An Isotache Model for Frozen Soil Taking Account the Effect of Creep on Plastic Yield Pressure

Xiaoliang Yao,Jilin Qi,Xiangping Qiao,Mengxin Liu 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.2

Plastic yield pressure is a key factor influencing mechanical behavior of frozen soil. In this paper, an isotache model taking account the effect of creep on plastic yield pressure was modified to describe the mechanical behavior of frozen soil. A series K0 compression tests after different creep time and at different temperature were carried out on a fine grained soil obtained from Qinghai-Tibet plateau. Based on analysis of the tested results, it was proved that the strain development of the tested frozen soil obeys the postulation of parallel lines in isotache model. Meanwhile, the development of plastic yield pressure with creep strain is inversely related to temperature, which can be reasonably described by exponential function deduced from the isotache model. The sharp strain increase of frozen soil can be captured by the isotache model when the surcharge loading exceeds the plastic yield pressure. After modifying the isotache model as temperature dependent, mechanical behavior of frozen soil at different temperature can be described reasonably, and the development of plastic yield pressure with creep strain and temperature can be calculated conveniently.

Consolidation of Thawing Permafrost Considering Phase Change

Jilin Qi,Xiaoliang Yao,Fan Yu 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.6

When permafrost thaws, consolidation occurs under surcharge loads, leading to settlement which is one of the largest threats to infrastructures constructed in permafrost regions. This paper proposes a three dimensional thaw consolidation theory combining Biot’s consolidation theory with heat conductive equations considering ice-water phase change effects through specific heat. Numerical simulation was implemented. The theory was verified by comparing the degree of consolidation and pore pressure ratio calculated by this theory with that from closed form solutions for a simplified one dimensional problem. Thaw consolidation tests were carried out on frozen soil samples with four water contents and under two surcharge loads. Strains occurring in the tests were compared with those from the numerical calculations. It is found that with low water contents in the frozen soil, strain from thaw consolidation was relatively small, and was well simulated by the proposed theory. With increase in water content of frozen soils, the discrepancy between calculated and test results increases.

Stability analysis of deepwater compliant vertical access riser about parametric excitation

Lou, Min,Hu, Ping,Qi, Xiaoliang,Li, Hongwei The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

Stability analysis of deepwater compliant vertical access riser about parametric excitation

Min Lou,Ping Hu,Xiaoliang Qi,Hongwei Li 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

Influencing factor analysis of water invasion in condensate gas reservoir with bottom water based on fuzzy comprehensive evaluation and orthogonal experiment

Wende Yan,Zhilin Qi,Yingzhong Yuan,Xiaoliang Huang,Jiqiang Li 한국자원공학회 2019 Geosystem engineering Vol.22 No.6

Condensate oil and water invasion coexist in the condensate gas reservoir with bottom water. Because of influences of condensate oil pollution and water invasion, gas recovery obviously decreases. There are many factors influencing water invasion in a condensate gas reservoir with bottom water, including static petrophysical properties and dynamic operational conditions. Various factors play different roles in the process of water invasion, and the comprehensive effects of them on water invasion are difficult to be determined because these factors interfere with each other. With gas reservoir engineering method and numerical simulation technology, the factors including acuifer size, height of water avoidance, permeability, effective gas pay thickness, condensate oil saturation and gas well production rate on water invasion are researched. Water breakthrough time, stable production period and gas recovery are calculated for different cases under different parameter combinations through fuzzy comprehensive evaluation and orthogonal experiment design. Then sensitivities of these factors are analyzed and main factors influencing water invasion are selected and sequenced. The research supply theoretical basis for preventing and controlling water invasion thus improves development effect of condensate gas reservoir with bottom water.

Experimental investigation of the preferred Strouhal number used in self-resonating pulsed waterjet

Deng Li,Youping Chen,Yong Kang,Zu’an Wang,Xiaoliang Wang,Qi Fan,Miao Yuan 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.9

Self-resonating pulsed waterjet (SRPW) is superior to plain waterjet in many ways and is being employed in numerous applications. To further improve the performance of SRPW, the optimal value of the preferred Strouhal number (S d ), which is used to determine the chamber length of a self-resonating nozzle, was experimentally studied at inlet pressures of 10 MPa and 20 MPa. The axial pressure oscillation peak and amplitude were used to evaluate the performance of SRPW, in order to find the optimum S d value. Results show that S dvalue determines the self-resonance behavior of an organ-pipe nozzle and greatly affects the intensity of the axial pressure oscillation. Under the experimental conditions, the optimum S d values are 0.315 and 0.278 respectively, corresponding to inlet pressures of 10 MPa and 20 MPa. Compared with the default value of 0.3 obtained from air jet experiment, the optimum S d value at inlet pressure of 10 MPa is a little larger and oppositely a bit smaller at inlet pressure of 20 MPa. Thus, if the inlet pressure is not considered, S d value of 0.3 is reasonable for determining the chamber length of a self-resonating nozzle for generating effective SRPW.

Optimal LQG Control for Networked Control Systems with Remote and Local Controllers

Xiao Liang,Juanjuan Xu,Xiao Lu,Qingyuan Qi,Haixia Wang,Rong Gao 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.1

We consider the finite horizon optimal LQG control problem for networked control systems with a remote controller, a local controller and communication channels with packet dropouts and transmission delays. The local controller can directly observe state signals and send them to the remote controller via a packet-dropout channel. Then the remote controller sends the received measurement signals to the local controller. Afterwards, the two controllers operate the plant through a delayed channel. The contributions of this paper are as follows: Firstly, at the side of the remote controller, we develop an optimal estimator to show that the separation principle holds. Secondly, we derive a non- homogeneous relationship between the state and the costate of systems in virtue of the maximum principle. Finally, a necessary and sufficient condition for the optimal control problem is derived in terms of the two coupled Riccati equations. Numerical examples are employed to illustrate the theoretical results.