铰接圆柱体在二色波中的二阶低频力

考虑了铰接圆柱体的响应，给出了二色波中铰接在海底的圆柱体的二阶低频力。在未求出二阶速度势的情况下，利用其定解条件给出了二阶速度势的影响，给出了二阶低频力的解析表示式。二阶低频力主要由一阶速度势决定。二阶入射速度势以及圆柱的二阶响应对二阶低频力的影响可以忽略。

低频力作用下压电发电模型及实验研究

以PZT／PVDF复合压电材料采用热压工艺制备了压电厚膜，并制做了不锈钢／压电厚膜／金电极结构的压电振子。为了表征压电振子的阻抗特性，在室温下对样品介电特性进行了测量和分析。利用制备的压电振子采用简支支撑方式设计和制作了压电发电装置，运用压电方程对该装置建立了压电发电数学模型，并根据模型影响参数进行压电发电实验研究。实验结果表明，单片压电厚膜在外加作用力频率从0～2Hz发生变化时，在负载电阻值为105k1）左右时单个压电振子可以获得约130μw的最大输出电功率。研究中还发现增加并联的厚膜片数目可以成比例的增加输出功率。

船舶推进器低频宽带非定常力试验研究

低频宽带力是船舶推进器非定常力的重要组成部分,一方面它会直接辐射引起低频段较高的噪声,另一方面还会通过轴系传递到船体,引起船体振动并辐射噪声,因而对其研究具有重要意义。本文利用试验手段对船舶推进器低频宽带非定常力进行了系列研究,利用自主研制的非定常力动力仪,在大型循环水槽不同网格模拟伴流场中对不同叶数、不同材料推进器模型进行了低频宽带力测量,得到了低频宽带力的典型频谱特征规律,以及宽带力随速度、湍流参数、材料、叶数变化的定量关系。研究成果可为船舶推进器低频宽带力的理论预报方法提供试验验证数据,同时为宽带力的频谱特征规律分析提供了试验支撑。

低频简支梁压电发电装置实验研究

利用制备的压电厚膜采用简支支撑方式,设计和制作了压电发电装置,并对该发电装置进行了压电发电实验研究.实验结果表明,单片压电厚膜在外加作用力频率从0～2 Hz发生变化时,在负载电阻值为105 kΩ时可获得约130μW的最大输出电功率.研究中还发现增加并联的厚片数目可成比例地增加输出功率,因此能满足用于无线车辆检测传感器的功率要求.

驱动桥桥壳承载能力试验研究

某型工程车辆,在可靠性试验过程中,驱动桥桥壳若为冲焊结构,会经常从推力杆支座焊缝位置开裂,影响试验效率。对桥壳进行试验研究发现平衡悬架结构在搓衣板路上存在低频“拍击”附加力,并会引起簧上共振,使推力杆座焊缝位置的应力异常增大,容易产生裂纹。

基于多体分析的浅水FPSO和水下软钢臂系泊系统运动特性研究

基于多体动力分析方法进行FPSO和水下软钢臂系泊系统的运动特性研究。相较于非线性弹簧模拟软钢臂系泊系统或者其他近似模拟方法,多体分析方法可以充分考虑系泊系统具体结构形式及其动力项对FPSO运动性能的影响,更好的预报系统运动响应和系泊力。本文将FPSO和水下钢臂结构模拟成2个具有6自由度的独立结构,两者用系泊链组进行连接。基于三维势流理论应用汇源分布法,首先在频域内进行FPSO的水动力参数分析,进而在时域内对系统进行耦合动力分析。本文重点讨论系泊系统黏性力和二阶波浪力对系统响应的影响,计算结果发现系泊系统黏性力对系泊力有一定影响,而在浅水条件下二阶波浪力的计算对准确预报系统运动及系泊力非常重要。

Strength weakening effect of high static pre-stressed granite subjected to low-frequency dynamic disturbance under uniaxial compression

This study aimed to elucidate the strength weakening effect of high static pre-stressed rocks subjected to low-frequency disturbances under uniaxial compression.Based on the uniaxial compressive strength(UCS)of granite under static loading,70%,80%,and 90%of UCS were selected as the initial high static pre-stress(σ_(p)),and then the pre-stressed rock specimens were disturbed by sinusoidal stress with amplitudes of 30%,20%,and 10%of UCS under low-frequency frequencies(f)of 1,2,5,and 10 Hz,respectively.The results show that the rockburst failure of pre-stressed granite is caused by low-frequency disturbance,and the failure strength is much lower than UCS.When theσp or f is constant,the specimen strength gradually decreases as the f or σ_(p) increases.The experimental study illustrates the influence mechanism of the strength weakening effect of high static pre-stress rocks under low-frequency dynamic disturbance,that is,high static pre-stress is the premise and leading factor of rock strength weakening,while low-frequency dynamic disturbance induces rock failure and affects the strength weakening degree.

极浅水单点系泊系统的设计研究

在分析研究单点系泊系统的主要形式、特点和适用范围的基础上,选取了软刚臂单点系泊系统作为的"海洋石油113"新单点系泊系统,针对其设计中遇到的难题,进行了深入研究,归纳总结了极浅水海域单点系泊系统的设计时所重点关注的设计基础、低频波浪力、触底和上浪等关键问题,为今后极浅水单点系泊系统设计提供一点借鉴经验。

不同轨道型式的地铁车辆-轨道耦合振动特性研究

对某地铁线路的轨道型式类型及占比进行统计,对不同轨道型式下的车辆-轨道振动进行测试,分析了轮轨系统的动态响应,深入研究了普通道床+ZX-2扣件、普通道床+剪切扣件、普通道床+压缩扣件等典型轨道型式下轮轨耦合振动特性,以及车轮多边形轮周对轮轨振动特性的影响。结果表明,不同扣件刚度对轮轨振动特性的影响明显。其中:采用普通道床+ZX-2扣件时,轮轨间发生中低频轮轨力共振,振动主频为58 Hz,振动能量增大;采用普通道床+剪切扣件、普通道床+压缩扣件时,轮轨未发生共振,振动能量分配均衡;多边形车轮转频倍频与轮轨系统的固有频率发生了共振,振动能量显著增大。

Use of low-frequency signals to improve imaging quality under high-velocity basalt

Wave equation wave field numerical modeling technology is applied to the observation that deep layer imaging is difficult below a screening layer of high-velocity basalt. Three simple high-velocity basalt models are designed on the basis of basalt formation characteristics. The analysis of deep-layer reflection seismic signal energy shows that lowfrequency seismic signals are capable of both penetrating the thin high-velocity basalt layer and reducing the diffraction noise caused by the rough surfaces. The simulation experiment of a complete 2D basalt model confirms that the low-frequency signals can be used to boost the quality of deep-layer imaging under the high-velocity basalt layer and achieve good results in low-pass filter processing of actual data.

Low Frequency Oscillations of the Heat Distribution in the Global Upper Ocean Layers

The heat distributions in the upper layers of the ocean have been studied and some important low frequency oscillations （LFOs） are already found and quantified by using various characteristic factors. In this paper, the ‘heat center＇ of a sea area is defined with a simple method. Then the temperature data set of the upper layer of the global ocean （from surface down to 400 m, 1955-2003） is analyzed to detect the possible LFOs. Not only some zonal LFOs, which were reported early, but also some strong LFOs of the vertical and meridional heat distribution, which might imply some physical sense, are detected. It should be noted that the similar vertical oscillation pattern can be found in the Pacific Ocean, Atlantic Ocean and Indian Ocean. Results from some preliminary studies show that the vertical LFO might be caused by the solar irradiance anomalies. This study may help reveal some unknown dynamical processes in the global oceans and may also benefit other related studies.

Effects of heavy ions on kinetic Alfven waves

Kinetic Alfven Wave (KAW) is one of the low-frequency electromagnetic fluctuations that are identified extensively in space plasmas by in situ observations of satellites and has been an interesting topic for discussion widely in the fields of laboratory, space, and astrophysical plasmas because of its potential importance in plasma particle energization. Some satellite observations show that the number density ratio of the oxygen ions to the ambient plasma is 30% similar to 50%, sometimes, even as high as 80%. In this paper, effects of heavy ion species on KAWs are studied in a low-beta plasma. The results show that heavy ions not only considerably reduce the propagation speed of KAWs, but also remarkably influence the parallel component of perturbed electric field of KAWs (to the ambient magnetic field). The ratio of parallel to perpendicular components of perturbed field decreases (or increases) with the heavy ion abundance for KAWs dominated by the electron inertial length (or by ion acoustic gyroradius). In particular, the resonant condition of KAWs with thermal electrons is modified by the heavy ion species.

Coordinated and uncoordinated design of LFO damping controllers with IPFC and PSS using ICA and SFLA

A single machine-infinite-bus(SMIB) system including the interline power flow controllers(IPFCs) and the power system stabilizer(PSS) controller is addressed. The linearized system model is considered for investigating the interactions among IPFC and PSS controllers. To improve the stability of whole system again different disturbances, a lead-lag controller is considered to produce supplementary signal. The proposed supplementary controller is implemented to improve the damping of the power system low frequency oscillations(LFOs). Imperialist optimization algorithm(ICA) and shuffled frog leaping algorithm(SFLA) are implemented to search for optimal supplementary controllers and PSS parameters. Moreover, singular value decomposition(SVD) method is utilized to select the most effective damping control signal of IPFC lead-lag controllers. To evaluate the system performance, different operating conditions are considered. Reponses of system in five modes including uncoordinated and coordinated modes of IPFC and PSS using ICA and SFLA are studied and compared. Considering the results, response of system without controller shows the highest overshoot and the longest settling time for rotor angel at the different operating conditions. In this mode of system, rotor speed has the highest overshoot. Rotor angel in the system with only PSS includes lower overshoot and oscillation than system without controller. When PSS is only implemented, rotor speed deviation has the longest settling time. Rotor speed deviation in the uncoordinated mode of IPFC and PSS shows lower overshoot than system with only PSS and without controller. It is noticeable that in this mode, rotor angel has higher overshoot than system with only PSS. The superiority of the suggested ICA-based coordinated controllers is obvious compared with SFLA-based coordinated controllers and other system modes. Responses of coordinated PSS and IPFC SFLA-based supplementary controllers include higher peak amplitude and longer settling time compared with coordinated IPFC and PSS ICA-based controllers. This comparison shows that overshoots, undershoots and the settling times are reduced considerably in coordinated mode of IPFC based controller and PSS using ICA. Analysis of the system performance shows that the proposed method has excellent response to different faults in power system.

Improving Dynamic Stability of Yunnan Provincial and South China Power System by PSS

For solving the dynamic instability problem of Yunnan Provincial Power System (YNPS) and the South China Interconnected Power System (SCIPS), Lubuge Hydropower Station was chosen to install Power System Stabilizer (PSS). This paper introduces the principles and methods of parameter selection for PSS, in addition to field test. The test results show that the PSS installed can significantly improve the system damping.

Analysis and compensation of low frequency characteristics of sensors for vibration testing

In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal pressure is proposed.This method uses a sinusoidal pressure dynamic system with two-way dual channel import and export synchronization technology to study the low frequency characteristics of a piezoelectric sensor of PCB company,and its lower cut-off frequency is 0.26 Hz.It is also studied that when the frequency of the measured vibration or shock signal is 1-200 kHz,the error range of signal positive pressure action time is 4.87%-0.03%.The dynamic compensation for the low frequency of the vibration sensor is carried out,and the compensation effect is good.

Validation of DFIG and PMSG Wind Turbines' LVRT Capabilities Through Real Field Tests

Low voltage ride through (LVRT) capability has become more and more an issue for newly integrated wind turbines. The LVRT programs described in this paper developed field tests for newly installed wind turbines on wind farms in Northeast China. It is therefore different from other papers that only validate LVRT control strategies through running computer software simulations. To examine a single wind turbine's LVRT capability, the wind turbine's terminal voltage dip was realized by using a grid voltage dip emulator, which was located on the 690 V side of the generator transformer. In this paper, by artificially making various grid faults, the dynamic behavior of DFIG and PMSG wind turbines are analyzed and compared, control strategies such as active/passive crowbar and chopper protection schemes are verified, and new active/reactive power compensation methods are investigated and compared.

Peak-to-average power ratio reduction using selective mapping with unequal power distribution

A new approach for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems was proposed.This approach is based on assigning powers to the different subcarriers of OFDM using an unequal power distribution strategy.In addition,a reduced complexity selective mapping (RC-SLM) scheme was proposed.The proposed scheme is based on partitioning the frequency domain symbol sequence into several sub-blocks,and then each sub-block is multiplied by different phase sequences whose length is shorter than that used in the conventional SLM scheme.Then,a kind of low complexity conversions is used to replace the IFFT blocks.The performance of the proposed RC-SLM scheme along with the new approach was studied with computer simulation.The obtained results show that the proposed RC-SLM scheme is able to achieve the lowest computational complexity when compared with other low complexity schemes proposed in the literature while at the same time improves the PAPR reduction performance by about 0.3 dB.

Improving Low Bitrate Video Coding via Computation Incorporating A Priori Information

The growing number of mobile users, as well as the diversification in types of services have resulted in increasing demands for wireless network bandwidth in recent years. Although evolving transmission techniques are able to enlarge the network capacity to some degree, they still cannot satisfy the requirements of mobile users. Meanwhile, following Moore's Law, the data processing capabilities of mobile user terminals are continuously improving. In this paper, we explore possible methods of trading strong computational power at wireless terminals for transmission efficiency of communications. Taking the specific scenario of wireless video conversation, we propose a model-based video coding scheme by learning the structures in multimedia contents. Benefiting from both strong computing capability and pre-learned model priors, only low-dimensional parameters need to be transmitted; and the intact multimedia contents can also be reconstructed at the receivers in real-time. Experiment results indicate that, compared to conventional video codecs, the proposed scheme significantly reduces the data rate with the aid of computational capability at wireless terminals.

Power-line Modem over the Low Voltage Grid Using Direct Sequence Spread Spectrum Techniques

Power-line networks are designed to deliver electricity. They reach most of the domiciles and other buildings nowadays, so most of the people have access to it. On the other hand the backbone for the communications networks is not available in all countries especially the developing ones. A high cost and changing the design for the networks may be needed to construct this backbone. If data can be transmitted over the power-line networks, a recognized cost and time save can be achieved. In Egypt, the infrastructure is not always available for constructing a communications network backbone due to the already designed buildings before the need for these backbones. In this paper, we overcome this problem by designing a reliable Power-line Modem that operates safely on the low voltage grid. The modem is based on the Direct Sequence Spread Spectrum technique. It uses the mains zero crossing as an efficient way for the synchronization between the transmitter and the receiver. The Modem takes into account the problems of the Power-line including noise, attenuation and impedance dismatching.

Smart Meters and Under-Frequency Load Shedding

In some countries, there exists a risk of power deficit in the EPS （electrical power system）. This is a very serious problem and there are various solutions to deal with it. A power deficit in the EPS leads to frequency decrease in the power system. A dedicated automation to load shedding is used to maintain proper EPS operation. For some time, it has applied a mechanism called demand-side response, which in case of an emergency situation allows for a ＂more civilized＂ rationing of electricity to customers, with their consent. Such programs require that the utilities pay the customers for their agreement. The author proposes a new solution, intermediate between strict ALS （acting relieving automation） and demand-side response programs, where the companies have to send information about the price of energy or control signals to households.