Theoretical Study on Dynamic Filtration with the Membrane in Simple Harmonic Motion

A simple harmonic motion is proposed to make the membrane move in a simpleharmonic way so as to enhance the membrane filtration, and minimize the membrane fouling andconcentration polarization. The velocity distribution and pressure distribution are deduced from theNavier-Stokes equation on the basis of a laminar flow when the membrane rotates at the speed of Asin(αt). And then the shear stress, shear force, moment of force on the membrane surface and powerconsumed by viscous force are calculated. The velocity distribution demonstrates that the phase ofmembrane velocity does not synchronize with that of shear stress. The simple harmonic motion canresult in self-cleaning, optimize energy utilization, provide the velocity field with instability,and make the feed fluid fluctuation. It also results in higher shear stress on the membrane surfacethan the constant motion when they consume the same quantitative energy.

Three-dimensional dynamic sea surface modeling based on ocean wave spectrum

In conventional marine seismic exploration data processing,the sea surface is usually treated as a horizontal free boundary.However,the sea surface is affected by wind and waves and there often exists dynamic small-range fluctuations.These dynamic fluctuations will change the energy propagation path and affect the final imaging results.In theoretical research,different sea surface conditions need to be described,so it is necessary to study the modeling method of dynamic undulating sea surface.Starting from the commonly used sea surface mathematical simulation methods,this paper mainly studies the realization process of simple harmonic wave and Gerstner wave sea surface simulation methods based on ocean wave spectrum,and compares their advantages and disadvantages.Aiming at the shortcomings of the simple harmonic method and Gerstner method in calculational speed and sea surface simulation effect,a method based on wave equation and using dynamic boundary conditions for sea surface simulation is proposed.The calculational speed of this method is much faster than the commonly used simple harmonic method and Gerstner wave method.In addition,this paper also compares the new method with the more commonly used higher-order spectral methods to show the characteristics of the improved wave equation method.

Influence of input acoustic power on regenerator's performance

Performance of a pulse tube cooler significantly depends on the efficient operation of its regenerator. Influence of input acoustic power on regenerator's performance is simulated and analyzed with simple harmonic analysis method. Given regenera-tor's dimensions and pressure ratio,there is an optimal input acoustic power for achieving a highest coefficient of performance,due to a compromise between relative time-averaged total energy flux in regenerator and relative acoustic power at regenerator's cold end. Additionally,optimal dimensions of regenerator are also estimated and presented for different input acoustic powers. The computed optimal diameter obviously increases with increase of input acoustic power,while the optimal length decreases slightly,and as a result,a larger input acoustic power requires a smaller aspect ratio (length over diameter).