Experimental and Numerical Study on Vibration of the Full-Revolving Propulsion Ship Stern

In order to solve the severe vibration problems of an ocean engineering ship with a full-revolving propulsion system, the navigation tests, including forced vibration response test and modal test, are carded out in its stem. It is concluded from the comparison of the time-domain waveform and spectrum from different measurement points that three main factors lead to a high-level stern vibration. Firstly, the specific dynamic stiffness of a water tank is relatively small compared with its neighbor hold, which makes it act like a vibration isolator preventing vibrational energy transmitting to the main hold. Secondly, there exists high-density local modes in the working frequency range of the main engine and thus the local resonance occurs. Thirdly, the abnormal engagement of gears caused by the large deflection of the shaft bearing due to its low mounting rigidity leads to violent extra impulse excitations at high speeds. Then the modification against the dynamic defects is given by simply improving the specific stiffness of the water tanks. And the effect is validated by the FEM calculation. Some important experience is obtained with the problems being solved, which is useful in the design of ships with the same propulsion system. It is also believed that the dynamic consideration is as important as the static analysis for the ships, and that most of the vibration problems may be avoided with a proper acoustic design.

Grouping bi-chi-squared method for pulsar navigation experiment using observations of Rossi X-ray timing explorer

X-ray pulsar-based navigation is a revolutionary technology which is capable of providing the required navigation information in the solar system. Performing as an important pulsar-based navigation technique, the Significance Enhancement of Pulse-profile with Orbit-dynamics(SEPO)can estimate orbital elements by using the distortion of pulse profile. Based on the SEPO technique,we propose a grouping bi-chi-squared technique and adopt the observations of Rossi X-ray Timing Explorer(RXTE) to carry out experimental verification. The pulsar timing is refined to determine spin parameters of the Crab pulsar(PSR B0531+21) during the observation periods, and a short-term dynamic model for RXTE satellite is established by considering the effects of diverse perturbations.Experimental results suggest that the position and velocity errors are 16.3 km(3σ) and 13.3 m/s(3σ) with two adjacent observations split by one day(exposure time of 1.5 ks), outperforming those of the POLAR experiment whose results are 19.2 km(3σ) and 432 m/s(3σ). The approach provided is particularly applicable to the estimation of orbital elements via using high-flux observations.