Master Structure Research Articles

A diffusion model for a one-dimensional structure, coupled with an auxiliary system

This paper extends the concept of a local energy approach to homogeneous structures which are coupled with an auxiliary resonant system. The case of a one-dimensional homogeneous master structure (bar, beam) coupled over its length with a homogeneous auxiliary system composed of resonant arbitrary subsystems is analyzed. It is shown that under specific assumptions, the vibrational energy density of the coupled master structure can be predicted by solving a simple energetic boundary value problem that accounts for the mechanical coupling with the auxiliary subsystem. In the context of vibrational energy propagation, an important question is whether heterogeneity introduced by the auxiliary system enhances the diffusive behavior of the master structure. Numerical results for various types of auxiliary systems show that the effective diffusion coefficient of the coupled system is generally increased compared to the uncoupled master structure.

Fabrication of Anti-reflective Structure by Nano Casting Method

Reproducing process of nano structures is newly proposed by the nano casting method. The replicated mold is fabricated using UV curable resin from the master structure by the nano casting method. Using the replicated mold, fine structures are again transferred to the polymer by the nano casting method. The damages to the original structures are relaxed in the replication process and the replicated mold is utilized repeatedly. Fine pattern reproduction using PMMA is successfully demonstrated from the quartz original anti-reflective structure. However, the problem is the releasing process from the replicated polymer mold.

Modeling and fast output sampling feedback control of a smart Timoshenko cantilever beam

This paper features about the modeling and design of a fast output sampling feedback controller for a smart Timoshenko beam system for a SISO case by considering the first 3 vibratory modes. The beam structure is modeled in state space form using FEM technique and the Timoshenko beam theory by dividing the beam into 4 finite elements and placing the piezoelectric sensor/actuator at one location as a collocated pair, i.e., as surface mounted sensor/actuator, say, at FE position 2. State space models are developed for various aspect ratios by considering the shear effects and the axial displacements. The effects of changing the aspect ratio on the master structure is observed and the performance of the designed FOS controller on the beam system is evaluated for vibration control.

A theoretical formulation of the dynamical response of a master structure coupled with elastic continuous fuzzy subsystems with discrete attachments

We present the formulation of the dynamic response of a master structure coupled with a locally homogeneous and orthotropic structural fuzzy, with discrete attachment, composed of elastic continuous fuzzy subsystems. As introduced by Soize, the master structure is the part of the coupled system which is accessible by classical modeling, whereas the structural fuzzy represents systems connected to the master structure, whose characteristics are imprecisely known. A deterministic formulation of the boundary impedance of a general continuous structural fuzzy, which models its action on the master structure, is derived: it is shown that the formulation is different from the solution proposed by Soize in the context of the type I fuzzy law, established from the deterministic model of a linear oscillator excited by its support. Finally, the general boundary impedance is applied to the special situation of a structural fuzzy composed of elastic bars whose geometrical parameters are randomly defined, and numerical results are presented.

The Sol-Gel Process for Realisation of Optical Micro-Structures in Glass

We have applied the sol-gel process to generate optical microstructures in glass using in-house developed sol-gel materials. The synthesis of our sol-gel glass materials is based on the formation of particles of controlled size from organo-metallic compounds. The overall shrinkage during annealing of the gel material is negligible and does not imply crack formation. Silica, titania and binary oxides of silica titania oxide sol-gel materials have been used. A two-step pattern transfer is employed to replicate the structure in glass: first a polydimethylsiloxane (PDMS) replica is obtained from a Si, polymethylmethacrylate (PMMA) or polyimide (PI) master structure, and secondly, a layer of sol-gel material is applied on the PDMS 'soft-replica' to get diffractive micro-/nano-structures in glass after drying and annealing. These structures are characterised. by a scanning electron microscope (SEM) and by an optical diffraction setup.

Environmental engineering education at Ghent University, Flanders (Belgium)

Since the 1980s, environmental engineering education has been a rapidly growing discipline in many universities. This paper discusses the history, the current status and the near future of environmental engineering education at Ghent University. This university, with about 50% of the Flemish university environmental engineering students, can be considered as representative for the situation in Flanders, Belgium. In contrast to many other universities, environmental engineering education at Ghent University does not have its historical roots in civil engineering, but has been developed from the curricula organized by the former Faculty of Agricultural Sciences. As part of a reorganisation of the education and research activities at this faculty, a curriculum leading to the degree of "bio-engineer in environmental technology" was established in 1991. This curriculum covers a 5-year study and is constructed around 8 main components. Exchange of students with other European universities, e.g. within the Socrates framework, has become a prominent aspect of student life and education. This paper also briefly describes the employment opportunities of graduated bio-engineers in environmental technology. Finally, the current implementation of the bachelor's-master's structure, leading to a "master of science in environmental technology" degree is summarized.

VIBRATION CONTROL OF A SMART STRUCTURE USING PERIODIC OUTPUT FEEDBACK TECHNIQUE

ABSTRACTActive vibration control is an important problem in structures. One of the ways to tackle this problem is to make the structure smart, adaptive and self‐controlling. The objective of active vibration control is to reduce the vibration of a system by automatic modification of the system's structural response. This work features the modeling and design of a Periodic Output Feedback (POF) control technique for the vibration control of a smart flexible cantilever beam system for a Single Input Single Output case. A POF controller is designed for the beam by bonding patches of piezoelectric layer as sensor/actuator to the master structure at different locations along the length of the beam. The entire structure is modeled in state space form using the Finite Element Method by dividing the structure into 3, 4, 5 elements, thus giving rise to three types of systems, viz., system 1 (beam divided into 3 finite elements), system 2 (4 finite elements), system 3 (5 finite elements).POF controllers are designed for the above three types of systems for different sensor/actuator locations along the length of the beam by retaining the first two vibratory modes. The smart cantilever beam model is developed using the concept of piezoelectric bonding and Euler‐Bernouli theory principles. The effect of placing the sensor/actuator at various locations along the length of the beam for all the three types of systems considered is observed and the conclusions are drawn for the best performance and for the smallest magnitude of the control input required to control the vibrations of the beam. The tip displacements with the controller is obtained. Performance of the system is also observed by retaining the first 3 vibratory modes and the conclusions are drawn.

Nano-replication of diffractive optical elements in sol–gel derived glasses

A novel technological approach to generate glass micro- and nano-structures using in-house developed sol–gel materials, PDMS molding and thermal densification procedures was developed and presented. The synthesis of our sol–gel glass materials is based on the formation of particles of controlled size from organo-metallic compounds. The overall shrinkage during annealing of the gel material is negligible and does not imply crack formation. Silica, titania and binary oxides of silica titania oxide sol–gel materials are used in a nano-replication process. A two-step pattern transfer is employed to replicate the structure in glass: first a polydimethylsiloxane (PDMS) replica is obtained from a Si or PMMA/PI master structure, and secondly, a layer of sol–gel material is applied on the PDMS ‘soft-replica’ to get micro-/nano-structure in glass after drying and annealing. Diffraction gratings and fresnel lenses with nano-scale features are realized and characterized.

New Formation Technology of Plasma Display Panel Barrier-Rib Structure Using Silicone Rubber Mold Transferred from SU-8 Master Structure

A new formation technology for a plasma display panel (PDP) barrier-rib structure is presented to realize a barrier rib with a high aspect ratio and reduce the manufacturing cost. In this study, we used an SU-8 50 photoresist, which is sensitive to UV irradiation, instead of polymethylmethacrylate (PMMA) which is sensitive to X-ray irradiation, so that the silicone rubber mold could be applicable to a large-area PDP. The first step is to produce an SU-8 master structure using amorphous silicon as an adhesion layer between a glass substrate and SU-8 photoresist. Second, a precise soft mold is manufactured for mass replication of the PDP barrier-rib construction, by molding liquid silicone rubber onto the glass substrate with lithographically defined SU-8 master structures. Third, a PDP barrier-rib structure is formed using the pattern-transferring process with a reusable silicone rubber mold. This is a very simple and inexpensive process consisting with printing of barrier-rib paste, drying, pattern-transferring, and sintering. The pattern-transferring process with a soft mold also demonstrates that the disadvantages of the conventional mold pressing process with a hard mold can be overcome. Consequently, by using the pattern-transferring process with the silicone rubber mold transferred from the SU-8 master structure, the desired barrier-rib shapes can be realized with a high aspect ratio and various dimensions.

Dissipation induced by substructures and distribution of vibratory energy in a complex system

This work is concerned with the problem of energy transfer that takes place between a master structure and the substructures attached to it. The response of the system is characterized by the impedance of the substructures and it determines whether the induced damping is real or apparent. When the dissipation is real the master structure has a larger loss factor than that of the substructures and there will be continuous transfer of vibratory energy from the master structure to substructures. However, in the case of apparent damping, one can observe that the vibration energy is transferred back and forth between the master and substructures. Some combinations of the master and substructures have been considered to examine this phenomenon and to determine the criteria for damping. It has found that a modal overlapping condition, which corresponds to bandwidths that exceed the spacing of those natural frequencies, is crucial in determining the characteristics of the system damping. The result of this paper is consistent with that found with the fuzzy structure and SEA framework. [Work sponsored by Ministry of Education, Korean Government under the BK21 program and Ministry of Science and Tech., Korean Government under National Research Lab. program.]

On the dynamics of fuzzy structures

In this presentation, one proposes a prediction at low- and mid-frequencies of the dynamics of fuzzy structures. As introduced by Soize, the term ‘‘fuzzy structure’’ designates a master structure, whose geometrical, material characteristics, boundary conditions, and excitations are known, coupled with complex systems, called the structural fuzzy or fuzzy, whose characteristics are imprecisely known. Previous works done on this subject analyze the concept of a master structure coupled with a locally homogeneous fuzzy, composed of a large number of linear oscillators excited by their supports. In the present work, the concept of a homogeneous fuzzy is extended to an elastic continuum medium. One theoretically formulates the action of the elastic fuzzy on the master structure: it is shown that the proposed formulation is different from the solution proposed by Soize, derived from the model of a linear oscillator excited by its support. The proposed theory is successfully applied to the case of a homogeneous structural fuzzy composed of a large number of elastic bars whose lengths and cross sections are randomly chosen.

Absorption and trapping of vibration energy by complex resonators

This presentation examines conditions that can enhance apparent damping of a master structure due to its coupling with a complex resonator that does not exhibit classical dissipation properties. The model uses a set of multistage parallel oscillators within which energy is trapped. The method presented here for predicting the apparent damping is based on evaluation of the asymptotic response of the master structure utilizing the Hilbert transform. The result is a functional relationship between the frequency distribution within the system and the resulting apparent damping. This study leads to a nonclassical dynamic absorber, consisting of a multistage parallel oscillators, in terms of its absorption and trapping characteristics. The energy is absorbed from the master at a rate determined by the apparent damping and trapped for a given time interval as measured by the return time. The theoretical results suggest optimal configurations to decrease the absorption time and to increase the trapping time (up to an infinite delay). The results of numerical simulations performed on complex vibro-acoustic systems support the proposed theoretical approach. [Research sponsored by INSEAN and NSF.]

Further assessment of the coupling load decomposition technique for the vibration analyses of planar coupled structures

Vibration analyses of various line-coupled structures are conducted in this paper using the newly developed Coupling Load Decomposition technique. Examples are given to illustrate how this approach may be used in practice. Various factors related to the practical application of the technique are investigated. The approach is applied to systems composed of a main plate as the master structure and different substructures. Plate-like structures and beam-stiffened plates are studied and the results are compared to finite element results. Applications to the case of periodic structures or systems with repeated substructures are also investigated. It is shown that the method is very efficient in such cases leading to satisfactory results in low and medium frequency ranges.

Patterning Solid-Supported Lipid Bilayer Membranes by Lithographic Polymerization of a Diacetylene Lipid

Micropatterned lipid bilayers have been created on solid supports by using lithographic polymerization of a diacetylene lipid (see picture). The domains of polymerized (light) serve, after removal of the monomers, as a two-dimensional master structure for the incorporation of biologically relevant lipid bilayer membranes.

Patterning Solid-Supported Lipid Bilayer Membranes by Lithographic Polymerization of a Diacetylene Lipid

Micropatterned lipid bilayers have been created on solid supports by using lithographic polymerization of a diacetylene lipid (see picture). The domains of polymerized (light) serve, after removal of the monomers, as a two-dimensional master structure for the incorporation of biologically relevant lipid bilayer membranes.

Micropatterned solid-supported membranes formed by micromolding in capillaries.

The formation of individually addressable micropatterned solid-supported lipid bilayers has been accomplished by means of micromolding in capillaries. Small unilamellar vesicles were spread on glass slides to form planar supported membranes along microscopic capillaries molded as trenches into a polydimethylsiloxane (PDMS) elastomer. PDMS provides an elastic and transparent carrier for microcapillaries molded from silicon wafers displaying the desired inverse trenches. The so-called master structure has been conventionally etched into silicon by photolithography. The cured PDMS elastomer was briefly exposed to an oxygen plasma, rendering the surface hydrophilic, and subsequently attached to a glass surface in order to form hydrophilic capillaries equipped with flow-promoting pads on either side. One flowpad acts as a reservoir to be filled with the vesicle suspension, while the other one serves as a collector to ensure a sufficient capillary flow to cover the substrate completely. Formation of planar lipid bilayers on the glass slide along the capillaries was followed by imaging the flow and spreading of fluorescently labeled DMPC liposomes with confocal laser scanning microscopy. By means of scanning force microscopy in aqueous solution the formed lipid structures were identified and the height of the lipid bilayers was accurately determined. With both techniques, it was shown that the patterned bilayers remain separated and persist for several hours on the substrate in aqueous solution.

Modal Overlap and Dissipation Effects of a Cantilever Beam with Multiple Attached Oscillators

This work was prompted by a study performed by Strasberg [7] in which numerous small spring-mass-damper systems are attached to a large suspended mass representing the master structure. The isolated natural frequency of each attached system was selected to match in average the natural frequency of the isolated master structure. Strasberg found that the critical issue when an impulse excitation is applied to the master structure is the bandwidth of the isolated attached systems in comparison to the spacing between the natural frequencies of the system. Modal overlap, which corresponds to bandwidths that exceed the spacing of those frequencies, was shown to greatly influence the response of the master structure. Light damping, for which there is little or no modal overlap, corresponds to an impulse response that consists of a sequence of nearly periodic exponentially decaying pulses, and the transfer function for harmonic excitation of the master structure indicates that the substructure acts as a vibration absorber for the master structure. Increased damping leads to modal overlap, with the result that the impulse response consists of a single decaying pulse. The frequency domain transfer function indicates that the vibration absorber effect is enhanced. The present work explores these issues for continuous systems by replacing the one degree of freedom master structure with a cantilever beam. The system parameters are selected to match Strasberg’s model, with the suspended oscillators placed randomly along the beam. The beam displacement is represented as a Ritz series whose basis functions are the cantilever beam modes. The coupled equations are solved by a state-space eigenmode analysis that yields a closed form representation of the response in terms of the complex eigenmode properties. The continuous fuzzy structure is shown not to display the transfer of energy between the master structure and the substructure that was exhibited by the discrete fuzzy structure, apparently because of the asynchronous motion of the attachment points resulting from the spatial variability of the beam’s motion. The vibration absorber effect for harmonic excitation is only obtained for the heavy damping in the case of a beam.

ANALYSIS OF FLOQUET WAVE GENERATION AND PROPAGATION IN A PLATE WITH MULTIPLE ARRAYS OF LINE ATTACHMENTS

A variety of engineering structures consist of a homogeneous “master structure”, such as a plate or shell, to which are attached multiple arrays of substructures, such as ribs or stringers. The goal of this work is to understand the effects of array impedance and spacing on energy flow in the master structure. Such an understanding may ultimately lead to a design process encompassing both the attenuation of vibrational energy and the support of static loads. Here, the vibrational response of a locally excited master structure is studied analytically for a class of structures involving an arbitrary number of substructure arrays. The approach is presented in the context of an elastic plate which is reinforced by multiple arrays of line attachments and acted upon by a line force. Extension of the analysis to other geometries and loadings is straightforward. A recursive analytical procedure is presented by which Floquet wavenumbers of a structure with p arrays are computed from the wavenumbers of a structure with p−1 of the arrays attached. In this way, the Floquet wavenumbers of any multiple array structure can be computed by first considering the master structure alone and then computing the effect of attaching each array in turn. The imaginary parts of the Floquet wavenumbers quantify the attenuation of response along the structure. In addition, the spatial response is obtained analytically as a sum of two Floquet waves through simplification and transformation of the wavenumber domain solution. By way of example, a three-array structure is considered to illustrate the recursive computation of the wavenumbers and to demonstrate the correlation between the imaginary parts of the wavenumbers and the spatial attenuation of the structural response.

When is a ‘‘fuzzy’’ not a fuzzy (continued)?

The term ‘‘fuzzy substructures’’ as originally coined by C. Soize includes four categories of substructures whose influence on the vibratory behavior of the master structure to which they are attached may be significantly different. Either (1) the substructures are sufficiently numerous and their modal antiresonant frequencies sufficiently close to each other to result in modal overlap over the frequency range of interest; or (2) they do not have modal overlap; also, either (a) successive modal frequencies are separated by a constant frequency increment, or (b) the frequency increments are irregular. The effect of category (1) substructures on the master structure is independent of the detailed spacing between modal frequencies, provided modal overlap exists, for both steady-state and transient excitation. Contrariwise, the effect of category (2) substructures on the transient behavior of the master structure does depend on whether or not the modal frequencies are equally spaced. Although the statistical average behavior of an ensemble of such (2b) substructures may be similar to that of category (1), individual members of the ensemble may behave quite differently from their average. The differences will be exhibited by examples. To avoid confusion, it is suggested that the term ‘‘fuzzy structures’’ be limited to substructures with modal overlap

Estimation of fuzzy structure parameters for continuous junctions

The fuzzy structure theory introduced 15 years ago is designed to predict the frequency response functions of structures and structural acoustic systems with structural complexity, in the low- and medium-frequency ranges. This paper constitutes a first validation of the fuzzy structure theory for continuous junctions between the master structure and the fuzzy substructures. In addition, a method to estimate the fuzzy structure parameters introduced in the fuzzy structure theory is presented and it is validated for the case of continuous junctions. This validation obtained by numerical simulations opens the field of experimental identifications.