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Small axial fans have become widely used as cooling devices in recent years. Because of their increasing importance, studies have been conducted on ways to improve the performance and reduce the noise of such fans. In this report, a small axial fan with a diameter of 85 mm (a type popularity used in personal computer or workstation) was selected for further examination. The influence on aerodynamic performance and noise of such frame design parameters as blade tip clearance results in a decrease of discrete frequency noise and an increase of broad-spectrum noise. As for the most suitable design refinement in terms of fan efficiency, we found that the treatment of outlet corner roundness and altering spoke skew to the direction counter to that of fan rotation was effective. Keywords : Axial Flow Fan, Performance, Efficiency, Noise, Frame 1. Introduction Small axial fans have taken an important place in thermal design as the electronic products have become increasingly miniaturized. Concurrently, huge numbers of these inexpensive fans have been produced for use in products such as personal computers. And, while improvements in the mechanical performance of a single small fan would not make much difference in immediate environmental terms, given the immense number of such fans, there are increasing demands from society that designers ensure maximum levels of efficiency. Several reports have been published about improving the efficiency and reducing the noise from axial fans, but these reports address large fans with diameters of 300 mm or greater. Kamaya et al. examined the characteristics of a small fan with a diameter of 120 mm, but few other researchers have published reports on fans of this size. The objective of the research by Kamaya et al. was reduce the noise emitted by the fan adjusting the clearance between the fan blades and the frame, and the shapes as seen from in front of the fan. In addition to the shape of the blades, determining the optimum configuration and dimensions of the frame are essential considerations for improving efficiency and reducing the noise of an axial fan. However, due to their low Reynolds number (Re≈10

The crack arose during actual operation, in an impeller of large-sized blower, at the joint part of the main board and blade. For the purpose to clarify, this phenomenon, dynamic analysis and static analysis using the finite element method were performed. The analysis results showed that the cause of a crack of impeller is the stress which occurs owing to the deformation of the side board by centrifugal force. This deformation is wave like one which is same pitch as blade. Then, the structural modification by pseudo-inverse method was performed for the purpose of stress reduction. In this case, designer does not want the minimum weight optimum design but the minimum modification design. Pseudo-inverse method may modify the structure with the minimum distance in the design variable space to satisfy the stress restriction. Some cases are tried. When the design variables were 3 main parts thicknesses, those are main board, side board and blade, practical solution is deduced for 8 calculations to satisfy the stress limit with 10% weight increase.

Recently, solving vibration problems in the prediction step is strongly required to shorten the development time. The purpose of this research is to clarify and improve vibration characteristics of products such as sporting goods by experiment and calculation. A familiar tennis racket was chosen and its vibration characteristics were investigated by actual impact test and experimental modal analysis. It was clarified that the largest vibration was generated at the first mode. Structural optimization of the simplified plate could diminish the peak by shifting the node of the mode to the excitation response point. Design variables were the masses given to the circumference or the thickness of elements.

Small fans are especially used in information device for its cooling. Since packaging density has been increasing, requirements of not only performance improvement but also noise reduction arise strongly. An experimental research on small multi-blade fan was carried out in order to improve performance and reduce noise. In this report, effects of scroll angle, tongue clearance and inlet diameter on small multi-blade fan with impeller diameter of 100 mm were investigated. The optimal index efficiency and noise were found by making a scroll starting point radius and a scrool termination radius into a design index, instead of the scrool design by a conventional clearance and a scroll angle. In order to reduce noise, we found that we should set the radius of scroll beginning into about 0.65 times of the outlet diameter of the impeller. And for improving efficiency, we should set the radius of scroll end into about 0.9 times of the outlet diameter of the impeller.

This study is concerned with the motion and vibration control strategy for the flexible-link mechanism in order to achieve the high performance and stability. Reducing vibration and making positioning time faster are simultaneously required in this system. Technology of smart structures is introduced in the flexible-link system to achieve the vibration reduction. The smart flexible-link is composed of the flexible-link and the piezoelectric film which has the sensor/actuator function for itself, and so its mechanism is extremely suitable for controlling the vibration. First, a modeling method of the flexible multibody systems is presented based on modal analysis considering the characteristics of the piezoelectric film. In this method, each flexible body modeled by FEM is transformed into the modal space at the 1st stage of the model reduction and then the total system is constructed by synthesizing each modal model and reducing it into the modal space at the 2nd stage reduction. The control system is constructed with the designed dynamic compensator based on the mixed H2/H∞ control problem, resulting in the enhanced performance and stability.

Layout optimization of junctions yields the minimum number of junctions. And a fewer junctions means fewer joint components or fewer spot-welding operations, and this leads to higher production efficiency. A method is developed for optimizing the layout of junctions between two structures so as to minimize the relative displacement between them when one of them is oscillated by noise disturbances. A quadratic response function serves as the expected value of relative displacement between the two structures and as the objective function in the optimization process. A set of evenly distributed variable-spring elements joins the two solid structures in a single junction surface, and the distribution of elasticity indices is continually revised. After optimization, those spring elements with elasticity indices higher than a certain threshold are considered to represent rigid joints, while lower elasticity indices indicate the absence of any joints. The optimized elasticity-index distribution thus shows where to place junctions. Use of variable-strength spring joints like this makes it easier to determine optimum junction positions. This is because it eliminates the need to renew the entire FEM model for each case.

The machine is the organic system which consists of many parts. All parts act cooperating one another, transferring and changing the energy according to their specific rolls, and as the result of their dynamic collaborations, the machine fulfills its mission as the required performance. The authors introduced a new approach on modeling and proposed the concept of the functional model in the previous report, in order to explain these rolls of parts as the functions. It is indispensable for computer aided development of machines in actual maker companies to construct the virtual product with which connecting parts from small scale to large scale units, assembling the machine from parts to total product, exchanging parts and disassembling the machine have to be performed easily by simulation in the computer. As the means to make this possible, a method for expansion and unification of the functional model is presented in this report. This method is shaped up with three examples.

In this paper, we will show the effect of vibration reduction of first-bending mode of railway car body by using coupling damper, from the results of calculated riding quality level and vertical acceleration peak for shinkansen vehicle. It is important to decrease this vibration because the natural frequency generally exists in the range that human feel it so sensitive that it has large effect on comfortability in riding. In this study, we make a train set model composed of five single car FEM models and coupling model, that is a linear spring and damper element connected parallel. From the resuits of calculation at several damping values, we find that this noticed vibration is decreased at all considered speeds (240, 275, 300, 320 km/h) but decreasing level is different at each speed. From investigation of vibration shape at natural frequency of noticed vibration (9.0 Hz), we make clear that difference of vibrated phase among each car make this phenomenon. On running 275 km/h, vibration level is too high, and vibration-reduction effect is small, because each car vibrates with same phase, as a result, relative velocity between each car is not effectively generated at each coupling damper.

Nonlinear characteristics are included in most machines and structures, and spoil frequently their reliability and quality. But sometimes on the contrary, nonlinear characteristics take important roles, because they are utilized for realizing the functions not obtained using only linear characteristics. In this case, modeling of nonlinear characteristics becomes key point of product development. It is difficult in general to model nonlinear characteristics using conventional approaches. Nonlinear characteristics are explained in this report by the new approach on modeling proposed by the authors. The functional models of ten kinds of nonlinear systems, namely nonlinear stiffness, nonlinear resistance force, clearance, friction, one way element, rattle element, variable moment of inertia, swing element, Geneva element and temperature dependency of electric resistance are presented as the basic examples.

A new approach on modeling is put forward in order to compose the virtual prototype which is indispensable for fully computer integrated concurrent devolopment of products. A basic concept of functional model is proposed for embodying this approach. This model is used mainly for explaining and simulating the functions and the efficiencies of various machines which are composed of many mechanical, fluid-mechanical and electrical parts. All organizations and engineers of various specialties in charge of the development can collaborate with one another using this model. This model can be used in all stages of product development from the initial plan through the design to the trial testing. Models of parts compose an organic system in the total product model. Functional models of some simple mechanical, electrical and fluid-mechanical systems are illustrated, and its validity and usefulness of the proposed approach are demonstrated.

In this paper, we make a model of shinkansen super express train and try to forecast of vertical Vibration, especially the first body bending vibration mode. Modeling process is two steps. First step is to make an FEM model of body structure, which is composed by frame and skin of train. We check the accuracy by simulation of static load test. Second step is to add underfloor equipment, upper floor, partition and weight to body structure model, and we called it car body model. Vehicle model is made from car body model and bogie nlodel. By using vehicle model, we obtained good agreement of vertical vibration, natural frequency and acceleration power spectrum density with experimental results of on-track testing especially in the range less than 20 Hz. From the results, we can say that underfloor equipment and upper floor should be included in the model of body, and traction device and anti yaw damper should be included in the bogie model to obtain sufficient accuracy of first bodybending vibration.

The increasing attention on the applications of advanced robust control theories to automotive motivates the further investigation of truck cab model device for active vibration control.A balanced state-space model is necessary when designing a robust controller.Hence, the state-space frequency domain identification method is used to construct a model for model-based robust control design.Then H∞ control theory and μ synthesis are readily to be used in order to calculate a controller for vibration suppression.The ν-tool is exploited to evaluate the quantitative margin for robust stability and performance.Finally, the closed-loop system achieved the satisfactory control results.

In the case of very lightly damped structures that the leakage error can be a serious problem, burst random controlled excitation is very useful for obtaining the reliable frequency response function. Here burst random controlled excitation uses velocity feedback to control the system response to decay enough within the sampling time. In ordinary measurement, velocity is usually acquired by transforming the measured acceleratory signal. As a matter of course, measured signal contains noise. There is a possibility that the transforming acceleration into velocity may increase the influence of noise. Consequently authors consider that velocity obtained from acceleratory signal is uncertain to apply to the above purpose. So in this paper we choose force feedback instead of velocity feedback and examine burst random controlled excitation. As a result of it some interesting knowledges are obatined.

State-space solutions of the H∞ controller are well developed. Hence, for real structure control design, the first step is to derive a state-space model of the structure. There are several analytical and experimental dynamic modeling methods that can be used. It is difficult to obtain an accurate model for a flexible and complex structure by the finite-element method (FEM). Therefore experimental modeling is attempted. In this work, we used the eigensystem realization algorithm (ERA) time-domain method based on system impulse response data, to establish a state-space model in order to design the H∞ control law for vibration suppression. The robust control implementation is exerted on a test bed (truck cab model) with three degrees of freedom. The validity of experimental state-space modeling is confirmed and the robust control performance is achieved.

A method for designing an engine mounting system using hydraulic insulators has been developed with the aim of controlling low-frequency engine vibrations in the roll and bounce modes. This method includes a design optimization theory for each hydraulic insulator and a procedure for determining the equivalent mass for various modes at the mount locations, and is applicable to integrated system optimization. Computer simulation results show that resonance peaks can be effectively reduced with a hydraulic engine mount system designed on the basis of this method.

This method is proposed for a FEM model which has a large number of elements. This minimizes the length of the modification vector in design variable space. In this paper, an expansion is introduced to satisfy unequal behaviour constraints and side constraints. Also, a new approach searching for the minimum norm of design variables is added. The calculations with a small model elucidate the effectiveness of this theory.

An approach for integrated optimum design of a structure and H∞ control system using a genetic algorithm is proposed. The size and shape of the structure, and the sites at which the sensors and the actuators are set are adopted as the design variables. Since the sensors and the actuators are placed only on the nodes of the finite-element model in this study, the design variables are discrete. Therefore, in order to solve this problem, a genetic algorithm is used as the optimization technique. The approach is applied to vibration control of a planar plate. A frequency weighting function and mode weighting coefficient are used in the H∞ control problem. The mode weighting coefficient enables control of multiple natural modes without increasing the order of the controller. Effectiveness and practicability of the approach are verified by both simulation and experiment.

A structural topology optimization technique which optimizes the frequency response characteristics is proposed in this paper. The natural frequency and the linear quadratic performance index with respect to the response are defined as the objective function. The density of each finite element is adopted as the design variable and the optimum distribution of the density is sought based on the quasi-Newton method. Minimizig the performance index against the white and the colored noise disturbances, frequency response shaping is achieved. In order to realize the actual structure, a method to separate the value of the density to zero and one, in which the penalty function to divide the density into the two values is introduced in the objective function, is also proposed.

Parameters such as the principal moment of inertia, principal axis of inertia, and location of center of gravity are necessary for simulation of the dynamic properties for the design of a mechanical system. Usually some of these rigid body properties are identified by the pendulum method, which is an experimental procedure to obtain these from the period of the suspended specimen using the principle of a pendulum. However, as the specimen becomes more complex in shape or heavier, the resulting parameters are identified with poorer accuracy, because the accuracy of location of the center of gravity decreases. Therefore, the authors examine an approach for experimental identification of the characteristic matrices, i. e., the mass, the damping and the stiffness matrices, using the modal parameters obtained by modal testing applied to obtain the automotive subsystem's rigid body properties. From these results, it is shown that this approach can be used for obtaining the rigid body properties of mechanical systems.

The design variables of both the structural and the control parameters are optimized simultaneously by the sensitivity analyse to minimize the response due to disturbances of both white noise and colored noise subjected to a constraint so that the system is stable corresponding to high-order natural modes. Three kinds of models are adopted in the approach, namely, the original spatial model by finite element method, the reduced modal model for designing the control system, and the original modal model for assuring stability of the system. The validity and the usefulness of the present approach are verified by a vibration control experiment of a steel plate

The relationship between kinematic energy flow and the effect of the dynamic absorber on suppression of vibration is studied. Energy flow is shown as vibration intensity. It is clarified by simulation that the effect varies according to where the absorber is attached, even if all positions have the same maximum amplitude of vibration.

Energy flows are analyzed in some typical structures undergoing the forced vibration. Energy flows are shown as the vibration intensity vectors. The followings become evident : three types of energy flows exist in the forced vibration of a rectangular plate ; energy flow patterns of multiple resonance peaks of which the resonance frequencies are near each other are apt to be the same because of mutual interference ; an energy vortex appears in the case of two-point excitation ; and energy flows on the box Can be analyzed with the plate theory.

Recently, the necessity of lighting and high-speed for the machines is increasing. This paper concerns the vibration and motion control by the the control system which combined a servo controller with a hybrid dynamic absorber. In our method, the vibration control and the servo control are designed independently. Firstly, the dynamics of the tower structure and the servo motor are modeled. It is shown experimentally that although vibration control by the servo controller alone causes the instability due to nonlinear elements such as the friction or the rattle, the hybrid dynamic absorber is hard to cause this sort of the instability. On the comparison of the vibration control effect and the control force, the hybrid dynamic absorber needs the less force. Finally, to know its effect we evaluated the motion (triangle wave, sine wave) of the flexible structure. Effectiveness of this vibration and motion control method to the flexible structure is demonstrated by simulation and experiment.

The natural modes and corresponding frequencies of a C-type press machine are analysed by the component mode synthesis method. The total structure is divided into 32 components. The natural modes of each component are calculated individually by the finite element method. The degrees of freedom of the components are reduced with the local model coordinates. The equations of motion of all components are combined to make up the total equation of motion. The impact force and the dynamic response of this press machine at the moment of actual punching of a steel plate are measured. The same dynamic response is calculated by the time-domain simulation analysis. The calculated result of the relative displacement between the punch and the die agrees well with the measured result in actual punching. The optimum design is performed by a sensitivity analysis. As a result, the maximum value of the relative displacement between the punch and the die decreases to 40 percent of the usual machine value.

This paper discusses an application of the pseudo-least-squares method to dynamic optimization, with a theoretical extension to inequality behaviour constraints. The application is to a large-scale model, with as many as 8259 degrees of freedom and 1508 design variables. The large-scale model is an engine cylinder block model which has been chosen from the improvement of its torsional resonant frequency. The necessary calculations were completed in eight repetition cycles in the case of a combination of equality and inequality behaviour constraints. The CPU time used for optimization was 0.05 minutes, while the CPU times for eigenvalue analysis and sensitivity analysis were 6.4 and 3.4 minutes, respectively. The results revealed some new information, which we used to manufacture a prototype of an engine block on the basis of the final calculation model. The test result proved quite satisfactory.