Prismatic and full-waveform joint inversion

Prismatic wave is that it has three of which is located at the reflection interface reflection paths and two reflection points, one and the other is located at the steep dip angle reflection layer, so that contains a lot of the high and steep reflection interface information that primary cannot reach. Prismatic wave field information can be separated by applying Born approximation to traditional reverse time migration profile, and then the prismatic wave is used to update velocity to improve the inversion efficiency for the salt dame flanks and some other high and steep structure. Under the guidance of this idea, a prismatic waveform inversion method is proposed （abbreviated as PWI）. PWI has a significant drawback that an iteration time of PWI is more than twice as that of FWI, meanwhile, the full wave field information cannot all be used, for this problem, we propose a joint inversion method to combine prismatic waveform inversion with full waveform inversion. In this method, FWI and PWI are applied alternately to invert the velocity. Model tests suggest that the joint inversion method is less dependence on the high and steep structure information in the initial model and improve high inversion efficiency and accuracy for the model with steep dip angle structure.

Fragment spatial distribution of prismatic casing under internal explosive loading

Non-cylindrical casings filled with explosives have undergone rapid development in warhead design and explosion control.The fragment spatial distribution of prismatic casings is more complex than that of traditional cylindrical casings.In this study,numerical and experimental investigations into the fragment spatial distribution of a prismatic casing were conducted.A new numerical method,which adds the Lagrangian marker points to the Eulerian grid,was proposed to track the multi-material interfaces and material dynamic fractures.Physical quantity mappings between the Lagrangian marker points and Eulerian grid were achieved by their topological relationship.Thereafter,the fragment spatial distributions of the prismatic casing with different fragment sizes,fragment shapes,and casing geometries were obtained using the numerical method.Moreover,fragment spatial distribution experiments were conducted on the prismatic casing with different fragment sizes and shapes,and the experimental data were compared with the numerical results.The effects of the fragment and casing geometry on the fragment spatial distributions were determined by analyzing the numerical results and experimental data.Finally,a formula including the casing geometry parameters was fitted to predict the fragment spatial distribution of the prismatic casing under internal explosive loading.

Size effect on cubic and prismatic compressive strength of cement paste

A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.

COMPUTER DYNAMIC SIMULATION FOR PRISMATIC PARTS MANUFACTURED ON MACHINING CENTER

This paper describes a dynamic simulation system for manufacturing prismatic components on machining centers named NCDSS. It is a subsystem of CAD/CAPP/NC integrated system for prismatic parts that we are working on. Based on the system of CAD and CAPP, it can automati. cally generate NC program used on machining centers and can simulate the machining process in the sequence of technology. Techniques of automatically producing NC program for prismaic parts and the method of dynamic simulation are also discussed.

Motion planning for redundant prismatic-jointed manipulators in the free-floating mode

This paper investigates the motion planning of redundant free-floating manipulators with seven prismatic joints. On the earth, prismatic-jointed manipulators could only position their end-effectors in a desired way. However, in space, the end-effectors of free-floating manipulators can achieve both the desired orientation and desired position due to the dynamical coupling between manipulator and satellite movement, which is formally expressed by linear and angular momentum conservation laws. In this study, a tractable algorithm particle swarm optimization combined with differential evolution （PSODE） is provided to deal with the motion planning of redundant free-floating prismatic-jointed manipulators, which could avoid the pseudo inverse of the Jacobian matrix. The polynomial functions, as argument in sine functions are used to specify the joint paths. The co- efficients of the polynomials are optimized to achieve the desired end-effector orientation and position, and simulta- neously minimize the unit-mass-kinetic energy using the redundancy. Relevant simulations prove that this method pro- vides satisfactory smooth paths for redundant free-floating prismatic-jointed manipulators. This study could help to recognize the advantages of redundant prismatic-jointed space manipulators.

Fracture Behavior of Alumina-based Prismatic Ceramic Composites

The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation 'for crack propagation and fracture morphology, the fracture behavior of the prismatic composites was analyzed. In the bending test, the composites displayed a non-catastrophic behavior and a graceful failure with reasonable load-carrying capability.

An Integrated Geometric Modeling Methodology for 2.5D Cylindrical Prismatic Part for Computer Aided Process Planning

The field of solid modeling has created numerous techniques for unambiguous computer representations of three-dimensional objects. Its data structures and algorithms have been used in a broad range of applications: Computer-Aided Design and Computer-Aided Manufacturing (CAD/ CAM), robotics, computer vision, computer graphics and visualization, virtual reality, etc. This research paper is used to generate process plan from feature-based modeling, based on an integrated geometric modeling system that supports both feature-based modeling and information storage. Present system is developed only for milling components and limited to selective machining features for prismatic components and further implemented for more machining features to develop algorithms for modeling the components through the input of machining features. As a result, feature information is directly available to downstream activities, and feature extraction is no longer needed. The various systematic steps involved in this approach are study of Design, identification of Features, selection of Processes, Tools and Machines, Machining and Inspection [DFPTMMI]. Machining features generated in the design stage are recognized and stored under the Visual Basic control of CATIA software ActiveX interface. Algorithms are developed for individual features and these algorithms are embedded in Visual Basic forms. This system is discussed and suited for 2.5 Dimensional part approach, however, that can be extended to 3 dimensional prismatic part and complex features machining. Finally a process planning chart has been presented as a model process planning.

On Some Bending Problems of Prismatic Shell with the Thickness Vanishing at Infinity

The present work is devoted to the bending problems of prismatic shell with the thickness vanishing at infinity as an exponential function. The bending equation in the zero approximation of Vekua＇s hierarchical models is considered. The problem is reduced to the Dirichlet boundary value problem for elliptic type partial differential equations on half-plane. The solution of the problem under consideration is constructed in the integral form.

A Method for Automatically Establishing a Mathematical Model of Kinematic Analysis to a Planar Mechanism with a Multiple Joint and Prismatic Pair

A method for automatically establishing a mathematical model of kinematic analysis to a planar mechanism with multiple joint and prismatic pair is presented. The breadth （ or depth ） first search spanning tree can be obtained based on an adjacency matrix of the mechanism. Then the kinematic chain （or mechanism）＇s basic loops can be obtained. On the basis of these basic loops, a mathematical model of kinematic analysis can be established and solved automatically. In the sense of a calculative mechanism, structural analysis of the kinematic chain relates to the kinematic analysis of a mechanism. Thus, an effective way is supplied to the given mechanism＇s kinematic analysis for automatic modeling and solving, and a method is supplied to the structural type to optimize kinematic synthesis.

An insight into a novel Mg2InSm prismatic plate in Mg-In-Sm alloy

Prismatic precipitate platelet is always purposefully designed in the microstructure of magnesium alloys due to its greater contribution to yield stress.In this study,with an introduction of In into Mg-Sm system,a category of novel{1010}_(α) prismatic platelets has replaced thoroughly the traditionalβ’precipitate formed in magnesium rare earth(Mg-RE)alloys.Herein,the microstructural characteristics of platelet are investigated particularly by atomic scale scanning transmission electron microscopy.It is confirmed that the platelet has a Mg_(2) InSm composition and can maintain a coherent relationship with α-Mg matrix.Importantly,on account of the similarities between In and Mg atoms,the Mg_(2) InSm prismatic platelet could be structurally categorized as a generalizedβ"precipitate with a(Mg_(2) In)Sm-type DO_(19) structure when both In and Mg are regarded as an equivalent atom.Thus,the addition of In into Mg-Sm alloy induces the formation ofβ"precipitate.Furthermore,the formedβ"prismatic platelets generally have a large average aspect ratio.The findings are of great significance to construct the effective precipitation strengthening phases and optimize the microstructure of Mg-based alloys.

Light losses in hollow, prismatic light guides related to prism defects: a transmittance model

Hollow, cylindrical, prismatic light guides （CPLGs） are optical components that, using total internal reflection （TIR）, are able to transmit high-diameter light beams in daylight and artificial lighting applications without relevant losses. It is necessary to study the prism defects of their surfaces to quantify the behavior of these optical components. In this Letter, we analyze a CPLG made of a transparent dielectric material. Scanning electron microscopy （SEM） and the topographic optical profilometry by absorption in fluids （TOPAF） imaging tech- nique are conducted to determine if there are defects in the corners of the prisms. A model for light guide trans- mittance that is dependent on prism defects is proposed. Finally, a simulation and an experimental study are carried out to check the validity of the proposed model.

Prismatic mesh generation based on anisotropic volume harmonic field

In this paper,we present an effective prismatic mesh generation method for viscous flow simulations.To address the prismatic mesh collisions in recessed cavities or slit areas,we exploit 3D tensors controlled anisotropic volume harmonic field to generate prismatic meshes.Specially,a well-fitting tetrahedral mesh is first constructed to serve as the discrete computation domain of volume harmonic fields.Then,3D tensors are exploited to control the volume harmonic field that better fits the shape geometry.From the topological perspective,the generation of the prismatic mesh can be treated as a topology-preserved morphing of the viscous wall.Therefore,iso-surfaces in the volume harmonic field should be homeomorphic to the viscous wall while fitting its shapes.Finally,a full prismatic mesh can be induced by estimating the forward directions and visible regions in the volume harmonic field.Moreover,to be compatible with different simulation situations,the thickness of prismatic meshes should be variable.Our approach provides local adjustable thickness of prismatic meshes,which can be achieved by controlling local 3D tensors.The proposed anisotropic volume harmonic field based prismatic meshes are efficient and robust,and a full prismatic mesh can be guaranteed without low quality collisions.Various experiments have shown that our proposed prismatic meshes have obvious advantages in terms of efficiency and effectiveness.

Preparation of α-High Strength Gypsum from Flue Gas Desulfurization Gypsum Pretreated by Hydrothermal-aging Method

The synthesis of α-calcium sulfate hemihydrate (α-CSH) from flue gas desulfurization (FGD)gypsum is a good way to realize the comprehensive utilization of FGD gypsum. To obtainα-CSH with the satisfactory performances, a facile hydrothermal-aging pretreatment process for FGD gypsum raw materials was proposed, where FGD gypsum was firstly hydrothermally converted to α-CSH whiskers, and α-CSH whiskers were further hydrated to synthesize CaSO4·2H2O (CSD) by aging under the regulation of N,N'-methylenebisacrylamide (MBA). The effects of aging time, MBA addition, aging temperature, and pH on the morphology of the synthesized CSD were investigated. The synthesized CSD crystals exhibit highly uniform prismatic morphology with the length of ca 100μm and the whiteness of 91.56%. The regulation mechanism of MBA was also illustrated. The synthesized CSD crystals with prismatic morphology were further used as raw materials to synthesize the short columnar α-CSH. The absolute dry compressive strength of paste prepared from the short columnar α-CSH is 40.85 MPa, which reaches α40 strength grade.

Influence of grain size on the tensile ductility and deformation modes of rolled Mg–1.02 wt.%Zn alloy

The influence of grain size on the tensile deformation and ductility for Mg–1.02%Zn(wt.%)alloy was investigated.The uniform elongation is nearly insensitive to the increase of grain size,but the post-uniform elongation is significantly decreased with increasing grain size.The high ductility in the fine-grained samples is due to the lower frequency of twins and increased dynamic recovery from the enhanced activation of prismatic<a>slip.

Effects of Li addition on the microstructure and tensile properties of the extruded Mg-1Zn-xLi alloy

Li addition is verified to be an effective method to increase the room temperature ductility and formability of Mg alloys.In the present study,the microstructure,texture,and tensile properties of the extruded Mg-1Zn-xLi(wt%,x=0,1,3,5)alloy sheets were studied by X-ray diffraction(XRD),scanning electron microscope(SEM),and electron backscatter diffraction(EBSD).It was found that Li addition resulted in the grain coarsening and the development of new transverse direction(TD)-tilting and{101^(-)0}parallel to extrusion direction textures,which was related to the improved dynamic recrystallization and the increased prismatic slip during extrusion.The Mg-1 Zn-5 Li sheet showed the weakest texture,which contained both basal and TD-tilting oriented grains.No additional phase was formed with Li addition.The yield strength of Mg-1Zn-xLi sheets gradually decreased with increasing Li content,which was mainly related to the grain coarsening and texture weakening.In addition,the ductility of the Mg-1Zn-xLi sheet was remarkably enhanced by Li addition.The elongation of the Mg-1 Zn-5 Li sheet was 30.3%along the TD,which was three times than that of Mg-1 Zn sheet.Microstructural analysis implied that this significant ductility enhancement was associated with the improvement activation of prismatic and basal slips during the tensile tests.This study may provide insights into the development of high-ductility,low-density Mg-Zn-Li based alloys.

Quasi in-situ EBSD analysis of twinning-detwinning and slip behaviors in textured AZ31 magnesium alloy subjected to compressive-tensile loading

Twinning and detwinning behavior,together with slip behavior,are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction(RD)after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique.The results show that twinning firstly takes place under the compressive strain along the RD.With the increasing compressive strain,{1012}tensile twins firstly nucleate,then propagate,and finally thicken.While under a reversed tensile strain along the RD,detwinning occurs.No nucleation happens during detwinning.Thus,tensile twins can detwin at lower tensile strain,followed by thinning,shortening,and vanishing.Slips are also activated to accommodate the plastic deformation.In the matrix,prismatic slip can only dominate at relatively high strains.Otherwise,basal slip dominates.While in the twins,prismatic slip can activate at lower strains,which is ascribed to the texture reorientation.

Atomic scale structural characterization of {10 12} twin boundaries in zinc

The structure and the migration mechanisms of {10 12} twin boundaries（TBs） of pure zinc deformed by rolling were studied using high-resolution transmission electron microscopy（HRTEM） at atomic scale. We found the presence of basal/prismatic（BP/PB） planes serrations on {10 12} TBs and the coexistence of two kinds of TBs with different structures in the same {10 12} twin： TBs composed of {10 12} coherent twin boundaries（CTBs） plus short BP/PB serrations, and TBs composed of successive BP/PB segments without {10 12} CTBs. The formation of BP/PB serrations has no relation to the c/a ratio of hexagonal-closepacked（HCP） metals because the BP/PB serrations are energetically preferred and geometrically favored. Based on dislocation theory, we proposed the migration mechanisms of the TBs to be the glide of twinning dislocations（TDs） on the CTBs and the climb of interface dislocations（IDs） on the BP/PB segments.

Developing a Computer Program for Detailed Study of Planing Hull＇s Spray Based on Morabito＇s Approach

Recently, Morabito(2010) has studied the water spray phenomena in planing hulls and presented new analytical equations. However, these equations have not been used for detailed parametric studies of water spray around planing hulls. In this paper, a straight forward analysis is conducted to apply these analytical equations for finding the spray geometry profile by developing a computer program based on presented computational process. The obtained results of the developed computer program are compared against existing data in the literature and favorable accuracy is achieved. Parametric studies have been conducted for different physical parameters. Positions of spray apex are computed and three dimensional profiles of spray are examined. It is concluded that spray height increases by an increase in the speed coefficient or the deadrise angle. Ultimately, a computational process is added to Savitsky's method and variations of spray apex are computed for different velocities. It is shown that vertical, lateral, and longitudinal positions of spray increase as the craft speed increases. On the other hand, two new angles are defined in top view and it is concluded that they have direct relation with the trim angle. However, they show inverse relation with the deadrise angle.

Numerical simulation and experimental verification of a novel double-layered split die for high-pressure apparatus used for synthesizing superhard materials

Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. The stress distributions of the DLSDs with different numbers of divided blocks were investigated by the finite element method and compared with the stress distributions of the conventional belt-type die(BTD). The results show that the cylinders and first-layer supporting rings of the DLSDs have dramatically smaller stresses than those of the BTD. In addition, increasing the number of divided blocks from 4 to 10 gradually increases the stress of the cylinder but has minimal influence on the stress of the supporting rings. The pressure-bearing capacities of the DLSDs with different numbers of divided blocks, especially with fewer blocks, are all remarkably higher than the pressure-bearing capacity of the BTD. The contrast experiments were also carried out to verify the simulated results. It is concluded that the pressure-bearing capacities of the DLSDs with 4 and 8 divided blocks are 1.58 and 1.45 times greater than that of the BTD. This work is rewarding for the commercial synthesis of high-quality, large-sized superhard materials using a double-layered split high-pressure die.

Steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration and its application

Steeply dipping structural imaging is a significant challenge because surface geophones cannot obtain seismic primary reflection wave information from steeply dipping structures.Prismatic waves with a significant amount of steeply dipping information can be used to improve the imaging eff ect on steeply dipping structures.Subsurface attenuation leads to amplitude loss and phase distortion of seismic waves,and ignoring this attenuation during imaging can cause blurring of migration amplitudes.In this study,we proposed a steeply dipping structural target-oriented viscoacoustic least-squares reverse time migration(LSRTM)method with prismatic and primary waves as an objective function based on the viscous wave equation,while deriving Q-compensated wavefield propagation and joint operators of prismatic and primary waves and the Q-compensated demigration operator.Numerical examples on synthetic and field data verified the advantages of the proposed viscoacoustic LSRTM method of joint primary and prismatic waves over conventional viscoacoustic LSRTM and non-compensated LSRTM when using attenuating observed data.