Semirigid Model Research Articles

Comprehensive Study of Equilibrium Structure of Trans-Azobenzene: Gas Electron Diffraction and Quantum Chemical Calculations

The geometrical re parameters of trans-azobenzene (E-AB) free molecule were refined by gas electron diffraction (GED) method using available experimental data obtained previously by S. Konaka and coworkers. Structural analysis was carried out by various techniques. First of all, these included the widely used molecular orbital constrained gas electron diffraction method and regularization method. The results of the refinements using different models were also compared—a semirigid model, three variants of one-dimensional dynamic models, and a two-dimensional pseudoconformer model. Several descriptions have been used due to the fact that E-AB has a shallow potential energy surface along the rotation coordinates of phenyl groups. Despite this, it turned out that the semirigid model is suitable for use for E-AB and allows good agreement with experimental data to be achieved. According to the results of GED structural analysis, coupled with the results of DLPNO-CCSD(T0) calculations, E-AB has a planar structure. Based only on GED data, it is impossible to unambiguously determine the rotational angle of the phenyl group due to the facts that (i) with rotation over a wide range of angles, the bonded distances in the molecule change insignificantly and (ii) potential function in a structural analysis within a dynamic model is not determined with the necessary accuracy. This work also examines the sensitivity of the GED method to structural changes caused by trans-cis isomerization. The paper also analyzes the applicability of different variants of density functional theory (DFT) calculations in GED structural analysis using E-AB as an example. There are not enough similar methodological works in the literature. This experimental and methodological information is especially important and relevant for planning and implementing GED experiments and corresponding processing of the results for azobenzene derivatives, in which the conformer and isomeric diversity are even more complicated due to the presence of different substituents.

Assessing injury risks of reclined occupants in a frontal crash preceded by braking with varied seatbelt designs using the SAFER Human Body Model

Objective This study investigated the effects of different seatbelt geometries and load-limiting levels on the kinematics and injury risks of a reclined occupant during a whole-sequence frontal crash scenario, using simulations with the Active SAFER Human Body Model (Active SHBM). Methods The Active SHBM was positioned in a reclined position (50°) on a semi-rigid seat model. A whole-sequence frontal crash scenario, an 11 m/s2 Automated Emergency Braking (AEB) phase followed by a frontal crash at 50 km/h, was simulated. The seatbelt geometry was varied using either a B-pillar-integrated (BPI) or Belt-in-seat (BIS) design. The shoulder belt load-limiting level of the BPI seatbelt was also varied to achieve either similar shoulder belt forces (BPI_Lower_LL) or comparable upper body displacements (BPI_Higher_LL) to the BIS seatbelt. Kinematics of different body regions and seatbelt forces were compared. The risks of sustaining a mild traumatic brain injury (mTBI), two or more fractured ribs (NFR2+), and lumbar spine vertebral fractures were also compared. Results During the pre-crash phase, head, first thoracic vertebra, and first lumbar vertebra displacements were greater with the BPI seatbelt than with the BIS, mainly due to the lack of initial contact between the torso and the seatbelt. Pelvis pre-crash displacements, however, remained consistent across seatbelt types. In the in-crash phase, variations in shoulder belt forces were directly influenced by the different load-limiting levels of the shoulder belt. The mTBI (around 20%) and NFR2+ (around 70–100%) risks were amplified with BPI seatbelts, especially at higher load-limiting force. However, the BPI design demonstrated reduced lumbar spine fracture risks (from 30% to 1%). Conclusions The BIS seatbelt appears promising, as seen with the reduced mTBI and NFR2+ risks, for ensuring the protection of reclined occupants in frontal crashes. However, additional solutions, such as lap belt load limiting, should be considered to reduce lumbar spine loading.

Equilibrium structures of selenium compounds: The torsionally flexible molecule of selenophenol.

The equilibrium structure of selenophenol has been investigated using rotational spectroscopy and high-level quantum mechanical calculations, offering electronic and structural insight into the scarcely studied selenium compounds. The jet-cooled broadband microwave spectrum was measured in the 2-8GHz cm-wave region using broadband (chirped-pulse) fast-passage techniques. Additional measurements up to 18GHz used narrow-band impulse excitation. Spectral signatures were obtained for six isotopic species of selenium (80Se, 78Se, 76Se, 82Se, 77Se, and 74Se), together with different monosubstituted 13C species. The (unsplit) rotational transitions associated with the non-inverting μa-dipole selection rules could be partially reproduced with a semirigid rotor model. However, the internal rotation barrier of the selenol group splits the vibrational ground state into two subtorsional levels, doubling the dipole-inverting μb transitions. The simulation of the double-minimum internal rotation gives a very low barrier height (B3PW91: 42cm-1), much smaller than for thiophenol (277cm-1). A monodimensional Hamiltonian then predicts a huge vibrational separation of 72.2GHz, justifying the non-observation of μb transitions in our frequency range. The experimental rotational parameters were compared with different MP2 and density functional theory calculations. The equilibrium structure was determined using several high-level abinitio calculations. A final Born-Oppenheimer (reBO) structure was obtained at the coupled-cluster CCSD(T)_ae/cc-wCVTZ level of theory, including small corrections for the wCVTZ → wCVQZ basis set enlargement calculated at the MP2 level. The mass-dependent method with predicates was used to produce an alternative rm(2) structure. The comparison between the two methods confirms the high accuracy of the reBO structure and offers information on other chalcogen-containing molecules.

The Microwave Rotational Electric Resonance (RER) Spectrum of Benzothiazole.

The microwave spectra of benzothiazole were measured in the frequency range 2-26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer. Hyperfine splittings arising from the quadrupole coupling of the 14N nucleus were fully resolved and analyzed simultaneously with the rotational frequencies. In total, 194 and 92 hyperfine components of the main species and the 34S isotopologue, respectively, were measured and fitted to measurement accuracy using a semi-rigid rotor model supplemented by a Hamiltonian accounting for the 14N nuclear quadrupole coupling effect. Highly accurate rotational constants, centrifugal distortion constants, and 14N nuclear quadrupole coupling constants were deduced. A large number of method and basis set combinations were used to optimize the molecular geometry of benzothiazole, and the calculated rotational constants were compared with the experimentally determined constants in the course of a benchmarking effort. The similar value of the χcc quadrupole coupling constant when compared to other thiazole derivatives indicates only very small changes of the electronic environment at the nitrogen nucleus in these compounds. The small negative inertial defect of -0.056 uÅ2 hints that low-frequency out-of-plane vibrations are present in benzothiazole, similar to the observation for some other planar aromatic molecules.

NUMERICAL INVESTIGATIONS ON THE DYNAMIC BEHAVIOUR OF A 2-DOF AIRFOIL WITH APPLICATION IN ENERGY HARVESTING SYSTEM

This article presents the basic airfoil model with two degrees of freedom - the semi-rigid model, where its forced vibrations were considered, and the exciting force is the aerodynamic force, including its periodic changes, that is, gusts. Since the phenomenological model under study has a coupled form, its versions after decoupling are presented, which has an impact on the results of the final research. The airfoil model presented in this way was shown from the application side in the system of a simple energy harvester based on a deformable beam with piezoelectric elements. The result of the simulation tests is a preliminary analysis of the possibility of using the airfoil as a vibration generator for the energy harvesting system. Along with the application of the mechanical part, a numerical simulation of the electrical part was also implemented, related to the transformation of the voltage generated by piezoelectric elements into a constant voltage signal with a connected receiver with power consumption similar to the Atmega microcontroller with battery charging.

An innovative type of module-to-core wall connections for high-rise steel modular buildings

High-rise steel modular buildings are normally designed and constructed using a structural system that consists of cast-in-situ concrete for the stability core and steel-framed volumetric modules for residential areas. In such systems, various connections, such as the module-to-core wall (M2C) connection, play a critical role in the lateral loading transfer and structural response. However, there is a lack of systematic understanding of the mechanical behaviours of M2C connections in high-rise buildings under dominant lateral effects. This study aims to develop an innovative fully bolted type of M2C connection to address lateral loads, such as the strong wind effects of high-rise buildings. This study was conducted by combining a comprehensive literature review of connection designs of high-rise steel modular buildings and a case study using a 31-storey student hostel building in Hong Kong. Under monotonic sliding and cyclic loading, the developed type of M2C connection was found to have good mechanical properties. The resistance of the developed connection was found to be governed by the bending capacity of the steel beams of the modules under cyclic loading, whereas the failure of the developed connection resulted from the shear failure of the anchor rods under monotonic sliding. Four design principles were proposed for the developed connection type to improve its capacity and ductility. The findings should provide a theoretical reference and practical guidance to design M2C connections in high-rise steel modular buildings. • High-rise steel modular buildings present mixed-type deformation under lateral loads. • Semi-rigid conceptual model was proposed for module-to-core-wall connections based on deformation and stiffness property. • An innovative fully bolted module-to-core-wall connection was developed with construction efficiency. • The developed module-to-core-wall connection type was examined with good mechanical properties. • Four design principles were proposed for module-to-core-wall connections in steel modular buildings.

Molecular Dynamics Study of Structural and Transport Properties of Silver Iodide Using Effective Charges.

The superionic conductor, solid state, and body-centered cubic structure, silver iodide at room temperature, has been studied via molecular dynamics simulations. The calculated results using pairwise Coulomb-Buckingham potential, zero pressure on the sample, a semi-rigid model system of 1000 Ag and 1000 I ions, () as a statistical ensemble, and an effective charge of for the pairs Ag-Ag and I-I, were found to be consistent with experimental data and one study using , different potential, and simulation software. For the pair Ag-I, there is a discrepancy due to the high silver ion diffusion. The calculated value of the diffusion constant of the silver ion is greater than iodide ion. The dynamic transport properties (mean square displacement, velocity autocorrelation function) results indicated typical behavior reported by other authors, using different potentials in their DM simulations for iodine and silver ions.

Form finding of assembled lattice structure considering the effect of joint stiffness

Joint stiffness can have a significant effect on the stability of single-layer lattice structure. However, it is yet unclear what is the degree of influence of joint stiffness on the form finding of assembled lattice structures. This paper presents a form finding method that suits assembled free-form single-layer lattice structures while the effect of joint stiffness on the form finding of the structure is investigated. Based on the experimental results of Ring-Sleeve joint, spring elements are initially used to simulate the joint stiffness and then finite element models of the assembled single-layer lattice structures with semi-rigid joints are established. The effect of joint stiffness on the structural form finding is studied by changing the spring stiffness. Thereafter, the optimal shapes of the assembled lattice structures with different joint stiffness and improved buckling load capacity are obtained. Finally, the mechanical properties of the resulted structures with different joint stiffness are extensively compared. The results show that different joint stiffness generate different structural shapes, and the greater joint stiffness results in higher structural height. Furthermore, both the structural buckling load capacity and the imperfection sensitivity increase with the increase of joint stiffness. Overall, the buckling load capacity of the semi-rigid model is lower than that of the replaced model that obtained based on the rigid structure.

A BP Neural Network Method for Grade Classification of Loose Damage in Semirigid Pavement Bases

This study aims to address the problem that loose damage of the pavement base course cannot currently be quantitatively identified, and thus the classification and recognition of the extent of looseness mainly rely on empirical judgments. Based on the finite‐difference time‐domain (FDTD) method, a backpropagation (BP) neural network identification method for loose damage of a semirigid base is presented. The FDTD method is used to simulate a semirigid base road model numerically with different degrees of looseness, and the eigenvalue parameters for recognition of the presence and extent of the looseness of the base layer are obtained. Then, a BP neural network identification method is used to classify and identify the loose damage of the base course. The results show that the classification and recognition of simulated electromagnetic waves have an accuracy of over 90%; the classification and recognition of radar data from an actual project have a recognition accuracy of over 80%. The good agreement between the classification and recognition results for the simulated data and measured data verifies the feasibility of the classification and recognition method, which can provide a new method for the use of ground‐penetrating radar to detect loose damage and the extent of looseness in the base.

Review on Aluminum and Steel Semi-rigid Connections Behavior Design Model

Several research reports agree on the influence of joint rotational behavior on the stability of space frames. One must therefore consider it in space structures study. Joint rotational behavior is generally considered in space structures study by means of its moment-rotation behavior curve. Models such as analytical, empirical, experimental, informational, mechanical and numerical mostly are used to determine joint mechanical behavior. This review paper presents an overview of available methods for the prediction of semi rigid connections behavior of under both static and dynamic loads. Advantages, disadvantages, and principal characteristics of each model stretched out. The modeling of joint behavior in studying space structures is associated with a mathematical representation model of the joint moment-rotation curve. Several models, linear, bilinear, multilinear and nonlinear representations are developed through the years to picture accurately the joints moment rotation behavior. The most precise representation applies continuous nonlinear functions, even though the multilinear representation is generally used for mechanical models. Using test data on aluminum and steel bolted connections conducted at Harbin Institute of Technology a simple stable quartic polynomial model is proposed to represent the behavior of the connections. In addition, Three others models are also proposed, including an Odd power Polynomial Model as proposed by Frye & Morris Model, a three parameter Power Model in accordance to the Kishi & Chen Model, and a four-parameter exponential model in line with the Yee & Melchers Model. These three models are compared with the simple quartic polynomial model proposed in this paper. As a result, the proposed connection design model, independent of test data, can be used directly by designers to assess semi-rigid, bolted connection behavior in Space Structures. The present work will give support to engineers for easy and accurate choice of the joint behavior prediction model and portrait correctly the behavior of the joints for best use in semi-rigid space structures construction.

Strain energy release rate and mode partitioning of moment-loaded elastically coupled laminated beams with hygrothermal stresses

New closed-form, analytical solutions are derived for the strain energy release rate (SERR) and mode partitioning of uneven bending moments-loaded tests on layered beams with bending-extension coupling and residual hygrothermal stresses. The analytical modeling utilizes Timoshenko beam kinematics, a semi-rigid interface model, and the global method to perform mode partitioning. The proposed solutions are validated via the finite element method in two typical examples of metal-composite joints. In addition, experiments using the double cantilever beam with uneven bending moments test setup are performed in a titanium-carbon fiber reinforced plastic adhesive joint, and data reduction is performed utilizing the new analytical solutions. We demonstrate that the residual thermal stresses effect on the SERR and mode mixity of the metal/composite interfaces can be non-negligible and, thus, should be considered in the design and analysis of such structures. The proposed formulas serve as a data reduction scheme for the fracture toughness and mode mixity determination in the general case of layered beams with bending-extension coupling and hygrothermal stresses, when utilizing uneven bending moments for the characterization tests.

Comparisons of finite element models used to predict bending strength of mortise-and-tenon joints

This study aimed to obtain a better method for establishing a finite element model of mortise-and-tenon (M-T) joints. Three types of M-T joint finite element models, which included a whole rigid model, a tie rigid model, and a semi-rigid model, were established and compared with experimental results by predicting the bending moment capacity (BMC) of M-T joints based on the finite element method (FEM). The results showed that the semi-rigid model performed much better than the tie rigid model, followed by the whole rigid model. For the semi-rigid model, the ratios of FEM ranged from 0.85 to 1.09. For the whole rigid model and tie rigid model, the BMC of the M-T joint was overestimated. In addition, the results showed that tenon size remarkably affected the BMC and stiffness of the M-T joint, and tenon width had a greater effect on the BMC of the M-T joint than the tenon length.

The heavy atom substitution and semi-experimental equilibrium structures of 2-ethylfuran obtained by microwave spectroscopy

The substitution rs and semi-experimental equilibrium reSE structures of the two conformers of 2-ethylfuran were obtained using a combination of microwave spectroscopy and quantum chemistry. The microwave spectrum was recorded using a molecular jet Fourier-transform spectrometer operating in the frequency range of 2.0 GHz–26.5 GHz. The spectra of all 13C and 18O isotopologues of both conformers could be measured in their natural abundances and the experimental gas-phase heavy atom structures were determined. All spectra were fitted using a semi-rigid rotor model including centrifugal distortion correction. The molecular geometries were compared with those of related molecules within the frame of the current literature. This work indicated that in some cases, the time required for recording survey scans of a Fourier-transform resonator setup can be reduced significantly with supports from adequate quantum chemical methods and spectral analysis skill.

Study on the moment-rotation behavior of eccentric rectangular hollow section cross-type connections under out-of-plane bending moment and chord stress

This paper studies the moment-rotation behavior of unstiffened eccentric rectangular hollow section (ERHS) cross-type connections under out-of-plane bending moment (OPBM) and chord stress. A finite element (FE) model is established and calibrated by experimental data. A parametric study on the out-of-plane moment-rotation behavior of the ERHS connections is conducted. Based on the results, a mathematical model (essentially a semi-rigid model) considering strength degradation and chord stress is established to describe the moment-rotation behavior of the ERHS connections with a brace-to-chord depth ratio less than 0.95. The yield line and three-beam models are used to formulate the two key parameters of the semi-rigid model, the intercept moment and the flexural initial stiffness. The established semi-rigid model is verified via numerical and experimental results. It is found that the failure mode of the ERHS connection is chord wall plasticization, and the numerical model can well simulate the failure mode and Mo-ψo curves of the specimen. Moreover, it is shown that the rigid joint assumption is applicable to the ERHS connection with a brace-to-chord depth ratio equal to 1.0 and a chord half depth-to-thickness ratio less than 15. The presented research can help advance the understanding of the behavior of ERHS connections under OPBM and the proposed equations will facilitate future applications.

Analysis on the Stability of double-fastener type Tubular Scaffold

The fastener type scaffold has the advantages of dismounting convenience, wide universality and good integral rigidity, which can bring convenience for construction. In this paper, the finite element software ANSYS10.0 has been used to construct a semi-rigid tubular scaffold model, on which certain concentrated load has been applied for numerical analysis. This paper mainly studies the effect of steel-tube thickness and the arrangement of connecting tubes on the stability of scaffold, so provide a theoretical basis for the practical construction and design of scaffold, and to reduce the incidence of accidents.

Design framework for the structural analysis of free-form timber plate structures using wood-wood connections

Abstract Geometrically complex timber plate structures using wood-wood connections are increasingly designed thanks to digital fabrication. Whereas their fabrication has been automated using computer-aided design programming, research focused on the development of automated numerical tools for their structural analysis has been very limited. This paper presents a method to automate the generation of a finite element model for the analysis of structures with a large number of joints. The model is developed taking the example of recently developed double-layered timber plate shells. Vertical displacements obtained with the semi-rigid spring model proposed are in good agreement with experimental tests performed on small-scale prototypes, whereas rigid modelling of the connections highly underestimates displacements of the structure. Semi-rigidity of the connections in translation as well as in rotation was shown to highly influence the model. The generation of the numerical model was successfully automated for large-scale structures.

Study on the secondary stresses of joint effects in transmission tubular towers

Transmission tubular towers are widely used in urban and large span transmission network, analyzed as ideal frame-truss systems without explicitly considering slippage effects in bolted joints. In this paper, a special beam element considering bolt slip effect is established based on the secondary development module UPFs provided by ANSYS software. A series of semi-rigid model of transmission tubular tower with different parameter features are simulated by directly calling the special beam elements instead of using spring elements and ordinary beam elements. Distribution form and influence factor of secondary stresses of main members in transmission tubular tower leg considering the bolt slippage effect is analyzed. The results indicate that secondary stresses are mainly related to three factors: the layout scheme of auxiliary members, the main member slenderness ratio, the angle between main members and diagonal members. By contrast, it is found that secondary stresses of two lattices are mainly larger than that of a lattice. Under two lattices the angle between the main member and the diagonal member is the major influence factor, while, a lattice, the secondary stresses are mainly depended on the main member slender ratio. Design suggestions are given based on the analysis results.

Structure and Dynamics of the Methane-Propane van der Waals Complex

Microwave transitions in the region 7-26 GHz were measured for the methane-propane van der Waals complex. The nearly free internal rotation of methane within the complex gives rise to three states that do not relax even in a 5 K supersonic expansion. Eighteen lines have been assigned to the lowest state and are well fitted to a semirigid rotor model, with rotational constants A = 7553.8229 (24) MHz, B = 2483.9200 (8) MHz, and C = 2041.8692 (5) MHz, and six distortion constants. The structure has the methane positioned above the plane defined by the propane carbon atoms with a center-of-mass van der Waals bond distance of 3.98 Å. This is significantly larger than the equilibrium value of 3.71 Å found with ab initio calculations done at the CCSD(T)-F12a/aug-cc-pVTZ level of theory. Further calculations encompassing a large range of angular orientations of the methane subunit indicate that angular motion produces a large zero-point contribution to the energy, which not only lowers the effective barrier to internal rotation of the methane but also increases the radial distance between subunits. Therefore, although in the lowest energy structure the methane can get close to the propane by interdigitating the hydrogens atoms, the zero-point energy effectively flattens out the potential so that the hydrogens become less restricting.

Semi-rigid beam element model for progressive collapse analysis of steel frame structures

Semi-rigid connections are widely used in steel frame structures. The bending and axial stiffness of connections have a significant influence on the mechanical performance of frame structures. However, most finite-element models of an actual project established in general finite-element software are rigid or hinge-connected for simplicity. Thus, the results are not consistent with the actual situation and may cause large errors. To estimate the influence of joint stiffness, including bending and axial stiffness, a novel numerical beam model is proposed in this paper. This method can be used for inelastic analysis with axial and bending stiffness considered separately. The accuracy of the proposed element model is first validated by comparing it with an ordinary beam element. Then, the model is used for seismic analysis of a steel frame structure, and the influence of bending stiffness on the dynamic response of a steel frame is derived. Progressive collapse analysis is conducted, and the influence of bending and axial stiffness on the mechanical behaviour of the steel frame structure during collapse is also determined. The proposed element model can consider semi-rigid joints and inelasticity at the same time with high accuracy, and it can be conveniently incorporated in general finite-element software.

Boundary Element Analyses on the Adhesive Contact between an Elastic Cylinder and a Rigid Half-Space

Boundary element method is used to analyze the adhesive contact between an elastic cylinder and a rigid half-space. Lennard-Jones potential is used for the surface traction. In the past, the simulation for the adhesive contact between cylinders usually used parabolic approximation for cylinder surface, and used line loading acting on a half-space. Since line loading may cause infinite deformation, only contact half-width/load relation and pull-off force can be obtained. In this paper, the adhesive contact between an exact elastic cylinder and a rigid half-space is investigated. The S-shaped load-approach curve and the whole solution are obtained. Using the load-approach curves, the pull-off force, pull-off distance and jump-in distance are obtained. The effects of Tabor parameter and radius are investigated. The result is compared with the numerical simulation for the adhesive contact between an elastic parabolically approximated cylinder and a rigid half-space and the two-dimensional JKR model. For large Tabor parameters, two-dimensional JKR model can approximate the adhesive contact. For small Tabor parameters, two-dimensional Bradley model can approximate the adhesive contact. The radii do affect the load-approach relation for large Tabor parameters, and have very small effects for small Tabor parameters. A semi-rigid cylinder model is proposed. This model can predict the load-approach curves for small Tabor parameters and can predict the jump-in distance for large Tabor parameters. In addition, a modified load-approach relation for two-dimensional JKR model is proposed. This relation can approximate the load-approach relation and predict the pull-off distance for large Tabor parameters. It is also found that the radius does not affect the pull-off force.