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1.
For a channel-shoal system in a funnel-shaped basin the impact of dredging and dumping is investigated using a complex process-based
model. First, the residual flow and sediment transport circulations are analysed for the channel-shoal pattern, which has
emerged after a long-term model simulation. Results are compared to the Western Scheldt estuary, which forms the inspiration
for this study. Subsequently, different dredge and dump scenarios are modelled, according to a conceptual model, in which
ebb-and flood-channels and enclosed shoals form morphodynamic units (cells) with their own sediment circulation. Model results
show that dumping sediment in a channel further reduces the channel depth and induces erosion in the opposite channel, which
enhances tilting of the cross-section of the cell and eventually can lead to the degeneration of a multiple channel system
into a single channel. The impact of different dredging and dumping cases agrees with results from a stability analysis. This
means that this type of model applied to a realistic geometry can potentially be used for better prediction of the impact
of human interventions. 相似文献
2.
An automatic generation method of geological cross-sections in dredging engineering based on 3D geological solid models is presented.The 3D geological models are built applying the non-uniform rational B-splines(NURBS) technique,and a 2D profile can be calculated and generated automatically through Boolean operation to meet the demands of dredging projects.Moreover,an automatic marking method for geological attributes is put forward based on database technology,and the geological attributes include the profile name,scale,horizontal and vertical relative coordinates,geological lithology,and 2D standard lithology legend.At the same time,the automatic marking method can also provide an interactive mode for geological engineers to edit and modify the profile in the modeling system.Practical engineering applications show that the automatic generation method is a simple,flexible,fast and precise visual graphics rendering process that can create 2D standard profiles automatically and efficiently.This method also provides a convenient support tool for geological engineering digital analysis. 相似文献
3.
In this study, ground vibrations due to dynamic loadings from trains moving in subway tunnels were investigated using a 2.5D finite element model of an underground tunnel and surrounding soil interactions. In our model, wave propagation in the infinitely extended ground is dealt with using a simple, yet efficient gradually damped artificial boundary. Based on the assumption of invariant geometry and material distribution in the tunnel??s direction, the Fourier transform of the spatial dimension in this direction is applied to represent the waves in terms of the wave-number. Finite element discretization is employed in the cross-section perpendicular to the tunnel direction and the governing equations are solved for every discrete wave-number. The 3D ground responses are calculated from the wave-number expansion by employing the inverse Fourier transform. The accuracy of the proposed analysis method is verified by a semi-analytical solution of a rectangular load moving inside a soil stratum. A case study of subway train induced ground vibration is presented and the dependency of wave attenuation at the ground surface on the vibration frequency of the moving load is discussed. 相似文献
4.
梁伟文 《深圳职业技术学院学报》2011,10(3):3-6
以Loop细分曲面为例,根据细分曲面的网格迭代特性,讨论了细分曲面的精加工刀具轨迹生成方法,对精加工时使用球头刀和刀具接触位置的偏移来生成刀具轨迹位置.在刀具轨迹生成过程中提出一种Z-map空间网格点存储技术,同时为了提高加工质量提出干涉检查和修正方法,并进行了实例验证.结果表明该类型刀具轨迹生成方法对于网格曲面的加工是可行、有效的. 相似文献
5.
若要对新风机进行噪声分析及优化,必须建立其CAD参数化模型.而新风机通道形状十分复杂,采用传统CAD软件正向准确地设计出实体模型较为困难.基于此,采用逆向工程技术对XHBX-D2TH型号的新风换气机进行三维建模与装配.首先,采用三维数字化仪获取实物表面三坐标信息;然后,应用逆向工程软件Geomagic Studio对扫描仪获得的点云数据进行预处理和封装;最后,利用软件CATIA进行实体建模与装配,所得结构符合工程实际. 相似文献
6.
The siltation induced by wind waves in an entrance channel is one of the prime factors influencing the operation efficiency of a port.It is necessary to predict the siltation accurately for dredging and ship operation passing through the entrance of the port.However,it is difficult to apply the traditional method to predicting entrance siltation because of its complex computational procedure and lacking the data of ocean dynamic elements in the specified sea area.From the view of energy conservation,a direct relationship between wind conditions and sediment deposition can be founded.On the basis of the above methodology,an empirical formula expressed by wind conditions for forecasting the siltation in the entrance channel is set up.The wind conditions are easily obtained from the local meteorological stations or weather maps,so the formula established in this paper is more convenient and practical than the traditional method.A case study is provided,in which the emopirical formula is calibrated and verified utilizing the measured wind and siltation conditions in the entrance channel of the port.Comparisons between computed values and measured data show satisfactory agreement. 相似文献
7.
Parametric design of a part with free-form surfaces 总被引：1，自引：0，他引：1
KIM Yeoung-il KIM Li-ra JUN Cha-soo 《浙江大学学报(A卷英文版)》2006,7(9):1530-1534
INTRODUCTION A 3D solid model is used in various processes such as design, engineering evaluation, drafting, manufacturing, and so on. It is a time-consuming and skill-required job to create a complicated 3D solid model. Most commercial CAD tools support func- tions to generate engineering drawings from solid models automatically. However, adjusting layouts, dimensioning, and inserting annotations are required and they are tedious and time-consuming work. Most current CAD/CAM/CAE so… 相似文献
8.
改进传统的活动形状模型法,准确地提取人脸特征点后,利用人脸特征点初步估计人脸姿态,以初步估计值为初始值,通过线性回归迭代算法,精确估计3D人脸空间姿态。实验结果表明,本文提出的新方法不仅可以获得稳定和唯一的3D人脸空间姿态．而且与同类方法比较具有较好的姿态估计精确度。 相似文献
9.
以南宁地铁一号线南湖段下穿隧道为工程背景,建立隧道开挖的三维有限元模型,通过数值分析,得到盾构施工过程中地层变形的分布规律,讨论盾构施工过程中注浆压力对地表沉降、水平位移及拱顶位移的影响,分析掌子面压力对地表隆起的影响规律。研究结果表明,注浆压力对地表变形会产生明显的影响,随着注浆压力的增大,地表沉降及水平位移明显减小。当掌子面压力大于0.1 MPa时,会引起掌子面前方土体产生向上的位移,地表隆起量随掌子面压力的增加而增大。 相似文献
10.
A method for computing the visible regions of free-form surfaces is proposed in this paper. Our work is focused on accurately
calculating the visible regions of the sequenced rational Bézier surfaces forming a solid model and having coincident edges
but no inner-intersection among them. The proposed method calculates the silhouettes of the surfaces without tessellating
them into triangle meshes commonly used in previous methods so that arbitrary precision can be obtained. The computed silhouettes
of visible surfaces are projected onto a plane orthogonal to the parallel light. Then their spatial relationship is applied
to calculate the boundaries of mutual-occlusion regions. As the connectivity of the surfaces on the solid model is taken into
account, a surface clustering technique is also employed and the mutual-occlusion calculation is accelerated. Experimental
results showed that our method is efficient and robust, and can also handle complex shapes with arbitrary precision.
Project supported by the National Basic Research Program (973) of China (No. 2002CB312106) and the National Natural Science
Foundation of China (Nos. 60533070, and 60403047). The third author was supported by the project sponsored by a Foundation
for the Author of National Excellent Doctoral Dissertation of China (No. 200342) and a Program for New Century Excellent Talents
in University (No. NCET-04-0088), China 相似文献
11.
Tomographic particle image velocimetry(Tomo-PIV) is a state-of-the-art experimental technique based on a method of optical tomography to achieve the three-dimensional(3D) reconstruction for threedimensional three-component(3D-3C) flow velocity measurements. 3D reconstruction for Tomo-PIV is carried out herein. Meanwhile, a 3D simplified tomographic reconstruction model reduced from a 3D volume light intensity field with 2D projection images into a 2D Tomo-slice plane with 1D projecting lines, i.e., simplifying this 3D reconstruction into a problem of 2D Tomo-slice plane reconstruction, is applied thereafter. Two kinds of the most well-known algebraic reconstruction techniques, algebraic reconstruction technique(ART) and multiple algebraic reconstruction technique(MART), are compared as well. The principles of the two reconstruction algorithms are discussed in detail, which has been performed by a series of simulation images, yielding the corresponding reconstruction images that show different features between the ART and MART algorithm, and then their advantages and disadvantages are discussed. Further discussions are made for the standard particle image reconstruction when the background noise of the pre-initial particle image has been removed. Results show that the particle image reconstruction has been greatly improved. The MART algorithm is much better than the ART. Furthermore, the computational analyses of two parameters(the particle density and the number of cameras), are performed to study their effects on the reconstruction. Lastly, the 3D volume particle field is reconstructed by using the improved algorithm based on the simplified 3D tomographic reconstruction model, which proves that the algorithm simplification is feasible and it can be applied to the reconstruction of 3D volume particle field in a Tomo-PIV system. 相似文献
12.
为了提高包含有交界面的三维复杂流动问题的求解精度，将二维坐标系中的Youngs算法公式推广到三维坐标系应用，根据流体体积分数的定义，在二维直角坐标系Youngs算法的基础上，把介质分界面近似为平面，通过引入修正系数，实现了Youngs算法在三维坐标系中的应用，给出计算方法，并编写程序进行算例验证，数值模拟了具有复杂边界的空中爆炸形成冲击波的形成和传播过程，通过数值试验，证明了Youngs算法在三维坐标系中成功的应用． 相似文献
13.
LENG Biao QIN Zheng LI Li-qun 《浙江大学学报(A卷英文版)》2007,8(12):1953-1961
In this paper, we present a novel Support Vector Machine active learning algorithm for effective 3D model retrieval using the concept of relevance feedback. The proposed method learns from the most informative objects which are marked by the user, and then creates a boundary separating the relevant models from irrelevant ones. What it needs is only a small number of 3D models labelled by the user. It can grasp the user's semantic knowledge rapidly and accurately. Experimental results showed that the proposed algorithm significantly improves the retrieval effectiveness. Compared with four state-of-the-art query refinement schemes for 3D model retrieval, it provides superior retrieval performance after no more than two rounds of relevance 相似文献
14.
无人机倾斜摄影技术已成功应用于各项国民经济建设,如地籍测量、大面积区域测量等,但大多采用价格昂贵的固定翼和多镜头的旋翼无人机,针对带状地形图的应用研究较少。鉴于此,采用消费级大疆精灵4无人机和ContextCapture三维建模软件,通过外业数据采集和内业数据处理,生成三维模型、DOM、DSM、三维点云数据,利用清华山维（EPS）采集数据、CASS7.1进行编辑。获得数字线划图（DLG）,并将其与利用RTK测量的地形图进行对比分析,通过对3类主要地物的精度比对,得出道路精度为0.042m,满足1∶500带状地形图测图要求。 相似文献
15.
Daniel Preece Sarah B. Williams Richard Lam Renate Weller 《Anatomical sciences education》2013,6(4):216-224
Three‐dimensional (3D) information plays an important part in medical and veterinary education. Appreciating complex 3D spatial relationships requires a strong foundational understanding of anatomy and mental 3D visualization skills. Novel learning resources have been introduced to anatomy training to achieve this. Objective evaluation of their comparative efficacies remains scarce in the literature. This study developed and evaluated the use of a physical model in demonstrating the complex spatial relationships of the equine foot. It was hypothesized that the newly developed physical model would be more effective for students to learn magnetic resonance imaging (MRI) anatomy of the foot than textbooks or computer‐based 3D models. Third year veterinary medicine students were randomly assigned to one of three teaching aid groups (physical model; textbooks; 3D computer model). The comparative efficacies of the three teaching aids were assessed through students' abilities to identify anatomical structures on MR images. Overall mean MRI assessment scores were significantly higher in students utilizing the physical model (86.39%) compared with students using textbooks (62.61%) and the 3D computer model (63.68%) (P < 0.001), with no significant difference between the textbook and 3D computer model groups (P = 0.685). Student feedback was also more positive in the physical model group compared with both the textbook and 3D computer model groups. Our results suggest that physical models may hold a significant advantage over alternative learning resources in enhancing visuospatial and 3D understanding of complex anatomical architecture, and that 3D computer models have significant limitations with regards to 3D learning. Anat Sci Educ 6: 216–224. © 2013 American Association of Anatomists. 相似文献
16.
In freeform surface modelling, developable surfaces have much application value. But, in 3D space, there is not always a regular developable surface which interpolates the given boundary of an arbitrary piecewise smooth closed curve. In this paper, tensor product Bézier surfaces interpolating the closed curves are determined and the resulting surface is a minimum of the functional defined by the L2-integral norm of the Gaussian curvature. The Gaussian curvature of the surfaces is minimized by the method of solving nonlinear optimization problems. An improved approach trust-region form method is proposed. A simple application example is also given. 相似文献
17.
Vicky Vandenbossche Joris Van de Velde Stind Avet Wouter Willaert Stian Soltvedt Noeska Smit Emmanuel Audenaert 《Anatomical sciences education》2022,15(4):731-744
High-fidelity anatomical models can be produced with three-dimensional (3D) scanning techniques and as such be digitally preserved, archived, and subsequently rendered through various media. Here, a novel methodology—digital body preservation—is presented for combining and matching scan geometry with radiographic imaging. The technique encompasses joining layers of 3D surface scans in an anatomical correct spatial relationship. To do so, a computed tomography (CT) volume is used as template to join and merge different surface scan geometries by means of nonrigid registration into a single environment. In addition, the use and applicability of the generated 3D models in digital learning modalities is presented. Finally, as computational expense is usually the main bottleneck in extended 3D applications, the influence of mesh simplification in combination with texture mapping on the quality of 3D models was investigated. The physical fidelity of the simplified meshes was evaluated in relation to their resolution and with respect to key anatomical features. Large- and medium-scale features were well preserved despite extensive 3D mesh simplification. Subtle fine-scale features, particular in curved areas demonstrated the major limitation to extensive mesh size reduction. Depending on the local topography, workable mesh sizes ranging from 10% to 3% of the original size could be obtained, making them usable in various learning applications and environments. 相似文献
18.
Three‐dimensional printing of X‐ray computed tomography datasets with multiple materials using open‐source data processing 
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下载免费PDF全文 Ian M. Sander Matthew T. McGoldrick My N. Helms Aislinn Betts Anthony van Avermaete Elizabeth Owers Evan Doney Taimi Liepert Glen Niebur Douglas Liepert W. Matthew Leevy 《Anatomical sciences education》2017,10(4):383-391
Advances in three‐dimensional (3D) printing allow for digital files to be turned into a “printed” physical product. For example, complex anatomical models derived from clinical or pre‐clinical X‐ray computed tomography (CT) data of patients or research specimens can be constructed using various printable materials. Although 3D printing has the potential to advance learning, many academic programs have been slow to adopt its use in the classroom despite increased availability of the equipment and digital databases already established for educational use. Herein, a protocol is reported for the production of enlarged bone core and accurate representation of human sinus passages in a 3D printed format using entirely consumer‐grade printers and a combination of free‐software platforms. The comparative resolutions of three surface rendering programs were also determined using the sinuses, a human body, and a human wrist data files to compare the abilities of different software available for surface map generation of biomedical data. Data shows that 3D Slicer provided highest compatibility and surface resolution for anatomical 3D printing. Generated surface maps were then 3D printed via fused deposition modeling (FDM printing). In conclusion, a methodological approach that explains the production of anatomical models using entirely consumer‐grade, fused deposition modeling machines, and a combination of free software platforms is presented in this report. The methods outlined will facilitate the incorporation of 3D printed anatomical models in the classroom. Anat Sci Educ 10: 383–391. © 2017 American Association of Anatomists. 相似文献
19.
清末,海河工程局和浚浦工程局相继在津沪两地诞生,主要负责两大港口的航道疏浚和维护,成为中国近代疏浚业的发端.两局均实行总工程司(师)负责制,其聘用的流程和规定形成严格的制度,提名筛选,不任人唯亲,这是明显区别于当时很多洋务企业的特征.其聘用机制、工作权威性与独立性,反映了两局机构性质和运营特点.通过引进外国技术和聘用外国专家,广泛而全面地接触和引进当时世界上最先进的疏浚技术和装备,采用西方经营管理模式,并加以本土化适应和改造,推动了中国疏浚事业的高起点发展;并培养了专业技术和管理人才,进而为中国现代水运建设事业奠定了基础. 相似文献
20.
Due to the complex nature of multi-source geological data, it is difficult to rebuild every geological struc-ture through a single 3D modeling method. The multi-source data interpretation method put forward in this analysis is based on a database-driven pattern and focuses on the discrete and irregular features of geological data. The geological data from a variety of sources covering a range of accuracy, resolution, quantity and quality are classified and inte-grated according to their reliability and consistency for 3D modeling. The new interpolation-approximation fitting construction algorithm of geological surfaces with the non-uniform rational B-spline （NURBS） technique is then pre-sented. The NURBS technique can retain the balance among the requirements for accuracy, surface continuity and data storage of geological structures. Finally, four alternative 3D modeling approaches are demonstrated with reference to some examples, which are selected according to the data quantity and accuracy specification. The proposed approaches offer flexible modeling patterns for different practical engineering demands. 相似文献