Tatacipta Dirgantara

Gait Parameters Determination by 2D Optical Motion Analyzer System

In the present work, an optical motion-capture system combined with software for 2D clinical gait analysis is utilized to determine spatiotemporal gait parameters such as stride-length, cadence, cycle-time, and speed as well as joint angles. The developed system consists of a video camera with a maximum speed of 90 fps, LED markers, PC and technical computing software, which are developed for tracking markers attached to human body during motion and to calculate kinematics and kinetics parameters of human gait. Gait data of 60 subjects within the age group between 18 to 49 years are measured as part of an effort to develop normal walking database of Indonesian people. In the experiments, the subject is instructed to walk in a specially-arranged measurement area, which is calibrated using the Direct Linear Transformation (DLT) method. Before the measurement, the body posture of each subject is evaluated to ensure normalcy. To validate the system, the obtained gait data is compared to the available normal walking database, and the results obtained by the system show good compatibility.

Development of an optical motion-capture system for 3D gait analysis

This work presents the development of an optical motion-capture system for 3D gait analysis. The system consists of two video cameras with speed of 25 fps, flash lighter, LED markers, and two PCs and technical computing software, which are used to acquire marker motion attached to human body during walking. The developed system has five module to obtain real coordinate of markers, i.e. pre-processing, camera calibration, marker detection and tracking, 3D reconstruction, and post-processing module. In the experiment, two camcorders are synchronized using flashlight. The recorded videos from experiment are extracted into frames. The synchronized framesare converted into binary images and marker position can be detected and tracked using least distance method. 3D Direct Linear Transformation method has been used to reconstruct 3D marker position in real coordinate. The marker positions data obtained from experiment could then be used for further kinematics and kinetics analysis of human gait.

Development of an affordable system for 2D kinematics and dynamics analysis of human gait

Development of a low-cost, yet reliable, system for 2D gait analysis is presented in this paper. The system consists of a home video camera with speed of 25 fps, LED markers, PC and a technical computing software, which are used for capturing and processing the digital image of markers attached to human body during motion. In the experiments, a person is instructed to walk in a specially arranged measurement area. The recorded images are then digitally processed to detect and track the 2D coordinate of the markers over time. To conduct a dynamics analysis, a mathematical formulation for human motion is constructed where the body is modeled by a system of five rigid bars connected by joints. Finally, a program is developed to plot and calculate the kinematics and dynamics data of human gait, where the markers position data over time, and other variables such as dimensions and weight of the body are used as the input in the program.

Tracking of Markers for 2D and 3D Gait Analysis Using Home Video Cameras

This work presents the development of an affordable optical motion-capture system which uses home video cameras for 2D and 3D gait analysis. The 2D gait analyzer system consists of one camcorder and one PC while the 3D gait analyzer system uses two camcorders, a flash and two PCs. Both systems make use of 25 fps camcorder, LED markers and technical computing software to track motions of markers attached to human body during walking. In the experiment for 3D gait analyzer system, the two cameras are synchronized by using flash. The recorded videos for both systems are extracted into frames and then converted into binary images, and bridge morphological operation is applied for unconnected pixel to facilitate marker detection process. Least distance method is then employed to track the markers motions, and 3D Direct Linear Transformation is used to reconstruct 3D markers positions. The correlation between length in pixel and in the real world resulted from calibration process is used to reconstruct 2D markers positions. To evaluate the reliability of the 2D and 3D optical motion-capture system developed in the present work, spatio-temporal and kinematics parameters calculated from the obtained markers positions are qualitatively compared with the ones from literature, and the results show good compatibility.

Development of a Railway Track Displacement Monitoring by Using Digital Image Correlation Technique

To avoid an unnecessary catastrophic accident due to a failure of a railway track, it is important to have a reliable condition monitoring system for the railway track. The integrity of the railway track can be assessed by monitoring the displacement field of the track, which can then be used to determine the strain and stress field. By knowing the stress history of the track and the S–N curves of the track material, the remaining life of the railway track can be predicted. In the present work, a simple system to monitor and record the displacement field of the railway track has been developed by using Digital Image Correlation (DIC) technique. The set–up to monitor the displacement field of the railway track was developed using a high speed video camera of Nikon J1 to capture the image of the railway track when the train passing through. The DIC technique was then employed off line to measure the displacement field of the 2D image captured. The results showed that the full field displacement measured by using DIC technique gives a good agreement compared to the finite element results. The full field displacement can be used to calculate the strain-stress field, and later on the remaining life assessment can be conducted based on the results.

Numerical and Experimental Impact Analysis of Square Crash Box Structure with Holes

Numerical and experimental study of the effects of center holes located at opposite sides on dynamic axial crushing of thin-walled square aluminum extrusions column are presented in this paper. The results showed that, by inserting the holes, the impact energy absorption characteristic in a progressive buckling can be improved as the starting location of the plastic deformation is always from holes and peak crush force can be decrease, so that the deceleration does not exceed the limit that can injure the passenger when frontal impact occurs. Here, the results of numerical simulations, conducted using an explicit finite element code, are compared with experimental results for various hole diameter. The results shows that the peak crushing force is decrease, while the mean crushing force is relatively constant.

Low Velocity Impact Analyses of Prismatic Columns Using Finite Element Method

This paper presents the study of prismatic columns of different cross sections subjected to low velocity impact, which are commonly used as energy absorber components in vehicles. The impacts of the columns were numerically analyzed using FEM. Four cross sections were considered, i.e. square, hexagonal, octagonal and circular. For each cross section, columns with several combinations of perimeters and thicknesses were analyzed. The results showed that, for columns with equal perimeter and thickness, those with circular cross sections have the highest mean crushing force and those with square cross sections have the lowest crushing forces. Furthermore, keeping all other parameters constant, columns with thicker wall have significantly higher crushing force while columns with longer perimeter have only slightly higher crushing force. This parametric information will be very useful for modern automotive industry in designing front longitudinal members within an acceptable safety level.

Probabilistic Fracture Mechanics Analysis of Multiple Cracks in Cylindrical Pressure Vessel

In this work, a probabilistic fracture mechanics analysis of multiple cracks in a cylindrical pressure vessel was conducted. The analysis was performed to predict service life of a pressure vessel with a certain level of reliability if the vessel has a multiple internal surface cracks that interact each other. The stress intensity factor of multiple cracks configuration was determined from the stress intensity factor of a single surface crack in a plate subjected to uni-axial load and the interaction factor between the cracks. In this work, the Swift’s crack link-up criterion was employed. These parameters together with several other stochastic parameters, i.e. initial crack size, Paris’s crack propagation constants and fracture toughness, were then used to calculate the probability of failure with a certain level of reliability. The failure probability was simulated using guided direct simulation, for cycle-by-cycle crack propagation, to find the expected service life and the mode of failure (leak or break). A case study of a high-pressure vessel having different initial crack sizes have been simulated and the service life with 99,99% reliability were determined.

PERFORMANCE EVALUATION OF THE CORRELATION AND SMOOTHING METHODS OF THE DIGITAL IMAGE CORRELATION AND ITS APPLICATION TO THE OPENING SPECIMENS

Digital Image Correlation (DIC) has been known as one of the non-intrusive experimental methods in solid mechanics. This method has several advantages such as full-field examination, robustness of the algorithms, and the instantaneous visualization of the results. The key of this method is to find the displacement vectors by using a certain correlation method. In this paper, two correlation methods are performed and evaluated, i.e. cross-correlation and FFT (Fast Fourier Transformation) correlation. Performance of these methods in term of error analysis and processing time wre evaluated. Error analysis was performed by using self-generated artificial images with several desired parameters. The results showed that the cross-correlation has less fluctuation results and more constant accuracy. The average processing time of FFT technique is 64% of the cross correlaton. Smoothing algorithms are applied to the displacement results. The results of the smoothing process are compared to the original one to verify the effect of the algorithms. This smoothing process is the important step if the derivative parameters of the displacements such as stress and strain distribution need to be obtained. The complete DIC algorithms are then applied to measure the displacements of the plate with circular and rectangular opening specimens by using experimental images. The result showed that this technique can produce displacement field with good accuracy.

Nonlinear analysis of cracked plates

This paper presents the geometrically nonlinear analysis of cracked plates by the dual boundary element method. Extrapolation of displacements on the crack surfaces is used to compute the stress intensity factors. The normalized stress intensity factors for the cracked square plate with fully clamped and simply supported boundary conditions are presented.