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Optical displacement detection is widely used in various micro-electro-mechanical system (MEMS) sensors because of its high sensitivity. The optical accelerometer has a high theoretical resolution. However, due to the small working range of optical detection, the open-loop measuring range of a high-resolution optical accelerometer is usually only tens to hundreds of milligrams. To increase the measurement range, we propose a high-resolution micro-optical accelerometer with electromagnetic force feedback. The optical principle, mechanical structure, and manufacturing process are analyzed. The accelerometer is predicted to work in the first modal with displacement sensitivity at 2.56 µm/g, corresponding to 0th diffraction beam optical sensitivity 1.93%/nm. The designed electromagnetic driver can increase the acceleration measurement range from 0.012 to ± 20 g . These results provide a theoretical basis for the design and fabrication of a high-resolution micro-optical accelerometer with an electromagnetic driver. The electromagnetic drive scheme introduced effectively improves the dynamic range of high-precision optical accelerometers and can be applied to other optical MEMS sensors.

According to logging data of the field, while drilling in the deep water without riser, rules of motion and stress distribution of drilling string is really complicated without the constraint of riser because of the comprehensive action of working load, environmental load, movement of platform, whirl of drilling string and so on. Especially with the increase of water depth, the drill string will vibrate severely when the speed reaches the critical value, which easily causes the dynamic failure of the drill string. Based on rotor dynamics theory, this paper has established the mechanics calculation model of nonlinear support drill string without riser to analyze the influences of bearing stiffness, water depth and section size of drill string on critical speed of drilling string. The result shows that critical speed of whirl of drilling string is decreased with the increase of wall thickness; critical speed of whirl of drilling string is decreased with the increase of the length of string in water; critical speed of whirl of drilling string is increased with the increase of the stiffness of bearing. According to the results, reasonable speed of drilling string has been given to prevent resonance. The results can be used as reference for deepwater drilling operations without riser.