Liang Ren

Dalian University of Technology | DUT · State Key Laboratory of Coastal and Offshore Engineering

A mechanics-based methodology called the inverse unit load method (IULM) is proposed for the distributed bending stiffness estimation of girder bridges utilizing in situ deflection responses. This inverse problem has important implications for bridge health monitoring and rapid bridge detection procedures. The IULM formulation is derived from a reg...

Fracture is the main form of marine structural failure due to the action of waves and oceans. It is necessary to monitor the initiation and extension of cracks in a timely and accurate manner, and the stress intensity factor (SIF) is an important indicator for analysing the propagation of cracks. Based on existing research, this paper combines the...

Jacket platform is the marine structure that anchor piles to the sea floor, among which the leg is one of the most important components of fixed marine structure. Most of the existing stress and strain monitoring methods for offshore platform ignore the existing forces in the structures caused by deck load and installation errors before the monitor...

In this study, corrosion-induced mortar/concrete cracking is experimentally investigated with optical frequency domain reflectometry (OFDR) distributed optical fiber sensors, and numerical simulation is performed with finite-element method (FEM). Mortar/concrete cylindrical specimens are instrumented with OFDR distributed optical fiber sensors and...

Floating Production Storage and Offloading (FPSO) is essential offshore equipment for developing offshore oil and gas. Due to the complex sea conditions, FPSOs will be subjected to long-term alternate loads under some circumstances. Thus, it is inevitable that small cracks occur in the upper part of the module pier. Those cracks may influence the s...

Monitoring of cracks on offshore platforms is necessary to ensure the safe operation and prolong their service life. The crack extension width is of great significance for the calculation of stress intensity factor (SIF). This paper developed a measuring device for crack extension width based on Fiber Bragg Grating (FBG) sensing technique. The desi...

Dynamic displacement plays an essential role in structural health monitoring. To overcome the shortcomings of displacement measured directly, such as installation difficulty of monitoring devices, this paper proposes a smart reconstruction method, which can realize real-time intelligent online reconstruction of structural displacement. Unlike the e...

Low localization accuracy and instability have always been two primary problems for the pipeline leak detection and localization method based on the negative pressure wave (NPW) technique. In this paper, based on compressed sensing (CS) theory, a novel pipeline leak detection and localization method is proposed to replace the solutions of the arriv...

Crack is one of the main causes for the failure of marine structure due to the action of waves and ocean. It is necessary to monitor the initiation and extension of the crack timely and accurately, so as to provide effective suggestion for maintenance and prolong the service life of the structure. A novel distributed optical fiber sensing tape base...

Deflection is of great significance for evaluating the safety performance of long-span bridges, while it is difficult or expensive to be directly measured in actual projects despite numerous displacement sensors have been developed. This paper proposes a displacement reconstruction framework to obtain the dynamic deflection of beam structures using...

Pipeline leakage and pipeline internal corrosion are two serious threats to pipeline safety operation. In this study, based on the measurement theory of pipeline internal diameter variation and a numerical simulation analysis of existing sensor shortcomings, a novel FBG pipe-fixture sensor is designed and developed to detect pipeline leakage and mo...

The inverse finite element method (iFEM) is a mechanics-based algorithm for dynamic tracking of full-field structural displacements. Accurate deformed structural-shape can be attained without any material properties and loading information, even when some discrete locations lack in-situ strain measurements. The structure is discretized by inverse f...

This paper presents a novel pipeline deformation monitoring method using the inverse finite element method (iFEM) based on the iBeam3 element. This element uses only two end nodes to reconstruct pipeline deformation without any material and/or loading information because only the strain-displacement relationship is employed in the algorithm. A seri...

The real-time estimation of structural deformations using discrete strain data, known as shape sensing, is critical to the health monitoring of structures such as bridges. An innovative methodology called the inverse finite-element method (iFEM) is proposed to solve this issue. In this paper, a novel two-node inverse beam element, iBeam3, is develo...

The inverse finite element method (iFEM) is a mechanics-based algorithm for deformed-shape estimation of structures. In this paper, an enhanced inverse beam element named iEBT2 is developed based on classical beam theory. The element formulation is derived by minimizing a weighted-errors functional that consists of experimental and numerical sectio...

Many transmission towers have collapsed during typhoon events, and the design wind loads in most current standards consider only the turbulence characteristics of monsoons. The gust response factor (GRF) is a parameter that is directly related to the wind field characteristics, and thus, it is necessary to address GRFs under typhoons to improve the...

Pipeline, serving as one of the most important gas transportation methods, can cause serious consequences in the event of leakage, so leakage monitoring is particularly important. In our previous study, a fiber Bragg grating hoop strain sensor was developed to detect pipeline leakage by measuring circumferential strain, and this sensor was utilized...

The modal parameters of transmission tower-line systems constitute the basis of their wind and seismic design. However, such structures become complicated spatial systems due to the coupling effects between the towers and lines, making it difficult to evaluate the modal parameters of a transmission tower. To study the tower-line coupling effects on...

The significance of implementing structural health monitoring (SHM) system for civil engineering, especially infrastructure engineering, has been recognized. Distributed optical fiber sensor (DOFS) based on optical frequency domain reflectometer (OFDR) offers an attractive technique for in situ strain measurement due to its high resolution and high...

Achieving uniform bolt preload distribution is crucial but not easy for a multi-bolt connection. Tightening sequence is one of the primary factors that affect the bolt preload distribution. Different national codes specify details of tightening sequence of a multi-bolt connection. However, few studies have been conducted on the effect of tightening...

Many transmission towers have collapsed under typhoons in recent years, mainly due to the unclear behaviors of their structural properties, introducing many deficiencies in the design process. Therefore, implementing structural health monitoring is of great importance for investigating the structural features of large-span transmission lines. This...

This paper presents a novel gas pipeline burst detection and localization method eliminating the negative pressure wave (NPW) velocity and improving the leak localization accuracy. For burst detection, a novel fiber Bragg grating (FBG) caliber-based sensor is developed that can accurately measure NPW signals. Based on the sensor array, a leak local...

The roof of Dalian gymnasium was designed in the form of suspen-dome structure. A structural health–monitoring system has been developed for the roof structure to guarantee the safety condition during construction process as well as in future service. In this article, a monitoring scheme was proposed in detail according to the mechanical characteri...

A pipeline's safe usage is of critical concern. In our previous work, a fiber Bragg grating hoop strain sensor was developed to measure the hoop strain variation in a pressurized pipeline. In this paper, a support vector machine (SVM) learning method is applied to identify pipeline leakage accidents from different hoop strain signals and then furth...

The magnetic permeability changes of ferromagnetic materials under elastic stress offer the potential to measure tension based on the inverse magnetostrictive effect. The elasto-magnetic (EM) sensor is the most promising technology for monitoring tension in steel structures. Nevertheless, difference in the device channel or variation of the externa...

Pipelines provide a convenient mode of transportation of fluids, and their safe usage is one of the foremost concerns. In our previous work, a hoop strain-based negative pressure wave (NPW) approach was proposed to detect and localize pipeline leakages by employing a series of bare fiber Bragg grating (FBG) sensors. To enhance the leakage detection...

Pipelines function as blood vessels serving to bring life-necessities, their safe usage is one of the foremost concerns. In our previous work, fiber Bragg grating (FBG) hoop strain sensor with enhanced sensitivity was developed to measure the hoop strain variation on a pressurized pipeline. In this paper, combined with multi-class support vector ma...

Pipeline is an important structure to transport oil and gas through long distances. However, pipeline also suffers from many threats especially corrosion and leakage. Therefore, it is necessary to conduct pipeline safety monitoring. With the advantage of high precision in distributed strain measurement, the optical frequency domain reflectometry (O...

This paper develops a new type of smart bolt that can simultaneously measure the axial and shear forces through the use of embedded fiber Bragg gratings (FBG) sensors. Based on the linear relationship between the equivalent bending moment and the shear force, the equation to calculate the shear force using the Bragg wavelength variation is derived....

Pipelines function as blood vessels serving to bring life-necessities, so their safe usage is one of the foremost concerns. In our previous work, a fiber Bragg grating (FBG) hoop strain sensor with enhanced sensitivity was developed to measure the pressure drop induced by pipeline leakage. Some hoop strain information during the leakage transient p...

In combination of the actual project in Dalian Baiyun Mountain Tunnel, this paper introduces the principle of fiber optic sensor monitoring system based on optical time domain reflectometer. Then, based on the orthogonal design and even design scheme, this paper carries out a numerical experiment on the tunnel surrounding rock and establishes a reg...

This study investigated damage detection of cable structures in bridge engineering using the virtual distortion method (VDM). The main theory of damage detection based on the VDM, including the influence matrix, the stiffness reduction, and an optimized algorithm, was applied to damage detection in hangers in a real three-dimensional finite-element...

According to the inverse magnetostrictive effect, magnetic permeability variations in ferromagnetic materials under elastic stress offer the potential to measure tension. In this study, a prototype sensor was designed, fabricated, and tested. An eddy current sensor (ECS) with a single coil structure was used to detect tension due to its lower cost,...

Nowadays there exist various kinds of special vehicles designed for some purposes, which are different from regular vehicles in overall dimension and design. In that case, accidents such as overturning will lead to large economical loss and casualties. There are still no technical specifications to follow to ensure the safe operation and driving of...

Pipeline leakage and corrosion are two serious threats to pipeline safety operation. Therefore, to ensure the safety operation of long-distance pipeline, it is of great significance to conduct pipeline monitoring. Since hoop strain is an effective indicator to reflect the inner pressure fluctuation and the wall thickness reduction of the pipeline, a m...

For resolving deficiencies of conventional tension measurement methods, this paper proposes a novel eddy current sensor with a single-coil structure based on the inverse magnetostrictive effect. An inductor-resistor-capacitor (LRC) model of eddy current sensor, which considers more parameters than the traditional inductor-resistor (LR) model, was es...

Mechanical performance monitoring of civil infrastructure using fiber Bragg grating (FBG) sensors has received significant public attention in recent years. However, there is currently little research on the mechanical performance monitoring of piles used in high-piled wharfs in coastal ports during pile driving using the FBG sensor technique. Base...

In this paper, an innovative method for rapid detection and location determination of pipeline leakage utilizing lead zirconate titanate (PZT) sensors is proposed. The negative pressure wave (NPW) is a stress wave generated by leakage in the pipeline, and propagates along the pipeline from the leakage point to both ends. Thus the NPW is associated...

Purpose Magnetic permeability variations of ferromagnetic materials under elastic stress offer the potential to monitor tension based on the inverse magnetostrictive effect. The purpose of this paper is to propose an innovative self-inductance tension eddy current sensor to detect tension. Design/methodology/approach The effectiveness of conventio...

A pipeline is often an important structure with very long service life. It is of great significance to monitor the corrosion level of a pipeline to ensure its safety operation. This paper aims to develop a new nondestructive method to detect the pipeline corrosion. It is assumed that the pipeline corrosion will result in a variation of the circumfe...

This paper describes the backgrounds, motivations and recent history of structural health monitoring (SHM) developments to various types of engineering structures. Extensive applications of SHM technologies in bridges, high-rise buildings, sport avenues, offshore platforms, underground structures, dams, etc. in mainland China are summarily categori...

The measurement of high frequency vibrations is important in many scientific and engineering problems. This paper presents a novel, cost effective method using fiber optic fiber Bragg gratings (FBGs) for the measurement of high frequency vibrations. The method uses wavelength matched FBG sensors, with the first sensor acting as a transmission filte...

Associated with a project, the application of real-time monitoring and early warning system in the retrofitting process of structures was investigated. Based on the software ANSYS, structural analysis and thermal analysis were carried out to determine the distribution of sensors and the early warning threshold value in monitoring process. SHM syste...

The high-voltage power transmission tower-line system, which is a high flexible structure, is very susceptible to the wind-induced vibrations. This paper proposes the utilization of the internal resonance feature of the spring pendulum to reduce the wind-induced vibration of a transmission tower. The kinetic expression of the spring pendulum system...

Wind energy is one of the most important renewable energy sources and many countries are predicted to increase wind energy portion of their whole national energy supply to about twenty percent in the next decade. One potential obstacle in the use of wind turbines to harvest wind energy is the maintenance of the wind turbine blades. The blades are a...

For the low strength of model material, it is difficult to test the deformation of the small-scale dam model during shaking table tests. Based on the principle friction, a type of fiber Bragg grating (FBG) strain sensor with enhanced strain sensitivity was developed to measure the strain of low-strength material. The principle of the small-scale FB...

The peripheral structure of Dalian stadium is a long-span spatial truss structure. To ensure the safety of the peripheral structure during construction and operation period, the permanent structure health monitoring system is implemented. This paper first introduces the structural features of the Dalian stadium, and then illustrates the permanent m...

Researchers and administrative authorities have long recognized the significance of implementing long-term structural health monitoring (SHM) systems for civil infrastructures, especially large-span space structures or other complex infrastructures, in order to secure structural safety and issue warnings regarding the structural damage prior to cos...

Leakage is the most common cause of natural gas pipeline accidents. This work was devoted to natural gas pipeline leakage detection, which is based on detecting negative pressure wave signals caused by leakage. The FBG strain sensor, which is based on monitoring the hoop strain of a pipeline to detect negative pressure wave signals, is fabricated a...

Pipelines are widely used for the transport of a large variety of fluids, such as natural gas, across long distances. While pipelines provide a convenient mode of transportation of fluids, their safe usage is one of the foremost concerns especially if their contents are harmful to the environment or if the hosting area is prone to third-party intru...

The vortex-induced vibrations (VIV) is an important topic of study in many different scientific and engineering fields. While VIV can be of benefit in some cases, oftentimes, it is an undesirable phenomenon that can be quite dangerous. In particular for offshore pipelines, VIV can lead to fatiguing of the pipe structure and can cause disastrous con...

Prestressed concrete (PC) bridge girders have extra flexural strength due to embedded prestressing tendons. The level of strength depends on the integrity of the concrete-tendon bond in pretensioned PC structures, and this bond can be degraded in the presence of an adequately large mechanical force or over time because of accumulated damage. Bond d...

Concrete structures rely greatly on the integrity of their supporting rebars to remain serviceable for their intended purposes. Unfortunately, rebars are vulnerable to corrosion due to the ingress of water from the environment, which often also carries a multitude of ionic particles that encourage corrosion. Liquid phase water may enter the structu...

Pipeline monitoring is an important task for the economic and safe operation of pipelines as well as for loss prevention and environmental protection. The circumferential strain is of significance in pipeline integrity monitoring. In this paper, an indirect pipeline corrosion monitoring method based on the circumferential strain measurement is firs...

Methods that more quickly locate leakages in natural gas pipelines are urgently required. In this paper, an improved negative pressure wave method based on FBG based strain sensors and wavelet analysis is proposed. This method takes into account the variation in the negative pressure wave propagation velocity and the gas velocity variation, uses th...

It is important to clarify the variational rules between dynamic characteristics and gust response factors (GRFs) of an ultra high-voltage (UHV) transmission tower for the structural design. In this paper, the synchronous multisensors on-site monitoring has been carried out under field wind conditions, which includes field fluctuating wind velocity...

Ice load is one of the most dangerous factors which threaten the health of offshore structures in cold area. The ice-loading model experiment is an effective method to identify the ice load and to evaluate its influence towards structures. Fiber Bragg grating (FBG) with advantages of reliability, durability and high accuracy, has become one of the...

The importance of real-time detection of cable force during stretching construction can hardly be overstated, especially in long-span space cable system. In this paper, a novel approach to monitor the cable structure health using fiber Bragg grating (FBG) sensors was elaborated and applied in monitoring the tensioning process of suspend-cable dome...

Basic principle and merits of fiber Bragg grating (FBG) are introduced. A novelty strain sensor and a temperature sensor with FBG technology are presented. Theoretical and experimental analyses of FBG sensor are implemented. The variations of temperature and strain profiles during curing process are experimentally explored by embedded FBG sensors....

Fiber Bragg grating(FBG) sensor presents superiority in the measurement of strain in structural monitoring system since its reliability, durability, high accuracy and ease of implementation. In this work, a novel FBG strain sensor is developed and experiments are conducted on the universal material testing machine to calibrate its strain transferri...

Fiber Bragg grating (FBG) sensors have attracted a considerable amount of interest for their superior characteristics. However, the FBG sensors made on bare fibers are easily damaged. For their safe use in engineering, the glass core of optical fibers is coated with softer low modulus protective coatings. A portion of the host material strain is ab...

Accurate measurement of strain variation and effective prediction of failure within models has been a major objective for strain sensors in dam model tests. In this paper, a FBG strain sensor with enhanced strain sensitivity and packaged by two gripper tubes is presented and applied in the seismic tests of a small scale dam model. This paper discus...

An extensive model test program had been carried out to investigate the issues of ice loading on bridge pier model. This paper investigated design principle of three kinds of FBG sensor modules, including FBG-based displacement sensor module, FBG-based strain sensor module and FBG-based force sensor module. A series of calibration tests of all FBG...

Accurate measurement of strain variation and effective prediction of failure within models have been major objectives for strain sensors in dam model tests. In this paper, a fiber Bragg grating (FBG) strain sensor with enhanced strain sensitivity that is packaged by two gripper tubes is presented and applied in the seismic tests of a small-scale da...

Biomechanical studies often involve measurements of the strains developed in tendons or ligaments in posture or locomotion. Fiber-optic sensors present an attractive option for the measurement of strains in tendons and ligaments because of their low cost, ease of implementation, and increased accuracy compared with other implantable transducers. A...

When a fiber Bragg grating (FBG) sensor is embedded in a structure to sense its strain, a portion of strain is absorbed by the protective interlayer of the fiber optical sensor. If an angle exists between the FBG sensor axis and external principal stress direction of the host material, the strain transfer from the host material to the sensor will b...

The dynamic response of offshore platform under seismic excitation is a coupled vibration of liquid and solid interaction. In recent years, the computation of dynamic responses and design of offshore platform have attracted the attention of many researchers. This paper presents a shaking table test of offshore platform model scaled down an actual o...

Biomechanical studies often involve measurements of the strains developed in tendons or ligaments in posture or locomotion. Fiber optic sensors present an attractive option for measurement of strains in tendons and ligaments due to their low cost, ease of implementation, and increased accuracy compared to other implantable transducers. A new displa...

Fiber Bragg grating (FBG) sensors show superior potential for structural health monitoring of civil structures to ensure their structural integrity, durability, and reliability. In this work, FBG sensors, including strain and temperature sensors, are applied for health monitoring of the oil production offshore platform number CB271, which is locate...

Optical fiber sensors have received increasing attention in the fields of civil engineering due to their advantages such as explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, which was packa...

Optic fiber Bragg grating sensor is a new type of sensor, which plays an important role in structural healthy monitoring. When the optic fiber Bragg grating sensor is embedded in the structure or adhered to the structure, there is a strain transferring course between structure and sensor for the existence of interlayer. Important factors that affec...

The past decade has seen rapid advances in research, development, and application of optical fiber Bragg grating technology. Sensors based on this technology have special advantages of being lightweight and small in size, inert and corrosion resistant, immune to electromagnetic interference (EMI), easily multiplexed and multifunctional (they can me...

We develop an analytical model for the relationship between the strain measured by a fiber Bragg grating sensor and the actual structural strain. The values of the average strain transfer rates calculated from the analytical model agree well with available experiment data. Based on the analytical model, the critical adherence length of an optical f...

Optical fiber sensors have received increasing attention in the fields of aeronautic and civil engineering for their superior ability of explosion proof, immunity to electromagnetic interference and high accuracy, especially fitting for measurement applications in harsh environment. In this paper, a novel FBG (fiber Bragg grating) strain sensor, wh...

Concrete is the material widely used in civil engineering. Cracks of concrete are mainly caused by the ununiform shrink in the cure period. The basic principle and merits of FBG are introduced. In order to monitor the shrink strain and temperature of concrete during the cure period, this paper presents a novelty strain sensor and temperature sensor...

This paper discusses of the monitoring of the temperature distribution by an optical fiber Bragg grating sensor system. The sensors are embedded in a pipe underground. Ground-source heat pump system utilizes the thermal energy of the underground soil to heat or cool a building. Optical fiber Bragg grating sensors are used to measure the temperature...

Optical fiber sensors show superior potential for structural health monitoring of civil structures to ensure their structural integrity, durability and reliability. Apparent advantages of applying fiber optic sensors to a marine structure include fiber optic sensors' immunity of electromagnetic interference and electrical hazard when used near meta...