Enriched Constant Elements in the Boundary Element Method for Solving 2D Acoustic Problems at Higher Frequencies

The boundary element method(BEM)is a popular method for solving acoustic wave propagation problems,especially those in exterior domains,owing to its ease in handling radiation conditions at infinity.However,BEM models must meet the requirement of 6–10 elements per wavelength,using the conventional constant,linear,or quadratic elements.Therefore,a large storage size of memory and long solution time are often needed in solving higher-frequency problems.In this work,we propose two new types of enriched elements based on conventional constant boundary elements to improve the computational efficiency of the 2D acoustic BEM.The first one uses a plane wave expansion,which can be used to model scattering problems.The second one uses a special plane wave expansion,which can be used tomodel radiation problems.Five examples are investigated to showthe advantages of the enriched elements.Compared with the conventional constant elements,the new enriched elements can deliver results with the same accuracy and in less computational time.This improvement in the computational efficiency is more evident at higher frequencies(with the nondimensional wave numbers exceeding 100).The paper concludes with the potential of our proposed enriched elements and plans for their further improvement.

Zircon deposit and rare earth element enriched metasomatic alkaline rocks at Kyemyeongsan Formation, Chungju, Korea: Paleozoic magmatism and Zr-REE-Nb mineralization

The zircon ore deposit in metasediments and peralkaline granite of the Kyemyeongsan Formation is located in southwest of Chungju city, Korea. The deposit, closely associated with REE and Nb,is composed of metasomatic alkaline rocks and rare metal alkali granite, and was formed in late Carboniferous (340～343Ma). Zircon occurs in different paragenetic sequence: (1) earlier rare metal alkali granite, (2) later metasomatic zircon ore. The metasomatic zone contains abundant microcline, albite and quartz with minor biotite, magnetite, hornblende, allanite and zircon. The alkali granites have high silica (72.13～74.52wt.% as SiO 2), and total iron content (5.95～6.89%), and are characterized by low Al 2O 3 content (7.12～9.74%). They also show variable K 2O content (3.60～6.98%), and high ratios of K 2O/Na 2O. The REE patterns of rare metal alkali granite are similar to those of felsic volcanics from rifts, or back arc basins in, or near continental crust. Zircon ores are characterized by high iron content and low Al 2O 3, SiO 2, and K 2O content and have unusually high total REE content (0.18～2.33%). REE patterns show relatively flat to somewhat heavy REE (HREE) depleted characteristics (Ce/Yb=0.39～5.17) with large Eu negative anomaly (Eu/Eu *=0.16～0.29). Laser ablation microprobe inductively coupled plasma mass spectrometer (LAM ICP MS) analyses has been carried on zircon. The REE patterns of mineral zircons are almost the same to those of zircon ores and rare metal alkali granites, which may reflect the inability of zircons to effectively fractionated REE at formation of origin. The Sm Nd isochron age of the zircon ore and rare metal alkali granite are 330Ma, and 331Ma, respectively with ε Nd(t) being range from -2.00 to -1.84. This data suggest that the ore forming material came from the mantle. Alkali granite has suffered extensive post magmatic metasomatism of a high temperature to produce zircon ores. Geochemical characteristics show that metasomatism of alkaline fluid was probably the dominant ore forming process in Chungju district.

The effect of Fe-Mn minerals and seawater interface and enrich-ment mechanism of ore-forming elements of polymetallic crusts and nodules from the South China Sea

Ferromanganese crusts and nodules are important submarine mineral resources that contain various metal elements with significant economic value. In this study, polymetallic crusts and nodules obtained from the South China Sea （SCS） were determined by using X-ray power diffraction （XRD）, Raman spectroscopy （RS）, Fourier transform infrared spectroscopy （FTIR）, and X-ray photoelectron spectroscopy （XPS） to systematically investigate and analyze the mineralogical and spectral characteristics of the Fe-Mn minerals. XRD measurements revealed that the SCS polymetallic crusts and nodules were composed of vernadite, quartz, and plagioclase. The nodules also contained todorokite. The Fe-phase minerals of the SCS crusts and nodules were composed of amorphous Fe oxide/hydroxide, and the Mn- and Fe-phases minerals exhibited relatively poor degrees of crystallization. FTIR results showed that the Fe-Mn minerals in the crusts and nodules included a large number of surface hydroxyl groups. These surface hydroxyl groups contained protons that could provide reactive sites for complexation of ore-forming elements in seawater. XPS results indicated that the surfaces of the Fe-Mn minerals mainly contained Fe, Mn, and O. Fe was present in the trivalent oxidation state, while Mn, which may contain several bivalent oxidation state, was present in the tetravalent and trivalent oxidation states. The SCS polymetallic crusts and nodules were compared with Pacific seamount crusts, and results showed that the surface hydroxyl （-OH） groups of the SCS crusts and nodules numbered more than the lattice oxygen （O^2-）. But the lattice oxygen of Pacific seamount crusts numbered more than the surface hydroxyl groups. This characteristic indicated that the degree of crystallization of Fe-Mn minerals from the Pacific Ocean was higher than that of minerals from the South China Sea. Comprehensive studies showed that ore-forming elements in the interface between seawater and the Fe-Mn minerals in the submarine ferromanganese crusts and nodules employed the following enrichment mechanisms： （1） the metal ion complexed with the surface hydroxyl of Fe-Mn minerals to form hydroxyl complexes, which were connected by coordination bonds or stable inner-sphere complexes that exchanged protons on the mineral surfaces; （2） the charged surfaces of the minerals and metal cations formed outer-sphere complexes, which made up the electrostatic double layer, through electrostatic adsorption; and （3） the metal cations isomorphously exchanged the Mn and Fe ions of the mineral lattice structure.

Comparing mineral weathering and elemental transport between earth's critical zone with different parent rocks in Yanshan Mountain,Hebei province,China

Bedrock weathering performs a significant influence on the evolution of Earth’s critical zone.Carbonate rock(dolostone),metamorphic rock(gneiss),and sedimentary rock(sandstone)geological formations in Yanshan Mountain,Hebei Province,are taken as objects to probe the controlling of geological formations on weathering characteristics,migration,and enrichment of elements as well as structure of Earth’s critical zone under the identical climate conditions through geological field survey,analysis on minerals component,element distribution in the weathering profile.The dolostone geological formation(DGF)is lithologically dominated by dolostone,characterized by the strongest and predominant chemical weathering.During bedrock weathering and pedogenesis,DGF is marked by significant depletion of CaO,Mg O,S,Mn,Mo and enrichment of N,K,Fe_(2)O_(3),and Zn with concentrations of P,Cu,and B keeping stable.Shortage of soil-forming materials and significant loss are driven by soil erosion,which results in thin regolith and soil.The soil thickness is less than 10 cm,and the regolith thickness is less than 30 cm.The vegetation community is predominantly rock arbor or brush,which is calcivorous and tolerant of barrenness.Plagiogneiss is a dominant rock type of gneiss geological formation(GGF),characterized by the weakest weathering and fast chemical and physical weathering rate.GGF is masked by significant depletion of P,K,CaO,MgO,Fe_(2)O_(3),Mn,Cu and enrichment of N,S,Mo,and B,with contents of Zn keeping stable.Both soil and regolith developed in GGF are relatively thick for one of the reasons that biotite expands during weathering.The soil thickness is more than 50 cm,and the regolith thickness ranges from 100 to 200 cm.The vegetation community is predominantly high-quality economic forests and various arbors because of the enrichment of nutrients in GGF.Sandstone is primarily a rock type of sandstone geological formation(SGF),characterized by moderate weathering degree and slow chemical weathering rate.SGF is marked by significant depletion of P,K,CaO,MgO,Fe_(2)O_(3),and enrichment of N,S,Mn,Cu,Zn,and Mo,with fluctuant changes of Zn and B.The thickness of soil developed in SGF varies between that of DGF and GGF.The soil thickness ranges from 30 to 50 cm,and the regolith thickness ranges from 50 to 100 cm.Chinese pines are widely spread on the shady slopes of SGF.Research provides theoretical support for screening dominant ecological resource areas,ecological industry development and ecological protection and restoration for Yanshan Mountain,Hebei Province.

STUDY ON ENRICHMENT AND SEPARATION OF TRACE ELEMENTS WITH SILICA GELS MODIFIED BY HETEROCYCLIC AZO DYES

Two types of modified silica gels were prepared by adsorption method and bonding method respectively. Enrichment and separation of trace metal ions have been done by using the column packed with modified silica gels.

Enrichment rules and exploration practices of Paleogene shale oil in Jiyang Depression, Bohai Bay Basin, China

Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and pilot fracturing data of multiple wells, the geological characteristics of the upper submember of the Sha 4 Member to the lower submember of the Sha 3 Member of Paleogene(Es4s-Es3x) in the Jiyang Depression were investigated to find out factors controlling the enrichment of shale oil and the accumulation model of shale oil, and a comprehensive evaluation method for shale oil sweet spots was established. It is found through the study that the target shale layer is characterized by strong heterogeneity, weak diagenesis, low thermal evolution and high content of clay and carbonate minerals. Shale lithofacies, microcrack, thin interlayer and abnormal pressure are the main factors affecting enrichment and stable production of shale oil, the organic rich laminar shale has the best storage and oil-bearing capacity, microcrack network system improve the storage capacity and permeability of the shale, the thin interlayer is the main flow channel for stable shale oil production, and the abnormal high pressure layer is rich in free state shale oil and high in oil content. The shale oil layers in the target section were divided into three types: matrix, interlayer and fracture ones. According to the occurrence state and exploration practice of shale oil at home and abroad, it is concluded that the interlayer shale oil is the most profitable type at present. The selection parameters for the different types of shale oil were determined, and accordingly the favorable areas were pointed out by comprehensive evaluation of multiple factors. Vertical wells in the interlayer shale oil reservoir, such as Fan 159, Fan 143 and GX 26, were stimulated by volume fracturing and high conductivity channel fracturing jointly. After fracturing, they had a daily oil production of over 6 t, up to 44 t, and stable productivity. Shale oil is expected to become an important replacement energy resource in the Jiyang Depression.

Element migration and phase distribution characteristics during crystallization of rare earth phase in rare earth slag

The crystallization experiment of molten rare earth(RE)slag under different cooling rates was carried out.The characteristics of element migration and phase distribution during RE phase crystallization were studied by using different equipment.The experimental results show that there are two RE phases in the RE slag,namely(Ca,Ce,La)_(5)(SiO_(4))6F and(Ca,Ce,La,Mg)_(3)(Ti,Al,Nb)_(2)O_(7).During the cooling crystallization process of molten RE slag,Ca and P elements in the RE phase of(Ca,Ce,La)_(5)(SiO_(4))_(6)F migrate from inside to outside,and finally gather at the outer edge of the phase to form phase Ca_(3)(PO4)2.The RE phase(Ca,Ce,La)_(5)(SiO_(4))_(6)F is distributed inside the furnace-cooled slag,and the RE phase(Ca,Ce,-La,Mg)_(3)(Ti,AI,Nb)_(2)O_(7)is distributed in the surface layer of the furnace-cooled slag.And based on the phase distribution characteristics,the central hollowing method is proposed to realize the preliminary enrichment of valuable elements Ti,Nb and RE in RE slag.

Multi-performance evaluation of high-throughput accelerated corrosion test for high-strength low-alloy 921A steel

The corrosion behavior of high-strength low-alloy 921A steel in a simulated marine atmospheric environment was studied using a high-throughput experimental method.The corrosion behavior,corrosion morphology,and corrosion products of 921A steels were analyzed using various techniques,including corrosion mass loss method,polarization curve,white-light interferometry,scanning electron microscopy,energy-dispersive spectrometry,microbeam X-ray fluorescence spectrometry,X-ray diffraction technique,and X-ray photoelectron spectroscopy.The test results indicated that 921A steel exhibits better corrosion resistance than Q450NQR1 steel in simulated harsh atmospheric environments,as evidenced by a lower corrosion mass loss rate throughout the corrosion tests.The corrosion products of both steels consisted ofα-FeOOH,Fe_(3)O_(4),andγ-FeOOH,withα-FeOOH being more prevalent in the rust layer of 921A steel than in Q450NQR1 steel.The inner rust layer of 921A steel also exhibited an appositional enrichment region of Cr,Ni,Mo,and V,leading to its superior corrosion resistance compared to that of Q450NQR1 steel.The efficacy of high-throughput accelerated corrosion experimental methods was highlighted for evaluating the corrosion resistance of steel materials in harsh environmental conditions.The findings suggest that 921A steel exhibits better corrosion resistance compared to Q450NQR1 steel and has the potential to be more suitable in harsh marine atmospheric environments.The characterization of the rust layer structures and composition reveals the parallel enrichment of certain elements in the inner rust layer of 921A steel,which enhances its corrosion resistance.

Elemental compositions of PM_(2.5) and TSP in Lijiang,southeastern edge of Tibetan Plateau during pre-monsoon period

PM2.5 and total suspended particulate （TSP） samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements （Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu） were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM2.5 and TSP samples. The enrichment factors （EFs） ofSi, Ti, Ca, Fe, K and Mn were all below 10 for both PM2.5 and TSP, and these elements also had lower PM2.5/TSP ratios （0.32-0.34）, suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM2.5 and TSP samples, with their PM2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.

Free vibration analysis of functionally graded porous curved nanobeams on elastic foundation in hygro-thermo-magnetic environment

Herein,a two-node beam element enriched based on the Lagrange and Hermite interpolation function is proposed to solve the governing equation of a functionally graded porous(FGP)curved nanobeam on an elastic foundation in a hygro–thermo–magnetic environment.The material properties of curved nanobeams change continuously along the thickness via a power-law distribution,and the porosity distributions are described by an uneven porosity distribution.The effects of magnetic fields,temperature,and moisture on the curved nanobeam are assumed to result in axial loads and not affect the mechanical properties of the material.The equilibrium equations of the curved nanobeam are derived using Hamilton’s principle based on various beam theories,including the classical theory,first-order shear deformation theory,and higher-order shear deformation theory,and the nonlocal elasticity theory.The accuracy of the proposed method is verified by comparing the results obtained with those of previous reliable studies.Additionally,the effects of different parameters on the free vibration behavior of the FGP curved nanobeams are investigated comprehensively.

Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service

Evaluating the residual life of exposed components in power industry is a very important procedure inroutine examination. The microstructures of a series of X20CrMoV12.1 martensitic superheater tube samples in a boiler in different service periods were investigated extensively to extract a quantitative relationship. During long-term service from start to rupture, hardness decreased monotonically with life depletion, and the decrease of hardness in prior austenite grain boundary was steeper than that in the matrix. Microstructure observation showed obvious damage characteristics, including carbide coarsening and martensite decomposing, and the martensite structure decomposed completely in rupture state. The morphology, distribution and composition of the main precipitates M23 C6 varied distinctly. The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size. The composition of coarsened M23 C6 carbide shows the most regular trend of Cr enrichment and the statistical result of Cr enrichment in M23 C6 shows a linear correlation between the ratio of Cr to Fe and service time to the power of 3/2, which may be considered as an index of material degradation due to long-term service exposure.