Multi-layer quasi-zero-stiffness meta-structure for high-efficiency vibration isolation at low frequency

An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is used to design the unit cel,i.e.,the single-layer QZS(SL-QZS)meta-structure.Second,the stiffness feature of the unit cell is investigated and verified through static experiments.Third,the unit cells are stacked one by one along the direction of vibration isolation,and thus the ML-QZS meta-structure is constructed.Fourth,the dynamic modeling of the ML-QZS vibration isolation metastructure is conducted,and the dynamic responses are obtained from the equations of motion,and verified by finite element(FE)simulations.Finally,a prototype of the ML-QZS vibration isolation meta-structure is fabricated by additive manufacturing,and the vibration isolation performance is evaluated experimentally.The results show that the vibration isolation performance substantially enhances when the number of unit cells increases.More importantly,the ML-QZS meta-structure can be easily extended in the direction of vibration isolation when the unit cells are properly stacked.Hence,the ML-FQZS vibration isolation meta-structure should be a fascinating solution for highly efficient vibration isolation performance at low frequency.

Capacity and Flexibility Improvement of Traffic Aggregation for Fixed 5G:Key Enabling Technologies,Challenges and Trends

As the emergence of various highbandwidth services and the requirements to support 5G/Wi-Fi 6 wireless networks,the next generation fixed networks,i.e.F5G,are expected to be realized in the 5G era.F5G is endowed with new characteristics,including ultra-high bandwidth,all-optical connections and optimal service experience.With the prospect of optical-to-everywhere,optical technologies are used for mobile front-haul,mid-haul,and back-haul.Optical access networks would play an important role in F5G to support radio access network and fixed access network.Low-latency PON is a key for cost effective-haul traffic aggregation.In terms of signal transmission,intensity modulation directdetection(IM-DD)is a promising scheme due to its simple architecture.The fundamental challenge associated with direct-detection is the disappearance of the transmitted signal’s phase.In access network,the flexibility and low latency are the two key factors affecting service experience.In this article,we review the evolution of PONs and the challenges of current PONs in detail.We analyze key enabling digital signal processing(DSP)techniques,including detection linearization for direct-detection and simplified coherent detection,adaptive equalizers,digital filer enabled flexible access network and low-latency inter-ONU communications.Finally,we discuss the developing trends of future optical access networks.

MLSE-assisted decision feedback equalizer for error-propagation suppression in high-speed IM-DD transmission systems

We propose a trellis-compressed maximum likelihood sequence estimation(TC-MLSE)-assisted sliding-block decision feedback equalizer(DFE)to suppress the error propagation resulting from the DFE in high-speed systems.We use an out-ofrange detector to detect the end of burst errors from the DFE and activate the optional TC-MLSE to correct burst errors.We conduct experiments to transmit a 201-Gbit/s PAM-8 signal.The results show that the proposed method achieves a bit error rate of 3.65×10^(-3),which is close to that of MLSE.The optional MLSE is only activated when needed and processes 11.4%of the total symbols.Moreover,the proposed method compresses the maximum length of burst errors from 19 to 5.

A review of passenger ride comfort in railway:assessment and improvement method

Passenger ride comfort has become a focus of attention in rail transportation equipment design,manufacture and later operation to meet people’s demand for travel quality.However,comfort is a very subjective concept,which is difficult to quantify and evaluate directly,and can be affected by various factors,leading to the corresponding technologies for ride comfort improvement becoming diverse.In this paper,recent research on the assessment method and improvement measures of railway passenger ride comfort is reviewed.The main types of ride comfort are summarized first according to the sources of discomfort,including static comfort,vibration comfort,noise comfort,aural pressure comfort,thermal comfort and visual comfort.The current assessment methods of ride comfort are introduced from the aspects of environmental parameters and human parameters based on the nature of evaluation indicators.Finally,the improvement technologies for each type of ride comfort are presented.

Structural optimization design of a bolster based on a simulation-driven design

A simulation-driven design method which uses multiple optimization methods can effectively promote innovative structural design tion analysis can enormously improve the efficiency of modelling and solving.This study establishes a general workflow of structural and reduce the product development cycle.Meanwhile,the sub-model technology which has more detailed simulation and optimizaoptimization for a stainless-steel metro bolster by combining the simulation-driven design method and sub-model technology.In the sub-model definition phase,the end underframe sub-model which contains the bolster is obtained based on the whole car body finite element(FE)model,and the effectiveness of the end underframe sub-model is also proved.In the conceptual design phase,the is determined according to manufacturing processes and design experiences.In the detailed design phase,the thickness of each topology path inside the bolster is obtained by the topology method and the optimized structure of the inner ribs inside the bolster part of the bolster is determined by size optimization.The simulation analyses indicate that the requirements of static strength and can be decreased by 17.79% compared with the original bolster structure,which means that not only the lightweight design goal fatigue strength are fulfilled by the optimized bolster structure.Besides,the weight can be reduced by 11.18% and the weld length is achicved.but also the welding auantity and manufacturing difficulty are geatly reduced.The results show the effectiveness of the simulation-driven design method based on the sub-model technology in the structural optimization for key parts of rail transit vehicles.