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Old-well sidetracking is a key method for controlling low-productivity wells in the Bohai oilfield. This study employs reservoir engineering and numerical simulation techniques to investigate the maximum drainage radius and natural coning control mechanism in heavy-oil reservoirs with bottom water. Based on these findings, an alternate production technology was developed for dual-branch horizontal wells. The technology creates a new branch through sidetracking, connecting and isolating the old and new wellbores using a combination of wall hangers and branch guides. Initially, the old wellbore with an ultra-high water cut is temporarily sealed. When the new branch reaches a high water-cut stage, production is switched back to the old wellbore. This technology was successfully applied to three wells in the Bohai oilfield, resulting in the new branch achieving expected production levels, while reopening the old wellbore increased daily oil output by 27 m3 and reduced water cut by 5.6%. Cumulative oil production from these wells reached 95,000 m3. This technology improves well-slot resource utilization, enhances recovery rates, and has significant potential for broader application. [ABSTRACT FROM AUTHOR]

The inertial navigation system is aligned and leveled before the launch of a long-range vehicle. However, the non-uniformity of the Earth can lead to initial state errors including initial positioning errors and initial orientation errors, causing navigation errors in flight dynamics and eventually impact-point deviations up to approximately 1 km. In order to analyze the propagation mechanisms of initial state errors and rapidly estimate their influence magnitudes, navigation perturbation equation subject to apparent acceleration coupling is established based on state space perturbation theory in the launch inertial coordinate system. Afterwards, a series of analytical form of deviations are derived including gravitational acceleration deviation, apparent acceleration projection deviation, apparent acceleration coupling deviation, initial velocity errors and initial position errors. Then, the analytical propagation model of engine-cutoff state deviations and impact-point deviations are acquired by solving the navigation perturbation equation. In the simulations, computer codes are programmed to calculate the propagation matrices of engine-cutoff state deviations and impact-point deviations in the case of fixed launch azimuth, followed by the propagation mechanism analyses of initial state errors. Next, two more scenarios of different launch azimuths and different launch points are simulated to further verify the reliability of the proposed analytical propagation model. The results show that analytical solutions of the propagation model proposed in this paper can well coincide with numerical solutions, with relative errors being all less than 1%, which is also suitable for multiple distinct simulation scenarios compared with previous methods. [ABSTRACT FROM AUTHOR]

Considering the voltage difference between the neutral points of the DC side and the AC side, this study first establishes the differential mathematical model of the modular multilevel converter (MMC). Then, through the proposed successive approximation approach, the analytical expressions of the electrical quantities are derived, including the arm voltage and current, the output voltage and current, the capacitor voltage and current, the voltage difference between two neutral points, the instantaneous active and reactive power, the arm reactance voltage and the current of switching devices. The proposed successive approximation approach contains three main steps. In step 1, the preliminary analytical expressions of the MMC's electrical quantities based on the ideal step wave of the arm voltage with constant SM's capacitor voltage is deduced; step 2 is to derive the final analytical expressions of the MMC's electrical quantities according to the time-varying SM's capacitor voltage expression which is derived in the first step; and the convergence is analysed in step 3. A simulation model of the MMC is realised in PSCAD/EMTDC and the results show that the complete analytical model coincides well with the simulation results and has a higher accuracy than the traditional model. [ABSTRACT FROM AUTHOR]

Transient excitation boosting control (TEBC) is a cost-effective emergency control technique to improve the power system transient stability. However, it is found in this study that the conventional TEBCs have some drawbacks and may be ineffective or even worsen the system stability in some cases. To overcome these problems, a novel widearea measurement system (WAMS)-based TEBC (WTEBC) is proposed in this study. The proposed control law is as follows: boosting the excitation of the critical machines (CMs) in the critical swing and stopping their excitation boosting as the rotor angles of the CMs drop below a threshold after the critical swing. The implementations of the above control law in the special protection system are also provided. The simulation results from the 4-machine system and the China Southern power grid prove the superiority of the WTEBC over the conventional TEBCs. Furthermore, it also indicates that the stabilising effect is quite significant as long as the round-trip WAMS delay is <0.3 s, which further confirms the feasibility of the WTEBC in the practical engineering. [ABSTRACT FROM AUTHOR]

This paper proposes a LCC and MMC hybrid HVDC topology with dc line fault clearance capability suitable for bulk power transmission, in which the rectifier adopts a line commutated converter (LCC) and the inverters adopt two modular multilevel converters (MMCs). Resiliency to dc line faults can be achieved by alpha-retard of the LCC and the high power diodes installed in the overhead line close to the inverters. The start-up process is implemented in two stages. A hybrid HVDC system is modeled in PSCAD/EMTDC to demonstrate the effectiveness of the control system and the start-up scheme. Moreover, simulation results of a dc line fault confirm the feasibility that the fault current paths can be blocked by alpha-retard of the LCC and the installed high power diodes, and the whole system is able to restart after clearance of the transient dc line fault. [ABSTRACT FROM AUTHOR]

To study the torsional oscillation phenomena of turbine-generators, a fundamental approach is by electromagnetic transient simulation. In this paper, the structure of the damping coefficient matrix of the shaft torsional model for turbine-generators is studied, and a method to determine the values of the elements of the damping coefficient matrix is developed. Through the analysis of different damping components, the most concerned damping component is identified. Based on the complex modal analysis method widely used in the mechanical vibration engineering, the relationship between the damping coefficient matrix and the torsional mode damping is established, furthermore, an iterative method to compute the damping coefficient matrix is developed. A test study on the turbine-generator shaft torsional model of the IEEE first SSR benchmark system indicates that the proposed torsional damping modeling technique in electromagnetic transient simulation is valid and effective. [ABSTRACT FROM AUTHOR]

Chaotic systems perform well as a new rich source of cryptography and pseudo-random coding. Unfortunately their digital dynamical properties would degrade due to the finite computing precision. Proposed in this paper is a modified digital chaotic sequence generator based on chaotic logistic systems with a coupling structure where one chaotic subsystem generates perturbation signals to disturb the control parameter of the other one. The numerical simulations show that the length of chaotic orbits, the output distribution of chaotic system, and the security of chaotic sequences have been greatly improved. Moreover the chaotic sequence period can be extended at least by one order of magnitude longer than that of the uncoupled logistic system and the difficulty in decrypting increases 2128*2128 times indicating that the dynamical degradation of digital chaos is effectively improved. A field programmable gate array (FPGA) implementation of an algorithm is given and the corresponding experiment shows that the output speed of the generated chaotic sequences can reach 571.4 Mbps indicating that the designed generator can be applied to the real-time video image encryption. [ABSTRACT FROM AUTHOR]

This paper presents an integrated linear and nonlinear control for a unified power flow controller (UPFC). Three Pulse-Width Modulation (PWM) parameters of the UPFC are controlled by Proportional-Integral-Differential (PID) laws, and an analytic expression of the nonlinear control law for the UPFC phase angle ρ 2 is obtained by a feedback linearization method. This combined linear and nonlinear control strategy enables the UPFC to improve power system transient stability and dynamic performance effectively. Simulation results illustrate the effectiveness of the developed control strategy. [ABSTRACT FROM AUTHOR]

The contact effect on the performances of organic thin film transistors is studied here. A C60 ultrathin layer is inserted between Al source--drain electrode and pentacene to reduce the contact resistance. By a 3 nm C60 modification, the injection barrier is lowered and the contact resistance is reduced. Thus, the field-effect mobility increases from 0.12 to 0.52 cm2/(V*s). It means that inserting a C60 ultra thin layer is a good method to improve the organic thin film transistor (OTFT) performance. The output curve is simulated by using a charge drift model. Considering the contact effect, the field effect mobility is improved to 1.15 cm2/(V*s). It indicates that further reducing the contact resistance of OTFTs should be carried out. [ABSTRACT FROM AUTHOR]

This paper proposes a universal system control strategy for voltage source converter (VSC) based high voltage direct current (HVDC) systems. The framework of the designed control strategy consists of five layer structures considering the topology and control characteristics of the VSC-HVDC system. The control commands sent from the topmost layer can be transmitted to the next layer based on the existing communication system. When the commands are sent to each substation, the following transmission of commands between the four lower layers are realized using the internal communication system while ignoring the communication delay. This hierarchical control strategy can be easily applied to any VSC-HVDC system with any topology. Furthermore, an integrated controller for each converter is designed and implemented considering all of the possible operating states. The modular-designed integrated controller makes it quite easy to extend its operating states if necessary, and it is available for any kind of VSC. A detailed model of a VSC-HVDC system containing a DC hub is built in the PSCAD/EMTDC environment. Simulation results based on three operating conditions (the start-up process, the voltage margin control method and the master-slave control method) demonstrate the flexibility and validity of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The influence of the cooling water on the vibration mode and damping characteristics of an engine was evaluated through experimental and simulation methods. The wet mode method of the fluid–structure interaction field was applied in numerical analysis, which led to several significant conclusions. Several additional fluid related modes were present when the effect of cooling water was considered. Meanwhile, the frequencies of other modes were almost the same. On the other hand, the damping characteristics of an engine were changed while the cooling water was used. For Rayleigh damping, the cooling water effect has made the mass matrix scale factor α nearly double and the stiffness matrix scale factor β almost unchanged. The engine surface vibration acceleration magnitude was calculated by means of the multi-body dynamic analysis. It was shown that the calculated vibration acceleration magnitude was close to the measured one when the cooling water was taken into account. Furthermore, acoustic simulation results were estimated by Boundary Element Method, which revealed that the sound power level of the radiation noise of most engine components was lower than that with the fluid structure interaction model being applied in the engine block modeling. The overall sound power level of the whole engine radiation noise was increased by 3.6 dB when the effect of the cooling water was considered, which demonstrated that the effect of the cooling water on the engine vibro-acoustic characteristics should not be neglected during the computation. This paper has disclosed the influences of the cooling water on the engine structural modes, damping, sound power level of the engine radiation noise and a systematic approach for evaluation of the influences. [ABSTRACT FROM AUTHOR]