Rotating unbalance is one of the main sources of vibration in a rotor system. Vibration due to unbalance may cause noise, decreased life of bearings, unsafe work conditions, and reduced machine life. Different methods have been studied on the identification of unbalance in the rotor system. This study aims to estimate the unbalance using frequency response function of the rotor system and operating deflection shape, i.e., vibration responses under the unbalance. Frequency response function is obtained by conducting eigen-analysis in MATLAB using equations of motion obtained by Jeffcott rotor model. The commercial finite element package, COMSOL Multiphysics software is used to model the rotor system with rotating unbalance and computes the forced vibration response. Frequency response function and frequency domain response are used to inverse estimate the rotating unbalance. The estimation error between estimated unbalances and corresponding prescribed values is lower than 0.1%. This study also shows the use of COMSOL Multibody Dynamics module to simulate the vibration due to the rotating unbalance.

Project scheduling is an important task in project management which monitors the project duration, resource utilization and affects the benefit of project for all kinds of project such as construction, IT, renewable energy, product design and manufacturing etc. Among many methods for project management, critical path method (CPM) is one of the better-known planning and control techniques in project scheduling. In this study, CPM-based computerized program was developed together with modeling of step by step calculations of parameters of interest such as earliest starts and finishes, slack and float times of project activities resulting in determination of critical path for the project. One advantage of computer implementation of CPM using MATLAB in this study is that unlike conventional method, it eliminates necessity to conventionally draw network diagram to perform critical path analysis.

Crack in a structural member alters local stiffness that affects the dynamic characteristics such as natural frequency and mode shape of the structure. Identification of crack location and size is one key destination of structural health monitoring. In this paper, we propose a correlation-based inverse method for identification of crack location and size in a cantilever beam. First, natural frequencies of healthy and cracked cantilever beams were computed using finite element method and verified with experimental tests. Next, changes in natural frequencies with respect to crack locations and sizes were analyzed and the correlation model between natural frequency and crack parameters was constructed by non-linear curve-fitting. Finally, in the inverse analysis, correlation model was used to identify crack location and size based on the knowledge of the first and second natural frequencies from the measurements. Results indicate that the inverse method with new correlation model can identify crack location and size. The proposed identification method demonstrated for simple cantilever beam can be adapted for crack identification in complex structures. The proposed method is simple and easy to identify crack location and depth; its main advantage is that knowledge of only the first and second natural frequencies are required to predict crack parameters.

This paper presents the change in the optimal cross-sectional areas of 25-bar truss structure due to thermal expansion. The 25-bar spatial truss is commonly used in structural engineering as a benchmark for structural optimization. Previous studies used different optimization methods to compute the optimal cross-sectional areas of the truss structures related to the minimal weight of each bar element. However, most of the previous studies conducted the optimization under mechanical load only and reported almost the same optimal areas and minimum weight with slight variations depending on the method used. However, very little has been done on the structural optimization with the consideration of thermal expansion. This study aimed to investigate the effect of thermal expansion in structural optimization and conducted optimization of this structure under the thermal load and the same mechanical load case with the previous studies. The difference in the optimal areas between with and without thermal expansion is analysed through optimization of both cases using MATLAB Optimization Toolbox. The optimization method used is fmincon with Sequential Quadratic Programming (SQP) . The result shows both an increase and decrease in optimal cross-sectional areas. The optimal weight of the structure increases by 12.26% at the surrounding temperature of 30°C. Therefore, this study highlights the needs of consideration of thermal load in optimizing the cross-sectional areas of the structure for minimum weight and this is particularly of important consideration in designing the truss structures in tropical climate. One of the limitations of this study that the SQP may not be appropriate for large structure and hence the robustness of the method should be tested with more variable.

We present a millimeter scale fluidic channel for concentrating and filtering microsized particles suspended in the fluid medium. The device takes on an h-shape with a narrow inlet and a wide outlet. By setting up an ultrasonic standing wave across the channel width, microparticles with positive acoustic contrast factor are constrained to move along pressure nodal lines within the fluid. The acoustic radiation force acts on the particles in the transverse direction, keeping the particles to the lower part of the outlet. As a result, a suspension with higher particle concentration is formed at the lower part of the outlet, while clean fluid can be extracted at the upper part of the outlet. A series of experimental results were obtained to study the performance of this concentration process for various volume flowrates and ultrasonic power used. For high ultrasonic power, the microparticles were found to be trapped in the fluid channel. A numerical model was also developed to study the strength of the acoustic energy density in the channel and its influence on the performance of the concentrator. This ultrasonic concentrator has potential in biomedical and environmental applications where cells and micro-organisms need to be filtered out from a fluid suspension.