The treatment of secondary strains within a strain-based failure assessment diagram

Ainsworth, R.A.,Budden, P.J.,Oh, C.Y.,Kim, Y.J. Applied Science Publishers ; Elsevier Science Ltd 2013 The International journal of pressure vessels and Vol.104 No.-

In a companion paper, proposals for the shape of a strain-based failure assessment diagram (FAD) have been made. The developments in that paper and in related works on strain-based fracture assessment have largely been for remotely applied strains, such as those produced by welding. This paper re-writes existing methods for treating secondary stresses within stress-based FADs in the framework of the proposed strain-based FAD. It is shown that residual strains must be included fully in the elastic regime but at large applied strains their contribution to fracture can be relaxed considerably. Practical methods for inclusion of secondary strains within the strain-based FAD are then developed and shown to be conservative relative to some detailed finite element calculations.

Effect of reinforcement on plastic limit loads of branch junctions

Kim, Y.J.,Myeong, M.S.,Yoon, K.B. Applied Science Publishers ; Elsevier Science Ltd 2009 The International journal of pressure vessels and Vol.86 No.8

This paper provides effects of reinforcement shape and area on plastic limit loads of branch junctions under internal pressure and in-plane/out-of-plane bending, via detailed three-dimensional finite element limit analysis assuming elastic-perfectly plastic material behaviour. It is found that reinforcement is most effective when (in-plane/out-of-plane) bending is applied to the branch pipe. When bending is applied to the run pipe, reinforcement is less effective when bending is applied to the branch pipe. The reinforcement effect is the least effective for internal pressure.

Generation of plastic influence functions for J-integral and crack opening displacement of thin-walled pipes with a short circumferential through-wall crack

Park, J.S.,Choi, Y.H.,Im, S. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.117 No.-

Fracture mechanics parameters such as the J-integral and crack opening displacement (COD), are necessary for Leak-Before-Break (LBB) evaluation. The famous two estimation methods, the GE/EPRI and the Reference Stress Method (RSM), have their applicability limit with regard to the ratio of a pipe mean radius to thickness (R<SUB>m</SUB>/t). In order to extend their applicability limit to a thin walled pipe, several finite element analyses are performed for the J-integral and COD, and then new plastic influence functions are developed for thin-walled pipes with a short circumferential through-wall crack. With the newly generated plastic influence functions, the GE/EPRI and the RSM give closer results with those obtained from detailed finite element analyses. In addition, C*-integral and COD rate are estimated by using the new plastic influence functions and they are well matched with elastic-creep finite element analysis results under the power-law creep condition. Since the LBB concept can be applied to a piping system in a Korean Sodium-cooled Fast Reactor (SFR) which is designed to have thin-walled pipes and to operate in high temperature enough to cause creep, this paper can be applied for the LBB assessment of thin-walled pipes with a short through-wall crack in the SFR.

Knowledge based decision making method for the selection of mixed refrigerant systems for energy efficient LNG processes

Khan, M.S.,Lee, S.,Rangaiah, G.P.,Lee, M. Applied Science Publishers 2013 APPLIED ENERGY Vol.111 No.-

Mixed refrigerant (MR) systems are used in many industrial applications because of their high energy efficiency, compact design and energy-efficient heat transfer compared to other processes operating with pure refrigerants. The performance of MR systems depends strongly on the optimum refrigerant composition, which is difficult to obtain. This paper proposes a simple and practical method for selecting the appropriate refrigerant composition, which was inspired by (i) knowledge of the boiling point difference in MR components, and (ii) their specific refrigeration effect in bringing a MR system close to reversible operation. A feasibility plot and composite curves were used for full enforcement of the approach temperature. The proposed knowledge-based optimization approach was described and applied to a single MR and a propane precooled MR system for natural gas liquefaction. Maximization of the heat exchanger exergy efficiency was considered as the optimization objective to achieve an energy efficient design goal. Several case studies on single MR and propane precooled MR processes were performed to show the effectiveness of the proposed method. The application of the proposed method is not restricted to liquefiers, and can be applied to any refrigerator and cryogenic cooler where a MR is involved.

A review on carbon dioxide capture and storage technology using coal fly ash

Applied Science Publishers 2013 APPLIED ENERGY Vol.106 No.-

This work reviews the availability and the potential of the carbon capture and storage (CCS) technology using coal fly ash (FA). Because the technology can be effectively applied on-site to coal fired power plants and as FA contains sufficient alkali components, the technology may be another option of CCS technology to a limited extent. The technology can be divided into wet and dry processes. In the former, the available components for CCS in FA are leached into solution by the solvent where they are subsequently consumed for carbonation to store CO<SUB>2</SUB>. Particularly, the CO<SUB>2</SUB> storage capacity of CaO-enriched FA solution mixed with brine under high pressure may be equal to or greater than the true CO<SUB>2</SUB> emission reduction achieved by applying FA as a cement additive. In the dry process, FA can be used as a direct support or as the raw material of the sorbent supports for CO<SUB>2</SUB> capture. The dry process is effectively applied for CO<SUB>2</SUB> capture rather than storage because the sorbents should be regenerated. Another advantage of the technology is the stabilization of the harmful components present in FA, which are mostly co-precipitated with carbonated FA during the process.

Injection strategy for simultaneous reduction of NO_x and soot emissions using two-stage injection in DME fueled engine

Park, S.H.,Yoon, S.H. Applied Science Publishers 2015 APPLIED ENERGY Vol.143 No.-

The ultimate purpose of this study is the reduction of exhaust emissions from a dimethyl ether (DME) fueled diesel engine without deterioration of engine performance, such as indicated mean effective pressure (IMEP) and indicated specific fuel consumption (ISFC). In this study, we applied multiple injection strategies to achieve the research goal. In a comparison between diesel and DME single injection combustion, the IMEP in both fuels was similar around the top dead center (TDC) injection condition (this is the typical injection timing). However, the nitrogen oxide (NO<SUB>x</SUB>) emission in DME was higher than that in diesel. The single injection combustion in DME and diesel was compared on the basis of the same energy input condition. When the injection timing was advanced in order to reduce the DME NO<SUB>x</SUB> emission, the IMEP in DME decreased below the diesel level. Therefore, multiple injection strategies, including pilot injection, split injection, and advanced+post injection, were applied in this study. In the experimental results, the pilot injection strategy with advanced main injection (2<SUP>nd</SUP> injection) resulted in the lowest NOx, HC, and CO emissions. In the case of soot emission, DME itself has soot free combustion, and emitted an ignorable amount of soot. Moreover, the pilot injection strategy showed the highest IMEP level and the lowest ISFC level in the test conditions.

Limit loads and fracture mechanics parameters for thick-walled pipes

Kim, N.H.,Oh, C.S.,Kim, Y.J.,Kim, J.S.,Jerng, D.W.,Budden, P.J. Applied Science Publishers ; Elsevier Science Ltd 2011 The International journal of pressure vessels and Vol.88 No.10

In this paper, information on plastic limit loads and both elastic and elastic-plastic fracture mechanics parameters is given for cracked thick-walled pipes with mean radius-to-thickness ratios ranging from two to five. It is found that existing limit load expressions for thin-walled pipes can be applied to thick-walled pipes, provided that they are normalized with respect to the corresponding un-cracked thick-walled pipe values. For elastic fracture mechanics parameters, FE values of the influence functions for the stress intensity factor and the crack opening displacement are tabulated. For elastic-plastic J, it is shown that existing reference stress based J estimates can be applied, provided that a proper limit load for thick-walled pipes is used.

Economic evaluation for adoption of cogeneration system

Oh, S.D.,Oh, H.S.,Kwak, H.Y. Applied Science Publishers 2007 APPLIED ENERGY Vol.84 No.3

An optimal planning for gas turbine cogeneration system was applied to find whether or not the adoption of the system to an office building or hotel in Seoul, Korea is profitable. The planning problem considered in this study is to determine the optimal configuration of the system equipments and optimal operational policy of the system when the annual energy demands of electric power, heat and cooling are given a priori. The optimal configuration of the system equipments has been determined based on annual cost method with proper choice of representative energy demand patterns obtained for the building and hotel in a 1-year period. A mixed-integer linear programming and the branch and bound algorithm have been used to obtain the optimal solution. The planning method employed here may be applied to making decision on the adoption of the cogeneration plant to any specific office building or hotel.

Decentralized control of a scalable photovoltaic (PV)-battery hybrid power system

Kim, M.,Bae, S. Applied Science Publishers 2017 APPLIED ENERGY Vol.188 No.-

<P>This paper presents the design and control of a sustainable standalone photovoltaic (PV)-battery hybrid power system (HPS). The research aims to develop an approach that contributes to increased level of reliability and scalability for an HPS. To achieve such objectives, a PV-battery HPS with a passively connected battery was studied. A quantitative hardware reliability analysis was performed to assess the effect of energy storage configuration to the overall system reliability. Instead of requiring the feedback control information of load power through a centralized supervisory controller, the power flow in the proposed HPS is managed by a decentralized control approach that takes advantage of the system architecture. Reliable system operation of an HPS is achieved through the proposed control approach by not requiring a separate supervisory controller. Furthermore, performance degradation of energy storage can be prevented by selecting the controller gains such that the charge rate does not exceed operational requirements. The performance of the proposed system architecture with the control strategy was verified by simulation results using realistic irradiance data and a battery model in which its temperature effect was considered. With an objective to support scalable operation, details on how the proposed design could be applied were also studied so that the HPS could satisfy potential system growth requirements. Such scalability was verified by simulating various cases that involve connection and disconnection of sources and loads. The quantitative reliability analysis and verification results show that the proposed architecture with power control strategy provides a straightforward approach for designing a reliable and scalable PV-Battery HPS. Although PVs and batteries have been used in this paper, the design and control approach can be applied to other hybrid power systems (HPSs) that involve the connection of various power sources. (C) 2016 Elsevier Ltd. All rights reserved.</P>

A novel off-grid hybrid power system comprised of solar photovoltaic, wind, and hydro energy sources

Bhandari, B.,Lee, K.T.,Lee, C.S.,Song, C.K.,Maskey, R.K.,Ahn, S.H. Applied Science Publishers 2014 APPLIED ENERGY Vol.133 No.-

Several factors must be considered before adopting a full-phase power generation system based on renewable energy sources. Long-term necessary data (for one year if possible) should be collected before making any decisions concerning implementation of such a systems. To accurately assess the potential of available resources, we measured solar irradiation, wind speed, and ambient temperature at two high-altitude locations in Nepal: the Lama Hotel in Rasuwa District and Thingan in Makawanpur District. Here, we propose two practical, economical hybridization methods for small off-grid systems consisting entirely of renewable energy sources-specifically solar photovoltaic (PV), wind, and micro-hydro sources. One of the methods was tested experimentally, and the results can be applied to help achieve Millennium Development Goal 7: Ensuring environmental sustainability. Hydro, wind, and solar photovoltaic energy are the top renewable energy sources in terms of globally installed capacity. However, no reports have been published about off-grid hybrid systems comprised of all three sources, making this implementation the first of its kind anywhere. This research may be applied as a practical guide for implementing similar systems in various locations. Of the four off-grid PV systems installed by the authors for village electrification in Nepal, one was further hybridized with wind and hydro power sources. This paper presents a novel approach for connecting renewable energy sources to a utility mini-grid.