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Conservative Results (conservative + result)
Selected AbstractsEffect of train dynamics on seismic response of steel monorail bridges under moderate ground motionEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2006Chul-Woo Kim Abstract This study is intended to investigate the seismic response of steel monorail bridges using three-dimensional dynamic response analysis. We particularly consider monorail bridge,train interaction when subjected to ground motion that occurs with high probability. A monorail train car with two bogies with pneumatic tires for running, steering and stabilizing wheels is assumed to be represented sufficiently by a discrete rigid multi-body system with 15 degrees of freedom (DOFs). Bridges are considered as an assemblage of beam elements with 6 DOFs at each node. Modal analysis is used for dynamic response analysis under moderate earthquakes. The seismic response of an advanced monorail bridge that adopts a simplified structural system and composite girders is investigated through comparison with seismic responses of a conventional bridge. The acceleration response of a monorail train is also calculated to investigate the effect of structural types of bridges on the train's dynamic response during earthquakes. Results show that the seismic responses of the advanced bridges are greater than those of the conventional monorail bridge because of the simplified structural system and increased girder weight that is attributable to composite girders of the advanced bridge. Moreover, the train on the advanced bridge shows greater dynamic response than that on the conventional bridge. Observations reveal that the dynamic monorail train system acts as a damper on the monorail bridge. That fact shows that the existing design, which considers a train as additional mass, yields a conservative result. Copyright © 2006 John Wiley & Sons, Ltd. [source] Delay-dependent stability and stabilization of neutral time-delay systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2009Jian Sun Abstract This paper is concerned with the problem of stability and stabilization of neutral time-delay systems. A new delay-dependent stability condition is derived in terms of linear matrix inequality by constructing a new Lyapunov functional and using some integral inequalities without introducing any free-weighting matrices. On the basis of the obtained stability condition, a stabilizing method is also proposed. Using an iterative algorithm, the state feedback controller can be obtained. Numerical examples illustrate that the proposed methods are effective and lead to less conservative results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Delay-range-dependent robust stability and stabilization for uncertain systems with time-varying delayINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 13 2008Tao Li Abstract This paper concerns delay-range-dependent robust stability and stabilization for time-delay system with linear fractional form uncertainty. The time delay is assumed to be a time-varying continuous function belonging to a given range. On the basis of a novel Lyapunov,Krasovskii functional, which includes the information of the range, delay-range-dependent stability criteria are established in terms of linear matrix inequality. It is shown that the new criteria can provide less conservative results than some existing ones. Moreover, the stability criteria are also used to design the stabilizing state-feedback controllers. Numerical examples are given to demonstrate the applicability of the proposed approach. Copyright © 2007 John Wiley & Sons, Ltd. [source] Robust performance for both fixed and worst-case inputsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 3 2005Nicola Elia Abstract We consider the problem of robust performance analysis when some of the exogenous inputs acting on the system are assumed to be fixed and known, while others are unknown but bounded. In particular, we consider the case where performance is measured by the ,, norm of the output signals, and the uncertainty on the nominal model is described by LTV perturbations of bounded ,, -induced norm. We first address the special case when all the exogenous inputs are fixed and known. We propose upper and lower bounds for the measure of robust performance. Two upper bounds are derived, which trade off accuracy versus computational expense. Both conditions are much less conservative than what one would obtain from assuming a worst-case exogenous input. We then generalize the conditions to the more general case, where both fixed and worst-case inputs act on the system. All these conditions are readily computable, and yield much less conservative results than one would obtain from applying standard worst-case analysis methods. Copyright © 2005 John Wiley & Sons, Ltd. [source] Absolute stability of nonlinear systems with disc and norm-bounded perturbationsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2004Serkan T. Impram Abstract Absolute stability of uncertain nonlinear systems is studied using the celebrated Popov and circle criteria. Uncertainty is assumed to exist in terms of disc and norm-bounded perturbations in the linear plant. The use of circular arithmetic is proposed as an accurate but computationally more demanding alternative to the already existing approach based on strict positive realness conditions which is easier and faster to implement but gives, in general, conservative results. Numerical examples are given in order to illustrate the salient features of the mathematical developments. Copyright © 2004 John Wiley & Sons, Ltd. [source] LETHALITY CONTRIBUTION FROM THE TUBULAR HEAT EXCHANGER DURING HIGH-TEMPERATURE SHORT-TIME PROCESSING OF A MODEL LIQUID FOODJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2004G.B. AWUAH ABSTRACT Experiments were conducted using Bacillus stearothermophilus spores in 0.5% w/w carboxymethylcellulose suspension to evaluate come-up contributions from the tubular heat exchanger. A lab-scale UHT/HTST simulator that allowed samples to be collected at the exit of the heat exchanger and holding tube was used with operating temperatures up to 270F. The bulk mean residence time in the heat exchanger ranged from 30 to 89 sec, while that in the holding tube ranged from 4 to 14 sec. It was observed that between 40% and 51% of the cumulative lethality () at the exit of the holding tube, was contributed by come-up in the tubular heat exchanger. This come-up contribution was determined on the basis of having anof 8.5 min in the holding tube alone. It was evident that come-up lethality will depend on product initial temperature, residence time and temperature history in the heat exchanger, with higher temperatures obviously contributing more lethality. Therefore, the entire aseptic system becomes even more complex since several critical parameters need to be monitored, controlled and documented. Experimental data compared favorably with computer-simulated data using the AseptiCALÔ software, with the software package giving more conservative results. Ultimately, come-up credit (CUC) should be tested on a pilot scale or industrial setup by way of reduced residence time (i.e. increased fluid flow rate), reduced holding tube length or temperature in order to determine if CUC can be applied towards the lethality required for the product. Monitoring and control devices become critical to ensure consistency and reproducibility in product residence time and time,temperature history, in the tubular heat exchanger. [source] Multi-objective state feedback control for linear delay systemsASIAN JOURNAL OF CONTROL, Issue 4 2010Wei Xie Abstract This paper provides new linear matrix inequalities (LMI)-based formulae for mixed H2/H, state-feedback synthesis of linear continuous-time systems with state delays of any size. The proposed delay-independent LMI-based conditions enable us to parameterize a memoryless state-feedback controller without involving the Lyapunov variables in the formula. Compared with previous results based on a common Lyapunov variable, the proposed formula provides less conservative results. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Poly-quadratic stability of discrete-time nonlinear systems in Takagi-Sugeno's form,ASIAN JOURNAL OF CONTROL, Issue 6 2009Baocang Ding Abstract This paper studies poly-quadratic stability of nonlinear systems represented by a Takagi-Sugeno (T-S) discrete fuzzy model. A system is poly-quadratically stable when its stability can be verified by a parameter dependent Lyapunov function. There are already some results in this area. This paper, however, presents less conservative results by adopting more slack-matrix-variables in the linear matrix inequalities (LMIs). The parallel distributed compensation (PDC) law is utilized in both the analysis and the synthesis problems. The effectiveness of the new results in this paper is validated by a simulation example. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Robust H, control for uncertain discrete-time systems with probabilistic state delays,ASIAN JOURNAL OF CONTROL, Issue 5 2009Engang Tian Abstract In this paper, we propose a novel design problem of robust H, control for discrete-time systems with probabilistic time delay, where both the variation range of the delay and the probability distribution of the delay taking values in an interval are available. Based on the information on the probability distribution of the delay taking values in an interval, a new modeling method is put forward, with which the probabilistic effects of the delay are reflected into a parameter matrix of certain transformed system. Based on such a new model, criteria for the H, control design are derived by using a combination of the convexity of the matrix equations, the Lyapunov functional method and the linear matrix inequality technique. It is shown via numerical examples that our developed method in the paper can lead to less conservative results than those obtained by existing methods and, furthermore, if the probability distribution of the delay occurrence is available, the allowable upper bound of the delay may be larger than those derived for the case when only the variation range of the delay can be known. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Anpassung des Verkehrslastmodells des DIN FB 101 für kommunale BrückenBETON- UND STAHLBETONBAU, Issue 5 2007Balthasar Novák Prof. Dr.-Ing. Für den Verantwortungsbereich des BMVBS ist das kürzlich eingeführte Lastmodell LM1 für die Verkehrslasten auf Brücken ohne weitere Reduktionen für alle neuen Brückenbauwerke anzusetzen. Dies führt jedoch leider gerade im Bereich der Kommunen zu teilweise konservativen Ergebnissen, da die geometrischen Abmessungen von kommunalen Brücken deutlich von den "üblichen" Abmessungen von Autobahnen und Bundesstraßen abweichen können und die Belastung aus dem LM1 durch den realen Verkehr nicht erzeugt werden kann. Es werden Vorschläge präsentiert, wie bei bestimmten geometrischen Randbedingungen und abhängig vom statischen System eine weitere Abminderung des LM1 möglich ist, ohne das Sicherheitsniveau zu verlassen. Die Arbeit entstand in enger Zusammenarbeit mit den Städten Frankfurt/Main, Leipzig und Stuttgart. Adjusted Traffic Load for Bridges under Communal Responsibility Recently the traffic loads of bridges of the EC1 have been introduced in Germany under the responsibility of the Federal Ministry of Transport, Building and Urban Affairs. Usually the Load Model LM1 has to be used for all new bridge structures with the adjusted values of ,Q1 = 0, 8, ,Q2 = 0, 8, ,Q3 = 0. A further classification has not been defined. This makes sense for the highway bridges and federal road bridges, because usually they have longer spans where a further reduction of the ,-values is not justified. In the sphere of influence of cities and villages the situation is totally different, because many bridges are short and are buildt as single span girder bridges or single frame bridges. In case of those bridges the LM1 leads to conservative results because the geometry and the total weight and the axle weight of the real lorries are limited and cannot develop those high inner forces and moments. The authors developed a proposal for further reduction of the ,-values dependent on the geometry and the statical system of the bridge without leaving the safety level of the Eurocode. Also for strengthening existing bridges these values can be used. The development has been undertaken in colaboration with the civil engineering offices in Frankfurth/Main, Leipzig and Stuttgart. 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