l. dong

To improve the overall performance of marine centrifugal pumps (MCPs), their vibration and noise performances were optimized using the hydraulic design of the volute casing parameters considering a constant hydraulic performance at a specific speed of 66.7. Numerical simulations of the full flow field, vibration, and noise were conducted for each of five volute base circle diameters. The impact of dynamic and static disturbances on the flow and vibration and noise characteristics were investigated. These results provide some theoretical and technical support for the design and application of MCPs. The flow pattern inside the volute becomes more uniform as the D3 increases, but the pressure pulsation decreases. The total vibration levels of the inlet flange, outlet flange, and pump base decreased by 8.3%, 7.9%, and 12.3% respectively. The sound pressure of the flow noise at each characteristic frequency showed a different degree of decreasing trend.

To reduce the noise in a pump piping system and increase the usage time of equipment, a new type of porous muffler is proposed in this paper. A water guide cone is incorporated into the muffler structure, which may help to redirect the fluid media in the piping system. The porous structure is adapted from a muffler shell, water cone wall and round bottom plate. According to this structure, the muffler sample is made, and a pump pipeline system test bench is set up. The outlet noise of the pump pipeline system is measured after installing the muffler. At the same time, the muffler is numerically simulated by combining computational fluid mechanics and Lighthill acoustic theory. The characteristics of the flow field and external sound field under three different flow conditions of 200 m3/h, 400 m3/h and 600 m3/h are assessed. The numerical simulation results show the same dominant frequency and trend as the experimental results. The rationality of the numerical simulation is verified. Research shows that: the level of sound pressure at the muffler's outlet is lower than at the inlet, causing muffling, and the characteristics of a quadrupole sound source appear at the outlet. The proposed muffler has a certain effect in reducing noise in the pump pipeline system.

To research the effect of the volute geometry on the radial force characteristics of the centrifugal pump during the starting process, choosing a centrifugal pump with a head of 87m as the research object. The pumping chamber is redesigned into a single-volute and a double-volute with similar external characteristics, and a circulation pipeline system is established. RNG k-ε turbulence model is employed to calculate the unsteady starting process of two kinds of centrifugal pumps. The variation trends of radial force received by the impeller and volute during the start-up process are obtained. The radial force characteristics and internal flow field evolution of two centrifugal pumps are compared and analyzed. The results show that the radial force vector distribution of the impeller changes in spiral periodicity during the startup process, and the spiral geometry is influenced by the number of impeller blades. The direction of the spiral is opposite to the rotational speed. The double-volute geometry can effectively reduce the radial force and pulsation amplitude of the impeller during the start-up process of the centrifugal pump, reducing the radial force by about 80% at rated speed. But the radial force vector distribution of the double-volute is more complicated and disordered than the single-volute.

Cavitation monitoring is particularly important for pump efficiency and stability. It is easy to misjudge cavitation by using a given threshold of a single eigenvalue. In this work, based on the vibration signal, a method for multi-resolution cavitation status recognition of centrifugal pump is proposed to improve the accuracy and universality of cavitation status recognition., wavelet packet decomposition (WPD) is used to extract the statistical eigenvalues of multi-scale time-varying moment of cavitation signal after reducing the clutter, such as root mean square value, energy entropy value and so on. The characteristic matrix is constructed. Principal component analysis method (PCA) is employed to reduce the dimension of the characteristic matrix and remove the redundancy, which constructs the radial basis function (RBF) neural network as the input. The results show that the overall recognition rate of non-cavitation, inception cavitation and serious cavitation by using the vibration signal of one measuring point is more than 97.7%. The recognition rate of inception cavitation is more than 80%. Based on the vibration signal information fusion method of two measuring points, the recognition rate of centrifugal pump inception cavitation status reaches more than 99%, and the recognition rate of vibration signal information fusion method of three measuring points reaches 100% for all three cavitation statuses. Due to the influence of factors such as change of external excitation and abrupt change of working conditions, sensor data acquisition is often subjected to unpredictable disturbance. To study the ability of single-point cavitation status recognition method to resist unknown disturbances, by constantly adjusting the value of the interference coefficient of the interference term. It is found that the recognition rate of cavitation status using single measuring point decreases almost linearly with the increase of the interference coefficient. When five measuring points are used for information fusion cavitation status recognition, the cavitation status recognition rate still reaches over 90% even if the interference factor of one measuring point reaches 50%.