The Effect of the Gap Ratio on the Flow and Heat Transfer over a Bluff Body in Near-Wall Conditions

In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been conducted.The former were carried out using an open circulating water tank experimental platform and a single cylinder and square column as geometrical models(their characteristic length being D).The latter were based on the well-known SIMPLE algorithm for incompressible flow.The results show that the gap ratio is an important factor affecting the wake characteristics of near-wall bluff bodies.When the gap ratio is small,the influence of the wall on the bluff body wake is large.With an increase in the gap extension,periodic vortex shedding is enabled and heat transfer is strengthened accordingly;in addition,the vortex shedding period is larger for the square column.The square column displays hysteresis compared with the cylinder at the same gap ratio(the critical gap ratio of cylinder is 0.2~0.4,while that of square column is 0.4
0.6).

Continuous cleaning of A356 alloy melt using high frequency electromagnetic field

A set of device for electromagnetic separation (EMS) was designed and applied to process the continuous flowing melt. Tensile test was employed to compare effect of electromagnetic separation with that of the traditional processes. Compared with filtration by ceramic foam filter and process without filtration, multiple process combined with filtration and electromagnetic separation can effectively remove most of inclusions with diameter finer than 10 μm in A356 alloy casting, hence improve its tensile properties. After being processed by electromagnetic filtration, the tensile strength of A356 scrap is enhanced by 8.27%, approaching the level of fresh A356 alloy.

Improvement of Friction and Wear Resistance for Ta or Ta+C Implanted H21 Steel

Ta and C ions extracted from a metal vapor vacuum arc ion source were implanted into H21 steel,with an implantation dose of 3×10^(17)cm^(-2),extraction acceleration 42kV,and average ion beam flux about 40μA.cm^(-2).Rutherford backscattering spectrum was used to measure the surface composition after Ta or Ta+C implantation.Observation of phase induced by Ta and C implantation was carried out by x-ray diffraction analysis.Experimental results showed that the wear rate of the implanted layer dropped 30%for Ta ion implantation and by a factor of 2.5 for Ta+C dual ion implantation.Thus Ta+C dual ion implantation was found to significantly reduce the friction coefficient of H21 steel.The wear mechanisms of the implanted layer were discussed.

Design of Automatic cutting and coating collection System Based on Optical Fiber

In order to meet the requirement of fiber splicing, the problem of low efficiency and manual operation is adopted. The device is designed and fabricated to meet the convenience and convenience of splicing and equipping in optical fber production. The simulation design and control system design of SolidEdge are discussed. At present, there is no such device in the market, and it has certain value in optical fber equipment.

Existence and Multiplicity of Positive Solutions for a Singular Third-Order Three-Point Boundary Value Problem with a Parameter

In this paper, we investigate the existence of positive solutions for a singular third-order three-point boundary value problem with a parameter. By using fixed point index theory, some existence, multiplicity and nonexistence results for positive solutions are derived in terms of different values of λ.

Experiment Study on the Exhaust-Gas Heat Exchanger for Small and Medium-Sized Marine Diesel Engine

This paper aims to design a special exchanger to recover the exhaust gas heat of marine diesel engines used in small and medium-sized fishing vessels,which can then be used to heat water up to 55°C–85°C for membrane desalination devices to produce fresh water.A new exhaust-gas heat exchanger of fins and tube,with a reinforced heat transfer tube section,unequal spacing fins,a mixing zone between the fin groups and four routes tube bundle,was designed.Numerical simulations were also used to provide reference information for structural design.Experiments were carried out for exhaust gas waste heat recovery from a marine diesel engine in an engine test bench utilizing the heat exchanger.The experimental results show that the difference between heat absorption by water and heat reduction of exhaust gas is less than 6.5%.After the water flow rate was adjusted,the exhaust gas waste heat recovery efficiency was higher than 70%,and the exhaust-gas heat exchanger’s outlet water temperature was 55°C–85°C at different engine loads.This means that the heat recovery from the exhaust gas of a marine diesel engine meets the requirement to drive a membrane desalination device to produce fresh water for fishers working in small and medium-sized fishing vessels.

Application and study in aluminum melt degassing technologies

The classification, characteristics and current situation of aluminum melt hydrogen-removal methods and technologies have been summarized. The latest studies and research results of aluminum melt degassing technology have been summed up. The tendency and prospect of aluminum degassing technology was discussed.

The relationships among aerosol optical depth, ice, phytoplankton and dimethylsulfide and the implication for future climate in the Greenland Sea

The sea-to-air flux of dimethylsulphide（DMS） is one of the major sources of marine biogenic aerosol, and can have an important radiative impact on climate, especially in the Arctic Ocean. Satellite-derived aerosol optical depth（AOD） is used as a proxy for aerosol burden which is dominated by biogenic aerosol during summer and autumn. The spring sea ice melt period is a strong source of aerosol precursors in the Arctic. However, high aerosol levels in early spring are likely related to advection of continental pollution from the south（Arctic haze）.Higher AOD was generally registered in the southern part of the study region. Sea ice concentration（SIC） and AOD were positively correlated, while cloud cover（CLD） and AOD were negative correlation. The seasonal peaks of SIC and CLD were both one month ahead of the peak in AOD. There is a strong positive correlation between AOD and SIC. Melting ice is positively correlated with chlorophyll a（CHL） almost through March to September,but negatively correlated with AOD in spring and early summer. Elevated spring and early summer AOD most likely were influenced by combination of melting ice and higher spring wind in the region. The peak of DMS flux occurred in spring due to the elevated spring wind and more melting ice. DMS concentration and AOD were positively correlated with melting ice from March to May. Elevated AOD in early autumn was likely related to the emission of biogenic aerosols associated with phytoplankton synthesis of DMS. The DMS flux would increase more than triple by 2100 in the Greenland Sea. The significant increase of biogenic aerosols could offset the warming in the Greenland Sea.

Mixed mode oscillations as well as the bifurcation mechanism in a Duffing’s oscillator with two external periodic excitations

The main purpose of the paper is to present an approach to account for the mechanism of bursting oscillations occurring in the systems with multiple periodic excitations. Since the traditional slow-fast analysis method can be used only for the systems with two scales in time domain, when there exists an order gap between the exciting frequencies and the natural frequency, how to explore the mechanism of the complicated dynamics remains an open problem, especially for the case when two exciting terms exist. To explain our approach, a relative simple Duffing’s oscillator with two external periodic excitations is introduced as an example. For the case when one exciting frequency is integer times of the other exciting frequency, by employing Moivre’s equation, the two exciting terms can be transformed into the functions of one basic periodic exciting term. Regarding the basic periodic exciting term as a slow-varying parameter, the two exciting terms can be changed into the functions of the slow-varying parameter, based on which the whole model can be transformed into a generalized autonomous system with one slow-varying parameter. Equilibrium branches as well as the related bifurcations of the generalized autonomous system can be derived with the variations of the amplitudes of the two excitations, which describes the relationship between the state variables of the generalized autonomous system and the slow-varying parameter. Considering the slow-varying parameter as a generalized state variable, one may obtain the so-called transformed phase portraits, which present the relationship between the state variable and the slowvarying parameter. The bifurcation mechanism of the mixed oscillations can be obtained by overlapping the equilibrium branches and the transformed phase portraits. Upon the approach, different types of bursting oscillations are presented. It is pointed that when the trajectory moves almost strictly along the segments of the stable equilibrium branches to the fold bifurcation points, jumping phenomena to other stable equilibrium segments can be observed, leading to the repetitive spiking oscillations, which can be approximated by the transient procedure from the bifurcation points to the stable equilibrium segments. Furthermore, because of the distributions of stable segments on the equilibrium branches of the generalized autonomous system may vary with the exciting amplitudes, the forms of bursting oscillations may change. When more fold bifurcations involve in the bursting attractors, more forms of quiescent states as well as spiking states exist in the oscillations,leading to different types of bursting oscillations.