大尺寸718塑料模具钢在线变频幅淬火工艺

通过间接热力耦合对120 mm厚718塑料模具钢连续淬火、多道次淬火及变频幅淬火3种在线淬火工艺冷却过程温度场和应力/应变场进行了三维数值模拟。结果表明:与连续淬火工艺相比,多道次淬火工艺可获得较小的表心温差、等效塑性应变及等效应力最大值,但等效应力平均值有所增大,且淬火时间较长;与前两种工艺相比,变频幅淬火工艺可获得最小的表心温差、等效塑性应变、等效应力,以及比多道次淬火工艺较短的淬火时间,且由于关闭了部分喷嘴,起到了节水节能的作用,为优化大尺寸718塑料模具钢在线淬火工艺提供参考。

R&S公司变频多通道幅相一致性测试方案

介绍了3种变频通道幅相一致性测试方法,每一种方法均有各自的应用优势和特点。方法一,测试装置简洁,校准简便,测试幅相一致性的同时,还可以测试诸如变频损耗、群时延等指标,而且非常适用于含有多级变频的通道测试;方法二是测试通道间幅相一致性的比较直观的方法,但是需要进行复杂的系统校准,操作相对复杂;相比之下,方法三更具优势,该方法更加简便、灵活,无需进行复杂的系统校准。

Dispersion characteristics of seabed Scholte waves with variable velocity seawater in deep water

Acoustic velocity varies in deep-water environments.To obtain accurate inversion interpretations,it is necessary to develop a horizontally layered seawater–seabed(HLSS)model with continuously varying velocities.In this work,we used an HLSS model based on wave theory to deduce the Scholte wave dispersion equations and established an HLSS model based on the acoustic velocity profile and the submarine medium parameters of the South China Sea.We studied the dispersion characteristics of Scholte waves and theoretically calculated the amplitude–depth distribution.We also examined the influence of deep-water environments on the dispersion characteristics of Scholte waves.Using the real geological parameters of the Dongsha Islands in the South China Sea,we exploited the spectral element method to simulate seismic wave propagation in the fluid–solid interface and extracted the Scholte wave dispersion curves using multichannel analysis of surface waves(MASW).The consistent theoretical and extracted dispersion curve results verified the accuracy of our method.Numerical experiments showed that the dispersion characteristics of Scholte waves in deep water are weaker than those in shallow water.In addition to the seawater depth and the physical parameters of seabed sediments,the seawater’s variable velocity also influences Scholte wave dispersion characteristics.

STUDY ON FREQUENCY CODING ANTI-INTERFERENCE SYSTEM FOR DATA TRANSMISSION IN SHALLOW WATER ACOUSTIC CHANNELS

Achieving reliable underwater communication in shallow water acoustic channels is a difficult task because of the random time varying nature of multipath propagation, severe amplitude fluctuation, and spatial variability of the channel conditions. This paper describes a new signal processing technique frequency coding and decoding by means of real time measurement of signal width, jamming and suppressing multipath interference and using redundant coder. The application of the technique to the model ZTY 1 status monitor for underwater system of seabed is introduced in this paper. The main principle, the technique specifications and the key techniques of the system are discussed here. Theoretical estimations and experimental results proved that the performance of the system is excellent. The method can be used for some other related low data rate data transmission detecting in shallow water acoustic channel.

Modeling and parameter identification of amplitude- and frequency-dependent rubber isolator

A model to describe the hysteresis damping characteristic of rubber material was presented.It consists of a parallel spring and damper,whose coefficients change with the vibration amplitude and frequency.In order to acquire these relations,force decomposition was carried out according to some sine vibration measurement data of nonlinear forces changing with the deformation of the rubber material.The nonlinear force is decomposed into a spring force and a damper force,which are represented by the amplitude-and frequency-dependent spring and damper coefficients,respectively.Repeating this step for different measurements gives different coefficients corresponding to different amplitudes and frequencies.Then,the application of a parameter identification method provides the requested approximation functions over amplitude and frequency.Using those formulae,as an example,the dynamic characteristic of a hollow shaft system supported by rubber rings was analyzed and the acceleration response curve in the centroid position was calculated.Comparisons with the sine vibration experiments of the real system show a maximal inaccuracy of 8.5%.Application of this model and procedure can simplify the modeling and analysis of mechanical systems including rubber materials.

Turbo-Coded Modulation of EVRC Speech Encoder with Unequal Error Protection for Fading Channels

The Enhanced Variable Rate Codec (EVRC) is a standard for the Speech Service Option 3 for Wideband Spread Spectrum Digital System, which has been employed in both IS-95 cellular systems and ANSI J-STC-008 PCS (Personal Communications Systems). This paper investigated the combination of turbo codes with Unequal Error Protection (UEP) and 16-QAM modulation for EVRC codec of Rate 1 to get power and bandwidth efficient coding scheme. The results show that the UEP system outperforms the Equal Error Protection (EEP) one by 1.45 dB at BER of 10 -5.