Holographic evaluation of the displacement and material dynamics of active cast compliant array structures

Section I - Compliant Structures in Nature Chapter 1: Compliant structures and materials in animals Chapter 2: Compliance in plants Section II - Compliant Materials Chapter 3: Reinforced polyurethane flexible foams Chapter 4: Electroactive polymers as artificial muscles Section III - Compliant Mechanics Chapter 5: Mechanics of compliant structures Section IV - Compliant Structures in Engineering Chapter 6: Pressurized membranes in nature, technology and engineering Chapter 7: Rope and rope-like structures Chapter 8: Flexible-wing-based micro air vehicles Chapter 9: Compliant habitats Chapter 10: Gossamer spacecraft Section V - Compliant Structure Design Chapter 11: Design of compliant structures

Optimal rigid and porous material distributions for noise barrier by acoustic topology optimization

Cellular materials' two important properties—structure and mechanism—can be selectively used for materials design; in particular, they are used to determine the modulus and yield strain. The objective of this study is to gain a better understanding of these two properties and to explore the synthesis of compliant cellular materials (CCMs) with compliant porous structures (CPSs) generated from modified hexagonal honeycombs. An in-plane constitutive CCM model with CPSs of elliptical holes is constructed using the strain energy method, which uses the deformation of hinges around holes and the rotation of links. A finite element (FE) based simulation is conducted to validate the analytical model. The moduli and yield strains of the CCMs with an aluminum alloy are about 4.42 GPa and 0.57% in one direction and about 2.14 MPa and 20.9% in the other direction. CCMs have extremely high positive and negative Poisson's ratios (NPRs) (νxy* ∼ ±40) due to the large rotation of the link member in the transverse direction caused by an input displacement in the longitudinal direction. A parametric study of CCMs with varying flexure hinge geometries using different porous shapes shows that the hinge shape can control the yield strength and strain but does not affect Poisson's ratio which is mainly influenced by rotation of the link members. The synthesized CPSs can also be used to design a new CCM with a Poisson's ratio of zero using a puzzle-piece CPS assembly. This paper demonstrates that compliant mesostructures can be used for next generation materials design in tailoring mechanical properties such as moduli, strength, strain, and Poisson's ratios.

Free-Flooded Ring (FFR) transducer array for use in Sonar system can be driven with large amplitude in a wide frequency band due to its structural characteristics, in which two resonances of a ring mode (1st radial mode) and an inner cavity vibration mode occur in a low frequency band. Since its sound wave generation characteristics are not influenced by the water pressure, the FFR transducer array is widely used in the deep sea. So FFR has been recognized as a low-frequency active sound source and has received much attention ever since. In order to utilize the FFR transducer array for SONAR systems in military and industrial applications, its equivalent electric circuit model is necessary especially to design the matching circuit between the driving power amplifier and the FFR transducer array. Thus this paper proposes the equivalent electric circuit model of FFR transducer array by using measured values of parameter, and suggest the improved method of parameter identification. Finally it verifies the effectiveness of the proposed circuit model of FFR transducer array by experimental measurements.

Early emphasis was on low-frequency source arrays. Work in this field led to pioneering computer activities. Interaction impedances involved various “simple” baffle conditions in small or infinite arrays. Operational troubles in arrays led to velocity control concepts. Computerized mathematical models of longitudinal vibrators were developed during the 1960's following advances in dissipative anisotropic piezoelectric devices. The behavior of source amplifiers was included in the matrix representation of amplifier and transducer arrays with electrical and radiation interactions. Using circulant and Toeplitz symmetry, complicated sonar array system analyses were completed with less computer storage and execution time than less realistic methods. Modeling of array structure and baffles has improved by combined Helmholtz integral equation formulations (CHIEF). Finite-element techniques model systems such as source transducer arrays and self-noise in the towed receiving arrays. Lately, increased effort has been on passive-receive-array improvements. The issue of optimal array design is of different character for source and receiver systems due to ambient noise anisotropy. Transducer progress for long-range sonar systems has been more significant than that for commercial loudspeakers and high-frequency sonars.

The vision of a more electric aerospace drives the pursuit of novel actuation technologies, capable of replacing the conventional fueldraulic actuators while delivering large stroke, speed, and load, within compact and robust designs. Piezoelectric-based actuators emerge as strong candidates due to their high specific power, broad operational temperature range, and miniaturization capability. However, their adoption in aerospace remains challenging due to performance and spatial integration constraints with existing actuators. This thesis advances the stick-slip stepping actuator, identified as a particularly promising topology for its high-speed and control simplicity. A key research gap identified is the need for comprehensive dynamic modeling and a system-level, interdisciplinary approach to capture the complex interactions among the design and operational parameters, that is, electrical driving signals, frictional contact mechanics, inertia, and mechanical design. Firstly, a transient finite element model of a linear actuator configuration is developed to reveal the complete phenomenon of stick-slip motion. A parametric study examined the impact of driving signals, with results verified through experimental prototyping. Secondly, with these insights into the actuator’s motion modes, the interactions between frictional contact and the driving signal’s operating frequency are investigated. By tailoring contact dynamics using different material combinations, the actuator’s performance is enhanced without requiring additional structures. For instance, increasing the friction coefficient from 0.4 to 0.7 would improve the actuator’s load capacity by 42%, while maintaining comparable stepping displacements at frequencies above 100 Hz - particularly suitable for the intended high speed, load, and compact applications. However, limited stepping displacement at lower operating frequencies is observed due to the passive nature of the stick-slip cycle. Therefore, a novel concept of a morphable actuator is developed, which enables active control of the stick and slip stages, allowing complete disengagement of the end-effector from the bearing to significantly enhance motion, including that at low operating frequencies. A compact, single-unit rotary actuator is designed by integrating a macro-fibre composite piezoelectric element within the compliant structure, and a transient numerical model is developed to analyze the dynamic interactions between its mechanical structure and operating signals. Findings indicated that at 1 Hz, more than fivefold improvement in the bearing stepping angle could be achieved as compared to without its morphing ability. Furthermore, the actuator demonstrated a vertical load capacity exceeding 3 kg, which is more than ten times the mass of the bearing itself. In conclusion, these design strategies and contributions establish the foundation for more-electric actuator technologies in the future, opening avenues for their applications in domains such as aerospace, where performance, compactness, and durability are crucial.

Efforts to develop a procedurally robust method for automated classification of multibeam backscatter have taken a variety of approaches (e.g., image-based, textural, angular range analysis). For image-based classification, little research has focused on the roles of operational parameters of vessel and sonar system in affecting the final classification. Repeat multibeam surveys (2005 and 2006) conducted at the same area with different sounding densities were classified using QTC-Multiview. Comparison of class areas revealed 78% agreement between classifications derived from the two surveys. Cross-tabulation of ground truth video and class demonstrate 71% agreement in the low-density survey and 77% for the high-density. Differences between classifications are primarily attributed to variation in along track data density, errors in the compensation process, and/ or insufficient quality control of the input data. Natural change detection at the scales observed was determined not to be practically discernable from the errors associated with the classification process.

Chapter 5 - Device Application Examples

We present a design of an acoustic levitator consisting of three pairs of opposite transducer arrays. Three orthogonal standing waves create a large number of acoustic traps at which the particles are levitated in mid-air. By changing the phase difference of transducer arrays, three-dimensional manipulation of particles is successfully realized. Moreover, the relationship between the translation of particles and the phase difference is experimentally investigated, and the result is in agreement with the theoretical calculation. This design can expand the application of acoustic levitation in many fields, such as biomedicine, ultrasonic motor and new materials processing.

Thermionic hollow cathodes have been widely used in wide variety of areas such as spacecraft electric propulsion systems, material processing and lasers for more than half a century as efficient electron sources. Especially in electric propulsion systems, hollow cathodes are being used as electron sources for propellant ionization and ion beam neutralization. Moreover, it is also a promising candidate for utilization as a stand‐alone propulsion system in microsatellites or nanosatellites due to its small physical size, low power consumption and ease of operation. On the other hand, the small geometry of the typical orificed hollow cathodes makes the plasma diagnostics difficult which is why numerical studies become important for understanding the driving physical processes behind their operation, and the effects of the geometry and the operation parameters on cathode performance. In this paper, a global numerical model for the insert and orifice plasma of a hollow cathode is presented where volume averaged plasma parameters are considered for both regions. The results of this study show that the developed model can be used for designing and sizing orificed hollow cathodes as comparisons with the results of experimental and other numerical studies are in good agreement with the ones obtained from the developed model. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Capabilities and advantages of laser ablation processes utilizing ultrashort pulses have been demonstrated in various applications of scientific and industrial nature. Of particular interest are applications that require high geometrical accuracy, excellent surface integrity and thus tolerate only a negligible heat-affected zone in the processed area. In this context, this work presents a detailed study of the ablation characteristics of common ultrahard composite materials utilized in the cutting tool industry, namely polycrystalline diamond (PCD) and polycrystalline cubic boron nitride composite (PCBN). Due to the high hardness of these materials, conventional mechanical processing is time consuming and costly. Herein, laser ablation is an appealing solution, since no process forces and no wear have to be taken into consideration. However, an industrially viable process requires a detailed understanding of the ablation characteristics of each material. Therefore, the influence of various process parameters on material removal and processing quality at 10 ps pulse duration are investigated for several PCD and PCBN grades. The main focus of this study examines the effect of different laser energy input distributions, such as pulse frequency and burst pulses, on the processing conditions in deep cutting kerfs and the resulting processing speed. Based on these results, recommendations for efficient processing of such materials are derived.

Plant cell walls are complex systems that exhibit the characteristics of both rigid and soft material depending on their external perturbations. The three main polymeric components in a plant primary cell wall are cellulose fibrils, hemicellulose, and pectins. These components interact in a hierarchical fashion giving rise to mesoscale structural features such as cellulose bundles, lamella stacking, and so on. Although several studies have focused on understanding these unique structural features, a clear picture linking them to cell wall mechanics is still lacking. As a first step toward this goal, a phenomenological model of plant cell wall has been developed in this work by using available experimental data to investigate the underlying connections between mesoscale structural features and the motions of fibrils during deformation. In this model cellulose fibrils exhibit motions such as angular reorientations and kinking upon forced stretching. These motions are dependent on the orientation of fibrils with respect to the stretch direction, i.e., fibrils that are at an angle to the stretch direction exhibit predominant angular reorientations, while fibrils transverse to the stretch direction undergo kinking as a result of transverse compression. Varying the chain length of pectin had negligible effects on these motions. One of the main contributions from this work is the development of a simple model that can be easily fine-tuned to test other hypotheses and extended to include additional experimental knowledge about the structural aspects of cell walls in the future.

The objects of the study are polymeric composites synthesized by mixing chemically and structurally complementary natural (Agar-Agar [AA], Chitosan [CS]) and Synthetic (Poly-N-Vinylpyrrolidone [PVP]) macromolecules in the presence of low molecular weight substrates (Polyethylene Glycol [PEG-400], Glycerol [GL]) as plasticizer to regulate the surface properties and volume characteristics of hydro-gel materials with functionally specified operational parameters, such as high adhesive affinity to damaged tissues, biological compatibility with body and organ fluids, high esterase and antimicrobial activity

Service performance seems to be the ultimate test of successful synthesis, processing, characterization and testing of polymeric materials. Viscoelasticity and the time dependence of mechanical properties can be considered as a nuisance, but in fact they provide us with the capability of prediction of long-term performance in service on the basis of short-term tests. The material characteristics and their influence on long-term life prediction are evaluated using two concepts, the cooperative response of the material and the chain relaxation capability (CRC). We show quantitative predictions using the time-temperature correspondence, time-strain correspondence, frequency-temperature correspondence, stress-time correspondence and the slow crack propagation on the basis of these concepts. The predictions include the use of a generalized temperature shift factor aT formula. Our formula includes the W-L-F equation of 1955 as a special case and has a much larger range of applications. Our stress shift factor a [sgrave] equation provides a prediction tool for a phenomenon demonstrated experimentally already in 1948.

Effect of spray-dried powder granulometry on the porous microstructure of polished porcelain tile