Enclosure design for a high-speed permanent magnet rotor
ENCLOSURE DESIGN FOR A HIGH-SPEED PERMANENT
MAGNET ROTOR
A. Borisavljevic*, H. Polinder*, J.A. Ferreira*
*Delft University of Technology, Mekelweg 4, 2628CD Delft, The Netherlands, email: a.borisavljevic@tudelft.nl
Keywords: rotor enclosure, retaining sleeve, rotor bandage, high-speed machines, PM machines
Abstract
High-speed permanent magnet rotors need a non-magnetic enclosure so as to ensure structural integrity of the rotor at elevated speeds. Optimal design of the enclosure is the focus of this paper. Analytical modelling of mechanical stress in the rotor is presented. The model distinguishes between influences of enclosure geometry and fitting on the stress, while also considering rotational speed and operating temperature. Through analytical modelling, a relatively simple approach of optimizing the enclosure is achieved. This optimization approach was used in the design of a carbon fibre enclosure of an unconventional high-speed rotor with a disc shape. It is shown that a planar analytical model of stress with isotropic material assumption is sufficiently good for structural optimization of a permanent magnet rotor.
1 Introduction
Permanent magnet (PM) machines have become prevalent in very high-speed applications, especially among low-volume machines. Demand for ultra-high-speed machines is growing; however, mechanical stress in the rotor remains one of the major limitations for speed [1]. Permanent magnets represent the most mechanically vulnerable rotor part and they cannot sustain the tension caused by centrifugal forces to which the rotor is subjected during high-speed rotation. Therefore, the magnet must be contained in a non-magnetic enclosure/sleeve which would limit stresses in the magnet and ensure the transfer of torque from the magnet to the shaft at elevated speeds.
Many authors have studied properties of the enclosure and its influence on the magnetic field and losses in the rotor, eg.
[2][3]. Little has been published, however, on mechanical design of high-speed PM rotors and optimization of the rotor structure. Larsonneur [4] observed the existence of an optimal interference fit between the magnet and the enclosure for maximum permissible speed. Binder et al. [5] showed advantages of using surface-mounted magnets for high speed and also the validity of analytical mechanical modelling for the case of magnets without pole spacers. Zwyssig et al. [6] considered not only the enclosure’s strength, but also the compatibility of its thermal properties with the permanent magnet. This paper aims to determine and quantify the influence of enclosure geometry and fitting on mechanical stress in a high-speed rotor, while also considering rotational speed and operating temperature. Through analytical modelling, a relatively simple approach of optimizing the enclosure is achieved. This optimization approach was used in the design of a carbon fibre enclosure of an unconventional high-speed rotor for a micromilling spindle.
2 Test application: Disc-shaped PM rotor
Within the Microfactory project [7] downsized high-speed spindles for micro-milling are researched. New spindle technologies are sought so as to overcome current machine limits and facilitate ultra-fast milling.
A special setup with a disc-shaped rotor suspended in static air bearings has been realized [8]. The rotor has higher polar than transversal inertia, a property which offers important rotordynamical advantages: one rigid critical speed less and no flexural bendings within a conceivable speed range. An injection-moulded plastic-bonded magnet is applied to the rotor in a ring shape. The targeted speed of 200.000 rpm would bring the rotor’s tangential speed to the vicinity of 300 m/s. Proper enclosing of the magnet becomes crucial, particularly for a high-speed rotor with a high diameter to
length ratio.
Figure 1: A rotor drawing (dimensions in mm)
3 Material considerations
2.1 Permanent magnet
Optimum air-gap flux density in very high-speed PM machines is usually quite low [9] and such machines do not necessarily require high-energy permanent magnets.
I njection-moulded bonded NdFeB magnets offer important advantages such as high resistivity to magnetically induced
losses and shape flexibility, while their remanent field is sufficient for the application. Still, the possibility of plastic deformation and creep of the polymer material remain a great concern.
High temperature polymer polyphenylene-sulfide (PPS), favourable for injection moulding [10], was chosen as the plastic binder. Although PPS allows somewhat smaller volume fraction of permanent magnet material than some other polymer binders (e.g. nylon) and, accordingly, poorer magnetic properties [11], PPS-based bonded magnets have superior mechanical properties with respect to other bonded magnet types in terms of strength and processability [10][11]. -PS also exhibits, for a polymer, high melting temperature (280°C) and PPS-based magnets can maintain structural integrity even at the temperature of 180°C [12]. Yet, at about 85°C glass transition occurs in PPS [10] causing softening of the amorphous phase and a great reduction in strength [13]. Therefore, that temperature is taken as the rotor temperature limit.
material property PPS NdFeB bond 1density [g/cm 3] 1.35-1.7 7.35-7.6 4.82
compressive modulus [GPa] 2.8-3 140-170 31.73compressive strength [MPa] 125-185 800-1100 120
Poisson’s ratio 0.36-0.4 0.24 0.34
CTE [μm/m/°C]
40-55 4-8 4.741
values that were used in modelling; 2 measured; 3 taken from [12]; 4
calculated using rule of mixtures
Table 1: Properties of the bonded magnet and its constituents
Scarce of data on mechanical properties of bonded magnets hampered the work on modelling of stress in the rotor. A valuable study on this issue was performed by M.G. Garell et al. [12] who offered data on tensile modulus and strength. However, the magnet endures compression from the enclosure and the properties must have been assessed for that condition. I n the modelling (see succeeding sections) it was assumed that the compressive modulus is equal to the tensile modulus. Further, compression was assumed to be limited by the compressive strength of PPS and the value of 120 MPa was imposed on the maximum stress in the magnet. Finally, Poisson’s ratio and coefficient of thermal expansion (CTE) were estimated from the rules of mixtures [16]:
(1)bond pps NdFeB p p Q Q Q (1)
(1)(1)pps pps NdFeB NdFeB
bond pps NdFeB
p E p E p E p E D D D
(2)
where p (= 0.6) is the volume fraction of permanent magnet material in the bond and pps E and NdFeB E are tensile module of PPS and NdFeB magnet respectively. 2.1 Enclosure
Carbon fibres were chosen as the enclosure material for their
light weight and exceptional strength. For a rotor whose expected tip circumferential speed is beyond 250 m/s, this was the most appropriate choice.
material property
&fibres A fibres density [g/cm 3] 1.55 elastic modulus [GPa] 186.2 9.5 maximum stress [MPa]
1400 -100
Poisson’s ratio ?12 = 0.3
CTE [μm/m/°C]
-1 54 Table 2: Properties of the carbon fibres
The main drawback of using carbon fibres is their negligible
thermal expansion in contrast with that of permanent magnets; therefore, additional stress on the enclosure is expected at elevated rotor temperatures. Furthermore, while able to withstand extreme tensions, carbon fibres are rather sensitive to bending [5] and they need to be protected from being cut at edges of neighbouring materials.
Carbon fibres exhibit strong orthotropic nature since the fibres’ mechanical properties differ considerably in different directions and strongly depend on the cross-sectional type [14]. This makes precise analytical modelling burdensome. In subsequent sections both iso- and orthotropic modelling of stress in the rotor is presented. I n the example with the isotropic assumption, only properties in the direction of fibres from Table 2 (|| fibres) were considered. The values of the maximum stresses in the table have assumed a great safety margin.
4 Stress in the rotor: 2D isotropic modelling
A PM rotor will be represented as a compound of three
adjacent cylinders which correspond to the iron shaft, magnet and enclosure (Figure 2). The materials are assumed to be isotropic and linear and the mechanical stress is modelled in 2D. The enclosure is shrink- or press-fitted onto the magnet with an interference fit ?. The operating temperature of the rotor is assumed to be uniformly distributed in the rotor and represented as the temperature increment ?T=T-T 0, where T and T 0 are operating and room temperature respectively. The structure rotates with a constant angular velocity ?.Figure 2: Cross-section of a PM rotor
To facilitate a relatively simple analytical solution of the stress within the cylinders, an approach suitable for plain
elastic problems will be taken. For such problems,
generalized Hooke's law takes on the following form in the cylindrical system [15]:
N N N ******
**11r r t t M E E T E E H V D Q H V D H V D Q ao
?aoaoao?? '?????????????? ????
(3) where ? and ? denote strain and stress, and indices r and t correspond to radial and tangential direction respectively.
Starred coefficients in (3) have different correlations with material properties based on whether plain stress or plain strain representation is assumed. The plain strain model is suitable for slender cylinders, thus for long rotors, while plain stress model is valid for disks, thus for short, disk-shaped
rotors and laminated long rotors. Since the application rotor has a disc shape, the plain stress model is adopted for which the starred coefficients are simply equal to Young’s modulus, Poisson’s ratio and CTE of the given material: ***,,E E Q Q D D (4) (see e.g. [15] for the coefficients of the plain strain model).
From (3) the vector of stress components is:
11
M M T V H D ' (5)
To obtain expressions for the stress distribution, radial
displacement will be used. The correlations between the
displacement and strain are:
,r t du u
dr r
H H (6) and the force-equilibrium equation is:
20r t
r d r dr r
V V V U : (7) where ? denotes mass density.
By combining equations (5), (6) and (7) we obtain the governing differential equation for radial displacement: 22
222110d u du u r r dr E dr r Q U : (8) whose solution is given in:
223
18r
B u A r r E
Q U : (9)
where A and B are coefficients obtained from the boundary conditions.
After substituting (6) into (5) with respect to (9), expressions for radial and tangential stresses in the rotor regions are achieved. Boundary coefficients in each region are then obtained from the boundary equations: (1)(1)3(0)()()0,1,2
()(),1,2
()0
r ri bi r i bi r i bi ri bi i r e r r i u r u r i r V V V G V z f
(10) where, in our case, ?1=0 and ?2=?, and r b represents radius at
a boundary: r b1=r Fe ,r b2=r m .
Solution of the system of equations (10) is achieved using a symbolic solver and, finally, analytical expressions for radial and tangential stress in the rotor are obtained. The expressions are rather lengthy; however, influences of static pressure
(fitting), centrifugal force (rotation) and temperature
increment on the stress can be clearly distinguished. Thus,
both radial and tangential stresses can be expressed in the following way:
2()()()()r F G H T V G : ' (11)
where F, G and H are functions of geometry (cylinders’ radii r Fe ,r m and r e
) and material properties (E ,?,?).
5 Enclosure optimization
Goal of the optimization of the rotor enclosure was maximizing the rotational speed that the rotor could withstand. The dimensions of the PM motor were previously determined in the electromagnetic design [8]. Maximum
permissible thickness of the enclosure that could be fit in the air-gap is 2 mm. Temperature of the PPS glass-transition – 85oC, ?T § 60oC – is set as the rotor temperature limit. The thickness of the enclosure and interference fit must be adequately chosen so that the contact pressure between the
adjacent cylinders is maintained throughout the whole speed
range at the operating temperature, i.e.:
max 00,0r bi nom r T T V d :d :d 'd ' (12) At the same time, equivalent stress in each rotor part must be considerably below the material ultimate stress: eq max max 0,0,0e nom r r r T T V V d d d :d :d 'd '
(13)Figure 3: Finding optimal interference fit, similarly as in [4]
I t can be shown that critical stresses in this type of rotor (Figure 2) are radial (contact) stress at the magnet-iron boundary and tangential stress (tension) at the enclosure inner surface. As a result of modelling from the previous section, analytical expressions for these stresses can be presented as:
2,111m r crit e e e
F r
G r
H r T V G : ' (14) 2,222e t crit e e e F r G r H r T V G : '
(15)
where F 1,2,G 1,2 and H 1,2 are positive functions of the enclosure outer radius r e .
If the interference fit is very high, contact pressure between magnet and iron will be maintained (?r,crit <0), but the maximum stress ?e max in the enclosure will be reached at a
certain speed. Conversely, if the fit is very low, loss-of-contact limit will be met with increasing speed. It can be thus
inferred from (14) and (15) that for an expected operating temperature there is an optimal value of the interference for which both limits defined by (12) and (13) are reached at a
same rotational speed max (see Figure 3 and [4]). This speed can be adjusted by the enclosure radius r e so that the theoretical maximum rotational speed max is a considerable margin higher than the operating speed.
Hence, the optimal fit and theoretical maximum speed are obtained as functions of the enclosure radius r e from the following system of equations:
,max ,max max
,,00,,60m r crit opt e e t crit opt T T C V G G V G G V : : ' : : ' q (16) As it was expected, the highest speed could be reached with the highest allowable enclosure thickness of 2 mm. Optimal
interference fit is obtained from (16) to be 110 ?m.
Finally, in this design, additional limit is forced on the fitting by the magnet compression strength. Compliance of the
calculated interference fit to that limit needs to be ensured. Namely, because of the polymer used in the magnet, compression strength of the bonded magnet is much lower than that of sintered magnets (Table 1), maximum amount of
a press-fit that can be applied on the magnet is expected to be rather low. To account for this, maximum permissible fit ?max is calculated from the equation: ,max 0,0m m
eq crit T V V : ' (17)
where ?m eq,crit is von Mises stress in the magnet at the magnet
inner surface:
,m eq crit V (18) and ?m max
is assumed compression strength of the magnet.
From (17) maximum interference fit is calculated to be 95 ?m and, since it is smaller than the previously calculated optimal fit, it is set as the definite value of the interference fit between the magnet and enclosure.
6 Orthotropic modelling
I
n the modelling in Section 4 isotropic behaviour was assumed for all the rotor materials although, in reality, carbon fibre composites exhibit great differences between physical properties in different directions (Table 2). In order to check adequacy of such a model for representing stress in this class of rotors, two more accurate models were used which
consider orthotropic properties as well: orthotropic analytical
model and FE model. Values for enclosure thickness and fit (2 mm, 95 ?m) obtained from the optimization in the previous
section were maintained in these models and the results were compared with results of isotropic modelling. 6.1 Analytical orthotropic model Hooke’s law for the planar stress example in an orthotropic material has the following form [16]:
1221
11r t r r r t t t r t E E T E E Q H V D H V D Q ao ??aoaoao
?? '?????????????? ???? (19) where:
1221
t r
E E Q Q .
(20) Similarly as in Section 4, after combining equations (19), (6)
and (7) we obtain differential equation over radial displacement in the following form: 222
210d u du u P
h T Q r r dr r dr r UZ ' (21) where h , P and Q are constants dependent on material properties. The equation yields the expression for
displacement:
2319
h h P Q u A B r T r h h U ' : (22)
and further derivation of stress components terms is performed in the same way as in Section 4. I t should be notified that even with the use of a symbolic solver, derivation of the orthotropic solution for stress is
rather lengthy and burdensome.
6.2 Finite element model Finite element modelling was performed using Ansys
structural analysis. The model used PLANE82 elements for
2D structural modelling while the contact area between the
magnet and enclosure was modelled using CONTA172 and TARGE169.6.2 Results comparison
Results of the three models are given in Figure 4 including three examples that represent still rotor and the rotor rotating at the target speed of 200.000 rpm at both room and maximum temperature. The table contains values of relevant stresses at the inner surfaces of the magnet and enclosure. I t can be seen that the isotropic model is generally in good agreement with other two modes. An exception is stress in the magnet at the maximum speed: when the compression weakens, discrepancies between models become larger.
Mechanical stress room temperature, zero speed room temperature, 200.000 rpm 85°C, 200.000 rpm [MPa]
isotropic orthotropic FEM 2D isotropic orthotropic FEM 2D isotropic orthotropic FEM 2D
enclosure, inner, radial -118.3 -109.8-109-117-108.7-108-128 -122.8-117enclosure, inner, tangential 921 940.69351088110811101176 11881160magnet, inner, radial -137.8 -128-127-26.8-17.1-13.1-43.7 -37.4-25.9magnet, inner, tangential -56 -52-51.6-0.44 3.52 5.18 6.54 9.138.75magnet, inner, von Mises
120
111.3
110
26.6
19.1
16.3
47.3
42.7
31.2
Figure 4: Results of the used models
Nevertheless, the rotor designed using isotropic model meets all the requirements. As calculated by the FE model, compression in the magnet at stand-still and tension in the fibres at the maximum speed is slightly smaller than predicted by the isotropic model. Contact pressure between magnet and shaft is maintained throughout the whole speed range. Temperature rise causes additional stress in the rotor but also increases the contact pressure between the cylinders.
Although orthotropic analytical model predict the stress more accurately, the accuracy improvement does not justify great increase in complexity with respect to the isotropic model.
7 Final design and production
Although it is a commonly applied technique in high-speed rotors, the test application rotor could not be simply enclosed by pressing a fibre ring over a bare magnet without causing its damage. Polymer magnet would also buckle if it was simply pressed by the carbon fibres.
Therefore, the rotor structure was designed so as to ensure structural integrity of both magnet and fibres. A quarter of a
cross-section of the final rotor is given in Figure 5.
Figure 5: Final rotor structure
n the final design glass fibres were used to enable safe pressing of the carbon fibre ring and to protect carbon fibres from bending at corners of the magnet. The procedure followed for enclosing the magnet was:
First the glass fibre rings are pressed on the shaft over top and bottom faces of the magnet. Outer surfaces of the magnet and the glass fibre rings are then polished before pressing of the enclosure. In the same time, carbon fibres are wound around a
very thin glass fibre ring whose inner radius is for 95 ?m smaller then the outer radius of the magnet. Finally, the carbon/glass fibre ring is pressed onto the rotor.
7.1 3D finite element model of the final rotor
The rotor final structure was modelled in 3D using Ansys Workbench software.
Compression at the magnet inner surface resulting only from the press-fit is much smaller than calculated from the 2D modelling. However, what concerns is a large stress concentration at the line close to boundary between the iron
shaft and glass fibre ring (pointed by arrows at Figure 6). Figure 6: Magnet stress due to enclosure fitting
Further, according to this model, if the rotor remained at room temperature, the contact between the magnet and iron would be lost beyond 180.000 rpm. Maximum possible speed is
increased, though, if the operating temperature rises.
Figure 7: Magnet stress at maximum speed and temperature
Maximum equivalent stress in the magnet at the maximum speed and temperature is at the outer magnet surface and amounts to 110 MPa (Figure 7) which is still below the compression limit.
Maximum tensile stress in carbon fibres – 1147 MPa – is in a
very good agreement with results from 2D modelling.
Figure 8: A photo of the final rotor
8 Conclusions
Design of a retaining enclosure/sleeve for a high-speed permanent magnet rotor was analyzed in the paper. I t was shown that the 2D analytical modelling is a relatively simple but efficient tool for design and optimization of the rotor structure. The model distinguishes the influences of the interference fit, temperature and rotational speed on mechanical stress in the rotor. The thickness and fitting of the enclosure are optimized from the model with respect to two critical stresses: tension in the enclosure and contact pressure at the magnet-iron boundary.
The design approach was tested on the example of a disc-shaped rotor with a plastic-bonded magnet. Use of a polymer material in the magnet and rather high diameter to length ratio of the rotor posed a challenge both to modelling and production. Polymer binder – PPS – brought an additional constraint on the magnet compressive stress that was eventually decisive for the value of the enclosure press-fit. Modelling with an isotropic assumption for the rotor materials was sufficiently accurate even though carbon fibres were used for the enclosure. Based on the 3D FEM, the limiting speed of the final rotor is at the verge of 200.000 rpm which is the required maximum speed of the rotor. Acknowledgements
This research is carried out within the Micro-Ned program, which is subsidized by the Dutch Bsik. The authors would like to thank Dr. Frank T?ubner from Rosseta Techniek GmbH for his valuable contribution to the rotor design. References
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情节就是叙事性文学作品中所描写的事件及其发展变化的过程,它由一系列具 有矛盾冲突的具体事件组成。 分析故事情节可从以下几个方面入手: ①理清结构。小说的情节大体由开端、发展、高潮、结局几部分构成,可以据此划分层次。 ②寻找线索。线索就是情节发展中的脉胳,有时还就是矛盾冲突的焦点。通过寻找线索,有利于掌握情节,有时也有利于抓住小说的矛盾冲突,便于把握主题。 ③抓住场面。情节由场面组成。有的小说情节复杂,有的小说情节不连贯, 在这种情况下,抓住场面分析就可以不受情节、结构的限制,直接掌握作品的中心事件与主要矛盾。 第三、分析典型环境。 ①典型环境就是指文学作品中形成人物性格并驱使人物行动的生活场所,就 是一 定历史时代、社会现实及其发展趋势的具体体现。 ②典型环境就是指文艺作品中典型人物所生活的形成其性格并驱使其行动 的 特定环境。 典型环境主要就是社会环境,也包括自然环境。 分析典型环境从以下方面入手:
英语作文关于共享单车的篇精编
(一) 假定你是红星中学初三学生李华。你的美国朋友Jim在给你的邮件中提到他对中国新近出现的一种共享单车“mobike”很感兴趣，并请你做个简要介绍。请你给Jim回信，内容包括： 1. 这种单车的使用方法(如：APP查看车辆、扫码开锁等); 2. 这种单车的优势; 3. 你对这种单车的看法。 注意：1. 词数不少于80; 2. 开头和结尾已给出，不计入总词数。 提示词：智能手机smartphone, 二维码the QR code 参考范文 Dear Jim, I’m writing to tell you more about the new form of sharing bike mobike mentioned in your latest letter. It’s very convenient to use if you have a smartphone. What you do is find a nearest mobikethrough the APP, scan the QR code on the bike, and enjoy your trip. Compared to other forms of sharing bike, the greatest advantage of mobike is that you can easily find one and never worry about where to park it. It is becoming a new trend as a means of transportation, which relieves the traffic pressure and does good to the environment as well. Hope to ride a mobike with you in China. Yours, Li Hua (二) 最近很多大城市都投放了共享单车(shared bikes)，比如摩拜单车(Mobike)、Ofo共享单车等。由于它们方便停放，骑车也能起到锻炼身体的作用，作为代步工具很受大家欢迎。但是，各地也出现了很多毁车现象，比如刮掉车上的二维码(QR code)、上私锁等。 你对这种现象怎么看?你对共享单车公司有什么建议吗?写一篇符合逻辑的英语短文，80词左右。 参考词汇：bike-sharing companies 共享单车公司，Mobike 和Ofo 是两家共享单车公司，convenience 方便，register登记 参考范文 The shared bikes like Mobike and Ofo bring great convenience to people. You needn’t lock them by simply using your smart phone. They can take you where the subway and bus don’t go. And they can be left anywhere in public for the next user. However, bad things happen. Some people damage the QR code on the bike, or use their own lock, which causes trouble to other users. In my opinion, it’s difficult to turn these people’s ideas in a short time. Therefore, bike-sharing companies like Mobike and Ofo need to do something. For example, those who damage the bike should pay for their actions. Also, because people use their real name toregister as a user, it’s a good way to connect to one’s personal credit. In the end, what I want to say is to take good care of public services. (三) 共享单车(bicycle sharing)已成为时下最热的话题之一，请你就这一话题写一篇短文。内容须包括三方面：1. 共享单车蓬勃发展，成为社会热潮;2. 共享单车带来便利，但也存在问题;3. 我对解决问题的建议。 参考范文 Bicycle Sharing With the development of technology, bicycle sharing comes into people's lives. It becomes more and more popular and much news reported it. At the same time, we should see that there are some problems caused by bicycle sharing. On one side, bicycle sharing makes it very convenient of people traveling. You can find a bicycle anywhere at any time when you want to go out for a cycling, and the price of one trip is very low. It can save time for people. On the other side, its management is not perfect. Even kids can open the lock and ride the bicycle, there is no doubt that such behavior is very dangerous.
初中语文古文赏析曹操《短歌行》赏析(林庚)
教育资料 《短歌行》 《短歌行》赏析(林庚) 曹操这一首《短歌行》是建安时代杰出的名作，它代表着人生的两面，一方面是人生的忧患，一方面是人生的欢乐。而所谓两面也就是人生的全面。整个的人生中自然含有一个生活的态度，这就具体地表现在成为《楚辞》与《诗经》传统的产儿。它一方面不失为《楚辞》中永恒的追求，一方面不失为一个平实的生活表现，因而也就为建安诗坛铺平了道路。 这首诗从“对酒当歌，人生几何”到“但为君故，沉吟至今”，充分表现着《楚辞》里的哀怨。一方面是人生的无常，一方面是永恒的渴望。而“呦呦鹿鸣”以下四句却是尽情的欢乐。你不晓得何以由哀怨这一端忽然会走到欢乐那一端去，转折得天衣无缝，仿佛本来就该是这么一回事似的。这才是真正的人生的感受。这一段如是，下一段也如是。“明明如月，何时可掇?忧从中来，不可断绝。越陌度阡，枉用相存。契阔谈宴，心念旧恩。月明星稀，乌鹊南飞。绕树三匝，何枝可依。”缠绵的情调，把你又带回更深的哀怨中去。但“山不厌高，海不厌深”，终于走入“周公吐哺，天下归心”的结论。上下两段是一个章法，但是你并不觉得重复，你只觉得卷在悲哀与欢乐的旋涡中，不知道什么时候悲哀没有了，变成欢乐，也不知道什么时候欢乐没有了，又变成悲哀，这岂不是一个整个的人生吗?把整个的人生表现在一个刹那的感觉上，又都归于一个最实在的生活上。“我有嘉宾，鼓瑟吹笙”，不正是当时的情景吗?“周公吐哺，天下归心”，不正是当时的信心吗? “青青子衿”到“鼓瑟吹笙”两段连贯之妙，古今无二。《诗经》中现成的句法一变而有了《楚辞》的精神，全在“沉吟至今”的点窜，那是“青青子衿”的更深的解释，《诗经》与《楚辞》因此才有了更深的默契，从《楚辞》又回到《诗经》，这样与《鹿鸣》之诗乃打成一片，这是一个完满的行程，也便是人生旅程的意义。“月明星稀”何以会变成“山不厌高，海不厌深”?几乎更不可解。莫非由于“明月出天山”，“海上生明月”吗?古辞说：“枯桑知天风，海水知天寒”，枯桑何以知天风，因为它高；海水何以知天寒，因为它深。唐人诗“一叶落知天下秋”，我们对于宇宙万有正应该有一个“知”字。然则既然是山，岂可不高?既然是海，岂可不深呢?“并刀如水，吴盐胜雪”，既是刀，就应该雪亮；既是盐，就应该雪白，那么就不必问山与海了。 山海之情，成为漫漫旅程的归宿，这不但是乌鹊南飞，且成为人生的思慕。山既尽其高，海既尽其深。人在其中乃有一颗赤子的心。孟子主尽性，因此养成他浩然之气。天下所以归心，我们乃不觉得是一个夸张。 .
白居易题王处士郊居赏析翻译
题王处士郊居 唐代 半依云渚半依山，爱此令人不欲还。负郭田园九八顷， 向阳茅屋两三间。寒松纵老风标在，野鹤虽饥饮啄闲。 一卧江村来早晚，著书盈帙鬓毛斑。 这是一首兰于：的诗 翻译 赏析 个人作品 主题 题材集中是白居易讽喻诗的艺术特色之一。他一般只选择最典型的一件事，突出一个主题，“一吟悲一事”，主题非常明确。为使主题更明确传达给读者，或诗题下加小序点明主题，或“卒章显其志”突出主题。其次，白诗的艺术特色还表现在刻画人物上，他能抓住人物的特征，用白描方法勾勒出鲜明生动的人物形象。但白诗的诗意并不浅显，他常以浅白之句寄托讽喻之意，取得怵目惊心的艺术效果。《轻肥》一诗描写了内臣、大夫、将军们赴会的气概和席上酒食的丰盛，结句却写道：“是岁江南旱，衢州人食人”，这是一幅多么惨烈的情景。
闲适诗和讽喻诗是白居易特别看重的两类诗作，二者都具有尚实、尚俗、务尽的特点，但在内容和情调上却很不相同。讽喻诗志在“兼济”，与社会政治紧相兰联，多写得意激气烈；闲适诗则意在“独善”，“知足保和，吟玩性情” ，仍而 表现出淡泊平和、闲逸悠然的情调。 白居易的闲适诗在后代有很大影响，其浅切平易的语言风格、淡泊悠闲的意绪情调，都曾屡屡为人称道，但相比之下，这些诗中所表现的那种退避政治、知足保和的“闲适”思想，以及归趋佛老、效法陶渊明的生活态度，因与后世文人的心理较为吺吅，所以影响更为深远。如白居易有“相争两蜗角，所得一牛毛”、“蜗 牛角上争何事，石火光中寄此身”的诗句，而“后之使蜗角事悉稽之”。即以宋人所取名号论，“醉翁、迂叟、东坡之名，皆出于白乐天诗云”。宋人周必大指出：“本朝苏文忠公不轻许可，独敬爱乐天，屡形诗篇。盖其文章皆主辞达，而忠厚好施，刚直尽言，与人有情，于物无着，大略相似。谪居黄州，始号东坡，其原必起于乐天忠州之作也。”凡此种种，都展示出白居易及其诗的影响轨迹。 诗歌理论 白居易的思想，综吅儒、佛、道三家，以儒家思想为主导。孟子说的“达则兼济天下，穷则独善其身”是他终生遵循的信条。其“兼济”之志，以儒家仁政为主，也包括黄老之说、管萧之术和申韩之法；其“独善”之心，则吸取了老庄的知足、齐物、逍遥观念和佛家的“解脱”思想。二者大致以白氏被贬江州司马为界。白居易不仅留下近三千首诗，还提出一整奖诗歌理论。他把诗比作果树，提出“根情、苗言、华声、实义”的观点，他认为“情”是诗歌的根本条件，“感人心者莫先乎情”，而情感的产生又是有感于事而系于时政。因此，诗歌创作不能离开现实，必须取材于现实生活中的各种事件，反映一个时代的社会政治状况。他继承了《诗经》以来的比兴美刺传统，重视诗歌的现实内容和社会作用。强调诗歌揭露、批评政治弊端的功能。他在诗歌表现方法上提出一系列原则。《与元九书》中他提出了著名的“文章吅为时而著，歌诗吅为事而作”的现实主义创作原则。
小说鉴赏的基本常识
小说的基本常识 （一）小说的基本常识 1、小说是通过人物、情节和环境的具体描写来反映现实生活的一种文学体裁。人物、情节、环境是小说的三要素。 2、小说刻画人物形象的方法包括：语言描写、肖像描写、行动描写、心理描写和细节描写。 3、小说中的环境包括自然环境和社会环境。 4、小说的叙述方式包括顺叙、倒叙、插叙等。 (二)小说的特点 1、完整的故事情节 2、鲜明的人物形象 3、典型的环境 4、深刻的主题 5、精巧的构思 (三)高考命题要点 1.把握故事情节 2.揣摩人物形象 3.注意环境描写 4.概括主题内容 5.品味语言特色 6.分析写作技巧 一、小说情节的把握 把握好故事情节，是读懂小说的关键，是欣赏小说艺术特点的基础，也是整体感知文章的起点。命题者在为小说命题时，也必定以此为出发点，先从整体上设置理解文章内容的试题。 （一）高考中有关小说情节的命题指向 1、用一句话或简明的语句概括故事情节，或文中共写了哪几件事，请依次加以概括； 2、对某一情节的特点和作用进行分析； 3、对情节的高潮部分或结尾部分作用的理解； 4、小说在叙述故事情节过程中顺叙、倒叙、插叙等方法的使用； 5、哪一个情节最吸引你； 6、情节的合理性探究。（二）小说中情节的作用 1、交代人物活动的环境； 2、设置悬念，引起读者阅读的兴趣； 3、为后面的情节发展作铺垫或埋下伏笔； 4、照应前文； 5、线索或推动情节发展； 6、刻画人物性格； 7、表现主旨或深化主题。（三）情节安排的方式及作用 1、就全文来说有一波三折式。作用是引人入胜，扣人心弦，增强故事的戏剧性、可读性。 2、就开头结尾来说有首尾呼应式。作用是使结构紧密、完整。 3、就开头来说有倒叙式（把结局放到开头来写），如《祝福》，先写祥林嫂的死，然后再写祥林嫂是怎样一步步被封建礼教逼向死亡之地的。起到制造悬念的作用。 4、就结尾来说有戛然而止，留下空白式。此外，还有出人意料式、悲剧、喜剧式等。 5、贯穿情节的线索。可作线索的小说因素有：事、物、人、情、时间、空间，如《药》中的“人血馒头”、《故乡》中的“我”等。 （四）分析小说情节的入手方式： 1、抓住场面； 2、寻找线索； 3、理清小说的结构。 （五）分析小说情节时的注意事项 1、情节的发展变化是矛盾冲突发展的体现，分析小说的情节时必须抓住主要的矛盾冲突。 2、分析情节不是鉴赏小说的目的，而是手段，是为理解人物性格、把握小说主题服务的。所以，在分析情节的过程中，要随时注意体会它对人物性格的形成及对揭示小说主题的作用。 （六）情节安排的顺序及作用 1、顺叙：按时间（空间）顺序来写，情节发展脉络分明，层次清晰。
汽车利弊英语作文4篇
[标签:标题] 篇一：关于汽车的英语作文 好的 Nowadays, with the rapid improvement of people’s living standards, cars have become an indispensable part of people's lives,so that more and more people have a car of their own, especially in cities. It brings some benefits for us but also causes many problems at the same time. For one thing,there’s no doubt that cars provide much convenience for people to go where they want to quickly and easily. Especially on weekday,driving a car can save a lot of time for us to go to work.When some places are too far away from our home, driving our own car is also convenient, we can go wherever we want. However,for another, too many cars will lead to the pressure of public transport, a series of problems will appear.First of all,it will bring about more air pollution,a large amount of polluted air given off by cars do great harm to our health.What’s more, as the existing roads are not so wide for the increasing number of cars,undoubtedly,traffic jams will become more and more serious. Last but not least, cars also place burden on the public facilities in providing more parking lots. As far as I am concerned,everything has its advantages and disadvantages. It’s high time that effective action must be token to limit the ever growing number of cars, the government should take measures to control the air pollution from the cars. Some roads should be widened and more new roads should be constructed. Only in this way，will people benefit from the popularity of cars. 坏的 Nowadays, with the rapid improvement of people's living standards, cars have become an indispensable part of people's lives,so that more and more people have a car of their own, especially in cities.It brings some benefit for us but also causes many problems at the same time. For one thing,it's no doubt that that cars provide much convenience for people to go where they want to quickly and easily. Especially on weekday,driving a car can save a lot of time for us to go to work.When some places are too far away from our home, driving our own car is also convenient, we can go wherever we want. However,for another, too many cars will lead to the pressure of public transport, a series of problems will appear.First of all,it will bring about more air pollution,a large amount of polluted air given off by cars do great harm to our health .What's more, as the existing roads are not so wide for the increasing number of cars,undoubtedly,traffic jams will become more and more serious. Last but not least, cars also place burden on the public facilities in providing more parking lots. As far as I am concerned,everything has its advantages and disadvantages. It's high time that effective action must be token to limit the ever growing number of cars, the government should take measures to control the air pollution from the cars. Some roads should be widened and more new roads should be constructed. Only in this way,will people benefit from the popularity of cars. 篇二：雅思作文高分范文：私家车的利与弊 智课网IELTS备考资料 雅思作文高分范文：私家车的利与弊
高中语文文言文曹操《短歌行(对酒当歌)》原文、翻译、赏析
曹操《短歌行【对酒当歌】》原文、翻译、赏析译文 原文 面对美酒应该高歌，人生短促日月如梭。对酒当歌，人生几何？ 好比晨露转瞬即逝，失去的时日实在太多！譬如朝露，去日苦多。 席上歌声激昂慷慨，忧郁长久填满心窝。慨当以慷，忧思难忘。 靠什么来排解忧闷？唯有狂饮方可解脱。何以解忧？唯有杜康。 那穿着青领（周代学士的服装）的学子哟，你们令我朝夕思慕。青青子衿，悠悠我心。 正是因为你们的缘故，我一直低唱着《子衿》歌。但为君故，沉吟至今。 阳光下鹿群呦呦欢鸣，悠然自得啃食在绿坡。呦呦鹿鸣，食野之苹。 一旦四方贤才光临舍下，我将奏瑟吹笙宴请宾客。我有嘉宾，鼓瑟吹笙。 当空悬挂的皓月哟，你运转着，永不停止；明明如月，何时可掇？ 我久蓄于怀的忧愤哟，突然喷涌而出汇成长河。忧从中来，不可断绝。 远方宾客踏着田间小路，一个个屈驾前来探望我。越陌度阡，枉用相存。 彼此久别重逢谈心宴饮，争着将往日的情谊诉说。契阔谈讌，心念旧恩。 明月升起，星星闪烁，一群寻巢乌鹊向南飞去。月明星稀，乌鹊南飞。 绕树飞了三周却没敛绕树三匝，何枝
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