• Wind and Structures
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• 제20권3호
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• pp.449-468
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• 2015

Current wind-resistance designs of large-scale indirect dry cooling towers (IDCTs) exclude an important factor: the influence of the ventilation rate for radiator shutter on wind loads on the outer surfaces of the tower shell. More seemingly overlooked aspects are the effects of various ventilation rates on the wind pressure distribution on the tower surfaces of two IDCTs, and the feature of the flow field around them. In order to investigate the effects of the radiator shutter ventilation rates on the aerodynamic interference between IDCTs, this paper established the numerical wind tunnel model based on the Computational Fluid Dynamic (CFD) technology, and analyzed the influences of various radiator shutter ventilation rates on the aerodynamic loads acting upon a single and two extra-large IDCTs during building, installation, and operation stages. Through the comparison with the results of physical wind tunnel test and different design codes, the results indicated that: the influence of the ventilation rate on the flow field and shape coefficients on the outer surface of a single IDCT is weak, and the curve of mean shape coefficients is close to the reference curve provided by the current design code. In a two-tower combination, the ventilation rate significantly affects the downwind surface of the front tower and the upwind surface of the back tower, and the larger positive pressure shifts down along the upwind surface of the back tower as the ventilation rate increases. The ventilation rate significantly influences the drag force coefficient of the back tower in a two-tower combination, the drag force coefficient increases with the ventilation rate and reaches the maximum in a building status of full ventilation, and the maximum drag coefficient is 11% greater than that with complete closure.

• Membrane and Water Treatment
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• 제7권2호
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• pp.127-141
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• 2016

Electrodialysis (ED) is known to be a useful membrane process for desalination, concentration, separation, and purification in many fields. In this process, it is desirable to work at high current density in order to achieve fast desalination with the lowest possible effective membrane area. In practice, however, operating currents are restricted by the occurrence of concentration polarization phenomena. Many studies showed the occurrence of a limiting current density (LCD). The limiting current density in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Therefore, its reliable determination is required for designing an efficient electrodialysis plant. The purpose of this study is the development of a predictive model of the limiting current density in an electrodialysis process using response surface methodology (RSM). A two-factor central composite design (CCD) of RSM was used to analyze the effect of operation conditions (the initial salt concentration (C) and the linear flow velocity of solution to be treated (u)) on the limiting current density and to establish a regression model. All experiments were carried out on synthetic brackish water solutions using a laboratory scale electrodialysis cell. The limiting current density for each experiment was determined using the Cowan-Brown method. A suitable regression model for predicting LCD within the ranges of variables used was developed based on experimental results. The proposed mathematical quadratic model was simple. Its quality was evaluated by regression analysis and by the Analysis Of Variance, popularly known as the ANOVA.

• Structural Monitoring and Maintenance
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• 제1권4호
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• pp.371-392
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• 2014

Long-span cable-supported bridges are flexible structures vulnerable to unsymmetric loadings such as railway traffic and strong wind. The torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds may deform the railway track laid on the bridge deck and affect the running safety of trains and the comfort of passengers, and even lead the bridge to collapse. Therefore, it is eager to figure out the torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds. The Tsing Ma Bridge (TMB) in Hong Kong is a suspension bridge with a main span of 1,377 m, and is currently the world's longest suspension bridge carrying both road and rail traffic. Moreover, this bridge is located in one of the most active typhoon-prone regions in the world. A wind and structural health monitoring system (WASHMS) was installed on the TMB in 1997, and after 17 years of successful operation it is still working well as desired. Making use of one-year monitoring data acquired by the WASHMS, the torsional dynamic responses of the bridge deck under rail traffic and strong winds are analyzed. The monitoring results demonstrate that the differences of vertical displacement at the opposite edges and the corresponding rotations of the bridge deck are less than 60 mm and $0.1^{\circ}$ respectively under weak winds, and less than 300 mm and $0.6^{\circ}$ respectively under typhoons, implying that the torsional dynamic response of the bridge deck under rail traffic and wind loading is not significant due to the rational design.

• Structural Engineering and Mechanics
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• 제61권2호
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• pp.245-253
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• 2017

The increasing lack of good quality soils allowing the development of roadway, motorway, or railway networks, as well as large scale industrial facilities, necessitates the use of reinforcement techniques. Their aim is the improvement of the global performance of compressible soils, both in terms of settlement reduction and increase of the load bearing capacity. Among the various available techniques, the improvement of soils by incorporating vertical stiff piles appears to be a particularly appropriate solution, since it is easy to implement and does not require any substitution of significant soft soil volumes. The technique consists in driving a group of regularly spaced piles through a soft soil layer down to an underlying competent substratum. The surface load being thus transferred to this substratum by means of those reinforcing piles, which illustrates the case of a piled embankment. The differential settlements at the base of the embankment between the soft soil and the stiff piles lead to an "arching effect" in the embankment due to shearing mechanisms. This effect, which can be accentuated by the use of large pile caps, allows partial load transfer onto the pile, as well as surface settlement reduction, thus ensuring that the surface structure works properly. A technique for producing rigid piles has been developed to achieve in a single operation a rigid circular pile associated with a cone shaped head reversed on the place of a rigid circular pile. This technique has been used with success in a pile-supported road near Bourgoin-Jallieu (France). In this article, a numerical study based on this real case is proposed to highlight the functioning mode of this new technique in the case of industrial slabs.

• Advances in Energy Research
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• 제7권1호
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• Computers and Concrete
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• 제10권2호
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• pp.135-147
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• 2012

At mesoscale, concrete is considered as a three-phase composite material consisting of the aggregate particles, the cement matrix and the interfacial transition zone (ITZ). The reconstruction of the internal structures for concrete composites requires the identification of the boundary of the aggregate particles and the cement matrix using digital imaging technology followed by post-processing through MATLAB. A parameter study covers the subsection transformation, median filter, and open and close operation of the digital image sample to obtain the optimal parameter for performing the image processing technology. The subsection transformation is performed using a grey histogram of the digital image samples with a threshold value of [120, 210] followed by median filtering with a $16{\times}16$ square module based on the dimensions of the aggregate particles and their internal impurity. We then select a "disk" tectonic structure with a specific radius, which performs open and close operations on the images. The edges of the aggregate particles (similar to the original digital images) are obtained using the canny edge detection method. The finite element model at mesoscale can be established using the proposed image processing technology. The location of the crack determined through the numerical method is identical to the experimental result, and the load-displacement curve determined through the numerical method is in close agreement with the experimental results. Comparisons of the numerical and experimental results show that the proposed image processing technology is highly effective in reconstructing the internal structures of concrete composites.

• Membrane and Water Treatment
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• 제3권3호
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• pp.169-179
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• 2012

One of the major limitations in the use of commercial aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes is to maintain high performance over a long period of operation, due to the sensitivity of polyamide (PA) skin layer to oxidizing agents, such as chlorine, even at very low concentrations in feed water. This article reports surface modification of a commercial TFC RO membrane (BW30-Dow Filmtec) by covering it with a thin film of poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde (GA) to improve its resistance to chlorine. Crosslinking reaction was carried out at 25 and $40^{\circ}C$ by using PVA 1.0 wt.% solutions at different GA/PVA mass ratio, namely 0.0022, 0.0043 and 0.013. Water swelling measurements indicated a maximum crosslinking density for PVA films prepared at $40^{\circ}C$ and GA/PVA 0.0043. ATR-FTIR and TGA analysis confirmed the reaction between GA and PVA. SEM images of the original and modified membranes were used to evaluate the surface coating. Chlorine resistance of original and modified membranes was evaluated by exposing it to an oxidant solution (NaClO 300 mg/L, NaCl 2,000 mg/L, pH 9.5) and measuring water permeability and salt rejection during more than 100 h period. The surface modification effectively was demonstrated by increasing the chlorine resistance of PA commercial membrane from 1,000 ppm.h to more than 15.000 ppm.h.

• 한국정밀공학회지
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• 제15권2호
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• pp.124-133
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• 1998

This paper describes a research work of developing a computer-aided design of blanking and piercing for irregular-shaped sheet metal products. An approach to the development of compact and practical CAB system is based on the knowledge-based rules. Knowledge for the CAD system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. The system has been written in AutoLISP on the AutoCAD with a personal computer. Based on knowledge-based rules, the system, STRT-DES, is designed by considering several factors, such as complexities of blank geometry and punch profile, availability of press equipment and standard parts, utilization ratio which minimizes the scrap in a single or a pairwise operation, bridge width, grain orientation and design requirements which maximize the strength of the part when subsequent bending is involved. This system checks a forming feasibility with both internal and external features, a dimension of blanked hole, and a corner and a fillet radius for irregualrly shaped sheet metal products. Therefore this system can carry out a die design for each process which is obtained from results of an automated blank layout drawing with a best utilization ratio for irregular shape of product that was successful in production feasibility check module and those of an automated strip layout drawing and generate part drawings and the assembly drawing of die set in graphic forms.

• Smart Structures and Systems
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• 제18권4호
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• pp.643-662
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• 2016

The monitoring of structural integrity of pipeline tapered thread connections is of great significance in terms of safe operation in the industry. In order to detect effectively the loosening degree of tapered thread connection, an active sensing method using piezoceramic transducers was developed based on time reversal technique in this paper. As the piezoeramic transducers can be either as actuators or sensors to generate or detect stress waves, the energy transmission for tapered thread connection was analyzed. Subsequently, the detection principle for tapered thread connection based on time reversal was introduced. Finally, the inherent relationship between the contact area and tightness degree of tapered thread connection for the pipe structural model was investigated. Seven different contact area scenarios were tested. Each scenario was created by loosening connectors ranging from 3 turns to 4.5 turns in the right tapered threads when the contact area in the left tapered threads were 4.5 turns. The experiments were separately conducted with a highly noisy environment and various excitation signal amplitudes. The results show the focused peaks based on time reversal have the monotonously rising trend with the increase of the contact areas of tapered threads within an acceptable monitoring resolution for metal pipes. Compared with the energy method, the proposed time reversal based method to monitor tapered threads loosening demonstrates to be more robust in rejecting noise in Structural Health Monitoring (SHM) applications.

• Structural Engineering and Mechanics
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• 제57권6호
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• pp.1125-1142
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• 2016

Tunneling is one of the challenging tasks in civil engineering because it involves a variety of decision making and engineering judgment based on knowledge and experience. One of the challenges is to construct tunnels in risky areas under shallow overburden. In order to prevent the collapse of ceilings and walls of a large tunnels, in such conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. This research deals with the numerical modeling of L-profiles and pipe fore-poling pre-support systems in the adit tunnel in northwestern Iran. The first part of the adit tunnel has been drilled in alluvial material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the results of numerical modeling done using FLAC3D, as well as observations during drilling, indicate the tunnel instability. To improve operational safety and to prevent collapse, pre-support systems, including pipe fore-poling and L-profiles were designed and implemented. The results of the numerical modeling coupled with monitoring during operation, as well as the results of instrumentation, indicate the efficacy of both these methods in tunnel collapse prevention. Moreover, the results of modeling using FLAC3D and SECTION BUILDER suggest a double angle with equal legs ($2L100{\times}100{\times}10mm$) in both box profile and tee array as an alternative section to pipe fore-poling system while neither $L80{\times}80{\times}8mm$ nor $2L80{\times}80{\times}8mm$ can sustain the axial and shear stresses exerted on pipe fore-poling system.