Active Structural Systems Research Articles

Topology optimization of multi-material active structures to reduce energy consumption and carbon footprint

A multi-material active structure is a mechanical system made of passive and active materials with the ability to alter its configuration, form, or properties in response to changes in the environment. Active structures have been investigated to design lightweight structures and structures with the ability to “smartly” alter their shapes and/or internal forces. Recently, the potential of active structures to reduce environmental impact, i.e., reduce energy consumption and greenhouse gas (GHG) emissions, has been investigated. It has been verified that, compared to passive structures, active structures can not only use less material but also consume less energy and cause less GHG emissions during their service life, and thus have a significant potential to be applied as environment-friendly mechanical structures. This study aims to develop a general topology optimization (TO) approach to design novel multi-material active structural systems to reduce environmental impact. The approach is based on the density-based TO scheme. Passive and active materials are considered in the TO process and are required to be optimally distributed according to the optimization objective and constraints. The energy consumption or GHG emissions caused by the structure during its service life are treated as the objective function to be minimized under multiple displacement requirements. Typical examples are carried out to verify the developed approach. Results show that the topology optimized active structures may not only achieve significant weight savings but also less energy consumption and GHG emissions compared to equivalent topology optimized passive structures, which indicates that the developed approach has the potential to be applied to design novel structural systems with lighter weight, larger span, and with less environmental impact compared to conventional passive structural systems.

한국춤의 심미구조에 내재된 역학적 사유규범

The purpose of the current study is to specify the nature of Korean dance by clarifying the dynamic contemplative norm inherent in the aesthetic structure of Korean dance. The traditional styles of Korean dance conveyed a universal aesthetic view and the cognitive systems developed through dynamics have solidified the aesthetic structure of Korean dance to define the awareness of aesthetic truth. The aesthetic structure of Korean dance can be discussed in terms of the spiritual, emotional, and active structural systems. The spiritual structure is identified as the ‘spirit of dance’ where the concept of Oneness of Heaven and Men in the Book of Changes underlies as the nature of Korean dance. The emotional structure is the orientation of body and mind. The mind reflects the abstract spirit and its emotion is expressed through the body to convey the contents of dance. The active structure embodies the natural meaning of mind through the circulating process of generation and extinction of breaths. The dynamic contemplative norm inherent in the aesthetic structure is threefold: first, the contemplative norm of ‘the law of heaven, earth, and men’ explains the law of universe and nature and specifies the natural principle of Korean dance as a ‘metaphysical law’ to conceptualize the property of space through the generation and change of universe and humankind. Second, the contemplative norm of ‘law of change’ is specified in terms of time and space in the phrase, ‘the law of one ying and one yang,’ and interprets the law of Yixue in terms of time and space. Third, the contemplative norm of ‘law of sun and moon’ is specified in terms of time in the phrase, ‘endlessly created universe’ and clarifies the property of time through yin and yang, the law of universe.

Surface hydrothermal activity controlled by the active structural system in the self-sealing geothermal field of Acoculco (Mexico)

The active volcanic caldera of Acoculco has been explored in the last few years to develop geothermal energy from non-conventional sources. This caldera located in eastern Mexico has been classified as a Hot Dry Rock geothermal system. Our results bring a new understanding to the interaction between two intra-caldera fault systems in terms of their permeability and degassing processes through self-potential, temperature, and CO2 flux surveys. We demonstrate the absence of hydrothermal fluid circulation with convective activity, and we provide new evidence for the origin of cold degassing. These outcomes may have important implications for future exploitation targets in the area.

GEOLOGICAL LINE SELECTION OF XIANSHUIHE STRUCTURAL ZONE OF SICHUAN-TIBET RAILWAY

The Kangding segment of the Sichuan-Tibet Railway passes through the Xianshuihe active structural system, where a series of significant engineering geological problems exist such as intensive earthquake and active faults, high-level slippage flow, unstable high and steep bank slopes, high geostress, rockburst and large deformation, high geo-temperature and high stress water inrush. This segment possesses the greatest seismic and geological risks. and it is to find proper reference. Based on the selecting process for ten years, we have chosen the feasible and safe plan of the Sandaoqiao station, Zheduoshan crop and Zheduoshan Mountain tunnel. In this study, through a systematic geological line selection in the Xianshuihe structural belt, we sum up the geological line selection should follow the order of regional stability line selection, engineering geological disasters over ground line selection, very difficult engineering geological problems in underground engineering geological line selection, integrated geological line selection, cross line selection etc. Based on the fundamental line selection, structure, lithology and groundwater should be considered. Giving priority to give way and then passing through are suggested in the deep and large fault. Considering the effects of lithology, defective engineering rock mass(soluble rock, alteration rock and structural soft rock) should be avoided and the hard engineering rock mass is preferred. Considering groundwater, karst groundwater area should shorten the length of horizontal circulating band, groundwater rich area should build line in side and high areas and discharge groundwater along slope, geothermal anomaly area should choose low temperature gallery. This achievement can provide a reference for the constructions of the Jinshajiang suture and Jiali structural belt of the Sichuan-Tibet railway and planed Yunnan-Tibet railway.

Smart Polymers for Advanced Applications: A Mechanical Perspective Review

Responsive materials, as well as active structural systems, are nowadays widely used to develop unprecedented smart devices, sensors or actuators; their functionalities come from the ability of responding to environmental stimuli with a detectable reaction. Depending on the responsive material under study, the triggering stimuli can have a different nature, ranging from physical (temperature, light, electric or magnetic field, mechanical stress, ...), chemical (pH, ligands, …), or biological (enzymes, …) type. Such a responsiveness can be obtained by properly designing the meso- or macroscopic arrangement of the constitutive elements, as occurs in metamaterials, or can be obtained by using responsive materials per se, whose responsiveness comes from the chemistry underneath their microstructure. In fact, when the responsiveness at the molecular level is properly organized, the nanoscale response can be collectively detected at the macroscale, leading to a responsive material. In the present paper, we review the huge world of responsive polymers, by outlining the main features, characteristics and responsive mechanisms of smart polymers and by providing a mechanical modeling perspective, both at the molecular as well as at the continuum scale level. We aim at providing a comprehensive overview of the main features and modeling aspects of the most diffused smart polymers. The quantitative mechanical description of active materials plays a key role in their development and use, enabling the design of advanced devices as well as to engineer the materials’ microstructure according to the desired functionality.

Direct Displacement Control of Deformed Double Layer Dome

Space structures such as double layer dome is light and active structural system that used for various structural application, for instance structural covers large areas such as exhibition halls, stadium and concert halls. They are aesthetically pleasing in appearance as well as the architectural requirement, in which tolerances of structural shape under changing service conditions are very significant, which high appearance accuracy is requested in some applications. Due to many reasons such as loading, these type of structures may suffer from a noticeable deflection, which leads to a significant potential undesired appearance of the shape. In this situation, the displacements may need to be reduced or eliminated. In this study, by applying the shape adjustment technique that its scheme is depend on the linear force method, shape restoration is performed to the double layer dome model in three different cases corresponding to the directions of loadings were considered. The improvement of controlling nodal displacement can be achieved through using a rather simple and direct method, due to calculating necessary length of actuators by applying a single formulation. It is found that if the number of provided actuators are satisfactory, controlling of all the displaced joints could be performed by a very small percentage of discrepancy, even if the controlled joints connection is not direct with the adjustable members. The technique of shape adjustment is very efficient for double layer dome model, and it can roughly eliminate the displacement of definite joints (Exterior joints only) by simply changing the length of certain bars by eo amount

Direct Displacement Control of Deformed Double Layer Dome

Space structures such as double layer dome is light and active structural system that used for various structural application, for instance structural covers large areas such as exhibition halls, stadium and concert halls. They are aesthetically pleasing in appearance as well as the architectural requirement, in which tolerances of structural shape under changing service conditions are very significant, which high appearance accuracy is requested in some applications. Due to many reasons such as loading, these type of structures may suffer from a noticeable deflection, which leads to a significant potential undesired appearance of the shape. In this situation, the displacements may need to be reduced or eliminated. In this study, by applying the shape adjustment technique that its scheme is depend on the linear force method, shape restoration is performed to the double layer dome model in three different cases corresponding to the directions of loadings were considered. The improvement of controlling nodal displacement can be achieved through using a rather simple and direct method, due to calculating necessary length of actuators by applying a single formulation. It is found that if the number of provided actuators are satisfactory, controlling of all the displaced joints could be performed by a very small percentage of discrepancy, even if the controlled joints connection is not direct with the adjustable members. The technique of shape adjustment is very efficient for double layer dome model, and it can roughly eliminate the displacement of definite joints (Exterior joints only) by simply changing the length of certain bars by eo amount

Neotectonics, active tectonics and earthquake geology： terminology, applications and advances

Neotectonics and active tectonics are sub-disciplines of tectonics that study the process of recent tectonic deformation and tectonic geomorphic evolution on the Earth. The time scale of neotectonics research is closely related to the geodynamics of a specific region; it typically concerns geological processes at time scales from Ma to ka, and emphasizes on the relationship between the past and present tectonic deformation. On the other hand, research in active tectonics pays greater attention to geological–geomorphological processes since 100˜150ka, and focuses on present and future tectonic deformation. Research on neotectonics and active tectonics for seismic hazard assessment is a significant aspect of earthquake geology work. This, along with other related researches, is the primary basis of earthquake forecasting and prediction, urban and rural earthquake prevention, disaster mitigation, and project planning and design for effective circumvention and mitigation of geological hazards caused by active faults. Recent advances in these fields have indicated that the fast development and application of Quaternary chronology, open access space observation, and geographic information system (GIS), have substantially increased the level and precision of quantitative research on neotectonic evolution, tectonic morphology, fault activity and palaeo-seismology. This has led to the promotion and growth of digitalization and sharing of active fault data, and has also improved the reliability and accuracy of seismic hazard assessment. However, in countries and areas with high density of active faults and complex tectonic systems, such as China, research on neotectonics and active tectonics for seismic hazard assessment needs to be even further strengthened. There is a need for fast and effective regional surveying of active faults by the use of remote sensing and Digital Elevation Models (DEM) imaging, so as to study active structural systems. Therefore, to consolidate the geological foundation for prevention and mitigation of seismogeological disasters. Besides, the relationship between fault activity and risk should be distinguished, and attention should be paid to areas having strong-earthquake risk in stable continental regions and having low-slip-rate faults.

Mechanics of materials with embedded unstable molecules

Active structural systems and materials, typically used to develop sensors or actuators, are those capable of responding to external stimuli with some physical detectable reactions. The triggering stimuli can be of various nature, ranging from temperature, pH, light, mechanical stress, etc. In this context, responsive materials have the capability to react at the molecular level, showing some changes in their microstructure that can be detected and measured at the meso- or macro-scale level. This ability can be obtained in polymers and polymer-like materials through the introduction in their network of switchable molecules, characterized by two geometrically distinct stable states, where the switch from one to the other can be seen as an instability phenomenon. In this research, we present a continuum mechanical model, developed starting from the micromechanics of the polymer network joined to molecules whose switching instability is induced by mechanical or chemical actions. The theoretical framework is presented by considering the general case of poly-disperse polymers and some final examples are given and discussed. The proposed model can be used as a tool for the development and design of smart responsive systems, applicable across a wide range of length scales.

VIBRATION CONTROL OF STRUCTURES USING MAGNETO-RHEOLOGICAL DAMPERS WITH H∞ METHOD

In this study, the vibration mitigation of the structures under the earthquake excitation using magneto-rheological (MR) damper is researched. For this purpose, one MR damper is installed to an eight story structure and the system performance is investigated. MR damper is installed between the second floor and the ground. The MR damper is a semi-active control device that can be controlled by only the voltage transmitted to the electromagnetic coils. Since the MR damper is a semi active device, damping force can be changed by applied voltage. Therefore, determination of the applied voltage is important for vibration reduction. A robust controller is designed for determination of the MR damper voltage. H∞ method and model reduction approach are used for robust control design and application. The performance of the proposed method is tested by numerical simulation on the semi active structural system with MR damper. The performance of the control algorithm and the effect of the MR damper arrangement is evaluated using earthquake (El-centro earthquake) data. The results are compared with situations in which MR damper is not connected and when the MR damper is situation of semi-active controlled. The evaluations are based on the displacement and acceleration responses. The simulation results showed that the arrangement of the MR damper connected between the second floor and the ground is effective in reducing the vibration amplitudes.

Influence of structural architecture on linear shape memory alloy actuator performance and morphing system layout optimisation

In this work, a design strategy is presented, addressed to adaptive structural systems, driven by shape memory alloy actuators. The peculiar behaviour of shape memory alloy materials, non-linear and fully dependent on three parameters (stress, strain and temperature), and the load path itself complicate the numerical simulation process. This is even more evident if those active elements are integrated within complex structures. Actuators generate forces. Integrated shape memory alloy–based structural actuator capability is strongly influenced by the hosting structure stiffness. It does in turn depend on the geometrical configuration. The structural architecture may be then said to modulate the performance of the aforementioned devices. The layout modifies in fact the structural resistance that opposes the action of a generic shape memory alloy actuator, even if the same topological point is referred to. This opposition affects the change of phase process (martensite ↔ austenite) regulating shape memory alloy peculiar phenomena and then impacts its performance. For simple, linear shape memory alloy actuators, the structure may be represented as an oriented spring where all the information of the parent structure is concentrated in its scalar stiffness property. This value is a function of the specific layout. A way to compute this equivalent structural stiffness comes directly by its definition: the ratio between the generated actuation force and the derived homologue structural displacement, that is, displacement occurring along the same force direction. Because such stiffness is what the shape memory alloy actuator feels, in this article it is referred as ‘perceived stiffness’. In this article, the structural layout effect on linear shape memory alloy actuator performance is initially evaluated for a simple spring. The approach is then extended to a complex active structural system, element of an aircraft wing morphing architecture. The referred device is capable of deforming wing regions while resisting the aerodynamic and the structural loads and recovering the original shape, once the actuation stops. Structural actuator geometry is optimised as a function of the attained structural displacement (figure of merit). The work is concluded with a discussion on the achieved results, namely, rotation, vertical displacement, internal stress (strain) levels and activation temperature.

River terrace development in response to folding above active wedge thrusts in Houli, Central Taiwan

Folding at the leading edge of the western Taiwan thrust belt is well preserved by a flight of fluvial terraces at Houli. Strain in this region is driven by slip on the north trending Changhua and Sanyi blind wedge thrusts and occurs at the boundary between the Miaoli and Taichung neotectonic domains located respectively to the north and south. In the past century, two large historical earthquakes occurred in these two domains and produced surface ruptures within or close to the study area, indicating Houli is not only tectonically active but also critical for understanding the interaction between the neighboring active systems. Although abundant river terraces and their deformation by active structures have long been well known in the area, a kinematical model for this region has not yet been proposed. We have therefore remapped the geomorphic features using the 40 m DEM and aerial photos to identify often subtle structural features in order to separate the effects of folding interference produced by different active structural systems. Besides the Tuntzuchiao fault (TTCF), which generated the 1935 earthquake, two other active regional scale structural systems have been reported in Houli area: the Tiechanshan (TCS) anticline and the Changhua fault (CHF). Our results demonstrate a number of tectonic scarps and warped surfaces in association with the CHF and its coupled back thrust, indicating that the CHF system is active. In contrast, the flight of fluvial terraces distributed in the middle of the study area cannot be related to the growth of the TCS anticline. Instead, terraces here record growth of another smaller and previously unknown anticline, Yuehmei (tentatively named in this study and shortened to YM in the text). Although it has developed parallel to the TCS anticline, relevant seismic profiles show the YM anticline as a local drag-fold attached to the southern limb of the TCS anticline and restricted in the Houli area. Based on the above observation, the TCS anticline can be interpreted as becoming less active where strain is instead transferred to the more rapidly uplifting YM anticline. This structural switch may be the result of interference between the newly developed southern Taichung system and the preexisting TCS anticline.

Compensation for Distributed Hysteresis Operators in Active Structural Systems

A class of integral, hysteretic control in uence operators is derived for the representation of structural systems exhibiting hysteresis due to active materials. The hysteretic control in uence operator is deŽ ned in terms of a probability distribution, or more generally a measure, that describes the concentration of a particular hysteresis kernel. SpeciŽ cally, two types of hysteresis kernels are studied in detail: the ideal relay kernel leading to a Preisach integral hysteresis operator and a generalized play kernel leading to a Krasnosel’skii–Pokrovskii operator. When combined with the thermal and structural dynamics equations, the governing equations are history-dependent integropartial differential equations, coupled in a cascade structure. Existence, uniqueness, and convergence of Galerkin approximation methods have been derived for the forward simulation and model identiŽ cation. The cascade structure of the coupled, nonlinear partial differential equations is advantageous in that model reference control and model reference adaptive control strategies can be derived for the systems under consideration. Numerical and experimental results that validate the theoretical developments are presented.

Analysis of piezoelastic structures with laminated piezoelectric triangle shell elements

In the recent development of active structural systems and microelectromechanical systems, piezoelectrics are widely used as sensors and actuators. Because of the limitations of theoretical and experimental models in design applications, finite element development and analysis are proposed and presented in this paper. A new laminated quadratic C° piezoelastic triangular shell finite element is developed using the layerwise constant shear angle theory. Element and system equations are also derived. The developed piezoelastic triangular shell element is used to model 1) a piezoelectric bimorph pointer and 2) a semicircular ring shell. Finite element (triangular shell finite element) solutions are compared closely with the theoretical, experimental, and finite element (thin solid finite element) results in the bimorph pointer case. Natural frequencies and distributed control effects of the ring shell with piezoelectric actuators of various length are also studied. Finite element analyses suggested that the inherent piezoelectric effect has little effect on natural frequencies of the ring shell. Vibration control effect increases as the actuator length increases, and it starts leveling off at the seven-patch (70%) actuator. Coupling and control spillover of lower natural modes are also observed.

Aeroservoelasticity

The flutter behabiour of an aircraft with power operated control surfaces integrated in a flight mechanical control system or in other active systems may be described by the classical flutter equation supplemented by actuator and control terms. The flutter response of such a fly-by-wire aircraft is expressed by means of a set of structural mode shapes of the aircraft and rigid control surface rotations. Since the fly-by-wire aircraft is an active structural system it must be modified such that the mode shapes correspond to a conservative structural system. In such an aeroelastic model the instabilities of controllers and actuators are not captured because their appropriate degrees of freedom are not contained in the equations. Therefore a transformation of the flutter equation into a state-space form is necessary, and equations for describing the controllers and actuators must be added. For such a state-space description of the flutter equation representation of the unsteady airloads different from that for the classical flutter equation is necessary. In this paper the ‘Padé approximation’ and the ‘modal synthesis method’ are used and the advantages and disadvantages are discussed by examples, also in comparison with the results of the supplemented classical flutter equation. The influence of nonlinearities such as dead zones and hysteresis, and the time delays caused by digital processing on the flutter results is discussed for a fly-by-wire aircraft with an additional active system.