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High-speed rendering pipeline for polygon-based holograms

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Photonics Research 2023年第2期11卷 313-328页

作者： FAN WANG TOMOYOSHI ITO TOMOYOSHI SHIMOBABA Graduate School of Engineering Chiba UniversityChiba 263-8522Japan

As an important three-dimensional(3D) display technology, computer-generated holograms(CGHs) have been facing challenges of computational efficiency and realism. The polygon-based method, as the mainstream CGH algorithm, has been widely studied and improved over the past 20 years. However, few comprehensive and high-speed methods have been proposed. In this study, we propose an analytical spectrum method based on the principle of spectral energy concentration, which can achieve a speedup of nearly 30 times and generate highresolution(8K) holograms with low memory requirements. Based on the Phong illumination model and the subtriangles method, we propose a shading rendering algorithm to achieve a very smooth and realistic reconstruction with only a small increase in computational effort. Benefiting from the idea of triangular subdivision and octree structures, the proposed original occlusion culling scheme can closely crop the overlapping areas with almost no additional overhead, thus rendering a 3D parallax sense. With this, we built a comprehensive high-speed rendering pipeline of polygon-based holograms capable of computing any complex 3D object. Numerical and optical reconstructions confirmed the generalizability of the pipeline.

关键词： rendering polygon computer

A simulation-based study on longitudinal gust response of flexible flapping wings

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Acta Mechanica Sinica 2018年第6期34卷 1048-1060页

作者： Toshiyuki Nakata Ryusuke Noda Shinobu Kumagai Hao Liu Graduate School of Engineering Chiba UniversityChiba 263-8522Japan Department of Mechanical Engineering Kanto Gakuin UniversityKanagawa 263-8501Japan

Winged animals such as insects are capable of flying and surviving in an unsteady and unpredictable aerial *** generate and control aerodynamic forces by flapping their flexible *** the dynamic shape changes of their flapping wings are known to enhance the efficiency of their flight,they can also affect the stability of a flapping wing flyer under unpredictable disturbances by responding to the sudden changes of aerodynamic forces on the *** order to test the hypothesis,the gust response of flexible flapping wings is investigated numerically with a specific focus on the passive maintenance of aerodynamic forces by the wing *** computational model is based on a dynamic flight simulator that can incorporate the realistic morphology,the kinematics,the structural dynamics,the aerodynamics and the fluid-structure interactions of a hovering *** longitudinal gusts are imposed against the tethered model of a hovering hawkmoth with flexible flapping *** is found that the aerodynamic forces on the flapping wings are affected by the gust,because of the increase or decrease in relative wingtip velocity or kinematic angle of *** passive shape change of flexible wings can,however,reduce the changes in the magnitude and direction of aerodynamic forces by the gusts from various directions,except for the downward *** adaptive response of the flexible structure to stabilise the attitude can be classified into the mechanical feedback,which works passively with minimal delay,and is of great importance to the design of bio-inspired flapping wings for micro-air vehicles.

关键词： Insect flight Flapping wing Flexible wing Gust response Fluid-structure interaction Mechanical feedback

Compelling Challenges in Antenna Technologies for Future Medical Applications

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Engineering 2022年第4期8卷 15-17页

作者： Koichi Ito Center for Frontier Medical Engineering Chiba UniversityChiba 263-8522Japan

*** Numerous types of antennas have been developed,tested,and utilized for medical applications such as diagnosis,treatment,data transmission,and wireless power transfer(WPT).Recently,compact and robust antennas are needed to realize implantable and wearable wireless devices for medical applications such as delivering drugs from implanted capsules,stimulating nerve systems,and monitoring physiological data[1].Because antennas for medical applications are used close to or in a human body,their effects on the human body should be included in their development and evaluation[2].However,it is rather difficult due to ethical and practical reasons to employ a real human body when experimentally evaluating the characteristics of antennas or wireless devices for medical ***,numerical simulations are generally conducted as an alternative,using elaborate digital human models[3].Many different types of software are now commercially available for this purpose,along with digital human-body models.

关键词： antennas utilized diagnosis

Multi-criteria technique for mapping of debris-covered and clean-ice glaciers in the Shaksgam valley using Landsat TM and ASTER GDEM

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Journal of Mountain Science 2016年第4期13卷 703-714页

作者： Alifu HAIRETI Ryutaro TATEISHI Bayan ALSAAIDEH Saeid GHARECHELOU geosystem and biological sciences division graduate schools of sciencechiba university1-33 Yayoi-choInage-kuChiba-shiChiba 263-8522Japan center for environmental remote sensing chiba university1-33 Yayoi-choInage-kuChiba-shiChiba 263-8522Japan

Glaciers in the Shaksgam valley provide important fresh water resources to neighbourhood livelihood. Repeated creation of the glacier inventories is important to assess glacier–climate interactions and to predict future runoff from glacierized catchments. For this study, we applied a multi-criteria technique to map the glaciers of the Shaksgam valley of China, using Landsat Thematic Mapper(Landsat TM)(2009) and Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model version two(ASTER GDEM V2) data. The geomorphometric parameters slope, plan, and profile curvature were generated from ASTER GDEM. Then they were organized in similar surface groups using cluster analysis. For accurate mapping of supraglacial debris area, clustering results were combined with a thermal mask generated from the Landsat TM thermal band. The debris-free glaciers were identified using the band ratio(TM band 4/TM band 5) technique. Final vector maps of the glaciers were created using overlay tools in a geographic information system(GIS).Accuracy of the generated glacier outlines was assessed through comparison with glacier outlines based on the Second Chinese Glacier Inventory(SCGI) data and glacier outlines created from high-resolution Google Earth? images of 2009. Glacier areas derived using the proposed approach were 3% less than in the reference datasets. Furthermore, final glacier maps show satisfactory mapping results, but identification of the debris-cover glacier terminus(covered by thick debris layer) is still problematic. Therefore, manual editing was necessary to improve the final glacier maps.

关键词： Remote sensing Glacier inventory Shaksgam valley Landsat TM ASTER GDEM

Near wake vortex dynamics of a hovering hawkmoth

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Acta Mechanica Sinica 2009年第1期25卷 23-36页

作者： Hikaru Aono Wei Shyy Hao Liu Department of Aerospace Engineering University of Michigan Ann Arbor MI 48109 USA Graduate School of Engineering Chiba University Chiba 263-8522 Japan

Numerical investigation of vortex dynamics in near wake of a hovering hawkmoth and hovering aerodynamics is conducted to support the development of a biology-inspired dynamic flight simulator for flapping wingbased micro air vehicles. Realistic wing-body morphologies and kinematics are adopted in the numerical simulations. The computed results show 3D mechanisms of vortical flow structures in hawkmoth-like hovering. A horseshoe-shaped primary vortex is observed to wrap around each wing during the early down- and upstroke; the horseshoe-shaped vortex subsequently grows into a doughnut-shaped vortex ring with an intense jet-flow present in its core, forming a downwash. The doughnut-shaped vortex rings of the wing pair eventu- ally break up into two circular vortex rings as they propagate downstream in the wake. The aerodynamic yawing and rolling torques are canceled out due to the symmetric wing kinematics even though the aerodynamic pitching torque shows significant variation with time. On the other hand, the time- varying the aerodynamics pitching torque could make the body a longitudinal oscillation over one flapping cycle.

关键词： Aerodynamics Hovering Hawkmoth Vortical flow structure

Towards long-multitemporal change detection using SVI differencing by integrated DWT ISOCLUS: a model for forest temporal dynamics mapping

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International Journal of Digital Earth 2011年第2期4卷 108-132页

作者： Yashon O.Oumaa Ryutaro Tateishi Tateishi Laboratory Centre for Environmental Remote Sensing(CEReS)Graduate School of Science and TechnologyChiba University1-33 Yayoi-choInage-kuChiba 263-8522Japan Tateishi Laboratory Centre for Environmental Remote Sensing(CEReS)Chiba University1-33 Yayoi-choInage-kuChiba 263-8522Japan

Characterisation and mapping of land cover/land use within forest areas over long-multitemporal intervals is a complex *** complexity is mainly due to the location and extent of such areas and,as a consequence,to the lack of full continuous cloud-free coverage of those large regions by one single remote sensing *** order to provide improved long-multitemporal forest change detection using Landsat MSS and ETMin part of *** rainforest,and to develop a model for forest change monitoring,wavelet transforms analysis was tested against the ISOCLUS algorithm for the derivation of changes in natural forest cover,as determined using four simple ratio-based Vegetation Indices:Simple Ratio(SR),Normalised Difference Vegetation Index(NDVI),Renormalised Difference Vegetation Index(RDVI)and modified simple ratio(MSR).Based on statistical and empirical accuracy assessments,RDVI presented the optimal index for the case *** overall accuracy statistic of the wavelet derived change/no-change was used to rank the performances of the indices as:RDVI(91.68%),MSR(82.55%),NDVI(79.73%)and SR(65.34%).The integrated discrete wavelet transformISOCLUS(DWTISOCLUS)result was 42.65%higher than the independent ISOCLUS approach in mapping the change/no-change *** methodology suggested in this study presents a cost-effective and practical method to detect land-cover changes in support of decision-making for updating forest databases,and for long-term monitoring of vegetation changes from multisensor *** current research contributes to Digital Earth with regards to geo-data acquisition,data mining and representation of one forest systems.

关键词： digital earth long-multitemporal forest change detection Spectral Vegetation Index Differencing(SVID) ISOCLUS discrete wavelet transform(DWT) integrated DWTISOCLUS

A Three-axis PD Control Model for Bumblebee Hovering Stabilization

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Journal of Bionic Engineering 2018年第3期15卷 494-504页

作者： Xiangdong Zhang Hao Liu Shanghai Jiao Tong University and chiba University International Cooperative Research Centre (SJTU-CU ICRC) Shanghai Jiao Tong University Shanghai 200240 China Graduate School of Engineering Chiba University Chiba 263-8522 Japan

Flight stabilization in insects is normally achieved through a closed-loop system integrating the intemal dynamics and feedback control. Recent studies have reported that flight instability may exist in most flying insects but how insects achieve the flight stabilization still remains poorly understood. Here we propose a control model specified for bumblebee hovering stabilization by applying a three-axis PD （proportional-derivative）-controller to a free-flying bumblebee computational model with six Degrees of Freedom （DoFs）. Morphological and kinematic models of a realistic bumblebee in hovering are built up based on measurements whereas a versatile bio-inspired dynamic flight simulator is employed in simulations. A simplified flight dynamic model is further developed as a fast model for control parameter tuning. Our results demonstrate that the stabilizing control model is capable of achieving the hovering stabilization with small perturbations in terms of 6-DoF, implying that the simplified linear algorithms can still work reasonably for bumblebee hovering. A further sensitivity analysis of the control parameters reveals that yaw control via manipulating pitch angle of the wing is mostly sensitive, implicating that bumblebee may utilize alternative yaw control strategies.

关键词： flapping bumblebee flight stabilization PD controller multi-axis control

ANALYSIS OF SHAKEDOWN OF FG BREE PLATE SUBJECTED TO COUPLED THERMAL-MECHANICAL LOADINGS

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Acta Mechanica Solida Sinica 2009年第2期22卷 95-108页

作者： Xianghe Peng Ning Hu Hengwei Zheng Cuirong Fang Department of Engineering Mechanics Chongqing University Chongqing 400044 China Department of Mechanical Engineering Chiba University 1-33 Yayoi Inage-ku Chiba 263-8522 Japan

The static and kinematic shakedown of a functionally graded （FG） Bree plate is analyzed. The plate is subjected to coupled constant mechanical load and cyclically varying temperature. The material is assumed linearly elastic and nonlinear isotropic hardening with elastic modulus,yield strength and the thermal expansion coeffcient varying exponentially through the thickness of the plate. The boundaries between the shakedown area and the areas of elasticity,incremental collapse and reversed plasticity are determined,respectively. The shakedown of the counterpart made of homogeneous material with average material properties is also analyzed. The comparison between the results obtained in the two cases exhibits distinct qualitative and quantitative difference,indicating the importance of shakedown analysis for FG structures. Since FG structures are usually used in the cases where severe coupled cyclic thermal and mechanical loadings are applied,the approach developed and the results obtained are significant for the analysis and design of such kind of structures.

关键词： functionally graded material the Bree plate coupled thermal-mechanical loading,shakedown

Nanoengineering of Curved Supramolecular Polymers:Toward Single-Chain Mesoscale Materials

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Accounts of Materials Research 2022年第2期3卷 259-271页

作者： Sougata Datta Sho Takahashi Shiki Yagai Department of Applied Chemistry and Biotechnology Graduate School of EngineeringChiba UniversityChiba 263-8522Japan Division of Advanced Science and Engineering Graduate School of Engineering and Institute for Global Prominent Research(IGPR)Chiba UniversityChiba 263-8522Japan

CONSPECTUS:Recently,supramolecular polymers(SPs),which depend on the formation of reversible bonds between monomers,have attracted attention as a class of materials that can overcome the potential environmental problems of conventional polymeric *** development of various supramolecular polymers is important not only for their direct application as materials but also because their unique polymerization processes and dynamic properties have a profound influence on the development of polymeric and small-molecule-based functional *** other words,by limiting the dimensionality of molecular assemblies to one dimension,we can discover the essential aspects of selfassembly and *** particular,supramolecular polymerization,in whichπ-electron-rich planar molecules are stacked one-dimensionally via multiple interactions,is interesting because it gives“π-stacked SPs”with one-dimensional crystal-like *** excellent intrinsic(internal)structural order ofπ-stacked SPs is difficult to observe in higher-order structures that exhibit only a monotonous linear ***,our research has shown that when internal structural order intrinsically generates curvature,the curvature appears as a major feature of the entire polymer *** intrinsic curvature allows the formation of diverse topologies such as toroids,random coils,waves,spirals,and helicoids usingπ-stacked SPs and also allows structural changes at the single-polymer-chain level along a topology-dependent energy *** other words,π-stacked SP-based nanomaterials could enable free control of the structure at the single-polymer-chain *** Account will focus on our research into curved supramolecular polymers(CSPs)during the last five *** are formed by the hydrogen bonding between barbituratecontainingπ-conjugated molecules to produce giant supramolecular *** first give an overview of the molecular design of the monomers required for the formation of CSP

关键词： materials curvature bonds