Mechanisms of earthquake-induced deformation in slopes and embankments

Earthquake-induced deformation in slopes and embankments results from several mechanisms acting alone or in combination: (1) sliding displacement along a localized failure surface [i.e., "sliding block" displacement], (2) deformation resulting from the densification of unsaturated soil termed "seismic compression" and (3) deformation resulting from accumulation of plastic strains in highly stressed regions of a slope. In contrast to sliding, which involves highly localized deformations, the latter two mechanisms are collectively referred to as "distributed deformations" and can by themselves result in damaging displacements to facilities and infrastructure.This research uses physical and numerical modelling in parallel to investigate the mechanisms governing earthquake induced deformations in slopes. The physical modelling portion of this research utilized both geotechnical centrifuge and 1-g shaking table experimental methods to examine the contribution of distributed deformation to overall earthquake-induced displacement in slopes. The numerical analyses, which were calibrated to physical model experimental data, provided additional insight into the seismic performance of the models.This research was precipitated, in part, by observations from past earthquakes suggesting that mechanisms other then sliding may be responsible for seismically induced displacement in unsaturated granular slopes (e.g. embankments). In the absence of fully documented case histories to identify and document these mechanisms, centrifuge model experiments were performed to investigate the mechanism(s) that govern the seismic performance of these types of slopes. The experimental results suggests that, for the range of test conditions considered in this study (slope geometry; amplitude, frequency and duration of input motions), seismic compression was the principle mechanism of deformation in the unsaturated granular soil; deformation resulting from the shearing, as indicated by the development of localized surfaces, was not observed. The centrifuge model response was numerically simulated using the FINN soil constitutive as implemented in the computer code FLAC. The numerical simulations, which allowed for the one-step, fully coupled analysis of seismic compression, matched well with both the dynamic and deformation response of the model slopes.Earthquake reconnaissance reports also indicate that distributed deformations can occur in slopes comprised of cohesive soils. To investigate this phenomena, a second phase of study was undertaken where shaking table tests were performed on small scale cohesive slopes comprised of "model clay" (a saturated mixture of kaolinite and bentonite). Parallel numerical simulations of the shaking table test were performed using a strain-softening soil constitutive model as implemented in FLAC. The numerical simulations and shaking table experimental results were in very good agreement.The physical model tests provide a unique dataset that allowed topographic amplification to be considered empirically. Analyses of the experimental results indicate that amplification at the slopes crest occurs almost entirely as a result of site effects; the contribution from topographic amplification was negligible for most of the cases. Overall amplification was consistently higher at the steeper crest of the two slopes for all the tests (both centrifuge and shaking table), most likely as a result of topography.Ph.D., Civil Engineering -- Drexel University, 200

Enhancement of microgrid operation by considering the cascaded impact of communication delay on system stability and power management

Power management, system stability and communication structure are three key aspects of microgrids (MGs) that have been explored in many research studies. However, the cascaded effect of communication structure on system stability followed by the impact of stability on the power management has not been fully explored in the literature yet and needs more attention. This paper not only explores this cascaded impact, but also provides a comprehensive platform to optimally consider three layers of MG design and operation from this perspective. For generation cost minimization and stability assessment, the proposed platform uses an adaptive particle swarm optimization (PSO) while a new class of data exchange scheme based on IEC 61850 protocol is proposed to reduce the communication time delays among the inverters of distributed generations and the MG control center. This paper also considers the system stability using small-signal model of a MG in a real-time manner as an embedded function in the PSO. In this context investigations have been conducted by modeling an isolated MG with solar farm, fuel cell generator and micro-turbine in MATLAB Simulink. Detailed simulation results indicate the proposed power and stability management method effectively reduces the MG generation cost through maximizing the utilization of the available renewable generations while considering system stability. © 2020 Elsevier Lt

Understanding power transformer frequency response analysis signatures

This paper presents a comprehensive analysis of the effects of various faults on the FRA signatures of a transformer simulated by a high-frequency model. The faults were simulated through changes in the values of some of the electrical components in the model. It was found that radial displacement of a winding alters the FRA signature over the entire frequency range (10 Hz-1 MHz), whereas changes due to axial displacement occur only at frequencies above 200 kHz. A Table listing various transformer faults and the associated changes in the FRA signature was compiled and could be used in the formulation of standard codes for power transformer FRA signature interpretation

Impact of transformer model parameters variation on FRA signature

Power transformers are critical components within the electrical power network. In the event that a failure occurs in service, the impact can be far reaching. Not only causing extended outages, but costly repairs and potentially serious injury or fatality can result. The concept of Frequency Response Analysis (FRA) has been successfully used as a diagnostic technique to detect winding deformation, core and clamping structure for power transformers. However, because FRA has been relying on graphical analysis, it calls for an expert person to analyse the results. So far, there are no standard codes for FRA interpretation. This paper investigates the impact of parameters variation of a high frequency transformer model based on distributed parameters approach on the FRA signature. The physical meaning of the model parameters allows the identification of the problem inside the transformer and helps in establishing a standard code for FRA signature interpretation

Standardization of DGA interpretation techniques using fuzzy logic approach

Dissolved gas analysis (DGA) of transformer oil is one of the most effective power transformer condition monitoring tools. There are many interpretation techniques for DGA results. However, all of these techniques rely on personnel experience more than standard mathematical formulation. As a result, various DGA interpretation techniques do not necessarily lead to the same conclusion for the same oil sample. DGA interpretation is yet a challenge in the power transformer condition monitoring research area. To alleviate this issue, this paper introduces a fuzzy logic approach to help in standardizing DGA results quantification and classification using various interpretation techniques such as key gas, Rogers ratio, IEC ratio, Doernenburg and Duval triangle methods. In this context, DGA results for 2000 oil samples have been collected from different transformers of different ratings, life span and operating conditions. Traditional DGA interpretation techniques are used to analyze the results which are then compared with the results of the fuzzy logic models. Results show that the fuzzy logic models enhance the consistency among all current interpretation techniques and can eliminate the need for expert personal to interpret DGA results

Characterization of transformer FRA signature under various winding faults

Frequency response analysis (FRA) is gaining global popularity in detecting power transformer winding and core deformations due to the development of FRA test equipment. However, because FRA relies on graphical analysis, interpretation of its signatures is still a very specialized area that calls for skillful personnel to detect the sort and likely place of the fault as so far, there is no reliable standard code for FRA signature classification and quantification. This paper aims to initiate the establishment of standard codes for FRA signature interpretation through comprehensive simulation analysis on a detailed transformer distributed parameters-based model. Various mechanical faults such as axial displacement, buckling stress, disk space variation and bushing fault are simulated on the model to study its impact on the FRA signature. The main contribution of this paper is the comprehensive table it presents for FRA signature sensitivity to winding and core deformations that can be used for classification and quantification of the transformer FRA signature

Online Transformer Internal Fault Detection Based on Instantaneous Voltage and Current Measurements Considering Impact of Harmonics

This paper investigates the performance of a recently proposed online transformer internal fault detection technique and examines impact of harmonics through detailed nonlinear simulation of a transformer using three-dimensional finite element modelling. The proposed online technique is based on considering the correlation between the instantaneous input and output voltage difference (ΔV) and the input current of a particular phase as a finger print of the transformer that could be measured every cycle to identify any incipient mechanical deformation within power transformers. To precisely emulate real transformer operation under various winding mechanical deformations, a detailed three-dimensional finite-element model is developed. Detailed simulations with (non)sinusoidal excitation are performed and analysed to demonstrate the unique impact of each fault on the ΔV-I locus. Impact of harmonic order, magnitude and phase angle is also investigated. Furthermore, practical measurements have been performed to validate the effect of winding short circuit fault on the proposed ΔV-I locus without and with the impact of system harmonics

Application of HEC-RAS for Drainage Capacity Analysis in Sungai Jempol, Negeri Sembilan

Floodplain research is important for human existence and the social economy. It can be observed that the positions of buildings impacted by flooding, such as bridges and roads, cannot be properly matched to the floodplain site in stream floodplain analysis using most computer models. The purpose of this study is to develop an output of Hydrologic Engineering Center’s River Analysis System (HEC-RAS) hydraulic model that will allow for one-dimensional steady flow analysis and stimulate the flood area for 20, 50 and 100 years. This study is applied to Sungai Jempol catchment area, located in Jempol. Floodplain data features such as length of streams, bank position, streamline and cross-sections were used to produce river flow and its cross-sectional shape for each station along the study area. Total of 3 flow rate values were used to indicate an increase in the water level in order to accommodate the additional amount of water that flow into river. The results show that water will overflow into the floodplain at maximum flow rate of 9m3/s or 20 years of return period. The hydraulic model had indicated that 5 out of 30 stations were unable to accommodate the maximum flow rate and thus will led to flooding. By developing the hydraulic model, it clearly shows that the results are more reliable and the affected area can be easily identified. The developed flood model can be a very useful tool in flood management of Sungai Jempol in terms of river development planning, flood mitigation measures, flood evacuation planning and addressing public awareness. This study proved that HEC-RAS is one of effective instrument for analysis and modeling

Observation of temporary accommodation for construction workers according to the code of practice for temporary construction site workers amenities and accommodation (ms2593:2015) in Johor, Malaysia

The Malaysian government is currently improving the quality of workers temporary accommodation by introducing MS2593:2015 (Code of Practice for Temporary Site Workers Amenities and Accommodation) in 2015. It is in line with the initiative in the Construction Industry Transformation Programme (2016-2020) to increase the quality and well-being of construction workers in Malaysia. Thus, to gauge the current practice of temporary accommodation on complying with the particular guideline, this paper has put forth the observation of such accommodation towards elements in Section 3 within MS2593:2015. A total of seventeen (17) temporary accommodation provided by Grade 6 and Grade 7 contractors in Johor were selected and assessed. The results disclosed that most of the temporary accommodation was not complying with the guideline, where only thirteen (13) out of fifty-eight (58) elements have recorded full compliance (100%), and the lowest compliance percentage (5.9%) are discovered in the Section 3.12 (Signage). In a nutshell, given the significant gap of compliance between current practices of temporary accommodation and MS2593:2015, a holistic initiative need to be in place for the guideline to be worthwhile

Novel Control Algorithm for control of qZSI as Front - End Converter during nonsunlight hours

Degrading effect of energy generation from fossil fuel are extensively discussed and debated leading to paradigm shift to renewable energy generation. Energy generation from PV panels is the best alternative for state of Qatar which gets abundant sunlight throughout the year. Development of energy generation from PV panels helps in achieving the notion of "Energy Security". Energy security refers to availability of reliable, cheap and quality power for consumption from customer point of view. Development in power electronics helps in achieving this idea by developing and operating converters circuits with good efficiency, efficacy, reliable, robust and free from maintenance. Encouraging the nurture and development of local energy suppliers will help in minimizing the cost of installation and maintenance. Including these economic constraints in the design of converters has become a crucial factor in developing industry oriented products through academic research. Suitability of several power converters for synchronizing the power generated from PV panels to utility grid. Recently developed Impedance source based converters are highly suitable for synchronizing the power generated from renewable energy to the utility grid. They eliminate the need for extra dc-dc converter by boosting the input voltage supplied from PV panels. Impedance source based converters are categorized as: Z Source Inverter and quasi Z Source Inverter (qZSI). qZSI is preferred due to its higher performance and continuous input current. Several methods are discussed in the literature to achieve boosting of input voltage. Inverter control requires modification in conventional Sine-Triangle compared based PWM. Operation of qZSI at different MPPT algorithms is also discussed. Cascaded qZSI operation to achieve higher power rating are also discussed. Implementation of advanced control techniques such as Model predictive control is also presented. Energy efficient qZSI achieved through different methods are also discussed. This paper presents novel control algorithm for control of qZSI as Front-End Converter (FEC) during non-sunshine hours. During sunshine hours, qZSI is controlled to inject active and reactive power into the grid. In absence of sunlight, qZSI can be operated as FEC to control reactive power management with the utility grid. To validate the proposed control algorithm, simulation results are presented for grid-connected qZSI powered from solar panel as shown in Fig. 1. Simulation results are formulated into following three sections: (a) Control of qZSI for active and reactive power management, (b) Transient response for qZSI to FEC transition and (c) Control of FEC for reactive power management.Control Algorithm: Control algorithm must satisfy the following requirements: a) When controlled as qZSI, i) Boosting of input voltage must be controlled to achieve the desired output rms voltage ii) Current injected into the grid can be at any power factor - unity, lagging or leading. b) Smooth transition from qZSI to FEC. c) When operated as FEC, i) DC Bus Voltage must be maintained constant and ii) Controlled reactive power management must be achieved. Proposed control algorithm is as shown in Fig. 2. It consists of two types of control blocks. Control blocks which are specific to a type of control algorithm and other which are common for both. Converter reference voltage generation and conventional Sine - Triangle comparison is common to control algorithms of both the inverters. For control of the inverter as qZSI, condition of Vin>Vth must be satisfied which means voltage generated from PV panels is sufficient for grid synchronization. During this mode, S1 and S3 are closed and S2 is opened. qZSI control consists of grid current control and dc bus voltage (Vdc) control. Active and reactive power demand is converted to current proportional and passed through PI controller to generate the converter voltage reference. DC Bus voltage controller gives the shoot-through duty cycle (D). Based on the value of D, shoot-through pulses are ORed with conventional pulses generated by sine-triangle comparison. When Vin>Vth is not satisfied, then the position of relays is changed. S1 and S3 are opened and S2 is closed. Due to this, the solar panel is disconnected from the inverter. The dc bus formed due to series connection of C1 and C2 must be controlled from the grid voltage. The dedicated control block shown in Fig. 2 for FEC generates the active current reference and add it up with required reactive current reference to give the grid current reference. This is passed through PI Controller to give the converter voltage reference. Conventional Sine-triangle comparison is performed to generate switching pulses.SIMULATION RESULTS To verify the control algorithm, the simulation results are shown in Fig. 3. Up to t = 2 sec, the inverter is operated as qZSI injecting controlled active power into the grid. At t = 2 sec, the relays are operated disconnecting the solar panel at the input and now inverter is controlled as FEC. Due to this, the dc bus voltage shoots up which is controlled with the control algorithm. To maintain the dc bus voltage, active current is drawn from the grid. Active current drawn is negligible compared to reactive power managed with the utility grid. Figure 3(a) shows the response of dc bus tracking during the operation. In qZSI mode, active power injection is controlled as shown in Fig. 3(b) and Fig. 3(c). When the inverter is controlled as FEC, reactive power absorbed and supplied are shown in Fig. 3(d) and Fig. 3(e) respectively.qscienc