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<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" article-type="research-article" dtd-version="1.2" xml:lang="en"><front><journal-meta><journal-id journal-id-type="publisher-id">Transactions of the St. Petersburg State Marine Technical University</journal-id><journal-title-group><journal-title xml:lang="en">Transactions of the St. Petersburg State Marine Technical University</journal-title><trans-title-group xml:lang="ru"><trans-title>Труды Санкт-Петербургского государственного морского технического университета</trans-title></trans-title-group></journal-title-group><issn publication-format="print">2414-1437</issn><publisher><publisher-name xml:lang="en">Saint Petersburg State Marine Technical University</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="publisher-id">707433</article-id><article-id pub-id-type="doi">10.52899/24141437_2026_02_195</article-id><article-id pub-id-type="edn">XIFCSV</article-id><article-categories><subj-group subj-group-type="toc-heading" xml:lang="en"><subject>Mechanical engineering</subject></subj-group><subj-group subj-group-type="toc-heading" xml:lang="ru"><subject>Машиностроение</subject></subj-group><subj-group subj-group-type="article-type"><subject>Research Article</subject></subj-group></article-categories><title-group><article-title xml:lang="en">Nonlinear forces and second-order motion amplitudes acting on a systematic series of ships</article-title><trans-title-group xml:lang="ru"><trans-title>Нелинейные силы и амплитуды качки второго порядка, действующие на масштабную серию судов</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author"><contrib-id contrib-id-type="spin">1753-4952</contrib-id><name-alternatives><name xml:lang="en"><surname>Semenova</surname><given-names>Viktoriya Yu.</given-names></name><name xml:lang="ru"><surname>Семёнова</surname><given-names>Виктория Юрьевна</given-names></name></name-alternatives><address><country country="RU">Russian Federation</country></address><bio xml:lang="en"><p>Dr. Sci. (Engineering), Professor, Head of the Department of ship theory</p></bio><bio xml:lang="ru"><p>д-р тех. наук, профессор, заведующая кафедрой теории корабля</p></bio><email>sem_viktoria@mail.ru</email><xref ref-type="aff" rid="aff1"/></contrib><contrib contrib-type="author"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0001-5175-6594</contrib-id><contrib-id contrib-id-type="spin">8594-4692</contrib-id><name-alternatives><name xml:lang="en"><surname>Albaev</surname><given-names>Danil A.</given-names></name><name xml:lang="ru"><surname>Альбаев</surname><given-names>Данил Айдарович</given-names></name></name-alternatives><address><country country="RU">Russian Federation</country></address><bio xml:lang="en"><p>Cand. Sci. (Engineering), Associate Professor of the Department of theory of the ship</p></bio><bio xml:lang="ru"><p>канд. техн. наук, доцент кафедры теории корабля</p></bio><email>albaevdanil@gmail.com</email><xref ref-type="aff" rid="aff1"/></contrib><contrib contrib-type="author"><name-alternatives><name xml:lang="en"><surname>Sun</surname><given-names>Hechen</given-names></name><name xml:lang="ru"><surname>Сунь</surname><given-names>Хэчэнь</given-names></name></name-alternatives><address><country country="RU">Russian Federation</country></address><bio xml:lang="en"><p>Master's student</p></bio><bio xml:lang="ru"><p>магистрант</p></bio><email>sun.hechen@yandex.ru</email><xref ref-type="aff" rid="aff1"/></contrib></contrib-group><aff-alternatives id="aff1"><aff><institution xml:lang="en">Saint Petersburg State Marine Technical University</institution></aff><aff><institution xml:lang="ru">Санкт-Петербургский государственный морской технический университет</institution></aff></aff-alternatives><pub-date date-type="pub" iso-8601-date="2026-06-26" publication-format="electronic"><day>26</day><month>06</month><year>2026</year></pub-date><volume>5</volume><issue>2</issue><issue-title xml:lang="en"/><issue-title xml:lang="ru"/><fpage>195</fpage><lpage>206</lpage><history><date date-type="received" iso-8601-date="2026-05-14"><day>14</day><month>05</month><year>2026</year></date><date date-type="accepted" iso-8601-date="2026-05-28"><day>28</day><month>05</month><year>2026</year></date></history><permissions><copyright-statement xml:lang="en">Copyright ©; 2026, Semenova V.Y., Albaev D.A., Sun H.</copyright-statement><copyright-statement xml:lang="ru">Copyright ©; 2026, Семёнова В.Ю., Альбаев Д.А., Сунь Х.</copyright-statement><copyright-year>2026</copyright-year><copyright-holder xml:lang="en">Semenova V.Y., Albaev D.A., Sun H.</copyright-holder><copyright-holder xml:lang="ru">Семёнова В.Ю., Альбаев Д.А., Сунь Х.</copyright-holder><ali:free_to_read xmlns:ali="http://www.niso.org/schemas/ali/1.0/"/><license><ali:license_ref xmlns:ali="http://www.niso.org/schemas/ali/1.0/">https://creativecommons.org/licenses/by/4.0</ali:license_ref></license></permissions><self-uri xlink:href="https://vietnamjournal.ru/2414-1437/article/view/707433">https://vietnamjournal.ru/2414-1437/article/view/707433</self-uri><abstract xml:lang="en"><p><bold>Background:</bold> Numerous studies have demonstrated the significant influence of second-order nonlinear forces on the resulting motion amplitudes. Most calculations were performed for individual ships, but no studies have been conducted on the influence of individual ship parameters on the values of nonlinear forces and the resulting motion amplitudes. Therefore, studying the effect of changes in ship length on second-order nonlinear motion amplitudes is a pressing issue.</p> <p><bold>Aim:<italic> </italic></bold>This study aimed to investigate the influence of changes in the length of ships of a systematic series on nonlinear motion amplitudes.</p> <p><bold>Methods:</bold> The method of integral equations was used to calculate nonlinear forces and the amplitudes of nonlinear motions caused by them.</p> <p><bold>Results:</bold> Analysis of the obtained results showed that reducing ship size leads to increased amplitudes of nonlinear transverse motion types and an expansion of the zone of nonlinearity influence. Under irregular wave conditions, reducing ship size leads to an increased influence of nonlinear factors at sea state 7.8.</p> <p><bold>Conclusion:<italic> </italic></bold>The paper presents the results of calculations of nonlinear motion amplitudes and wave drift forces for a systematic series of ships under regular and irregular wave conditions, taking into account second-order nonlinear forces. A study was conducted on the influence of the main dimensions of the ship on nonlinear motion amplitudes.</p></abstract><trans-abstract xml:lang="ru"><p><bold>Актуальность. </bold>В многочисленных работах было показано значительное влияние нелинейных сил второго порядка на вызываемые ими амплитуды качки. Большинство расчётов выполнено для отдельных судов, но исследования влияния отдельных параметров судов на значения нелинейных сил и вызываемых ими амплитуд качки не проводилось. В связи с этим, исследование влияния изменения длины судна на амплитуды нелинейной качки второго порядка является актуальной задачей.</p> <p><bold>Цель.</bold> Изучение влияния изменения длины судов масштабной серии на амплитуды нелинейной качки.</p> <p><bold>Методы. </bold>Для расчётов нелинейных сил и вызываемых ими амплитуд нелинейной качки используется метод интегральных уравнений.</p> <p><bold>Результаты. </bold>Анализ полученных результатов показал, что уменьшение размеров судна приводит к увеличению амплитуд нелинейных поперечных видов качки, расширению зоны влияния нелинейности. В условиях нерегулярного волнения уменьшение размеров судна приводит к росту влияния нелинейных факторов на волнении 7,8 балла.</p> <p><bold>Заключение. </bold>В работе приведены результаты расчётов амплитуд нелинейной качки, сил волнового дрейфа для масштабной серии судов в условиях регулярного и нерегулярного волнения с учётом нелинейных сил второго порядка. Выполнено исследование влияния главных размеров судна на амплитуды нелинейной качки.</p></trans-abstract><kwd-group xml:lang="en"><kwd>nonlinear forces</kwd><kwd>small parameter method</kwd><kwd>motion amplitudes</kwd><kwd>wave drift forces</kwd><kwd>integral equation method</kwd></kwd-group><kwd-group xml:lang="ru"><kwd>нелинейные силы</kwd><kwd>метод малого параметра</kwd><kwd>амплитуды качки</kwd><kwd>силы волнового дрейфа</kwd><kwd>метод интегральных уравнений</kwd></kwd-group><funding-group/></article-meta></front><body></body><back><ref-list><ref id="B1"><label>1.</label><citation-alternatives><mixed-citation xml:lang="en">Molin B. Second-order diffraction loads upon three-dimensional bodies. Applied Ocean Research. 1979;1(4):197–202.</mixed-citation><mixed-citation xml:lang="ru">Molin B. Second-order diffraction loads upon three-dimensional bodies // Applied Ocean Research. 1979. Vol. 1, N 4. 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