Computational fluid dynamic simulation of an inter-phasing pulse tube cooler

An inter-phasing pulse tube cooler （IPPTC） consists of two pulse tube units, which are connected to each other at hot ends of the pulse tubes through a needle valve. This paper presents the computational fluid dynamic （CFD） results of an IPPTC using a 2D axis-symmetrical model. General results such as the phase difference between pressure and velocity at cold end and hot end, the temperature profiles along the wall, the available lowest temperature as well as its oscillations and the coefficient of performance （COP） for IPPTC are presented. The formation of DC flow and its effects on the performance of the cooler are investigated and analyzed in detail. Turbulence, which is partially responsible for the poor overall performance of a single orifice pulse tube cooler （OPTC）, is found to be much reduced in IPPTC and its performance is improved significantly compared with the single OPTC.     

Scour and scour countermeasures at bridge sites

This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer＇s ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.     

Orientalism and Heart of Darkness

Heart of Darkness was written by Joseph Conrad and published as a whole in 1902.The story begins on a British ship"the Nellie"moored on the coast of the Thames.It mainly talks about what Marlow sees and thinks when he begins his journey up to the Congo Riveres and reveals a turning process of a white colonizer called Kurts who is at the very beginning,an idealistic white colonizer trying to bring"civilization"and"progress"to the Africa but in the end falls into a greedy,cruel person.The novel,on the one hand,describes the terrible life of African peple and reveals the tyranne,greed of western colonism and stong racism;and on the other hand,it also shows readers a strong orientalism towards the Africa.So my purpose of the paper is to analyse how Orientalism is revealed in the Heart of Darkness.     

Inverse displacement analysis of the general six degree-of-freedom serial robot based on optimization method

The paper presents a new solution of inverse displacement analysis of the general six degree-of-freedom serial robot. The inverse displacement analysis of the general serial robot is transformed into a minimization problem and then the optimization method is adopted to solve the nonlinear least squares problem with the analytic form of new Jacobian matrix. In this way, joint variables of the general serial robot can be searched out quickly under the desired precision when positions of the three non-collinear end effector points are given. Compared with the general Newton iterative method, the proposed algorithm can search out the solution when the robot is at the singular configuration and the initial configuration used in the optimization method may also be the singular configuration. So the convergence domain is bigger than that of the general Newton iterative method. Another advantage of the proposed algorithm is that positions of the three non-collinear end effector points are usually much easier to be measured than the orientation of the end effector. The inverse displacement analysis of the general 6R (six-revolute-joint) serial robot is illustrated as an example and the simulation results verify the efficiency of the proposed algorithm. Because the three non-collinear points can be selected at random, the method can be applied to any other types of serial robots.     

Dynamic Simulation on Collision Between Ship and Offshore Wind Turbine简

By using ABAQUS/Explicit, the dynamic process of an offshore wind turbine（OWT） stricken by a ship of 5000DWT in the front direction is simulated. The OWT is located on a large-scale prestressing bucket foundation constructed by an integrated installation technique. According to the simulation results, under the ship collision, a cer-tain range of plastic zone appears within a local area of arc transition structure of the bucket foundation, and the con-crete plastic zone is seriously damaged. As the stress level of OWT tower is relatively low, the OWT tower is less af-fected. A great inertial force is generated at the top of the OWT tower as the mass of nacelle and blades is up to 400 t. The displacement of the tower is in the opposite direction of the ship collision at the end of 1 s under the action of iner-tial force. There is only a minor damage in the ship bow. Most of the kinetic energy is transformed into the plastic dissipation and absorbed by the arc transition structure of bucket foundation.     

心路历程--叛逆

Dear Friends,Some of our previous columns have been on serious themes. We havedelved into subjects like Love and Death and Ambition and Success. This ispretty heavy stuff. Now, it is time to let our imagination flow into fantasy.In America and in other western nations, every Chinese restaurant serves"fortune cookies" at the end of each meal. Inside each of these cookies is a small slipof paper with a brief message. It is customary for the diners to read their "fortunes"     

Stress and Displacement Distribution of Soft Clay Slope with 2D and 3D Elastoplastic Finite Element Method

Based on elastoplastic model, 2D and 3D finite element method (FEM) are used to calculate the stress and displacement distribution in the soft clay slope under gravity and uniform load at the slope top. Stability analyses indicate that 3D boundary effect varies with the stress level of the slope. When the slope is stable, end effect of 3D space is not remarkable. When the stability decreases, end effect occurs; when the slope is at limit state, end effect reaches maximum. The energy causing slope failure spreads preferentially along y-z section, and when the failure resistance capability reaches the limit state, the energy can extend along x-axis direction. The 3D effect of the slope under uniform load on the top is related to the ratio of load influence width to slope height, and the effect is remarkable with the decrease of the ratio.     

英语专业八级模拟试题(英文)

Part ⅠLISTENING COMPREHENSION (40MIN)(略) Part ⅡProofreading and Error Correction (15 MINS. )The following passage contains TEN errors. Each line contains a maximum of one error. In each case, only one word is involved. You should proofread the passage and correct it in the following way:For a wrong word : underline the wrong word and write the correct one in the blank provided at the end of the line.For a missingword: mark the position of the missing word with a " A " sign and write the word you believe to be missing in the blank provided at the end of the line.For an unnecessarvword . Cross out the unnecessary word with a slash"/" and put the word in the blank provided at     

A Thematic Analysis of Cold Mountain——On W.P. Inman's Spiritual Pilgrimage

Cold Mountain is a physical and spiritual healing place,at the same time is Inman’s home and a refuge for his soul where he himself can retreat from the sufferings of the war.A redemptive journey to Cold Mounain which is fraught with physical and psychological hardships helps Inman to reconstruct the broken soul but Inman’s real redemption:an escape from a world where he has become so hopeless and meaningless can only obtain through death in the end.     

Dynamic analysis of a high-speed train operating on a curved track with failed fasteners

A high-speed train-track coupling dynamic model is used to investigate the dynamic behavior of a high-speed train operating on a curved track with failed fasteners. The model considers a high-speed train consisting of eight vehicles coupled with a ballasted track. The vehicle is modeled as a multi-body system, and the rail is modeled with a Timoshenko beam resting on the discrete sleepers. The vehicle model considers the effect of the end connections of the neighboring vehicles on the dynamic behavior. The track model takes into account the lateral, vertical, and torsional deformations of the rails and the effect of the discrete sleeper support on the coupling dynamics of the vehicles and the track. The sleepers are assumed to move backward at a con- stant speed to simulate the vehicle running along the track at the same speed. The train model couples with the track model by using a Hertzian contact model for the wheel/rail normal force calculation, and the nonlinear creep theory by Shen et al. （1984） is used for wheel/rail tangent force calculation. In the analysis, a curved track of 7000-m radius with failed fasteners is selected, and the effects of train operational speed and the number of failed fasteners on the dynamic behaviors of the train and the track are investigated in detail. Furthermore, the wheel/rail forces and derailment coefficient and the wheelset loading reduction are analyzed when the high-speed train passes over the curved track with the different number of continuously failed fasteners at different operational speeds. Through the detailed numerical analysis, it is found that the high-speed train can operate normally on the curved track of 7000-m radius at the speeds of 200 km/h to 350 km/h.     

trast of score at the

beginning and at the end of 2:00 is the most distinct.These results suggest that psychological fatigue of drivers is subject to time of     

Digital Signal Processing Based Real Time Vehicular Detection System

Traffic monitoring is of major importance for enforcing traffic management policies. To accomplish this task, the detection of vehicle can be achieved by exploiting image analysis techniques. In this paper, a solution is presented to obtain various traffic parameters through vehicular video detection system( VVDS). VVDS exploits the algorithm based on virtual loops to detect moving vehicle in real time. This algorithm uses the background differencing method, and vehicles can be detected through luminance difference of pixels between background image and current image. Furthermore a novel technology named as spatio-temporal image sequences analysis is applied to background differencing to improve detection accuracy. Then a hardware implementation of a digital signal processing (DSP) based board is described in detail and the board can simultaneously process fourchannel video from different cameras. The benefit of usage of DSP is that images of a roadway can be processed at frame rate due to DSP‘s high performance. In the end, VVDS is tested on realworld scenes and experiment results show that the system is both fast and robust to the surveillance of transportation.     

New Year Wishes from Crazy English:Teens

Wow! January sure is an exciting month! First we get to celebrate the New Year with a day off school and a big party, and then at the end of the month it's the Spring Festival and we have an even bigger holiday and even more cel-     

Sensitivity analyses of cables to suspen-dome structural system

The construction of the cables is a key step for erecting suspen-dome structures. In practical engineering, it is difficult to ensure that the designed pre-stresses of cables have been exactly introduced into the structures in the site; so it is necessary to evaluate the influence of the variation of the pre-stresses on the structural behavior. In the present work, an orthogonal design method was employed to investigate the pre-stressed cables' sensitivity to the suspen-dome system. The investigation was concentrated on a Kiewitt suspen-dome. Parametric studies were carried out to study the sensitivity of the structure's static behavior, dynamic behavior, and buckling loads when the pre-stresses in the cables varied. The investigation indicated that suspen-dome structures are sensitive to the pre-stresses in all cables; and that the sensitivity depended on the location of the cables and the kind of structural behavior. Useful suggestions are given at the end of the paper.     

Student Evaluations as Effective Indicators of Learning Outcomes：Evi-dence from Japanese University Students in English Language Courses

The term“student learning outcomes”refers to the knowledge, skills, and abilitiesthat students achieve during a course, and is typically assessed based on student evaluations conducted at the end of th...     

My Hometown

My hometown is a beautiful young city-Dongying, which was found-ed in 1983. It lies at the end of the Yellow River. It is on the east of Binzhou. My hometown was very poor twenty years ago. At that time most people didn't have enough food to eat. After the founding of the city, our government paid great attention to improve the people's living conditions. Now many tall buildings and factories have been built. The city is becoming cleaner and tidier. It changes so much that lots of people w…     

Design optimization on the front wheel orientation parameters of a vehicle

1. Introduction In order to improve the driving operation performance, the front suspension of a vehicle is generally of McPherson independent style, which can simplify the structure, lighten the unsprung mass, and conveniently arrange the engine and steering system. Moreover, it can adapt to many types of springs and is of advantage to adjust the height of the vehicle. In such a system, the axis of the kingpin is the line between the upper damper end and the intersection of the transverse ar…     

Unit 13 The water planet

一、课文导读 I. Read the text, and finish the following cloze. The water molecule is __ up of two hydrogen atoms and one oxygen atom. The water molecule is polar--it has a __ negative end and a slightly positive end. Because water is polar, it __ __ nutrients quickly. The chemical structure of water also makes it different from most other it is a liquid at room temperature and has a relatively high freezing point.     

An Improvement of MPEG-4 Rate Control Algorithm

Frame skipping in low bit video coding could significantly reduce the visual quality of reconstructed video. At the same time, if the complexity of the video sequence remains high for a long period, then driving up the long term average bit rate, the only resort of MPEG-4 Q2 rate control algorithm results in using a high quantization scale, which shows a poor visual quality of the reconstructed video. This paper analyzes the main causes of frame skipping in current MPEG-4 frame rate control scheme, and presents a new rate control algorithm based on the quadratic R-D model over a CBR channel. Key features of the present work are. 1) the bits allocated to each P-frame or B-frame are in proportion to its distance from the end of this GOP, i.e. more bits are allocated to the frames that are nearer to their reference Ⅰ -frame: 2) the target buffer level is changeable in the GOP, at the end of each GOP( five P-frames or B-frames), the target buffer level is linearly reduced from 1/2 to 1/4 of buffer size, to other frames, the target buffer level is set to 1/2 of buffer size: 3 ) a selective and judicious use of the reduced resolution mode, in addition to a modulation of the quantization scale parameter, is to control the average long term bit rate. Experimental results with different video sequences of varied complexity, encoded at low bit rates show better efficacy of the proposed algorithm than MPEG-4 Q2 rate control scheme, and the experimental results also show that the improved algorithm has significantly reduced the number of frame skipping, increased the overall PSNR, and improved the perceptual quality.     

综合型阅读理解训练

A friend＇s grandfather came to America from Britain. He went into a cafeteria in Manhattan to get something to eat. He sat down at an empty table and waited for someone to take his order. Of course nobody did. At last, a woman with a plate full of food sat down in front of him and told him how a cafeteria worked. ＂Start out at the end,＂ she said. ＂Just go along the line and pick out what you want. At the other end they＇ll tell you how much you have to pay.＂