Optimization of a hybrid vibration absorber for vibration control of structures under random force excitation

A recently reported design of a hybrid vibration absorber (HVA) which is optimized to suppress resonant vibration of a single degree-of-freedom (SDOF) system is re-optimized for suppressing wide frequency band vibration of the SDOF system under stationary random force excitation. The proposed HVA makes use of the feedback signals from the displacement and velocity of the absorber mass for minimizing the vibration response of the dynamic structure based on the H₂ optimization criterion. The objective of the optimal design is to minimize the mean square vibration amplitude of a dynamic structure under a wideband excitation, i.e., the total area under the vibration response spectrum is minimized in this criterion. One of the inherent limitations of the traditional passive vibration absorber is that its vibration suppression is low if the mass ratio between the absorber mass and the mass of the primary structure is low. The active element of the proposed HVA helps further reduce the vibration of the controlled structure and it can provide significant vibration absorption performance even at a low mass ratio. Both the passive and active elements are optimized together for the minimization of the mean square vibration amplitude of the primary system. The proposed HVA are tested on a SDOF system and continuous vibrating structures with comparisons to the traditional passive vibration absorber.     

Theoretical and experimental studies on air gap membrane distillation

Air gap membrane distillation (AGMD) is an innovative membrane separation technique for pure water extraction from aqueous solutions. In this study, both theoretical and experimental investigations are carried out on AGMD of different aqueous solutions, namely, tap water, salted water, dyed solutions, acid solutions, and alkali solutions. A simple mechanistic model of heat and mass transfer associated with AGMD is developed. Simple relationships of permeate flux, total heating or cooling load and thermal efficiency of AGMD with respect to the membrane distillation temperature difference are obtained. Effects of solution concentration and the width of the air gap in AGMD are analyzed. In the experimental study, the experiments were conducted using 1m PTFE membrane with a membrane distillation temperature difference up to 55^∘C. The AGMD system yields a permeate flux of pure water of up to 28kg/m²h. Direct comparison of the experimental results with the proposed modeling predictions shows a fairly good match. Received on 19 May 1998     

Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

The effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005     

LOCKING PROBLEM AND VARIABLE REDUCING PROCEDURE IN TREFFTZ METHOD

The Trefftz-type boundary solution methods^[1] are applied in analysing moderately thick plate bending problems. A new type of locking problem caused by the overflow of Trefftz functions has been found and a so-called variable-reducing procedure for eliminating such a phenomenon is also proposed. Supported by National Natural Science Foundation of China(No. 19872019) and Solid Mechanics Open Research Laboratory of Tongji University     

Lie Derivations of Triangular Algebras

We investigate Lie derivations on a class of algebras called triangular algebras. In particular, we give sufficient conditions such that every Lie derivation on such an algebra is a sum of derivation on and a mapping from to its centre.