Efektivitas Daylight Mirror Shaft sebagai Sistem Pencahayaan Alami Ruang Bawah Tanah pada Langit Tropis

Title: Effectiveness of Daylight Mirror Shafts as Natural Daylighting System for Basements under Tropic Sky Conditions Basements have lots of potential as functional spaces, but have mostly been neglected due to lighting issues. Therefore, this study will explore the daylight mirror shaft system as a daylight strategy for basements, which features the placement of a reflecting surface on a light shaft to redirect daylight. The system was introduced by Heliobus®, a daylighting company from Switzerland. To see the effectiveness of implementing the system in Indonesia, a study was made on its performance on the climate sky condition. Furthermore, a study was made on the effect of different opening orientations and light shaft placements toward the illuminance level achieved. The lighting data was obtained using the simulation softwares Lightstanza. Results show that the performance of the system on climate sky condition can provide sufficient light for 41% of a basement. The use of mirrors on the light shaft could also increase the lighting levels by 2.1 times compared to a shaft without a mirror. Moreover, it was found that different opening orientations and light shaft placements didn’t give a significant effect on the lighting quantity. Overall, the study shows that the system’s implementation on climate skies still require adjustments through further studies to be effective.

Shafting Torsional Vibration Analysis of 1000 MW Unit under Electrical Short-Circuit Fault

Taking a 1000 MW turbine generator as the research object, the short-circuit fault in electrical disturbance is analyzed. Since it is very difficult to carry out fault analysis experiments and research on actual systems, simulation analysis is one of the more effective means of electrical fault diagnosis; the simulation’s results approach the actual behavior of the system and are ideal tools for power system analysis, and can provide an empirical basis for practical applications. The short-circuit fault model of the SIMULINK power system is built to analyze the two types of faults of generator terminals short-circuit and power grid short-circuit. The impact load spectrum, fault current and speed fluctuation between low-voltage rotors were extracted and analyzed. The conclusion is that the impact value of electromagnetic torque at the generator terminal is greater than that on the power grid side. The impact value of a two-phase short-circuit at the generator terminal is the largest, and that of a three-phase short-circuit on the power grid side is the smallest. The transient impulse current of a three-phase short-circuit at any fault point is greater than that of a two-phase short-circuit; the impulse current of the grid side short-circuit is much greater than that of the generator terminal short-circuit; the speed fluctuation and fluctuation difference caused by the three-phase short-circuit in the grid side are the largest. The alternating frequency of the transient electromagnetic force of the four kinds of faults avoids the natural frequency of the torsional vibration of the shaft system, and the torsional resonance of the shaft system in the time domain of the short-circuit fault will not appear. However, after the fault is removed, the residual small fluctuation torque in the system has a potential impact on the rotor system. This research shows an analysis of the structural integrity and safe operation of turbine generator units after a short-circuit fault, which can not only be applied to engineering practice, but also provide a theoretical basis for subsequent research.

Research an Online Monitoring Method of Propulsion Shafting Alignment Adapting to Hull Deformation

Hull deformations are caused by factors such as loading status, wave load, diving depth of underwater vehicles, etc. This causes a change in the shafting alignment state of the ship's propulsion shafting.This affects the alignment state of the ship propulsion shafting. It is very important for engineering significance to research an online monitoring method of propulsion shafting alignment that adapts to the influence of hull deformation. Based on Euler's rigid body attitude theory, this paper constructs a spatial attitude relationship model of the main and driven shafts of the ship's propulsion shafting. By converting to a fixed earth coordinate system, their absolute position-posture can be obtained. Using laser displacement sensor measurement technology, an online monitoring method of propulsion shafting alignment that adapts to the influence of hull deformation is established, which was verified by experiments. This method is suitable for situations where both the main shaft and the driven shaft may have rigid body posture changes. It can provide shafting alignment control compensation for the influence of hull deformation under different working conditions. This will greatly reduce the operating noise of the shaft system and the mechanical operation failure caused by the misalignment of the ship's propulsion shafting.

Modelling and Dynamic Analysis of an Unbalanced and Cracked Cardan Shaft for Vehicle Propeller Shaft Systems

The vibrational behaviour of misaligned rotating machinery is described and analysed in this paper. The model, constructed based on the equations of vehicle dynamics, considered the dynamic excitation of a single Hooke’s joint. The system adopted the breathing functions from a recent publication to approximate the actual breathing mechanism of a cracked driveshaft. The study aimed to understand the transmission of a nonlinear signal from the unbalanced and cracked driveshaft to an unbalanced driven shaft via a Hooke’s joint. The governing equation of the system was established based on the energy principle and the Lagrangian approach. The instantaneous frequency (IF) identification of the cracked driveshaft was extracted based on the synchrosqueezing wavelet technique. To correlate the results, the nonlinear synchrosqueezing wavelet transforms combined with the classical waves techniques were experimentally used in various scenarios for dynamic analysis of the Cardan shaft system. The variations in the dynamic response in the form of a rising trend of higher harmonics of rotational frequency and increased level of sub-harmonic peaks in both shafts were presented as significant crack indicators. The synchrosqueezing response showed breathing crack excitation played a crucial role in the mixed faults response and caused divergence of the vibration amplitudes in the rotor’s deflections. The simulation and test results demonstrated that the driveshaft damage features impacted the transfer motion to the driven shaft and the Hooke’s joint coupling was the principal source of instability in the system. The proposed model offers new perspectives on vibration monitoring and enhancement analysis to cover complex Cardan shaft systems.

Method to Evaluate the Impact of Integration of PMSG on Stability of Synchronous Generator Shaft Under Weak Grid Connection

With the continuous growth in the amount of wind power accessed by the AC grid, the impact of the grid connection of wind-power generators with the power system has gradually increased. In this study, the subsynchronous oscillation of a synchronous generator (SG) shaft caused by the integration of direct-drive permanent-magnet synchronous generators (PMSGs) was investigated. The mechanism governing the effect of the connection strength between the PMSG and AC power system on the stability of the generator shaft system was analyzed based on the complex torque coefficient method. When the connection strength between the PMSG and AC power system weakens, the same voltage variation that occurs at the point of common coupling of the PMSG stimulates more intense power fluctuations in the PMSG, and the electrical damping injected by the PMSG into the SG increases considerably. This may cause the oscillation mode dominated by the generator shaft system to move to the right half of the complex plane, thereby reducing the stability of the generator shaft system. In addition, the evaluation process of the influence of the PMSG on the SG shaft system was summarized, and the proposed method can determine the stability of the AC power system after the integration of the PMSG. Finally, the effectiveness of the proposed method was validated via study cases, and conclusions were drawn. This method is expected to serve as a useful tool for the risk assessment of subsynchronous oscillations in wind farms.

Whirl Analysis of an Overhung Disk Shaft System Mounted on Non-rigid Bearings

Eigenvalues of a simple rotating flexible disk-shaft system are obtained using different methods. The shaft is supported radially by non-rigid bearings, while the disk is situated at one end of the shaft. Eigenvalues from a finite element and a multi-body dynamic tool are compared against an established analytical formulation. The Campbell diagram based on natural frequencies obtained from the tools differ from the analytical values because of oversimplification in the analytical model. Later, detailed whirl analysis is performed using AVL Excite multi-body tool that includes understanding forward and reverse whirls in absolute and relative coordinate systems and their relationships. Responses to periodic force and base excitations at a constant rotational speed of the shaft are obtained and a modified Campbell diagram based on this is developed. Whirl of the center of the disk is plotted as an orbital or phase plot and its rotational direction noted. Finally, based on the above plots, forward and reverse whirl zones for the two excitation types are established.