Dynamic simulation of mid-water trawl in fishing simulator
In order to simulate the dynamic behaviors of mid-water trawl in fishing simulator, a hydrodynamic model of mid-water trawl is established according to lumped mass model and researches on the numerical method for solving the model have also been done. In the modeling process, the mid-water trawl has been simplified by using an equivalent method, then the trawl is divided into finite mass points connected with springs without mass and fluid force of each mass point is calculated by simplifying the point to a spherical object or a rod-shaped object. To take a relative bigger step size for calculation, calculated positions of mass points instituting variables of position are used to calculate connected mass points' elastic force and every mass point's equations can be solely solved. Simulation researches of a mid-water trawl have been done, and simulated results are compared with that of flume experiments, which verifies model's rationality.
Validity and visualization of a numerical model used to determine dynamic configurations of fishing nets
ABSTRACT:  The aim of the present study was to develop a numerical calculation method to simulate the three-dimensional dynamic behavior of fishing nets. In a previous study, we presented a formulation to calculate net configurations. In this method, fishing nets were modeled as a group of lumped mass points interconnected with springs that have no mass. To verify the validity of calculation results using a computational model, we performed the flume tank experiments with a rectangular net and compared results with those of the numerical simulation of experiments. Using our method, numerical calculations for a rectangular net in a steady flow can provide accurate results. The calculated load and tension force distribution of the flat net were generally in accordance with the results of the flume tank experiments. This study shows that our method is valid for the simulation of fishing nets; furthermore, we have resolved earlier problems that were associated with this model.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.