检索结果-南通市图书馆

Elastically restrained Bernoulli-Euler beams applied to rotary machinery modelling

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2011年第1期27卷 56-62页

作者： Tiago A.N.Silva Nuno M.M.Maia ISEL Polytechnic Institute of LisbonDepartment of Mechanical EngineeringRua Conselheiro Emídio Navarro idmec-ist Technical University of LisbonDepartment of Mechanical Engineering

Facing the lateral vibration problem of a machine rotor as a beam on elastic supports in bending,the authors deal with the free vibration of elastically restrained Bernoulli-Euler beams carrying a finite number of concentrated elements along their *** on Rayleigh’s quotient,an iterative strategy is developed to find the approximated torsional stiffness coefficients,which allows the reconciliation between the theoretical model results and the experimental ones,obtained through impact *** mentioned algorithm treats the vibration of continuous beams under a determined set of boundary and continuity conditions, including different torsional stiffness coefficients and the effect of attached concentrated masses and rotational inertias, not only in the energetic terms of the Rayleigh’s quotient but also on the mode shapes,considering the shape functions defined in *** loading cases are examined and examples are given to illustrate the validity of the model and accuracy of the obtained natural frequencies.

关键词： Transverse vibration of beams · Elastic supports · Torsional stiffness coefficients

Fracture Loci in Sheet Metal Forming: A Review

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2015年第12期28卷 1415-1425页

作者： M.Beatriz Silva Kerim Isik A.Erman Tekkaya Paulo A.F.Martins idmec Instituto Superior Técnico Universidade de Lisboa Institute of Forming Technology and Lightweight Construction Technical University of Dortmund

Fracture in sheet metal forming usually occurs as ductile fracture, rarely as brittle fracture, at the operating temperatures and rates of loading that are typical of real processes in two different modes：（1） tensile and（2） in-plane shear（respectively, the same as modes I and II of fracture mechanics）. The circumstances under which each mode will occur are identified in terms of plastic flow and ductile damage by means of an analytical approach to characterize fracture loci under plane stress conditions that takes anisotropy into consideration. Fracture loci was characterized by means of the fracture forming limit line and by the shear fracture forming limit line in the fracture forming limit diagram. Experiments were performed with single point incremental forming and double-notched test specimens loaded in tension, torsion and in-plane shear give support to the presentation and allow determining the fracture loci of AA1050-H111 aluminium sheets with1 mm thickness. The relation between fracture toughness and the fracture forming limits was also investigated by comparing experimental values of the strains at fracture obtained from a truncated conical part produced by single point incremental forming and from double-notched test specimens loaded in tension.

关键词： Sheet forming Fracture Fracture forming limit diagram

Nonlocal material properties of single-walled carbon nanotubes

在线全文

学校读者我要写书评

暂无评论

International Journal of Smart and Nano Materials 2012年第2期3卷 141-151页

作者： J.V.Araújo dos Santos C.M.Mota Soares idmec Instituto Superior TécnicoUniversidade Técnica de Lisboa1049-001 LisboaPortugal

Natural frequencies of single-walled carbon nanotubes(SWCNTs)obtained using a model based on Eringen’s nonlocal continuum mechanics and the Timoshenko beam theory are compared with those obtained by molecular dynamics *** goal was to determine the values of the material constant,considered here as a nonlocal property,as a function of the length and the diameter of *** present approach has the advantage of eliminating the SWCNT thickness from the computations.A sensitivity analysis of natural frequencies to changes in the nonlocal material constant is also carried out and it shows that the influence of the nonlocal effects decreases with an increase in the SWCNT *** matching of natural frequencies shows that the nonlocal material constant varies with the natural frequency and the SWCNT length and diameter.

关键词： nonlocal mechanics molecular dynamics simulation single-walled carbon nanotube Timoshenko beam

Optimal distribution of active piezoelectric elements for noise attenuation in sandwich panels

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

International Journal of Smart and Nano Materials 2020年第4期11卷 400-416页

作者： J.F.A.Madeira A.L.Araujo idmec Instituto Superior TecnicoUniversidade de LisboaLisboaPortugal ADM ISELInstituto Politecnico de LisboaLisboaPortugal

In this paper,a multiobjective optimization approach for obtaining the optimal distribution of surface-bonded piezoelectric sensors and actua-tors for noise attenuation in sandwich panels is *** noise attenuation is achieved by using negative velocity feedback control with co-located sensors and *** control gains are also optimized in order to obtain the most efficient noise attenuation in a given frequency *** in-house implementation of a viscoelastic soft core sandwich plate finite element,including surface-bonded piezoelectric sensors and actuators with active control capabilities,is used for obtaining the frequency response of the *** sound transmission capability of the panels is evaluated using the radiated sound power,along with the Rayleigh integral approach,which is suitable for lightly coupled structural/acoustic *** Direct MultiSearch(DMS)optimization algorithm is used to minimize the added weight due to the piezoelectric material,minimizing also the number of required controllers and maximizing the noise *** total length of the radiated sound power curve is shown to be an effective measure of noise attenuation in a given frequency ***-off Pareto fronts and the obtained optimal configurations are presented and discussed.

关键词： Sandwich structures piezoelectricity viscoelasticity active damping multiobjective optimization

Analysis of a passive ankle exoskeleton for reduction of metabolic costs during walking

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Defence Technology（防务技术） 2024年第7期37卷 62-68页

作者： Luís Quinto Pedro Pinheiro Sergio B.Goncalves Ivo Roupa Paula Simoes Miguel Tavares da Silva CINAMIL Academia MilitarInstituto Universitario MilitarLisbonPortugal idmec Instituto Superior TecnicoUniversidade de LisboaLisbonPortugal

Modern conflicts demand substantial physical and psychological exertion,often resulting in fatigue and diminished combat or operational *** exoskeletons have been developed recently to address these challenges,presenting various limitations that affect their operational or everyday *** article evaluates the performance of a dual-purpose passive ankle exoskeleton developed for the reduction of metabolic costs during walking,seeking to identify a force element that could be applied to the target *** on the 6-min walk test,twenty-nine subjects participated in the study using three different force *** results indicate that it is possible to reduce metabolic expenditure while using the developed ***,the comfort and range of motion results verify the exoskeleton's suitability for use in uneven terrain and during extended ***,the choice of the force element should be tailored to each user,and the control system should be adjustable to optimise the exoskeleton's performance.

关键词： Ankle passive exoskeleton Metabolic cost reduction Dual-use exoskeleton Gait Biomechanics

Improving Linked-Lists Using Tree Search Algorithms for Neighbor Finding in Variable-Resolution Smoothed Particle Hydrodynamics

在线全文

学校读者我要写书评

暂无评论

Communications in Computational Physics 2019年第6期26卷 57-86页

作者： Shahab Khorasanizade J.M.M.Sousa idmec Instituto Superior T́ecnicoUniversidade de LisboaAv.Rovisco Pais1049-001 LisboaPortugal

Improving linked-lists for neighbor finding with the use of tree search algorithms is proposed here,aiming to cope with highly non-uniform resolution simulations employing a meshless *** new procedure,coined Quadtree Cells Grid,has been implemented in Smoothed Particle Hydrodynamics(SPH).The SPH scheme employed is adaptive,thus allowing for particle refinement in desired regions of the *** to the wide range of coexisting particle mass levels,standard linked-list neighbor search algorithms become ***,an alternative is found based on the use of hierarchical data structures,using quadtrees(in 2D problems).The present algorithm exploits the advantages of both linked-lists and quadtree meth-ods with the goal of increasing computational efficiency,when dealing with highly non-uniform particle *** cases involving two distinct flow problems have demonstrated that the computational cost of the current adaptive neighbor finding algorithm scales linearly with the total number of particles,thus retrieving this characteristic of linkedlists in uniform grid ***,the memory usage increased as a result of the more complex data structure.

关键词： Smoothed particle hydrodynamics linked-list quadtree neighbor finding variable resolution

Energy efficiency in a water supply system:Energy consumption and CO_2 emission

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Water Science and Engineering 2010年第3期3卷 331-340页

作者： Helena M.RAMOS Filipe VIEIRA Dídia I.C.COVAS Department of Civil Engineering ISTTechnical University of Lisbon CEHIDRO IST-DECivilLisbon 1049-001Portugal

This paper presents important fundamentals associated with water and energy efficiency and highlights the importance of using renewable energy sources. A model of multi-criteria optimization for energy efficiency based on water and environmental management policies, including the preservation of water resources and the control of water pressure and energy consumption through a hybrid energy solution, was developed and applied to a water supply system. The methodology developed includes three solutions：（1） the use of a water turbine in pipe systems where pressures are higher than necessary and pressure-reducing valves are installed, （2） the optimization of pumping operation according to the electricity tariff and water demand, and （3） the use of other renewable energy sources, including a wind turbine, to supply energy to the pumping station, with the remaining energy being sold to the national electric grid. The use of an integrated solution （water and energy-） proves to be a valuable input for creating benefits from available hydro energy in the water supply system in order to produce clean power, and the use of a wind source allows for the reduction of energy consumption in pumping stations, as well as of the CO2 emission to the atmosphere.

关键词： multi-criteria optimization energy efficiency water supply renewable energy sources CO2 emission

Autonomic and sensory nerve dysfunction in primary biliary cirrhosis

在线全文

学校读者我要写书评

暂无评论

World Journal of Gastroenterology 2004年第20期10卷 3039-3043页

作者： Katalin Keresztes lldikó istenes Aniko Folhoffer Peter L Lakatos Andrea Horvath Timea Csak Peter Varga Peter Kempler Ferenc Szalay ist Department of Medicine Semmelweis UniversityBudapestHungary ist Department of Medicine Semmelweis UniversityBudapestHungary Professor MDPhD

AIM:Cardiovascular autonomic and peripheral sensoryneuropathy is a known complication of chronic alcoholicand non-alcoholic liver *** aimed to assess theprevalence and risk factors for peripheral sensory nerveand autonomic dysfunction using sensitive methods inpatients with primary biliary cirrhosis (PBC).METHODS:Twenty-four AMA M2 positive female patientswith clinical,biochemical and histological evidence of PBCand 20 age matched healthy female subjects were *** standard cardiovascular reflex tests and 2d-h heartrate variability(HRV)analysis were performed to defineautonomic *** sensory nerve function onmedian and peroneal nerves was characterized by currentperception threshold(CPT),measured by a neuroselectivediagnostic stimulator(Neurotron,Baltimore,MD).RESULTS:Fourteen of 24 patients(58%)had at least oneabnormal cardiovascular reflex test and thirteen(54%)had peripheral sensory *** heart rateresponse to deep breathing(P=0.001),standing(P=0.03)and Valsalva manoeuvre(P=0.01),and more profounddecrease of blood pressure after standing(P=0.03)wasfound in PBC patients than in *** a novel findingwe proved that both time domain and frequency domainparameters of 24-h HRV were significantly reduced in PBCpatients compared to *** patient had at leastone abnormal parameter of *** CPT values indicatedhyperaesthesia as a characteristic feature at peronealnerve testing at three frequencies(2000 Hz:P=0.005;250 Hz:P=0.002;5 Hz:P=0.004)in PBC compared *** of autonomic dysfunction with theseverity and duration of the disease was *** power of HRV correlated with lower CPT values atmedian nerve testing at 250 Hz(P=0.0001)and at 5 Hz(P=0.002),as well as with those at peroneal nerve testingat 2000 Hz(P=0.01).CONCLUSION:Autonomic and sensory nerve dysfunctionsare frequent in ***-four-hour HRV analysis is moresensitive than standard cardiovascular tests for detectingof both pa

关键词： Aged Autonomic Nervous System Diseases Cross-Sectional Studies Female Humans Liver Cirrhosis, Biliary Median Nerve Middle Aged Peripheral Nervous System Diseases Sensory Thresholds

Easy proft maximization method for open-pit mining

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2013年第5期5卷 350-353页

作者： C.Dinis da Gama ist – Technical University of Lisbon

A methodology applicable at any phase of a surface mining project for evaluating its current technical and economic feasibility is *** requires the typically available quantitative data on the ore-body,with its three-dimensional block model developed upon accurate *** it allows estimations of exploitable reserves in function of various cut-off grades,such as the average grade of mineable ore,the tonnages of ore and waste rock,stripping ratios and proft estimates for different production *** cost evaluations of essential mine operations are available(such as ore mining,waste removal,ore concentration,transportation,indirect project costs and expected concentrate selling prices),the methodology will provide clear indications on the economic feasibility of mining,including the best available options at any *** expressions are developed on the basis of a proft mathematical function and an application example is presented with data available from an existing iron ore deposit.

关键词： Open-pit Proft maximization Ore grade Stripping ratio Economic feasibility