Theory and Application of the Numerical Simulation in the Frozen Soil Problems

The freezing-thawing processes in soils are important components of terrestrial hydrology, which significantly influence energy and water exchanges between land surface and sub-surface. Long-term changes in frost and thaw depths are also an important indicator of climate change. A water-heat coupled movements model is established with frozen soil in this paper, which treats the freezing/thawing front as a moving interface governed by some Stefan problems with two free boundaries. The numerical simulation is conducted by using the modified finite difference method. The model is validated to compare its predictions with GEWEX Asian Monsoon Experiment(GAME)-Tibet observations at D66 site in Tibetan Plateau. The results show that the simulated soil temperature, soil water content and frost/thaw depth are in excellent agreement with the measured values. Finally, optimal error estimation for L^∞ norm is derived on the model problem by using coordinate transformation method. The numerical simulation system is established on the basis of rigorous mathematics and mechanics, which successfully solved the important and difficult problems of environmental science.

A Primitive-Based Reverse Modeling Method for Obtaining the Editable CAD model of Reversed Parts

By the traditional inversion methods, the model of the part reversed is obtained in mesh feature , which is hard to edit and redesign. In the paper, for the revised part, a modeling method to obtain the editable CAD mode was proposed. Firstly, an approach to construct the primitive structure tree used to describe the geometric structure of a part was proposed, by which the all the basic geometry primitives and their Boolean operations are logically arranged in tree format. Then, for each basic geometry primitive, a method to calculate the characteristics parameters and position and posture was proposed, which could be used to guide reversion measurement and modeling. For the basic primitives made of quadratic surface, a method for modeling the torus surface, whose model little research has been carried on, was proposed in which the torus surface equation is deduced by coordinate transformation method, has 8 independent parameters. Last, based on the guidance of primitive structure tree, a process for the characteristics parameters, minimum measuring points, forward modeling, positioning and assembly process was proposed, which could be used to direct measurements and to forward modeling. The example showed that the method proposed could be used to reverse the parts in the editable CAD model and provide for subsequent optimization design services.

Acoustic Metamaterial Design Method Based on Green Coordinate Transformation

Acoustic metamaterials have great application prospects in eliminating vibration and noise, but they are difficult to manufacture due to their anisotropy. This paper utilizes the Green coordinate transformation method to design acoustic metamaterials by combining with the transformation acoustics theory. Because the Green coordinate transformation is the pseudo-conformal mapping in three-dimensional coordinates, the anisotropy of designed metamaterials can be weakened. And also, the genetic algorithm is employed to optimize the anisotropy of metamaterials and reduce the designed metamaterial parameter difference further. Finally, the membrane-imbedded-type metamaterial is applied to realize the design and to illustrate the effectiveness of the proposed method by manipulating the acoustic wave propagation path.

CYFFD Parameterization Method for Cylindrical Components of Aircrafts

This paper proposes a parameterization method using cylindrical coordinates based free-form deformation(CYFFD) technique by introducing a coordinate transformation method and a virtual lattice method. The method is suitable for axisymmetric and non-axisymmetric cylindrical applications. CYFFD is able to deform radially and circumferentially and to maintain first order and curvature continuity across frame border. First, the coordinate transformation step helps capture geometrical characteristics of cylindrical objects to conduct radial and circumferential deformation. Due to the need of delicate shape design, FFD lattice need be set up closely around cylinder-like objects and this will cause the boundary of FFD frame to intersect with the objects, which lead to derivative discontinuity at the intersection. The virtual lattice method is introduced to reuse some control points as virtual ones so that first order and curvature continuity can be preserved. A cylinder deformation example compares the capability of CYFFD with that of conventional FFD for radial and circumferential deformation and keeping derivative continuity. An airplane nose example shows the possibility to use CYFFD and NFFD together for complex shape. A nacelle deformation example and fitting example show that CYFFD is valuable for non-axisymmetric cylindrical objects with complex shapes. The optimization example on cylinder nose shape indicates that CYFFD can give good optimization results and it is valuable for parameterizing cylinder-like objects.

THE COORDINATE TRANSFORMATION METHOD OF HIGH RESOLUTION DEM DATA

Coordinate transformation methods of DEM data can be divided into two categories. One reconstruct based on original vector elevation data. The other transforms DEM data blocks by transforming parameters. But the former doesn’t work in the absence of original vector data, and the later may cause errors at joint places between adjoining blocks of high resolution DEM data. In view of this problem, a method dealing with high resolution DEM data coordinate transformation is proposed. The method transforms DEM data into discrete vector elevation points, and then adjusts positions of points by bi-linear interpolation respectively. Finally, a TIN is generated by transformed points, and the new DEM data in target coordinate system is reconstructed based on TIN. An algorithm which can find blocks and transform automatically is given in this paper. The method is tested in different terrains and proved to be feasible and valid.

A multi-block finite difference method for seismic wave equation in auxiliary coordinate system with irregular fluid–solid interface

Purpose The purpose of this paper is to develop a new finite difference method for solving the seismic wave propagation in fluid-solid media, which can be described by the acoustic and viscoelastic wave equations for the fluid and solid parts, respectively. Design/methodology/approach In this paper, the authors introduced a coordinate transformation method for seismic wave simulation method. In the new method, the irregular fluid–solid interface is transformed into a horizontal interface. Then, a multi-block coordinate transformation method is proposed to mesh every layer to curved grids and transforms every interface to horizontal interface. Meanwhile, a variable grid size is used in different regions according to the shape and the velocity within each region. Finally, a Lebedev-standard staggered coupled grid scheme for curved grids is applied in the multi-block coordinate transformation method to reduce the computational cost. Findings The instability in the auxiliary coordinate system caused by the standard staggered grid scheme is resolved using a curved grid viscoelastic wave field separation strategy. Several numerical examples are solved using this new method. It has been shown that the new method is stable, efficient and highly accurate in solving the seismic wave equation defined on domain with irregular fluid–solid interface. Originality/value First, the irregular fluid–solid interface is transformed into a horizontal interface by using the coordinate transformation method. The conversion between pressures and stresses is easy to implement and adaptive to different irregular fluid–solid interface models, because the normal stress and shear stress vanish when the normal angle is 90° in the interface. Moreover, in the new method, the strong false artificial boundary reflection and instability caused by ladder-shaped grid discretion are resolved as well.