Conversion of the wavelength distribution to the energy spectrum of the wave

When designing a vessel, spectral calculating methods of wave induced oscillation are used, and during vessel operation, available technical means allow us to obtain only the pitch spectrum. For a complete solution of navigational tasks, it is necessary to have a wave disturbance spectrum and pitch amplitude-frequency characteristic as well. The latter function can be received in sailing, if obtaining the actual wave disturbance spectrum is possible. The lack of available and sufficiently accurate methods of actual wave disturbance assessment in modern navigation creates the need to use statistical mathematical models in addition to available information in order to connect various wave elements. Taking into account the possibility of obtaining the wavelength distribution from the wave field radar image, a hypothesis is formulated about the possibility of using a statistical mathematical connection between the wind wave lengths and heights. Within the proposed hypothesis, an algorithm is presented for converting the actual wavelength probability distribution obtained from wave field radar images into the disturbance frequency spectrum. The conclusion is made about possible application of the hypothesis in pitch transfer function assessment.

Ship course control system with compensation of external disturbance on steering gear

The article focuses on developing synthesis methods for automatic heading control systems for the rudder-controlled sea vessel. The solution of the problem of vessel heading control is carried out in the conditions of heavy sea. The disturbing effect of the external water environment causes the vessel yawning, which results in exceeding activity of the steering gear. This leads to its increased wear and loss in the longitudinal speed of the vessel. To reduce the wave effect there has been supposed an approach based on the additionally introduced internal model of the ship dynamics. The given approach is aimed at improving the operation of the steering gear in rough seas. To implement the proposed algorithm, changes are made to the original system by introducing an internal model in parallel to the control object and modifying the feedback channel of the control system. To describe the sea vessel dynamics there is used the 1st order Nomoto model, the steering gear model is implemented in accordance with the imposed speed limits and the rudder shift value. Wave disturbance is close to harmonic disturbance. The identification of the parameters of the internal model can be carried out in advance, both by maneuvering tests and by the process of operation. Numerical simulations carried out in the MATLAB/Simulink system confirmed the advantage of the proposed approach. The synthesis of control in a system with an internal model makes it possible to significantly neutralize the influence of wave disturbance. The modifications introduced to the original control system help to improve functioning of the steering gear, significantly reducing the number of rudder shifts during operation.

Study on the influence of stress wave disturbance on ultra-low friction effect of broken blocks

With the increase of mine mining depth, deep rock mass tends to be broken into block medium. The roof-rock layer-floor can be regarded as block system fractured rock mass. Under the condition of high ground stress and mining disturbance, the ultra-low friction effect of block system fractured rock mass is easy to occur, and then induce rock burst and other disasters. Taking the block rock mass as the research object, the self-developed ultra-low friction test system is used to carry out the experimental research on the ultra-low friction effect of the broken block under the condition of stress wave disturbance. Taking the horizontal displacement of the working block as the characteristic parameter reflecting the ultra-low friction effect, by changing the stress wave disturbance frequency and amplitude, the characteristic law of the horizontal displacement, acceleration and energy of the working block during the occurrence of the ultra-low friction effect is analyzed. The research results show that the stress wave disturbance frequency is related to the generation of ultra-low friction of the broken block. The disturbance frequency of the stress wave is within 1 ~ 3Hz, and the maximum acceleration and horizontal displacement of different broken degree blocks increase significantly. This frequency range is prone to ultra-low friction effect. The greater the intensity of the stress wave disturbance, the higher the degree of block fragmentation, and the more likely to have ultra-low friction effects between the blocks. The greater the intensity of the horizontal impact load, the higher the degree of rock mass fragmentation, the easier it is for ultra-low friction effects to occur. Stress wave disturbance and horizontal impact are the main reasons for the sliding instability of broken blocks. When the dominant frequency of the kinetic energy of the broken block is within 20 Hz, the ultra-low friction effect is more likely to occur.