The vibrations behavior analysis is an essential step in the mechanical design process.Several methods such as analytical modelling,numerical analysis and experimental measurements can be used for this purpose.However...The vibrations behavior analysis is an essential step in the mechanical design process.Several methods such as analytical modelling,numerical analysis and experimental measurements can be used for this purpose.However,the numerical or analytical models should be validated through experimental measurements,usually expensive.This paper introduces an inexpensive smartphone as an accurate,non-intrusive vibrations’behavior measurement device.An experimental measurement procedure based on the video processing method is presented.This procedure allows the measurement of the natural frequencies and the mode shapes of a vibrating structure,simply by using a smartphone built-in camera.The experimental results are compared to those obtained using an accurate analytical model,where the natural frequencies error is less than 2.7%and the modal assurance criterion is higher than 0.89.In order to highlight the obtained results,a comparison has been done using a high quality and high frame per second(fps)camera-based measurement of material properties.Since the highest recovered natural frequency and its associated mode shape depend on the frame per second rate of the recorded video,this procedure has great potential in low frequencies problems such as for big structures like buildings and bridges.This validated technique re-introduces the personal smartphone as an accurate inexpensive non-contacting vibration measurement tool.展开更多
Vibration can be introduced in all mechanical fields in our life.Engineers try to avoid its negative effect leading in some cases to deformation in the machines.Many researches are dedicated to study the identificatio...Vibration can be introduced in all mechanical fields in our life.Engineers try to avoid its negative effect leading in some cases to deformation in the machines.Many researches are dedicated to study the identification of damping especially in multi degree of freedom systems with particular attention to the source of energy dissipation.They focus on developing new tools or methods which may be used in real problems to obtain accurate results about the amount(or value)and the location of energy dissipation in the structure.The aim of this paper is to present an original procedure aims to experimentally determine the modal damping ratio of a mechanical structure.The proposed procedure consists of extracting the Frequency Response Function of the vibrating system using the video magnification method and then calculate the modal damping ratio using the 3-dB method.These experimental measurements are carried out by giving an external force on a cantilever beam,then the modal damping ratios are extracted using motion magnification.The obtained results show a relative error less than 4.2% between the experimental measurements and the analytical calculation for the Frequency Response Function(FRF)curves.The novelty of the paper is to combine the video magnification technique and the 3dB method in a procedure that aims to experimentally measure the modal damping of a mechanical structure.The proposed procedure in this paper represents the damping identification as a simple and easy engineering application.展开更多
Tremor is considered as the most common faced abnormal involuntary movement disorder and the source of functional disability. Parkinson disease (PD) is a slowly progressive degenerative disorder of the central nervous...Tremor is considered as the most common faced abnormal involuntary movement disorder and the source of functional disability. Parkinson disease (PD) is a slowly progressive degenerative disorder of the central nervous system caused by the lack in the level of dopamine. Levodopa is the most effective dopaminergic medication used to manage Parkinson symptoms. However, it will be the source of the motor fluctuation after several years. An uncommon type of medication is suggested to suppress the resting tremor of PD patients. In this paper, a vibration absorber is used as a mechanical treatment and designed to reduce critical angular displacement amplitude at the resonance frequency. Human hand is modeled dynamically at the musculoskeletal level to reflect Parkinsonism. Motion is considered due to shoulder, elbow, Biceps brachii and wrist muscles activation. Absorber’s geometry, materials properties and parameters are well chosen to satisfy the tuning condition. The solution to the equation of motion for the hand is shown in the frequency and time domains to check the performance of the absorber in reducing the flexion angular motion at the wrist joint. Results show that the absorber was very effective over a good frequency bandwidth. It was able to reduce 93% of tremors amplitude at the wrist joint in the frequency domain. This type of absorber has low cost, can operate without power requirements, and has a simple design. Since its effectiveness was proved when tested numerically, it is recommended to proceed to the manufacturing process and the experimental study.展开更多
文摘The vibrations behavior analysis is an essential step in the mechanical design process.Several methods such as analytical modelling,numerical analysis and experimental measurements can be used for this purpose.However,the numerical or analytical models should be validated through experimental measurements,usually expensive.This paper introduces an inexpensive smartphone as an accurate,non-intrusive vibrations’behavior measurement device.An experimental measurement procedure based on the video processing method is presented.This procedure allows the measurement of the natural frequencies and the mode shapes of a vibrating structure,simply by using a smartphone built-in camera.The experimental results are compared to those obtained using an accurate analytical model,where the natural frequencies error is less than 2.7%and the modal assurance criterion is higher than 0.89.In order to highlight the obtained results,a comparison has been done using a high quality and high frame per second(fps)camera-based measurement of material properties.Since the highest recovered natural frequency and its associated mode shape depend on the frame per second rate of the recorded video,this procedure has great potential in low frequencies problems such as for big structures like buildings and bridges.This validated technique re-introduces the personal smartphone as an accurate inexpensive non-contacting vibration measurement tool.
文摘Vibration can be introduced in all mechanical fields in our life.Engineers try to avoid its negative effect leading in some cases to deformation in the machines.Many researches are dedicated to study the identification of damping especially in multi degree of freedom systems with particular attention to the source of energy dissipation.They focus on developing new tools or methods which may be used in real problems to obtain accurate results about the amount(or value)and the location of energy dissipation in the structure.The aim of this paper is to present an original procedure aims to experimentally determine the modal damping ratio of a mechanical structure.The proposed procedure consists of extracting the Frequency Response Function of the vibrating system using the video magnification method and then calculate the modal damping ratio using the 3-dB method.These experimental measurements are carried out by giving an external force on a cantilever beam,then the modal damping ratios are extracted using motion magnification.The obtained results show a relative error less than 4.2% between the experimental measurements and the analytical calculation for the Frequency Response Function(FRF)curves.The novelty of the paper is to combine the video magnification technique and the 3dB method in a procedure that aims to experimentally measure the modal damping of a mechanical structure.The proposed procedure in this paper represents the damping identification as a simple and easy engineering application.
文摘Tremor is considered as the most common faced abnormal involuntary movement disorder and the source of functional disability. Parkinson disease (PD) is a slowly progressive degenerative disorder of the central nervous system caused by the lack in the level of dopamine. Levodopa is the most effective dopaminergic medication used to manage Parkinson symptoms. However, it will be the source of the motor fluctuation after several years. An uncommon type of medication is suggested to suppress the resting tremor of PD patients. In this paper, a vibration absorber is used as a mechanical treatment and designed to reduce critical angular displacement amplitude at the resonance frequency. Human hand is modeled dynamically at the musculoskeletal level to reflect Parkinsonism. Motion is considered due to shoulder, elbow, Biceps brachii and wrist muscles activation. Absorber’s geometry, materials properties and parameters are well chosen to satisfy the tuning condition. The solution to the equation of motion for the hand is shown in the frequency and time domains to check the performance of the absorber in reducing the flexion angular motion at the wrist joint. Results show that the absorber was very effective over a good frequency bandwidth. It was able to reduce 93% of tremors amplitude at the wrist joint in the frequency domain. This type of absorber has low cost, can operate without power requirements, and has a simple design. Since its effectiveness was proved when tested numerically, it is recommended to proceed to the manufacturing process and the experimental study.
