Hybrid Substructure Research Articles

Fidelity Assessment of Real-Time Hybrid Substructure Testing: a Review and the Application of Artificial Neural Networks

Real-Time Hybrid Substructure (RTHS) testing is a commonly used method to investigate the dynamical influence of a component on a mechanical system. In RTHS, a part of the dynamical system is tested experimentally, while the remaining structure is simulated numerically in a co-simulation. There are several error sources in the RTHS loop that distort the test outcome. To investigate the reliability of the test, the fidelity of the test must be quantified. In many engineering applications, however, there is no reference solution available to which the test outcome can be validated against. This work reviews currently existing accuracy measures used in RTHS. Furthermore, using Artificial Neural Networks (ANN) to predict the fidelity of the RTHS test outcome when no reference solution is available is proposed. Appropriate input features for the network, such as dynamic properties of the system and existing error indicators, are discussed. ANN training was performed on a data set from a virtual RTHS (vRTHS) simulation of a dynamical system with contact. The training process was successful, meaning that the correlation between the ANN prediction and the true fidelity value was > 99 %. Then, the network was applied to data of experimental RTHS tests of the same dynamical system and achieved a correlation of 98 %, which proves that the relation found by the ANN captured the relation between the chosen input features and the error measure. The application of the trained ANN to data from a linear vRTHS test revealed that further improvement of the network and the choice of input features is necessary. This work suggests that ANNs could be a meaningful tool to predict the fidelity of the RTHS test outcome in the absence of a reference solution, especially if more data from different RTHS tests were aggregated to train them.

Dynamical stability analysis of MDOF real-time hybrid system

Abstract Real-time hybrid simulation is an advanced testing methodology to evaluate structural responses under realistic operating conditions. Typically, the real-time hybrid system uses actuation and control system to apply load and motion boundary conditions on the experimental substructure. The inherent system dynamics present phase lags, in addition to the communication delays, that both cause negative damping in the real-time hybrid system. In this study, the dynamic equation of motion is derived for a generalized multiple-degree-of-freedom hybrid system. The negative damping effect is quantified, which depends not only on the actuator motion control performance, but also more importantly on the partition between the numerical and experimental substructures (i.e. how the stiffness and mass are assumed in both substructures). It is demonstrated the worst-case hybrid substructure partition may have very narrow stability margin in its tolerance of any system delay. The proposed equation of motion gains system level understanding of any arbitrary hybrid substructure partition; thus allow both frequency domain system analysis and time domain evaluation. The benchmark problem is studied to validate the proposed equation of motion compared with the virtual testing method, both approaches show excellent correlation. These pre-testing assessments could establish quantitative predictive measures about the system stability limit and performance criteria. Thus they are very important in the early design stage of a feasible real-time hybrid implementation, help reduce the risks of unintended physical testing responses.

Efficient solution of the multiple seismic pounding problem using hierarchical substructure techniques

Structural pounding is one of the major reasons for severe structural damage or even collapse. Thus, detailed simulations, including dynamic contact formulations, are often required in order to obtain reliable response information of structures. This leads inevitably to computationally expensive analysis. Therefore, in this paper, an effective hierarchical substructure method, adapted to structural pounding problems, is introduced. Based on that, a hybrid substructure method is presented. Both strategies are presented on an academic multiple pounding example, applying both a sinusoidal and a real earthquake excitation. It is shown that both strategies enable accurate low-order representations of the complex full dynamic contact problem. Thereafter, the new approaches are compared with the classical modal truncation strategy and an improved controlled modal truncation strategy. It is shown that an extensive improvement of the approximation of the full response can be achieved applying the new hierarchical substructure and the new hybrid substructure approach.

Silver-cotton nanocomposites: Nano-design of microfibrillar structure causes morphological changes and increased tenacity

The interactions of nanoparticles with polymer hosts have important implications for directing the macroscopic properties of composite fibers, yet little is known about such interactions with hierarchically ordered natural polymers due to the difficulty of achieving uniform dispersion of nanoparticles within semi-crystalline natural fiber. In this study we have homogeneously dispersed silver nanoparticles throughout an entire volume of cotton fiber. The resulting electrostatic interaction and distinct supramolecular structure of the cotton fiber provided a favorable environment for the controlled formation of nanoparticles (12 ± 3 nm in diameter). With a high surface-to-volume ratio, the extensive interfacial contacts of the nanoparticles efficiently “glued” the structural elements of microfibrils together, producing a unique inorganic-organic hybrid substructure that reinforced the multilayered architecture of the cotton fiber.

Safety Evaluation of a Hybrid Substructure for Offshore Wind Turbine

Towers and rotor-nacelles are being enlarged to respond to the need for higher gross generation of the wind turbines. However, the accompanying enlargement of the substructure supporting these larger offshore wind turbines makes it strongly influenced by the effect of wave forces. In the present study, the hybrid substructure is suggested to reduce the wave forces by composing a multicylinder having different radii near free surface and a gravity substructure at the bottom of the multicylinder. In addition, the reaction forces acting on the substructure due to the very large dead load of the offshore wind turbine require very firm foundations. This implies that the dynamic pile-soil interaction has to be fully considered. Therefore, ENSOFT Group V7.0 is used to calculate the stiffness matrices on the pile-soil interaction conditions. These matrices are then used together with the loads at TP (Transition Piece) obtained from GH-Bladed for the structural analysis of the hybrid substructure by ANSYS ASAS. The structural strength and deformation are evaluated to derive an ultimate structural safety of the hybrid substructure for various soil conditions and show that the first few natural frequencies of the substructure are heavily influenced by the wind turbine. Therefore, modal analysis is carried out through GH-Bladed to examine the resonance between the wind turbine and the hybrid substructure.

Numerical analysis of a hybrid substructure for offshore wind turbines

For the reliable design of substructure supporting offshore wind turbines it is very important to reduce the effects of wave forces. Since the substructure is strongly influenced by the effects of wave forces as the size of substructure increases. In the present study, the hybrid substructure with multi-cylinder is newly suggested to reduce the effects of wave forces. Using diffraction theory the scattering waves in a fluid region are expressed by an Eigenfunction expansion method with three dimensional potential theory to calculate the wave force acting on the hybrid substructure. The wave force and wave run-up acting on the hybrid substructure is presented to examine the water wave interaction according to the variation of cylindrical size and the distance among cylinders. It is found that the suggested hybrid substructure with multi-cylinder is very useful to reduce the effects of wave forces acting on the substructure for offshore wind turbines.

Cyclic plastic deformation of overbend pipe during deepwater S-lay operation

In deepwater S-lay operations, the combined influences of stinger curvature, axial tension and roller support force can induce very large plastic deformation in the pipe. Dynamic loads from vessel motion and pipe sliding down the stinger lead the cyclic plastic deformation. This paper investigates the cyclic plastic stress history of the overbend pipe subjected to the dynamic pipelaying loading. The dynamic roller support forces are obtained through an innovative large scale hybrid substructure experiment constructed to simulate the pipe-stinger impact behavior. The measured roller forces are used to verify a 3D finite element analysis results developed with ABAQUS/Standard to observe the dynamic pipe stress history. The results confirm that the roller support can induce stress concentration in the pipe and the combined dynamic pipelaying loadings can cause extensive cyclic plastic deformation.

Phosphomolybdate Clusters as Molecular Building Blocks in the Design of One‐, Two‐ and Three‐Dimensional Organic—Inorganic Hybrid Materials

AbstractFor Abstract see ChemInform Abstract in Full Text.

Phosphomolybdate clusters as molecular building blocks in the design of one-, two- and three-dimensional organic–inorganic hybrid materials

An attractive approach to the design of inorganic solids exploits the tethering of inorganic clusters through organic spacers to produce hybrid materials with composite properties. We have recently described a modified strategy in which polyoxometalate clusters are linked through organic subunits to give an anionic hybrid substructure which may be further modified through the introduction of secondary metal–ligand complex (SMLC) cations, serving as a third component building block. In this application, the molybdophosphonate cluster {Mo 5O 15(O 3PR) 2} 4− serves as a secondary building unit (SBU) with alkyl (CH 2) n or aromatic –(C 6H 4) n – tethers providing one-dimensional structural expansion. A binucleating ligand such as tetrapyridylpyrazine (tpyprz) is used to bridge secondary metal sites into a binuclear {Cu 2(tpyprz)} 4+ SBU which may link phosphomolybdate clusters into two- or three-dimensional structures. The influence of a variety of structural determinants is discussed, including the tether length of the diphosphonate ligand, the coordination preferences of the secondary metal, expansion of the ligand component of the SMLC, and substitution of As for P in the oxide SBU.

Substructure search procedures for macromolecular structures.

This paper accompanies a lecture given at the 2003 CCP4 Study Weekend on experimental phasing. The first part is an overview of the fundamentals of Patterson methods and direct methods with the audience of the CCP4 Study Weekend in mind. In the second part, a new hybrid substructure search is outlined.

Horizontal Underbalanced Drilling of Gas Wells with Coiled Tubing

Abstract Coiled tubing drilling technology is gaining popularity and momentum as a significant and reliable method of drilling horizontal underbalanced wells. It is quickly moving into new frontiers. To this point, most efforts in the Western Canadian Basin have been focused towards sweet oil reservoirs in the 900–1300 m true vertical depth (TVD) range, however there is an ever-increasing interest in deeper and gas-producing formations. Fig. 1 shows a composite vertical section of the horizontal or directional under-balanced wells drilled with coiled tubing in Canada, and also highlights the aforementioned trend towards oil over gas. Significant design challenges on both conventional and coiled tubing drilling operations are imposed when attempting to drill these formations underbalanced. Coiled tubing is an ideal technology for underbalanced drilling due to its absence of drillstring connections resulting in continuous underbalanced capabilities. This also makes it suitable for sour well drilling and live well intervention without the risk of surface releases of reservoir gas. Through the use of pressure deployment procedures it is possible to complete the drilling operation without need to kill the well, thereby maintaining under-balanced conditions right through to the production phase. The use of coiled tubing also provides a means for continuous wireline communication with downhole steering, logging and pressure recording devices. Coiled tubing drilling rigs currently exist in several different forms and setups, but generally consist of a drilling coil, injector to feed the tubing into or out of the well, (blowout prevention) (BOP) system for well control and return fluid path, and a control cab and power unit. The coiled tubing drilling equipment used to drill the case studies presented later in this paper consisted of either 60.3 or 73.0 mm coiled tubing and injector with a hydraulic power unit with control cabin and accumulator. A coiled tubing hybrid mast unit and substructure complete with V-door and catwalk was used. Pumping equipment included a fluid pumper capable of liquid rates of 0.10–1.5 m3/min, nitrogen pumper capable of 10–120 m3/min, and a nitrogen bulk storage unit of 50,000 m3 capacity. When drilling sour gas formations, a chemical injection pump for corrosion inhibition is typically used.

Free-interface methods of substructure coupling for dynamic analysis

Benfield, et al. (1972) showed that among fixed-interface, free-interface, and hybrid substructure coupling methods, the fixed-interface methods as the most accurate and the free-interface methods are the least accurate. In the present note, a substructure coupling method is proposed which employs free-interface substructure modes supplemented by 'reduced flexibility.' Substructure coupling based on the improved substructure model is discussed, and a numerical comparison with Hou's free-interface method is given. To simplify representation of the method proposed, the substructure equations are developed first for constrained substructures, and then the equations representing substructures with rigid-body modes are given. Finally, the equations for coupling of substructures are derived. Example calculations are included.