Tensioned String Research Articles

Solving AdS3 string theory at minimal tension: tree-level correlators

We revisit the minimal tension (k = 1) string theory on AdS3 × S3 × \U0001d54b4. We propose a new free-field description of the worldsheet theory and show how localization of string amplitudes emerges from the path integral. We exemplify our proposal by reproducing the worldsheet partition function of the psu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathfrak{psu} $$\\end{document}(1, 1|2)1 WZW model and providing explicit expressions for spectrally-flowed vertex operators and DDF operators. We compute string correlators in the path integral formalism and obtain a precise tree-level match with correlation functions of the boundary symmetric orbifold.

Analysis of deformation in tensegrity structures with curved compressed members

Tensegrity structures are prestressed structures consisting of compressed members connected by prestressed tensioned members. Due to their properties, such as flexibility and lightness, mobile robots based on these structures are an attractive subject of research and are suitable for space applications. In this work, a mobile robot based on a tensegrity structure with two curved members connected by eight tensioned strings is analyzed in terms of deformation in the curved members. Further, the difference in locomotion trajectory between the undeformed and deformed structure after the prestress is analyzed. For that, the theory of large deflections of rod-like structures is used. To determine the relationship between acting forces and the deformation, the structure is optimized using minimization algorithms in Python. The results are validated by parameter studies in FEM. The analysis shows that the distance between the two curved members significantly influences the structure’s locomotion. It can be said that the deformation of the components significantly influences the locomotion of tensegrity structures and should be considered when analyzing highly compliant structures.

Finite Element Analysis of UHV Transmission Line Stringing System Based on APDL

Nowadays, the tension stringing construction is used in UHV transmission lines. However, in the tension stringing system of UHV transmission lines, due to the flexibility of cables, such as guide ropes, ground wires, etc., in systems, the vibration will be occurred during the construction process. In order to analyze the vibration, the finite element analysis method is required for the system. In this paper, a certain position in the stringing process of the first and the last electric tower of the third section of a 1000kV UHV project was taken as the research object, the setting of constraint conditions, modal analysis and power spectrum analysis were carried out for the fast simulation calculation using APDL, the ANSYS parametric design language. It can be concluded that this method can improve efficiency of modeling and simulation and realize the rapid finite element analysis.

Symmetries and covering maps for the minimal tension string on AdS3× S3× T4

This paper considers a recently-proposed string theory on AdS3 × S3 × T4 with one unit of NS-NS flux (k = 1). We discuss interpretations of the target space, including connections to twistor geometry and a more conventional spacetime interpretation via the Wakimoto representation. We propose an alternative perspective on the role of the Wakimoto formalism in the k = 1 string, for which no large radius limit is required by the inclusion of extra operator insertions in the path integral. This provides an exact Wakimoto description of the worldsheet CFT. We also discuss an additional local worldsheet symmetry, Q(z), that emerges when k = 1 and show that this symmetry plays an important role in the localisation of the path integral to a sum over covering maps. We demonstrate the emergence of a rigid worldsheet translation symmetry in the radial direction of the AdS3, for which again the presence of Q(z) is crucial. We conjecture that this radial symmetry plays a key role in understanding, in the case of the k = 1 string, the encoding of the bulk physics on the two-dimensional boundary.

Experimental Study on Torsional Friction of Stringing Blocks on Conductor in Tension Stringing Construction

An experimental study was conducted to analyze the torsional friction effect of stringing blocks on the conductor during tension stringing construction. By analyzing the torsional friction force of stringing blocks on the conductor, the torsional friction experimental device of the stringing blocks on the conductor was designed. The torsional friction torque of the JL/G1A-630/45-45/7 Aluminum Conductor Steel Reinforced (ACSR) under the different tensions and wrap angles passing through the stringing blocks was measured, and then the friction coefficient was obtained. The experimental results show that the torsional friction coefficient of the stringing blocks to the conductor μ decreases with the increase of the tension of the conductor and the wrap angle passing through the stringing blocks. The relationship between the coefficient of friction and the wrap angle and tension of the conductor passing through the stringing blocks is obtained by fitting, and the formula for calculating the torsional frictional torque is obtained.

From Homogeneous and Isotropic Universes to Braneworlds with Dynamical Tension Strings

Cosmological solutions are studied in the context of the modified measure formulation of string theory, then the string tension is a dynamical variable and the string the tension is an additional dynamical degree of freedom and its value is dynamically generated. These tensions are then not universal, rather each string generates its own tension which can have a different value for each of the string world sheets and in an ensemble of strings the values of the tensions can have a certain dispersion. We consider a new background field that can couple to these strings, the “tension scalar” which is capable of changing locally along the world sheet and then the value of the tension of the string changes accordingly. When many types of strings probing the same region of space are considered this tension scalar is constrained by the requirement of quantum conformal invariance. For the case of two types of strings probing the same region of space with different dynamically generated tensions, there are two different metrics, associated to the different strings. Each of these metrics have to satisfy vacuum Einstein’s equations and the consistency of these two Einstein’s equations determine the tension scalar. The universal metric, common to both strings generically does not satisfy Einstein’s equation. The two string dependent metrics considered here are flat space in Minkowski space and Minkowski space after a special conformal transformation. The limit where the two string tensions are the same is studied, it leads to a well defined solution. If the string tension difference between the two types of strings is very small but finite, the approximately homogeneous and isotropic cosmological solution lasts for a long time, inversely proportional to the string tension difference and then the homogeneity and isotropy of the cosmology disappears and the solution turns into an expanding Braneworld where the strings are confined between two expanding bubbles separated by a very small distance at large times.

A Review of Integrated Control Technology of Tension Stringing Equipment in Transmission Line Erection

The comprehensive control technology of tension stringing equipment for transmission line erection is a method that uses modern information technology, communication technology, automation technology and other means to remotely control and monitor the state of the tensioning equipment, and realize the acquisition and control of the main working state of the tensioner, as well as real-time monitoring and control. This method has important roles and values in improving the operation efficiency and reliability of the tensioning equipment, reducing the construction cost and risk, ensuring the quality and safety of the erection construction, etc. This paper reviews the research status and progress in this field, mainly introduces the research achievements in three aspects: online monitoring and intelligent control system of tensioning equipment, control strategy based on nonlinear control technology, and control strategy based on fuzzy logic, as well as their roles in improving the machine performance and safety. This paper also analyzes the problems and challenges in this field, and puts forward the future development direction. This paper provides a valuable reference for the researchers and engineers in this field, and also provides some inspiration and suggestions for the future research or exploration in this field.

Improved Teaching Learning Algorithm with Laplacian operator for solving nonlinear engineering optimization problems

Teaching Learning Algorithm (TLA) is a recently developed nature-inspired optimization technique applicable to complex optimization problems. This paper proposes an improved TLA version using the Laplacian operator of the Genetic Algorithm (GA), named LX-TLA. The proposed algorithm is tested on benchmark optimization problems, including unimodal and multimodal problems. The numerical results are obtained in the form of objective function values, and a t-test is applied to compare the performance of LX-TLA and basic TLA. Convergence plots are given to provide insight into the convergence behavior of LX-TLA. The results reveal that proposed algorithm provides effective and efficient performance in solving benchmark test functions. The proposed algorithm is also applied to engineering design problems, such as Tuned Mass Damper (TMD), truss structure, welded beam, tension string, and pressure vessel. The results obtained using LX-TLA are compared with other nature-inspired optimization algorithms. The results demonstrate that the proposed algorithm is a robust and effective tool for solving complex optimization problems.

Automatic Site Selection Method for Stretch Field with Multi-factor Coupling Constraints

In the construction of extra high voltage and ultra-high voltage paying-off, the national code requires the unified use of “tension stringing” technology. The site selection of stretch field is an important part of tension stringing. The traditional site selection of the stretch field is mainly determined by the experience of the designer, which has many disadvantages. This paper presents a method of automatic site selection for stretch field. First, two-dimensional and three-dimensional map data are fused in order to obtain the geographic information data on the line; secondly, according to the geographic information data, combined with the line segmentation rules, the segmentation of the entire line is realized to obtain the preliminary site location; finally, according to the factors affecting the establishment of the site, such as the length of the segment, the type of towers, the number of block, buildings, vegetation, road conditions, as well as site area, etc., a mathematical model for optimal site selection of the stretch field is established , with the goal of minimizing the cost of construction, automatic iterative optimization of the model is conducted, to find the optimal site location The proposed method of automatic site selection of the stretch field combines accurate geographic information data, considers various influencing factors, avoids various problems caused by manual experience site selection, improves site selection efficiency and construction safety, and saves construction cost. Experimental results show that this method can get better position of the stretch field.

Automatic Geographic Information Classification Method Based on SVM for Site Selection of Stretch Field

In tension stringing construction, the site selection of the stretch field is related to the efficiency, safety and cost of the whole wire construction. Surrounding geographic information impacts the site selection extremely seriously. Accurate grasp of the surrounding geographic information along the transmission line is the key to ensure the optimal site selection of the stretch field. Aiming at the geographic image data along the transmission lines collected by the UAV, firstly, the map data is blocked using the image gradient information and the geometric topological relationship in the image; then, the histogram features of the gradient direction are extracted from the blocked data; finally, the support vector machine is used to train the extracted features, and the map data is classified according to the model obtained from the training, and finally the automatic classification and recognition of the geographic information along the transmission lines is obtained. The proposed method can achieve high recognition accuracy by using small samples for training. Through practice, the proposed method can accurately classify map data, thus providing a reliable guarantee for determining the surrounding geographic influences when selecting a site for a stretch field.

Research on Physical Model and Criterion of Loose Strands in Tension Stringing Construction

In tension stringing construction, the conductor defects of loose strand often occur, which affects the construction quality and conductor life. There is no suitable method to express the physical state of such loose strand at present. Through the study of the loose strands section of the conductor, the physical model of the loose strands of the conductor is established, and the physical calculation formula of scattered strands and lantern included in loose strands defect is proposed, as well as the discrimination coefficient of the scattered strands k 1 and the lantern k 2 . 3D scanning technology of industrial CT was used to scan and model the loose strand samples of JL/G1A-630/45-45/7 and JL1/G2A-1250/100-84/19 ACSR obtained from the loose strand reproduction test of conductor. The CT scanning model is evenly intercepted to measure multiple sections, and the scattered strands coefficient and the lantern coefficient are calculated. The results show that: When k 1 and k 2 ≥ 1.2, the scattered strands and lantern defects of the conductor are more obvious, which can be used as a criterion.

Research on Construction Monitoring Technology of Stringing Block of Transmission Line

In view of the monitoring and analysis requirements of the stringing block in the process of tension stringing construction, multi-parameter sensing monitoring units such as spatial attitude and load are used to realize real-time collection and transmission of multi-parameter data such as the three-axis attitude angle, the spatial position and load information of the stringing block. The calculation method of the spatial attitude angle of the stringing block is proposed, which can obtain the calculation results of the stringing block load and the change of the space attitude angle through the running state of the traction rope and wire at different stages, and realize the monitoring of the construction process.

Plate Condition Monitoring System Based on LoRa Wireless Transmission

In the process of tension stringing of transmission lines, the condition of the plate needs manual reporting, so its safety is poor, and its efficiency is low. To solve this problem, this study constructs a plate condition monitoring system of tension stringing based on the LoRa wireless transmission. This system consists of a data acquisition system, a wireless communication transmission system, and a monitoring and warning center. The STM32 is used to process the data collected by the sensors, and the LoRa wireless communication system is designed by way of adaptive dynamic change of LoRa’s network ID, and the networking mode of the multi-node relay, and the data is sent to the upper computer from a distance, and the upper computer software is implemented by MFC, which can monitor the condition of the plate in real-time. The test results show that the packet loss rate of LoRa is less than 5%, and the condition data of the plate can be transmitted to the monitoring software through LoRa and displayed. This system has the advantages of strong confidentiality, far transmission, and high safety, which can be used for real-time monitoring of the condition of the plate in the process of tension stringing.

Effect of pitch on mechanical properties of braided wire rope under winding and traction condition

In the tension stringing construction process of power transmission and transformation engineering, the braided wire ropes (BWRs) are in the state of winding and stretching when passing through the friction drum. Pitch is an important structural parameter of BWRs, which directly influences the mechanical behaviors under these conditions. Based on the YS9-8×19 wire rope, this project studies the effect of the rope strand pitch on the curvature and winding from both qualitative and quantitative aspects. Qualitative analysis initially explores the effect of the pitch on the mechanical behaviors. Based on the established “rope-wheel” solid model and numerical simulation model, the stress distribution and the variation trend of the maximum equivalent stress corresponding to different pitches in the winding traction state are obtained through the quantitative analyses of the numerical simulations under the same loads with different pitches. The reasonable pitch range of the BWR subjected to traction and bending load is further concluded, to provide the data reference for the manufacture of related wire ropes.

Numerical Simulation of the Dynamic Responses of Electric Power Fitting of Transmission Lines after Ice Shedding

As the key connecting components between tower and conductors, electric power fittings play an important role in the provision of the safe operation of transmission lines. Taking 500 kV transmission lines as the research object, electric power fittings failure in heavy icing areas is studied. The following three questions are considered: first, the influence of different ice-shedding methods on the tension of quad bundle conductors; second, the influence of the spans number, span length, height difference, and ice thickness on the conductor tension under the most dangerous ice-shedding mode; lastly, the mechanical characteristics of tension string and suspension string under ice-shedding condition in the stable wind. The results show that the von Mises stress of the parts that connect with the iced conductor in the tension string model is greater than those of the parts connected with the ice-shedding conductor. What is more, the shackle is the most vulnerable part of the whole model, which is prone to wear and damage, and the failure is most likely to occur at the upper shackle. The middle part in the rectangular hanging plate which is connected with the iced conductor is prone to damage, for its maximum stress has already exceeded the yield stress, with a danger degree inferior only to the shackle. In the suspension string model, the von Mises stress of each part is relatively small and does not reach the yield stress. Similarly, the shackle is most likely to be damaged in the overall model, while other parts maintain larger safety margins. The structure of the parts with smaller stress can be optimized according to the simulation results where design margins may be reduced and additional cost benefits realized.

Tension Force Detection of Short Suspender by Using Laser Doppler Vibrometer

In this study, the vibration frequency of steel rod-type short suspenders simulated by three types of prestressed steel rebars with aspect ratios of 14, 20.8, and 37.8 was detected accurately and remotely by using Laser Doppler Vibrometer (LDV); then the tension force state of short suspenders was evaluated through the quadratic regression relationships between vibration frequency and tension force. The results showed that the vibration frequency of steel rod-type short suspenders increases with the increase in tension force, and there is a good correlation between vibration frequency and prestress. Furthermore, when the prestress applied is the same, the vibration frequency of short suspenders decreases with the increase of their aspect ratios, indicating aspect ratio plays a decisive role on the change of vibration frequency. The errors between the tension force obtained by experiment and tension string theoretical calculation for short suspenders are large, due to the nonrigid boundary condition. The establishment of quadratic regression relationships between vibration frequency and tension force effectively avoids the influence of various factors on the existing calculation model such as mass, stiffness, and constraint type, and makes the detection accuracy of tension force achieve 98%.

Brane world creation from flat or almost flat space in dynamical tension string theories

There is great interest in the construction of brane worlds, where matter and gravity are forced to be effective only in a lower dimensional surface, the brane . How these could appear as a consequence of string theory is a crucial question and this has been widely discussed. Here we will examine a distinct scenario that appears in dynamical tension theories and where string tension is positive between two surfaces separated by a short distance and at the two surfaces themselves the string tensions become infinite, therefore producing an effective confinement of the strings and therefore of all matter and gravity to the space between these to surfaces, which is in fact a new type of stringy brane world scenario. The basic formulation for obtaining this scenario consist of assuming two types of strings characterized by a different constant of integration related to the spontaneous string tension generation. These string tension multiplied by the embedding metric define conformally related metrics that both satisfy Einsteins equation. The braneworlds appear very naturally when these two metrics are both flat spaces related by a special conformal transformation. The two types of string tensions are determined and they blow up at two close expanding surfaces. A puzzling aspect appears then: the construction is based on flat spaces, but then there are also strings with very large tension near the boundaries of the braneworld,so can the back reaction from the infinite tension strings destroy the flat space background? Fortunatelly that can be resolved using the mechanism Universe creation from almost flat (or empty) spaces, which incorporates a gas of very large string tensions in a membrane, studied before in 1+1 membranes in a 2+1 embedding space and now is generalized for a 1+(D-2) membrane moving in a 1+(D-1) space.

Research on the Approximate Calculation Method of the Fundamental Frequency and Its Characteristics on a Tensioned String Bridge

As a new type of composite bridge, the dynamic structural characteristics of a tensioned string bridge need to be deeply studied. In this paper, based on the structural characteristics of a tensioned string bridge, the Rayleigh method is used to derive formulas for calculating the frequencies of vertical, antisymmetric and lateral bending vibrations. The characteristics of the vertical and lateral bending vibration frequencies are summarized. The fundamental frequencies of the antisymmetric vertical bending and lateral bending of the tensioned string bridge are the same as that of the single-span beam under the corresponding constraint conditions. The shape and physical characteristics of the main cable have no effect on the frequency. The vertical bending symmetrical vibration frequency of the tensioned string bridge is greater than the corresponding symmetrical vibration frequency of the simply supported beam. The shape and physical characteristics of the main cable have a greater impact on the vertical bending symmetrical vibration frequency than the lateral bending frequency, and the vertical bending symmetrical vibration frequency increases with an increasing rise-to-span ratio. The tension force of the main cable has no influence on the frequency of tensioned string bridges. The first-order frequency of the tensioned string bridge is generally the vertical bending symmetrical vibration frequency. By adopting a tensioned string bridge structure, the fundamental frequency of a structure can be greatly increased, thereby increasing the overall rigidity of the structure. Finally, an engineering example is applied with the finite element parameter analysis method to study the vibration frequency characteristics of the tensioned string bridge, which verifies the correctness of the formula derived in this paper. The finite element analysis results show that the errors between the derived formula in this paper and the finite element calculation results are less than 2%, indicating that the formula derived in this paper has high calculation accuracy and can meet the calculation accuracy requirements of engineering applications.

Simulation of Continuous Tension Stringing Process of Conductor with Bending Stiffness Model

At present, there is no research on the calculation of tension variation of the conductor with bending stiffness model between the continuous span during tension stringing construction. Aiming at the typical terrain with large elevation difference in UHV project, a vector finite element method for calculating the tension of the conductor with bending stiffness model passes through the pulley in the process of tension stringing is proposed. The process of the wire rope under the action of the tractor pulling the conductor passes through the pulley continuously is realized. The variations of tension of tensioner and tractor, reaction force of pulley and envelope angle of the conductor passes through the pulley are obtained by simulation of tension stringing conditions such as 1 pulls 1, 1 pulls 2, etc, which provides reference for equipment selection for the tension stringing construction of mountain terrain with large elevation difference.

Gravitational waves from melting cosmic strings

Appearance of cosmic strings in the early Universe is a common manifestation of new physics typically linked to some high energy scale. In this paper, we discuss a different situation, where a model underlying cosmic string formation is approximately scale free. String tension is naturally related to the square of the temperature of the hot primordial plasma in such a setting, and hence decreases with (cosmic) time. With gravitational backreaction neglected, the dynamicsof these melting strings in an expanding Universe is equivalent to the dynamics of constant tension strings in a Minkowski spacetime.We provide an estimate for the emission of gravitational waves from string loops. Contrary to the standard case, the resulting spectrum is markedly non-flat and has a characteristic falloffat frequencies below the peak one. The peak frequency is defined by the underlying model and lies in the range accessible by the future detectors for very weak couplings involved.