Identification of Primary Failure Modes of Tunnel System and Influence of Supporting Structures on Tunnel System Reliability using Multiple Response Surfaces

Zhiliang Liu,Liang Li,Guangming Yu,Jun Hu,Houlai Lin,Chunli Li,Shibao Lu,Kaiqi Meng,Jun Lei 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.2

A method of calculating the failure probability of the tunnel system combining finite element numerical simulation with multiple response surface method (MRSM) and Monte-Carlo simulation (MCS) is presented. The applicability of the proposed methodology is verified through a subway interval soft rock tunnel in Qingdao, China. The sensitivity of Monte-Carlo sampling number and coefficients of variation for rock masses on the failure probability of tunnel system is conducted. The primary failure modes in tunnel system are identified by reanalyzing the failure samples. The simulation results demonstrate that the failure probability of a tunnel system within soft upper and hard lower surrounding rock mass is mainly attributed to the soft upper part of the surrounding rock. The coefficients of variation of the elastic modulus E1 and the internal friction angle ϕ1 of the pebble layer (soft upper part) have significant effect on the failure probability. The failure probability of tunnel system increases as the coefficients of variation of E1 and ϕ1 increase. Two primary failure modes are found to contribute to the tunnel system reliability. The effect of rock bolt length L and pipe-roof thickness H on tunnel system reliability and two primary failure modes as well are investigated. The simulation results indicate that both the enhancements in L and H tend to be more effective than the enhancement in either L or H if a small target failure probability of tunnel system is expected. The supporting structures design can be performed based on the potential sets of (L, H) satisfying target failure probability.

Residual Synchronization Error Elimination in OFDM Baseband Receivers

Xingbo Hu,Yumei Huang,Zhiliang Hong 한국전자통신연구원 2007 ETRI Journal Vol.29 No.5

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot-aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay-based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision-directed channel gain update algorithm based on recursive least-squares criterion, which offers faster convergence and smaller error than the least-mean-squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.

Novel Active Voltage Quality Regulator with Adaptive DC-Link Voltage Control

Guochun Xiao,Zhong Zeng,Kai Liu,Zhiliang Hu,Zhaoan Wang 전력전자학회 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.6

In this paper, a novel Active Voltage Quality Regulator (AVQR) topology with a thyristor rectifier and an adaptive dclink voltage control strategy are proposed. The proposed AVQR can efficiently mitigate the long duration variations (e.g.undervoltages/overvoltages), voltage imbalances and voltage harmonics. Compared with conventional AVQRs, it can regulate the load voltage very well with a much lower dc-link voltage. This is accomplished by replacing the diode rectifier with a thyristor rectifier. Moreover, its dc-link voltage can vary with the deviations of the supply voltage through the proposed adaptive dc-link voltage control strategy. All of these contribute to its significantly higher efficiency for online operating, which is very important and attractive for many applications. The proposed topology and control strategy are theoretically analyzed in detail. Simulation results are also provided in the paper. Finally, the feasibility and effectiveness of the proposed method are verified by means of experimental results from a 2kVA prototype. Both of the simulation and experimental results show that the proposed AVQR can achieve a much higher efficiency and similar regulation performance when compared with the conventional ones.

A Hybrid Link Protection Scheme for Ensuring Network Service Availability in Link-state Routing Networks

Haijun Geng,Han Zhang,Xingang Shi,Zhiliang Wang,Xia Yin,Ju Zhang,Zhiguo Hu,Yong Wu 한국통신학회 2020 Journal of communications and networks Vol.22 No.1

The internet is playing an increasingly crucial role inboth personal and business activities. In addition, with the emergenceof real-time, delay sensitive and mission-critical applications,stringent network availability requirement is put forward for internetservice providers (ISPs). However, commonly deployed intradomainlink-state routing protocols react to link failures by globallyexchanging link state advertisements and recalculating routingtable, inevitably causing significant forwarding discontinuityafter a failure. Therefore, the loop-free criterion (LFC) approachhas been widely deployed by many ISPs for coping with the singlenetwork component failure scenario in large internet backbones. The success of LFC lies in its inherent simplicity, but this comesat the expense of letting certain failure scenarios go unprotected. To achieve full failure coverage with LFC without incurring significantextra overhead, we propose a novel link protection scheme,hybrid link protection (HLP), to achieve failure resilient routing. Compared to previous schemes, HLP ensures high network availabilityin a more efficient way. HLP is implemented in two stages. Stage one provides an efficient LFC based method (MNP-e). Thecomplexity of the algorithm is less than that of Dijkstra’s algorithmand can provide the similar network availability with LFC. Stage two provides backup path protection (BPP) based on MNP-e,where only a minimum number of links need to be protected, usingspecial paths and packet headers, to meet the network availabilityrequirement. We evaluate these algorithms in a wide spread ofrelevant topologies, both real and synthetic, and the results revealthat HLP can achieve high network availability without introducingconspicuous overhead. HLP not only needs around 10% time ofthat of full protection, but also provides full protection capabilitiesthat full protection provide.

Novel Active Voltage Quality Regulator with Adaptive DC-Link Voltage Control

Xiao, Guochun,Zeng, Zhong,Liu, Kai,Hu, Zhiliang,Wang, Zhaoan The Korean Institute of Power Electronics 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.6

In this paper, a novel Active Voltage Quality Regulator (AVQR) topology with a thyristor rectifier and an adaptive dclink voltage control strategy are proposed. The proposed AVQR can efficiently mitigate the long duration variations (e.g. undervoltages/overvoltages), voltage imbalances and voltage harmonics. Compared with conventional AVQRs, it can regulate the load voltage very well with a much lower dc-link voltage. This is accomplished by replacing the diode rectifier with a thyristor rectifier. Moreover, its dc-link voltage can vary with the deviations of the supply voltage through the proposed adaptive dc-link voltage control strategy. All of these contribute to its significantly higher efficiency for online operating, which is very important and attractive for many applications. The proposed topology and control strategy are theoretically analyzed in detail. Simulation results are also provided in the paper. Finally, the feasibility and effectiveness of the proposed method are verified by means of experimental results from a 2kVA prototype. Both of the simulation and experimental results show that the proposed AVQR can achieve a much higher efficiency and similar regulation performance when compared with the conventional ones.