Publications

The special temperature-pressure environment and narrow safety density window of the deepwater formation pose a great challenge to wellbore pressure control during drilling. The downhole variable-gradient drilling method is an effective idea to solve this challenge. However, previous studies mainly focused on the theoretical adaptability analysis of this method, while the experimental feasibility verification has not yet been reported. In this paper, based on the segmental control principle of wellbore fluid density, we set up an indoor physical experiment system to investigate the feasibility of variable-gradient drilling method based on downhole cyclone separator. Using this experimental system, we investigated the effect of drilling fluid physical parameters, hollow glass microsphere (HGMS) performance parameters and engineering parameters on the separator separation efficiency, wellbore pressure gradient and HGMS slip rate. The experimental results revealed that the separator could separate the HGMSs into the annulus from the fluid mixture in the drill pipe. The separation efficiency increased with the increase in the HGMS diameter, HGMS concentration and flow rate, while decreased with the increase in the HGMS density and fluid viscosity. The HGMS density and HGMS concentration were the key factors affecting the annulus pressure gradient value, and the separator separation efficiency was the main factor determining the difference of the annulus pressure gradient. The HGMS slip rate was highly sensitive to its diameter and fluid viscosity, and a combination of optimal HGMS diameter and fluid viscosity could avoid the drilling risk caused by the HGMS slippage. Therefore, the variable-gradient drilling method based on downhole separator is feasible, which is able to create two or more pressure gradients in the annulus. This study could provide guidance for the optimization of key parameters and the development of equipment related to the variable-gradient drilling.

Abstract Compared with acceleration-based modal analysis, displacement can provide a more reliable and robust identification result for output-only modal analysis of long-span bridges. However, the estimated displacements from acceleration records are frequently unavailable due to unrealistic drifts. Aiming at obtaining more accurate and stable results for determining the modal parameters, this study develops a multi-rate weighted data fusion approach for estimating displacement responses in dynamic monitoring of structures based on global navigation satellite system (GNSS) and acceleration measurements. The approach initially derives the local estimations from displacement and acceleration sensors via a Kalman filter algorithm with colored measurement noise, and later uses a weighted fusion criterion of scalar linear minimum variance to fuse the results of local estimations. Then, structural modal pamameters are identified by employing data-driven stochastic subspace identification (SSI) algorithm. The proposed approach is validated in a four degree-of-freedom numerical model and then applied to a long-span bridge in engineering practice. The results illustrate that the proposed approach can reduce the error of GNSS-obtained displacement and expand recognizable frequency range by introducing dynamic displacement component from acceleration measurement.

A numerical procedure including the incremental strain-controlled strategy proposed by the authors is presented here for analyzing the equilibrium path of elastic-plastic frame. Some numerical examples demonstrate that this strategy is an effective means to generate consistent stiffness matrix. The programming code for the incremental strain-controlled strategy can be easily produced from those for the well-known load-controlled scheme and/or displacement-controlled scheme.The incremental strain-controlled strategy can be conducted independently of the setting of system coordinates which is important to generate consistent stiffness matrix by means of the displacement-controlled scheme.

The attitude determination of satellite has been executed in many satellite missions using different sensors like magnetometer, gyroscopes and sun sensors but the cost, weight and power requirements motivate the researchers for standalone GPS based attitude determination system. The attitude determination of small satellites can be obtained by using the phase based measurements from at least three commercialofftheshelf (COTS) GPS antennas/receivers mounted on the surface of the satellite with known baseline measurements. The code measurements are not as accurate as the phase measurements so this research contribution presents the GPS phase-based attitude determination algorithm while post processing the static test data and implementing the algorithm in MATLAB environment. The single-point positioning is used for determining the position of the Master antenna, and differential positioning is done to find the slave antennas' position and baseline coordinates after implementing the LAMBDA method for ambiguity resolution. Finally, attitude is determined and compared using the Unscented Kalman filter. Various GPS signal and system errors like ephemeris, clock. Ionospheric and Tropospheric errors along with satellite geometry are also calculated. The GNSS Based attitude determination for short baseline using COTS GPS receiver with three antennas are explored analytically and implemented in MATLAB environment using the real static GPS data in RINEX format

Based on the curve steel box girder bridge on a city interchange ramp,refer to the existing research result and formerly design experience,summarized the key points of design and construction scheme.

With the growing demand for high-performance polymer composites, conventional single- and twin-screw extruders often fall short of meeting industrial requirements for effective mixing and compounding. This research investigates the kinematic behavior of the plasticization and transport mechanisms in tri-screw extruders when subjected to a vibrational force field. The study specifically examines how applying vibrational force technology can improve the efficiency of polymer mixing. Vibration force field means that in a three-screw mechanism, an axial vibration is applied to the middle screw to produce a vibration force field. Through the development of mathematical and physical models, this study analyzed the motion dynamics of the screw and the influence of a vibrational force field on polymer transport and mixing efficiency. The findings indicate that, in comparison to traditional twin-screw extruders, tri-screw systems can achieve higher shear and elongational rates, leading to enhanced polymer mixing uniformity. Furthermore, applying an axial vibrational force field significantly influenced the shear and elongational strain rates of the material, thereby optimizing its rheological behavior and processing quality. This research not only establishes a theoretical foundation for the design and optimization of tri-screw extruders but also opens new pathways for the efficient processing of high-viscosity composite materials.

The elastic-plastic behavior of the circle-castellated steel beam is analyzed using finite element method. Stress distribution, expansion of plastic zone and flexural deflection are investigated under two simulation loads of the uniform pressure and concentration force. The results show that this kind of beam provide references for us to strengthen structural bear capacity.