The floating roofs are widely used to prevent evaporation of content in the large oil storage tanks. The 2003 Tokachi-Oki Earthquake caused severe damage to the floating roofs due to liquid sloshing. This accident becomes a cause and the structural integrity of the floating roofs for the sloshing has been actively studied. This paper presents the axisymmetric finite element analysis for the sloshing response of floating roofs in cylindrical storage tanks. The hydrodynamic coupling of fluid and floating roof under seismic excitation is taken into consideration in the analysis. It is assumed that the fluid is compressive and inviscid, and the roof is linear elastic while the sidewall and the bottom are rigid. The fluid behavior is formulated in terms of displacement as the Lagrangian approach. In order to remove the spurious modes, the free vibration analysis is carried out. The highly precise response solutions are given if the effective modes are only taken into consideration in the modal composition.
This paper investigates a feedforward control technique for saving the operating energy of a 2-DOF flexible manipulator with a point-to-point (PTP) motion, in which the residual vibration also can be suppressed. The 2-DOF manipulator has one prismatic joint and one revolute joint. The Lagrangian approach in conjunction with the assumed modes method is applied to derive the equations of motion of the manipulator system. For the PTP motion task, the trajectory of the translational motion is set to a cycloidal motion. On the other hand, the trajectory of the rotational motion is designed to simultaneously minimize the residual vibration and the operating energy. In the present method, we attempt to express the trajectory of the joint angle by an artificial neural network (ANN), and then a vector evaluated particle swarm optimization (VEPSO) algorithm, which is a multi-objective optimization algorithm, is used for learning the ANN. By operating the manipulator along the trajectory obtained by the proposed method, the residual vibrations can be suppressed under the minimum energy condition. The numerical simulation results are compared with the experimental results; this comparison reveals the applicability and effectiveness of the proposed method.
Colloidal dampers are able to dissipate large amounts of mechanical energy without significant heating, and such result is surprising since traditional hydro-pneumatic absorbers transform almost integrally the dissipated energy into heat. Trying to get deeper insight into this phenomenon, in this experimental work, using a thermographical method the temperature distributions on the external surface of a colloidal damper are recorded during its forced heating followed by its natural cooling. Employed compression-decompression cylinder is axially divided into two chambers, one of constant volume and the other of variable volume. Silica particles are introduced inside the cavity of fixed volume (silica tank), and a micro-filter is used to separate it by the chamber of variable volume, in which only water is supplied. Two main heat sources are identified as the silica tank (colloidal effect) and the packing used to seal the cylinder (frictional effect). Tests prove that heating/cooling through colloidal effect is much slower than heating/cooling through frictional effect. However, depending on the working frequency, generated heat power through colloidal effect can exceed the generated heat power through frictional effect. Based on the experimentally observed slow speed of heating/cooling through colloidal effect, one suggests that silica tank can be regarded from a thermal standpoint as a thermostat. Mechanism of energy dissipation is justified based on the molecular and cluster vibration modes of the liquid water, variation of the radiation absorption coefficient of liquid water versus the electromagnetic wavelength, and changes in the arrangement of water octamers.
In this study, an accuracy evaluation index for running transfer path analysis (TPA) employing principal component regression method was considered and the reliability was verified. To evaluate the TPA accuracy, the consistency of response signals in which the calculated response signal from the TPA model was compared with the measured response signal was used frequently until now. Also, the condition number that indicates the inverse matrix condition used in the calculation procedure of acceleration transfer function was employed in some cases. In addition to these accuracy evaluation methods, correlated principal component number (CPCN), that indicates the number of principal component correlating with the response signal generated at the running test, was proposed. The reliabilities of these accuracy evaluation methods were verified through simulation. As a result, the conventional two methods (consistency method and condition number) could not evaluate the accuracy well. However, CPCN index could indicate the frequency bands where the TPA accuracy was high or low. Consequently, the new index was found to be a suitable index for accuracy evaluation of the running TPA.
In sampled-data positioning control systems, the vibrations caused by the mechanical resonances around a sampling frequency are not only the difficult to observe but readily excited by the control input in transient-state characteristics. To address this problem, we developed a control method that can suppress the zero-order-hold induced residual vibration in the sampled-data positioning control system. The study is on a shock response spectrum (SRS) analysis that handles the transient-state characteristics of mechanical resonances. The control method uses multi-rate notch filters that modify the acceleration input signals beyond the Nyquist frequency. We designed the notch filter based on the SRS analysis because the frequency response on the Bode diagram was not suitable for analyzing transient characteristics. The results of SRS analyses showed that the multi-rate notch filter was able to decrease the amplitude of residual vibrations caused by the mechanical resonances around the sampling frequency. To demonstrate the validity of the proposed method, simulations were conducted on a sampled-data positioning control system.
Common autovehicle suspensions employ hydro-pneumatic absorbers placed in parallel with compression springs that provide the necessary restoring force. Since the spring can be omitted, compact and lighter design can be achieved by using the recently proposed colloidal suspensions. In this work, frontal and rear colloidal suspensions were designed to replace the classical suspensions, and tests of an autovehicle traveling on normal road with an asphalt step were performed. From the impulse response of tested autovehicle one evaluates its comfortableness, both based on the K factor method and based on the equivalent acceleration recommended by the ISO 2631 standard. Such testing method allows comfortableness evaluation without using an expensive test rig on which the autovehicle is placed over four actuators and excited to simulate the real road conditions. Results obtained are firstly validated in the case of classical suspensions consisted of oil dampers mounted in parallel with compression springs. Then, colloidal dampers with and without attached compression springs were evaluated. Relationship between the travel speed of the autovehicle and the level of vibration perception, as well as the influence on the sickness, concentration and health was obtained for various values of the tire inflation pressure. Ride-comfort decreases at augmentation of the travel speed and the tire inflation pressure. Although the colloidal suspension was found to provide inferior comfortableness than the classical suspension, results obtained are encouraging, since better performances are to be expected by optimal design of the colloidal spring.
Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventionally Casting) alloys to meet the requirement of the high temperature operation and to improve the thermal efficiency. The SC blade consists of one columnar grain, and the DS blade consists of several columnar grains where the growing direction of the columnar crystal is set to the direction of the centrifugal force. Therefore, the vibration analysis of the SC and DS blades has to be carried out, taking account of the anisotropy. In this study, first, the effect of the anisotropy of elastic constants on the vibration characteristics of the SC and DS blades are investigated in detail. Second, the validity of the assumption of the transverse isotropy for the DS blade is examined, carrying out the Monte Carlo simulation. From these results, it is concluded that the actual DS blade can be treated as a transversely isotropic material.
It is well known that asymmetric vane spacing can result in decreased levels of the excitation at specific frequencies. In this paper, the resonant response reduction of mistuned bladed disks due to asymmetric vane spacing is studied theoretically for the most probable asymmetric vane, in which the vane count of the upper and lower half is slightly different. First, a method for predicting the maximum amplitude of the mistuned bladed disk for the asymmetric vane spacing is proposed. Second, a parametric study is carried out using Monte Carlo simulation to clarify the vibration response characteristics of the mistuned bladed disk for the asymmetric vane spacing. From these results, it is concluded that for the mistuned bladed disk, the asymmetric vane spacing is effective to reduce the resonant response, and the maximum response of the mistuned bladed disk rotating through asymmetric vane spacing can be roughly estimated by the maximum response of the mistuned bladed disk to symmetric vane spacing multiplied by the response reduction effect for free-standing blade without the circumferential coupling, unless the multi-resonances happen to appear. On the other hand, if the multi-resonances occur, it is possible that the asymmetric vane spacing increases the resonant response level.
In this paper, a method employing PARAFAC (Parallel Factor Analysis) is proposed to filter out noise from the signal of the FBG (Fiber Bragg Grating) sensor based on the AWG (Arrayed Waveguide Grating). The experimental results show that the performance of the proposed method is similar to that of the conventional signal-averaging method, which identifies the signal in the case of multiple measurements. PARAFAC is one of several decomposition methods for three-way data and the decomposition is unique without additional orthogonality or independence constraints. When Bragg wavelength of the FBG varies upon receiving an ultrasonic wave, the outputs of two adjacent AWG ports fluctuate in anti-phase. We use wavelet transform to pre-process the AWG ports data series, then the coefficients of the wavelet transform are decomposed by PARAFAC to trilinear components, which represent frequency, temporal, and phase profiles. The factor for which the ports fluctuate in anti-phase is chosen as the target signal and restored to three-way data. The performance of the proposing method is examined in experiments and its validity is shown.
In this study, we develop an effective noncontact technique for analyzing sports motion. We propose a new method for detecting sports motion by measuring the current generated due to a change in the capacitance between a given electrode and the human body. The technique involves the detection of electrostatic induction current of the order of approximately sub-picoamperes flowing through the electrode that is placed at a distance of 3 m from a subject. An occurrence model is proposed for the electrostatic induction current generated due to a change in the electric potential of the human body. This model can be used to effectively explain the behavior of the electrostatic induction current flowing through the measurement electrode. We apply the noncontact technique to detect the timing of athlete's foot contact or off with the ground during pitching and batting motions in baseball. Thus, we could quantitatively estimate the timing of contact and noncontact of an athlete's foot with the ground from the time of occurrence of the peaks. Our technique enables easy in-situ detection of the timing of contact and noncontact of an athlete's foot with the ground during pitching and batting motions.
This paper describes the application of the canonical theory to a constrained multibody system in the absolute nodal coordinate formulation. In the canonical theory, the constraints make it difficult to formulate the equations of motion because of the primary constraints of the Hamiltonian system. In order to solve this problem, the Dirac's approach with Poisson's bracket is used to derive the canonical equations. The governing equation of multibody systems with constraints is usually expressed as the differential-algebraic equations. In contrast, the canonical theory for the constrained system proposed by Dirac leads to the ordinary differential equations without constraints. In this study, it is demonstrated that the linear and the nonlinear canonical equations which the elastic force is formulated in the element coordinate system. The natural frequency and the eigenmode of the beam are obtained by the linearized canonical equations. These results show that the natural frequency and the eigenmode satisfy the boundary conditions introduced by the constraints. Moreover, the numerical examples of the nonlinear problems with the canonical equation and the differential-algebraic equation are presented in order to verify the proposed formulation.
We report herein on how we developed our innovative digital self-powered autonomous system for vibration controller using a digital micro-processor. The invented unit is a completely self-powered control system that does not require any external power-supply at all. Nevertheless, this digital, self-directive, and self-powered approach enables the system to be programmable and thus versatile in control scheme. The digital-autonomous controller is much more advanced and progressive than conventional analog-autonomous ones that are clumsy and awkward. This digital system can be implemented in multiple-input multiple-output systems to suppress even complicated structural vibrations. This is quite useful for various applications to energy-saving or energy-shortage systems, such as large space structures, artificial satellites, and isolated lunar bases, which all are vulnerable to long night-time without solar-power. Experiments demonstrate that displacement is reduced by as much as 35 %, which is quite a striking and attractive number. Energy dissipation in experiments is measured by various cases. Furthermore, we investigate the influence of voltage offset of AD port of the microprocessor both on estimation error and on suppression performance.
We have developed a novel relative-story displacement sensor for structural health monitoring which is capable of measuring the 5-DOF movement of building layers. Three pairs of infrared-light emitting diode arrays and position sensitive detector units were used for simultaneously measuring the relative displacement, the local inclination angle, and the torsion angle between two adjacent layers. For verification, laboratory tests were carried out using a shaking table, a motorized micrometer, and a rotation stage. In the static experiment, it is verified that the local inclination angle and the torsion angle can be measured as well as the relative-story displacement using the sensor system. The resolution of the sensor system in the displacement measurement, that in the inclination angle measurement, and that in the torsion angle measurement were evaluated to be 0.10 mm, 34.4 μrad, and 14.6 μrad, respectively. In the dynamic response experiment, the accuracy of the sensor system was experimentally evaluated to be 0.20 mm in the relative-displacement measurement, 110 μrad in the inclination angle measurement, and 90 μrad in the torsion angle measurement, respectively. These results indicate that the developed sensor system has a sufficient accuracy for structural health monitoring.
This paper describes a simple vibration suppression control method for a small-size helicopter with slung load system. The vibration suppression control for slung load is essential to improve stability of the flight because weight of a helicopter is relatively light. In past studies, the subject is analyzed by using the model which is a couple of rigid bodies containing a helicopter and a slung load, and controlled by state feedback combined with some sort of estimators. It requires accurate model and system parameters. However it is difficult for general users to build an appropriate model and to identify system parameters in terms of small-size helicopters. In this work we develop a simple control method which superposes vibration control of slung load on postural control of helicopter. By using delayed feedback, we can suppress the vibration without using state feedback in hovering situation. Furthermore, we will demonstrate a technique designing control parameters and verify the effectiveness by experiments.
Poles of overhead contact line are designed based on the earthquake resistant guide, but a line hardware or an electric wire often breaks in middle scale of earthquake. In order to analyze the dynamic characteristics of overhead contact equipment under the condition of earthquake excitation, we developed 3-dimensional dynamic simulation method of overhead contact system. Moreover, we carried out bending and stretching tests of stranded conductors and exciting tests of concrete and steel-pipe poles. From these results, it is confirmed that the real bending rigidity and the bending stress of a stranded conductor are lower than that of a single wire. This paper describes the vibration displacement and the material stress of the overhead contact lines and feeders, etc. caused by the assumed earthquake. We propose the earthquake-resistant performance and its improvement methods of overhead contact systems.
This study presents Active Wheel Damper (AWD) unit which can be fixed on the flexible structures such as cantilever beam with ease. The AWD uses a gyro sensor to measure the absolute angular velocity due to the vibration of deflection of the structure directly, and can construct sky-hook control with no difficulty by direct feedback of the angular velocity. In this study, Sky-hook With Adaptive Disturbance Cancellation (SWADC) control, which is constructed as a combined control system of sky-hook control and adaptive disturbance cancellation control, is also proposed to enhance the performance of vibration suppression of AWD unit. Adaptive algorithm, which can estimate the frequency of the vibration of the structure in real-time, is derived based on adaptive notch filter algorithm, and estimated frequency is used for the model of disturbance observer which estimates harmonic disturbance. Performance of vibration suppression of the AWD is shown by simulation and experiment in this study.
An inverted pendulum vehicle controlled by movement of driver's center of gravity, such as Winglet or Segway is one of Personal Mobility Vehicles (PMV). PMV is sometimes expected to be used in pedestrian space. However the dynamics of an inverted pendulum vehicle and a driver haven't been studied enough. In this study, the coupling model of the vehicle and human is built using Multibody Dynamics. The vehicle is expressed by 2 rigid bodies (tire and body) and a human is expressed by 8 rigid bodies(foot, lower leg, femoral, body, head, upper arm, lower arm, and hand). Two types of impulses as external forces are inputted to the different part of the coupling model (vehicle body, human body, and head) . We investigate the behaviors of a human model, especially its motion of center of gravity. It was found that inputting the external force to the location which is far from the center of gravity of a human makes human to keep his posture more difficult.
The purpose of this paper is to propose one analytical method to make stochastic floor response spectra in order to easily estimate the dynamic characteristics of secondary system such as piping, equipment and so on, mounted on a structure owing to an earthquake. Because of the increase of uncertainty at earthquake level, the design level for earthquake is tending upward. This is implying that the aseismic design of secondary system based on elastic design becomes more difficult from the viewpoint of economic design. Thus, as a first step, this paper derives the stochastic floor response spectra in consideration of a simple nonlinear design and/or a seismic risk analysis in future. The nonlinear properties of the secondary system are modeled in terms of an equation of motion which linearly involves the auxiliary variable as part of the restoring force and the auxiliary equation which describes a nonlinear relationship. Total equations including the auxiliary equation are linearized using a stochastic linearization technique. Then executing the statistical calculation to obtain the non-stationary variance relating to relative displacement of secondary system and utilizing a proposed idea to estimate the extreme value, finally the stochastic floor response spectra can be derived. The analytical results are compared with those by Monte Carlo simulation.
The purpose of this study is to reduce the structural noise level caused by the electromagnetic force of coils for front-loading design of the transformer noise. To research the phenomenon of electromagnetic-induced vibration, first we observed the radial and vertical directional vibration of coils, and confirmed the radial directional vibration amplitude can not be ignored compared to the vertical directional vibration amplitudes. Thus, for the analysis of the electromagneticinduced vibration noise, we found the continuum mechanics model to be necessary, and the old analysis model using mass and springs cannot simulate the vibration. Second, we made the proposed model of continuum mechanics and the old model using mass and springs for a transformer, and calculated the vibration modes and responses of the coils. The calculation results of the proposed model were in good agreement with the experimental results, but the old model was not in good agreement. Finally, we calculated the vibration level with the proposed model of the transformer and the tank, as well as the vibration level of the tank, by coupled fluid analysis and structure-born sound analysis. Also, we calculated the noise level around the tank with boundary element analysis. Considering the vibration mode differences between the calculation model and practical model, we could analyze the noise level within 5 dB error. Furthermore, we could obtain the highest vibration level when the vibration resonant frequency agreed with twice the driving frequency.
A smart sensor is required if we are to popularize health monitoring using the vibration of a structure. This device is used to evaluate the vibration characteristic of the structure. To detect the variance in the vibration characteristic from the vibration data of a structure, a time-frequency analysis technique that can detect the change of the frequency components of the vibration data over time is needed. This report proposes the real-time data processing method with narrowband band-pass filters based on the one degree of freedom vibration system for the evaluation of structural vibration characteristics. This method is applicable to processors with low computation loads and memory capacities.
The method of collision analysis between granular materials and a plate is investigated numerically and experimentally. The motions of granular materials and the plate are analyzed by using the discrete element method and the finite element method, respectively. The damping characteristics of the plate are given by the Rayleigh damping. The validity of the analysis method is examined by a comparison of the experimental results. In the experimental approach, the response of an aluminum thin plate was measured when some steel balls collided with it. The contact behavior of the plate is evaluated by the displacement response and the frequency response of the plate.
Absolute Nodal Coordinate Formulation (ANCF) is a kind of finite element method for the flexible multibody system with large deformation and large rotation. There are few studies which extract controllers from the mathematical expressions derived by ANCF. The main aim of this study is to propose a controller design procedure by the use of the mathematical expression which is derived by ANCF. A flexible beam is introduced as a controlled object and the control torque is applied to one end of the beam. Control objective is to rotate the beam to the desired position as well as to suppress the residual vibration of the beam. In the proposed method, ANCF model employed in this paper is derived by the use of continuum mechanics approach. Some assumptions and manipulations of the derived ANCF model yields a suitable expression for controller design of μ -synthesis framework. The validity of the proposed method is demonstrated by numerical simulations. Furthermore, influences on control performance of controller parameters are investigated.
The dynamic stability problem of machines and structures is one of the important subjects for a long time. Recently, they are considered to be relatively flexible for loads as they become large-sized and light-weighted. By the way, in the conventional dynamic stability analysis, many problems of the structural analysis have been dealt with as a conservative system. However, in the problems which are acted by fluid forces such as air and water in space structures and marine structures so on, the dynamics of structures are affected by the deflection of the structure. That is, the treatment of a nonconservative system such as a follower force becomes important. In addition, in the structural destruction troubles of machines and structures which have happened in the past, the dynamic instability which the follower force induced may be thought to be one of the causes although the detailed elucidations of troubles have not been done. In this paper, the stability of non-conservative system of a beam is investigated when the fluid force acting on a cantilever subjected to the axial flow is considered to be an axial force. The fundamental study is performed by using the discrete model of 2 degree of freedom systems. Moreover, this is expanded to the continuous system of a cantilever. And, the physical consistency between a discrete model and a continuous one and the effect of damping are discussed.
In the authors' previous study, the vibration energy harvester of the piezoelectric bimorph cantilever type was proposed for vibration condition monitoring applications of rotating machinery. Proposed energy harvester consists of the surface bonded two Macro-Fiber Composites (MFCs). In this study, energy transfer efficiency was derived from the energy balance equation during the natural period of the proposed vibration energy harvester. The maximum AC power through 114.3 Kilo-Ohm resistor which includes instrument internal resistances experimentally obtained 242.07 microwatt when subjected to vibration source input magnitude of 0.71(mm/s rms) at the resonant frequency of the harvester (29.42 Hz). The impedance matching between MFCs and the electrical resistive load was effective for maximizing AC power transfer of the vibration energy harvester. Estimated energy transfer from mechanical system to electrical system shows the agreement with the experimentally evaluated generating power during the natural period of the vibration energy harvester with about 3% difference. Estimated energy transfer efficiency was about 30%.
Since composite materials are known to have high specific stiffness and strength, they have been widely used in many industrial fields, including windmill turbine blades. Such light-weight composite structures under body forces are required to study their vibration characteristics to prevent fatigue failure and noise. In this report, the effect of centrifugal forces is studied on natural frequencies of laminated composite plates as such a model of blade. The stress distribution of plates under centrifugal forces is first solved by the Ritz method, and the natural frequencies under in-plane stresses are calculated in the Ritz method by using in-plane stress distributions determined in the first problem. The numerical results obtained by the present method are compared with those from FEM. It is found that both results for the plate with various aspect ratios agree well and this validates the present calculation method. As an application of the present method, lay-up configurations of composite laminated plates are optimized for maximizing frequencies of arbitrary modes under centrifugal forces by a layerwise optimization (LO) method. The optimum lay-up configuration determined by the LO method with the present model results in higher natural frequencies than plates with typical lay-up configurations.
Operations of hydraulic excavators require high operation skill and operators have possibilities to work in unsafe environment. To solve these problems, automatic digging control is often studied, but there are few studies focused on improvement of efficiency. A high efficiency digging algorithm for a hydraulic excavator has not been established because the relationship between digging motion and digging performance is very complex. A simulation model which is able to consider interaction between soil and machine would help to establish a digging algorithm for improving energetic efficiency. In this paper, an example for improvement of digging efficiency is shown by our developed distinct element method (DEM) simulation. First, in order to improve the accuracy of the DEM simulation, the parameter identification test is carried out to identify damping ratio and friction coefficient between soil particles. Besides, accuracy of digging efficiency evaluation by the developed simulation is shown by a developed digging test device which can reproduces excavation by hydraulic excavator. Finally, digging simulations are conducted by our suggested automatic digging algorithm. Varying control parameters, influences of control parameters are estimated. These simulation results show that the simulation is able to specified control parameters which promote digging efficiency. Our research evaluates effectiveness of model-based development for automatic digging which enhances efficiency.
In walking analysis, which is one useful method for efficient physical rehabilitation, the ground reaction force, the center of pressure and the body orientation data are measured during walking. In the past, these data were measured by a 3D motion analysis system consisting of high-speed cameras and force plates, which must be installed in the floor. However, a conventional 3D motion analysis system can measure the ground reaction force and the center of pressure just on force plates during a few steps. In addition, the subjects' stride lengths are limited because they have to walk on the center of the force plate. These problems can be resolved by converting conventional devices into wearable devices. We used a measuring device consisting of portable force plates and motion sensors. We developed a walking analysis system that calculates the ground reaction force, the center of pressure, and the body orientations and measured a walking subject to estimate this system. We simultaneously used a conventional 3D motion analysis system to compare with our development system and showed its validity for measurements of ground reaction force, the center of pressure and posture of lower limb.
When there is an undulating wear on overhead rigid conductor line, arc due to contact loss is generated between the conductor line and a pantograph. The arcs cause extreme wear of contact lines and contact strips of the pantograph. However the mechanism of the undulating wear formation has not been clarified. This paper to make clear the mechanism of the formation of the undulating wear through on-site investigation of overhead rigid conductor lines and excitation tests of the pantograph. It was been clarified that the dynamic characteristics of pantograph and the distance between pantograph heads play a causal role in the undulating wear formation. Firstly, a periodic unevenness is generated by mechanical wear that is caused due to the dynamic characteristics of pantograph, especially anti-resonance phenomenon of pantograph. When the wear amplitude of unevenness grows to the extent with which pantographs cannot comply, arc due to contact loss occurs between overhead rigid conduct line and the pantograph. By this arc, electric wear is generated in a hollow of unevenness, then the undulating wear of which wavelength is related to the interval of pantograph head grows.
An active base isolation system, which uses absolute vibration control technology, has been applied to the real full scale building, Obayashi Corporation Technical Research Institute Main Building ‘Techno-Station’. This building is the first active base isolation building all over the world. The absolute vibration control is an active vibration control method for base isolated structures to stay in the absolute space and to have vibration free environment, by applying control forces through actuators during earthquakes. Four 1100kN hydraulic actuators, two in each horizontal direction, are installed in the Techno Station to reduce the seismic response to 1/10 of the conventional passive base isolation system. When applying active control to a real full scale building, it is necessary to install fail safe mechanism in case that actuators are over-loaded by input ground motion of more than expected level or unstable control condition. As fail safe mechanism for this absolute vibration control, the trigger system using friction dampers has been developed and is installed between actuators and reaction foundations.
There are several kinds of blade root structures to support centrifugal forces acting on steam turbine blades such as straddle mount type root, T-root, axial or side entry root and fork type root. Steam turbine blades are surrounded by contact surfaces at a cover and the above blade root. It is known that contact conditions affect vibration characteristics of turbine blades. In this paper, the effects of contact surfaces on vibration characteristics of steam turbine blades with straddle mount type root were investigated. For that purpose, developed analysis method was applied, and natural frequencies and non-linear frequency responses of a steam turbine blade with contact surfaces at the cover and straddle mount type root were obtained using this method. From these results, it was concluded as follows. (1) Natural frequencies of the blade gradually decrease with increasing rotation speed due to the variation of contact area of the blade root. (2) The effect of friction damping at the cover was dominant and the effects at others were small. To verify these results, natural frequencies and dynamic responses of the blades during rotation were obtained in a spin pit test. Calculated results showed good agreement with experiment results and the analysis method was verified.
Noise control has been developed to establish the comfortable soundscape even if our house life. Floor impact noise such as the sound of footsteps or falling object becomes a problem in an apartment house. Floor impact noise has a peak at the low-frequency range. Passive noise control is not effective against low-frequency noise. Therefore, the purpose of this paper is to control the impact noise using active noise control. Since each impact noise is generated in a short period, LMS algorithm is difficult to use because of its slow convergence characteristics. On the other hand, frequency domain adaptive algorithm is known for fast convergence characteristics. In this paper, the effectiveness of active noise control using frequency domain adaptive algorithm is confirmed through simulations and experiments.
Though the rolling ball bearing greatly contributes to decrease the friction energy of the machine movement, we require the development of lower friction torque technology of ball bearing to achieve more efficient machine. Especially, the fluid resistance makes an important role when the ball bearing is soaked in lubricant. Estimation of the loss of torque by the fluid resistance brings the reduction in the design cost. Therefore, in our research, it aims to develop the simulation technology of the fluid resistance by the ALE (Arbitrary Lagrangian and Eulerian) Finite Element Method. As the first step, we have established the simulation technology of movement analysis for the only ball bearing. In this report, we did the movement analysis numerical simulation of the ball bearing that considered the contact ellipse and EHL (Elastohydrodynamic Lubrication) Theory. As the result, we improved validity of the analysis from the perspective of the contact reaction force.
In three-dimension acoustic field, it is difficult to control in the whole room using active noise control (ANC) technique. Instead, around-head-control is investigated in this paper. By using around-head-control method, an object person can get the noise reduction effect without controlling in the whole space, because it makes around the head quiet locally. Therefore, to realize around-head-control, it is necessary for a controller to follow the head movement. However, there is a problem that the control effect under the movement is worse, and the recovery of control effect after movement is slow by conventional ANC. Against this problem, we propose the new method of improving the adaptation speed when an evaluation point moves. In the algorithm, the updating size appropriate to each coefficient of the adaptive filter is calculated by using a step size vector. The step size vector is calculated from the coefficient of adaptive filter before updating. The validity of the proposal method is shown by the numerical simulation and the experiment in an anechoic chamber.
The gyroscopic exercise tool which utilizes the gyroscopic effect caused by the whirling motion of the high speed rotating body to train the hand muscle is considered. This tool utilizes the contact phenomenon between the rotor and the case. When the input motion with 3-5 Hz is added to the case, the rotor spins in thousands rpm whirling with the precession motion which is synchronous to the input case motion. Conventional studies on this tool have assumed the continuous rolling motion of the rotor to the case. This paper does not set this assumption, and investigates the dynamical modeling of this tool considering the contact/non-contact conditions and the slip between the rotor and the case. Two kinds of motions are observed in the numerical simulation, one is the uniform precession which was observed in the conventional studies and the other is the periodically reverse precession. These two motions are physically explained, and are also observed in the experiment.
The damping force of a magnetic damper is based on the Lorentz force. That is to say, the magnetic damping force is generated in the direction opposite to the relative motion of a conductor with respect to a magnet. Normally, a magnetic damper uses two conducting plates facing the opposite sides of a magnet. If only one side of the magnet is used, the magnetic damping force is less. In the present work, a new magnetic damper composed of Halbach magnet arrays arranged in three parallel lines is proposed. A basic Halbach magnet array consists of five magnet cubes that are glued in the specific directions relative to each other, and is characterized as having a strong magnetic field on one side and a weak field on the other. For this reason, it is possible to realize a high-performance magnetic damper using only one side of a magnet. The magnetic fields of the Halbach magnet arrays of the new magnetic damper we are proposing, together with other magnet arrays, were investigated analytically using Biot-Savart’s Law. Furthermore, the proposed magnetic damper was fabricated and tested. The experimental results were compared with the analytical results. As a result, the effectiveness of the new magnetic damper was confirmed.
This paper investigates the concise 1D-FEM models of an open crack in a rotating shaft for quantitative analysis. The parameter of these models have been required to determine experimentally, which was the major drawback of these models. Therefore, in this paper, the decision procedures of the parameters in these models are discussed. The characteristics of the parameters regarding shaft's diameter and depth of crack are investigated by using numerical data obtained from 3D-FEM software. Then, the governing equation of the parameter for one model is deduced in terms of depth of crack. The validity of the decision procedure and the deduced governing equation of the model's parameter is clarified experimentally.
This paper presents control system design for occupant lower extremity protection in the event of a frontal car crash. A semi-active knee bolster is used to protect occupant lower extremities. The semi-active knee bolster varies the damping coefficient of the knee bolster. The control system design of the semi-active knee bolster is based on a design method of an active knee bolster. LQI (Linear Quadratic Integration) control with an initial value compensation input is applied. We obtain an optimal reference signal of the contact force between the knees and the instrument panel by considering characteristics of the semi-active actuator and the closed loop control system. The control system of the semi-active knee bolster follows the reference signal of the contact force. The protective control system with the semi-active knee bolster is effective for reducing the femur load, verified by carrying out simulations and experiments.
A model-based performance monitoring method for a heat utilization process in a distributed energy system is developed in this study. This performance monitoring has three components: a static input-output model for the target process, a dynamic compensation function, and a failure detection function. First, the static input-output model estimates the values of output process variables in response to the variations in measured values of input process variables. Then, the dynamic characteristics of the output process variables are provided by the dynamic compensation where they are indentified as first order lag elements. Finally, the estimated values of the output process variables, which consider the dynamic characteristics, are compared with the measured values of the output process variables in order to detect device failures. Through a numerical simulation for a heat utilization process in a gas engine cogeneration system that has a radiator with a considerable lag characteristic, the effectiveness of the developed performance monitoring method in a dynamic state is verified. The result shows the sufficiency of the estimation accuracy of the output process variables and the capability of detecting device failures, including the deterioration in the heat transfer performance in the radiator and heat exchanger, in a dynamic state.
In order to reduce the noise level in the cabin, it is important to extract the characteristics of acoustic system (dynamic properties of the cavity). When frequency response functions (FRFs) of the acoustic system are measured, acoustic excitation by an audio speaker is generally used and its capabilities have been already illustrated. However, to expand the availability of the acoustic excitation, it is necessary to reduce the number of excitation points and to predict the FRF with respect to the point where it was not actually excited (the unexcited FRF). It has been well known that in order to predict the unexcited FRF, a set of modal parameter can be used, where the auto FRF is thought to be included in the data set. However, for the acoustic system the auto FRF is hardly measured because the speaker is not able to apply the excitation at an exact point, but to apply a volume velocity at a small area. Therefore, this paper presents a new method to predict the unexcited FRF under the condition that the auto FRF is not included in the data set. In this paper, modal parameters of the acoustic system of a real automobile cabin are estimated, and the FRF is predicted by the proposed approach. The predicted FRFs are compared with the measured FRFs.
The flutter is a dangerous phenomenon bringing down the destruction of aerofoil, so the prediction of the flutter speed is strongly required. In this paper, the theoretical calculation for a two-dimensional flat-plate aerofoil was carried out by using the unsteady aerofoil theory and the wind tunnel experiments for the flat-plate aerofoil was also carried out to clarify the relationship between the flutter speed and various parameters such as the elastic axis position, the bending natural frequency and the torsional natural frequency of the aerofoil. The results are summarized as follows: (1) The flutter speed decreases with going the elastic axis position downstream but increases beyond a certain elastic axis position. (2) The combination of the bending and torsional natural frequencies which makes the flutter speed minimum is the combination which the difference of two combined natural frequencies becomes minimum. (3) When the torsional natural frequency becomes higher than the bending natural frequency, the relation between these two frequencies becomes linear.
It is available, for the garbage assembling issue of the disposed empty PET bottles, that PET bottle could be folded up easily and effectively by both hands. Then, based on the geometrical theory of cylindrical Origami proposed by Nojima, we designed some kinds of CAD model of PET bottle with regular folding lines in circular direction and evaluated the function of folding up for axial compressive loading by CAE. Two main useful results are obtained as follows. One is that the empty PET bottle with the configuration of inclined main folding lines could be folded up by hands. The second is that the PET bottle in full, with the configuration above mentioned, could have the stiffness necessary for keeping in a pile of bottles' case and vending machine by the effect of increased internal pressure which is loaded on the folding surface of the bottle wall.
This paper deals with vibration displacement prediction formulae based on energy balance for boiler structures. The boiler structure is a coupled structure, which consists of the boiler, its support structure and seismic ties installed between the boiler and the support structure. Vibration displacement prediction formulae based on energy balance originally developed by Akiyama et al. were for non-coupled structures like multi-story buildings with elasto-plastic dampers. The formula could predict the vibration displacements using energy spectra as earthquake inputs. However, the formulae could not be applied to the coupled structures like the boiler structures. Considering 1st natural mode of the coupled structure enabled authors to formulate the prediction formulae for the boiler structures. The formulae developed by authors were verified with time history analysis results using a lumped mass vibration model of the boiler structure.
The influence to the torsional resonance of the positioning error, the eccentricity or shape error, which is made during the milling process, of the planetary gear center or the internal gear of the star type planetary gear trains are discussed using the simulating program. The program was previously confirmed that it can sufficiently simulate the vibration occurrence speed of the rotational shaft and the vibration orbit of the floating sun gear. In the conclusion, the position error of the internal gear center and the planetary gear center make the change of the self-centering position of the floating sun gear and the shape of the movable area of the sun gear. But they are not the cause of the resonance, because the resonance does not occur without the forced torque. The eccentricity of the planetary gear can be the cause of the resonance when the rotation speed of the planetary gear becomes the natural frequency of the rotating shaft. But the eccentricity of the internal gear is not the cause of the resonance. The triangle shape error of the internal gear, which is measured in the experiment, also simulated. And it is made clear that the shape error can be the cause of the resonance. This can be considered that the transmission error can be made by the coincidence of the shape and the number of planetary gears.
The purpose of this study is to evaluate strength of tapered roller bearing loaded vibrations. We modeled the tapered roller bearing to the flexible multi-body model, and calculated the stress of retainer by mechanical simulation. The simulation result shows that the stress of retainer became large when rollers vibrate in yaw motion, and the largest part of the stress was the root of retainer bridge. And we evaluated fatigue strength based on the calculated stress of retainer by this simulation. However, such a simulation using a flexible multi-body model had a problem to take a lot of time. So, we could not calculate the stress in various conditions. For this problem, we confirmed that the major frequency of the stress in the root of the retainer bridge is below the first natural frequency of the retainer. We found that this simulation can be calculated by the solid body model to save time. And we calculated the stress in the root of bridge per unit force by the static analysis. Therefore, we became able to calculate this stress by the force calculated by the solid body model analysis. Using this solid body model, we calculated the force between the retainer and rollers in various conditions. We found this force increased depending on vibration acceleration, rotation speed of inner race, and radial force though it didn't increase depending on rotation direction of inner race. And we found the fatigue failure vibration acceleration of the tapered roller bearing.
Packaging is essential to most kinds of industries. The basic part of the vertical form, fill and seal packaging machine is the forming collar. The forming collar provides the shape over which packaging film is smoothly formed into a cylindrical shape at high speed. Describing the forming collar geometry and hence its design is, however, remarkably difficult. And performance assessment for designing correct forming collar is not exited. This paper presents, for the first time, a method for the assessment by calculating the stress of the film on the geometry of the forming collar. Developable surface and non-developable surface are discriminated with this created method. Effect of mesh size of the finite element method for this analysis is analyzed. And accuracy of this method is confirmed to be put to practical usage.
The 5-DOF self-bearing motor possesses the functions of a motor, two radial AMBs, and an axial AMB. Therefore, it is possible to miniaturize the AMB system with maintaining high performance. In this paper, an interior permanent magnet (IPM) type 5-DOF self-bearing motor is proposed. The IPM rotor generates bias fluxes to not only the radial direction but also the overhanging stator direction without side surface permanent magnets. Optimum configuration of the permanent magnets is analyzed using 3 dimensional finite element method. The results show the feasibility of the more compact and highly-reliable 5-DOF self-bearing motor.
The FDC (Flow Dynamics Conveyer) has been often used in power plants and iron works because of superiority in quiet compared with a roller type conveyer and it is excellent in a low noise and low power. The FDC consists of a trough and a belt, and the air is supplied from many holes provided on the trough. However, a large vibration which is called abnormal vibration occurs when the flow rate becomes a certain value. Ishihara et.al showed by the experiment in the previous study that the abnormal vibration occurs when the angle of belt θ increases and the floating amount H decreases. The purpose of this study is to verify it by the theoretical calculation. As a result, it was clarified that the tendency of the theoretical calculation result is in comparatively agreement with the tendency of the experimental result. And it could also be shown by the theoretical calculation that the taper channel becomes the cause of abnormal vibration
The authors proposed a new technique to improve the current collection performance of pantographs. For this purpose, the pan springs, which are usually coil springs, are replaced with variable stiffness device, and its stiffness is varied so as to suppress the contact force fluctuation between pantograph and catenary. The 1st report outlined the proposed technique and validated it by the numerical simulation. This report firstly details the developed variable stiffness device necessary for applying the proposed technique and verifies the stiffness variability of the device. The device has two air springs arranged so that they are opposite to each other, whereby the stiffness of the device can be varied by altering the air pressures of both air springs. It then presents the vibration test for the variable stiffness device equipped pantograph. The test result shows the dynamic characteristics of pantograph can be controlled by varying the stiffness of the device.