Research On Mechanism Of Continuous Wave Signal Generator Controlled By DSP And The Wind Tunnel Simulation Test

MWD is a new logging technology which is developed in recent years, it can improve large displacement wells, horizontal wells in difficult engineering control and formation evaluation capabilities, improve the rate of oil drilling encountered. Data signal transmission plays a pivotal role in the MWD system design, and is the core in the system design. For low MWD data transmission rates and the difficult test questions in design process, the paper researched on mechanism of continuous wave signal generator controlled by DSP and the wind tunnel simulation test, made some progress and useful conclusions.In this paper, we explore the use of theoretical analysis, system design, computer simulation and wind tunnel simulation method of combining. At the basis of research on telemetry signal transmission mechanism, continuous wave signal generator working mechanism, the principle of wind tunnel tests and other analytical studies, completed a signal generator, DSP control system, wind tunnel test model of the structure and control system design. On this basis, wind tunnel tests and computer simulation experiments were done, and built a variable frequency pressure wave transmission predictive control model and the optimization algorithm model of impeller design. The main goal of the paper is to achieve higher data rates, improve the reliability of data transmissions, as well as enhance the system environmental adaptability, and to lay a foundation at theoretical and experimental methods for our own independent intellectual property rights of continuous mud wave MWD system.Analysis of the bottom telemetry signal transmission mechanism showed that the mud continuous wave represents the development direction of MWD wireless data transmission technology. By analyzing the data encoding, M-ary frequency modulation mode was selected to modulate the down-hole information. Compared with M-ary phase modulation transfer mode, M-ary frequency modulation mode has relative simple sending and receiving equipment and control system, and relative low bit error rate is conducive to improve data transfer rate. Ground to down-hole and down-hole to ground data transmission protocols were developed,and it created conditions to achieve variable frequency data transmission.Studying on rotation working mechanism of the down-hole pressure control signal generator have shown that the type and changes of the pressure fluctuation signal depend on the movement of the signal generator valve. The strength of the pressure wave signal primarily depends on the largest flow area and the smallest flow area of the rotary valve. Through analysis of signal generation and attenuation, completed the design of the structural model of the continuous wave signal generator and the design of DSP-based control system. It provided sending data conditions for wind tunnel simulation. DSP control signal generator sending data tests show that the system can meet the frequency range of 12Hz~36Hz M-ary digital FM transmission control requirement.Research and analysis on principle of wind-tunnel test show that the actual wind tunnel tests can only meet part of similarity criterion, do part of simulations. Similar models were Set up to do continuous wave signal transmission test by simulating down-hole multiphase flow with gas flow in the wind tunnel, and the flow area of the wind tunnel test model structure was corrected. Studies have shown that the wind tunnel can simulate the test of non-gas flow conditions. Through the wind tunnel simulation, the test efficiency could be improved and the test cost could be reduced.The simulation test shows that the thickness of the rotor blades, the gap between the rotors and stators, the taper of the rotors are the main factors which decide the rotor torque. On this basis the optimal valve design principles are given: To ensure the rotor valve is stable-opened, and to minimize the rotor valve torque. The rotary valve pressure changes simulation results show that the pressure response curves of round-shaped valve are more smoothing than the fan-shaped pressure response curve, and more similar to sine wave. Such characteristics of signal are favorable to signal transmission. The wind tunnel simulation tests proved that the conclusions by simulation tests and analysis computations are correct.A training algorithm was proposed to expand the hidden layer of back-propagation network, and combined with improved ant colony algorithm. The training accuracy and precision of prediction of the network were improved. Wind tunnel simulation tests show that symbol transmission frequency range of 12Hz~36Hz is suitable. A variable-frequency data transmission model was proposed. The data was sent in different M-ary frequency modulation. The signal was received in the wind tunnel test section and simulated and processed with Matlab. These data were trained as samples of the neural network. In practical applications, data reception bit error rate (BER) of different transmission modes will be predicted with well trained network. Suitable means of data transmission are selected according to the results of prediction. In this way, the system could achieve higher data rates, improve job reliability, and enhance the adaptability to the environment.