محمدرضا آشوری

Since resonant micro/nanoresonators are very delicate devices with very small dimensions, therefore, any defects and faults caused by the process of manufacturing and laboratory implementation can lead to fundamental changes in their vibration behaviors. Therefore, the effects of the mentioned disadvantages should be considered as much as possible to obtain more accurate sensors with higher efficiency. In this study, a general model of a doubly clamped microbeam (nanotube) with an asymmetric cross-section with external excitation is considered. Then, linear and non-linear behaviors of an ideal nanotube with a circular cross-section are investigated. The results of the simulations indicate a good agreement with the experimental references available in the literature. Then, taking into account the asymmetry in the resonator cross-section, the system is moved away from an ideal model to a more real model, and the possible effects of the asymmetric cross-section in adjustment, reduction, and vanish of internal resonance are investigated and studied. Finally, the advantages and disadvantages caused by asymmetries and the optimal use of such an opportunity to obtain more innovative and complete models with higher efficiency are explained.

Vibrational methods is one of the common nondestructive damage detection methods for detecting the damage parameters. The most important problem of these methods is their low sensitivity to detect the damage in the presence of noise. In this article, a hybrid damage detection method has been studied to increase the robustness of vibrational method to noise. First, the primary damage location has been detected by the wavelet transform. Next, all the damage parameters including location, depth and intensity of damage have been identified by the model updating process based on the Genetic Algorithm. The signal based on the strain energy ratio in intact and damaged states has been examined to primarily and approximately detect the location of damage thought applying wavelet transform. Also the selected error function in the updating process is based on the strain energy difference between these two states. Using the proposed method leads to raise level of robustness in the presence of noise, also the solution performs faster than the prior methods with the less computational cost. In this work, the solution robustness against noise in traditional model updating method and the proposed hybrid method based on the wavelet transform and updating process has been compared together. The case study has been the laminated composite plate with the delamination damage

In this paper the effect of breathing crack on the rotor-bearing system at two steady state and transient responses are discussed. Results are shown in fast fourier and continous wavelet coefficients diagram. Before extracting of system responses, system equation of motion matrix, modeling of crack and its breathing behavior simulation been done. Then with numerical method in solving of equation “Houbolt method“, rotor system responses at two operation mode, steady-state and start-up (Transient signal) for various crack depth has been calculated. For investigate about cracked rotor system responses, we used of signal graph, Fourier transform and finally continuous wavelet transform coefficients power spectra curve. With considering in Mentioned methods, signs of breathing crack in the rotor system are presented.

Increasing use of cell phone while driving is actually part of a disturbing trend of technological impact on reducing the driver's attention. Using the phone during driving increase crash probability between 3 to 6.5 times. Cell Phone may deviate drivers’ attention of the driving and it lead to a reduction in driver's situation awareness. The present study investigated the impact of Cell Phone on driver’s situation awareness and brake reaction time. For performing this study, 31 bus drivers drove in the bus driving simulator. Drivers’ situational awareness was measured by situation awareness global assessment technique. Gold Directed Task Analysis method used to analysis of driver’s cognitive tasks. The simulator was automatically recorded braking reaction time of the subjects. Results showed that all levels of drivers’ situation awareness significantly reduced after talking on the cellphone (p<0.001). It also became clear that talking mobile significantly increase drivers’ brake reaction time (p<0.001). Pearson correlation coefficients showed a significant negatively correlation between levels 2 and 3, and total situation awareness and brake reaction time while cellphone conversation (p<0.05). Overall, this study showed that talking on mobile while driving can be detrimental effect on situation awareness and performance.

The purpose of this paper is obtaining an optimal arrangement of permanent magnets in a non-contact eddy current damper in order to achieve the maximum damping coefficient (c) among dampers with the same dimension. Magnetic theory and eddy current equations have been employed and solved by finite element numerical method. The dominant damping parameters and the optimum ratio of the ferrite core and the permanent magnet for the specific dimension have been achieved. A damper with the dimensions obtained from design is manufactured in order to verify the result of simulations. A setup also is designed and manufactured to verify the damping coefficient. The damping coefficient of simulation and experimental setup is 69.50 and 68.37 respectively which shows a close correlation between simulation and experiment results. The damping coefficient of the designed damper has been increased by 22.5% compared with a same dimension damper. Furthermore, frequency response is obtained by MATLAB software and a decrease of vibration amplitude in eddy current damper has been investigated. The result showed 20 dB reduction in the peak amplitude of frequency response in the designed damper.

Drowsy driving is a main cause of severe accidents. Drowsiness is responsible for 30% to 37% of fatal road accident in Iran. In this paper، driver drowsiness is detected based on features related to the steering wheel angle and the lateral position of the vehicle. Data from the vehicle and the virtual road are used to extract drowsiness features. Experimental results using a driving simulator are presented. Participants were 21 to 28 year-old males with a high tendency to sleep (Epworth Sleepiness Scale≥10). The subjects had to drive a lane keeping scenario on a long and monotonous virtual road in both drowsy and alert states. The drowsiness criteria are validated with Karolinska Sleepiness Scale (KSS) and video rating based on KSS measurements. The results illustrate that the phase diagram of the steering wheel angle (Ellipse criterion)، the standard deviation of the steering wheel angle، and the mean and the standard deviation of the lateral position of the vehicle are highly correlated with drowsiness. The accuracy of the diagnosis was 77% for the Ellipse criterion، 76% for the standard deviation of the steering wheel angle، 67% for the standard deviation of the lateral position، and 65% for the mean value of the lateral position.

Conventional modal testing is known as a powerful tool for dynamic analysis of structures. However, for some engineering structures, conventional modal testing is difficult or even impossible to conduct due to the problems associated with the artificial excitation of structure. Operational Modal Analysis (OMA) is one solution to deal with these cases. In OMA the structure is excited by ambient forces and only the responses are measured and taken into account. Accelerometers are the traditional tools for measuring the responses of structure. It is well khonwn that the measured responses are contaminated by bias errors corresponding to the mass-loading effect of accelerometers. This causes the natural frequencies of structure are measured lower than the real values. In this paper a new method is proposed for eliminating the mass-loading effects of accelerometers from measured responses in OMA. A numerical model of a mass-spring-damper system is used for validation of the method. Also a steel plate is used for experimental validation of the proposed approach. The results are confirmed by those of conventional modal testing. Both numerical and experimental results show that the proposed method can effectively eliminate the mass-loading effects of accelerometers from measured responses in OMA. Also, the method has the ability to correct the measured natural frequencies from OMA accurately.

Conventional modal testing of large structures is always associated with difficulties in artificial excitation of the structure. Operational Modal Analysis (OMA) is one approach to overcome the excitation problem. In OMA only the responses are measured and the structure is excited by ambient forces. For large structures the simultaneous measurement of responses in all selected points is usually impossible due to not having enough available accelerometers or measurement channels. Therefore، the structure is tested in several steps. As a result، some reference points should be selected to correlate all of the measurements. In this article a new criterion is introduced for selection of reference points based on finite element model of structure. A beam is used for numerical validation of the method. A steel beam is also used for experimental case study. Both numerical and experimental results demonstrate the effectiveness of this criterion.

In this paper، a new FRF-based model updating method is proposed based on the Structural Modification Using experimental frequency Response Functions (SMURF) method. The method deals with the complex Frequency Response Functions (FRFs) and aims to update the lumped parameters of system. The parameters of FE model are updated accurately using only a limited data. A twelve Degrees Of Freedom system is considered as a test case in a simulated experiment. The convergence of the method and the accuracy with which it corrects the FE model are studied. Moreover، the effects of the number of modes، the frequency range of interest، the coordinate incompleteness and noise on the quality of the updated model are investigated. Finally a cantilever beam was used as experimental case study. The results show that the updated FRFs are in good agreement with their experimental counterparts.

One of the drawbacks of the operational modal analysis techniques is that there is no possibility of measurement of the responses in all required points، which is attributed to the limitations of either the number of accelerometers or the number of measurement channels. To overcome this shortcoming، an experiment should be performed in different steps and relations between these steps of the experiment are determined by selection of some specific points as reference points. Existing techniques use the correlation between measurement points to determine the reference points in which an increase in the environmental noise leads to the incapability of the method. In this paper، a new index for selection of reference points is introduced which is more efficient in the noisy environments. To evaluate the proposed method numerically، a comparison has been drawn between the results of this method and correlation approaches using a FE model of a beam. To validate the method، an experiment has been conducted on a steel plate. Obtained results from numerical and experimental cases show that the proposed index is more capable in reference point selection and calculation of the modal parameters of the structures comparing to the results of correlation method.

Conventional modal testing is a powerful tool for dynamic analysis of structures. One of the drawbacks of this technique is the problem of excitation of large structures such as: bridges، towers or trains. However، these structures are excited by ambient forces، such as wind، walking of people or passing the cars on bridges. Operational Modal Analysis (OMA) is the practical tool to overcome this problem. In OMA the structure is excited by ambient forces and only the responses are taken into account. In this article، the accuracy of one of OMA methods is investigated. The modal parameters of a cantilever beam are estimated both from Stochastic Subspace Identification–Covariance Driven (SSI-COV) method and Finite element method. The effect of noise and damping on the accuracy of modal parameters is investigated. Also، a crankshaft is considered for experimental investigation of the accuracy of SSI-COV method. The results show the applicability of SSI-COV method in practical cases.

Driver fatigue is one of the major causes of accidents in roads. It is suggested that driver fatigue and drowsiness accounted for more than 30% of road accidents. Therefore، it is important to use features for real-time detection of driver mental fatigue to minimize transportation fatalities. The purpose of this study was to explore the EEG alpha power variations in sleep deprived drivers on a car driving simulator. The present descriptive-analytical study was achieved on nineteen healthy male car drivers. After taking informed written consent، the subjects were requested to stay awake 18 hrs before the experiments and refrain from caffeinated drinks or any other stimulant as well as cigarette smoking for 12 hrs prior to the experiments. The drivers sleep patterns were studied through sleep diary for one week before the experiment. The participants performed a simulated driving task in a 110 Km monotonous route at the fixed speed of 90 km/hr. The subjective self-assessment of fatigue was performed in every 10 minute interval during the driving using Karolinska Sleepiness Scale (KSS). At the same time، video recordings from the drivers face and their behaviors were achieved in lateral and front views and rated by two trained observers. Continuous EEG and EOG records were taken with 16 channels during driving. After filtering and artifact removal، power spectrum density and fast Fourier transform (FFT) were used to determine the absolute and relative alpha powers in the initial and final 10 minutes of driving. To analyze the data، descriptive statistics، Pearson and Spearman coefficients and paired-sample T test were employed to describe and compare the variables. The findings showed a significant increase in KSS scores in the final 10 minutes of driving (p<0. 001). Similar results were obtained concerning video rating scores. Meanwhile، there was a significant increase in the absolute alpha power during the final section of driving (p=0. 006). Driver mental fatigue is considered as one of the major implications for road safety. This study suggests that alpha brain wave rhythm can be a good indicator for early prediction of driver fatigue.

Dynamic analysis of the civil structures such as bridges, towers and buildings is required for their design and maintenance. Modal analysis is a powerful tool to conduct some part of dynamic analysis in determination of the modal parameter in terms of natural frequencies, damping factors and mode shapes. However, excitation of these structures is usually difficult and sometimes impossible. As these structures are usually excited by ambient forces such as wind, this idea is suggested that the structure is modeled considering the natural forces as the inputs.However, the ambient forces are unknown and have a complicated nature to be measured. An alternative approach is using the operational modal analysis concepts in which only the responses are measured and the modal parameter are extracted. In this article Frequency Domain Decomposition (FDD) method is used for identification of the modal parameter of a clamped-clamped beam and the results are compared with those of the FEM. The operational modal analysis is conducted on a type of a bridge under ambient forces in a real test and the results are compared with those of the conventional Modal testing. The results confirm the method for engineering applications.

The closely spaced modes exist in symmetric structures such as circular plates, gears or disks. Theoretically, closely spaced modes are known as two separated modes with the same amount but, these modes are often detected as only one mode in the classical modal methods. In this article, at the first, some classical modal method is introduced and the most important of their difficulties is considered then, Operational Modal Analysis (OMA) is applied to abate these problems. The Stochastic Subspace Identification based on covariance (SSI-COV) driven is used for this purpose. Different conditions for closely spaced modes is considered and simulated on a free-free steel plate using Matlab software. In order to consider the SSI-COV method in identification of closely spaced modes experimentally, classical and operational modal testing are done on a steel ring. The numerical and experimental results from simulations demonstrate the effectiveness of OMA for identifying and separating the close modes.

Modal testing is a developing expertise in the field of structural dynamics. However، in practice the models that are produced by modal testing procedure face different errors. One of the sources of error is mass-loading effects of accelerometers. This article targets the elimination of mass-loading effects of accelerometers from measured frequency response functions. A strategy based on sensitivity analysis is introduced for this purpose. In this approach the amount of added masses and the locations of structural responses are selected based on the minimum error in correction method. A mass-spring-damper system is used to validate the method numerical. Also، a steel beam is examined to demonstrate the applicability of method in practical cases. The numerical and experimental case studies show the effectiveness of the proposed method.

In this research، simplified physical model of the submarine hull have been considered as a cylindrical shell contained ring stiffeners. The submarine identification done in low frequency، so goal the determination frequency response function is in frequency less than 100 Hz. For determination frequency response function must be derived mass matrix، stiffness matrix، and damping matrix of model of the submarine hull. For the extraction three matrixes explained، the structure model is in ANSYS11 software، and mesh is with triangular element. Displacement domain of each node considered in radial and axial direction، number of structural elements and nodes coordinates by MATLAB software is finite element analysis theory of rotating shell. Three matrix be derive، then result is natural frequency of submarine hull، and then figure of frequency response function drawing in range of frequency less 100 Hz. Of the success of using this method that is being investigated by the department of mechanics can be note to determine frequency response function of propeller-shafting system of submarine hull، coupling propeller-shafting system to submarine hull، the optimization of resonance changer in low frequencies due to reduction of transmission noise of propeller to submarine hull with technique Genetic Algorithms، description of the acoustic signature of submarine due to submarine propeller excitation. And this method can be considered one of maritime new technologies، and as applicable plan implement in the Islamic Republic of Iran Navy and marine industry.

Promotion of security level in urban roads network has important role in increasing confidence and efficiency and competence in transportation network and it is one of the most impressive and effective parameters in increasing immunity and safety, speed control of automobile, so as to it causes number decrease and severity of accidents between vehicles and security increase for passenger. In this case, speed bump and speed humps play important role in speed decrease of vehicles in city. Unfortunately in Iran some reasons as have because of incorrect designs, unlimited and excessive usage of speed bumps and also determining erection place  optionally without observing  global standards it caused that these tools and instruments have little effect on speed control and this case caused maximum loss and damage to automobile suspension system and it follows discomfort of all automobile’s passengers as an example vehicles that move with permissible speed while passing from speed bumps. One of the most important objections for these speed bumps is delay in giving agency vehicles and firefighting automobiles. In this article first of all, existing speed bumps is introduced and by designing and constructing pride automobile quarter model with Simulink software in MATLAB software, their effects on automobile and their passengers has been investigated. Then using ISO 2361-1 Standard, vertical acceleration in which the vehicle passenger feel comfortable is obtained and using Genetic Algorithms, a new design compatible with this standard is also obtained for the speed bump and hump. Using the speed bump and hump optimal design in urban roads network, passengers of the cars which pass them with permissible speed are in the most comfortable area and passengers of the cars which pass them with impermissible speed are in the least comfortable area.

Structural dynamics model updating has been defined as the adjustment of an existing analytical model using experimental data so that the model reflects the dynamic behavior of the structure more accurately. The aim of the present study was to develop a MATLAB program for FRF based updating structural dynamics models. Analytically generated test cases and experimental data for the 5-DOF lumped parameter system showed that the RFM can locate modeling errors in the realistic case of noisy and incomplete experimental data.

Classical modal testing of large structures such as bridges, towers and building is encountered with some problems such as exciting the structure and noisy environment. Therefore, researchers have proposed some new methods for identification of dynamic properties by measuring only the responses of structure. In this paper, one of the well-known methods entitled Frequency Domain Decomposition (FDD) is considered numerically and experimentally. The finite element method was used to conduct a model of a six stories building. The model was excited by random forces in a simulated test and modal parameters of the building were estimated. Also, the sensitivity of the results to the location and the type of excitation and measurement noise has been evaluated. To consider the FDD method experimentally, a clamped-clamped beam has been used. The classical and operational modal tests have been conducted on the beam and the modal parameters were estimated. The results of numerical and experimental studies show the effectiveness and accuracy of the FDD method in identification of modal parameters of structure.

Recently, identification of dynamic properties of structures such as bridges, towers and building, which are not easy to excite, is possible by measuring only the output responses. Due to measuring only the responses when the structure is excited only by ambient or operational forces, these methods are referred as output-only modal analysis or operational modal analysis (OMA). One drawback of OMA is that the mode shapes are not scaled. However the scaled mode shapes are required for some important applications such as damage detection or model updating. In this paper, a procedure is proposed for precise scaling of the operational mode shapes. The method is based on the sensitivity analysis of the effective parameters in the accuracy of scaling. The finite element model of a ten storey building is used to present the capability of the method. The natural frequencies and unscaled mode shapes have been estimated using FDD method and the mass change method is applied for scaling the mode shapes. The sensitivity of the results to the amount, location and the number of added masses and the number of modes under investigation have been evaluated. It is shown that the amount of added masses can be estimated by try and error of the FE model of structure and the masses should be distributed all over the structure to decrease the scaling error.

Apart from the analytical approach to develop a dynamic model for a mechanical structure, another approach is to establish an experimental model for the structure by performing vibration tests and subsequent analysis on the measured data. This process is known as ‘Modal Testing’. During the last three decades or so, modal testing has developed both in theory and in practice. One of the most important applications of modal testing is the validation of the mathematical models of dynamic structures by comparing the experimentally driven modal parameters with those of analytical models. Once the analytical model is validated, it can be used with confidence for further analysis such as response prediction, structural coupling, stress analysis, life time prediction, etc. In this article, the advantages and disadvantages (or limitations) of one of model updating methods are discussed. A 6 DOF lumped parameter system, is employed to investigate the effectiveness of the "Inverse Eigensensitivity Method" (IEM). Firstly the experimental data were simulated using the analytical model. Secondly error locations are found using macro elements. Finally, experimental dynamic properties obtained from the simulated experimental data are compared with the results of the finite element analysis and mass and stiffness error matrices are calculated by using Inverse Eigensensitivity Method" (IEM).