86,932 research outputs found
A Damage Identification procedure based on Hilbert transform: experimental validation
No full textThis paper aims at validating the feasibility of an identification procedure, based on the use of the Hilbert
transform, by means of experimental tests for shear-type multi-degree-of-freedom systems. Particularly,
a three-degree-of-freedom frame will be studied either numerically or experimentally by means of
a laboratory scale model built at the laboratory of the Structural, Aerospace and Geotechnical Engineering
Department (DISAG) of University of Palermo. Several damage scenarios have been considered to prove
the effectiveness of the procedure. Moreover, the experimental tests have been conducted by considering
two different input loads: pulse forces, simulated by means of an instrumental hammer, and wide band
noise base inputs, by a shake table.
In the first section the damage identification procedure, proposed in recent works, is presented. The
procedure is based on the minimization of an objective function mathematically based on the properties of
the analytical signal and the Hilbert transform. Second section reports the experimental model geometrical
data and the data acquisition set-up as built in the DISAG laboratory. In Section 3, the results of the
experimental campaigns are presented and discussed having considered three damage scenarios. The
validated procedure has been proved to be able to not only detect damage even at early stage but it also needs
processing of only few samples of the structural respons
Low stiffness variation in structural systems: identification and localization
No full textWhen a very low damage occurs, the undamaged structural response totally overlaps the damaged one
eitherintimedomainorinfrequencydomain;ontheotherhand,byconsideringsomecharacteristicsofthe
analytical signal, such as the phase, it has been possible to develop a damage identification procedure that
allows the identification and localization of damage even if the structure experiences multiple damages at
the same time. This procedure is also robust with respect to the presence of measuring noise. In order to
assess the validity of the proposed damage identification procedure, numerical applications on single
degree of freedom and 2 DOF and 4 DOF are presented using data records perturbed by measuring noise
too
On the dynamics of fractional visco-elastic beams
No full textWith increasing advanced manufacturing process, visco-elastic materials are very attractive for mitigation of vibrations, provided that you may have advanced studies for capturing the realistic behavior of such materials.
Experimental verification of the visco-elastic behavior is limited to some well-known low order models as the Maxwell or Kelvin models. However, both models are not sufficient to model the visco-elastic behavior of real materials, since only the Maxwell type can capture the relaxation tests and the Kelvin the creep tests, respectively. Very recently, it has been stressed that the most suitable model for capturing the visco-elastic behavior is the spring-pot, characterized by a fractional constitutive law.
Based on this assumption, the quasi-static behavior has been investigated very recently, however for noise control there is a need of exploiting the dynamic behavior of such a fractional visco-elastic beam.
The present paper introduces the dynamic response of fractional visco-elastic Euler-Bernoulli beam under dynamic loads
Effects of metolazone administration on congestion, diuretic response and renal function in patients with advanced heart failure
No full textBackground: Advanced heart failure (HF) is a condition often requiring elevated doses of loop diuretics. Therefore, these patients often experience poor diuretic response. Both conditions have a detrimental impact on prognosis and hospitalization. Aims: This retrospective, multicenter study evaluates the effect of the addition of oral metolazone on diuretic response (DR), clinical congestion, NTproBNP values, and renal function over hospitalization phase. Follow-up analysis for a 6-month follow-up period was performed. Methods: We enrolled 132 patients with acute decompensated heart failure (ADHF) in advanced NYHA class with reduced ejection fraction (EF < 40%) taking a mean furosemide amount of 250 ± 120 mg/day. Sixty-five patients received traditional loop diuretic treatment plus metolazone (Group M). The mean dose ranged from 7.5 to 15 mg for one week. Sixty-seven patients continued the furosemide (Group F). Congestion score was evaluated according to the ESC recommendations. DR was assessed by the formula diuresis/40 mg of furosemide. Results: Patients in Group M and patients in Group F showed a similar prevalence of baseline clinical congestion (3.1 ± 0.7 in Group F vs. 3 ± 0.8 in Group M) and chronic kidney disease (CKD) (51% in Group M vs. 57% in Group F; p = 0.38). Patients in Group M experienced a better congestion score at discharge compared to patients in Group F (C score: 1 ± 1 in Group M vs. 3 ± 1 in Group F p > 0.05). Clinical congestion resolution was also associated with weight reduction (−6 ± 2 in Group M vs. −3 ± 1 kg in Group F, p < 0.05). Better DR response was observed in Group M compared to F (940 ± 149 mL/40 mgFUROSEMIDE/die vs. 541 ± 314 mL/40 mgFUROSEMIDE/die; p < 0.01), whereas median ∆NTproBNP remained similar between the two groups (−4819 ± 8718 in Group M vs. −3954 ± 5560 pg/mL in Group F NS). These data were associated with better daily diuresis during hospitalization in Group M (2820 ± 900 vs. 2050 ± 1120 mL p < 0.05). No differences were found in terms of WRF development and electrolyte unbalance at discharge, although Group M had a significant saline solution administration during hospitalization. Follow-up analysis did not differ between the group but a reduced trend for recurrent hospitalization was observed in the M group (26% vs. 38%). Conclusions: Metolazone administration could be helpful in patients taking an elevated loop diuretics dose. Use of thiazide therapy is associated with better decongestion and DR. Current findings could suggest positive insights due to the reduced amount of loop diuretics in patients with advanced HF
A Novel Mathematical Model For TLCD: Theoretical And Experimental Investigations
No full textIn this paper, a novel mathematical model for the Tuned Liquid Column Damper (TLCD) is presented. Taking advantages of fractional derivatives and related concepts, a new equation of motion of the liquid inside the TLCD is obtained. Experimental laboratory tests have been performed in order to validate the proposed linear fractional formulation. Comparison among experimental results, numerical obtained using the classical formulation and numerical with the new linear fractional formulation are reported. Results in frequency domain show how the new linear fractional formulation can predict the real behavior of such a passive vibration control system, more correctly than the classical mathematical model, widely used in literature
Innovative modeling of Tuned Liquid Column Damper motion
No full textIn this paper a new model for the liquid motion within a Tuned Liquid Column Damper (TLCD) device is developed, based on the mathematical tool of fractional calculus. Although the increasing use of these devices for structural vibration control, it is shown that existing model does not always lead to accurate prediction of the liquid motion. A better model is then needed for accurate simulation of the behavior of TLCD systems. As regards, it has been demonstrated how correctly including the first linear liquid sloshing mode, through the equivalent mechanical analogy well established in literature, produces numerical results that highly match the corresponding experimental ones. Since the apparent effect of sloshing is the deviation of the natural frequency from the theoretical one, the authors propose a fractional differential equation of motion. The latter choice is supported by the fact that the introduction a fractional derivative of order α alters simultaneously both the resonant frequency and the degree of damping of the system. It will be shown, through an extensive experimental analysis, how the proposed model accurately describes liquid surface displacements
Optimal tuning of tuned liquid column damper systems in random vibration by means of an approximate formulation
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