Dissipation Units Research Articles

Tough supramolecular hydrogels of poly(N,N-dimethylacrylamide)-grafted poly(methacrylic acid) with cooperative hydrogen bonds as physical crosslinks.

Incorporating associative interactions as the energy dissipation units has been recognized as an effective strategy to develop tough hydrogels. For hydrogen-bond associations, however, it is highly challenging to stabilize them under aqueous conditions. Although affording cooperativity can enhance and stabilize the hydrogen bonds, it usually requires stepwise polymerization to form these cooperative associations between different polymers and networks. Here, we report a series of tough supramolecular hydrogels with robust hydrogen-bond associations between grafted polymers that are synthesized by polymerization of a macromonomer of poly(N,N-dimethylacrylamide) (PDMAA) and a small monomer of methacrylic acid. The grafted chains of PDMAA form cooperative hydrogen bonds with the main chain of poly(methacrylic acid) (PMAAc), forming supramolecular hydrogels with high toughness and good stability. The tough and stiff hydrogels are in a glassy state, exhibit forced elastic deformation at room temperature, and remain stable over a wide pH range. In contrast, hydrogels prepared by the copolymerization of DMAA and MAAc are swollen and weak in water due to the lack of successive hydrogen donor/acceptor units and the absence of cooperative hydrogen bonds. In addition, these tough hydrogels exhibit good recyclability and shape memory properties, owing to the supramolecular nature of the network and the temperature-dependent mechanical properties. The influence of polymer structure on the associative interactions and macroscopic properties of the hydrogels should be informative for the design of tough soft materials with versatile applications.

Influences of geometry configurations on the performance of micro-nozzles

Micro-nozzles play a critical role in various applications, such as micro-/nano-satellites in aerospace and heat dissipation and cooling in microelectronic systems (MEMS). The flows inside micro-nozzles can experience both continuum and rarefied flow due to their small size. In this research, we explore the optimal geometry configuration of micro-nozzles to achieve comprehensive performance and size, as well as background pressure compensation. Using classical computational fluid dynamics (CFD) and direct simulation Monte Carlo methods (DSMC), we investigate the effects of the expansion ratio, cross-profile shape, and plug on the performance of micro-nozzles operating over a wide range of pressures (0.5−100kPa). The results reveal that micro-nozzle performance is influenced by the interplay between flow expansion and viscous loss induced by the subsonic layer next to the micro-nozzle wall. The findings show that micro-nozzle performance improves with increasing expansion ratio in slip and continuum flow regimes, but decreases in the transition flow regime. Additionally, the results indicate that the axisymmetric micro-nozzle (with a circular cross-profile) outperforms the linear micro-nozzle (with a rectangular cross-profile) in terms of both performance and size when subject to the same conditions, making it the recommended choice for practical applications. We also find that plugs designed at the throat decrease performance, but increase stability under diverse background pressures. This study provides valuable insights for the design of high-efficiency micro-nozzles in applications such as nanosats and MEMS heat dissipation units.

Toward soft, stretchable and resilient high filled composite gels for potential application as thermal interface materials

Due to the different coefficients of thermal expansion between the heat generation and heat dissipation units, the applications of soft high filled composite gels as thermal interface materials require both high stretchability and excellent resilience. However, high stretchable composite gels reported far usually contain sacrificial species to dissipate energy, thus compromising their resilience. Herein, a soft (0.13 MPa), stretchable (172%), and resilient (>70%) composite gel with ultrahigh filler loading (90 wt%) is developed. The stretchability and resilience are realized by lengthening free polymer strands to form appropriate entanglements, in which the loose entanglements transfer the applied force into a large area and the stiff crosslinks prevent the entanglements from disentangling. In additional, the reversible elasticity of the filler network also dictates the resilience, so delaying its deconstruction allows for excellent resilience. The ultrahigh filler loading also endows the composite gel with high thermal conductivity (4.04 W·m−1·k−1), and the potential of the as-prepared composite gel for a TIM is discovered.

Numerical simulation and conceptual design of an MW-grade space heat pipe radiator

In recent years, nuclear reactor systems have been widely used in the space. The design of a radiator is of great importance as its heat dissipation performance directly determines the upper limit of the overall output power of the space nuclear propulsion system. In the present paper, a space radiator is divided into heat dissipation units, among which the heat pipes and fins are numerically modeled and analyzed. Kalium was selected as the working medium in the heat pipe, and the size of the heat pipe was designed based on the limitations, with the length of the evaporation section and the condensation section as 150 mm and 250 mm, respectively. VOF- Lee model was applied to simulate the phase-change heat transfer process inside the heat pipe, by setting the parameters of the hot-end temperature, the cold-end heat flux, etc. In addition, S2S model was used to examine the influences of thickness and width of the fin on the heat dissipation performance, so as to determine the optimal fin size. Finally, the heat pipes and fins were assembled into a whole radiative cooling system, with a mass-area ratio below 7 kg/m2 and a total heat dissipation power at 3.58 MW.

Thermo-Mechanical Design and Validation of Spaceborne High-Speed Digital Receiver Unit for Synthetic Aperture Radar Application

This paper presents the effectiveness of the thermo-mechanical design of a high-speed digital receiver unit (HSDRU) developed for spaceborne synthetic aperture radar applications. The main features of HSDRU’s thermo-mechanical design include the thermal management of high-heat dissipation units by adopting heat sinks with the additional function of structural stiffeners and securing the heat rejection path to the upper side of electronics that interfaces the foil radiator for the on-orbit passive thermal control of electronics exposed to deep space environments. The thermal design, which adopts a thermal gap pad, is closely related to the solder joint fatigue life in a launch vibration environment, owing to its initial compressive static load between the heat sink and heat dissipation units that enhances the heat transfer capability. The effectiveness of the design was validated via the qualification level of launch environment tests.

Modified strip model for indirect buckling restrained shear panel dampers

The indirect buckling restrained shear panel damper (IBRSPD) comprises stiffeners and energy dissipation units that are processed from a hot-rolled H-beam. Under shear loading, the web plates of the units induce a stable energy dissipation capacity to resist earthquakes, and the stiffeners can effectively limit the buckling of the web panels. Then, the partial tension field (PTF) is generated in the web plates owing to the indirect buckling restraint, which leads to the free boundary condition in the vertical edges. This mechanism has not been considered in previous models of the shear panel damper (SPD). In this study, a modified strip (MS) model is proposed to characterize the web plate behavior, and equations for the inclination angle of the PTF action are presented. According to the development degree of the PTF area, four stages are determined, and the components of the shear strength, namely, the shear buckling strength (SBS) and the PTF action, are calculated for each stage. Through monotonic analyses, a comparison between the finite element model and the MS model is conducted to verify the validation of the newly proposed model. In addition, the contributions of the SBS and PTF components are analyzed under cyclic loading while considering the loading history and the pinching effect. With respect to the energy dissipation capacity, the height of the IBRSPD is discussed in relation to the energy dissipation efficiency. Finally, the MS model is adopted in a seismic analysis to investigate the reduction of the seismic response.

Experimental investigation of modular buckling-restrained energy dissipaters with detachable features

In this study, a new modular energy dissipater (MED) consisting of an inner assembled core and outer restraining tube was developed. The inner core is fabricated by multiple identical energy dissipation units with threaded couplers in series. The outer tube is used to restrain the overall buckling of the inner assembled core. The MED is characterized by a standardized design, uniform process, modular assembly and units that are easy to replace after an earthquake. Seven energy dissipaters were tested to compare the hysteretic performance and failure mode of the MED with those of a nonmodular energy dissipater (NMED) under a low-cycle loading pattern. Test results showed that the hysteretic curves of the MED were plump in shape without pinching and did not exhibit a significant reduction in strength, and the axial deformation of MEDs is up to 4% before failure. The MED specimens perform an excellent low-cycle fatigue life. The mechanical connection in the assembled core of the MED resulted in significant slip deformation that could improve the low-cycle fatigue life of the MED compared with that of the NMED at the same strain amplitude. By adding the screws in the position of the threaded connection to form a thread-screw connection, the slip deformation could be considerably diminished. Compared with the NMED specimens, the initial axial stiffness of the MED specimens was lower; therefore, a computational formula for the initial elastic stiffness was proposed. All components, including the energy dissipation units, threaded couplers and end connection units, can be detached freely during the experiments, where the threaded couplers and connection units can be reused many times. The performance of the MED shows a minimum relationship with the reused energy dissipation units.

Super-tough and rapidly self-recoverable multi-bond network hydrogels facilitated by 2-ureido-4[1H]-pyrimidone dimers

Multi-bond network (MBN) hydrogels contain hierarchical dynamic bonds with different bond association energy as energy dissipation units, enabling super-tough mechanical properties. In this work, we copolymerize a protonated 2-ureido-4[1H]-pyrimidone (UPy)-contained monomer with acrylic acid in HCl solution. After removing excess HCl, UPy motifs are deprotonated and from dimers, thus generating an UPy-contained MBN hydrogel. The obtained MBN hydrogels (75 wt% water content) exhibit super-tough mechanical properties (0.39 MPa to 2.51 MPa tensile strength), with tremendous amount of energy (1.68 MJ/m3 to 11.1 MJ/m3) dissipated by the dissociation of UPy dimers. The introduction of ionic bonds can further improve the mechanical properties. Moreover, owing to their dynamic nature, both UPy dimers and ionic bonds can re-associate after being dissociated, resulting in excellent self-recovery ability (around 90% recovery efficiency within only 1 h). The excellent self-recovery ability mainly originates from the re-association of UPy dimers based on the high dimerization constant of UPy motifs

Hierarchical cross-linking for synergetic toughening in crustacean-mimetic nanocomposites.

The twisted plywood structure as found in crustacean shells possesses excellent mechanical properties with high stiffness and toughness. Synthetic mimics can be produced by evaporation-induced self-assembly of cellulose nanocrystals (CNCs) with polymer components into bulk films with a cholesteric liquid crystal structure. However, these are often excessively brittle and it has remained challenging to make materials combining high stiffness and toughness. Here, we describe self-assembling cholesteric CNC/polymer nanocomposites with a crustacean-mimetic structure and tunable photonic band gap, in which we engineer combinations of thermo-activated covalent and supramolecular hydrogen-bonded crosslinks to tailor the energy dissipation properties by precise molecular design. Toughening occurs upon increasing the polymer fractions in the nanocomposites, and, critically, combinations of both molecular bonding mechanisms lead to a considerable synergetic increase of stiffness and toughness - beyond the common rule of mixtures. Our concept following careful molecular design allows one to enter previously unreached areas of mechanical property charts for cholesteric CNC-based nanocomposites. The study shows that the subtle engineering of molecular energy dissipation units using sophisticated chemical approaches enables efficient enhancing of the properties of bioinspired CNC/polymer nanocomposites, and opens the design space for future molecular enhancement using tailor-made interactions.

A Multidirectional LSTM Model for Predicting the Stability of a Smart Grid

The grid denotes the electric grid which consists of communication lines, control stations, transformers, and distributors that aids in supplying power from the electrical plant to the consumers. Presently, the electric grid constitutes humongous power production units which generates millions of megawatts of power distributed across several demographic regions. There is a dire need to efficiently manage this power supplied to the various consumer domains such as industries, smart cities, household and organizations. In this regard, a smart grid with intelligent systems is being deployed to cater the dynamic power requirements. A smart grid system follows the Cyber-Physical Systems (CPS) model, in which Information Technology (IT) infrastructure is integrated with physical systems. In the scenario of the smart grid embedded with CPS, the Machine Learning (ML) module is the IT aspect and the power dissipation units are the physical entities. In this research, a novel Multidirectional Long Short-Term Memory (MLSTM) technique is being proposed to predict the stability of the smart grid network. The results obtained are evaluated against other popular Deep Learning approaches such as Gated Recurrent Units (GRU), traditional LSTM and Recurrent Neural Networks (RNN). The experimental results prove that the MLSTM approach outperforms the other ML approaches.

Broadband 120 MHz Impedance Quartz Crystal Microbalance (QCM) with Calibrated Resistance and Quantitative Dissipation for Biosensing Measurements at Higher Harmonic Frequencies.

We developed an impedance quartz crystal microbalance (QCM) approach with the ability to simultaneously record mass changes and calibrated energy dissipation with high sensitivity using an impedance analyzer. This impedance QCM measures frequency shifts and resistance changes of sensing quartz crystals very stable, accurately, and calibrated, thus yielding quantitative information on mass changes and dissipation. Resistance changes below 0.3 Ω were measured with corresponding dissipation values of 0.01 µU (micro dissipation units). The broadband impedance capabilities allow measurements between 20 Hz and 120 MHz including higher harmonic modes of up to 11th order for a 10 MHz fundamental resonance frequency quartz crystal. We demonstrate the adsorbed mass, calibrated resistance, and quantitative dissipation measurements on two biological systems including the high affinity based avidin-biotin interaction and nano-assemblies of polyelectrolyte layers. The binding affinity of a protein-antibody interaction was determined. The impedance QCM is a versatile and simple method for accurate and calibrated resistance and dissipation measurements with broadband measurement capabilities for higher harmonics measurements.

A new modular buckling restrained brace for seismic resistant buildings

This paper proposes an innovative BRB as a new energy dissipation device for earthquake resistant buildings. Its steel yielding core is modular, and this very design enables the yielding force and plastic deformation to be adjusted according to building requirements. Based on connecting several Seriated Modules, which are comprised of any constant number of Shear Basic Dissipation Units, deformation is proportional to the number of Seriated Modules and force to the number of Shear Basic Dissipation Units (on the Seriated Modules). Assembling the brace consists of sliding the greased yielding core into the restraining unit and coupling it with pins, thus providing easy inspection or replacement of the dissipation unit if required. Fully-scaled prototypes have been tested under reversal cyclic displacements and the hysteretic response has been proved stable and with a high cumulative ductility. The main parameters are the yielding force and the yielding displacement; which can be predicted with simple expressions. A methodology to design a restraining unit able to tackle of buckling by taking into account the initial sway deformation and the functional gap between the yielding core and the restraining unit is proposed. The hysteretic behavior has been simulated with conventional FEM software.

Monolayer graphene dispersion and radiative cooling for high power LED

Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation.

Seismic Behavior of Damage-Reduction Based, Energy Dissipation Composite Shear Walls

A new damage-reduction based composite shear wall was proposed. It combines with three different energy dissipation units, which are the CFST column, SP deep beam and RC strip. The CFST column is set to be exposed outside or concealed inside the concrete. CFST columns and SP deep beams constitutes the core structure. During loading, RC strips between columns work with the core structure so as to reduce the damage and consume the energy. Four specimens with different design parameters, including 2 shear walls with exposed CFST columns and 2 with concealed CFST columns, were tested under horizontal cyclic loading. The load-bearing capacity, stiffness, hysteretic property, ductility, and failure characteristic of specimens have been analyzed. Results show that the deformation of this wall is just between that of the slotted shear wall and the entire shear wall. The RC strips reduce the damage and the core structure presents ductile behavior during load. The new wall is designed based on damage-reduction and it shows good seismic energy dissipation mechanics. It can be applied to the design of shear wall in high-rise buildings.

Sensor and Numerical Simulator Evaluation for Porous Medium Desiccation and Rewetting at the Intermediate Laboratory Scale

Soil desiccation, in conjunction with surface infiltration control, is considered at the Hanford Site as a potential technology to limit the flux of technetium and other contaminants in the vadose zone to the groundwater. An intermediate‐scale experiment was conducted to test the response of a series of instruments to desiccation and subsequent rewetting of porous media. The instruments include thermistors, thermocouple psychrometers, dual‐probe heat pulse sensors, heat dissipation units, and humidity probes. The experiment was simulated with the multifluid flow simulator STOMP, using independently obtained hydraulic and thermal porous medium properties. All instrument types used for this experiment were able to indicate when the desiccation front passed a certain location. In most cases the changes were sharp, indicating rapid changes in moisture content, water potential, or humidity. However, a response to the changing conditions was recorded only when the drying front was very close to a sensor. Of the tested instruments, only the heat dissipation unit and humidity probes were able to detect rewetting. The numerical simulation results reasonably match the experimental data, indicating that the simulator captures the pertinent gas flow and transport processes related to desiccation and rewetting and may be useful in the design and analysis of field tests.

Flow characteristics in energy dissipation units of labyrinth path in the drip irrigation emitters with DPIV technology

The energy dissipation mechanism and anti-clogging properties of drip irrigation emitters are closely related to flow characteristics of the fluid in its flow paths, and flow field tests using modern flow visual technologies were carried out by a large number of designers. The Digital Particle ImageVelocimetry (DPIV) system was built for un-disturbed flow tests in the labyrinth path. In this article, the flow field was measured in the flow path section, the structural unit and the local region near sawtooth. Under the pressure level of 10 Kpa, 50 Kpa, 100 Kpa and 150 Kpa, the flows in the two labyrinth paths were in the turbulence state, with flow stagnation regions and whirlpool regions in the structure of the labyrinth path sections. The flow stagnation regions should be eliminated as much as possible. But the vortex should be fully developed, which could increase the self-cleaning capacity and the anti-clogging capacity of the emitter. With respect to the anti-clogging performance and the energy loss efficiency of the emitter, the M-type flow path is better than the K-type flow path.

Simulation of the seismic performance of the Bolu Viaduct subjected to near‐fault ground motions

AbstractThe seismic performance of the Bolu Viaduct in the Duzce, Turkey, earthquake of November 1999 was studied via a non‐linear, time‐history analysis of a multi‐degree of freedom model. The viaduct had a seismic isolation system consisting of yielding‐steel energy dissipation units and sliding pot bearings. The Duzce earthquake caused a surface rupture across the viaduct, which resulted in excessive superstructure movement and widespread failure of the seismic isolation system. The effect of the rupture was modeled by a static, differential ground displacement in the fault‐parallel direction across the rupture. The ground motions used in the analysis contain common near‐fault features including a directivity pulse in the fault‐normal direction and a fling step in the fault‐parallel direction. The analysis used a finite element package capable of modeling the mechanical behavior of the seismic isolation system and focused on the structural response of a 10‐span module of the viaduct. This analysis showed that the displacement of the superstructure relative to the piers exceeded the capacity of the bearings at an early stage of the earthquake, causing damage to the bearings as well as to the energy dissipation units. The analysis also indicated that shear keys, both longitudinal and transverse, played a critical role in preventing collapse of the deck spans. Published in 2004 by John Wiley & Sons, Ltd.