Improved Energy Dissipation Research Articles

Viscoelastic Properties and Shock Response of Coarse-Grained Models of Multiblock versus Diblock Copolymers: Insights into Dissipative Properties of Polyurea

We compare and contrast the microstructure, viscoelastic properties, and shock response of coarse-grained models of multiblock copolymer and diblock copolymers using molecular dynamics simulations. This study is motivated by the excellent dissipative and shock-mitigating properties of polyurea, speculated to arise from its multiblock chain architecture. Our microstructural analyses reveal that the multiblock copolymer microphase-separates into small, interconnected, rod-shaped, hard domains surrounded by a soft matrix, whereas the diblock copolymer forms larger, unconnected, hard domains. Our viscoelastic analyses indicate that compared with the diblock copolymer, the multiblock copolymer is not only more elastic but also more dissipative, as signified by its larger storage and loss modulus at low to intermediate frequencies. Our shock simulations and slip analyses reveal that shock waves propagate slower in the multiblock copolymer in comparison with the diblock copolymer, most likely due to the more deformable hard domains in the former system. These results suggest that the multiblock architecture of polyurea might impart polyurea with smaller, more deformable, and interconnected hard domains that lead to improved energy dissipation and lower shock speeds.

High strain-rate behavior of natural fiber-reinforced polymer composites

The high strain-rate constitutive behavior of polymer composites with various natural fibers is studied. Hemp, hemp/glass hybrid, cellulose, and wheat straw-reinforced polymeric composites have been manufactured, and a split-Hopkinson pressure bar apparatus has been designed to measure the dynamic stress–strain response of the materials. Using the apparatus, compressive stress–strain curves have been obtained that reveal the materials’ constitutive characteristics at strain rates between 600 and 2400 strain/s. Primary findings indicate that natural fibers in thermoset composites dissipate energy at lower levels of stress and higher strain than glass-reinforced composites. In the case of thermoplastic matrices, the effect on energy dissipation of natural fibers vs. conventional talc reinforcements is highly dependent on resin properties. Natural fibers in polypropylene homopolymer show improved reinforcement but have degraded energy dissipation compared to talc. Whereas in polypropylene copolymer, natural fibers result in improved energy dissipation compared to talc. These data are useful for proper design, analysis, and simulation of lightweight biocomposites.

Study on the Effect of Supporting Stiffness on Energy Dissipation Efficiency of Viscous Dampers

Viscous dampers are widely used in vibration energy dissipation project. The researches on viscous dampers used in energy dissipation project at present are more, and one of the main research contents is about how to improve energy dissipation efficiency. In the current study, the effect of the supporting stiffness in dampers is neglected, and only its strength and stiffness is verified. Based on the research on the principle and mechanical model of viscous damper, the influence of supporting stiffness on various energy dissipation working parameters has been analyzed in this paper. The results showed that, supporting stiffness has great influence on the energy dissipation efficiency, then with energy dissipation efficiency as the index, this paper derived the generality support stiffness design formula for energy consumption optimizing, which provide scientific basis for similar design.

Retraining local and global buckling behavior of steel plastic hinges using CFRP

Carbon fiber-reinforced polymer (CFRP) composites have been shown to be particularly well suited for external strengthening of reinforced concrete members. However, there is limited information about how they can be used to strengthen steel structures that are susceptible to local and global instabilities. This paper discusses test results of full-scale steel flexural specimens subjected to reversed cyclic loading, some of which are wrapped with CFRP in the plastic hinge region. The main variables investigated are lateral bracing, to study the effect of CFRP wrapping on local buckling and lateral torsional buckling, wrapping scheme, and number of layers of fibers. The test results show that application of CFRP in the plastic hinge region of flexural members has substantial benefits. In particular, the CFRP wraps can increase the size of the yielded plastic hinge region, slow down the occurrence of local buckling, and delay lateral torsional buckling. These benefits reduce strain demands in the critical plastic hinge region and substantially improve energy dissipation capacity within the plastic hinge region.

Size-dependent heterogeneity benefits the mechanical performance of bone

Heterogeneity of biological materials, such as bone, tooth, and mollusc shells, plays a key role in determining their mechanical performance (e.g. the strength, damage tolerance, etc.). Here, we quantify heterogeneities in elasticity and inelasticity of bovine cortical bone between 100 nm and a few microns and identify a characteristic length scale ( λ c) of approximately 200 nm. Below λ c the mechanical heterogeneity of bone is pronounced and exhibits a strong nonlinear size-dependence, while above λ c the heterogeneity is much less. Such size-dependent heterogeneity benefits the mechanical performance of bone since it not only promotes the energy dissipation at nanoscale, but also suppresses heterogeneity-induced stress concentration and strain localization at larger length scales. This is one of the possible mechanisms functioning at multiple length scales that make bone a well-designed tough natural material. Utilizing experimentally measured data, systematic computational simulations were carried out, showing that the heterogeneity in inelasticity, rather than elasticity, plays a dominant role in promoting energy dissipation during deformation. Possible parameters that determine the inelasticity heterogeneity (e.g. mean value and standard deviation of heterogeneous yield stress) and therefore affect energy dissipation are investigated under typical deformation modes of bone. The analysis presented suggests that there exists an optimum ratio of macroscopic strength to elastic modulus for improving energy dissipation under tension. All these findings are of great value to the design and synthesis of improved bio-inspired composites.

Novel acrylic nanocomposites containing in-situ formed calcium phosphate/layered silicate hybrid nanoparticles for photochemical rapid prototyping, rapid tooling and rapid manufacturing processes

Novel acrylic nanocomposites containing calcium phosphate/layered silicate hybrid nanoparticles have been developed for use in photochemical Rapid Prototyping processes like Structural Light Modulation (SLM) and Stereolithography (SL). When tertiary alkyl amines, protonated with phosphoric acid, were added to an acrylic suspension of calcium bentonite, the cation exchange of Ca2+ rendered bentonite organophilic, caused swelling, intercalation and dispersion of silicate nanoplatelets in the monomer. The simultaneous precipitation of calcium phosphate onto the silicate nanoplatelets accounted for the in-situ formation of hybrid nanoparticles. The uniform dispersions of such hybrid nanoparticles afforded a high degree of shear thinning, reflecting the presence of anisotropic filler particles, and increased photosensitivity in SLM with respect to the unfilled resin. Young’s modulus of green and postcured parts increased by 30% at a filler content of 15 wt.% with respect to that of the unfilled benchmark material. This enhanced stiffness was paralleled by 30% increased fracture toughness. As evidenced by fracture surface analysis using Environmental Electron Microscopy (ESEM) and optical microscopy, the improved energy dissipation at the crack tip correlated with roughness of the fracture surfaces, increasing with increasing filler content. Moreover, the examination of the volumetric polymerization shrinkage and the fabrication of H-shaped diagnostic specimens revealed that the nanocomposites were processed with high accuracy, increasing with increasing filler content. Nanocomposite morphologies, examined by means of Transmission Electron Microscopy (TEM), demonstrated that the large primary bentonite particles with average diameters >10 μm fragmented into much smaller particles with average diameters in the range of 1 μm. According to TEM and Wide Angle X-Ray Scattering (WAXS), such in-situ formed nanoparticles were composed of both stacks of organoclay nanoplatelets and also isolated nanoplatelets typical for fully exfoliated organoclays.

Energy-Aware Compilation for Embedded Processors with Technology Scaling Considerations

With scaling of technology feature sizes, the share of leakage in total energy consumption of digital systems is on the rise. Conventional dynamic voltage scaling (DVS) techniques fail to accurately address the impact of scaling on system energy consumption breakdown, and hence, are incapable of achieving energy efficient solutions in all technology nodes. To overcome this problem, we propose utilizing adaptive body biasing (ABB) to adjust transistors' threshold voltage at runtime. While ABB has intrinsic limitations with deep sub-micron scaling, we demonstrate that it can be favorably combined with DVS to reduce overall energy consumption down to 45 nm technology node. We develop a leakage-aware compilation methodology for embedded applications under hard or soft timing constraint. Our technique targets embedded processors with both DVS and ABB capabilities, and has the unique advantage of jointly optimizing active and leakage energy dissipation. Considering the delay and energy overhead of switching between operating modes of the processor and execution deadline constraints, our compiler improves the energy consumption of the generated code by average of 21.66% at 90 nm. While our technique's improvement in energy dissipation over conventional DVS is small (6.43%) at 130 nm, the average improvement continues to grow to 12.23%, 18.63% and 22.16% for 90 nm, 65 nm and 45 technology nodes, respectively. Extensive experiments validate the effectiveness of our approach, explore the involved trade-offs, and offer insights into future trends with respect to technology scaling.

The effects of diagonal web reinforcement on cyclic behaviour of lightweight structural walls

This study focuses on the seismic behaviour of lightweight reinforced concrete shear walls with different web reinforcement modes, with the aim of discovering an optimised web reinforcement mode to increase ductility and shear resistance. The paper describes a comprehensive experimental programme involving four lightweight concrete shear wall specimens with the same shear span ratio of 1·43. The wall specimens are reinforced against shear, either conventionally (orthogonal grids of web reinforcement) or with diagonal bars. The different deformation characteristics, hysteretic response, stiffness attenuation and energy dissipation capacity between four wall specimens are investigated. The test results clearly show that diagonal web reinforcement results in lower shear strains near the wall base and improved energy dissipation characteristics.

Anti-Seismic Behavior of Innovatory RC Frame Subjected to Severe Earthquake Action

The anti-seismic behavior of RC frame with buckling restrained braces (BRBs) subjected to severe earthquake action in seismic region was investigated in this paper. A design process of the buckling restrained braces used for stiffness-deficiency concrete frame structures was given, the design of the buckling restrained braces was conducted for a common frame structure, the layout of these braces in it was given by taking an actual engineering for illustrations, and the static analysis and time-history dynamic analysis were also performed. The results of computation showed that the use of buckling restrained braces has led to several functional improvements, such as the increase in structure stiffness, reduction of story displacement, and improved energy dissipation ability when compared with the frame without such braces. Analysis results showed further that RC frame with BRBs could absorb and dissipate seismic energy more effectively, improving anti-seismic performance of the framed structure.

Semi-active friction dampers for seismic control of structures

Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.

Effects of fibre-reinforced cement composites' ductility on the seismic performance of short coupling beams

The current study examines the effects of the deformation behaviour of cementitious material ductility on the seismic performance of shear-dominant coupling beams. Matrix ductility and reinforcement layouts comprise the main testing variables. Three short coupling beams with two different reinforcement arrangements and matrices are constructed and tested. They are subjected to cyclic loading under a suitable experimental set-up. All specimens are characterised by a shear span–depth ratio of 1·0. The reinforcement layouts consist of a classical scheme and diagonal scheme without confining ties. The effects of cement-based matrix ductility on crack patterns, failure modes, hysteretic characteristics and the ultimate shear load of the coupling beams are examined. The combination of a ductile cement-based matrix and steel reinforcement is found to result in improved energy dissipation capacity, simplification of reinforcement details, and damage-tolerant inelastic deformation behaviour. Test results show that high-performance hybrid fibre-reinforced cement-based composite (HPHFRCC) coupling beams behave better than normal reinforced concrete (RC) control beams. These results are evidenced by the tensile deformation capacity, damage tolerance and tensile strength of HPHFRCC material.

Efficient and scalable compiler-directed energy optimization for realtime applications

With continuing shrinkage of technology feature sizes, the share of leakage in total energy consumption of digital systems continues to grow. Coordinated supply voltage and body bias throttling enables the compiler to better optimize the total energy consumption of the system in future technology nodes. We present a compilation technique that targets realtime applications running on embedded processors with combined dynamic voltage scaling (DVS) and adaptive body biasing (ABB) capabilities. Considering the delay and energy penalty of switching between operating modes of the processor, our compiler judiciously inserts mode-switch instructions in selected locations of the code and generates executable binary that is guaranteed to meet the deadline constraint. More importantly, our algorithm runs very fast and comes reasonably close to the theoretical limit of energy optimization using DVS+ABB. At 65nm technology, we improve the energy dissipation of the generated code by an average of 33.20% under deadline constraints. While our technique's improvement in energy dissipation over conventional DVS is marginal (6.91%) at 130nm, the average improvement continues to grow to 13.19%, 22.97%, and 33.21% for 90nm, 65nm, and 45nm technology nodes, respectively. Compared to a recent ILP-based competitor, we improve the runtime by more than three orders of magnitude, while producing improved results.

Negative stiffness characteristics of active and semi-active control systems for stay cables

This paper examines the characteristics and effects of negative stiffness with active and semi-active control of stay cables for vibration reduction. The characteristics of negative stiffness of stay cable active and semi-active control are presented through numerical simulations. Three indices are defined to quantify the degree of negative stiffness. A pseudo-viscoelastic (P-VE) damper is proposed to replace an active or semi-active device to carry out numerical and theoretical analysis. An asymptotic solution of damping ratio of the combined cable/P-VE damper is obtained and the approximate optimal damping ratio of the combined cable/P-VE damper is further derived. The relationship between optimal damping ratio and the damping coefficient of the P-VE damper with various stiffness (both of negative and positive stiffness) is calculated by using the asymptotic solution and compared with that evaluated by using numerical analysis. The effect of negative stiffness on response reduction of cables is demonstrated by the improved energy dissipation ability of the damper and the increased approximate damping ratio because of the enhanced displacement of the cable at the location where it is attached to the damper. Copyright © 2007 John Wiley & Sons, Ltd.

Effects of Matrix Ductility on Damage Tolerance of Diagonally Reinforced Coupling Beams

This paper investigates the effect of the ductile deformation behavior of high performance hybrid fiber-reinforced cement-based composites (HPHFRCCs) on the shear behavior and damage of diagonally reinforced coupling beams under reversed cyclic loading. The effects of matrix ductility on deflections, crack widths, crack patterns, failure modes, and ultimate shear load of the coupling beams have been examined. The combination of a ductile cement-based matrix and steel reinforcement is found to result in improved energy dissipation capacity and damage-tolerant inelastic deformation behavior. Test results showed that the coupling beam constructed with an HPHFRCC material exhibited excellent strength, deformation capacity, and damage tolerance capacity, in comparison with the regular reinforced concrete beam.

Switching Oil Damper with Built-in Controller for Structural Control

This paper presents a simple semiactive oil damper developed for an actual application. This device can dissipate twice as much energy imposed by wind or earthquake forces as an ordinary passive damper by switching the opening of the on/off valve according to a signal from a controller. Because the system employs a decentralized control algorithm that uses only a built-in sensors' information, each device can be equipped with all the necessary control equipment such as sensors and a controller. This simple construction has several advantages in actual application. First, we discuss the control algorithm and compare the control performance with that of the passive damper. Second, we describe the construction of the developed full-scale device. Finally, we present the results of a dynamic loading test conducted on a full-scale device. The developed device showed stable performance under a nonstationary excitation as well as a harmonic loading, and the improved energy dissipation capacity was clearly recognized. It is also confirmed that the damper's dynamic behavior can be accurately simulated with simple analytical parameters.

Effect of Matrix Ductility on Deformation Behavior of Steel-Reinforced ECC Flexural Members under Reversed Cyclic Loading Conditions

Summarizes the results of research aimed at investigating the effect of ductile deformation behavior of engineered cementitious composites (ECC) on the response of steel reinforced flexural members to lateral load reversals. The combination of a ductile cementitious matrix and steel reinforcement is found to result in improved energy dissipation capacity, reduction of transverse steel reinforcement requirements, and damage-tolerant inelastic deformation behavior. Basic concepts and composite deformation mechanisms of steel reinforced ECC are provided, experimentally verified, and compared to conventional reinforced concrete using small-scale specimens. Results indicate advantageous synergistic effects between ECC matrix and steel reinforcement with respect to compatible deformation, structural composite integrity, and damage evolution, and suggest integrating advanced materials design into the structural design process.

Influence of Viscoelastic Dampers on the Seismic Response of a Lightly Reinforced Concrete Flat Slab Structure

A 1/3-scale model of a section of a three-story lightly reinforced concrete flat slab structure was constructed. Researchers installed a viscoelastic damper (VED) seismic rehabilitation system on the model and subjected it to seismic simulations on a shaking table. Successive simulations were conducted with increasing base accelerations until the horizontal displacement limit of the shaking table was reached. The dampers were then removed, and the simulations were repeated until structural failure occurred. This paper summarizes the responses of the model. Brief comparisons of the responses of the model with and without VEDs installed are made. The VEDs improved energy dissipation characteristics and serviceability of the structure by reducing interstory displacements. Earthquake simulation responses indicated that the damper configuration that was employed in the experimental investigation permitted rotations of the VEDs, which lowered their energy dissipation efficiency. An alternate arrangement for the VEDs is proposed to alleviate this problem.

Submerged Radial Hydraulic Jump

A slight flaring of the side walls of the stilling basin can be advantageous in reducing the exit velocities. The hydraulic jump in such a stilling basin is referred to as a radial hydraulic jump. When the sluice gates discharge directly to the stilling basin, a submerged radial hydraulic jump will probably occur. An experimental study produced surface profiles, bed pressure and length characteristics for the submerged radial jump. A fourth-degree polynomial was used to describe the surface profile. The submerged radial jump lengths were found to be from 50% to 70% of the corresponding submerged rectangular jump lengths. Improved energy dissipation is also characteristic of the radial jumps. The model consisted of a 1.0-m long stilling basin with a total divergence angle of 13.5? located downstream a sluice gate. A theoretical equation is proposed to describe the relationship among: gate submergence, exit depth, initial depth, initial Froude number and basin divergence.