Strojniški vestnik – Journal of Mechanical Engineering最新文献

{"title":"Experimental Investigation of an Automotive Air Conditioning System Using R444A and R152a Refrigerants as Alternatives of R134a","authors":"M. Di̇rek, M. S. Mert, Eren Soylu, F. Yüksel","doi":"10.5545/sv-jme.2019.6040","DOIUrl":"https://doi.org/10.5545/sv-jme.2019.6040","url":null,"abstract":"The European Union brings some restrictions to the use of some refrigerants, which has been higher than 150 global warming potential (GWP) value, in mobile air conditioning (MAC) systems as in directive no 2006/40/EC [1]. Then these GWP limits were extended air conditioning and refrigeration systems with regulation the Regulation (EU) No, 517/2014 [2]. Presently, most of the MAC systems use R134a as the refrigerant; however, the GWP value of the R134a is 1300 [3] and [4]. The refrigerants such as R1234yf, R1234ze(E), R152a and R444A, can be considered as alternative refrigerants having low GWP for automotive air conditioning systems. Table 1 shows the thermophysical properties of the above-mentioned refrigerants. Among them, R1234ze(E) can be used instead of R134a due to the their similar properties [5]. However, the cooling performance of R1234ze(E) is 30 % lower in average than that of R134a when used in a similar medium capacity vapor compression system [6] to [8]. Furthermore, the performance of R1234ze(E) can be improved when the mixture of some refrigerants used to obtain required properties. The R444A consists of 83 % R1234ze(E), 12 % R32 and 5 % R152a, (by mass) and its GWP value is 93 [4] and [9] which meets the European regulations. Devecioğlu and Oruç [10] calculated the performance parameters of R1234yf, R444A and R445A for a MAC system. It was found that the R444A and R445A have lower cooling capacity, but higher coefficient of performance (COP) than that of R1234yf. Lee et al. [11] investigated the performance of R444A, R445A, R152a, and R1234yf in an automotive air conditioning (AAC) system as an alternative to R134a. The highest COP was obtained when the system was working with R152a. Cheng et al. [9] tested an air source heat pump (HP) system using the different concentrations of R32/R1234ze(E) mixture numerically. It was determined that the heating and cooling capacities were improved compared to the R134a baseline system. Meng et al. [12] determined the performance of a refrigeration system using the mixture of R152a and R1234ze(E) refrigerants as an alternative to R134a. The mixture of 50 % R1234ze(E) and 50 % R152a was found to be the best alternative for R134a. It was demonstrated that the cooling capacity of R1234ze(E)/R152a mixture was very similar to R134a and can be used without any change in the compressor. Li et al. [13] reported that R134a Experimental Investigation of an Automotive Air Conditioning System Using R444A and R152a Refrigerants as Alternatives of R134a Direk, M. – Mert, M.S. – Soylu, E. – Yüksel, F. Mehmet Direk* – Mehmet Selçuk Mert – Eren Soylu – Fikret Yüksel Yalova University, Faculty of Engineering, Turkey","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128951799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Feature Enhancement Method for Drilling Vibration Signal by Using Wavelet Packet Multi-band Spectral Subtraction","authors":"Youhang Zhou, Yong Li, Hanjiang Liu","doi":"10.5545/SV-JME.2018.5726","DOIUrl":"https://doi.org/10.5545/SV-JME.2018.5726","url":null,"abstract":"According to the change in contact position between the drill edge and the workpiece, drilling machining is classified into three stages, namely, drilling guide, drilling, and drilling out [1]. In the monitoring of drilling, the signal features corresponding to the previous stage are extracted, and the mapping model is established to monitor the drilling process [2]. This can lay a theoretical foundation for realizing highprecision drilling quality analysis; the premise is how to achieve feature enhancement by implementing signal de-noising effectively in a complicated drilling environment. As it is an advanced sensor-and-signal processing technology, a growing number of scholars have been extensively adopting various kinds of sensors to ascertain the drilling process and drilling quality. The monitoring and prediction of tool wear and breakage in drilling are mainly done indirectly through thrust force [3] to [5]. Ferreiro et al. [6] and [7] and Peña et al. [8] completed the burr monitoring by extracting the features from the spindle torque signal in the drilling process. Ramirez et al. [9] established a temperature model for the drilling tool and combined the cutting force signal and temperature signal characteristics to evaluate the surface quality of the drilled surface. Xiao et al. [10] via constructing a valuable indicator, i.e., the wavelet energy ratio around the natural frequency of boring bar vibration signal to monitor tool wear and surface finish quality for deep hole boring, developed a method to monitor and evaluate tool wear during drilling through the monitoring of vibration and acoustic emission signals [11] and [12]. It is well known that the key to achieving the quality monitoring of drilling is to extract abnormal features from the monitoring signals, but the signal features representing drilling quality are often very weak, so it is necessary to pre-process the signal to intensify its features. The above researches on abnormal state monitoring and diagnosis during the machining process can be divided into two classifications: extracting the evident features of monitoring signals to determine abnormal tool damage and drilling quality, and ascertaining the tool wear and the quality of drilling trends by anatomizing the overall monitoring signal. The results of these studies have good guidance significance to ensure high-precision drilling quality. However, they cannot predict or inform when and where tool breakage and quality is abnormal. Therefore, it is of great necessity to ascertain the feature extraction problem of the drilling process signal, establish a mapping model of the monitoring signal and the drilling process, and accurately identify the time and location of abnormal Feature Enhancement Method for Drilling Vibration Signals by Using Wavelet Packet Multi-band Spectral Subtraction Zhou, Y. – Li, Y. – Liu, H. Youhang Zhou1,2,* – Yong Li1 – Hanjiang Liu1 1Xiangtan University, School of Mechanical Engineering, China 2X","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"24 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133846435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Research on Surface Roughness of Hardox Steels Parts Machined by Abrasive Waterjet","authors":"A. Filip, C. Morariu, L. Mihail, G. Oancea","doi":"10.5545/SV-JME.2019.5998","DOIUrl":"https://doi.org/10.5545/SV-JME.2019.5998","url":null,"abstract":"","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"92 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124707784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Functionality assessment of building a micro-climate system utilising solar energy in a cold climate","authors":"K. Januševičius, Juozas Bielskus, V. Martinaitis","doi":"10.5545/SV-JME.2018.5910","DOIUrl":"https://doi.org/10.5545/SV-JME.2018.5910","url":null,"abstract":"In September 2015, the United Nations (UN) Assembly approved the sustainable development agenda [1]. According to this agenda, member countries must take action in order to improve the sustainability of the planet. Goals up until the year 2030 were set. Multiple aspects of the 17 sustainable development goals determined by the UN were aimed at increasing the utilisation of renewable energy and improving energy efficiency [2]. It is clear that these goals could only be met by using complex measures, in terms of the most influential consumers, i.e. the built environment, due to its high environmental impact [3]. In EU households, heating and hot water alone account for 79 % (in industry 70.6 %) of total final energy consumption. Thus, it is important to focus on heating demands [4]. Approximately 84 % of heating and cooling is still generated from fossil fuels, while only 16 % is generated from renewable energy. In order to fulfil the EU’s climate and energy goals, the heating and cooling sector must sharply reduce its energy consumption and decrease its use of fossil fuels [5]. Integrated design efficiency and final product quality are highly dependent on primary actions at the initial stages of any project. According to value engineering principles [6], a function could be satisfied in different ways that allow for different performances. Those aspects determine the pathway characterized by [7], which specified that alternatives should be considered at the initial stage of design. In this phase, solutions can be integrated at the lowest resource cost. In this context, the cost of considering different design alternatives becomes an important aspect of an efficient design process. When designing sustainable buildings, passive and active energy conservation solutions, in combination with renewable energy utilisation, play an important role. The primary function of a complex microclimate Functionality Assessment of Building a Microclimate System Utilising Solar Energy in a Cold Climate Januševičius, K. – Bielskus, J. – Martinaitis, V. Karolis Januševičius1,* – Juozas Bielskus2 – Vytautas Martinaitis1 1 Vilnius Gediminas Technical University, Faculty of Environmental Engineering, Lithuania 2 Vilnius Gediminas Technical University, Civil Engineering Research Centre, Lithuania","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131928030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Coating Thickness on a Solid-Liquid Two-Phase Flow Centrifugal Pump under Water Medium","authors":"Kaikai Luo, Yong Wang, Hou-lin Liu, M. Dular, Jie Chen, Zi-long Zhang","doi":"10.5545/SV-JME.2018.5865","DOIUrl":"https://doi.org/10.5545/SV-JME.2018.5865","url":null,"abstract":"Spraying a coating on the surface of wet parts of a solid-liquid two-phase flow centrifugal pump could effectively increase its service life. To research the effect of coating thickness on the performance of the pump, a solid-liquid two-phase flow pump with a speed of n s = 81.5 was chosen, and polyurethane coatings with different thicknesses were sprayed on the surface of the blades of the impeller. The influence of coating thickness on the performance of the pump was tested under the condition of a water medium. Combined with numerical simulation, the internal flow, pressure fluctuations and radial force of the model pump were further analysed in detail. Keeping the blade outlet angle unchanged, the head and efficiency of the pump decrease with the increase of the coating thickness, and the amplitude of the decrease increases with the increase of the coating thickness. The peak value of pressure fluctuations increases with the increase of coating thickness. The pressure value on the impeller inlet increases first and then decreases with the increase of coating thickness. Radial force of impeller increases with the increase of coating thickness, and the radial force distributes in the triangle, which is the same as the number of blades.","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130159892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Active Structural Derivator in the Design Crystallization Phase of L7e Vehicle Structures","authors":"Roman Pawel Jedrzejczyk, M. Alb","doi":"10.5545/sv-jme.2018.5788","DOIUrl":"https://doi.org/10.5545/sv-jme.2018.5788","url":null,"abstract":"","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122993121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of Contaminated Fluid on the Working Performances\u0000of Hydraulic Directional Control Valves","authors":"Velibor Karanović, M. Jocanović, S. Baloš, D. Knežević, I. Macuzic","doi":"10.5545/sv-jme.2018.5856","DOIUrl":"https://doi.org/10.5545/sv-jme.2018.5856","url":null,"abstract":"0 INTRODUCTION It is very difficult to predict and precisely determine the impact of fluid cleanliness on the system operation or its components, due to many factors and a variety of hydraulic system applications. The hydraulic fluid contamination is an issue that can shorten the working life of hydraulic components, which has a direct impact on maintenance costs [1] to [3]. Also, contamination can be considered as a hydraulic system “intruder”, which has a direct or indirect influence on system behaviour and parameters such as precision, response time, repeatability, controllability, etc. [4] and [5]. Many well-regarded companies and other institutions dealing with manufacturing, maintenance and testing of hydraulic systems and equipment, based on their own experience from practice and experimental research, claim that the working fluid contamination represents the main cause of failures in 70 % to 80 % cases [2] and [6] to [9]. Additionally, the requirements for more precise control and higher efficiency of hydraulic systems, have resulted in the decreased clearances between working elements of hydraulic components and the increased working pressure values [10]. Due to the decreased clearance size, the adverse impact of micron-size solid contaminants becomes evident. Although it is wellknown that solid contaminants are destructive to hydraulic system components, as well as to the working fluid itself, there was no internationally accepted method for objectively determination of contamination tolerance for systems or each component separately [11], until 2017. In 2013, was initiated and consequently published ISO 12669:2017 standard, developed for determining the required cleanliness level (RCL) for a system [12]. This standard is now under review for five years period. Due to the lack of a standard procedure, the RCL choice is based on the system designer experience or on the third person recommendation (such as components manufacturer) and his experience. This doesn’t mean that optimal cleanliness level was selected for the specific system operation. The RCL selection by this method is strongly subjective, for which reason it does not provide consistency. Consequently, many system designers, as well as the users of hydraulic systems, are unsure and confused about the appropriate cleanliness level Impact of Contaminated Fluid on the Working Performances of Hydraulic Directional Control Valves Karanović, V. – Jocanović, M. – Baloš, S. – Knežević, D. – Mačužić, I. Velibor Karanović1,* – Mitar Jocanović1 – Sebastian Baloš1 – Darko Knežević2 – Ivan Mačužić3 1University of Novi Sad, Faculty of Technical Sciences, Serbia 2University of Banja Luka, Faculty of Mechanical Engineering, Bosnia and Herzegovina 3University of Kragujevac, Faculty of Engineering, Serbia","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114861063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An Exacting Wall-Penetration Pipe Analysis","authors":"P. Koc","doi":"10.5545/SV-JME.2018.5651","DOIUrl":"https://doi.org/10.5545/SV-JME.2018.5651","url":null,"abstract":"Existing piping systems sometimes need to operate at larger mechanical loads than they are originally designed to. Often, these beyond-the-original-design loads lessen the margin against piping failure so much that performing recalculations using original analysis methods cannot qualify the pipeline. To demonstrate suitability of the existing pipeline to increased loads and to avoid piping hardware modification, more advanced analysis methods need to be employed. In this paper, a single detail from the beyondthe-original-design analysis [1] of a buried thin-wall water pipeline in nuclear power plant (NPP) Krško is shown. That analysis, the description of which is beyond the aim of this paper, demonstrated that the most critical part of the system is the penetration of the buried pipeline into a power plant’s concrete building. Namely, because of a supposed beyond-theoriginal-design earthquake, relative displacements between the building’s basement wall and the surrounding soil evolve, which in turn imposes large deformation on a buried pipe at the site of the building wall’s penetration. The most significant mode of deformation is pipe denting at the pipe-to-concretewall seal location. Pipe denting strongly influence pipeline’s strength and fatigue life; therefore, the topic was addressed by researchers in the past [2] and [3] and is still attractive today [4] to [6]. The solutions to the problem are in the form of a pure theoretic analysis [2], or as guides extracted from recapitulation of many experiments [3], or, recently, from experiments supplemented with numerical analyses [4] to [6]. All researchers agree that the excessive size of the dent, the abrupt change of the dented surface curvature and the pre-existing pipe damage on the dent spot severely lessen pipe strength and fatigue life. Because the denting is a problem still under research, it is not included in piping structural design codes yet, therefore leaving the structural engineer on thin ice. The aim of this paper is twofold: describing the experimental-numerical analysis of the dented section of a pipeline at NPP Krško and demonstrating the pipeline qualification with the applicable American Society of Mechanical Engineers (ASME) Code [7] (which is the obligatory code for NPP Krško), although no rule regarding dents is given in [7]. An Exacting Wall-Penetration Pipe Analysis Koc, P. Pino Koc* University of Ljubljana, Faculty of Mathematics and Physics, Slovenia","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134146026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical and Experimental Study of a Novel Valve Using the Return Stream Energy to Adjust the Speed of a Hydraulic Actuator","authors":"G. Filo, E. Lisowski, D. Kwiatkowski, J. Rajda","doi":"10.5545/SV-JME.2018.5823","DOIUrl":"https://doi.org/10.5545/SV-JME.2018.5823","url":null,"abstract":"This article discusses the possibility of increasing the speed of movement of a single-sided hydraulic cylinder piston rod using a fluid stream from the return line. Directing the return stream back to the supply line instead of the fluid reservoir causes significant increase in the inflow rate to the actuator. This situation may arise when the piston rod of the cylinder is not fully loaded on part of the movement range. As part of this work, we proposed a solution in the form of a novel control valve, consisting of a throttle valve and a differential valve controlled by the pressure difference between the supply line and the return line. A geometric model was created using SolidWorks, then a simulation model was made in Matlab/Simulink. Next, simulations were carried out to prove that the use of the return fluid stream gives a possibility of a significant increase in the piston rod speed. The results of the numerical analyses were verified on a test bench where the valve prototype was tested. Speed characteristics of the piston rod against both payload force and throttle valve setting were determined. High convergence with the simulation results was obtained. It has also been confirmed that the proposed solution can be advantageous in practical applications.","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122520215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-Objective Optimization of the Dressing Parameters in Fine Cylindrical Grinding","authors":"Irina Stefanova Aleksandrova","doi":"10.5545/sv-jme.2018.5677","DOIUrl":"https://doi.org/10.5545/sv-jme.2018.5677","url":null,"abstract":"The optimum conditions for dressing grinding wheels determined and recommended in the literature are valid only for particular types and tools of dressing and grinding. In this paper, an attempt has been made to optimize the dressing process parameters in fine cylindrical grinding. To define the optimum values of the dressing process variables (radial feed rate of diamond roller dresser frd , dressing speed ratio qd , dress-out time td , diamond roller dresser grit size/grinding wheel grit size ratio qg , type of synthetic diamonds and direction of dressing), a multi-objective optimization has been performed based on a genetic algorithm. In the capacity of the optimization parameter, a generalized geometric-mean utility function has been chosen, which appears to be a complex indicator characterizing the roughness and accuracy of the ground surface, the grinding wheel lifetime and the manufacturing net costs of the grinding operation. The optimization problem has been solved in the following sequence: 1) a model of the generalized utility function has been created reflecting the complex effect of the dressing system parameters; 2) the optimum conditions of uni-directional and counter-directional dressing of aluminium oxide grinding wheels by experimental diamond roller dressers of synthetic diamonds of АС32 and АС80 types and different grit size at which the generalized utility function has a maximum have been determined; 3) a Pareto optimum solution has been found (frd = 0.2 mm/min; qd = 0.8; td = 4.65 s; qg = 2.56), which guarantees the best combination between the roughness and the deviation from cylindricity of the ground surface, the grinding wheel lifetime and the manufacturing net costs of the grinding operation.","PeriodicalId":135907,"journal":{"name":"Strojniški vestnik – Journal of Mechanical Engineering","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123972102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}