Simulation-Transactions of the Society for Modeling and Simulation International最新文献

筛选
英文 中文
V2X-assisted emergency vehicle transit in VANETs v2x辅助的VANETs紧急车辆运输
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-11-14 DOI: 10.1177/00375497231209774
Hasita Kaja, Jacob M Stoehr, Cory Beard
{"title":"V2X-assisted emergency vehicle transit in VANETs","authors":"Hasita Kaja, Jacob M Stoehr, Cory Beard","doi":"10.1177/00375497231209774","DOIUrl":"https://doi.org/10.1177/00375497231209774","url":null,"abstract":"Vehicular ad hoc networks (VANETs) can support safety-critical applications such as the safe and fast movement of emergency vehicles while preventing crashes, delays, and congestion involving emergency vehicles. A simulation approach to evaluate ambulance transit using VANET capabilities is presented in this paper for a real-life road network taken in and around the University of Missouri–Kansas City, USA. Three different VANET functional scenarios are compared with a base scenario (SC-1) which depicts the present-day traffic pattern and vehicle behaviors. In the three scenarios, the second one (SC-2) adds vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications along with the present-day traffic pattern; ambulances use VANETs simply to announce their arrival. The third scenario (SC-3) provides functionalities for ambulances to rerouting when they learn about a current or an anticipated road congestion. And the fourth scenario (SC-4) adds vehicle rerouting capabilities, so ambulance routes can be sent to vehicles, and they can avoid the ambulance path. Performance results are presented and evaluated for metrics such as delay, packet drop ratio, the average speed of the ambulance, average vehicle density, and ambulance message interval time. From the simulation results, it was observed that the ambulance transit time reduces by 12.52%, 14.65%, and 18.75% for SC-2, SC-3, and SC-4, respectively, as compared with SC-1, while the average ambulance speed increases by 14.49%, 15.57%, and 20.90% for SC-2, SC-3, and SC-4, respectively, when compared with SC-1. This paper provides substantial evidence that VANET capabilities for emergency vehicles can enhance crash protection and reduce the commute time for emergency response.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"6 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134991850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Validity Frame–enabled model-based engineering processes 有效性框架支持的基于模型的工程流程
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-11-08 DOI: 10.1177/00375497231205035
Bert Van Acker, Paul De Meulenaere, Hans Vangheluwe, Joachim Denil
{"title":"Validity Frame–enabled model-based engineering processes","authors":"Bert Van Acker, Paul De Meulenaere, Hans Vangheluwe, Joachim Denil","doi":"10.1177/00375497231205035","DOIUrl":"https://doi.org/10.1177/00375497231205035","url":null,"abstract":"Model-based systems engineering (MBSE) focuses on using models to support the design, optimization, simulation, and ultimately deployment of complex cyber-physical systems (CPSs). These models enable reasoning about and predicting the behavior of the (realized) real-world system in silico. The value of using such (predictive) model depends on its validity against its real-world counterpart. As such, the validity context of a model is critical to ensure correct model use. Reasoning on validity is only possible if the validity of the model was captured explicitly at design time. In previous work, the validity frame (VF) was presented as a way to explicitly capture a model’s validity; however, no guidance on the integration process within MBSE processes was given. Within this article, we present the creation and evolution of the model and its VFs to ensure model validity consistency and completeness. This evolution results in a set of interrelated models and VFs. By capturing these relations, we create a lightweight frame-enabled library of model variants. We show our contribution using an F1/10 vehicle simulation test bench.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"5 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135390751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Development of an agent-based model incorporating Function–Behavior–Structure framework to enable systems engineering design process evaluation 结合功能-行为-结构框架的基于主体的模型的开发,使系统工程设计过程评估成为可能
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-11-04 DOI: 10.1177/00375497231207877
Mitch Bott, Bryan Mesmer
{"title":"Development of an agent-based model incorporating Function–Behavior–Structure framework to enable systems engineering design process evaluation","authors":"Mitch Bott, Bryan Mesmer","doi":"10.1177/00375497231207877","DOIUrl":"https://doi.org/10.1177/00375497231207877","url":null,"abstract":"An important step in the development of any process is evaluation. Evaluation ensures that the process affects effectiveness, efficiency, or other metrics as designed. Without evaluation, processes must stand solely on the theories, axioms, and/or heuristics that formed them. Outcome or objectives-based evaluations are especially useful in seeing if the expected impact is realized. Systems and design engineering present problems for outcome evaluations due to system design efforts being long in duration, expensive, organization/team specific, and environment/context specific. These characteristics make repeating the same effort under the same conditions using different processes difficult, if not impossible. While a comparison of processes for evaluation in a real application may not be feasible, a simulation of the processes with agents that capture system design behaviors may produce findings to support hypotheses. This paper examines the use of agent-based modeling and simulation to compare pseudo-waterfall and pseudo-agile engineering processes for a simple design problem. The Function–Behavior–Structure (FBS) model of design is used along with empirical data from FBS studies to examine the performance of a two-person design team using pseudo-waterfall and pseudo-agile engineering processes. The results of this exercise show possible advantages of agile-like processes in total time to complete the design.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"6 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135773535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Mitigating the negative impact of new buildings on existing buildings' user comfort-a case study analysis. 减轻新建建筑对现有建筑用户舒适度的负面影响——案例分析。
IF 1.6 4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-11-01 Epub Date: 2022-06-07 DOI: 10.1177/00375497221101062
Vinu Subashini Rajus, Nicolas Arellano Risopatron, William O'Brien, Gabriel Wainer, Stephen Fai
{"title":"Mitigating the negative impact of new buildings on existing buildings' user comfort-a case study analysis.","authors":"Vinu Subashini Rajus,&nbsp;Nicolas Arellano Risopatron,&nbsp;William O'Brien,&nbsp;Gabriel Wainer,&nbsp;Stephen Fai","doi":"10.1177/00375497221101062","DOIUrl":"10.1177/00375497221101062","url":null,"abstract":"<p><p>Campus master plans are released every few years for developing and implementing its physical infrastructure. Open spaces, compactness, connectivity, greenness, and environmental impact have often been the focus on its framework. In particular, the effect of new building development on existing buildings' occupant comfort and design intent is mostly ignored. Providing guidelines to retain existing users' comfort for stakeholders involved in design decision making will result in improved design decisions. Hence, this research aims to provide a work methodology to mitigate the adverse effects of new buildings on existing buildings' user comfort through a case study at Carleton University. The case study shows a methodology to retain the existing users' comfort by analyzing Carleton University's master plan on massing studies, occupant survey to understand their comfort needs, performance analysis of the impact of the new building on the existing building user comfort. The analysis reveals the key parameters to consider in design for occupants' comfort. Finally, the research reinforces the generative design and the need for dynamic modeling in campus master plans to mitigate the negative implications of new development on occupants' comfort.</p>","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"99 11","pages":"1095-1115"},"PeriodicalIF":1.6,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ftp.ncbi.nlm.nih.gov/pub/pmc/oa_pdf/94/54/10.1177_00375497221101062.PMC10584660.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49693340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Dynamical simulation of the Syrian refugee crisis: quantifying the driving factors of forced migration 叙利亚难民危机的动态模拟:量化强迫移民的驱动因素
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-10-30 DOI: 10.1177/00375497231203708
Danilo R Diedrichs, Avyi Hill, Yeting Li, Amelia Miller Schubert
{"title":"Dynamical simulation of the Syrian refugee crisis: quantifying the driving factors of forced migration","authors":"Danilo R Diedrichs, Avyi Hill, Yeting Li, Amelia Miller Schubert","doi":"10.1177/00375497231203708","DOIUrl":"https://doi.org/10.1177/00375497231203708","url":null,"abstract":"With over 21 million refugees at the end of 2021, forced migration across national borders has become a global reality and a major international policy issue. This paper proposes a dynamical model based on the Syrian Refugee Crisis to quantify the factors that influence a refugee’s decision to migrate and the destination choice. The model simulates refugee migrations in space and time, from the moment they flee their country of origin until they are granted asylum in a host country or lose refugee status by attrition or repatriation. Migration is driven by comparative attractiveness scores based on differences in quality of life, political stability, societal violence, cultural familiarity, and distance between countries, while accounting for risk aversion and psychological inertia. By comparing simulation results to United Nations High Commissioner for Refugees (UNHCR) data, we determine weight parameters that quantify the relative importance of each attribute in inducing a migration flow. The model is a computationally efficient forecasting and ex-post analysis tool, providing insight into the dynamics of refugee flow and effect of immigration policies.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136102311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Special issue: Recent advances in simulation for architecture and urban design 特刊:建筑和城市设计模拟的最新进展
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-10-17 DOI: 10.1177/00375497231207402
Gabriel Wurzer
{"title":"Special issue: Recent advances in simulation for architecture and urban design","authors":"Gabriel Wurzer","doi":"10.1177/00375497231207402","DOIUrl":"https://doi.org/10.1177/00375497231207402","url":null,"abstract":"","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"218 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136037602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Freeway work zone effects on vehicular fuel consumption explored by a four-lane model 基于四车道模型的高速公路工作区域对车辆燃油消耗的影响
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-09-26 DOI: 10.1177/00375497231198859
Zhongmin Huang, MN Smirnova, Jiarui Bi, NN Smirnov, Zuojin Zhu
{"title":"Freeway work zone effects on vehicular fuel consumption explored by a four-lane model","authors":"Zhongmin Huang, MN Smirnova, Jiarui Bi, NN Smirnov, Zuojin Zhu","doi":"10.1177/00375497231198859","DOIUrl":"https://doi.org/10.1177/00375497231198859","url":null,"abstract":"A four-lane model is put forward to explore the effects on vehicular fuel consumption of a freeway work zone which has a length of 100 m and occupies lanes III and IV. The model equations are solved numerically in the simulation of vehicular flows by a method called WENO5–RK3. A vehicular fuel consumption model is presented, with an additional fuel consumption defined in comparison with the case in the absence of a work zone. Simulation results show that the freeway work zone affects vehicular fuel consumption significantly, triggers a traffic jam as soon as initial density normalized by jam density is beyond 0.18.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134958337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Trade-off between time and cost in project planning: a simulation-based optimization approach 项目规划中时间和成本的权衡:基于模拟的优化方法
4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-09-18 DOI: 10.1177/00375497231196889
Sena Senses, Mustafa Kumral
{"title":"Trade-off between time and cost in project planning: a simulation-based optimization approach","authors":"Sena Senses, Mustafa Kumral","doi":"10.1177/00375497231196889","DOIUrl":"https://doi.org/10.1177/00375497231196889","url":null,"abstract":"Mine development or construction projects should be carefully scheduled to meet the project objectives in terms of duration, budget, and scope since they include many highly time- and cost-sensitive activities. The inherent complexity in mining operations, coupled with material, equipment, and resource availabilities, commodity price cyclicality, and market trend uncertainties, can lead to a high risk to the project, resulting in schedule and cost overruns. Therefore, these projects must be planned and controlled efficiently to ensure that the required capital investment does not exceed the project budget and the project deadline is met. This paper proposes a simulation-based model to optimize the trade-off between time and cost of project planning problems under uncertainty. In doing so, equally probable realizations are generated considering different project duration crashing scenarios to quantify the impact of uncertainty on the total project cost and project completion time, and risks are assessed. A numerical example is provided to show the performance of the proposed approach through an underground mine development project. Statistical analysis of the results obtained from the developed simulation model identifies the risk of project completion time, the criticality of activities, and bottleneck activities of the project. In addition, the time–cost trade-off is achieved under the project deadline and budget constraints by implementing 20,736 different crashing scenarios. Finally, the results obtained from the developed formulation are compared with those obtained from the linear programming solution. The proposed approach has a strong potential to add value to project management of mining projects.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135206392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
A numerical investigation on indoor air ventilation design and aerosol transportation: a case study in a hospital hall 室内通风设计与气溶胶输送的数值研究:以某医院大厅为例
IF 1.6 4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-09-06 DOI: 10.1177/00375497231194348
Hongxin Yang, Xue Luo, Bin Chen, Heping Xie, Li Huang, Qiangqiang Shi, Yuanzhi Zhang, Meng Ni
{"title":"A numerical investigation on indoor air ventilation design and aerosol transportation: a case study in a hospital hall","authors":"Hongxin Yang, Xue Luo, Bin Chen, Heping Xie, Li Huang, Qiangqiang Shi, Yuanzhi Zhang, Meng Ni","doi":"10.1177/00375497231194348","DOIUrl":"https://doi.org/10.1177/00375497231194348","url":null,"abstract":"The transportation of indoor aerosol particles is closely related to the infection risk of various viruses. When the pandemic of COVID-19 is anticipated to coexist with human beings in the future, the design of airflow distribution in public buildings becomes more vital not only for thermal comfort but also for epidemic prevention through controlling indoor aerosol transportation. In this paper, the conditioning of indoor air in a hospital hall (Chongzhou Traditional Chinese Medicine Hospital in Chengdu, China) is case studied by numerically simulating the indoor thermal comfort and the aerosol transportation process analysis. Simulation results indicate that thermal comfort can be first achieved by appropriate air supply forms in summer. Under the combined operation of the nozzles, square diffusers, and the breathing plane, with an average velocity of 0.26 m/s, the average temperature, and the average air age are 23.43°C and 949.59 s, respectively. Second, the arrangement of air-exhaust outlets in this hospital hall is also redesigned and simulated with three new schemes of outlets design, of which the floor exhaust scheme is optimal with the fastest aerosol discharge speed (thus the strongest pollutant discharge capacity), i.e., 62% of aerosol particles discharged in 30 s and 99% of particles discharged in 150 s. This study makes a successful attempt to optimize indoor air ventilation for preventing airborne transmission of viruses, e.g., COVID-19, offering a feasible scheme for the air distribution design in densely populated areas such as hospital halls.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"111 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89190016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Agent-based simulation of seismic crisis including human behavior: application to the city of Beirut, Lebanon 包括人类行为在内的基于agent的地震危机模拟:在黎巴嫩贝鲁特市的应用
IF 1.6 4区 工程技术
Simulation-Transactions of the Society for Modeling and Simulation International Pub Date : 2023-09-01 DOI: 10.1177/00375497231194608
Rouba Iskandar, Julie Dugdale, Elise Beck, Cécile Cornou
{"title":"Agent-based simulation of seismic crisis including human behavior: application to the city of Beirut, Lebanon","authors":"Rouba Iskandar, Julie Dugdale, Elise Beck, Cécile Cornou","doi":"10.1177/00375497231194608","DOIUrl":"https://doi.org/10.1177/00375497231194608","url":null,"abstract":"Earthquake simulations at the urban scale usually focus on estimating the damages to the built environment and the consequent losses without fully taking into account human behavior in crisis. Yet, human behavior is a key element for improving crisis disaster management; therefore, it is important to include it in seismic crisis simulations. In this study, an agent-based model for the simulation of pedestrian evacuation during earthquakes at the city scale is developed following an interdisciplinary approach. The model recreates the urban conditions using Geographic Information System (GIS) and a synthetic population, in addition to the earthquake consequences on the urban fabric. Moreover, the model integrates realistic human behaviors calibrated using quantitative survey results. We simulate pedestrian outdoor mobility with the different constraints that affect it such as the topography and the presence of debris. The simulator is applied to the case of Beirut, Lebanon. A what-if approach is adopted to analyze the population’s safety in case of earthquakes in Beirut, particularly the open spaces’ capacity to provide shelters and the effect of debris and realistic human behaviors on people’s safety. The simulation results show that less than 40% of the population is able to arrive at an open space within 15 min after an earthquake. This number is further reduced when some open spaces are locked. Debris and realistic human behaviors significantly delay the arrivals to safe areas and, therefore, should not be neglected in earthquake simulations.","PeriodicalId":49516,"journal":{"name":"Simulation-Transactions of the Society for Modeling and Simulation International","volume":"10 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82599876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
相关产品
×
本文献相关产品
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信