فصلنامه علوم و فناوری دریا
سال بیست و هفتم شماره 106 (تابستان 1402)

NC-OFDM systems are in the categorized under the cognitive radio systems and have been developed with the aim of utilizing unused frequency bands of communication channels in mission-oriented scenarios. In this paper, the issue of blind synchronization of NC-OFDM systems and their resiliency against jamming is investigated. In this regard, it is assumed that single-tone and multi-tone jamming is applied to the received signal at the receiver with a power much higher than the transmitted power of the main signal. Also, it is assumed that the receiver has no information about the synchronization sequence used in the transmitter and is also confused about the length of the cyclic prefix used by the transmitter. In this regard, a thirteen-step blind synchronization algorithm is provided, which, if used, the NC-OFDM system gains a high resistance to jamming and the bit error rate does not change due to jamming.

One of the main concerns of the design of vessels, especially the high-speed vessels, is the control of their motions at sea. Several practical methods, including the use of fin, trim tab, T-foil, and various other modalities have been studied so far. What has been specifically investigated in this study is the study of the effect of T-foil on the reduction of Heave and Pitch motions in regular waves with different wavelengths and angles of impact. For the analysis, the numerical modeling method was used with the computational fluid dynamics method and the STAR CC + software was used for all experiments. In this study, in the no-foil mode and in order to calibrate the software setup, a comprehensive study was performed on the effect of the number of meshes and the time-step for solving the problem and the numerical results were compared with the experimental results for the no-foil mode, which has very good convergence. Then, by studying the T-foil on the reduction of the Heave and Pitch motions of the catamaran , it was concluded that the T-foil had a much more favorable effect on the reduction of the Heave and Pitch motions at angles of impact near 180 °. This is due to the angle of impact of the foil to the surface of the foil, which creates a lifting force in front of the vessel , which is the basis for the reduction of Pitch motion and the creation of longitudinal anti-Pitch moment.

One of the influential factors in the design of types of breakwaters that are applied from the sea is the interaction between waves and breakwaters in ports. Failure to pay attention to the different characteristics of wave parameters leads to damage to the breakwater. Since the lack of wave penetration is considered as the main condition for the safety of the port, it is very important to determine and predict the wave interaction parameters with the breakwater. Therefore, in this study, the effective parameters of the wave have been classified using modeling and support vector learning machine. The results of this research show that the support vector machine has a suitable performance in classifying the effects of waves on the breakwater into two categories, favorable and critical. Also, among the three linear, polynomial and Gaussian kernels examined in this research, Gaussian kernel had the best performance with 98% accuracy.

Macroalgae are a natural and effective component in fresh water, coastal waters and estuaries, which are mainly useful in aquatic ecosystems. They are a source of nutrition for herbivoreand detrital food webs and are also an important habitat for fish and invertebrates. If macroalgae overgrow in an ecosystem, they can cause macroalgae blooms. In this review, an introduction about macroalgae, especially coastal macroalgae and their types, is given. After that, the factors causing macroalgae bloom as well as adsorption of nutrients and other contaminants by macroalgae have been investigated. The effects that macroalgal blooms can have on human health have also been reviewed. In addition, macroalgae can have many ecosystem and ecological effects. These effects as well as economic effects have also been investigated. Finally, predictions about the future of these macroalgal blooms are also reviewed.

Among the various types of insurances that surround human life in the present age, marine insurances are of particular importance in terms of historical antiquity and also the value of the subjects of this insurance. Therefore, the present study deals with the validation of the strategic model of value creation in the marine insurance industry with a focus on blockchain technology. The present research is an applied research in terms of its purpose and descriptive survey in terms of its method and nature. This research has been carried out in the framework of quantitative approach and using structural equation method. In order to collect data, a questionnaire based on the foundation's data method was distributed, and after data collection, data analysis was done using SMART PLS software. The statistical population studied in this research is the staff of Imam Khomeini Naushahr University of Marine Sciences. In order to estimate the minimum sample size, the formula for determining the sample size of Karjesi and Morgan was used and 144 people were selected by simple random method. In a small part, content and face validity have been confirmed through factor analysis. In order to confirm reliability, composite reliability was used using PLS software. The findings indicated the confirmation of all the assumptions of the proposed model. The general results showed that considering that transportation, especially marine, is gaining a stronger position in the international market day by day, as a result, it is very important to know the technology-based value creation strategies in marine insurance and to examine the strategic value creation structures of marine insurance .

The current research was conducted with the aim of identifying the major challenges of maritime transportation security and evaluating their importance in influencing the country's defense supply chain. This research is based on the purpose of "development-applied" research and in terms of nature is "descriptive-survey" which has a "mixed" approach. The statistical population of the study included 40 experts in the field of maritime security who have more than 20 years of service and a master's degree or higher. In the qualitative part, 10 of them were purposefully selected and in the quantitative part in a total. In order to collect real data, "field studies" were used using the tools of "semi-structured interview" and "closed questionnaire". The interview questions and the questionnaire were confirmed by experts in terms of both visual and content validity. Cronbach's alpha coefficient of the questionnaire was 0.89 and the retest reliability of the interview test was %81, which indicates acceptable reliability. With the "content analysis" of the interviews, 5 major challenges with 40 basic themes were identified, according to which the adjustment questionnaire and the extracted data were analyzed using "descriptive statistics" using SPSS software and in order to rank the importance of each. The themes identified in influencing the defense supply chain have also been exploited by the "Friedman test". According to the obtained results, the challenges of infrastructure threats, cyber-attacks, political-security and military attacks, piracy and piracy were identified as the most important major challenges of maritime security affecting the defense supply chain.

Today, naval power is not limited to military power and includes the dimensions of maritime science and knowledge, naval fleet, geopolitical capacities, maritime services and maritime industries. These dimensions and components have a special place in the maritime power of the country. In the past years, we have seen that different military and civilian maritime departments are moving things forward separately, and along with these organizations, policy makers and high-ranking officials of the country and the army have aligned and synergistic approaches to the issue of the sea, presence at sea, sea-oriented development and They have not developed the sea power of the country. In this research, with a mixed approach and contextual case method and interview and questionnaire tools, while explaining the components of maritime power, we have tried to express the position of these components in the maritime civilization of the country. Based on this, with library, comparative and exploratory studies, research literature was compiled. Then, the shortcomings of the findings were completed using the opinions of experts and a number of new factors were added to the previous factors. Then, a research questionnaire was prepared, which was distributed among the research sample population and its results were summarized by going through the relevant steps and obtaining the necessary validity and reliability. In the following, the findings obtained from the results of the questionnaires, together with the analysis of discourse and the content of the interviews, were analyzed with descriptive statistics, SPSS software and inferential statistics methods using "SmartPLS" software. Finally, the dimensions and components of the maritime power of the Islamic Republic of Iran and the coefficients and priority of their influence on the implementation of the country's maritime civilization were determined. The five dimensions counted, in order of priority of impact, are: marine services, marine fleet, marine industries, capacities of political geography and marine sciences, each of which has components (60 components in total). At the end of the research, recommendations were made for establishing the maritime civilization of the country based on these dimensions and components.

A crisis is a condition that occurs due to the sudden occurrence of natural and unnatural incidents and events, disrupts human life and imposes a lot of damage, so that dealing with it requires the mobilization of resources and the implementation of basic and extraordinary measures compared to the normal state. Based on this, the main goal of this research is to investigate the effect of military mobile logistics on the crisis management of natural disasters in Nadaja preparedness systems. This research is based on the purpose of applied type and from the perspective of descriptive-survey research method and its investigation is also field. The statistical population of this research is all 120 officers of Amadi Nadaja, of which 92 people were selected as a sample using the Karjesi and Morgan table using the random sampling method. By examining the documents, texts, articles and theories presented in the field of logistics, the components affecting military mobile logistics were selected as responsibility (responsiveness), thrift, readiness, efficiency, information and technology, unity of purpose and timeliness. In order to investigate the effect of these components on natural disaster crisis management and its dimensions (prevention and reduction, preparedness, response and recovery and reconstruction), suitable hypotheses should be formulated. In this regard, one main hypothesis and seven sub-hypotheses were formulated and distributed among the statistical population of this research using the questionnaire made by the researcher of military mobile logistics with 27 items and the Kamani crisis management questionnaire (year 2008) with 32 items. The validity of the questionnaires was confirmed based on face validity and elite opinion and reliability based on Cronbach's alpha of 0.78 (military mobile logistics) and 0.85 (natural disaster crisis management). The obtained information was analyzed by the statistical method of structural equations with the help of PLS software. The results of the research indicate that the components of military mobile logistics have an impact on the success of natural disaster crisis management.