The integrated strapdown inertial navigation system/global position system (SINS/GPS) is a widely used procedure for position, velocity and attitude determination. There are two options for the state estimation procedure by a filtering system model and the integration filter, namely direct navigation mode that estimates the navigation parameters and indirect navigation mode that estimates the error of navigation parameters with a feedback calculation process. To a certain extent, they both have their own advantages. However, determining which one of the two navigation modes will be more celebrated than the other under different conditions is a beneficial but thus far less seriously treated issue. In this study, two navigation modes are systematically studied in terms of the filtering system model, filtering algorithm and application issues. The simulation test and car-mounted experiments for low-precision and high-precision SINS are carried out to compare the performance of two navigation modes under different conditions. The results prove that direct navigation mode outperforms indirect navigation mode in terms of estimation accuracy and stability for poor conditions, but for good conditions, the advantages of direct navigation mode are compromised due to the large computational burden. Therefore, this study is also expected to facilitate the selection of the appropriate navigation model in practice under different conditions.
As a standard method for noise analysis of fiber optic gyro (FOG), Allan variance has too large offline computational burden and data storages to be applied to online estimation. To overcome the barriers, the state space model is firstly established for FOG. Then the Sage-husa adaptive Kalman filter (SHAKF) is introduced in this field. Through recursive calculation of measurement noise covariance matrix, SHAKF can avoid the storage of large amounts of history data. However, the precision and stability of this method are still the primary matters that needed to be addressed. Based on this point, a new online method for estimation of the coefficient of angular random walk is proposed. In the method, estimator of measurement noise is constructed by the recursive form of Allan variance at the shortest sampling time. Then the estimator is embedded into the SHAKF framework resulting in a new adaptive filter. The estimations of measurement noise variance and Kalman filter are independent of each other in this method. Therefore, it can address the problem of filtering divergence and precision degrading effectively. Test results of both digital simulation and experimental data of FOG verify the validity and feasibility of the proposed method.
There are two options for the state estimation procedure by the integration filter for the integrated SINS/GPS, namely: direct navigation mode and indirect navigation mode. Determining which one of the two navigation modes will be more celebrated than the other under different conditions is an important but so far less seriously treated issue. The two navigation modes were systematically studied in terms of the system model, filtering algorithm and application issues. The car-mounted experiments were carried out to compare two navigation modes under different road conditions. The results show that direct navigation mode performs indirect navigation mode in terms of accuracy and stability. However, indirect navigation mode has low calculation burden and simple filter design.
The high temperature cooling water generated by the power system of underwater vehicle is discharged through the discharge port and mixed with seawater to form a thermal wake, whose thermal characteristics can be easily detected by infrared submersible technology. In order to explore the characteristics of the thermal wake of the underwater vehicle when it rotates in fresh water, this paper uses the finite volume method to establish a three-dimensional scaled SUBOFF mathematical model, and then combines the overlapping grid technology to numerically simulate the rotation of the underwater vehicle in the background waters. The thermal wake experimental platform is established to verify the reliability of the numerical simulation method by comparing the direct flight experiment with the simulation results. The near-field cooling water trajectory and far-field wake spatial evolution behind the rotary body are analyzed, and the abnormal characteristics of water surface temperature are obtained. The results show that the thermal wakes on the turning side and the deviation side are greatly affected by the vortex caused by the body, and have great differences in morphology, motion trajectory and temperature characteristics. When the thermal wakes on both sides rise to the water surface, an arc-shaped water surface temperature anomaly area composed of two high-temperature hot spots is formed.
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