Comparison of soil erosion models used to study the Chinese Loess Plateau

The Loess Plateau suffers from severe soil erosion that leads to a series of ecological and economic problems such as reduced land productivity, exacerbated rural poverty, decreased biodiversity and sedimentation of the riverbed in the lower reaches of the Yellow River. Soil erosion models are commonly used on the Loess Plateau to help target sustainable land management strategies to control soil erosion. In this study, we compared eleven soil erosion models that were previously used on the Loess Plateau. We studied their prediction accuracy, process representation, data and calibration requirements, and potential application in scenario studies. The selected models consisted of a broad range of model types, structures and scales. The comparison showed that process-based and empirical models did not necessarily yield more accurate results over one another for the Loess Plateau. Among the process-based models, Si’ model, WEPP and MMF had the highest prediction accuracy. However, some of the selected models were tested with total sediment load while others were tested with suspended sediment load (i.e. bedload is not included), which is subject to several drawbacks. Research questions that each of the models can address on the Loess Plateau were suggested. Further improvement of soil erosion models for the Loess Plateau should concentrate on enhancing the quality of data for model implementation and testing, incorporating key processes into process-based models according to their aims and scales, comparing models that address the same research questions, and implementing internal and spatial model testing

台灣海岸山脈東坡南北段河階地形之比較研究--以馬武窟溪和豐濱溪為例

[[abstract]]台灣海岸山脈是一地殼運動相當活躍的地區, 其地殼上升量有南北不等的情形, 而以 南段大於北段。 海岸山脈區內較大的河川大都在東坡發育, 成獨立的順向河注入太平洋, 沿岸均有發 達的階地。本文選取除了橫切海岸山脈中段的秀姑巒溪以外南北二最大河川--馬武窟 溪及豐濱溪進行研究, 發現兩流域內的河階地形有若干的異同, 值得研究。 將二河階群的特性分為形態、規模及堆積物等三要素加以調查、比較, 發現地殼運動 、氣候、沿岸地層的變化對河階的發育至為重要。 由馬武窟溪階地的階序及階產崖高度均較豐濱溪者為大, 可推測海岸山脈的地殼上升 量有南大於北的情形。這與海階的研究及大地測量的結果頗為吻合。而且由二者均屬 岩石河階的性質視之, 劇烈的地殼上升運動是促使河床回春下切, 而形成河階的主要 原因。 由階崖的比高、階面的寬度及階地堆積層逐漸向低位階減小的情形視之, 可能受晚更 新世以來的氣候逐漸變乾、而使流量減小所致。但此一推論, 目前尚缺乏更直接的證 據, 有等進一步研究。 馬武窟溪在硬岩區因側蝕不易, 而無階地發育, 豐濱溪全流域均屬軟岩區, 階地分佈 較連續; 而硬岩的擋水作用使馬武窟溪在硬岩區以上的河道趨向曲流形態發育, 而豐 濱溪無硬岩阻擋, 呈直流型流路; 曲流形態愈發達, 相對的也使馬武窟溪的坡降愈小 , 甚至比豐濱溪還小; 而二硬岩區所夾的軟岩區, 河道易側蝕, 搬運物因流速減緩, 易生較厚層堆積。這些都是受沿岸地層變化所影響之結果。 此外, 階地堆積層中的礫石其形態受母質的軟硬、始初狀態影響最大, 不與搬運距離 , 高、低位階有明顯的關係。礫石形態的差異仍是來自沿岸地層變化所引起。

楊守敬之藏書及其學術

[[abstract]]本論文主旨在研究揚守敬藏書事業及其文獻學之成就，並附帶討論清代私人藏書與日 本存藏中國古籍的情況，藉以凸顯楊氏在近代學術史上的地位。資料來源包括：楊氏 觀海堂現存藏書、楊氏本人著述、正史、筆記、各家藏書志、各學門研究專書、日本 人著述及單篇論文等。全文除引論、結論，凡六章、二十一節，約十二萬字。各章大 旨如下： 第一章說明清代學術之發達與私人藏書之興盛，有密切關係；並藉以點以楊氏之事業 實有社會風氣。 第二章說明歷代中國古書流傳日本之情形，及日本庋藏之本富，以知楊氏訪書東瀛， 有深厚之淵源。 第三章介紹楊氏生平、學術面貌，及其在日訪書之機緣、事實等。 第四章調查楊氏觀海堂藏書之下落及現況，以為研究其藏書題記之基礎。 第五章說明觀海堂藏書之研究價值。 第六章分析楊氏在各書之考證題記中，呈現之文獻學成就。

Investigation Study of the Influence of Pole Numbers on Torque Density and Flux-Weakening Ability of Fractional Slot Concentrated Winding Wheel-Hub Machines

Fractional slot concentrated winding machines (FSCWMs) with the low operation speed and large diameter usually have a large number of poles and slots; thus, numerous pole/slot combinations are feasible. The common practice to choose pole/slot combinations by multiplying the basic combinations may neglect some competitive candidates. Taking 36-slot FSCWMs as examples, this paper investigates the influence of pole numbers on torque density and flux-weakening ability, the two most vital performances of wheel-hub machine. It is shown that the machines with pole number slightly less than the slot number have the highest torque densities. Each component of synchronous inductance is separately analyzed, and its variation against pole numbers shows obvious regularity. Machines with pole numbers larger than the slot numbers have an excellent flux-weakening ability due to the large inductance and small permanent magnet flux linkage. The measurements together with the finite element analysis results confirm that the stator leakage inductance contributes the most to the superior flux-weakening ability. The identical analysis is also performed on 54-slot and 81-slot FSCWMs, with similar regularities observed.DC systems, Energy conversion & Storag

A Sliding-Mode Position Estimation Method with Chattering Suppression for LCL-Equipped High-Speed Surface-Mounted PMSM Drives

This article proposes a sliding-mode position estimation method for high-speed surface-mounted permanent magnet synchronous machines with LCL filter. The implementation of the LCL filter aims at smoothing the motor current and reducing the iron loss caused by the harmonic currents. First, the discrete-time model of the LCL-filtered motor drive system is developed. Based on the developed model, the sliding-mode observer is proposed with more robustness against the parameter variation to estimate the back EMF, which contains the information of the rotor speed and position. Because of the elimination of the capacitor voltage sensors, the augmented sliding surface is designed to achieve arbitrary pole placement with only output feedback. Besides, considering the analog-to-digital scaling error and pulsewidth modulation harmonics, a reaching law with enhanced chattering suppression ability is proposed. Compared with the conventional methods, the chattering problem is well alleviated and thus the speed estimation ripple is much reduced. Finally, the effectiveness of the proposed method, even with the mismatched parameters adopted is validated at 100 kr/min with the sampling frequency 20 kHz. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

Simplified Quadratic Optimization based IPMSM Full-Speed Range Rotor Position Estimation in Synchronous Rotating Frame

This article proposes a rotor position and speed estimation method for the interior permanent magnet synchronous machine (IPMSM) in the full-speed range. The proposed method is implemented in the synchronous rotating frame. Based on the voltage equation of the IPMSM in the synchronous rotating frame, a single-variable optimization problem is formulated to solve the rotor position at each current sampling step. After that, the solved position is fed into a phase-locked loop observer to obtain the estimated rotor speed and smooth out the estimation. The proposed position and speed estimation methods are effective from standstill to high speed, and no estimation algorithm switching is needed during speed variation. Details about the convexity of the optimization problem, the effects of parameter mismatch and sampling noise, and the solving method of the problem are discussed. Finally, experiments are conducted in both steady and dynamic situations to validate the effectiveness and robustness of the proposed algorithm.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

Position Sensorless Drive and Online Parameter Estimation for Surface-Mounted PMSMs Based on Adaptive Full-State Feedback Control

In this article, a position sensorless drive and online parameter estimation method for surface-mounted permanent magnet synchronous machines-based on adaptive full-state feedback current control is proposed. The position sensorless drive is established by the detection of the back-electromotive force in the gamma delta synchronous reference frame, which is effective at the medium-speed and high-speed range. Besides, accurate estimation of the winding resistance, the stator inductance, and the flux linkage of the PM is achieved independently. Compared with the traditional recursive-least-square methods, the proposed parameter identification method can be easily implemented because of the significantly reduced execution time. With the help of the parameter identification, the precise position estimation can be achieved by the proposed sensorless control method regardless of the parameter variation during the operation. The stability of the proposed method is proved by the Lyapunov-function method. Finally, the effectiveness of the proposed method is validated by the simulation and experimental results.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

A New Hybrid Method for Magnetic Field Calculation in IPMSM Accounting for Any Rotor Configuration

In this paper, a new hybrid model is proposed for the prediction of air gap magnetic field distribution (MFD) in interior permanent magnet machines with any rotor configuration. The slotless magnetic field is first predicted by finite-element method (FEM) with automatic scripting in MATLAB to consider saturation in the rotor iron. Afterward, the conformal mapping viz., Schwarz-Christoffel mapping is introduced to take the slotting effect into account. Consequently, the MFD could be calculated. The back electromagnetic forces, cogging torque, and output torque are obtained accordingly. Then a subdomain model is developed to consider the armature reaction. The results show that the proposed hybrid approach agrees well with the FEM. The model is further verified by experiments. The main contribution of this paper is to reduce the computation time remarkably while maintaining the calculation accuracy.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

General Analytical Modeling for Magnet Demagnetization in Surface Mounted Permanent Magnet Machines

This paper proposes an analytical model for the prediction of airgap magnetic field distribution for axial flux permanent magnet (AFPM) machine with partial magnet demagnetization. The AFPM machine geometry is first converted to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then current sheet representation of PM is derived to consider the partial demagnetization using superposition principle. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the results of proposed approach agrees with that of finite-element method. The model is further validated by experiments under both healthy and demagnetized conditions, which can validate the proposed approach. Main contribution of the work is to consider the partial irreversible demagnetization. Moreover, the proposed method is applicable for both AFPM and radial flux permanent magnet machine.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care  Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag

A New Rotor Structure for High Speed Flywheel Permanent Magnet Synchronous Machine

This paper presents a new rotor design with assembled permeable retaining sleeve (APRS) to improve performances of a high speed permanent magnet synchronous machine (PMSM). The APRS consists of equal number of permeable and nonmagnetic parts, which are alternately arranged and assembled together circumferentially via keyways. Electromagnetic and mechanical characteristics of the rotor applied to a high speed flywheel PMSM are analyzed using finite element method. Machine performances are compared to an original design with commonly used rotor structure. It shows that phase inductance of the high speed machine increases dramatically due to smaller effective air gap, which may benefit suppressing inverter current harmonics. Also, permanent magnet usage reduces by 9.4 % to obtain identical back electromotive force and torque constant. In addition, a smaller skin depth owing to high-permeability material and the circumferential segmentation of the retaining sleeve effectively reduce rotor eddy current. Associated loss decreases by 40.7 % under open-circuit condition. A prototype rotor is fabricated and preliminary experimental tests are performed to confirm the analysis results.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag