Understanding the vibration characteristics of the human-seat system is essential for evaluating ride comfort, and model-based simulation provides a practical means to analyze such characteristics under controlled conditions. In this study, a three-dimensional finite element model of the human-seat system was developed, representing major human body segments and the seat structure using concentrated masses, rigid beam elements, and spring-damper elements. The unknown mechanical parameters, including joint rotational stiffnesses and the stiffness and damping properties of the human-seat interfaces, were identified so that the transmissibility at key locations-including the buttocks-seat-cushion interface, the back-seat-back interface, and the head-agreed with experimental measurements below 50 Hz. The identified model successfully reproduced the dominant features of both the local transmissibility at the human-seat interfaces and the global dynamic behavior of the system, including modal characteristics observed in experiments. Using the identified transmissibility, responses during actual driving were predicted by combining the model-based transmissibility with the measured floor-input spectrum, and the predicted responses captured the major peaks in the measured spectra. In addition, responses estimated directly from the experimentally obtained transmissibility reproduced the measured driving responses with higher accuracy, demonstrating the practical effectiveness of transmissibility-based response prediction. These results indicate that the developed model is capable of predicting the key vibration responses relevant to ride comfort under automotive running conditions and suggest a practical approach for estimating local ride comfort by applying the ISO 2631-1 weighting curves to these responses.

The interior noise characteristics of railway vehicles vary depending on the position of the cabin. In general, interior noises are louder in the area directly above bogies (ends of the cabin) than in the center of the cabin. It has been known that structure-borne sounds from bogies contribute greatly to the interior noises directly above bogies. This paper describes, using measured data obtained with the rolling stock test plant at Railway Technical Research Institute (RTRI), the application of the operational transfer path analysis (OTPA) to determine the contribution ratio of each transmission path of vibration from bogies to cabin floors. It is considered that structure-borne sounds from bogies propagate mainly through the parts connecting the bogie and car body such as single-link-type traction devices (traction links), yaw dampers, and air springs. As a result of applying the OTPA and determining the contribution ratios, it has been confirmed that the contribution ratios varied depending on the position of the floor and the frequency band. In addition, the validity of the contribution has been verified by examining the linearity of input/output data and the correlations of input data using multiple coherence functions and partial coherence functions. Although a bogie vibrates rigidly in the low frequency range with the very high correlation between the vibrations of the bogie and the parts connecting the bogie and car body, the correlation becomes low in the high frequency region. Therefore, it is expected that the contribution of each transfer path can be well estimated by applying the OTPA in the high frequency range for structure-borne sounds from bogies.

This work investigates the availability of the baseline approach proposed in the previous researches, and expands the applicability of the method for noise and vibration optimization. Based on the s-plane extension theory, baseline was formed by introducing a virtual damping in the transfer function calculation formula. Sensitivity analysis based on baseline was conducted to predict the changing tendency by structure modification in the target frequency range. The validity of the proposed method is examined through numerical simulation with two finite element (FE) models. A simple hollow rectangular parallelepiped model was constructed for confirming the effect of baseline sensitivity analysis as a structural vibration reduction treatment. And a vehicle frame-panel structure was constructed for confirming the proposed method as a noise optimization example. In view of the model in discussion, the sum of squares sensitivity or root-mean-square sensitivity was calculated to determine the mass attachment location. The conventional sensitivity values using FRFs without virtual damping(FRF method) were also calculated for comparing with baseline sensitivity results. The FE models with mass attachment based on sensitivity analysis results were calculated for confirming the vibration reduction effects. The result shows that FRF method has a greater decrease at some single peak in the target frequency range, while the baseline method has a better reduction performance at multiple peaks in the target frequency range. The selection strategies of the two methods for the mass attachment location and the change of mode shape after mass attachment were discussed. The baseline sensitivity method presented in this study provides a feasible approach for noise and vibration performance improvement in the medium frequency band.

Monitoring technology such as predictive maintenance and anomality detection during cutting process has been required. A wireless tool holder with acceleration sensors has been developed for monitoring tool vibration. For advancing functionally of the device, we have been proposed a method using inverse filters for estimating cutting force and torque from acceleration sensor signals during machining. In this study, excitation forces (x direction force, y direction force) on a tool mounted on the holder of machining center were estimated by the proposed method. Firstly, inverse filters were determined from single-input, single-output signals by excitation experiment on non-operating state. Secondly, the proposed method was examined by estimating an impulse signal.

In recent years，research has been conducted on the effects of structural changes in subsystems on the global system for the purpose of optimizing the vehicle development process．However，no method has been established that can be applied to complex systems such as vehicles．Therefore，the goal of this study is to propose a new method that can be applied to vehicle models and provides guidelines for structural changes of subsystems to improve the vibration characteristics of the global system．In this study，we consider a structural modification in which the FRF of the subsystem is changed uniformly by using the amplitude coefficient γ ．The proposed method can predict the natural frequencies and the maximum value of FRF after the structural change．Both are formulated using transfer function synthesis method as the basic theory．By combining the prediction of natural frequencies with the prediction of FRF maximum value，a guideline for structural modification can be obtained．In fact，the proposed method is applied to a vehicle model and the structural modification is carried out according to the obtained guideline，and the FRF is successfully reduced．

In order to evaluate the ride comfort of a car, it is necessary to know the vibration characteristics of the human body. If the vibration characteristics can be well predicted by numerical simulation, the time for car development and the cost can be greatly reduced. Many models that can simulate the vibration characteristics of the human body have been studied but there is no human-seat coupled model that sufficiently expresses the vibration characteristics of both the human body and the seat. Therefore, in this study, we propose a human-with-seat model up to 50 Hz with regard to two car seats with different characteristics. The model is a FEM model with beam elements. The mass was the weight of the subject, node coordinates were measured by motion capture, and the stiffness and damping coefficient of the beam were unknown parameters. The analysis results show that the primary and secondary modes, which are the main modal characteristics of the human-seat system, can be reproduced.

Improving quietness is an important issue in automotive design. Many studies have been reported on the use of a stiffness sensitivity to identify effective design changes. However, calculating a stiffness sensitivity using experimental measurements requires a large number of strain sensors, making it difficult to use in automobile design. Therefore, we propose a simplified method to evaluate strain energy focusing on elastic deformation and to calculate stiffness sensitivity more easily. The validity of the proposed method is confirmed using a simple flat-plate FEM model.

Monitoring technology such as predictive maintenance and anomaly detection during cutting process has been required. A wireless tool holder with acceleration sensors has been developed for monitoring tool vibration. To advance the device functionally, we have proposed a method using inverse filters to estimate cutting force and torque from acceleration sensor signals during machining. In this study, excitation forces (x direction force, y direction force, torque) on a tip of a structure in rotating were estimated experimentally by the proposed method. Firstly, inverse filters were determined from single-input and single-output signals by excitation experiment of static structure on the surface of which acceleration sensors were placed in circular pattern. Secondly, the excitation forces were estimated by convolving the inverse filters with the acceleration signals when the tip of the structure on rotating was excited impulsively. In addition, the force magnitude, the angle of action, and the excitation direction were calculated by the estimated excitation forces. The estimation values of the force magnitude and the excitation direction almost exhibited corresponding measurement values when the rotation speed was 60 rpm. The experimental results show that the proposed method can effectively estimate excitation forces on the structure in rotating.

By a trial simulation, it was found that the frequency range of vibration reduction due to antiresonance was wider than that of the flam damper by installing several Dynamic Absorbers with similar natural frequencies and adjusting their damping factors. To expand this range to the maximum, we propose a parameter adjustment method for a Multi Dynamic Absorber using the basic theory of Transfer Path Analysis. A diagram showing the relationship between the numbers of installed dynamic dampers, the target value for reducing the vibration amplitude ratio, and the range of vibration reduction frequencies can be derived.

In recent years, the demand for improvement of ride comfort in automobiles has been increasing, and the demand for quietness in the vehicle interior also increased. In particular, noise in the low-frequency range is one of the most important interior properties and has been the subject of various studies, but there have been few studies on the transient noise generated in a vehicle cabin when a shock input is applied. In this study, we attempt to improve the transient response to reduce the booming noise in the low frequency range caused by the shock input. First, the vibration characteristics of the test vehicle were determined based on data obtained from experimental measurements. As a result, it was found that ceiling deformation, which adversely affects vibration noise, occurs at a specific frequency. Next, based on the experimental measurements, a sensitivity analysis was performed to determine the appropriate mass addition, and mass addition was actually performed on the test vehicle. As a result, the transient response to shock input was improved as the sensitivity analysis predicted.

Frequency response functions (FRFs) lie within the framework of the linear response theory in elastic structures. In FRFs, the inputs/outputs relationships are strictly determined, but there is no way of knowing how waves are propagated and converted from the input signals into the output signals. Thus, the wave propagation between the inputs and outputs cannot be clearly understood by the FRFs. In this study, we succeeded in visualizing the contents of these FRFs by decomposing them into geometric paths using a signal flow graph. Moreover, we succeeded in quantitatively evaluating the contributions of the paths to these FRFs. In terms of application, when the noise or vibration of industrial products is loud and unpleasant, this analytical methodology can help identify the cause behind such nuisance by using paths in contribution to FRFs. This methodology is expected to pave the way for taking quantitative countermeasures on the basis of analytical results.

This paper proposes a stiffness sensitivity analysis with principal strain application to decrease the out-of-plane vibration, which is the main source of the sound radiation of mechanical structures with thin plate parts. The sensitivity is evaluated as a differential coefficient of the target response with respect to the design variable, e.g., stiffness or mass. For suppressing the out-of-plane vibration, we pay attention to finding an appropriate location on the structure to add local stiffness. The location is decided according to stiffness sensitivity analysis results. The compliance frequency response function (FRF) is considered as the target response, and the thickness of stiffener is considered as the design variable. The validity of the proposed method is examined through numerical simulation with a finite element method (FEM) model of a thin plate. The modal principal strain distributions, stiffness sensitivity, and FRF changes by local thickening are calculated based on 4 selected natural modes. It is also examined by the experimental approach. The expected reduction of the response is attained by adding the stiffener (a thin stainless plate) to the appropriate location on the plate.

In the development of vehicles, it is quite important to improve ride comfort. And it is closely related to vibration. So, it is necessary to understand vibration characteristics of human. However, it is hard to conduct a human vibration experiment repeatedly or for long hours because of health and ethical issues. To solve this problem, a variety of human models are structed. In this study, the human model that is focused on seated postures using MBD is introduced. In this model, two postures are evaluated, which is upright and relaxed. And dynamic characteristics of each posture can be expressed by the model.

Computer-aided engineering (CAE) analysis is utilized in dynamic design in various industrial fields. However, if there is any difference between an actual structure and a numerical model, CAE cannot predict correct properties. When complex structures are targeted, it is difficult to identify factor locations accurately and efficiently. We had proposed a nodal constraint method that be to extract vibration characteristics of each component alone for a structure connected with various components for this problem. However, because of inverse matrix calculation in a theoretical formula used in the method, there is a problem that influence of noise is enlarged when the connecting part is many degrees of freedom. In this paper, we propose a method to reduce noise by applying singular value decomposition to the above problem. Furthermore, the validity of the method was examined by applying to an automobile component. As a result, it is confirmed that the proposed method effectively reduces noise.

This paper presents a new structural optimization method considering noise and vibration performance in structure design. As a conventional optimization method, a method focusing on frequency response function (FRF) with many peaks has been widely used. In this paper, we propose FRF baseline as an index that represents the trend of FRF in a wider frequency band. As a result of numerical simulation, it is confirmed that the optimization method based on FRF baseline is more efficient than the conventional method based on row FRF under certain conditions.

In vehicle development, structural design for noise reduction is becoming increasingly important. Noise reduction of panel is often achieved through add additional mass. However, this goes against the requirement of lightweight. And in mid-frequency range where mode density is high, the large amount of computational cost and time is required to establish effective countermeasures. Several methods have been proposed to define mode group, but they only apply to certain conditions. Therefore, the purpose of this study is to investigate mode grouping method leading to structural change for panel radiation noise reduction in mid-frequency range with high mode density. In this study, we evaluated by simulation using a frame-panel model and used FRF baseline estimate method to define mode group. Then, 46 modes in the target frequency range are classified into several groups by proposed method.

Vibration characteristics of a seated human body exposed to whole-body vibration are important factors in ride comfort of automobiles. In a frequency range below approximately 20 Hz, there are main resonance frequencies of the human body. Therefore many previous studies have discussed the vibration characteristics in this frequency range. However, it is necessary to focus on high-frequency vibration because recent development in vibration reduction technology of automobiles reduces low-frequency vibration and occupants can perceive high-frequency vibration. The purpose of this study is to examine the vibration characteristics of the seated human body in a frequency range below 50 Hz. For the purpose, vibration experiments for the human body with a shaking table were conducted. Subjects sat on a rigid seat fixed on the shaking table and were exposed to vertical vibration. Acceleration on the head and several positions on the spine was measured, and seat-to-measurement-point acceleration transmissibility was obtained. The modal characteristics were estimated from the measured data of the transmissibility by using multi-reference iterative curve fitting technique. Five modes were estimated below 50 Hz. The first, second, and third modes were in the frequency range below 20 Hz. The fourth and fifth modes were in a frequency range from 20 Hz to 50 Hz. The modal characteristics, which are a mode shape and a natural frequency, in the high-frequency range varied depending on the subjects, though the modal characteristics in the low-frequency range were almost the same regardless of the subjects.

In this paper, sensitivity analysis focusing on the vibration intensity is proposed. Although research on vibration intensity had been conducted, the method to control it has not been established. In this study, a sensitivity analysis equation to predict the change in vibration intensity due to the addition of mass, stiffness, and damping is derived, and the change in vibration intensity is examined using a finite element method (FEM) model, and appropriate structural changes are discussed. In the FEM beam model, the change in vibration intensity predicted by the proposed sensitivity analysis equation is found to be consistent with the actual change due to structural changes. The structural changes based on the sensitivity analysis allowed us to control the vibration intensity and to reduce the vibration intensity at the target location. This paper confirms the validity of the proposed sensitivity analysis formulae for mass addition and stiffness addition using FEM models.

Currently, Active Structural Intensity is mainly used for energy propagation evaluation in Intensity analysis. Therefore, this paper examines structural changes focusing on Reactive Structural Intensity, that expresses stationary component of energy transmission. We have derived the structural change sensitivity of Reactive Structural Intensity as well as Active Structural Intensity. Numerical simulation was performed with a spring mass damper system with four degrees of freedom. From the results of the sensitivity analysis, we achieved a reduction in intensity by adding mass.