission loss of the sound insulating plate itself. As sound insulating plates, the following three models are constructed; a single plate, double-leaf plates and the high-rigid sandwich panel called “trusscore panel”. It is also shown that sandwich trusscore panel works effectively at low frequency range since it is sufficiently rigid and that computed sound transmission loss of the trusscore panel has tendency as observed on a single plate having the equivalent weight and stiffness to the trusscore panel. Trusscore panels can be applied widely in industrial fields in the future such as walls or floors in a car, train or building to reduce interior noise.
Quadruped walking robots are expected to be utilized for various works on rugged terrain because it has minimum leg number to maintain static stability during walking motion and it can demonstrate high terrain adaptability by utilizing its high degrees of freedom. For these reasons, it has been studied for a long time. However, the study about traversing on rugged terrain by quadruped walking robot has not been done enough yet. In this paper, both basic strategy of motion control and mechanical design of a quadruped walking robots for large obstacle climbing are considered. In order to establish the basis of the control of quadruped walking robots to achieve large obstacle traversing motion with high energy efficiency, we make simulation experiments about body rising motion which essentially requires positive power consumption. We investigate the appropriate foot positions and internal forces which eliminate negative power consumption at the joint, then optimize the motion in consideration of characteristics of the installed actuators. Furthermore, a quadruped walking robot to go over large obstacle named“TITAN XII ”is proposed and its design concept and system integration are discussed. Finally, validity of simulation results and basic performance of TITAN XII are confirmed by experiments.
In this paper, we present a reduction method of the system matrix of a flexible thin plate element of 48 degrees of freedom, which is formulated on the basis of the absolute nodal coordinate method (ANCF) by use of the component mode synthesis method. We focus that the bending stiffness matrix expressed by the ANCF plate element is constant when the continuum mechanics approach is adopted and the in-plane strain is not so large. This feature allows applying the Craig-Bampton method to the equation of motion of the plate expressed by ANCF, and then it enable to reduce the dimension size of the system matrix of the plate. Three numerical examples that compare the presented method and the conventional ANCF plate are demonstrated to examine the performance and the accuracy of the presented method. From these examples, it is verified that the presented method can describe the large deformation and rotation effects as well as the conventional ANCF plate does. The use of the presented method is also verified to be able to reduce the computing time against the conventional ANCF plate. This feature is effective for carrying out numerical simulations for the structure composed of multiple plate elements when the number of elements increases.
One of the key factors affecting vehicle motion control is the nonlinearity of tire forces including coupling between longitudinal and lateral tire forces and saturation of the frictional force. In addition, uncertainties such as external disturbance and tire force modeling error affect state estimation accuracy. In this paper, we incorporate a nonlinear tire model in our previous method based on sliding mode control with repetitive numerical computation, in order to enhance the tracking performance in the nonlinear region of tire forces. To reduce the noise of velocity measurement of contact-type odometers, we apply an extended Luenberger type VSS observer which can cope with both nonlinearity and disturbance of the vehicle dynamics. The performance and computational effort of the proposed method are verified through numerical simulations and experiments using a small vehicle with an on-board embedded CPU.
In this study, we developed a behavior measurement system named “3D servo-sphere”. The system is composed of one sphere and three omni-wheels that support the sphere. A male silkworm moth, Bombyx mori, is put on the top of the sphere. The position and the body angle of a moth are observed by a high-speed camera that is installed above a moth. Since the system can rotate the sphere in 3-DOF independently, we can keep the position and the body angle at the origin without any body-fixture. By the proposed system, we can observe natural behavior of a moth during CPT ( Chemical Plume Tracing ) . The system also enables that we can give stimulus precisely without fixing the animal, because the feedback system keeps the position of the head of a moth. By using this, we can observe the relationship between input stimulus and output action in long run. By connecting to a virtual space in a computer, we can apply modeled environment to a real moth. The system will be effective to identify transfer functions from stimulus to behavior.
Flow cytometers have been widely used to characterize biological cells statistically. Moreover, complicated sample pre- and post- processing methods such as separation, staining, and sorting of cells are combined with various analyzers have been demonstrated. In order to improve the usability, flow cytometer and pre- and post- function might be integrated into one micro-fluidic system. Soft-lithography with Polydimetylsiloxane (PDMS) is a powerful fabrication technique to make those complicated micro-fluidic structures. However the process has a substantial weak point. It is not available for making 3-dimensional focusing channel which is necessary to form smooth sheath flow. Then, we propose a new structure to generate 3-dimesional focusing flow by using the unique material property of PDMS; “easily bent and twisted”. We developed a twisted micro-channel in order to form a sheath flow in an integrated micro-fluidic system using PDMS. The new device has a central straight channel and two parts of 2-dimensional merging channel. It is twisted 90 degrees in between the first part and the second part. Sheath flow forming was predicted by using numerical simulation. The micro-channel configuration (width, length etc.) were designed to form an isotropic focusing flow. A unique evaluation method to predict sheath flow formation was proposed and used to characterize the sheath flow by distribution of particle velocity at the micro-channel junctions.
A computer simulation method to predict the thermal distortion value of a high-pressure die cast part was investigated. The evaluated product was a flat-shape JIS ADC12 part. The actual distortion value of the part was measured by an optical 3D digitizer and it was compared with the predicted distortion value. In this method, the initial temperature distribution of the part was determined by casting simulation. The thermal distortion value during cooling was calculated by FEM analysis. The stress-strain relation was approximated by the elastic-perfectly plastic material model including the temperature dependence of the yield strength. It was found that the heat-transfer coefficient between the die and the injected molten metal is a critical factor to implement an accurate FEM simulation in the casting simulation. The heat-transfer coefficient value was accessed and confirmed using the temperature distribution measured by a thermo camera. The distortion values of the actual part optically measured as a function of the curing time well coincided with the simulated value. It was concluded that the method can predict the distortion within a practically accepted preciseness.
A new cleaning method of machine parts using water and micro-bubble with ultrasonic vibration (28 kHz, 100 W) is proposed considering precision of parts and environmental problems. As a specimen, a stainless plate evenly coated with tapping paste is used. The specimen is hung up in the water tank. Micro-bubble is applied from bottom of the water tank. Ultrasonic vibration is applied from upper side of the water tank. Cleaning effect of the proposed method is compared with that of micro-bubble cleaning (using micro-bubble only) and ultrasonic cleaning (using ultrasonic vibration only) on removal rate of tapping paste and turbidness of washing water after cleaning. Removal rate is obtained from measurement of residual amount of tapping paste at constant time intervals. Turbidness is evaluated in saturation using image processing of turbidness in washing water. As a result, removal rate of tapping paste in the proposed method is superior to micro-bubble cleaning and inferior to ultrasonic cleaning. However, saturation of washing water in the proposed method is inhibited more clearly than that in ultrasonic cleaning and almost same as that in micro-bubble cleaning. The proposed method is expected to be effective on cleaning more dirty and adhesive oil and reduce pollution of washing water.
Recently, solar power generation is widely prevalent in the world because it is expected as a renewable energy which doesn't discharge CO2 emission during generating electricity and saving natural resource. Therefore, solar power generation is requiring for high efficient and low cost to spread out further and protect the earth from global warming. High efficient generation becomes possible by focusing sunlight on an electric generating device, i.e. solar cell. Although aluminum is suitable for a concentrator, which is used for concentrating sunlight, mirror-like processing is very difficult because it has large and spherical surface. It is very important to obtain mirror-like surface for high efficient generation. Therefore, the polishing technology for aluminum was developed and evaluated. As a trial study, workpiece didn't have large spherical surface, but small and flat surface in this paper. Firstly, the polishing tool which attached polishing cloth consisting of splittable fiber was developed. Optimum polishing cloth for polishing of aluminum was investigated by trial and error approach. Influence of surface roughness on viscosity of slurry was also researched. Fine surface roughness was obtained by heating workpiece with optimum polishing condition. Finally, reflectance of polished surface was measured and industrial effectiveness was evaluated. It is concluded from the results that (1) the developed polishing technology was effective for processing the mirror-like surface of aluminum,(2) polished surface by using optimum processing condition has 83.8 % specular reflectance,(3) the solar power generation using polished aluminum has higher efficiency than conventional solar power generation on numerical simulation.
In deep drawing, area above the trimmed line is called earing. Reduction of the earing in deep drawing is one of the major issues for cost reduction. In addition, a high BHF causes tearing while a low BHF leads to wrinkling. Therefore it is important to determine an appropriate BHF through drawing. Recently, variable BHF (VBHF) approach which varies through the punch stroke has received a lot of attention, and its validity is discussed. In this study, both initial blank shape minimizing the earing and VBHF trajectory are simultaneously determined under tearing/wrinkling constants. Our design problem is formulated as a multi-objective design optimization for evaluation the earing. First objective function is the area above the trimmed line, and second one is the area below the trimmed line. In general, numerical simulation in sheet forming is so expensive that a sequential approximate optimization (SAO) using the radial basis function (RBF) network is adopted to identify the Pareto-frontier. The validity of the proposed approach is examined through numerical simulation. It can be found from the numerical result that earing is drastically reduced by the proposed approach.
This paper describes a parameter-free free-form optimization method for shell structures to reduce the noise in a closed acoustic field. Squared sound pressure, which is evaluated by solving fully coupled shell-acoustic interaction system, is selected as the objective function to be minimized. The optimum design problem is formulated as a distributed-parameter shape optimization problem under the assumptions that shell structures are varied in the out-of-plane direction to the surface and the thickness is constant. The shape gradient function and the optimality conditions are derived by using the material derivative method, and they are applied to the free-form optimization method for shells. The shape gradient function is applied to the shell surface as a fictitious distributed force under Robin condition for varying the surface, for minimizing the objective functional and for regularizing the mesh. With this method, the smooth optimal free-form of shell structures are obtained without any shape design parameterization. The validity of this method for the radiated noise reduction from vibrating shell structures in a closed space is verified through design examples.
The present paper is concerned with the development of a hip protector with a circular hole in the center to prevent hip fracture by fall. Firstly, we performed fall simulations by use of an elderly Japanese female model of a rigid whole body with a detailed finite element thigh model. The simulation showed that the hole in a hip protector significantly reduced impact, and that a protector with a hole of 50 mm diameter gave the minimum impact load in most cases. It also showed that thicker protectors and protectors of stiffer materials were more effective for hip fracture prevention. The effects of a protector offset from reference position, vacancies under the hole, and the shortening of protector length on the reduction ratio of impact were elucidated in detail. Secondly, based on the design guide suggested by the simulations, we developed a weight-drop test apparatus and performed experiments to examine the simulation results. It is ascertained that the hip protector with a hole of 50 mm diameter has excellent performance for hip fracture prevention.
This paper concerns a method of reducing noise level in a mail processing machine at low cost. A stack part of the mail processing machine is one of the main noise sources. This is because an installation area of the stack part is large and is widely open so as to take out mails, that a noise is emitted towards an operator. The purpose of this study is to propose a method to reduce a noise level of a stack part at low cost as an alternative for sound-absorption material. A broadband noise is generated from a mail processing machine as various kinds of mails are conveyed. Also, information such as installation environment and housing size is usually not provided at the design stage. So, we need a method of reducing noise level to derive a design parameter from a certain range of prediction. Based on the characteristics of a stack part of a mail processing machine, we examined a method using a back opening of a stack part to reduce noise that is amplified by internal resonance. The reduction of the sound at the front evaluation point is examined by a model with a front and a back opening which has a trade-off between decreasing internal sound and increasing diffracted sound. The fact that a sound pressure level at the front evaluation point reduced with a back opening was confirmed by using experimental equipment. We have applied this approach to mail processing machine, and experimental value roughly corresponded to calculated value. The reducing noise level of a slit-like back opening was -3dB with white noise, and it had the same effect as a sound-absorption material. We have proposed a low cost noise reducing method as substitute for a sound-absorption material that can be used at a design stage.