Investigations on the exterior flow field and the efficiency of the muzzle brake

Huanhao Zhang,Zhihua Chen,Xiaohai Jiang,Hongzhi Li 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.1

Numerical investigations of the projectile launch process with different muzzle brakes have been performed in a nearly realistic situation. Both two- and three-dimensional unsteady Euler equations are used as the governing equations. The hybrid Roe type scheme is employed to solve the flow fields with strong blast waves, and structured dynamic mesh technique is used for describing projectile motion. Based on the numerical solutions, the flow structures of a bare muzzle, the three-way and multi-hole muzzle brakes have been described, respectively, which agree well with our previous experimental shadowgraphs. Moreover, the efficiency of the three-way muzzle brake is calculated, which is also comparable to the corresponding experimental value. Our results showed that the numerical simulation can be a useful and efficient way for the design of new muzzle brakes.

Planning performance based contracts of repairable system using discrete event simulation

Xinghui Zhang,Jianshe Kang,Jinsong Zhao,Hongzhi Teng 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.10

This paper investigates a discrete event simulation approach for managing performance based contracts of repairable systems. We focuson an integrated service delivery environment where the manufacturer develops capital-intensive systems and also provides aftersalessupport. We propose a simulation model to calculate system availability comprehending four performance drivers: life time distribution,repair time distribution, spare parts inventory, and repair facility. This simulation model allows the service supplier to minimizethe total cost by optimizing the four performance drivers. In this simulation model, the failure time and repair time can follow arbitrarydistribution. This will allow the customer to monitor the supplier’s service through comparing the actual availability and its theoreticalvalue. The costs of three maintenance policies also can be studied under the performance based contracts framework. Two cases are consideredin this paper. One is a system containing single unit, one warehouse, and one repair center. Another is a system containing twofleets with different installed units, two spare part warehouses with one for each fleet, and a central repair depot.

On the photoluminescence of multi-sites Ce³⁺ in T-phase orthosilicate and energy transfer from Ce³⁺ to Tb³⁺

Tong, Xubo,Zhang, Xinmin,Wu, Luyi,Zhang, Hongzhi,Seo, Hyo Jin Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.748 No.-

<P><B>Abstract</B></P> <P>Ce<SUP>3+</SUP>, Tb<SUP>3+</SUP> co-doped T-phase orthosilicate Ba<SUB>1.2</SUB>Ca<SUB>0.8</SUB>SiO<SUB>4</SUB> phosphors were prepared by means of solid state reactions. The synthesized samples were investigated using XRD and PL emission and excitation spectra. The emission spectra for Ce<SUP>3+</SUP> doped Ba<SUB>1.2</SUB>Ca<SUB>0.8</SUB>SiO<SUB>4</SUB> phosphors show broad bands in the 320–550 nm spectral region. The excitation spectra exhibit several absorption peaks in the range of 250–400 nm. Both the emission and excitation spectra are dependent on the excitation or monitoring wavelengths. We attribute these results to Ce<SUP>3+</SUP> ions occupying two different crystallographic sites (i.e., Ce I and Ce II). The Ce<SUP>3+</SUP>, Tb<SUP>3+</SUP> co-doped Ba<SUB>1.2</SUB>Ca<SUB>0.8</SUB>SiO<SUB>4</SUB> phosphors show Tb<SUP>3+</SUP>-related line emissions in the 475–600 nm spectral region and Ce<SUP>3+</SUP>-related band emissions in the 350–525 nm spectral region when the 4<I>f</I> → 5d transition of Ce<SUP>3+</SUP> is excited (λ<SUB>ex</SUB> = 345 nm), indicating that energy transfer from Ce<SUP>3+</SUP> to Tb<SUP>3+</SUP> takes place. Moreover, the emission intensity of <SUP>5</SUP>D<SUB>4</SUB> → <SUP>7</SUP>F<SUB>5</SUB> transition for Ba<SUB>1.00</SUB>Ce<SUB>0.02</SUB>Tb<SUB>0.08</SUB>Li<SUB>0.10</SUB>Ca<SUB>0.8</SUB>SiO<SUB>4</SUB> is 30 times stronger than that of Ba<SUB>1.04</SUB>Tb<SUB>0.08</SUB>Li<SUB>0.08</SUB>Ca<SUB>0.8</SUB>SiO<SUB>4</SUB> sample under 345-nm UV excitation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PL spectra are dependent on excitation or monitoring wavelengths. </LI> <LI> Ce<SUP>3+</SUP> ions occupy two different crystallographic sites (i.e., Ce I and Ce II). </LI> <LI> Efficient energy transfer from Ce<SUP>3+</SUP> to Tb<SUP>3+</SUP> takes place. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A Sphere Filling Algorithm for Irregular Aggregate Particle Generation based on Nonlinear Optimization Method

Changhong Zhou,Hongzhi Yue,Yuhua Li,Miaomiao Zhang,Jiayin Liu,Shahroz Aijaz 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.1

The angularity of particles has important effects on the mechanical properties of asphalt mixture and other granular materials. To simulate these effects, the glue-sphere method was usually used to create an arbitrary polyhedron particle. Unlike other studies, this paper aims to efficiently fill a polyhedron with as few spheres as possible through optimization technology in order to reduce the cost of calculation during mixture simulation. Four contents are mainly discussed here: a) how to produce non-spherical aggregates and control their sizes with the minimal bounding box; b) how to fill convex non-spherical particles with the fewest balls as possible using the constrained nonlinear optimization method; c) how to compute the typical shape factors of these particles; and d) how the control parameters affect the filling effect. The algorithm for this study was programmed by MATLAB software and was proven to have better filling performance and less computational cost compared to other methods.

Microstructure of Gear Steels Treated by Shot Peening by X-Ray Line Profile Analysis Method

Pengfei Zhu,Hongzhi Yan,Jibo Zhou,Youliang Zhou,Yin Zhang,Zhi Chen 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.10

Shot peening is a common surface strengthening process of gears. It can induce compressive residual stress, refine grain size and increase dislocation density. However, there are limited reports on the quantitative analysis of dislocation substructures (type, fraction and arrangement), crystallite size and micro-strain in different crystal planes. To further reveal the microstructure strengthening mechanism of gears during shot peening, X-ray diffraction line profile analysis (XRDLPA) method is applied to study the effect of coverage on the microstructure of the gear steels. The results show that with increasing coverage, the dislocation density is increased from 2.62 × 1016 to 3.37 × 1016 m−2 in the form of screw-edge-mixed type as determined from the dislocation characteristic parameter q. The fraction of edge dislocation increases, whereas the fraction of screw dislocation decreases. The dislocation arrangement parameter M is decreased from 7.1 to 5.6, indicating that the formation of dislocation dipoles or dislocation cells in the surface layer can be further enhanced by increasing coverage. Due to the different degrees of atomic slip, the (200) crystallographic plane exhibits the smallest crystallite size and highest micro-strain, whereas the (222) plane shows the smallest micro-strain and the largest crystallite size. In addition, during shot peening, the enhancement of surface hardness of the gear steels is attributed to the phase transformation strengthening, grain-boundary hardening and dislocation hardening. The surface compressive stress of the gear steels induced by shot peening is affected not only by phase transformation, but also by Bauschinger effect, surface topography, grain refinement and so on.

A study of luminescence from Eu³⁺, Ce³⁺, Tb³⁺ and Ce³⁺/Tb³⁺ in new potassium gadolinium phosphate K₃Gd₅(PO₄)₆

Meng, Fangui,Zhang, Hongzhi,Chen, Cuili,Kim, Sun Il,Seo, Hyo Jin,Zhang, Xinmin Elsevier 2016 Journal of alloys and compounds Vol.671 No.-

<P><B>Abstract</B></P> <P>New potassium gadolinium phosphate [K<SUB>3</SUB>Gd<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>6</SUB>] doped with Eu<SUP>3+</SUP>, Ce<SUP>3+</SUP>, Tb<SUP>3+</SUP> and co-doped with Ce<SUP>3+</SUP> and Tb<SUP>3+</SUP> phosphors were prepared by high temperature solid state synthesis. Phase purity of the powders was checked by X-ray powder diffraction. Luminescence and excitation spectra of samples were reported. In particular, the interaction mechanism between Eu<SUP>3+</SUP> ions was investigated in terms of the Inokuti–Hirayama model; it was found that the interactions between Eu<SUP>3+</SUP> can be assigned to dipole–dipole interaction. K<SUB>3</SUB>Gd<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>6</SUB>:Eu<SUP>3+</SUP> could act as a candidate for solid state lighting due to its strong absorption band in the near-UV region (350–400 nm). The energy transfer from Ce<SUP>3+</SUP> to Tb<SUP>3+</SUP> was confirmed and the mechanism was studied using Dexter's theory; it is concluded that electric dipole–dipole interaction predominates in the energy transfer process from Ce<SUP>3+</SUP> to Tb<SUP>3+</SUP> in the K<SUB>3</SUB>Gd<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>6</SUB> host. The energy transfer efficiency and critical distance were also investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optical properties of K<SUB>3</SUB>Gd<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>6</SUB>:RE<SUP>3+</SUP> are investigated for the first time. </LI> <LI> The interaction mechanism between Eu<SUP>3+</SUP> ions is attributed to dipole–dipole type. </LI> <LI> K<SUB>3</SUB>Eu<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>6</SUB> is a candidate phosphor for application to solid state lighting. </LI> <LI> There exists an efficient energy transfer from Ce<SUP>3+</SUP> to Tb<SUP>3+</SUP> (<I>η</I> is up to 95%). </LI> <LI> The mechanism of energy transfer process is electric dipole–dipole interaction. </LI> </UL> </P>

Anchoring effect of Ni²⁺ in stabilizing reduced metallic particles for growing single-walled carbon nanotubes

He, Maoshuai,Wang, Xiao,Zhang, Lili,Wu, Qianru,Song, Xiaojie,Chernov, Alexander I.,Fedotov, Pavel V.,Obraztsova, Elena D.,Sainio, Jani,Jiang, Hua,Cui, Hongzhi,Ding, Feng,Kauppinen, Esko Elsevier 2018 Carbon Vol.128 No.-

<P><B>Abstract</B></P> <P>The suitability of the NiMgO catalyst as a catalyst in chiral-selective growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition has been assessed. It reveals that catalyst calcination temperature plays an important role in affecting the catalyst performances. Using CO as the carbon precursor and a chemical vapor deposition reaction temperature of 600 °C, NiMgO pre-calcined at 600 °C demonstrates the best performances in catalyzing the growth of SWNTs with predominant (6, 5) species. Systematic characterizations on catalysts calcinated at different temperatures indicate that Ni<SUP>2+</SUP> ions diffuse towards the interior of MgO matrix upon annealing. DFT-based calculations reveal that the binding energy between Ni<SUP>2+</SUP> and adjacent Ni(0) is larger than that between Mg<SUP>2+</SUP> and Ni (0), while Ni<SUP>2+</SUP> situated deep inside MgO has weak interactions with surface Ni atoms. This work highlights the importance of subsurface Ni<SUP>2+</SUP> in anchoring reduced surface Ni atom, which inhibits the aggregation of Ni particles and therefore, facilitates the growth of SWNTs with a narrow chirality distribution.</P> <P><B>Graphical abstract</B></P> <P>A Ni-incorporated MgO catalyst was developed for predominant synthesis of (6, 5) single walled carbon nanotubes. Density functional theory-based calculations revealed that the unreduced subsurface Ni stabilized reduced Ni atoms on the surface, facilitating the growth of carbon nanotubes with a narrow chirality distribution.</P> <P>[DISPLAY OMISSION]</P>

Numerical Simulation of the Twist Deformation for the Stiffened Panel with Laser Forming

Shouchong Fu,Lijun Yang,Hongzhi Zhang,Yang Wang,Guanxin Chi,Ye Ding 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.10

In the laser forming process of the panel with crossed reinforcing bars (PWCRB), a kind of stiffened panel, twisting of the panel occurred when it was formed under the integral continuous scanning strategy (ICSS). The twisting was restrained obviously when the middle stiffener was heated. In order to reveal the twisting mechanism, a FE model was established and corresponding simulations were conducted. Furthermore, an equivalent model of the sectional structure was established, and a model of the buckling critical load of the stiffener was established based on principle of minimum potential energy. It revealed that the buckling critical load of the middle stiffener was smaller than that of the marginal stiffener. The simulation results showed that the stiffeners suffered from pressure and bending moment during the forming process, which tended to induce the buckling of the stiffeners. Besides, the residual stress of the middle stiffener was larger than that of the marginal stiffener. The bending angle of the middle stiffener increased when it was heated. Besides, the lateral-torsional deformation of the middle stiffener decreased and the twisting of the panel was restrained. It demonstrated that the twisting phenomenon of the PWCRB was caused by the middle stiffener, which suffered from lateral-torsional buckling when the panel was formed with the ICSS.

Analyses of Effects of Process Parameters on Laser Bending of Stiffened Panels

Shouchong Fu,Lijun Yang,Hongzhi Zhang,Yang Wang,Guanxin Chi 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.4

In this paper, laser forming technology was extended to form the stiffened panels. Compared with the plate with constant thickness, the stiffened panel was a type of panel with complicated structure and was hard to form. In order to gain a profound insight into the deformation characteristics of the stiffened panel under laser forming, a finite element model was established. The effects of process parameters on the deformation characteristics were investigated in terms of temperature distribution, stress and strain distribution. The influences of the process parameters on the unexpected deformation were analyzed by analyzing the influences of the process parameters on the maximum temperature theoretically. The results showed that laser spot diameter had the most important effect on the maximum temperature followed by the laser power and scanning speed. So when the scanning speed changed, the variation of the difference of the plastic strain between the top and bottom surface was the smallest.When the laser spot diameter decreased, the increment of the maximum temperature, the plastic strain as well as the deformation of the middle position of the scanning path was the largest. The increase of the deformation of the middle position of the scanning path could decrease the degree of the nonuniformity of the deformation of the free end, namely increasing the quality of the formed panel.

Preparation and Photoelectric Properties of Silver Nanowire/ZnO Thin Film Ultraviolet Detector

Zhenfeng Li,Wei Xiao,Hongzhi Zhou,Zhiyuan Shi,Rongqing Li,Jia Zhang,Yang Li,Peng He,Shuye Y. Zhang 대한금속·재료학회 2023 ELECTRONIC MATERIALS LETTERS Vol.19 No.5

Ultraviolet (UV) detectors have important applications in many fi elds. ZnO is an excellent semiconductor material for the preparation of UV detectors because of its large direct gap in forbidden bandwidth, its intrinsic response band in the UV region, and its high exciton binding energy. In this paper, high-performance ZnO thin fi lms with the optically advantageous nonpolar structure were prepared by using an atomic layer deposition, and the dominant crystal plane gradually changes from the amorphous phase to the (100) crystal plane. The conventional photoconductor structure ZnO UV detector was enhanced by the surface plasmon exciton eff ect of Ag nanostructure. When the operating voltage is 5 V and the response light is 350 nm, there is a maximum optical responsiveness of up to 131 A/W. The UV/visible rejection ratio can reach 1824 times. When the ZnO thin fi lm deposition thickness is 400 deposition cycles and about 72 nm, the ZnO thin fi lm UV detector obtains the highest responsiveness (5 V, 365 nm) of 365 A/W. Comparing the photovoltaic performance of the ZnO thin-fi lm detector with the enhanced ZnO thin-fi lm detector and its optimal response wavelength, it is found that the enhanced ZnO thin-fi lm detector increased the photoresponse value by about 100 times. The optimal response wavelength in the UV region is blueshifted, and the UV-visible rejection ratio and optical response rate are signifi cantly improved.